A NEW SILURIAN XIPHO SURAN FRO M PODOLIA, U K R A I N E, USSR

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1 A NEW SILURIAN XIPHO SURAN FRO M PODOLIA, U K R A I N E, USSR by P A U L A. S E L D E N and D A N I E L M. D R Y G A N T Pasternakevia podolica gen. et sp. nov., from the Ludlow Series of Podolia, Ukraine, USSR, is described. It has a smooth, spatulate carapace and rounded genal cornua. The opisthosoma bears nine free tergites (second to tenth); the first tergite is reduced and hidden beneath the carapace. The tergites have a broad axial region and small pleurae; the second tergite is hypertrophic. Telson and appendages are not preserved. P. podolica resembles Pseudoniscus Nieszkowski, and Cyamocephalus Currie, ; it is thus placed in the infraorder Pseudoniscina Eldredge, , but certain characters are shared with the synziphosurines. It comes from the lagoonal deposits of the upper part of the Ustye Suite (Bagovytsa Horizon) where it occurred together with Baltoeurypterus tetragonophthalmus ABSTRACT. A single incomplete specimen of a xiphosuran, (Fischer, ). Pasternakevia podolica gen. et sp. nov. 13 лудловського ярусу Под1\ля (УРСР). Представлений вш гладким лопатовидним карапаксом 13 закругленими щдчними шипами i отстосомою. Ошстосома складаеться з дев'яти видимих тергтв; перший терпт редукований, схований т д карапаксом. Терпти мають широю ocboei частини та мал! плеври; другий терпт rinepтрофований. Тельсон i придатки не збереглися. Мечохвкт под1бний до Pseudoniscus Nieszkowski, та Cyamocephalus Currie, , у зв'язку з чим вынесений до шфразагону Pseudoniscina Eldredge, , хоч мае також i деяи ознаки синцифозур. Походить вш i 3 лагунних в1дклад1в верхньо!' частини уст1всько1 свгги баговицького горизонту, де знайдений разом i3 Baltoeurypterus tetragonophthalmus (Fischer, ). А Н О Т А Щ Я. Описуеться единий неповний екземпляр мечохвоста T H E late Silurian saw the climax of the first phase of evolution of the Xiphosura. In the Treatise (Stormer 1955) these middle Palaeozoic xiphosurans were united in the suborder Synziphosurina Packard, 1886, b u t some are n o w considered to belong t o the sister group, the suborder Limulina Richter, 1929 (Eldredge 1974; Bergstrom 1975), a n d the infraorder Pseudoniscina Eldredge, 1974 was erected for them and some primitive bellinuroids. X iphosuran phylogeny is founded to a large extent on scattered records of genera based on few, or commonly single, specimens; new finds often seem to confound rather than confirm established conceptions. The new genus described.below follows this pattern since, while it undoubtedly lies within the Pseudoniscina, it also shares at least one character with some synziphosurines. F o r this and other reasons outlined below and particularly if some bellinuroids are included in the Pseudoniscina (Eldredge 1974; cf. Fisher 1982, fig 1; 1984, fig. 2) the monophyletic status of the infraorder must be considered suspect. Eldredge (1974) convincingly argued that the most anterior opisthosomal tergite in synziphosu rines and pseudoniscines belongs to the second opisthosomal somite. T h e tergite corresponding to the first opisthosomal somite is reduced to the form of an articulating half ring a n d can only be seen in dorsally flexed specimens. O u r identification of the opisthosomal tergites follows that of Eldredge (1974), so that the nine visible tergites are numbered second to tenth (II X ). Stratigraphy and geological setting. T h e described specimen comes from dolomite marl (domerite) of the upper part (c m above the base) of the Ustye Suite of the Bagovytsa Horizon, which crops out on the left bank of the Dniester River c. 1 5 k m downstream of the village of Velyka Slobidka (Podolia, Ukraine, USSR; text fig. 1). Subsequent extensive searches failed t o reveal any more specimens of the genus. The section consists of light grey, vesicular, granular and platy, pelitomorphic, a n d rarely stroma tolitic dolomites alternating with fine, platy domerites (text fig. 2). Bed thicknesses are IPalaeontology, Vol. 30, Part 3,1987, pp The Palaeontological Association

2 538 PALAEONTOLOGY, VOLUME 30 TEXT-FIG. 1. Location map m, and suite thickness as a whole is 30 m. These rocks are lagoonal in origin and contain only rare remains of chelicerates, of which the best known is Baltoeurypterus tetragonophthalmus (Fischer, 1839); shrinkage cracks commonly occur on the surfaces of domerite beds (Nikiforova et al. 1972). In the lower part of the suite, rare, thick beds of limestones occur with abundant faunal remains which allow their correlation with Eltonian to lowermost Leintwardinian (Ludlow) strata of Britain (Tsegelnjuk et al. 1983; Drygant 1984); the layer with Pasternakevia correlates with the lowermost Leintwardinian. Preservation. The fossil consists of a single piece: the cast and internal mould of the whole carapace and slightly damaged opisthosoma of nine tergites. Since the animal is not flexed dorsally, the halfring belonging to the first opisthosomal somite cannot be seen and is presumed to be hidden beneath the carapace. The cuticle is rather thin, consisting of dark-grey matter which is clearly distinguished on the pale rock background. Though originally chitinous, the cuticle has almost certainly been replaced by material whose nature has not been determined. SYSTEMATIC PALAEONTOLOGY Phyliun CHELICERATA Heymons, 1901 Class XIPHOSURA Latreille, 1802 Order XIPHOSUREDA Latreille, 1802 Suborder LIMULINA Richter and Richter, 1929 Infraorder PSEUDONKCINA Eldredge, 1974 (emended) Genus PASTERNAKEVIA gen. nov. Type and only known species. Pasternakevia podolica sp. nov. Derivation of name. In honour of Professor S. I. Pasternak, a prominent researcher of the Cretaceous fauna of the Ukraine. Diagnosis. Carapace spatulate, nearly as long as opisthosoma (excluding telson); cardiac and ophthalmic morphology obscure; genal cornua broad and rounded, lacking anterior median projection.

$SELDEN AND DRYGANT: SILURIAN XIPHOSURAN 539 DOLOMIT E S pel \ tomorph ic, I / marls pi a I y (primary) z: z Il I clayey y 7\ dolomitized granula r, vcsjc - domer ites ular (secondary) (dolomite$

3 SELDEN AND DRYGANT: SILURIAN XIPHOSURAN 539 DOLOMIT E S pel \ tomorph ic, I / marls pi a I y (primary) z: z Il I clayey y 7\ dolomitized granula r, vcsjc - domer ites ular (secondary) (dolomite marls) with fragments Paste rnakevia TEXT-FIG. 2. Columnar section of the outcrop located on text-fig. 1 showing occurrence of Pasternakevia gen. nov. Nine opisthosomal tergites with broad axial region and small pleurae; tergite of first opisthosomal somite greatly reduced, that of second hypertrophied. No fused tergites. Pasternakevia podolica sp. nov. Text-fig. 3a, b, d Holotype. Lviv State Natural Museum of the Ukrainian Academy of Sciences (Monographical -Funds), No ; single dorsal piece (only known specimen) consisting of the carapace and opisthosomal tergites; from the upper part (c m above the base) of the Ustye Suite (Bagovytsa Horizon, middle Ludlow) on the left bank of the Dniester River c. 1-5 km downstream of the village of Velyka Slobidka (Podolia, Ukraine, USSR). Derivation of name. After Podolia, the region in which the locality lies. Diagnosis. As for the genus. Description. Pasternakevia is nearly half as wide as it is long (excluding the telson which is not preserved), with the carapace occupying 0-44 of its length. The three largest opisthosomal tergites are nearly as wide as the carapace and thus the body appears parallel-sided for much of its length. The carapace is spatulate, nearly as long sagitally (sag.) as it is wide; the sides are parallel in the posterior half, and the anterior rim of the carapace forms a semicircle. The posterior border of the carapace is gently procurved, meeting the lateral borders in blunt genal cornua. A long, crescentic feature on the carapace, widest anteriorly and tapering gradually to merge with the lateral borders near the genal angles, may represent the impression of the prosomal doublure or ventral marginal plate(s) adpressed against the carapace. The carapace is convex dorsally, the highest part being a broad circular area forming the posterior two-thirds; the surface slopes steeply away from this area to the crescentic feature and the genal areas. The posterior border is

540 P A L A E O N T O L O G Y, V O L U M E 30 3. a, b, d, Pasternakevia podolica gen. et sp. nov., No.

4 540 P A L A E O N T O L O G Y, V O L U M E a, b, d, Pasternakevia podolica gen. et sp. nov., No , holotype and only known specimen; upper part of Ustye Suite, Bagovytsa Horizon (middle Ludlow), near Velyka Slobidka, Ukraine, USSR; a, dorsal view in low-angle light, x 3 0 ; b, dorsal view in high-angle light, x l - 5 ; d, outline drawing of specimen showing main features and tergite numbers, x 3-0. c, Baltoeurypterus tetragonophthalmus (Fischer, 1839), No , from same horizon and locality as Pasternakevia, x 1. TEXT-FIG. gently arched. Typical xiphosuran carapace features cannot be discerned, except for a faint parabolic ridge situated centrally at the anterior side of the circular area; this could represent the anterior part of the cardiac lobe. Though obscured by a general wrinkling of the carapace surface, any original features must have been faintly expressed in life. Nine dorsal tergites are readily apparent on the opisthosoma (belonging to the second to tenth opisthosomal somites); the first tergite is presumed to be concealed beneath the carapace (see above). Since the telson is not preserved attached, we cannot be certain that the most posterior tergite is the last, but its small size suggests that it is. The second tergite is the largest and is obviously hypertrophied. The third is only half the length (sag.) of the second, but is as wide. The fourth is three-quarters the length (sag.) of the third, and is also as wide as the second and third. Thereafter the tergites are roughly the same length but become increasingly narrower (exsag.). Each tergite consists of a wide, raised axial part, occupying about two-thirds of the total width, and narrower (exsag.) pleurae. The axial part of the second tergite is greatly swollen. On the third to tenth tergites the axial part has straight anterior and posterior borders. The anterior and posterior borders of the axial region of the third and more posterior tergites are depressed to accommodate adjacent tergites during flexure of the opisthosoma; that anteriorly on the third tergite is recurved on its posterior side to accommodate the hypertrophied second tergite. The pleurae are separated from the axis by dark coloured depressions, possibly indicating the presence of muscle attachments beneath. Together, these depressions line up as a pair of axial furrows which run nearly straight and converge from the genal angles of the carapace to the presumed anterolateral corners of the telson. As the outline of the opisthosoma is broadly curved, the pleurae are widest on the middle tergites. The pleurae curve gently backwards as spatulate lobes, with the posterior more strongly

5 SELDEN AND DRYGANT: SILURIAN XIPHOSURAN 541 curved than the anterior. At least the third to the eighth pleurae bear furrows running from the anteromedial to posterolateral corners, becoming shallower posterolaterally. The opisthosoma lacks ornamentation. Dimensions {in mm). Lengths (sag.): total (excluding telson), 30-7; carapace, 13-5; opisthosoma (excluding telson), 17-2; tergites II, 4-8; III, 2-4; IV, 1-8; V, 1-6; VI, 1-1; VII, 1-4; VIII, 1-0; IX, 1-6; X, 1-5. Widths: carapace, 14-0; tergites II, 13-2; III, 13-2; IV, 13-2; V, 12-5; VI, 11-5; VII, 10-6; VIII, 8-1; IX, 7-0; X, 4-7. Discussion. Pasternakevia resembles Pseudoniscus, k n o w n from S a a r e m a a, E s t o n i a {P. clarkei R u e d e m a n n, 1916), L e s m a h a g o w, Scotland, a n d L u d l o w, E n g l a n d {Pseudoniscus spp., Eldredge 1974), all of which a r e L u d l o w in age. Similarities include: overall d i m e n s i o n s, s p a t u l a t e c a r a p a c e, n u m b e r of o p i s t h o s o m a l tergites, n o fused tergites, a n d lack of o p i s t h o s o m a l tagmosis (see Eldredge 1974, t a b l e 3). Pasternakevia differs from Pseudoniscus in lacking a n anterior m e d i a n c a r a p a c e projection, its b r o a d o p i s t h o s o m a l axial region, a n d h y p e r t r o p h i e d second tergite. A n o t h e r pseudoniscine, Cyamocephalus C u r r i e, 1927, resembles Pasternakevia. Cyamocephalus is k n o w n from r o c k s of L u d l o w age at L e s m a h a g o w, S c o t l a n d ( C. loganensis Currie, 1927), a n d L u d l o w, E n g l a n d ( C. cf. loganensis E l d r e d g e a n d Plotnick, 1974). B o t h Pasternakevia a n d Cyamocephalus lack the m e d i a n a n t e r i o r c a r a p a c e projection found in Pseudoniscus. Cyamocephalus h a s a long o p i s t h o s o m a with fused sixth a n d seventh o p i s t h o s o m a l tergites a n d the seventh h y p e r t r o p h i e d, features a b s e n t from Pseudoniscus a n d Pasternakevia. These dissimilarities w a r r a n t t h e s e p a r a t i o n of all three a n i m a l s at t h e generic level. T o include Pasternakevia within t h e infraorder Pseudoniscina Eldredge, 1974, this t a x o n requires e m e n d a t i o n t o r e m o v e t h e c h a r a c t e r 'second segment n o t h y p e r t r o p h i c '. A t present, it seems a p p r o p r i a t e t o include the g e n u s within Pseudoniscina with this e m e n d a t i o n. T h e presence of a h y p e r t r o p h i c second o p i s t h o s o m a l tergite is a c h a r a c t e r which Pasternakevia shares with the synziphosurines Bunodes Eichwald, 1854 a n d Limuloides Salter in W o o d w a r d, 1865 (Eldredge 1974). T h e question arises: is this c h a r a c t e r h o m o p l a s o u s, i.e. derived independently in t w o s e p a r a t e clades? Eldredge (1974), B e r g s t r o m (1975), a n d S t u r m e r a n d B e r g s t r o m (1981) agree that the synziphosurines {Bunodes, Weinbergina, Legrandella, a n d Limuloides) are s e p a r a t e from other X i p h o s u r a a t high t a x o n o m i c r a n k. H o w e v e r, the distinguishing characters (carapace m o r p h o l o g y a n d o p i s t h o s o m a l tagmosis) are n o t always strictly definable. I n t h e Pseudoniscidae, for example, the c a r a p a c e m o r p h o l o g y is typically obscure, a n d in a r e c o n s t r u c t i o n of Weinbergina by S t u r m e r a n d B e r g s t r o m (1981, e.g. fig. 5) the s e p a r a t i o n of p r e - a n d p o s t a b d o m e n is indistinct. T h e O r d o v i c i a n genus Lemoneites F l o w e r, 1968 also shares c h a r a c t e r s i n c o m m o n with b o t h synziphosurines a n d limulines (Eldredge 1974). C o n s e q u e n t l y, t h e c u r r e n t phylogeny of these lower a n d m i d d l e Palaeozoic X i p h o s u r a m u s t b e considered speculative; as m o r e n e w t a x a are described, character m a t r i x analyses (e.g. Eldredge 1974) will help to a n s w e r t h e h o m o p l a s y question a n d p r o d u c e new phylogenetic schemes. A s m e n t i o n e d a b o v e, in the d o l o m i t e rocks of U s t y e Suite of P o d o l i a a n o r m a l m a r i n e f a u n a is absent. Pasternakevia is a c c o m p a n i e d only by relatively few fossils of the eurypterid B. tetragonophthalmus (Fischer, 1839) (mainly as isolated p a r t s b u t occasionally as a l m o s t w h o l e animals; textfig. 3c), fragments of Pterygotus sp., a n d some unidentifiable a r t h r o p o d s. N o Baltoeurypterus specimen exceeds 10 c m in length; the fragments of Pterygotus indicate t h a t the c o m p l e t e animals were m u c h bigger. These chelicerates lived in a shallow l a g o o n, s e p a r a t e d from a n o p e n basin to the west by a chain of b i o h e r m s ( D r y g a n t 1984). Sedimentary c o n d i t i o n s in t h e l a g o o n were n o t stable, hence the d e p o s i t i o n of thin, rhythmical, magnesial sediments w h i c h were periodically enriched with clayey m a t e r i a l. C o m m o n desiccation cracks indicate frequent subaerial e x p o s u r e in s o m e places. T h e bed with Pasternakevia is a thin-bedded, clayey d o l o m i t e formed d u r i n g a regressive p h a s e, b u t before its m a x i m u m. T h e m o d e of life of Pasternakevia c a n n o t be d e t e r m i n e d w i t h certainty. S p h a e r o i d a l e n r o l m e n t w a s a l m o s t certainly possible, since it is k n o w n in Pseudoniscus ( B e r g s t r o m 1975) which h a s a similar gross m o r p h o l o g y. Flexure of t h e o p i s t h o s o m a i n t o a dorsally c o n c a v e s h a p e w a s also possible, a s evidenced by the t o p o g r a p h y of the axial region of the tergites. E n r o l l m e n t was

542 P A L A E O N T O L O G Y, V O L U M E 30 u n d o u b t e d l y a defence strategy, while flexure in t h e o p p o s i t e direction w a s used in righting the o v e r t u r n e d a n i m a l a n

6 542 P A L A E O N T O L O G Y, V O L U M E 30 u n d o u b t e d l y a defence strategy, while flexure in t h e o p p o s i t e direction w a s used in righting the o v e r t u r n e d a n i m a l a n d m a y also have been a help in b u r r o w i n g. T h e s p a t u l a t e c a r a p a c e, effaced features, a n d b r o a d axial region of t h e o p i s t h o s o m a give Pasternakevia a s t r e a m l i n e d s h a p e similar t o t h a t of b u r r o w i n g illaenid trilobites; it m i g h t also h a v e been a d v a n t a g e o u s t o a s w i m m i n g form, b u t a t small size a n d slow s w i m m i n g speeds (low R e y n o l d s n u m b e r s ) effacement confers little a d v a n t a g e, so b u r r o w i n g seems a m o r e likely e x p l a n a t i o n. T h e h y p e r t r o p h i c second tergite suggests enlarged ventral o r g a n s : genitalia or, m o r e likely, gills. It c o u l d be t h a t e n h a n c e d gas- o r ionexchange abilities enabled Pasternakevia t o inhabit a hypersaline e n v i r o n m e n t. Bunodes lunula Eichwald, 1854 also h a s a h y p e r t r o p h i c second tergite a n d is f o u n d i n similar d o l o m i t i c limestones in E s t o n i a, b u t it is there a c c o m p a n i e d b y Pseudoniscus aculeatus N i e s z k o w s k i, 1859, w h i c h h a s a n o r m a l second tergite, so this hypothesis r e m a i n s speculative. REFERENCES Functional morphology and evolution of xiphosurids. Fossils Strata, 4, j. M Notes on Paleozoic crustaceans. Rep. N.Y. St. Mus. nat. Hist, (for 1900), 54, appendix 3, CURRIE, L. D On Cyamocephalus, a new synziphosuran from the Upper Silurian of Lesmahago, Lanarkshire. Geol. Mag. 64, D R Y G A N T, D. M Correlation and conodonts from the Silurian-Lower Devonian deposits of the VolynoPodolian, 192 pp. Kiev. [In Russian.] EICHWALD, E. V O N, Die Grauwackenschichten von Liev- und Esthland. Bull. Soc. imp. Nat. Moscou, 27, ELDREDGE, N Revision of the suborder Synziphosurina (Chelicerata, Merostomata), with remarks on merostome phylogeny. Am. Mus. Novit. 2543, and PLOTNICK, R. E Revision of the pseudoniscine merostome genus Cyamocephalus Currie. Ibid. 2557,1-10. FISCHER, G., DE WALDHEIM Notice sur un crustace fossile du genre Eurypterus de Podolie. Bull. Soc. imp. Nat. Moscou, 11, FISHER, D. C Phylogenetic and macroevolutionary patterns within the Xiphosurida. Proc. N. Am. Palaeontol. Conv. 1, The Xiphosurida: archetypes of bradytely? In ELDREDGE, N. and STANLEY, s. M. (eds.). Living fossils, Springer-Verlag, Berlin, Heidelberg, and New York. FLOWER, R Merostomes from a Cotter Horizon of the El Paso Group. Mem. Inst. Min. Technol. New Mex. 22 (4), NIESZKOWSKI, J Zusätze zur Monographie der Trilobiten der Ostseeprovinzen, nebst der Beschreibung einiger neuen obersilurischen Crustaceen. Arch Naturk, Liv.-Est. u. Kurlands, (ser. 1), 1, NIKIFOROVA, O. [., PREDTECHENSKY, N. N. and ABUSHIK, A. F Silurian and Lower Devonian key sections of Podolia, 262 pp. Leningrad. [In Russian.] RUEDEMANN, R Account of some new or little-known species of fossils, mostly from Paleozoic rocks of New York. Bull. N. Y. St. Mus. 189, STORMER, L Merostomata. In MOORE, R. C. (ed.). Treatise on invertebrate paleontology. Part P. Arthropoda 2, P1-P41. Geological Society of America and Unversity of Kansas Press, Boulder, Colorado and Lawrence, Kansas. STÜRMER, w. and BERGSTRÖM, J Weinbergina, a xiphosuran arthropod from the Devonian Hunsrück Slate. Palaeont. Z. 55, BERGSTRÖM, J. CLARKE, TSEGELNJUK, P. D,, GRITSENKO, V. P., KONSTANTINENKO, L. L, ISHCHENKO, A. A., ABUSHIK, A. F., BOGOYAVLENSKAYA, o. v., D R Y G A N T, D. M., ZAIKA-KOVATSKY, V. S., KADLETS, N. M., KISELEV, G. N. and SYTOVA, V. A The Silurian of Podolia. The guide to excursion, 224 pp. Kiev. [In Russian and English.] P A U L A. SELDEN Department of Extra-Mural Studies, University of Manchester Manchester M13 9PL and DANffiL M. D R Y G A N T Typescript received 9 July 1986 Revised typescript received 1 October 1986 Institute of Geology and Geochemistry of Fuel Minerals Ukrainian Academy of Sciences, Naukova 3a, Lviv Ukraine, USSR

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