Palaeontology of the Bagh Beds-Part V. Ostreina II

Transcription

1 Proc. Indian Acad. Sci., Vol. 87 B (Animal Seiences-Z), No.6, June 1978, pp. printed in India Palaeontology of the Bagh Beds-Part V. Ostreina II G W CHIPLONKAR and R M BADVE Maharashtra Association for the Cultivation of Science, Pune MS received 26 February 1976; revised 13 January Abstract. A new genus Bosostrea and its five species are described. Among other oyster species already known from elsewhere but now found occurring in the Bagh Beds, Cameleolopha cameleo (Coq.) is of particular interest bearing on the age of these beds as it comes from the Cenomanian of Algeria, and Lopha (Actinostreon) semiplana (Sow.) is of interest as a species widely occurring in the Mediterranean Palaeo Zoo-Geographic Province. Keywords: Bosostrea; rapid speciation; crowding; ecological significance. 1. Introduction In an earlier paper dealing with the Bagh ostreiids, the present authors described Indostrea, a new genus with seven species (Chiplonkar and Badve 1976a). In this paper, another non-incubatory genus Bosostrea n.g. et five n. spp., Ceratostreon profunda n. sp., are described new to science, along with Ostrea sp. indet. Two species, Lopha (Actinostreon) semiplana (Sow.), and Cameleolopha cameleo (Coq.) are also being reported for the first time from these beds. Though not specificallydetermined, the record of Ostrea sp. indet. is of considerable importance in that it suggests probably the earliest marine incursion inter wedged with fluviatile Nimar Sandstone, the lowest member of the Bagh Beds. The material is collected from the following localities; Bagh (20 21' 30"; 74 04' 00') Khadlu (2 km South of Mongra); Mongra (22 00' 38" : 74 02' 30"); Moti Chikli (22 21' 00"; 74 19' 10"); Sitapuri ( ' 30" ; 74 47' 00"); Walpur (22 07' 30" ; 74 29' 00"). All the measurements are given in mm, the height/length are as in figure 1. The type specimens described here are deposited in the Museum of Geology and Palaeontology Department, Maharashtra Association for the Cultivation of Science, Pune. 2. Systematic account Suborder Superfamily Family Subfamily Ostreina Ferussac, 1822 Ostreacea Rafinesque, 1815 Gryphaeidae Vyalov, 1936 Exogyrinae Vyalov,

2 106 Tribe Genus G W Chiplonkar and R M Badve Exogyrini Vyalov, 1936 Ceratostreon Bayle, 1878 Ceratostreon profunda sp. nov. (figure I) Material: 2 specimens Holotype No. MACS G 637;paratype no. MACS G 718. Dimensions Height Length HjL Sp. no. mm mm MACS G Description: Both specimens of LV. Outline subovate with rather straight posterior margin; large area of attachment. Ornamentation of numerous, fine radial costae, irregularly disposed and bifurcating towards the ventral margin; posterior muscle mark suboval and subcentrally situated; a few of the costae with spiny outgrowths, particularly towards the ventral margin. Remarks: Ceratostreon decussata (Gold fuss) from the Campanian of Tunisia (Thomas and Peron, , p. 177, plate 25, figure 53) is much like the present species in outline and general pattern of its fine striae. Present species, however, has its fine striae more irregular, some of them developing spiny outgrowths towards the ventral margin. As compared to C. tamal/ini Pervenquiere (Weir 1930, p. 406, plate 39, figure 5-7) from the Turonian and the Senonian of Tunisia, South Central Sahara, etc., the present species has its shell distinctly taller than long, less extended posteriorly and its radial ornamentation more regular. Occurrence Family Subfamily Genus Type species Deola-Chirakhan Marl at Sitapuri. Ostreidae Refinesque, 1815 Ostreinae Rafinesque, 1815 Bosostrea n. gen. B. bosei gen. et sp. nov. Diagnosis of the genus: Outline variable, but often spatulate or narrowly oval; umbones opisthogyrate, generally not prominent; LV with or without appreciable umbonal cavity; posterior muscle mark usually subcentral and often closer to the hinge margin, comma shaped with dorso-posterior comer usually drawn out; commissural shelf narrow, shallow and extending only up to adductor muscle imprint; ligament area triangular higher than long; resilifer 3-4 times broader than bourrelets; RV ligamental area convex; chomata absent; may develop small auricles; area of attach ment not much conspicuous. Surface smooth but for gently undulating growth squamae and very fine concentric growth striae. Radial ornamentation totally absent on both the valves. Range: Cenomanian-Turonian. Remarks: The present genus like Crassostrea Sacco (Stenzel 1971, NII28, figures J 101,J 102,etc.) has its ligamental area higher than long and lacks chomatal pits; some of the species, e.g, B. bosei, B. trigonoidea, etc., have like those of Crassostrea a spatulate outline with the anterior and posterior margins sub-parallel. But it can be distinguished from Crassostrea by its less capaceous LV and more capaceous RV; the subscentral posterior muscle mark tends to approach the posterior margin and

3 Bagh oysters Figures (All figures are of natural size). 1. Ceratostreon profunda sp. nov. Side view of Lv MACS G B. bosei Gen et sp. nov. 2. s.v. LV MACS G s.v. LV MACS G s.v. LV MACS G 61I. S. i.v. LV MACS G s.v, RV MACS G SoV. LV MACS G s.v. LV MACS G B. lata sp. nov. 9. i.v. LV MACS G i.v. LV MACS G i.v, RV MACS G s.v. RV MACS G s.v. RV MACS G s.v, RV MACS G 620. Abbreviations: s.v. side view; i.v, internal view.

4 Bagh oysters 109 never goes in the ventral half of the valve. Radial ornamentation is totally absent. Also, some species of this genus show development of small auricles at the hinge margin. By its shell often spatulate to elongate, devoid of radial ornamentation and comma shaped subcentral muscle mark this genus resembles Indostrea (Chiplonkar & Badve 1976a), another nonincubatory genus, with which it is associated in the Bagh Beds. But absence of chomatal pits, less capaceous LV, and resilifer much broader than bourrelets distinguish this genus from Indostrea (Chiplonkar & Badve). The genus is named after P N Bose who was the pioneer worker on the Bagh Beds. Bosostrea bosei sp. nov. (figures 2-8, 15, 17,21) Material: Large numberofspecimens. Holotype no. MACS G 608. Paratypenos. MACS G 609 to 614 and MACS G 643 to 645. Dimensions Height Length HjL sp. no. mm mm MACS G MACS G MACS G MACS MACS G Description: Shell tall spatulate to narrowly oval with anterior and posterior margins subparallel over most of their course. Surface with fine concentric striae and widely spaced growth squamae; some of the specimens (MACS G 608) with small ill-defined auricles along the Iigamental area. RV weakly to moderately convex and noticeably capaceous; LV feebly convex with umbonal cavity in general not much developed and thus apparently less capaceous, commissural shelfalso not significantly developed. d 16 Figures B. bose; LV i.v. a auricle, b bourrelet, c resilifer, d posterior adductor imprint, b height, I length. 16. B. trigonoidea showing ornament.

5 110 G W Chiplonkar and R M Badve /8 /9 FIgures and 21. B. bosei showing variation in shape. 18. B. trigonoldea showing growth stages. 19. B. lata showing growth stages. 20. B. scidiformis showing growth stages. 22. B. flexuosashowing growth stages. Comma shaped muscle imprint close to the posterior margin and a little on the dorsal side of the centre of the valve. Besides the spatulate form of the species described above tendency of the shell to attain considerable height is also seen in some of the specimens, e.g. MACS G 611, MACS G 612, MACS G 614,etc., and which ordinarily may have been placed under a different species. But considering the stages by which these 2 tendencies are exhibited, we are inclined to consider them as falling under one species. Remarks: Bosostrea trigonoidea sp.nov. (vide infra) comes very close to this species but for the absence of auricles and its anterior and posterior sides gradually diverge right from the narrow umbonal region to the ventral margin where the shell attains its maximum width. Occurrence: Oyster bed near the top of the Nimar Sandstone at Khadlu, Moti ChikIi and Mongra. Bosostrea lata sp. nov. (figures 9-14, 19). Material: 6 specimens Holotype no. MACS G 168: Paratype nos. MACS G 615 to 617 and MACS G 619 & 620. Description: Specimens are incomplete to give any measurement but H/L ratio is

6 Bagh oysters III approximately obtained from the various growth stages as to give the ratio from 1 2 to 1 5. The adult growth stages make an angle of45 to 60 with the juvenile stage (MACS G 617 & 618). Umbones strongly opisthogyrate; LV is moderately capaceous with adductor muscle imprint very close to the hinge margin; ligamental area triangular and as long as high. Remark: Present species is close to B. bosei(vide supra) than to the other associated species and can be distinguished from it by its subrectangular outline, and small Iigamental area. Occurrence: Oyster bed near the top of the Nimar Sandstone at Moti Chikli, Mongra and Khad1u. Bosostrea trigonoidea sp. nov. (figures 16, 18,23-28) Material: Large number of specimens. Holotype nos. MACS G 622 to 626. Dimensions Height Sp. no. mm MACS G MACS G MACS G Paratype no. MACS G 621; Length mm H/L Description: Shell very tall, narrowly triangular or sub-spatulate; fairly straight posterior margin and the anterior margin broadly arcuate (sp. no. MACS G 621, MACS G 624, etc.), gradually diverging from the narrow umbonal region to give the shell its maximum width near the ventral margin. When preserved, juvenile stage oriented at an angle to the adult growth direction, maximum being at right angle, e.g., sp. no. MACS G 626, (figures 2-8). Umbonal region slightly more tumid than rest of the shell; undulatory growth straie distinct but not squamose. Both valves moderately capaceous; umbonal cavity in LV being less distinct. Posterior adductor muscle imprint between hinge and centre (figure 25). Remarks: This species is characteristically very narrow in the umbonal region and gradually attains maximum length near the ventral margin. This character helps to easily differentiate present species from other associated species. Occurrence: Oyster bed near the top of the Nimar Sandstone at Mongra, Moti chikli and Khadlu. Bosostera scidiformis sp. nov. (figures 20, 29-34). Material: Large number of specimens. nos. MACS G 628 to 632 and 646. Dimensions Sp. no. MACS H 627 MACS G 646 Height mm Length mm Holotype no. MACS G 627; Paratype Description: Shell exceedinglytall and narrow; some of the specimens being more than 100mm high, giving height to length ratio 4 : 1 to 6 : 1. Juvenile stage slightly H/L

7 112 G W Chiplonkar and R M Badve at an angle with rest of the shell, thus giving it a slight bend in the umbonal region; anterior and posterior margins subparallel with ventral margin broadly convex (MACS G 627, and MACS G 632). Both values with moderately developed commissural shelf (MACS G 627 and MACS G 629). Ligamental area triangular and as long as high. Posterior muscle mark between hinge and centre. Remarks: By being exceedingly tall with the anterior and posterior margins maintaining the subparallel nature throughout their course, commissural shelf better developed and ligamental area as broad as high this species can easily be separated from the associated tall species, e.g, B. trigonoidea, B.flexuosa and tall varieties ofb. bosei. Occurrence: Oyster bed near the top of the Nimar Sandstone at Mongra, Moti Chikli, and Khadlu. Bosostreafluexuosa sp. nov. (figures 22,35-38) Material: 5 specimens. Holotype no. MACS G 633; Paratype nos. MACS G 634 to 636. Dimensions Height Length H/L Sp. no. mm mm MACS G MACS G MACS G Description: All the specimens representing this species in our collection are closed shells and cemented firmly to the slabs. Shell very tall, flat, very narrow in the umbonal region and gradually broadening to a maximum width near the ventral margin; both valves moderately convex; surface ornamented with very fine concentric striae and smooth undulatory growth rugosities. Remarks: Present species differs from the similarly tall Bosostrea trigonoldea (vide supra) by its flexuous nature. Even in the absence of internal details, the species can be placed under Bosostrea by its external morphology and relation shown with other species ofthis genus. Occurrence: Oyster bed near the top of the Nimar Sandstone at Mongra, Moti Chikli and Khadlu. Interrelation ofthe species of Bosostrea: The 5 species of Bosostrea described here fall in 2 groups comprising: (a) very tall and narrow species namely B. tlexuosa, B. scidiformis and taller varieties ofb. bosei. (b) Broad and spatulate species, viz., B. bosei, B. trigonoidea and B. lata. Inverse relation between height and length of the shell would give the above two groups and if these were the only two parameters showing variations all our material studied here could have been assigned to a single species. But other morphological features also are so distinctive as to lead us to recognise the different species as described above. Though narrow and tall like B. scidiformis and the relatively taller members of B. bosei, the species B.flexuosa differs from them in having its maximum width in the

8 Bagh oysters :..d. ~ ~. " ~ ~ Figures (All figures are of natural size) B. trigonoidea sp. nov. 23. s.v, RV MACS G s.v. RV MACS G i.v, RV MACS G s.v, LV MACS G s.v, RV MACS G s.v, LV MACS G B. scidiformis sp. nov. 29. i.v. RV MACS G i.v, R V MACS G s.v. LV MACS G s.v. RV MACS G s.v, RV MACS G i.v. RV MACS G

9 114 G W Chiplonkar and R M Badve Figures (All figures are of natural size) B. fiexuosa sp, nov. 35. s.v, RV MACSG s.v. LV MACS G S.Y. RV MACS G S.Y. LV MACS G C. cameleo (Coq.) s.v. LV MACS G Lopha [Actinostreon) semiplana (Sow.). s.v. RV MACS G Ostrea sp. indet, 41. i.v, LV MACS G i.v, RV ' MACS G S.Y. RV MACS G 642.

10 Bagh oysters 115 ventral region. Also this increase in width is attained by gradual diverging of its anterior and posterior margins right from the umbones. While, in the remaining two species i.e., B. scidiformis and taller members of B. bosei the sides run more or less subparallel throughout their growth. Similarly difference between B. scidiformis and B. bosei is that the latter is distinctly broader and certain gradation is observed among the members of this species as regards the length and height. (Regarding 2 tendencies of growth in B. bosei see under that species.) B. trigonoidea has its maximum width towards the ventral side and thus its anterior and posterior sides are never parallel. This character links this species with B. flexuosa, but it differs from it in being usually less tumid and much broader. While, gradual widening in the umbonal region gives rise to ovate forms of B. bosei. In B. lata the posterior margin is very straight which along with the development of a small wing at the anterior side connects this species with B. bosei. Direction of growth stages coinciding with the central axis is the common feature between B. flexuosa and B. bosei. Palaeoecological considerations: Being closely related to the genus Crassostrea Sacco, this new Bagh genus Bosostrea must have been under very similar conditions of habitat and habit. Thus, like Crassostrea, Bosostrea had developed very thick and extensive banks which could be compared to the reef building activity of corals (Hecker 1958, Hopkins 1971). Gregarious and luxurient growth of this genus indicates as having enclosed waters ofbay or estury and even with some turbulance (Chiplonkar & Badav 1976b, Badve and Ghare 1977). It has been established that settling of larvae is induced by thick population of their own kind in case of sessile epifauna like that of Ostrea (Thorson 1970, p. 483; Moore 1958, p. 11 I). In case of Bosostrea like Crassostrea above mentioned character is coupled with high ability of proliferation resulting in formation of great oyster banks. Nevertheless, crowding of individuals has adverse effect on the population. It results in high mortality, reduced growth and highly distorted shells (Moore 1958). Abnormal elongation of the speciesas is much in evidence in case of the present oyster bed could be attributed to severe competition for food and water (Ager 1963,p. 143; Hecker 1958, p. 6). Hayasaka (as stated by Ager 1963, p. 144) studied this problem in C. vlrginica; while Ager (Ioc. cit.) quotes Jurassic example of O. hebridica var. elongatafrom Bathonian on the Dorset coast of England. On the basis of molluscan fauna like scapnitids and inoceramids Kauffman (1972) has studied relation between radiation and extinction with the phase of transgression and regression respectively. He has shown that during regression irregular but simple pattern of evolution prevails with the accelerated rate of speciation. Chiplonkar and Ghare (1977) suggested three phases of regression in the limestone members of the Bagh Beds on the basis of scaphitids. Badve and Ghare (1977) have attributed rapid speciation of Bosostrea to regressive pulse which set in after the depositionof Trace Fossils horizon towards the top of the Nimar Sandstone. Subfamily Genus Subgenus Lophinae Vyalov, 1936 Lopha Roding, 1798 Actionstreon Bayle, 1878

11 116 G W Chiplonkar and R M Badve Lopha (Actinostreon) Semiplana (Sowerby) (figure 40) 1825 O. semiplana Sow. : Sowerby, p. 144, pi. 489, figure O. semiplana Sow. : Coquand, p. 74, pi. 28, figures 1-25; pi. 35, figs. 1-2; pi. 38, figs Material : One specimen; Plesiotype no. MACS G 638 Dimensions Height length HJL Sp. no. mm mm MACS G Remarks: This well known species is reported from England, European countries (d'orbigny 1847, Geinitz 1872 and Leonard 1937) and North African countries (Coquand 1869, Stefani 1913, and Fourtau 1917) particularly the latter, ranging from Turonian to Santonian. Occurrence Oyster bed near the top of the Nimar Sandstone at Mangra. Genus : Cameleolopha Vyalov, 1936 Came/eolopha cameleo (Coquand) (figure 39) 1869 Ostrea came/eo Coquand : Coquand, p. 149, pi. 55, figs Material : One specimen; P/esiotype no. MACS G 639 Dimensions Height length HJL Sp. no. mm mm MACS G Remarks: By its tall shell, narrow, sharply crested and dichotomously branching radial ribs (12 to 20) the present specimen distinctly belongs to monotypic genus Cameleolopha Vyalov (Stenzel, 1971, p. NII64, figs. J 136, I a-d) and by its outline and proportions it agrees with species described by Coquand from the Cenomanian of Algeria. Occurrence: Nodular Limestone at Walpur. Ostrea sp. indet (figure 41-43) Material: Four specimens. Specimen nos. MACS G 640 to 642. Remarks: Four iii preserved casts have been collected from a shale band occurring near the local base of the Nimar Sandstone at the Bagh caves. Though the casts lack ornamentation and other morphological details yet they are referable with certainty to the genus Ostrea; but a more precise position is not possible. The RV (MACS G 640 and 641) is elongately ovate, shallow and with a broad ligamental area. The anterior side is broadly convex merging with the dorsal margin. The posterior margin is fairly straight and the ventral margin regularly convex. These specimens are of particular interest, because they come from what appears to be the lowest horizon in the Bagh sedimentation at which signs of marine incursion in the course ofdeposition of the Nimar Sandstone are noticeable (Chiplonkar and Badve 1972, p. 94). Occurrence: Purple shale band coming towards the local base ofthe Nimar Sandstone at Bagh caves.

12 Bagh oysters 117 Acknowledgements We are thankful to Dr G B Deodikar, for his keen interest in the present work. Thanks are also due to the Director-General, Geological Survey of India, for giving us access to their Central Library and the types in their museum, and to our colleagues Mr M A Ghare andmr P M Tapaswi for helping us with their useful comments and in the field work. References Ager D V 1963 Principals 0/Paleoecology (London: Mcgraw Hills) 371 p. Badve R M and Ghare M A 1977 Palaeoecological aspect of the Bagh Beds, India; Recent Researches in Geology 4, Prof. Chiplonkar Commen. Vol. (Delhi: Hindustan Pub. Corp.) pp Chiplonkar G Wand Badve R M 1972 Newer Observations on the Stratigraphy of the Bagh Beds; J. Geol. Soc. India Chiplonkar G Wand Badve R M 1976a Palaeontologyof the Bagh Beds-Part V Ostreina; Proc. Indian Acad, Sci. B Chiplonkar G Wand Badve R M 1976b Depositional conditions of the Bagh sediments as indicated by the oyster beds; Indian Geol. Congr. 1st Sess. Delhi Abst. p. 32 (in press) ChipJonkar G Wand Ghare M A 1977 Palaeontology of the Bagh Beds Part X-Scaphitidae; Proc. Indian Acad. Sci. B Coquand H 1869 Monographie du genae Ostrea, terrain cretace (Paris: J B Bailliere & fils) 215 p, Fourtau R 1917 Catalogue des invertebres Fossiles de I'Egypt terrain cretaces, Part II, Mollusca Lamellibranches; Geol. Surv. Egypt. Pal. Ser p. Geinitz H B Das Elbthalge birge in Sachsen; Palaeontographica HeckerRF 1957Introduction to Paleoecology Trans. M KElias and RC Moore 1965edn. (New York: American Elsevier Publishing Co. ) 166 p. Hopkins S H 1957' Oysters' in Treatise on Marine Ecology and Paleoecology Reprinted 1971 Ed. J W Hedgpeth (Boulder Colorado: Geol. Soc. Amer.) Geol. Soc. Am. Mem Kauffman E G 1972 Evolutionary rates and patterns of North American Cretaceous Mollusca; 24th Sess. Int. Geol. Congr, Montreal Sec 7 Paleontology Leonhard L 1937Fauna und Flora der Frankischen AlbuderdcckendenKreide-I. Die Lamellibranchiten (Ohne Inoceramen); Paleontographica 75, (5, 6) pp Moore H B 1962 Marine Ecology Second printing (New York: John Wiley) 493 p. Orbigny A de Paleontologiefrancais terrain cretace 3 Lamellibranches (paris: G Masson) 807 p, Sowerby J 1825 The Mineral Conchology ofgreat Britain 5 (London: Benjamin Meredith) 168 p. Stefani C de 1913Fossils deus creta superiore recoltti da M SForza in Tripolitania; Palaeontographica Italica Stenzel H B 1971 Oysters' in Treatise on Invertebrate Paleontology ed R C Moore (Kansas: Geol. Soc. Arner. & Univ. Kansas Press) Part N (3 of 3) Mollusca 6 Bivalvia N953-N1224 Thomas P and Peron A Description des invertebres fossiles des terrain cretaces de la region sud des hauts plateau de la Tunisie ; Explor. Sci. Tunisie 405 p. Thorson G 1957 Bortom Communities' in Treatise on Marine Ecology and Paleoecology Reprinted 1972ed J W Hedgpeth (Boulder Colorado: Geol, SOl:. Amer.) Geol. Soc. Amer. Mem Weir J 1930 Upper Cretaceous Fossils The Geological collection from the South Central Sahara made by Mr F Rodd in J W Gregory and others; Q. J. Geol. Soc