MAASTRICHTIAN CEPHALOPODS FROM CERRALVO, NORTH-EASTERN MEXICO

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1 MAASTRICHTIAN CEPHALOPODS FROM CERRALVO, NORTH-EASTERN MEXICO by CHRISTINA IFRIM, WOLFGANG STINNESBECK and JOSÉ GUADALUPE LÓPEZ-OLIVA ABSTRACT. Sediments of the Méndez Formation near Cerralvo, north-eastern Mexico, yield an abundant and diverse Maastrichtian ammonite assemblage. A total of 23 species referred to 18 genera are described, in addition to the possible coleoid Naefia neogaeia. The assemblage is considered to be of early Maastrichtian age on the basis of ammonite occurrences and has been dated to the lower Maastrichtian biozone CF 7 by planktic foraminifera. None of the ammonite species has been reported previously from the Méndez Formation and most species are recorded from Mexico for the first time. In addition to faunal elements known from other Gulf of Mexico localities [Baculites ovatus, Nostoceras (N.) alternatum, N. (N.) colubriformis, N. (N.) rugosum, Solenoceras reesidei] the assemblage is characterized by cosmopolitan (e.g. Anagaudryceras politissimum, Desmophyllites diphylloides, Diplomoceras cylindraceum, Gaudryceras kayei, Phyllopachyceras forbesianum, and Pseudophyllites indra) and Tethyan elements [e.g. Brahmaites (Anabrahmaites) vishnu, Fresvillia constricta, Hauericeras rembda, Solenoceras texanum, Tetragonites superstes]. Some ammonite species have been known from the Indopacific region a [e.g. Fresvillia aff. F. teres, Neophylloceras (Hypophylloceras) hetonaiense, Zelandites varuna] and are clearly cold-water species. The composition of the assemblage contrasts with other Gulf of Mexico faunas which is related to bathymetry. KEY WORDS: Ammonoidea, coleoidea, lower Maastrichtian, north-east Mexico, palaeobiogeographic distribution. D URING Campanian Maastrichtian times north-east Mexico formed part of a moderately deep water shelf-slope region that received a steady influx of terrigenous clastic sediments from the rising Sierra Madre Oriental (Laramide Orogeny) to the west and from an extensive deltaic complex to the north-west (e.g. Sohl et al. 1991). In the region north and west of Saltillo, siliciclastic deltaic and prodeltaic deposits of the Difunta Group (Text-fig. 1) contain abundant and diverse invertebrate assemblages, among them the ammonites Sphenodiscus, Coahuilites, Baculites and Pachydiscus (Böse 1928; Wolleben 1977; Vega- Vera and Perrilliat 1990; Vega et al. 1995). In the distal prodeltaic area east and south-east of Monterrey, a sequence up to 1000 m thick of rhythmically bedded marls and shales was deposited in the same period of time in the Gulf Coast Plain of north-east Mexico. This Méndez Formation characterises open marine basins with water depths of approximately 100 m near Los Ramones, 40 km north-east of Monterrey (Stinnesbeck et al. 1996; Keller et al. 1997), and more than 400 m in the La Sierrita region, 40 km east of Montemorelos (Keller et al. 1997; Stinnesbeck et al. 2001). The Méndez Formation is generally rich in planktic and benthic foraminiferal assemblages, but poor in body fossils. So far only isolated specimens of the bivalves Tampsia (Stephenson 1941) and Inoceramus (own collections) have been reported, in addition to an unspecified mosasaurid (Aranda-Manteca and Stinnesbeck 1995) and the ammonite Nostoceras (Medina-Barrera and Stinnesbeck 1993). Nostoceras is represented by a single final hook which probably relates to Nostoceras sternbergi and was found at km 11 5 on the road from La Palma to Rayones, south of Montemorelos, Nuevo León (see Text-fig. 1). The ammonite fauna described herein was collected from sediments of the Méndez Formation by a private collector (Sr. Rolando Gómez Martínez) and ourselves at Loma Los Martinitos, 15 km south-east of Cerralvo (Text-fig. 1). The locality is approximately 1 km south of the road between Cerralvo and Las Higueras (Lat N, Long W). The Méndez Formation at Loma Los Martinitos consists of grey marls and marly shales. It contains abundant planktic and benthic foraminifera which indicate an early Maastrichtian age, and deposition in inner to middle neritic environments. There is no true outcrop, [Palaeontology, Vol. 47, Part 6, 2004, pp , 4 pls] q The Palaeontological Association

2 1576 PALAEONTOLOGY, VOLUME 47 TEXT-FIG. 1. Map showing the geography, Maastrichtian palaeogeography, and fossil localities near Monterrey. 1, Cerralvo; 2, Sierra el Antrisco (Vega-Vera and Perrilliat 1990); 3, roadside locality in Medina-Barrera and Stinnesbeck (1993); 4, Vallecillo (Böse 1928). Fossils in Wolleben (1977) are from the Difunta Group between Saltillo and Monclova (La Popa Basin) and located to the west. and ammonites have been collected from weathered sediment surfaces of the Méndez Formation in a small area. We took a fresh sample of marl in the bed of a gully running through the area where layers of the Méndez marls are visible and lying horizontally. The geological situation suggests that originally all specimens were derived from an interval of less than 20 m of section. Most individuals are preserved as goethitic internal moulds, although some are preserved as a pseudomorph of goethite after the nacreous internal mould. Some specimens are covered by a thick goethite layer. Goethite is considered to be an oxidation product of pyrite that indicates low oxygen environments during deposition or early sediment diagenesis (e.g. Füchtbauer and Richter 1988; Valeton 1988). In our fauna only the innermost whorls were impregnated sufficiently to prevent them from implosion due to lithologic overburden or compaction of the host sediment. The inner whorls are preserved in three dimensions, whereas the outer whorls are flattened and broken away. Body chambers are not preserved with one exception. Due to recent weathering and surface transport, numerous specimens are abraded mechanically or broken. This partial preservation explains the small diameters of the Cerralvo specimens. The largest of more than 1000 specimens is a Hauericeras rembda with a phragmocone diameter of 40 3 mm, but the usual sizes of the phragmocones are between 10 and 20 mm. The small sizes are certainly not the result of

3 IFRIM ET AL.: MAASTRICHTIAN CEPHALOPODS 1577 unfavourable living conditions that may lead to dwarfism. The ammonites are associated in some layers with benthic faunal elements such as gastropods, bivalves, corals, and echinoids, which indicate that the benthic environment was well oxygenated. The gastropods are soft bottom inhabitants from the families Aporrhaidae and Ringiculidae (among them the genera Cylichna and Avellana) along with other neogastropods (S. Kiel, pers. comm. 2003). The few solitary corals (genera Parasmilia, Caryophyllia and Micrabacia) also indicate a soft bottom environment (R. Baron-Szabo, pers. comm. 2003). The most diverse group of molluscs besides ammonites are the bivalves with about ten genera, among them Nucula, Nuculana, Striarca, Pleuriocardia, and Thyrasira. Most of the bivalves are infaunal detritus feeders that indicate soft fine-grained sediment (J. Seeling, pers. comm. 2003). The Cerralvo ammonite fauna described herein consists of 23 species. None of them has been reported previously from the Méndez Formation. Gaudryceras kayei is one of the very few elements of the Cerralvo fauna to have been registered earlier for north-east Mexico. Böse (1928, pl. 10, figs 10 14; pl. 11, figs 5 10) reported this species from the?santonian (the origin of his specimens is doubtful; see below), but most species are recorded here from Mexico for the first time. In addition to ammonites, the Cerralvo cephalopod fauna includes Naefia neogaeia. Previously, this rare possible coleoid (?Sepiida, Groenlandibelidae) has only been recorded from Chile, Antarctica, Japan, California and India (e.g. Doyle 1986; Stilwell and Zinsmeister 1987; Hewitt et al. 1991). On the other hand, no belemnites are known to exist in the Méndez Formation or elsewhere in Campanian Maastrichtian of Mexico. SYSTEMATIC PALAEONTOLOGY All specimens described and figured here are registered and available at the Facultad de las Ciencias de la Tierra of the Universidad Autónoma de Nuevo León (UANL); additional material is housed in the Geological Institut at the University of Karlsruhe, Germany. Dimensions. Linear dimensions are given in mm, angles are given in degrees. Uncertain values due to deformation of the specimen and relations resulting from uncertain measurements are written in brackets. Abbreviations: D, diameter; WB, whorl breadth; WH, whorl height; U, umbilical diameter; A, apical angle of ancyloceratids; L, length of undeformed part (¼ distance of two measured sections). Suture terminology. Abbreviation of sutural elements corresponds to common terminology: E, external lobe; L, lateral lobe; U, auxiliary lobes (some with index: U 1,U 2,...);I,internal lobe. The saddles are named correspondingly: E/L, saddle between external and lateral lobe; L/U, saddle between lateral and outer auxiliary lobe. Other abbreviations. The registration is UANL, CE (Cerralvo), MAAS (Maastrichtian). Other collections mentioned are BMNH, The Natural History Museum, London; GK, Kyushu University, Fukuoka; GPK, Geological and Palaeontological Institute and Museum of the University of Kiel; IRSNB, Institut Royal des Sciences Naturelles, Brussels; TM, Transvaal Museum, Pretoria; USNM, National Museum of Natural History, Washington, DC. Systematics. Systematic nomenclature follows the Treatise of Invertebrate Paleontology (Wright et al. 1996) to subspecies level, except for the genus Gaudryceras and the subgenus Anabrahmaites. Synonymies. Only references to the original description, some synonyms and all references used for the definition of species are included. Where possible more complete synonymy lists are indicated. Subclass COLEOIDEA Bather, 1888 Order?SEPIIDA Zittel, 1895 Family GROENLANDIBELIDAE Jeletzky, 1966 Genus NAEFIA Wetzel, 1930 Type species. Naefia neogaeia Wetzel, 1930, by original designation.

4 1578 PALAEONTOLOGY, VOLUME 47 Naefia neogaeia Wetzel, 1930 Text-figure 2A B 1930 Naefia neogaeia Wetzel, p. 92, pl. 14, fig Naefia aff. neogaeia Wetzel, Doyle, p. 134, figs 1 4 (with additional synonymy). Type. The lectotype is GPK 121b from Wetzel s syntypes by subsequent designation of Jeletzky (1966, p. 104). Material. Four isolated camerae of the phragmocone, internal moulds. Description. The present material consists of small isolated camerae with almost circular cross sections (height to breadth ratio of 1 02), maximum diameters of mm, and a marginally ventral position of the siphuncle. Faint longitudinal striation is present on the dorsal side of the camerae. Septal sutures are nearly straight with the exception of a small ventral lobe (Text-fig. 2A, B2). The phragmocone was apparently orthoconic with an apical angle of less than 10 degrees. Remarks. Although fragmentary, the material described above is almost indistinguishable from Naefia neogaeia Wetzel in the overall form of the camerae, dimensions, whorl section, position of siphuncle and presence of a small ventral lobe. Occurrence. The type material of Naefia neogaeia is from the Upper Maastrichtian Quiriquina Formation of central Chile (Wetzel 1930; Stinnesbeck 1986, 1996). In addition, the species is known from the Campanian Maastrichtian of southern India (Doyle 1986), Antarctica (Stilwell and Zinsmeister 1987), California (Jeletzky in Hewitt et al. 1991) and the Upper Santonian Lower Campanian of Japan (Hewitt et al. 1991). The Mexican specimens described here are the first to be found outside the Indopacific hemisphere. Order AMMONOIDEA Zittel, 1884 Suborder PHYLLOCERATINA Arkell, 1950 Superfamily PHYLLOCERATACEAE Zittel, 1884 Family PHYLLOCERATIDAE Zittel, 1884 Subfamily PHYLLOCERATINAE Zittel, 1884 Genus HYPOPHYLLOCERAS Salfeld, 1924 Type species. Ammonites (Scaphites?) ramosus Meek, Subgenus HYPOHYLLOCERAS (NEOPHYLLOCERAS) Shimizu, 1934 Type species. As for genus. For discussion of genus and subgenus, see Henderson and McNamara (1985). Hypophylloceras (Neophylloceras) hetonaiense (Matsumoto, 1942) Text-figures 2F H, 3D? 1895 Phylloceras ramosum Meek; Steinmann, p. 80, pl. 5, fig. 4a b Neophylloceras hetonaiense Matsumoto, p. 675, figs 1a3, 1b Neophylloceras lambertense Usher, p. 50, pl. 1, figs 1 3.? 1953 Neophylloceras hetonaiense Matsumoto; Spath, p. 5, pl. 1, fig. 2. TEXT-FIG. 2. A B, Naefia neogaeia Wetzel, A, UANL CE MAAS-131. B, UANL CE MAAS-132. C E, Hypophylloceras (Neophylloceras) cf. H. (N.) surya (Forbes, 1846). C, UANL CE MAAS-002. D, UANL CE MAAS-001. E, UANL CE MAAS-003. F H, Hypophylloceras (Neophylloceras) hetonaiense (Matsumoto, 1942). F, UANL CE MAAS-007. G, UANL CE MAAS-009. H, UANL CE MAAS-011. All 2.

5 IFRIM ET AL.: MAASTRICHTIAN CEPHALOPODS b Neophylloceras hetonaiense Matsumoto; Matsumoto, p. 5, pl. 3, fig Neophylloceras hetonaiense Matsumoto; Jones, p. 23, pl. 6, figs 9 10; pl. 7, fig. 1; text-fig Phylloceras (Neophylloceras) hetonaiense (Matsumoto); Stinnesbeck, p. 190, pl. 7, figs 3 4; text-figs 16b, 17a (with full synonymy). Type. Lectotype GK. H3801a designated by Matsumoto (1959b, p. 5, pl. 3, fig. 1).

6 1580 PALAEONTOLOGY, VOLUME 47 Material. 20 internal moulds of which two show partially preserved ornament. Description. Shell discoidal and very involute with intermediate expansion rate. The umbilicus is narrow (U/D is approximately 0 07) and has a steep umbilical wall. Flanks are almost subparallel with their maximum breadth above the middle flank. The venter is widely arched. Lirae straight and slightly prorsiradiate on the flanks but slightly retracted ventrolaterally. They are faint in the dorsolateral area. Suture with complex incisions and slightly phylloid saddle terminations; the trifid lateral lobe is expanded and surrounded by tetraphylloid saddles. The sutural lobe is slightly retracted. Dimensions D WB WH WB/WH U U/D UANL CE MAAS UANL CE MAAS UANL CE MAAS UANL CE MAAS UANL CE MAAS UANL CE MAAS UANL CE MAAS UANL CE MAAS UANL CE MAAS (6 6) 11 2 (0 59) UANL CE MAAS Remarks. Both parallel (e.g. Stinnesbeck 1986) and convergent (e.g. Jones 1963) flanks have been described previously for this species. Thirteen of our tests are crushed, but specimens that are well preserved show little variation in test shape, and all of them have parallel flanks. Hypophylloceras (Neophylloceras) hetonaiense is similar to H. (N.) ramosum but differs by having less flexuous lirae. It differs from H. (N.) cottreaui (discussed below) owing to its much narrower umbilicus. Occurrence. Hypophylloceras (Neophylloceras) hetonaiense (Matsumoto) is known from the Campanian Maastrichtian of Japan (Matsumoto 1942), California (Matsumoto 1959b), Antarctica (Spath 1953) and Alaska (Jones 1963), and the Upper Maastrichtian of Chile (Stinnesbeck 1986). Hypophylloceras (Neophylloceras) hetonaiense seems to be a cold water species. Hypophylloceras (Neophylloceras) sp. cf. H. (N.) surya (Forbes, 1846) Text-figures 2C E, 3A 1846 Ammonites Surya Forbes, p. 106, pl. 7, fig Ammonites Surya Forbes; d Orbigny, p Phylloceras Surya (Forbes); Kossmat, p. 109 (13), pl. 16 (2), fig Epiphylloceras mikobokense Collignon, p. 24, pl. 2, figs 3, 3a; pl. 4, figs 5, 5a, 5b Phylloceras (Hypophylloceras) mikobokense (Forbes); Kennedy and Klinger, p. 368, pl. 12, fig Phylloceras (Neophylloceras) surya (Forbes); Henderson and McNamara, p. 42, pl. 1, figs 7 8, 11 12; pl. 2, figs 1 2; text-fig. 2g (with full synonymy) Phylloceras (Hypophylloceras) surya (Forbes); Stinnesbeck, p. 193, pl. 7, figs b Phylloceras (Neophylloceras) surya (Forbes); Kennedy and Henderson, p. 391, pl. 1, figs 1 7, 9, 13 14; pl. 15, figs 4 5 (with additional synonymy) Phylloceras (Neophylloceras) surya (Forbes); Ward and Kennedy, p. 16, figs 17.13, 18.3, 18.4, 18.16, Phylloceras (Neophylloceras) surya (Forbes); Birkelund, p. 43, pl. 2, fig Phylloceras (Neophylloceras) surya (Forbes); Fatmi and Kennedy, p. 643, figs , Types. Lectotype BMNH C51074 is the original of Kossmat, 1895, pl. 16 (2), fig. 1a c, by designation of Kennedy and Henderson (1992b, pl. 1, figs 13 14). Material. Six internal moulds, two of which are deformed; tests partially preserved. Description. Shell discoidal and involute with intermediate expansion rate. Compression of the whorl section increases with diameter. The wide umbilicus ( ) is surrounded by steep umbilical walls that pass into the flanks in a wide arch. The flanks are slightly convex with the maximum whorl breadth above the middle flank. Flanks converge

7 IFRIM ET AL.: MAASTRICHTIAN CEPHALOPODS 1581 TEXT-FIG. 3. Suture lines of the Phylloceratina and Lytoceratina. A, Hypophylloceras (Neophylloceras) cf. H. (N.) surya (Forbes, 1846). UANL CE MAAS-002. B C, Phyllopachyceras forbesianum (d Orbigny, 1850). B, UANL CE MAAS C, UANL CE MAAS-021. D, Hypophylloceras (Neophylloceras) hetonaiense (Matsumoto, 1942). UANL CE MAAS-009. E G, Tetragonites superstes van Hoepen, E, UANL CE MAAS-022. F, UANL CE MAAS-023. G, UANL CE MAAS-029. H, Pseudophyllites indra (Forbes, 1846). UANL CE MAAS-033. I J, Anagaudryceras politissimum (Kossmat, 1895). I, UANL CE MAAS-135. J, UANL CE MAAS-045. K, Saghalinites cala (Forbes, 1846). UANL CE MAAS-047. L N. Gaudryceras kayei (Forbes, 1846). L, UANL CE MAAS-039. M, UANL CE MAAS-037. N, UANL CE MAAS-042. O P, Zelandites varuna (Forbes, 1846). O, UANL CE MAAS-050. P, UANL CE MAAS-052. All 5. ventrally and pass into the broadly rounded venter in a wide bow. The dorsal flanks present six bullae per half whorl. Six to eight parallel, slightly prorsiradiate and concave lirae are present between two bullae, but they are not visible in the dorsal area. On the middle flank lirae are straight but become convex towards the venter where they cross rectiradially. Sutural lobes are deep and fine incisions with phylloid saddle terminations and a shallow ventral lobe. The sutural lobe is retracted. Dimensions D WB WH WB/WH U U/D UANL CE MAAS UANL CE MAAS UANL CE MAAS P. (N.) surya (Kennedy and Henderson 1992b) P. (H.) surya (Stinnesbeck, 1986) 30 2 (8 0) 16 5 (0 48) N. marshalli (Henderson, 1970) E. cottreaui (Collignon, 1956)

8 1582 PALAEONTOLOGY, VOLUME 47 TEXT-FIG. 4. Morphological relationship between whorl diameter and umbilical diameter in species of Hypophylloceras (Neophylloceras) with a large umbilicus. Remarks. The most conspicuous features of the specimens described here are the wide umbilicus and the dorsolateral bullae. Species of Hypophylloceras (Neophylloceras) with a similarly wide umbilicus are H. (N.) surya (Forbes, 1846), H. (N.) marshalli (Shimizu, 1935), and H. (N.) cottreaui (Collignon, 1956). In Text-figure 4 the whorl diameter is plotted against the umbilical diameter to evaluate a possible relationship of the Cerralvo specimens with one of the above species. Hypophylloceras (Neophylloceras) surya (Forbes, 1846) shows eight or more bullae per half whorl in more adult stages as compared to six per whorl reported here for the Cerralvo specimens (e.g. Henderson and McNamara 1985; Kennedy and Henderson 1992b). The specimens described here may be juveniles of this species as suggested by the U/D relationship (Text-fig. 4). However, in that case an increase in the number of umbilical bullae should exist during ontogeny, a change that has not been described so far. Hypophylloceras (Neophylloceras) cottreaui (Collignon, 1956) was described from a single specimen which is much larger than our juveniles. It differs from other Neophylloceras in having a very wide umbilicus (U/D = 0 17). In addition, it is more inflated and characterized by six strong bullae per half whorl arranged close to the umbilicus. The bullae were described by Collignon (1956, p. 25) as flat costae with quadratic cross section that are separated from each other by a deep groove. This feature cannot be evaluated properly in the specimens described here. In addition, umbilical tubercles were described by Collignon (1956) which are absent in the present specimens. Hypophylloceras (Neophylloceras) marshalli (Shimizu, 1935; Henderson 1970) is another species with a wide umbilicus and ornament of fine, closely spaced ribs which are slightly prorsiradiate on the dorsal flanks, straighten at the mid-flank and are rectiradiate across the venter; the dorsal flanks bear six folds in a half whorl (Henderson 1970, p. 3). The U/D relationship reported coincides with our material (Textfig. 4), but the sigmoidal bending of the dorsolateral ribs and their density differ from our specimens. On the other hand the specimen described by Henderson (1970) is larger (D is 42 0 mm). Another species with similar ornament is H. (N.) inflatum (Stinnesbeck, 1986), but this species differs considerably from the Cerralvo specimens in test size ratios and in having a whorl section that is much more inflated (Text-fig. 4). In addition, the ontogenesis of H. (N.) inflatum clearly follows a different path in the U/D relationship. Shell measurements (Text-fig. 4) suggest that the Cerralvo specimens may be juveniles of H. (N.) surya, although they are too small to allow precise determination.

9 Occurrence. Hypophylloceras (Neophylloceras) surya (Forbes) has been recorded from the Maastrichtian of southern India (Kennedy and Henderson 1992b), Madagascar (Collignon 1956), South Africa (Kennedy and Klinger 1976), western Australia (Henderson and McNamara 1985), the Biscay region, Alaska, California, Japan (Ward and Kennedy 1993) and Denmark (Birkelund 1993), and the Upper Maastrichtian of Pakistan (Fatmi and Kennedy 1999) and Chile (Stinnesbeck 1986). Genus PHYLLOPACHYCERAS Spath, 1927 Type species. Ammonites infundibulum d Orbigny, 1841, p. 131, pl. 39, figs 4 5, by original designation. Phyllopachyceras forbesianum (d Orbigny, 1850) Plate 1, figures 1 4; Text-figure 3B C 1846 Ammonites Royanus d Orbigny; Forbes, p. 108, pl. 8, fig Ammonites forbesianus d Orbigny, p Phylloceras forbesianum (d Orbigny), Kossmat p. 109, pl. 15, fig. 1a c Phyllopachyceras forbesianum (d Orbigny); Shimizu, p Phyllopachyceras forbesianum (d Orbigny); Jones, p. 24, pl. 41, figs 2, 4 6; text-fig Phyllopachyceras forbesianum (d Orbigny); Henderson, p. 7, pl. 1, figs 2, 4 5 (with additional synonymy) Partschiceras (Phyllopachyceras) forbesianum (d Orbigny); Henderson and McNamara, p. 43, pl. 1, figs 4 6; text-fig. 3f Partschiceras forbesianum (d Orbigny); Kennedy and Summesberger, p. 184, pl. 1, figs 2 3, 6; pl. 5, figs 3, b Phyllopachyceras forbesianum (d Orbigny); Kennedy and Henderson, p. 394, pl. 2, figs 1 12; text-fig. 3c (with additional synonymy) Phyllopachyceras forbesianum (d Orbigny), Ward and Kennedy, p. 17, text-figs , Type. Ammonites forbesianus Forbes (1846, pl. 8, fig.6) was introduced as a new name for Ammonites Royanus d Orbigny without designation of a holotype. Lectotype BMNH C51081 was subsequently designated by Kennedy and Henderson (1992b, p. 396, pl. 2, figs 1 3) from the original type series. Material. 104 internal moulds. IFRIM ET AL.: MAASTRICHTIAN CEPHALOPODS 1583 Description. Involute and inflated with high expansion rate. The umbilicus is deep and too small to be accurately measured. In juvenile specimens the steep umbilical wall bends widely into evenly convex flanks. The venter is broadly rounded. In consequence, the whorl section is almost circular. In more adult specimens the umbilical wall bends more narrowly into a slightly convex dorsolateral flank. The steep umbilical wall is almost absent and leads to a funnel-shaped umbilicus. Internal moulds are smooth. Where preserved the test is covered with dense lirae. Lirae are straight and slightly prorsiradiate on the middle flank and venter. The suture line displays tetraphylloid saddle terminations on the first two saddles, E exceeds L in depth. Dimensions D WB WH WB/WH UANL CE MAAS UANL CE MAAS UANL CE MAAS UANL CE MAAS UANL CE MAAS UANL CE MAAS UANL CE MAAS UANL CE MAAS UANL CE MAAS (11 6) 14 4 (0 81) Remarks. Most specimens are immature with almost circular whorl sections. Whorl section gradually increases in height beginning with a whorl diameter of 10 mm for some specimens, while others remain immature to a larger diameter.

10 1584 PALAEONTOLOGY, VOLUME 47 Occurrence. The earliest records of this cosmopolitan species are from the Santonian of Madagascar (Collignon 1956, 1969) and the Lower Campanian of Spain (Wiedmann 1962). Later records of Campanian Maastrichtian ages include southern India (Kennedy and Henderson 1992b), Japan (Matsumoto 1942), Alaska (Jones 1963), western Australia (Henderson and McNamara 1985), New Zealand (Marshall 1926; Henderson 1970), Austria (Kennedy and Summesberger 1986), the Biscay region of France and Spain (throughout the G. gansseri and A. mayaroensis zones; Ward and Kennedy 1993), Antarctica, South Africa, Germany, and the former USSR (see Kennedy and Henderson 1992b). During the Late Campanian Late Maastrichtian the species occurs world-wide through all latitudes (Alaska to the Antarctic Peninsula). Phyllopachyceras forbesianum is the most widespread among the species described herein. Suborder LYTOCERATINA Hyatt, 1900 Superfamily TETRAGONITACEAE Hyatt, 1900 Family TETRAGONITIDAE Hyatt, 1900 Subfamily TETRAGONITINAE Hyatt, 1900 Genus TETRAGONITES Kossmat, 1895 Type species. Ammonites timotheanus Pictet (1848, p. 295, pl. 2, fig. 6; pl. 3, fig. 1) by original designation. The genus was discussed by Kennedy and Klinger (1977). Tetragonites superstes van Hoepen, 1921 Plate 1, figures 5 8; Text-figure 3E G 1921 Tetragonites superstes van Hoepen, p. 10, pl. 2, figs 17 20; text-fig Tetragonites cf. epigonum Spath, p Tetragonites superstes van Hoepen; Spath, p. 119, pl. 6, fig Epigoniceras superstes (van Hoepen); Collignon, p. 87, pl. 11, fig. 3a b Epigoniceras superstes (van Hoepen); Collignon, p. 14, pl. 517, fig Tetragonites superstes van Hoepen; Kennedy and Klinger, p. 162, figs 7a d, h j, 8, 12a c. Type. The holotype of Tetragonites superstes is TM 564 by original designation (van Hoepen 1921, pl. 2, figs 17 18). Material. 27 internal moulds, shell rarely preserved. Description. Small and involute species with a moderate expansion rate. The whorl section is subrectangular to subelliptical with maximum whorl breadth below midflank. The umbilicus is of the shell diameter, rather deep, with a subvertical wall and previous whorls visible. The umbilical shoulder is abruptly rounded. The flanks are gently rounded to parallel and grade into broadly rounded convergent ventrolateral shoulders. Venter flattened. From a diameter of c. 15 mm on some specimens show faint grooves on the ventral margins that parallel a faint ridge on each umbilical shoulder. Internal moulds are smooth, but faint prorsiradiate growth striae are visible on internal whorls. The suture line has a large asymmetric trifid first lateral saddle (E/L), a smaller trifid second lateral saddle (L/U 2 ), and a suspensive lobe with a large trifid first auxiliary saddle. The first lateral lobe (L) is large and irregularly subdivided. The first of the four auxiliary lobes is trifid. These features are displayed through all growth stages documented here, but their dimensions and grades of incision increase considerably. EXPLANATION OF PLATE 1 Figs 1 4. Phyllopachyceras forbesianum (d Orbigny, 1850). 1, UANL CE MAAS , UANL CE MAAS , UANL CE MAAS , UANL CE MAAS-021. Figs 5 8. Tetragonites superstes (Van Hoepen, 1921). 5, UANL CE MAAS , UANL CE MAAS , UANL CE MAAS , UANL CE MAAS-030. All 2.

11 IFRIM et al., Phyllopachyceras, Tetragonites PLATE 1

12 1586 PALAEONTOLOGY, VOLUME 47 Dimensions D WB WH WB/WH U U/D UANL CE MAAS UANL CE MAAS UANL CE MAAS (2 8) (0 25) UANL CE MAAS UANL CE MAAS UANL CE MAAS UANL CE MAAS UANL CE MAAS (8 7) (12 4) Remarks. Tetragonites superstes resembles T. epigonus (Kossmat, 1895), but is less involute and less expanded during growth. According to Kennedy and Klinger (1977), T. popetensis (Yabe, 1903) is another species with similar morphology. It ranges from the Campanian to the Maastrichtian, and is known from California and Japan. However, this species differs by the presence of constrictions that are marked clearly on the shell. All other Tetragonites species are ornamented by distant ribs or constrictions. Occurrence. Tetragonites superstes van Hoepen has only been described from the Upper Santonian or Lower Campanian of South Africa (Kennedy and Klinger 1977) and Lower Middle Campanian of Madagascar (Collignon 1956). Genus SAGHALINITES Wright and Matsumoto, 1954 Type species. Ammonites cala Forbes (1846, p. 104, pl. 8, fig. 4a c) by original designation of Wright and Matsumoto (1954, p. 110). The genus was discussed by Kennedy and Klinger (1977). Saghalinites cala (Forbes, 1846) Text-figures 3K, 5C 1846 Ammonites cala Forbes, p. 104, pl. 8, fig. 4a c Lytoceras (Tetragonites) cala (Forbes); Kossmat, p. 136, pl. 17, fig. 12a d Tetragonites cala (Forbes) var. zeugitana; Pervinquière, p. 79, pl. 3, fig. 30, text-fig Tetragonites cala (Forbes); Shimizu, p Saghalinites cala (Forbes); Collignon, p Tetragonites (Saghalinites) cala (Forbes); Howarth, p. 10, pl. 1, fig. 11a b Saghalinites cala (Forbes); Kennedy and Klinger, p. 168, figs 10a b, 11a b, 12d g, 13a b, e k,?c d; 14a f; 15a f (with full synonymy). 1992b Saghalinites cala (Forbes); Kennedy and Henderson, p. 400, pl. 2, figs 13 15; pl. 3, figs 1 6; text-fig. 3b (with additional synonymy). Type. The lectotype BMNH C51057 is Forbes original from southern India (1846, p. 104, pl. 8, fig. 4a c) by subsequent designation of Kennedy and Klinger (1977, p. 169). Material. One well-preserved internal mould. Description. Small evolute test with low expansion rate. The rounded whorl section is little depressed (WB/WH is 1 16) with the greatest breadth below mid-flank. The wide, shallow umbilicus spans 46 per cent of the whorl diameter. The umbilical wall is short, but steep to vertical. Flanks are rounded and grade into a broadly rounded venter. The smooth surface displays five narrow, deep constrictions per whorl. They arise at the umbilical seam, pass straight and prorsiradiately across the umbilical wall and inner flank, and flex gently backward on the outer flank. On the venter constrictions form a shallow sinus. The suture line is tetragonitid with a stout lanceolate median saddle in the deep external lobe, trifid E/L and L/U and irregularly bifid L. The suspensive lobes are retracted. Dimensions. UANL CE MAAS-047: D, 15 6; WB, 6 4; WH, 5 5; WB/WH, 1 16; U, 7 1; U/D, Remarks. Saghalinites wrighti Birkelund is a species close to S. cala. They are almost indistinguishable, particularly during small growth stages. However, S. wrighti lacks constrictions in earliest growth stages

13 while in later growth stages constrictions are straight rather than flexuous. Saghalinites wrighti has been described by Birkelund (1965) and Kennedy and Klinger (1977), and its holotype was figured again by Ward and Kennedy (1993, fig. 20). Occurrence. Saghalinites cala is Maastrichtian in age in southern India (Forbes 1846), South Africa (Kennedy and Klinger 1977), and Antarctica (Howarth 1958). The doubtful record from Pondoland (Woods 1906) may be Santonian or Campanian, and a record from Tunisia (Pervinquière 1907) is from the Santonian (see Kennedy and Henderson 1992b). The species is also known from Japan (Shimizu 1935). Genus PSEUDOPHYLLITES Kossmat, 1895 Type species. Ammonites indra Forbes, 1846, p. 105, pl. 11, fig. 7, by original designation. Pseudophyllites indra (Forbes, 1846) Text-figures 3H, 5A B 1846 Ammonites indra Forbes, p. 105, pl. 11, fig Pseudophyllites indra (Forbes) Kossmat, p. 137, pl. 16, figs 6 9; pl. 17, figs 6 7; pl. 18, fig Pseudophyllites indra (Forbes); Jones, p. 25, pl. 7, figs 6 7; pl. 8; pl. 29, figs 7 12; text-fig Pseudophyllites indra (Forbes); Collignon, p. 2, pl. 639, fig. 2355; pl. 640, fig. 2363; p. 81, pl. 649, fig Pseudophyllites indra (Forbes); Kennedy and Klinger, pp , text-figs (with additional synonymy) Pseudophyllites indra (Forbes); Henderson and McNamara, p. 50, pl. 2, figs 7 8; pl. 3, figs 4 5; textfig. 5a d Pseudophyllites indra (Forbes); Stinnesbeck, p. 199, pl. 8, fig c Pseudophyllites indra (Forbes); Kennedy, p. 19, pl. 1, figs 1 5; text-figs 4e, 5a, 6a e (with additional synonymy). 1991b Pseudophyllites indra (Forbes); Cobban and Kennedy, p. E2, pl. 1, figs b Pseudophyllites indra (Forbes); Kennedy and Henderson, p. 398, pl. 3, figs 7 9, 13 27; pl. 4, figs Pseudophyllites indra (Forbes); Ward and Kennedy, p. 22, text-figs 17.8, , 19.7, 19.9, 19.13, , , Pseudophyllites indra (Forbes); Kennedy and Hancock, p. 577, pl. 1, figs 4, Pseudophyllites indra (Forbes); Cobban and Kennedy, p. 4, figs , 2.10 (with additional synonymy). Type. Lectotype BMNH C51068 is the original of Forbes (1846, pl. 11, fig. 7a, b) as designated by Kennedy and Klinger (1977). Material. Nine internal moulds. IFRIM ET AL.: MAASTRICHTIAN CEPHALOPODS 1587 Description. The test is involute and expands rapidly. Whorl section is rounded to slightly compressed. The umbilicus (U/D is c. 0 21) is small and deep, and grades into an outward sloping wall. The umbilical shoulder is abruptly rounded, flanks are initially rather flattened and convergent, and the venter is rounded. Internal moulds are smooth and no ornament is preserved on our Cerralvo specimens. The suture line is highly subdivided with a lanceolate ventral saddle, trifid first lateral saddle (E/L) and smaller bifid second lateral saddle (L/U). The bifid lateral lobe (L) is deeply incised and almost as deep as the ventral lobe. The sutural lobe is slightly retracted with a large bifid first umbilical saddle. The massive septal lobe of the internal suture line is accompanied by two lateral saddles on each side. Saddle terminations are typically subphylloid. Dimensions D WB WH WB/WH U U/D UANL CE MAAS UANL CE MAAS UANL CE MAAS UANL CE MAAS UANL CE MAAS

14 1588 PALAEONTOLOGY, VOLUME 47 Remarks. The lanceolate external saddle and the flat umbilical wall clearly separate P. indra from other species of the genus Pseudophyllites (Henderson and McNamara 1985). Occurrence. Pseudophyllites indra ranges from the Upper Santonian (Madagascar, Collignon 1971; South Africa, fide Kennedy and Klinger 1977) to the Upper Maastrichtian A. mayaroensis Zone (e.g. Ward and Kennedy 1993). The species occurs world-wide in lower and middle latitudes (Tethys). It is known to occur in Japan (Nagao and Saito 1934), Poland (Blaszkiewicz 1980), France and Spain (Ward and Kennedy 1993), the southern and eastern USA

15 IFRIM ET AL.: MAASTRICHTIAN CEPHALOPODS 1589 (e.g. Cobban and Kennedy 1991b, 1995), Austria (Kennedy and Summesberger 1986), southern India (Kennedy and Henderson 1992b), western Australia (Henderson and McNamara 1985), Alaska (Jones 1963), Chile (Stinnesbeck 1986), and other locations (see Ward and Kennedy 1993). In western Australia, Chile and the Biscay region of Spain and France, Pseudophyllites indra ranges into the Upper Maastrichtian A. mayaroensis Zone (Henderson and McNamara 1985; Stinnesbeck 1986; Ward and Kennedy 1993). Family GAUDRYCERATIDAE Spath, 1927 Genus GAUDRYCERAS de Grossouvre, 1894 Type species. Ammonites mitis (von Hauer, 1866, p. 305, pl. 2, figs 3 4) by the subsequent designation of Boule et al. [ , p. 183 (11)]. The genus was revised by Henderson and McNamara (1985). Gaudryceras kayei (Forbes, 1846) Text-figures 3L N, 5D, 6A C, H 1846 Ammonites kayei Forbes, p. 101, pl. 8, fig Lytoceras kayei (Forbes) Griesbach, p Gaudryceras kayei (Forbes) Woods, p. 335, pl. 41, fig. 8; pl. 42, fig Vertebrites kayei (Forbes) Collignon, p. 2, pl. 640, fig Vertebrites kayei (Forbes); Kennedy and Klinger, p. 160, fig. 5; pl. 14, fig. 2 (with full synonymy) Gaudryceras kayei (Forbes); Henderson and McNamara, p. 46, pl. 1, figs 9 10; text-fig. 4d Gaudryceras (Vertebrites) kayei (Forbes); Stinnesbeck, p. 198, pl. 8, figs 2 3, text-fig b Gaudryceras kayei (Forbes); Kennedy and Henderson, p. 402, pl. 5, figs 19 20, 24, 28 41; text-fig. 3d Gaudryceras kayei (Forbes); Ward and Kennedy, p. 17, text-figs 17.11, , Gaudryceras kayei (Forbes); Fatmi and Kennedy, p. 644, figs 5.1, 5.2, Type. Lectotype BMNH C51050 is the original of Forbes (1846, pl. 8, fig 3) by subsequent designation of Matsumoto and Yoshida (1979, p. 70). Material. 53 internal moulds, three with fragments of shell preserved within the umbilicus; 21 deformed or fragmented. Description. The earliest growth stages are characterized by a low expansion rate and trapezoid whorl section, similar to other gaudryceratids (see below). Ornament typical of larger individuals is already exposed. At a diameter of c. 5 mm the whorl section becomes gradually rounded, but the expansion rate remains unchanged. At this stage whorls are serpenticone. With increasing diameter the whorls become less evolute. Now the whorl section is slightly broadened, rounded to rectangular. Maximum whorl breadth is below the middle flank. The large flat umbilicus displays a low, rounded, umbilical wall that grades into broadly rounded flanks. The ventrolateral shoulders are rounded, but the venter is broad and rather flattened. From a shell diameter of 25 mm onwards whorls increase gradually in height, shell expansion rate increases, and U/D decreases. Ornament consists of fine, dense lirae that are strongly projected on the inner flank and curve slightly backwards on the outer flank. Internal moulds are smooth except for three to four constrictions per whorl. The suture line exposes a lanceolate external saddle that is little subdivided. It is extended at larger growth stages. The first lateral saddle (E/L) is large, strongly subdivided, asymmetrically bifid, while the secondary lateral saddle (L/U 2 ) is smaller, less complex and less irregularly bifid. The ventral lobe (E) and the trifid lateral lobe (L) are similar in depth. The first of 3 5 umbilical lobes is large and trifid and located on the retracted sutural lobe. During growth stages documented (maximum D = 38 mm) the umbilical lobes increase in number from three to five within the growth stages documented while the grade of incision of the suture line increases strongly. TEXT-FIG. 5. A B, Pseudophyllites indra (Forbes, 1846). A, UANL CE MAAS-035. B, UANL CE MAAS-033. C, Saghalinites cala (Forbes, 1846). UANL CE MAAS-047. D, Gaudryceras kayei (Forbes, 1846). UANL CE MAAS-043. All 2.

16 1590 PALAEONTOLOGY, VOLUME 47 Dimensions D WB WH WB/WH U U/D UANL CE MAAS UANL CE MAAS UANL CE MAAS-044 (5 7) UANL CE MAAS UANL CE MAAS UANL CE MAAS UANL CE MAAS (7 4) 7 6 (0 97) UANL CE MAAS-043 (38 0) (0 49) Remarks. This species is characterized by a very low expansion rate. The trapezoid whorl section of the smallest juvenile growth stages (D = 7 2 mm) corresponds to that of the other Cerralvo gaudryceratids. At slightly larger diameters (D > 8 mm) the whorl section is more rounded than in Zelandites varuna, andits grade of sutural incision is slightly lower. The typical ornament of the species is developed in very early stages. The G. kayei juvenile growth stage resembles Anagaudryceras politissimum but is distinguished by stronger ornament and the higher number of whorls at similar diameters. Occurrence. The species is known from Santonian Maastrichtian strata, and has been described from South Africa (Woods 1906; Kennedy and Klinger 1979), Tunisia (Pervinquière 1907), the Biscay region (Ward and Kennedy 1993), Pakistan (Fatmi and Kennedy 1999), southern India (Kennedy and Henderson 1992b), western Australia (Henderson and McNamara 1985), Chile (Stinnesbeck 1986), California (Matsumoto 1959b), and Madagascar (Collignon 1956), among other localities. The record of Böse (1928) from the Santonian of Mexico is doubtful. The specimens are reported from the Taylor marls... near Vallecillo, Nuevo León, two miles from town at old shaft on the road to Tortillas (p. 34). We have been to Vallecillo (Text-fig. 1) and searched for the locality described by Böse. The road mentioned by Böse is now Mexican Highway 85. No old mine shaft is displayed in the maps, and rocks in the area to the north and east of Vallecillo are conglomerates. No rocks that would correspond to the Taylor marls are known to occur close to the village, neither in lithology nor in age, and it is thus highly unlikely that the specimens originated from the area close to Vallecillo. Besides, in Texas, the Taylor Group is interpreted to be Campanian in age, and its Marlbrook Marl member is Upper Campanian (see Cobban et al. 1992; Cobban and Kennedy 1993b). Genus ANAGAUDRYCERAS Shimizu, 1934 Type species. Ammonites sacya Forbes (1846, p. 113, pl. 14, fig 9) by original designation by Shimizu (1934, p. 67). The genus was discussed extensively by Kennedy and Klinger (1979). Anagaudryceras politissimum (Kossmat, 1895) Text-figures 3I J, 6D E, I 1895 Lytoceras politissimum Kossmat, 1895, p. 128 (32), pl. 15 (1), fig Anagaudryceras politissimum (Kossmat) Collignon, p. 58, pl. 8, figs 2, 2a, 2b Anagaudryceras politissimum (Kossmat); Collignon, p. 4, pl. 641, fig Anagaudryceras politissimum (Kossmat); Kennedy and Klinger, p. 154, pl. 5, fig. 3 (with full synonymy) Anagaudryceras politissimum (Kossmat); Henderson and McNamara, p. 46, pl. 1, figs 9 10; text-fig. 4d (with additional synonymy) Anagaudryceras politissimum (Kossmat); Stinnesbeck, p. 194, pl. 7, fig. 9; pl. 8, fig. 1; text-figs Anagaudryceras politissimum (Kossmat); Ward and Kennedy, p. 21, pl. 17, figs 9, 12; pl. 19, figs 2, 6, Type. The holotype is the original of Kossmat (1895, p. 128 (32), pl. 15 (1), fig. 7) from southern India. Material. 27 juvenile specimens, four of which are earliest juvenile stages. Description. Initial whorls are serpenticone, with trapezoidal whorl section and low expansion rate. The broad, flat venter bends narrowly into short flanks that are not separated from the flat umbilical walls. WB/WH is c. 1 6, but most

17 IFRIM ET AL.: MAASTRICHTIAN CEPHALOPODS 1591 TEXT-FIG. 6. A C, H, Gaudryceras kayei (Forbes, 1846). A, UANL CE MAAS-042. B, UANL CE MAAS-037. C, UANL CE MAAS-038. H, UANL CE MAAS-039. D E, I, Anagaudryceras politissimum (Kossmat, 1895). D, UANL CE MAAS-045. E, UANL CE MAAS-046. I, UANL CE MAAS-049. F G, J, Zelandites varuna (Forbes, 1846). F, UANL CE MAAS-051. G, UANL CE MAAS-050. J, UANL CE MAAS-053. All 2. specimens are crushed. Nine to ten flat bullae per half whorl are present. Beginning at diameters of 7 mm whorl height increases and the whorl section gradually changes from trapezoidal to rounded. Coiling is evolute with little overlap of whorls, although overlap increases with growth. Expansion rate of the shell is low, but increases during ontogeny, thus

18 1592 PALAEONTOLOGY, VOLUME 47 resulting in a lower WB/WH ratio and smaller umbilicus. Two or more constrictions are present per whorl and accompanied by prominent ribs that are convex on the umbilical shoulder, but projected on the flank and venter. Suture line is finely incised with an extended median saddle and biphylloid terminations of E/L und L/U 2 saddles. Umbilical lobes are extended early on and complex, but do not increase in number. Dimensions D WB WH WB/WH U U/D UANL CE MAAS UANL CE MAAS UANL CE MAAS-048 (25 0) UANL CE MAAS Remarks. Initial whorls with trapezoidal whorl section resemble Gaudryceras kayei and Zelandites varuna. Anagaudryceras politissimum resembles G. kayei though all growth stages although there are clear differences. Gaudryceras kayei is characterized by a lower expansion rate, higher number of whorls at similar diameters and stronger ornament. The conch of A. politissimum inflates at a smaller growth stage than G. kayei. Occurrence. Turonian Santonian of southern India (Kossmat 1895), Santonian of Zululand (Kennedy and Klinger 1979), and Maastrichtian of Madagascar (Collignon 1956). In western Australia (Henderson and McNamara 1985), Chile (Stinnesbeck 1986, 1996) and the Biscay region (Ward and Kennedy 1993) this species was recorded to range high in the Upper Maastrichtian A. mayaroensis Zone. Genus ZELANDITES Marshall, 1926 Type species. Zelandites kaiparaensis Marshall (1926, p. 147) by original designation. The genus was discussed by Kennedy and Klinger (1979). Zelandites varuna (Forbes, 1846) Text-figures 3O P, 6F G, J 1846 Ammonites varuna Forbes, p. 107, pl. 8, fig Lytoceras (Gaudryceras) varuna (Forbes); Kossmat, p. 161, pl. 16, fig. 4; pl. 17, fig Zelandites varuna (Forbes) var. japonica Matsumoto, p. 140, pl. 14, figs 1 7; text-fig Zelandites varuna (Forbes); Collignon, p Zelandites varuna (Forbes); Kennedy and Klinger, p. 296, figs Zelandites varuna (Forbes); Macellari, p. 14, figs , Zelandites varuna (Forbes); Stinnesbeck, p, 195, pl. 8, figs 5 6; text-fig b Zelandites varuna (Forbes); Kennedy and Henderson, p. 404, pl. 5, figs 13 15; pl. 17, figs 2 3. Type. Lectotype BMNH C51059, designated by Kennedy and Henderson (1992b, p. 404) from Forbes original. Material. Nine internal moulds, two with test and ornament. Description. The specimens show two stages of growth that differ considerably. The early juvenile specimens (Textfig. 6F G) show a low whorl section in which whorl breadth is double whorl height (WB/WH is 2 1). The conch is evolute with a moderate expansion rate. The venter is very widely rounded and bends narrowly into funnel-shaped flanks that converge slightly towards the venter. Flanks bend into a very short umbilical wall shortly before touching the previous whorl. Ventrolateral shoulders are ornamented by faint bullae which disappear towards the venter and dorsum. Fine prorsiradiate lirae are visible in the wide umbilicus. The internal moulds show three constrictions per whorl that are each accompanied by a rib. Constrictions cross the venter in a wide concave arch and are slightly prorsiradiate on the flanks. During the fourth or fifth whorl (D is then 4 5 mm), a rapid change is notable into a more involute growth stage (compare Text-fig. 6F G). Whorl section becomes compressed and discoidal. The flanks are high and slightly convergent, and the venter narrowly rounded. Maximum whorl breadth is now in a dorsolateral position immediately above the umbilical wall, which is short and steep. At this stage a whorl covers c. 60 per cent of the former whorl so

19 IFRIM ET AL.: MAASTRICHTIAN CEPHALOPODS 1593 TEXT-FIG. 7. Relationship between WB/WH and diameter in Z. varuna (Forbes, 1846). Diamonds are specimens considered here; open circles are from Stinnesbeck (1986). that small juvenile growth stages are not visible any more (Text-fig. 6J). Faint broad ribs of the early juvenile conch continue on the ventrolateral shoulders, but become increasingly faint. Instead, faint striae cross the flanks. They present convex wide bows on the umbilical and ventrolateral shoulders, but are otherwise straight. They are not visible across the venter on any specimen. The suture line of the early juvenile stage is already complex; the median saddle is extended to a septum, E/L is biphylloid, L is bifid. The umbilical lobes are retracted parallel to the ornament. With increasing diameter the suture line becomes gradually more incised, and L exceeds E in depth. With the change to a high-whorled cross section more umbilical lobes evolve. Dimensions D WB WH WB/WH U U/D UANL CE MAAS UANL CE MAAS UANL CE MAAS UANL CE MAAS Remarks. Early juvenile growth stages of Z. varuna with a trapezoidal whorl section have never been shown. Only Stinnesbeck (1986) described juvenile forms of Z. varuna at different diameters. A comparison of the WB/WH ratio with WD reveals strong changes during early ontogeny (see Textfig. 7). Measurements of our specimens fit so well with those documented from Chile that we assign our juvenile specimens directly to Z. varuna. Occurrence. Maastrichtian of southern India (Kennedy and Henderson 1992b), Japan (Matsumoto 1938), and Madagascar (Collignon 1956); Upper Maastrichtian of Chile (Stinnesbeck 1986), Antarctica (Macellari 1986; Zinsmeister et al. 1989) and Sakhalin Island, the Russian Far East (Yazikova 1994). Suborder AMMONITINA Hyatt, 1889 Superfamily DESMOCERATACEAE Zittel, 1895 Family DESMOCERATIDAE Zittel, 1895 Subfamily DESMOCERATINAE Zittel, 1895 Genus DESMOPHYLLITES Spath, 1929 Type species. Desmoceras larteti Seunes, The genus was extensively discussed by Henderson and McNamara (1985).

20 1594 PALAEONTOLOGY, VOLUME 47 TEXT-FIG. 8. Suture lines of the Ammonitina. A B, Brahmaites (Anabrahmaites) vishnu (Forbes, 1846). A, UANL CE MAAS-081. B, UANL CE MAAS-085. C D, Desmophyllites diphylloides (Forbes, 1846). C, UANL CE MAAS-055. D, UANL CE MAAS-057. E F, Hauericeras rembda (Forbes, 1846). E, UANL CE MAAS-058. F, UANL CE MAAS G H, Menuites juv. sp. G, UANL CE MAAS-077. H, UANL CE MAAS-078. I J, Pachydiscus juv. sp. I, UANL CE MAAS-066. J, UANL CE MAAS-070. All 5. Desmophyllites diphylloides (Forbes, 1846) Text-figures 8C D, 9E F 1846 Ammonites diphylloides Forbes, p. 105, pl. 8, fig Desmoceras desmophylloides (Forbes); Kossmat, p. 108 (173), pl, 19 (25), figs Desmoceras phyllimorphum Kossmat, p. 110 (175), pl. 19 (25), fig Desmophyllites diphylloides (Forbes); Spath, p. 21, pl. 2, figs Desmophyllites diphylloides (Forbes); Matsumoto and Obata, p. 121, pl. 24, figs 1 5; pl. 30, fig Desmophyllites phyllimorphus (Kossmat); Jones, p. 34, pl. 10, figs Desmophyllites diphylloides (Forbes); Collignon, p. 37, pl. 655, fig Desmophyllites diphylloides (Forbes); Henderson and McNamara, p. 54, pl. 4, figs b Desmophyllites diphylloides (Forbes); Kennedy and Henderson, p. 405, pl. 6, figs 1 9; pl. 16, figs 1 3, 7 8; pl. 17, figs 4 7; text-fig. 3f (with full synonymy). Type. The lectotype is BMNH C22682, the original of Forbes (1846, pl. 8, fig. 8), by subsequent designation of Matsumoto and Obata (1955, p. 122). Material. 18 internal moulds. Description. Involute with intermediate expansion rate. The shell is slightly compressed, with WB/WH ratios of c The umbilicus is very small (only c. 7 per cent of the shell diameter) and presents subvertical walls with umbilical shoulders narrowly rounded and grading into subparallel flanks that bend into an evenly rounded venter. The highest whorl breadth is below the middle flank. Size relationships of the conch apparently do not change during early ontogeny. The shell of the Cerralvo specimens is not well preserved. Fine lirae are only visible in the ventral area of two specimens, and 6 8 shallow constrictions are present per half whorl, their number increasing with whorl diameter. On the flanks they are prorsiradiate and straight, but project forward on the venter in a linguoid convexity. The suture shows a trifid L which is equal in depth with E. The E/L and L/U saddles are tetraphylloid and asymmetrical. U has at

21 IFRIM ET AL.: MAASTRICHTIAN CEPHALOPODS 1595 TEXT-FIG. 9. A D, Brahmaites (Anabrahmaites) vishnu (Forbes, 1846). A, UANL CE MAAS-080. B, UANL CE MAAS C, UANL CE MAAS-085. D, UANL CE MAAS-084. E F, Desmophyllites diphylloides (Forbes, 1846). E, UANL CE MAAS-056. F, UANL CE MAAS-057. All 2. least five minor lobes on the dorsal flank arranged in a slightly rectiradiate line. These elements are present from earliest growth stages onwards as documented here, but in particular the number of auxiliary lobes increases with diameter. Dimensions D WB WH WB/WH U U/D UANL CE MAAS UANL CE MAAS

22 1596 PALAEONTOLOGY, VOLUME 47 UANL CE MAAS UANL CE MAAS Remarks. This species is characterized by a slightly compressed whorl section, parallel flanks, the tiny umbilicus, and 6 8 shallow constrictions per whorl; for discussion, see Kennedy and Henderson (1992b). Occurrence. Lower Santonian Upper Maastrichtian of southern India (Kennedy and Henderson 1992b), Tunisia (Pervinquière 1907), western Australia (Henderson and McNamara 1985), Japan (Matsumoto and Obata 1955), Alaska (Jones 1963), California (Matsumoto 1959b), southern USA (Kennedy and Cobban 1993a), British Columbia, South Africa, and south-east France ( fide Ward and Kennedy 1993). Subfamily HAUERICERATINAE Matsumoto, 1938 Genus HAUERICERAS de Grossouvre, 1894 Type species. Ammonites gardeni Baily (1855, p. 456, pl. 11, fig. 3), by original designation. Hauericeras rembda (Forbes, 1846) Plate 2, figures 4 6; Text-figure 8E F 1846 Ammonites rembda Forbes, p. 111, pl. 7, fig Ammonites durga Forbes, p. 104, pl. 7, fig Desmoceras (Hauericeras) rembda (Forbes); Kossmat, p. 124 (189), pl. 18 (24), fig Hauericeras (Gardeniceras)cf. rembda (Forbes); Matsumoto and Obata, p. 144, pl. 29, figs 6 7; textfig Hauericeras (Gardeniceras) rembda (Forbes); Collignon, p. 37, pl. 655, fig b Hauericeras rembda (Forbes); Kennedy and Henderson, p. 408, pl. 6, figs 10 24; pl. 17, fig. 1; text-fig. 3h (with full synonymy) Hauericeras rembda (Forbes); Ward and Kennedy, p. 24, fig Hauericeras rembda (Forbes); Cobban and Kennedy, p. 4, figs 2.6, 2.7, 3. Types. Lectotype BMNH C51024 of Ammonites rembda Forbes (1846, pl. 7, fig. 3) was designated by Matsumoto and Obata (1955, p. 145). Material. 35 internal moulds and fragments of the phragmocone, one specimen with parts of the body chamber preserved. Description. Evolute with low to intermediate expansion rate. The flat umbilicus spans c. 40 per cent of the shell diameter. Approximately one-third of the previous whorl is covered. The flanks are subparallel and slightly convex, with a short vertical wall and narrowly rounded umbilical shoulders. Maximum whorl breadth is at the middle flank. WB/WH decreases with growth due to a gradually compressed whorl section. Three to four deep biconvex constrictions are present per whorl. They are convex on the middle flank and concave and prorsiradiate on the outside to cross the venter in a projected bow. From a diameter of 33 mm onwards a faint keel is preserved on the largest specimen (UANL CE MAAS-063). E is broad and much shallower than the asymmetric trifid L. The umbilical suture line is slightly (early growth stages) to strongly (later growth stages) retracted. EXPLANATION OF PLATE 2 Figs 1 3. Menuites juv. sp. 1, UANL CE MAAS , UANL CE MAAS , UANL CE MAAS-078. Figs 4 6. Hauericeras rembda (Forbes, 1846). 4, UANL CE MAAS , UANL CE MAAS , UANL CE MAAS-063. All 2.

23 IFRIM et al., Hauericeras, Menuites PLATE 2

24 1598 PALAEONTOLOGY, VOLUME 47 Dimensions D WB WH WB/WH U U/D UANL CE MAAS UANL CE MAAS UANL CE MAAS UANL CE MAAS UANL CE MAAS UANL CE MAAS Remarks. Hauericeras rembda is more involute than H. fayoli (de Grossouvre, 1894) (for comparison, see Kennedy 1986c). Kennedy and Henderson (1992b) showed that H. rembda has a keel from a diameter of 20 mm onwards. In our material the keel appears only on our largest specimen at a diameter of 33 mm. The Cerralvo specimens display a juvenile suture line which is less complex even for the largest specimen than the suture line described by Kennedy and Henderson (1992b). Occurrence. Hauericeras rembda (Forbes) is known from Japan (Matsumoto and Obata 1955), the Gansserina gansseri Zone in the Biscay region (Ward and Kennedy 1993), the Upper Maastrichtian of the Valudavur Formation in southern India (Kennedy and Henderson 1992b), and the Maastrichtian of Madagascar (Collignon 1971). A single fragment has been recorded from the Maastrichtian of Alabama (Cobban and Kennedy 1995). Family PACHYDISCIDAE Spath, 1922 Genus PACHYDISCUS Zittel, 1884 Type species. Ammonites neubergicus von Hauer (1858, p. 12, pl. 2, figs 1 4), by subsequent designation of de Grossouvre (1894, p. 177). Subgenus PACHYDISCUS (PACHYDISCUS) Matsumoto, 1947 Type species. As for genus. Pachydiscus (Pachydiscus) juv. sp. Material. 60 internal moulds. Text-figures 8I J, 10A E Description. The test is moderately involute (U/D is c. 24 per cent of the shell diameter) and discoidal. Whorls are slightly compressed (WB/WH is c. 0 85). Maximum whorl breadth is situated half-way between the umbilicus and middle of the flank. Umbilical walls are overhanging, and bending is moderately narrow into weakly convex flanks that converge to a widely rounded venter. Internal moulds are smooth. The largest specimen is poorly preserved; in consequence it is not possible to recognize probable juvenile ornamentation. The suture line is moderately incised. The first saddle (E/L) is considerably larger than the second (L/U 2 ) and extended towards the venter. L is trifid. The auxiliary lobes are strongly retracted, and their number increases with growth and the grade of sutural incision. Dimensions D WB WH WB/WH U U/D UANL CE MAAS UANL CE MAAS UANL CE MAAS UANL CE MAAS UANL CE MAAS UANL CE MAAS-069 (13 0) (5 4) 5 6 (0 96) 3 5 (0 27) UANL CE MAAS UANL CE MAAS-071 (18 0) (5 5) 7 8 (0 71) 4 6 (0 26) UANL CE MAAS UANL CE MAAS (9 7) 12 6 (0 77)

25 IFRIM ET AL.: MAASTRICHTIAN CEPHALOPODS 1599 TEXT-FIG. 10. A E, Pachydiscus juv. sp. A, UANL CE MAAS-113. B, UANL CE MAAS-070. C, UANL CE MAAS-072. D, UANL CE MAAS-068. E, UANL CE MAAS-069. All 2. Remarks. The juvenile specimens of the Campanian P. (P.) travisi (Adkins 1929 loc. cit. Cobban and Kennedy 1993b) display whorl dimensions similar to our specimens, but are ornamented at diameters up to 25 mm by delicate concave ribs on the outer flank (Cobban and Kennedy 1993b, p. D3). Almost smooth internal moulds and whorl dimensions clearly relate the Cerralvo species with the group of P. (P.) neubergicus (von Hauer, 1858). The species P. (P.) neubergicus sensu stricto displays smooth early growth stages up to a diameter of about 25 mm (Henderson and McNamara 1985) and at larger diameters. Its whorl section is similar to that of the Cerralvo specimens, and faint umbilical ribs are visible on some of our specimens (e.g. Text-fig. 10A, D). Pachydiscus (P.) gollevillensis (d Orbigny, 1850), a species closely related to P. (P.) neubergicus, is more compressed at a comparable state of growth than our

26 1600 PALAEONTOLOGY, VOLUME 47 specimens. The same is true for closely related P. (P.) armenicus Atabekian and Akopian, 1969, but the early juvenile growth stages of these species are very similar, and the determination of Pachydiscus species is based on the adult ornamentation, which is not developed on our small specimens. Although our individuals show close affinities towards the group of P. (P.) neubergicus, they are too small and immature to allow a reliable determination of the species. Genus MENUITES Spath, 1922 Type species. Ammonites menu Forbes, 1846, p. 111, pl. 10, fig. 1, by original designation of Spath (1922, p. 123). Menuites juv. sp. Plate 2, figures 1 3; Text-figure 8G H Material. 42 internal moulds of juveniles of which four are deformed. Description. All specimens are juveniles. Their tests are globularly inflated, depressed (WB/WH is between 1 5 and 1 8) and involute. The umbilicus spans c. 20 per cent of the diameter but decreases during growth of the shell. The umbilical wall is overhanging and forms an approximate half circle between umbilical seam and flank. The flanks are reduced because the venter arches very widely. Maximum whorl breadth is located at the transition between umbilical wall and flank. The surfaces of most of the internal moulds are smooth, but faint bullae (c. 10 per whorl) are present on some of the larger specimens. The suture line is moderately incised with E larger than L. U is small and slightly retracted. Dimensions D WB WH WB/WH U U/D UANL CE MAAS UANL CE MAAS UANL CE MAAS UANL CE MAAS UANL CE MAAS UANL CE MAAS Remarks. The only documentation of equally small growth stages was by Henderson and McNamara (1985, pl. 8, figs 5 6), but their specimen of Menuites fresvillensis expands at a slightly larger rate. Relationships to other species were discussed there and in Kennedy (1986b). On the basis of this poor documentation of early juvenile growth stages of Menuites our species is indeterminable. Family KOSSMATICERATIDAE Spath, 1922 Subfamily KOSSMATICERATINAE Spath, 1922 Genus BRAHMAITES Kossmat, 1897 Type species. Ammonites Brahma Forbes (1846, p. 100, pl. 8, fig. 1) by original designation. Subgenus BRAHMAITES (ANABRAHMAITES) Yabe and Shimizu, 1924 Type species. Ammonites vishnu Forbes (1846, p. 100, pl. 7, fig. 9) by original designation. For discussion of the subgenus see Henderson and McNamara (1985, p. 67). Brahmaites (Anabrahmaites) vishnu (Forbes 1846) Text-figures 8A B, 9A D 1846 Ammonites vishnu Forbes, 1846, p. 100, pl. 7, fig Brahmaites haugi Seunes; Collignon, p. 45, pl. 7, fig. 3.

27 IFRIM ET AL.: MAASTRICHTIAN CEPHALOPODS Brahmaites vishnu (Forbes); Atabekian and Akopian, p. 37, pl. 2, fig b Brahmaites (Anabrahmaites) vishnu (Forbes); Kennedy and Henderson, p. 418, pl. 6, figs 25 26; pl. 9, figs 5 7, 17 20; pl. 10, fig. 5; pl. 17, figs 8, (with full synonymy), 1993 Brahmaites (Anabrahmaites) vishnu (Forbes); Kennedy and Hancock, p. 580, pl. 1, figs 5 6. Type. The lectotype, subsequently designated by Kennedy and Henderson (1992b), is BMNH C51026, the original of Forbes (1846, pl. 7, fig. 9). Material. 83 internal moulds, some with test preserved; all juveniles. Description. Moderately evolute with intermediate expansion rate. The broadly rounded venter grades into rounded flanks with maximum breadth above the middle flanks. Flanks bend narrowly into a steep overhanging short umbilical wall. Ornament on internal moulds is restricted to three constrictions per whorl, which are associated with two collar ribs. Ribs and constrictions are parallel. They are straight and prorsiradiate on the flanks, and cross the venter in a wide arch. On two examples with goethitized conchs ribs superimpose the constrictions. The suture line is moderately complex, E is approximately as deep as the trifid L. Bifid E/L and L/U become subdivided in larger specimens. The sutural lobe is retracted. Its length increases strongly with the growing number of umbilical lobes and the grade of incision. Dimensions D WB WH WB/WH U U/D UANL CE MAAS UANL CE MAAS UANL CE MAAS UANL CE MAAS UANL CE MAAS UANL CE MAAS Remarks. The umbilicus increases during growth from 27 per cent at a diameter of 8 4 mm to 35 per cent at a diameter of 16 5 mm. The absence of umbilical bullae and a depressed whorl section differentiate B. (A.) vishnu from Brahmaites (B.) brahma (Forbes, 1846). Occurrence. Brahmaites (Anabrahmaites) vishnu occurs in the Maastrichtian of southern India (Kennedy and Henderson 1992b), Armenia (Atabekian and Akopian 1970), Madagascar (Collignon 1938), south-west France and northern Spain (Ward and Kennedy 1993). In the US Gulf Coast area the genus Brahmaites was first described by Cobban and Kennedy (1991a) from the Nacatotch Sand, Arkansas, but these specimen have not been determined to species level. Suborder ANCYLOCERATINA Wiedmann, 1966 Superfamily TURRILITACEAE Gill, 1871 Family BACULITIDAE Gill, 1871 Genus BACULITES Lamarck, 1799 Type species. Baculites vertebralis Lamarck (1801, p. 103) by subsequent designation of Meek (1876, p. 391). Baculites ovatus Say, 1820 Plate 3, figures 1 3; Text-figures 11A E, 12A D 1820 Baculites ovata Say, p b Baculites ovatus Say; Cobban, p. 3, pl. 1, figs 1 31; pl. 2, figs 1 14; pl. 3, figs 1 6, 9 11; text-fig. 4 (with full synonymy) Baculites ovatus Say; Wolleben, p. 389, pl. 3, fig Baculites ovatus Say; Vega-Vera and Carmen Perrilliat, p. 19, pl. 4, figs b Baculites ovatus Say; Kennedy and Cobban, p. 426, text-figs , 14.5, 14.12, , 14.20, , , Baculites ovatus Say; Vega et al., p. 347.

28 1602 PALAEONTOLOGY, VOLUME 47 Type species. The holotype, by original designation of Say (1820, p. 41), recorded at the Academy of Natural Sciences, Philadelphia, may be lost (see Cobban, 1974b, p. 4). Material. 167 internal moulds, all fragments of the phragmocone. Description. The test is ovate in cross section and expands moderately quickly to fast with an apical angle of c. 8 degrees. The venter is more rounded in juveniles. Convex flanks grade into a widely rounded dorsum. Maximum breadth is above the middle flank. The flank is ornamented dorsolaterally with faint crescentic ribs, which are weak or absent in juveniles but more pronounced in adult individuals (rib index about 2). These ribs cross the dorsum in a convex arch. Ribs split into straight prorsiradiate striae on the flanks. Striae bend forward shortly before the venter and are then strongly projected. The rib index of these secondary ribs is c. 4. The suture line is composed of broad, little incised and subrectangular bifid saddles with phylloid saddle terminations. The dorsal saddle is lower than the lateral saddles. Lobes are also bifid and subrectangular. Two subsequent sutures overlap deeply at the L/U saddle, but are gradually separated during ontogeny and with increasing grade of incision. In more adult phragmocones, saddles and lobes become more rounded in outline. Dimensions WB WH WB/WH A L UANL CE MAAS UANL CE MAAS UANL CE MAAS-090 (5 1) (7 7) (0.66) UANL CE MAAS UANL CE MAAS (7) UANL CE MAAS UANL CE MAAS UANL CE MAAS UANL CE MAAS UANL CE MAAS between ribs Remarks. Some specimens assigned to B. ovatus are similar to Late Maastrichtian B. vertebralis (Lamarck, 1801). Particularly, specimens with rounded venter and distant, faint ribs look very much alike, but differ from B. vertebralis in having a slightly higher WB/WH ratio (e.g. UANL CE MAAS-094 and 095, Textfig. 11C D; see also Cobban 1974b, pl. 1, figs 21, 27 31). Baculites undatus Stephenson (1941) is strongly ornamented and differs from B. ovatus in having a stout, subelliptical whorl section and a lower rib index (primary rib index of B. undatus is c. 1). Small growth stages of B. ovatus are similar to B. occidentalis (Meek 1862), but no comparison exists so far for juveniles of these two species. Baculites occidentalis is known from the uppermost Campanian lowest Maastrichtian of Madagascar and the northern Pacific region (Ward 1978). Occurrence. Baculites ovatus Say is known to occur in the Navesinsk Formation in New Jersey (Cobban 1974b) and the Saratoga Chalk of Arkansas (Kennedy and Cobban 1993b). It has also been described from the Potrerillos Formation of the Difunta Group in north-east Mexico (Wolleben 1977; Vega et al. 1995, but only listed). The species seems to be restricted to the northern Gulf of Mexico region and the Atlantic coast of North America. EXPLANATION OF PLATE 3 Figs 1 3. Baculites ovatus Say, , UANL CE MAAS , UANL CE MAAS , UANL CE MAAS-089. All 2.

29 IFRIM et al., Baculites PLATE 3

30 1604 PALAEONTOLOGY, VOLUME 47 TEXT-FIG. 11. A E, Baculites ovatus Say, A, UANL CE MAAS-096. B, UANL CE MAAS-091. C, UANL CE MAAS-094. D, UANL CE MAAS-095. E, UANL CE MAAS-088. All 2. Genus FRESVILLIA Kennedy, 1986b Type species. Fresvillia constricta Kennedy, 1986b (p. 61, pl. 14, figs 39 42; text-fig. 10a) by original designation. Fresvillia constricta Kennedy, 1986b Text-figures 12E F, 13D E 1986b Fresvillia constricta Kennedy, p. 62, pl. 14, figs 39 42; text-fig. 10a. Type. The holotype is IRSNB from the Upper Maastrichtian of Manche, France, by original designation (Kennedy 1986b, pl. 14, figs 39 42; text-fig. 10a).

31 IFRIM ET AL.: MAASTRICHTIAN CEPHALOPODS 1605 TEXT-FIG. 12. Suture lines of the Baculitidae. A D, Baculites ovatus Say, A, UANL CE MAAS-090. B, UANL CE MAAS-086. C, UANL CE MAAS-093. ( 5). D, UANL CE MAAS-097. ( 3). E F, Fresvillia constricta Kennedy, 1986a. E, UANL CE MAAS-100. F, UANL CE MAAS-098. G, Fresvillia aff. F. teres (Forbes, 1846). UANL CE MAAS-102. ( 5). Material. 22 internal moulds, fragments of the phragmocone. Mostly deformed, no test preserved. Description. The straight test has a low expansion rate and an apical angle of c. 3 degrees. Shell is circular with a WB/WH ratio of c. 1. The phragmocone is smooth except for rare constrictions that are strongly projected forward on the flanks but disappear at middle-flank. They cross the dorsum in a wide arch. Striae are directed parallel to the constrictions but are extremely faint. The simple baculitid suture line is composed of moderately incised, symmetrical, bifid lobes and saddles with trigonal outline, and similar depths and heights. The dorsal saddle is slightly wider than other saddles and not strictly symmetrical. The ventral saddle is incised centrally at all growth stages.

32 1606 PALAEONTOLOGY, VOLUME 47 Dimensions WB WH WB/WH A L UANL CE MAAS UANL CE MAAS UANL CE MAAS Remarks. The circular whorl section and even suture line with triangular elements distinguish Fresvillia from Baculites; the conspicuous constrictions on the otherwise smooth internal moulds characterize the species and enable easy determination. Specimens with completely smooth surfaces are considered to belong to F. constricta because they are fragments without the distant constrictions. Fresvillia teres (Forbes) differs from F. constricta in having faint annular to ventrally prorsiradiate ribs. Occurrence. Fresvillia constricta Kennedy is known so far only from the Upper Maastrichtian Calcaire à Baculites, north-west France (Kennedy 1986b). Fresvillia aff. F. teres (Forbes, 1846) Text-figures 12G, 13A C, F 1846 Baculites teres Forbes; p. 115, pl. 10, fig a Fresvillia teres (Forbes); Kennedy and Henderson, p. 718, pl. 5, figs 14 17; text-fig. 2c (with full synonymy). Types. The holotype is BMNH C51152, the original of Forbes (1846, pl. 10, fig. 5) by original designation. Material. Eight internal moulds, juvenile fragments of the phragmocone, more or less deformed. Description. The straight shell is perfectly circular in cross section and expands slowly with a low apical angle of 3 4 degrees. Ornament consists of faint, broad, annular ribs that are weakest on the dorsum. They strengthen across the dorsolateral area. The rib index is c The baculitid suture is composed of triangular elements of equal height, which are moderately incised. The ventral saddle is incised centrally, the dorsal saddle is slightly narrower than the others. Dimensions WB WH WB/WH A L UANL CE MAAS (4) UANL CE MAAS UANL CE MAAS UANL CE MAAS Remarks. Whorl section and suture line are comparable to that of F. constricta.ribsoff. aff. F. teres are not as pronounced as described by Kennedy and Henderson (1992a) although this may be an artefact of weathering and/or abrasion. The Cerralvo specimens are here related to F. teres because of the similar rib index, although they lack the conspicuous backward sweeping towards the venter of the otherwise annular ribs. This absence could result from juvenile specimens. Occurrence. Fresvillia teres (Forbes) is restricted to the Maastrichtian, with records from India (Kennedy and Henderson 1992a), western Australia (Brunnschweiler 1966; Henderson et al. 1992), Alaska (Jones 1963) and California (Matsumoto 1959a).

33 IFRIM ET AL.: MAASTRICHTIAN CEPHALOPODS 1607 Family DIPLOMOCERATIDAE Spath, 1926 Subfamily DIPLOMOCERATINAE Spath, 1926 Genus DIPLOMOCERAS Hyatt, 1900 Type species. Baculites cylindraceus Defrance (1816, p. 160), by original designation. For a description of the genus, see Olivero and Zinsmeister (1989); for occurrence, see Kennedy (1986b). Diplomoceras cylindraceum (Defrance, 1816) Text-figures 13G H, 14E 1816 Baculites cylindracea Defrance, p a Diplomoceras cylindraceum (Defrance); Kennedy, p. 181, pl. 17, fig. 3; pl. 18, fig. 5; pl. 21, figs 2 3, 5 6; pl. 22, fig. 6; pl. 23, figs 1 2; pl. 24, figs 1 3; pl. 25, figs 1 8; pl. 26, fig. 18; pl. 33, fig. 16; pl. 36, fig. 6; text-figs 9 10 (with full synonymy). 1986b Diplomoceras cylindraceum (Defrance); Kennedy, p. 51, pl. 4, figs 1 2; pl. 9, figs 8 10; pl. 10; text-figs 3i l, 6, 7g m (with full synonymy) Diplomoceras lambi (Spath); Olivero and Zinsmeister, p. 627, figs Diplomoceras maximum (Spath); Olivero and Zinsmeister, p. 629, figs 2.5, , Diplomoceras cylindraceum (Defrance); Henderson et al., p. 140, figs 5, 6a e, h k, a Diplomoceras cylindraceum (Defrance); Kennedy and Henderson, p. 704, pl. 6, figs 1 3; text-figs 1b, 3 (with full synonymy). Type. The neotype, designated by Kennedy (1986a, p. 183, pl. 24, figs 1 3), is no in the IRSNB collections. Material. Three fragments. Description. The specimens are short straight fragments of the juvenile phragmocone. The largest and best preserved individual (Text-fig. 13H) has an oval cross section with broadly rounded flanks, and narrowly rounded dorsum and venter. A thin layer of the test is preserved so that the ornament is faintly visible. On the test ribs are dense and rectiradiate in the dorsal area but slightly retracted on the flanks to cross the venter at an angle of c. 80 degrees. The rib index is c. 12 for the largest individual. The suture line is visible on the smaller specimen illustrated (Text-fig. 13G). It is deeply incised with symmetrical bifid lobes and saddles. E is slightly extended and surrounded by high saddles; the sutural elements are lower towards the dorsum. Dimensions. UANL CE MAAS-105: WB, 4 1; WH, 6 6; WB/WH, UANL CE MAAS-106: WB, 7 6; WH, 9 7; WB/WH, Remarks. The suture line of the early juvenile specimen is little incised. Elements correspond to Diplomoceras cylindraceum (Defrance) as well as shell ornament, and the cross section is within the wide range of possible WB/WH ratios (see Kennedy and Henderson 1992a) known for the species. Occurrence. Diplomoceras cylindraceum ranges throughout the Maastrichtian, with records from France, Spain, Italy, The Netherlands, northern Germany, Denmark, Poland, Austria, the Ukrainian SSR, Arctic Siberia, Bulgaria, South Africa, Madagascar, Chile, Argentina, Brazil, California, British Columbia, Japan (fide Ward and Kennedy 1993), southern India (Kennedy and Henderson 1992a), western Australia (Henderson et al. 1992), the Antarctic Peninsula (Olivero and Zinsmeister 1989), and Alaska (Jones 1963). Hence, it is a cosmopolitan Maastrichtian species which is known in all latitudes from Alaska to Antarctica. Subfamily POLYPTYCHOCERATINAE Matsumoto, 1938 Genus SOLENOCERAS Conrad, 1860 Type species. Hamites annulifera Morton (1842, p. 213) by original designation by Conrad (1860, p. 284).

34 1608 PALAEONTOLOGY, VOLUME 47 TEXT-FIG. 13. A C, F, Fresvillia aff. F. teres (Forbes, 1846). A, UANL CE MAAS-102. B, UANL CE MAAS-104. C, UANL CE MAAS-103. F, UANL CE MAAS-101. D E, Fresvillia constricta Kennedy, 1986a. D, UANL CE MAAS E, UANL CE MAAS-99. G H, Diplomoceras cylindraceum (Defrance, 1816). G, UANL CE MAAS-105. H, UANL CE MAAS-106. All 2. Solenoceras reesidei Stephenson, 1941 Text-figure 15A C 1941 Solenoceras reesidei Stephenson, p. 399, pl. 77, figs 4 5; pl. 79, figs Solenoceras reesidei Stephenson; Cobban et al., p. A6, pl. 1, figs 18 22, text-fig a Solenoceras reesidei Stephenson; Cobban and Kennedy, p. B6, pl. 7, figs 1 9, 11 12, 14 15, 18, 25. Type. The holotype is USNM 77238, the original of Stephenson (1941, p. 401, pl. 77, figs 1 3).

35 IFRIM ET AL.: MAASTRICHTIAN CEPHALOPODS 1609 TEXT-FIG. 14. Suture lines of the genera Nostoceras and Diplomoceras. A B, Nostoceras (Nostoceras) alternatum (Tuomey, 1854). A, UANL CE MAAS-128. B, UANL CE MAAS-129. C, Nostoceras (Nostoceras) colubriformis Stephenson, UANL CE MAAS-117. D, Nostoceras (Nostoceras) rugosum Cobban and Kennedy, 1991b. UANL CE MAAS-123. E, Diplomoceras cylindraceum (Defrance, 1816). UANL CE MAAS-105. All 5. Material. 15 fragments, many crushed and/or covered with veins of goethite. One fragment uncrushed with the nacreous shell preserved. Description. U-shaped and straight shell fragments with low to intermediate expansion rates. Cross section of the test is oval. The cross section of the juvenile limb is rounded to compressed with ventrolateral shoulders and a narrow bow towards the dorsum. The dorsum of the more adult limb is concavely grooved and contains the juvenile shaft with rounded to triangular cross section. The test is ornamented with prominent simple ribs, with a rib index of c. 7. They are straight and retracted towards the venter. Faint pairs of tubercles are present on the venter of two specimens. The suture line is visible in part and very simple. Dimensions. UANL CE MAAS-109: WD, 8 1; WB, 5 6; WH, 5 6; WB/WH, Remarks. Ribs are more densely arranged than in S. texanum (Shumard, 1861), and the cross section of the smaller limb is more circular. The shell expands at a slightly faster rate, which leads to a stronger difference in diameter between the juvenile and adult limb at comparable distances from the hook. Solenoceras annulifer (Morton, 1841) and S. multicostatum (Stephenson, 1941) have finer ornament and depressed reniform sections up to the adult shaft. In comparison to S. multicostatum (Stephenson, 1941) both limbs of S. reesidei are pressed onto each other more narrowly. Occurrence. Solenoceras reesidei Stephenson is restricted to the northern Gulf of Mexico area and the Interior Seaway of the US. It was recorded from the Upper Campanian Baculites compressus and Baculites reesidei zones of the Pierre Shale, Colorado (Cobban et al. 1992), the Upper Campanian Coon Creek Tongue of the Ripley Formation in Tennessee (Cobban and Kennedy 1993a), and the Navarro Formation of Texas (Stephenson 1941; Cobban and Kennedy 1991a). Solenoceras sp. was recorded from the Potrerillos Formation (Difunta Group, north-eastern Mexico) and the Cárdenas Formation (east-central Mexico), but specimens were not figured or described (Vega et al. 1995). Solenoceras texanum (Shumard, 1861) Text-figure 15D E 1861 Ptychoceras texanus Shumard, p Solenoceras texanum (Shumard); Stephenson, p. 399, pl. 77, figs 4 5; pl. 79, figs Solenoceras cf. S. texanum (Shumard); Lewy, p. 127, pl. 3, fig. 8.

36 1610 PALAEONTOLOGY, VOLUME 47 TEXT-FIG. 15. A C, Solenoceras reesidei Stephenson, A, UANL CE MAAS-109. B, UANL CE MAAS-108. C, UANL CE MAAS-107. D E, Solenoceras texanum (Shumard, 1861). D, UANL CE MAAS-111. E, UANL CE MAAS-112. All Solenoceras sp. cf. S. texanum (Shumard); Klinger, p. 77, pl. 34, fig a Solenoceras texanum (Shumard); Cobban and Kennedy, p. C3, pl. 1, figs a Solenoceras texanum (Shumard); Cobban and Kennedy, p. B6, pl. 7, figs 10, 16 17, 19 24, 26 28, (with full synonymy). Type. Neotype USNM 21092a, designated by Stephenson (1941, p. 399, pl. 79, figs 1 2), is from the Nacatotch Sand of Texas. Material. 13 fragments, mostly crushed, one well preserved. Test usually preserved as goethite or nacre but covered with thick veins of goethite. Description. Two straight limbs with low expansion are pressed onto each other so that the whorl section of the test is compressed oval. The juvenile straight shell is slender and inflated triangular in whorl section. The venter is widely arched and grades into convex, convergent flanks that bend into the convex dorsum. The juvenile shaft is embedded in a concave groove in the adult dorsum. The surface is covered with simple sharp ribs (rib index c. 5). They are almost straight and bear pairs of tubercles on the ventral side. On the flanks of juvenile shafts they are slightly prorsiradiate.

37 IFRIM ET AL.: MAASTRICHTIAN CEPHALOPODS 1611 On the hook, ribs split into pairs to accommodate the increasing surface. They also change from prorsiradiate to a rursiradiate direction joining the two limbs. The whorl section increases considerably subsequent to the hook. The suture line is visible in parts and rather simple. Dimensions. UANL CE MAAS-110: WB, 3 8; WH, 3 8; WB/WH, UANL CE MAAS-111: WD, 9 0; thicker limb: WB, (4 1); WH, 5 3; WB/WH, (0 77); smaller limb: WB, 3 5; WH, 4 1; WB/WH, UANL CE MAAS-112: WD, 9 4; thicker limb: WB, 6 1; WH, 6 3; WB/WH, 0 97; smaller limb: WB, 5 3; WH, 3 6; WB/WH, Remarks. This species is characterized by having stronger ribs and a lower rib index than S. reesidei. According to Cobban and Kennedy (1991a, 1993a) the ribs are stronger than in S. reesidei and other species of Solenoceras. Occurrence. Solenoceras texanum is known from the Upper Campanian of Israel (Lewy 1969), the?maastrichtian of South Africa (Klinger 1976), and the Campanian Coon Creek Tongue of the Ripley Formation in Tennessee (Cobban and Kennedy 1993a). It was also recorded from the Upper Campanian and Lower Maastrichtian of the Nacatotch Sand of Texas (Stephenson 1941; Cobban and Kennedy 1991a). A fragment best referred to S. texanum comes from the Saratoga Chalk, Arkansas (Kennedy and Cobban 1993b). Family NOSTOCERATIDAE Hyatt, 1894 Genus NOSTOCERAS Hyatt, 1894 Type species. Nostoceras stantoni Hyatt (1894) by original designation. Type species. As for genus. Subgenus NOSTOCERAS (NOSTOCERAS) Hyatt, 1894 Nostoceras (Nostoceras) colubriformis Stephenson, 1941 Plate 4, figures 1 4; Text-figure 14C 1941 Nostoceras colubriformis Stephenson, p. 412, pl. 81, figs b Nostoceras (Nostoceras) colubriformis Stephenson; Kennedy and Cobban, p. 421, text-figs 7.1 4, Type. The holotype is USNM 77265, by original designation. Material. 108 specimens (72 sinistral, 36 dextral), all internal moulds, partially with goethitized test. One specimen with initial whorl. No final hook preserved. Description. Tests are evolute and highly trochospiral with a low expansion rate. Apical angle of 20 degrees in early juveniles increases to 35 degrees from the third whorl onwards. An initial whorl (diameter of c. 3 mm) is uncoiled at an angle of c. 408 from the succeeding trochospiral whorl. Juvenile whorl section is rounded to slightly subrectangular with WH/WB c Whorl sections are flattened at the contact between whorls. The outer surface of a whorl is covered by c. 40 prorsiradiate simple and forked ribs, and three to four constrictions per whorl. Bifurcation originates in weak bullae located on the outer whorl suture. A second row of elongated tubercles is present on the inner whorl suture. These rows are absent on the initial whorl but present on all succeeding ones. The number of rib bifurcations increases with whorl diameter. Tubercles described for Nostoceras (Nostoceras) colubriformis by Kennedy and Cobban (1993c) cannot be seen on the Cerralvo specimens, probably because of bad preservation of the test. No final hook is preserved. The suture line is simple and similar to that of other species of Nostoceras. Dimensions WD WB WH WB/WH A sense of coiling UANL CE MAAS sinistral UANL CE MAAS dextral

38 1612 PALAEONTOLOGY, VOLUME 47 UANL CE MAAS sinistral UANL CE MAAS sinistral UANL CE MAAS sinistral Remarks. The ribs are less sharp than described by Stephenson (1941) but with typical patterns for the species. The absence of faint tubercles described by Stephenson may be an artefact and result of abrasion. The species differs from Nostoceras (Nostoceras) alternatum described herein by having a more rounded whorl section and less prominent ornament. The initial whorl differs from that of N. (N.) rugosum in having a closed umbilicus and a different angle of uncoiling. Occurrence. Nostoceras (Nostoceras) colubriformis has been described from the Upper Campanian Saratoga Chalk of Arkansas (Kennedy and Cobban 1993b) and the Nacatotch Sand of the Maastrichtian Navarro Formation of Texas (Stephenson 1941). Nostoceras (Nostoceras) alternatum (Tuomey, 1854) Text-figures 14A B, 16A C 1854 Turrilites alternatus Tuomey, p b Nostoceras alternatum (Tuomey); Cobban, p. 86, figs 1w-rr, b Nostoceras alternatum (Tuomey); Cobban and Kennedy, p. E3, pl. 2, figs 5 27 (with full synonymy) Nostoceras alternatum (Tuomey); Cobban and Kennedy, p. 14, figs Type. Tuomey s holotype (1854, p. 168) is lost (see Cobban and Kennedy 1991b). Material. 108 specimens of which only 36 are dextral. Internal moulds with partially goethitized tests. No final hook preserved. Description. Sinistral and dextral coiling. Moderately evolute and trochospiral. Apical angle of degrees and intermediate expansion rate result in an open umbilicus on the abapical side. This umbilicus spans c. 21 per cent of the whorl diameter. Whorl cross section is rhomboidal and WB/WH c Approximately 25 single ribs per whorl are present internally and ventrally, and fork into pairs at sharp bullae on the lower flank or precisely on the whorl contact. Where test is preserved these bullae are extended to form short triangular spines which rest in the interspaces of ribs of the succeeding whorl. A second row of tubercles or bullae is located on the inner whorl contact. The two rows of bullae form a concave mould between them that accommodates the succeeding whorl. The suture line is simple and asymmetric. The E/L saddle is broad, rectangular, little incised and asymmetrically bifid. L/U, L and U are narrower and symmetrically bifid. Dimensions WD WB WH WB/WH U U/D A sense of coiling UANL CE MAAS dextral UANL CE MAAS sinistral UANL CE MAAS (1 7) (0 14) 50 sinistral UANL CE MAAS dextral UANL CE MAAS dextral EXPLANATION OF PLATE 4 Figs 1 4. Nostoceras (Nostoceras) colubriformis Stephenson, , UANL CE MAAS , UANL CE MAAS , UANL CE MAAS , UANL CE MAAS-118. Figs 5 7. Nostoceras (Nostoceras) rugosum Cobban and Kennedy, 1991b. 5, UANL CE MAAS , UANL CE MAAS , UANL CE MAAS-120. All 2.

39 IFRIM et al., Nostoceras PLATE 4

40 1614 PALAEONTOLOGY, VOLUME 47 TEXT-FIG. 16. A C, Nostoceras (Nostoceras) alternatum (Tuomey, 1854). A, UANL CE MAAS-127. B, UANL CE MAAS-129. C, UANL CE MAAS-126. All 2. Remarks. The species resembles N. (N.) approximans, N. (N.) hyatti and N. (N.) helicinum, species that do not have spines but rows of tubercles instead. These tubercles are located ventrolaterally with a short distance to the contact between succeeding whorls. In addition, all other species of Nostoceras have rounded whorl sections instead of rhomboidal. The ornament resembles that of N. (N.) rugosum, which differs from N.(N.) alternatum in having a smaller apical angle and lower expansion rate. Cobban (1974b) and Cobban and Kennedy (1991b) described a size dimorphism characterized by uncoiling of the final hook at different sizes. Unfortunately no final hook is preserved among the Cerralvo specimens so that this dimorphism cannot be observed. Occurrence. Nostoceras (Nostoceras) alternatum (Tuomey) is an upper Lower Maastrichtian biozonal marker in the Ripley Formation of Mississippi, Alabama and Georgia (Cobban 1974a; Cobban and Kennedy 1991b). The species has also been reported from the Maastrichtian Nacatotch Sand in Arkansas (Cobban and Kennedy 1991a) and the Navesinsk Formation in New Jersey (Cobban 1974b). Nostoceras (Nostoceras) rugosum Cobban and Kennedy, 1991a Plate 4, figures 5 7; Text-figure 14D 1991a Nostoceras (Nostoceras) rugosum, Cobban and Kennedy, p. C2, pl. 1, figs

41 IFRIM ET AL.: MAASTRICHTIAN CEPHALOPODS 1615 Type. The holotype is USNM by original designation of Cobban and Kennedy (1991a, p. C2, pl. 1, figs 26 27, 31). Material. 66 fragments of juveniles of which 27 are dextrally coiled (21 macroconchs, 18 microconchs, others indeterminable). Internal moulds with partially preserved test. One specimen with broken initial whorl. No final hook preserved. Description. The low expansion rate results in a highly trochispiral cone with an apical angle of 40 degrees. The sense of coiling is both dextral and sinistral, but sinistral phragmocones predominate. Whorls are evolute to serpenticone. Inner walls create a spindle. This species displays dimorphism. The whorl section of microconchs (Pl. 4, fig. 6) is rounded to slightly tearshaped, caused by a concave groove on the dorsum which accommodates the base of the previous whorl. External and internal whorls are widely arched. WH/WB is c Ornament in microconchs is similar to macroconchs but smoother. In macroconchs (Pl. 4, figs 5, 7) there are c. 50 weak ribs per whorl on the lower flank and contact to the succeeding whorl. They are slightly flexuous, in later juvenile growth stages prorsiradiate. Ribs fork into pairs at bullae at or directly above the whorl suture. This ornament of macroconchs results in a rounded to square-shaped whorl section. Where test is preserved there is a tubercle on each end of a bulla. Simple ribs are present irregularly in early growth stages, whereas trifid ribs occur in later growth stages. A second row of bullae is present on the inner whorl suture. Both rows of bullae are linked by straight prorsiradiate ribs which are located on the contact between whorls. Up to three constrictions are present per whorl and flanked by collared ribs. Ribs on microconchs are similar, but ridges are smaller and much weaker on the internal moulds. Our material includes a single initial whorl of Nostoceras (Nostoceras) rugosum, which is uncoiled at an undeterminable angle. Ornament is already present on the second whorl but too faint to be determined exactly. Only short parts of the suture line are preserved. It is asymmetrical, moderately incised and similar to that of Nostoceras (Nostoceras) colubriformis and N. (N.) alternatum. Dimensions WD WB WH WB/WH UANL CE MAAS dextrally coiled microconch UANL CE MAAS dextrally coiled macroconch UANL CE MAAS dextrally coiled macroconch UANL CE MAAS sinistrally coiled microconch UANL CE MAAS sinistrally coiled macroconch Remarks. Cobban and Kennedy (1991a) described dimorphism for the species based on uncoiling of the adult hook at different diameters. No hooks are preserved in the Cerralvo material and dimorphism can only be observed based on ornament. Microconchs strongly resemble N. (N.) colubriformis, but differences exist regarding rib index, apical angle, expansion rate, and WH/WD ratio. The sharp bullae on the lower outside of internal moulds also characterize Nostoceras (Nostoceras) rugosum but are absent in N. (N.) colubriformis. The initial whorl of the two species differs in angle of uncoiling. Macroconchs resemble N. (N.) alternatum in ornament but differ by a lower expansion rate and a lower apical angle. The high spire and subquadrate whorl section separate this species from all other Nostoceras except for N. (N.) pauper (Whitfield, 1892), which has a much lower apical angle, stronger ribs and more tubercles. Occurrence. In the Nacatotch Sand of Arkansas N. (N.) rugosum marks a biozone below the N. (N.) alternatum biozone (Cobban and Kennedy 1991a, b). It characterises a local assemblage zone above the Upper Campanian N. (N.) hyatti Zone and below the N. (N.) alternatum assemblage zone (Cobban and Kennedy 1991b). The Mexican specimens described here are the first recorded outside Hempstedt County, Arkansas. AMMONITE OCCURRENCES AND AGE OF THE CERRALVO FAUNA Stratigraphic ranges of Maastrichtian ammonites prior to their extinction are not well known. Correlations between ammonites, belemnites, planktic foraminifera and nannofossils are rare, and restricted to only a few sections. Ammonite zones and their taxa are well known for the Western Interior Seaway (Cobban 1993), and the timing of their boundaries is well studied (Obradovich 1993; Gradstein et al. 1995). The Western Interior ammonite zones can be correlated into the Gulf of Mexico where inoceramids occur (Walaszczyk et al. 2001).

42 1616 PALAEONTOLOGY, VOLUME 47 TABLE 1. Summary of occurrences of the Cerralvo species. Only localities are included regardless stratigraphic age or facies. Question marks indicate uncertain determinations or publications in which the species have not been figured. The records of north-east Mexico (*) include citations published herein. We assume that those of our specimens that have not been assigned to a species directly do represent that species. Another stratigraphically well-documented set of sections exists in the Biscay region (Ward and Kennedy 1993). The ammonite faunas described there have many species in common with the Cerralvo assemblage (Table 1), and are correlated to the Gansserina gansseri and Abathomphalus mayaroensis standard zones. One of the best-studied sections regarding stratigraphy is situated near Tercis, southern France. No generally accepted international standard existed for Maastrichtian ammonite chronology until the redefinition of the Campanian/Maastrichtian boundary at Tercis by the Maastrichtian working group of the Subcomission on Cretaceous Stratigraphy. Their results were presented by Odin and Lamaurelle in Unfortunately, the events described from Tercis to define the Campanian/Maastrichtian boundary cannot be correlated into the Gulf of Mexico Basin, and our research did not include nannofossils, dinocysts, or benthic foraminifera. The planktic foraminiferal zones used at Tercis (e.g. Hancock et al. 1993; Simmons et al. 1996; Christensen et al. 2000) are relatively imprecise and based on a species assemblage different from that in the Tethyan realm. Belemnites are not known from the Upper Cretaceous of North America so that the belemnite zonation that is widely used for correlation within Europe (e.g. Hancock et al. 1992; Odin and Lamaurelle 2001) cannot be applied in Mexico. The range of the stratigraphic index fossil Pachydiscus (P.) neubergicus is well known throughout Europe (see Christensen et al. 2000) but, as in many cases, is the only ammonite range well documented. This is also the case for the Tercis ammonite assemblage (cf. Hancock and Kennedy 1993). Unfortunately, P. (P.) neubergicus, the Lower Maastrichtian index fossil, cannot be identified with complete confidence within the Cerralvo ammonites (see systematic description) or in other sections in the Gulf of Mexico area. Planktic foraminiferal ranges are much better known for the Maastrichtian of the Tethys. While the standard planktic foraminiferal zonal scheme divides the Maastrichtian into three zones (Abathomphalus mayaroensis, Gansserina gansseri, Globotruncana aegyptiaca: e.g. Caron, 1985; see Text-fig. 17), a new

43 IFRIM ET AL.: MAASTRICHTIAN CEPHALOPODS 1617 zonal scheme has recently been introduced by Li and Keller (1998b) based on Tunisian sections and DSDP site 525; datum events and biozones presented there appear broadly valid throughout the central and western Tethys, including Mexico (e.g. Tantawy et al. 2001; Keller et al. 2002). This new zonal scheme subdivides the Maastrichtian into nine zones labelled CF1 CF8a and b (CF for Cretaceous Foraminifera) and thus provides the highest resolution age control known to date for the Maastrichtian. Planktic foraminiferal assemblages obtained from a single marl sample of the Méndez Formation at Loma Martínez can be applied well to this zonal scheme. We identified Gansserina gansseri; Globotruncana aegyptiaca, G. arca, G. esnehensis, G. linneiana, G. orientalis, G. rosetta, G. ventricosa; Globotruncanella petaloidea; Globotruncanita stuarti; Hedbergella holmdelensis, H. monmouthensis; Heterohelix dentata, H. glabrans, H. globulosa, H. moremani, H. planata, H. pulchra, H. punctulata, H. striata; Pseudoguembelina costulata, P. kempensis, P. palpebra; Pseudotextularia deformis, P. elegans, P. nutalli; Rugoglobigerina hexacamerata, R. macrocephala,andr. pennyi. The presence of G. gansseri marks the base of zone CF 7 (base of the former G. gansseri Zone) while the absence of R. contusa [first appearance datum (FAD) characterises the base of zone CF 6] excludes an age younger than CF 7. The microfauna thus dates the ammonite assemblage to the early Maastrichtian, between and Ma (Text-fig. 17; Li et al. 1999). Applying the standard zones of Caron (1985; Text-fig. 17) this time interval would belong to the late Maastrichtian that is defined by the FAD of Gansserina gansseri. This implies questions about the definition of the boundary between early and late Maastrichtian. A summary of definitions is given by Tantawy et al. (2001). Suggestions included the placement of the boundary at the FAD of Abathomphalus mayaroensis or Racemiguembelina fructicosa (Nederbragt 1991; Li et al. 1999), but the FAD of Abathomphalus mayaroensis is known to be diachronous and occurs earlier in high latitudes (see Pardo et al. 1996). Other authors have suggested the early/late Maastrichtian boundary to be defined by the FAD of Rosita contusa that also characterizes the base of biozone CF 6 of Li and Keller (1998a, b). This FAD coincides with the FAD of the Western Interior ammonite Hoploscaphites birkelundi, which is the boundary marker for the Western Interior (Walaszczyk et al. 2001; Text-fig. 17). We follow the opinion of Nederbragt (1991) and Li et al. (1999; see Text-fig. 17) and assign the age of the Cerralvo cephalopods to be of middle early Maastrichtian age. Geological data indicate that the Cerralvo ammonite fauna comes from a limited horizon of the Méndez Formation. In addition to microfaunas, biostratigraphic evidence can be obtained based on comparative ranges of the Cerralvo ammonites and by comparison of these taxa with ranges elsewhere. The lower Maastrichtian index fossil Pachydiscus (P.) neubergicus is absent, but the heteromorph ammonite Nostoceras (N.) alternatum is used as an index fossil for a lower Maastrichtian biozone in the US Gulf and Atlantic coast area (Cobban 1974a). This biozone was correlated to the Western Interior Baculites clinolobatus biozone through inoceramids (Cobban and Kennedy 1991b). This not only corroborates the Maastrichtian age indicated by the planktic foraminiferal fauna but restricts the Cerralvo assemblage to upper biozone CF 7 of Li and Keller (1998b; see Text-fig. 17). There are two species among the Cerralvo ammonites that do not fully correspond to the age. Zelandites varuna is Late Maastrichtian in age where well dated, but many records of this species are insufficiently dated, and its FAD remains unclear. The other species is Fresvillia constricta, which has only been described previously from a single outcrop in northern France. All specimens described here have been collected from weathered sediment surfaces of the Méndez Formation and have probably been washed out of an interval not exceeding 20 m of section. On the other hand, it is clear that for many ammonite species their precise ranges within the Maastrichtian are not yet known. PALAEOBIOGEOGRAPHIC DISTRIBUTION Biogeographic affinities The Maastrichtian ammonite assemblage of Cerralvo consists of a total of 23 species referred to 18 genera. Interpreting the biogeographic distribution of species we assume that specimens that are not assigned directly to a particular species (indicated by cf., aff.) are indeed members of that taxon. An overview of

44 1618 PALAEONTOLOGY, VOLUME 47 TEXT-FIG. 17. Stratigraphic zonations for the upper Campanian and Maastrichtian. Left and centre: zones based on planktic foraminifera; right: ammonite zones of the United States Western Interior Seaway (from Li et al. 1999; Walaszczyk et al. 2001). ammonite occurrences is given in Table 1. The localities or regions from which the species are described are shown in their palaeogeographic position in Text-figure 18. In our interpretation the concept of cold and warm water regions is used in a very broad and qualitative sense, only referring to latitudes. An important portion of our assemblage clearly resembles other Gulf of Mexico and western North Atlantic assemblages, notably the abundance of nostoceratids and baculitids. Nostoceras (N.) alternatum, N. (N.) colubriformis and N. (N.) rugosum have previously been recorded from the northern Gulf coast region and from the western North Atlantic coast in New Jersey. Baculites ovatus and Solenoceras reesidei also appear to be restricted to the middle, southern and eastern North American continent. In addition to these Gulf of Mexico affinities, European (Boreal) and Tethyan species are present, notably of the Biscay Region in southern France and northern Spain. For instance, the rare Fresvillia constricta has been recorded so far only from Europe while Brahmaites (Anabrahmaites) vishnu and Hauericeras rembda show a geographically widespread Tethyan up to Indopacific distribution throughout low and middle latitudes (called Tethys s.l. in Table 1). Diplomoceras cylindraceum, Hypophylloceras (Neophylloceras) cf. H. (N.) surya, Phyllopachyceras forbesianum and Pseudophyllites indra can be considered

45 IFRIM ET AL.: MAASTRICHTIAN CEPHALOPODS 1619 TEXT-FIG. 18. Palaeogeographic map for the Maastrichtian with ammonite localities. cosmopolitan species as they occur throughout all latitudes. Anagaudryceras politissimum, Desmophyllites diphylloides, and Gaudryceras kayei are rather similarly distributed, but have not been recorded from boreal Europe and are, therefore, not true generalists. Clearly, the most interesting and surprising aspect regarding the Cerralvo ammonites is the presence of ammonite species hitherto known from the Indopacific region, particularly the southern middle and high latitudes, notably the upper Valudavur Formation of southern India, the Miria Formation in western Australia, the Quiriquina Formation in Chile, and even the Lopez de Bertodano Formation in Antarctica (see Text-fig. 18). Species occurring there are Fresvillia teres, Hypophylloceras (Neophylloceras) hetonaiense, and Zelandites varuna. In addition, the possible coleoid Naefia neogaeia has also been recorded only from the Indopacific region. These species appear to have avoided low latitudes, preferring cold water regions. Their presence in the Cerralvo fauna is unexpected and suggests that: 1. A migrational pathway must have existed between the Western Tethys and the Pacific Ocean, allowing faunal interchange through north-east Mexico. The geographic position of this corridor is unknown at present. Clearly, it must have been located further to the south; towards the end of the Cretaceous Period western Mexico was affected by the Laramide orogenesis and both the Sierra Madre Oriental and Sierra Madre Occidental mountain belts began to rise. In south-west Mexico the Chiapas Pluton also formed a barrier between the Atlantic and Pacific oceans. 2. The Indopacific elements (see Table 1) of the Cerralvo fauna indicate an influence of cool temperate waters in a low latitude region. During Maastrichtian times north-east Mexico was located at approximately 258N, similar to present latitudes (e.g. see reconstruction in Longoria and Gamper 1993) suggesting subtropical tropical conditions. Only a few hundred kilometers to the south, the coeval Cárdenas Formation is characterized by abundant and diverse rudist assemblages (Myers 1968) which also indicate tropical conditions (Kauffman 1973). We correlated the Cerralvo assemblage to upper biozone CF 7 by combining foraminiferal and ammonite biostratigraphy. At precisely this time a minor drop in temperatures has been recorded by Barrera et al. (1997) and Li and Keller (1998b) based on planktic foraminiferal assemblages and stable isotopes. This drop in temperature did not cause a crisis among early Maastrichtian faunas but instead

46 1620 PALAEONTOLOGY, VOLUME 47 TEXT-FIG. 19. Map of Maastrichtian ammonite localities around the northern and western Gulf of Mexico. 1, Cerralvo; 2, Sierra el Antrisco (Vega-Vera and Perrilliat 1990); 3, La Popa Basin, Difunta Group (Wolleben 1977); 4, Méndez Formation, roadside (Medina-Barrera and Stinnesbeck 1993); 5, Mexican localities of Böse (1928); 6, Navarro Group localities of Texas (Stephenson 1941); 7, Brazos River, Texas (Kennedy et al. 2001); 8, Corsicana Formation of northeastern Texas (Kennedy and Cobban 1993c); 9, Nacatotch Sand, Hempstead County, Texas (Cobban and Kennedy 1991a); 10, south-west Arkansas (Cobban and Kennedy 1991b); 11, Saratoga Chalk, Arkansas (Kennedy and Cobban 1993b); 12, Prairie Bluff Chalk, Alabama and Mississippi (Cobban and Kennedy 1995). provoked an increase in species diversity among planktic foraminifera (Li and Keller 1998a). We suggest that this minor cooling event led to the ingression of cool- or even cold-water faunal elements into the warm waters of the Gulf of Mexico, causing a mixing of cephalopod assemblages from different latitudes and an increase in faunal diversity. Comparison of the Cerralvo ammonite assemblage with other Mexican ammonite faunas The Maastrichtian ammonite assemblage of Cerralvo is unique in Mexico and shows little apparent similarity with coeval faunas of the Difunta Group (e.g. Wolleben 1977; Vega-Vera and Perrilliat 1990) or southern Mexico (e.g. Cárdenas Formation in central-east Mexico, own collection). In these latter localities sphenodiscids (e.g. Sphenodiscus, Coahuilites) are the dominant elements whereas ammonites other than sphenodiscids are rare and restricted to Baculites and Pachydiscus. Unfortunately, the ammonite faunas of the Cárdenas Formation and Difunta Group (particularly the Potrerillos Formation) have only been listed by Vega et al. (1995) and not figured or formally described; in consequence it is unclear at present whether species reported from that area (e.g. Solenoceras sp., Baculites ovatus)coincide with elements from Cerralvo. The Indopacific-Tethyan and cosmopolitan assemblages in particular appear to be absent from both the Cárdenas and the Potrerillos formations. Ammonite faunas of the Maastrichtian Corsicana Formation in north-east Texas (e.g. Stephenson 1941), the Saratoga Chalk in Arkansas (e.g. Kennedy and Cobban 1993b) and other localities in the Gulf of Mexico region (see Text-fig. 19) are also characterized by the abundance of Sphenodiscus. Most Gulf Coast localities rich in invertebrates are from extremely shallow-water facies: deltaic to lagoonal in the case of the Potrerillos and Cárdenas formations. Sphenodiscus clearly favoured these shallow-water