(Asteroidea; Echinodermata) from the Upper Cretaceous (Coniacian)

I Pal ontZ 170 11/2 1181-187 I

2Abb

I Stuttart, M rz1996 I

A new genus and species of Asteriidae (Asteroidea; Echinodermata) from the Upper Cretaceous (Coniacian) of Angola, Africa DANIEL B. BLAKE, Urbana, G~RARD BRETON, Le Havre & SERGE GOFAS, Paris* With 2 figures K u r z f a s s u n g : Afraster scalariformis n. gen. et sp., aus der oberen Kreide (Coniac) von Angola, SWAfrika, wird in die Pedicellasterinae, eine Unterfamilie der Asteriidae gestellt. Eine assoziierte Foraminiferenfauna ist beherrscht vonplanktischen Arten; schelfbewohnende Lageniden sind jedoch auch nachgewiesen. Die Unterfamilie Pedicellasterinae zeichnet sich gegeniiber den sonst fOr die Familie typischen vier Reihen Podia dadurch aus, dat~ sie nur zwei Reihen aufweist. Eine enge Assoziation von Afraster mit Austern liif~t auf eine Ern~ihrung schliet~en, die typisch for moderne Asteriden ist; die Anordnung von Scheibe und Armen deutet ebenfalls auf dieses Verhalten hin. Afraster ist der Ersmachweis eines fossilen Seesterns aus Angola. A b s t r a c t : Afraster scalariforrnis n. gen. et sp., from the Upper Cretaceous (Coniacian) of Angola, southwest Africa, is assigned to the Pedicellasterinae, a subfamily of the Asteriidae. An associated foraminiferal fauna is dominated by planktic species; also present are lagenids that are indicative of a shelf setting. The subfamily Pedicellasterinae is peculiar in that only two rows of podia are present, rather than the four typical of the family. Intimate association of Afraster with oysters suggests the predatory habits typical of modern asteriids; general arm and disk arrangement also suggest such a behavior. Afraster is the first recorded fossil asteroid from Angola.

Introduction A f r a s t e r s c a l a r i f o r m i s n. gen. et sp. is important because it provides a fossil representation of a subfamily that is rare today and has only a very limited fossil record. The overall form of the new asteroid and its association with oysters suggests a feeding habit typical of modern members of the Asteriidae. A f r a s t e r s c a l a r i f o r m i s is the first fossil asteroid to be described from Angola, Africa. Members of the Asteriidae are common today in many areas, but most particularly midlatitude shallow shelf settings. Although fossils are comparatively infrequently reported in the literature, examples in museum collections suggest that the family is among the more frequently encountered post-Paleozoic fossil asteroid taxa; the many very small ossicles typical of members of the family are particularly susceptible to taphonomic alteration, and many occurrences remain unreported, perhaps obscuring their abundance. Available fossil occurrences in addition to that described here include those of HEss (1972), BLAKE & ZINSMEISTER(1988), and BLAKE (1990); older references are cited in these papers. The present example, the first fossil from southern Africa, joins the Eocene Antarctic occurrence described by BLAKE & ZINSMEISTER (1988) in suggesting that the family has had a long, broad distribution.

* Addresses of the authors: D. B. BLAKE, Department of Geology, University of Illinois at UrbanaChampaign, Urbana 61801, IL, USA; G. BRETON,Museum d'Histoire Naturelle, Place du Vieux-March~, F-76600 Le Havre; S. GoFas, Biologie des Invert~br& Matins et Malacologie, Museum National d'Histoire Naturelle, 55 rue Buffor~, F-75005 Paris. 0031-0220/96/0070-0181 $ 1.75 9 1996E. Schweizerbart'scheVerlagsbuchhandlung,D-70176Stuttgart

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Daniel B. Blake, G~rard Breton & Serge Gofas Occurrence

The collecting site is an outcrop of the N'Golome Marl Formation on the coast of northern Angola, near Pambala (province of Bengo) (Fig. 1). It is a maritime cliff with a lithology of alternating soft and consolidated foraminiferal marls, with many valves of large inoceramids lying parallel to the stratification. For details on regional stratigraphy, the reader is referred to the general account by BROGNON & VERRIER (1966) and to the geological map issued by the oil exploration company TOTAL (1987). The marls surrounding the specimen of Afraster scalariformis are very rich in foraminifera, mostly planktic. Despite the rather poor preservation due to recrystallization, the following taxa could be identified (following ROBASZYNSI(I ~ CARON 1979; ROBASZYNSKI et al. 1984, and CARON 1985): Dicarinella concavata (BROTZEN 1934) (14 specimens), D. hagni (SCHEIBNEROVA 1962), Marginotruncana sinuosa PORTHAULT 1970, M. marginata (REuss 1845), Archeoglobigerina bosquensis PESSAGNO 1967, Globigerinelloides sp., Heterohelix reussi (CusHMAN 1938), Hastigerinoides subdigitata (CARMAN 1929). The pelagic microfauna points to a late Coniacian age, the Dicarinella concavata Zone of SIOAL (1955), which is in good agreement with the Coniacian to Santonian age generally accepted for the N ' Golome marls. The Santonian marker species Dicarinella asymetrica, usually represented in younger samples in this area, was not found. The benthic species account for less than 10 percent of all individuals and are mainly Lenticulina and other lagenids; such taxa are common in shelf deposits of the Late Cretaceous.

Paleobiology The available specimen of Afraster scalariforrnis is on a small block, seemingly in living orientation, resting on the outer surface of a valve of inoceramid. The inoceramid is also encrusted by numerous small (2-12 mm) oysters. Oysters are a preferred prey of many modern asteriids; Afraster is significantly larger than its potential prey, and its sturdy arms, compressed ambulacra, and stoutly braced disk (see below) render it a morphologically plausible predator of oysters. FISHER (1928) reported the presence of a large stomach in the modern pedicellasteroids Pedicellaster magister and Ampheraster marianus, and presence of small gastropods of P. magister; he thought the gastropods were ingested entire. The present A. scalariformis is not oriented in the wrapped feeding posture typical of asteriids, nor are the podia quadriserial, as they are in typical members of the family; the inferred behavior must remain conjectural. Nevertheless, the specimen suggests that the asteriid predatory habit is an ancient one and that perhaps much asteriid morphology (but not quadriserial tube feet) arose with their peculiar behavior. Extant members of the Pedicellasterinae are represented b y few individuals in most museum collections, and most occurrences are from deeper water (from below 100 meters to hundreds of meters; see CLARK & DOWNEY 1992). The N ' Golome Marl Formation occurs on a huge platform with little or no terrigeneous input, and the foraminiferal marls represent an uncertain depth between 10 and 200 m. The lower depth would be shallow as compared to those of extant pedicellasterids, but the deeper value is within the range of contemporary occurrences.

Fig. 1. Simplified geological sketch of the northern part of Cuanza Basin, redrawn from TOTAL (1987), with the N' Golome formation highlighted. B: basement; LC: evaporitic and calcareous formations of the Lower Cretaceous; Ch Cabo Ledo Formation (Cenomanian); It: Itombe Formation (Turonian); Ng: N' Golome Formation (Coniacian-Santonian); Tb: Teba Formation (Campanian-Maastrichtian); Te: Tertiary. Arrow: the collecting site.

A new genus and species of Asteriidae (Asteroidea; Echinodermata)

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Daniel B. Blake, G~rard Breton & Serge Gofas Systematic

paleontology

Class A s t e r o i d e a DE BLAINVILLE 1830 O r d e r F o r c i p u l a t i d a PERRIER 1894 F a m i l y A s t e r i i d a e GRAY 1840 S u b f a m i l y P e d i c e l l a s t e r i n a e PERRIER 1884 The Pedicellasterinae is recognized for those relatively few members of the Asteriidae with two rows of tube feet in at least portions of the arms (CLARK & DOWNEY 1992). Extant members are somewhat varied, and it is uncertain whether or not the subfamily represents a monophyletic group because quadriserial tube feet occur in taxonomically divergent ancient and m o d e r n asteroids, and the occurrence of quadriserial tube feet in species of different pedicellasterid genera (e. g., Ampheraster marianus) suggests loss rather than comparatively recent acquisition in a single small, monophyletic group. Nevertheless, ambulacral ossicular morphology, although generalized, is comparatively u n i f o r m within living members of the subfamily, and Afraster is similar to living pedicellasterids in this development; in spite of its unusual robust construction, Afraster is considered a m e m b e r of the Pedicellasterinae. Genus

Afraster

n. gen.

Ty p e s e c i e s'. Afraster.scalariormis n..sp., from. the. of Angola, Africa. E t y m o ~(~g y : Aft, Africa, for t~e~ continent of origin. Coniacian D i a g n o s i s : Pedicellasterid with reticulate dorsal skeleton of few, well defined rows of robust cruciform ossicles; arms long, slender; disk small, strongly braced by double row of interbrachial superomarginals extending to central ring.

Afraster scalariformis

n. sp.

Fig. 2 A-D E t y m o 1o g y: scala, ae (L.), ladder, used as a plural scalae, arum; the ladder-like ossicular arrangement. M ate r ial: A single incomplete individual, resting on a bivalve fragment, with the dorsal surface exposed. The specimen consists of the disk and portions of four arms; the fifth is missing. The body is collapsed and flattened; the ventral ossicles are very poorly exposed. The specimen suffered minor distortion, and ossicular shapes and surficial detail have been somewhat alterea, nevertheless shape and arrangement are generally quite well preserved. This holotype is housed in the Museum National d'Histoire Naturelle, Institut de Pal~ontologie, 8 rue Buffon, 75005 Paris (France); n ~ R 11573. D i a g n o s i s : Same as the genus, by monotypy. D e s c r i p t i o n : Five-armed asteriid; arm radius (R) 29 mm, disk radius (r) approximately 6.5 m m (increased by taphonomic flattening). Arms perhaps subpetaloid near disk, but essentially parallel-sided proximally; arms tapering distally to probable r o u n d e d tip. O n disk, primary circlet consists of 10 ossicles (but perhaps modified at madreporic interbrachium) enclosing central area of tightly arranged (but p o o r l y preserved ossicles), which are up to about 1 m m diameter. Interbrachial primary circlet ossicles elliptical to crescentic, concave on distal side, about 2 m m wide, with dorsal surface domed, bearing up to five or six stout spinelets. First radial ossicles about 1.5 m m long, 1.25 m m wide; surface arched, with multiple circular spine Fig. 2. A-D: Afraster scalariformisn. gen. et sp. from N ' Golome Formation (Coniacian), Angola, Africa; A, • 2; B-D, • 6. A: Overall view of holotype resting on inoceramid valve, with small oysters, representing possible prey. C: Medial and distal view of incomplete arm, tip with spine-bearing marginal series, ambulacral, small oysters. B, D: Dorsal views of specimen with central disk, madreporite, central ossicles poorly preserved; well-aligned rows of arm ossicles. - Key: a, ambulacral; c, carinal; i, interbrachial superomarginal series; 1, lateral; m, madreporite; o, oysters; p, primary circlet; s, superomarginat; t?, questionable terminal; al, secondary lateral.


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bases near proximal edge; ossicles at madreporic interbrachium smaller. Madreporite irregular, subcircular, domed, about 2 mm in diameter, with radiating gyri. Five linear dorsal ossicular series clearly exposed on arms; carinal series well-defined along arm dorsal axis, one lateral series on each side of carinals, superomarginal series adjacent to laterals, five series together forming well-defined reticulate pattern. Proximal carinals cruciform, about 1.5 mm long, with longest of four flanges overlapping next proximal carinal; outer surface arched, one circular spine base developed on proximal flange; lateral flanges overlap adjacent primary lateral. Carinals probably reached terminal. Proximal primary laterals ellipitical to weakly cruciform, transversely elongate, about 2 m m wide (but partially obscured in life by adjacent ossicles); dorsal surface weakly arched, spines do not appear to have been present. Primary laterals, carinals approximately correspond in number. Secondary lateral present between each successive primary lateral pair; secondaries approximately 0.5 mm square, dorsal surface weakly arched, spines lacking. Lateral ossicles probably significantly reduced in size near arm tip, although contributing to closely armored tip. Ossicular series adjacent to laterals traceable to near to arm tip, therefore they are identified as superomarginals. Arm superomarginals cruciform, similar to carinals, but with central intersection of four flanges enlarged; superomarginals aligned, corresponding in number with adjacent laterals and carinals, overlapping laterals. Circular spine base present on proximal flange near to central intersection of four flanges; spines few, much of ossicular surface probably bare in life. Small groove developed on abutting surface of flanges. O n disk, two rows of superomarginals from adjacent arms come together, abut; facing flanges lost, so that double series forms stout interbrachial row extending to interbrachial ossicle of primary circlet. Radial groove probably separated series at surface. Superomarginals largest ossicles at arm tip. Inferomarginals very incompletely exposed, apparently paired with, similar in form to superomarginals. Cruciform shapes of major ossicular rows left openings for respiratory papulae. Ambulacral column compressed, podial pores uniserial. Medial ambulacral about 1.75 mm wide. Adradial head broad, flange-like, strongly overlapping adjacent ambulacral; abradial extension broad, central area low, therefore overall ossicular form crescentic. Terminal (?) about 0.75 m m long, 0.5 mm wide at proximal edge, tapering distally, rounded dorsally, with spine base at proximal edge. Adambulacrals poorly exposed, probably wide, robust. Actinals, jaw flame not exposed. R e m a r k s : In spite of incomplete preservation, the asteriid affmities of the fossil are clear. Overall form (long, slender arms and a small disk) is typical of many asteriids, as are the cruciform nature of the dorsal ossicles, the presence of well-defined carinal and lateral series, and comparatively few, clearly circular spine bases with distinct grooving on the articular surfaces of the ossicular flanges. Both the compressed nature of the ambulacral column and the shape of the ambulacrals is typical of asteriids; most members of the family have quadriserial podial pores, but both quadriserial and uniserial pores are known from the surviving Pedicellasterinae, and from the fossil record (HEss 1972). Pedicellariae are not preserved. In addition to the arrangement of the podial pores, Afraster is like some of the living pedicellasters in that the interbrachial superomarginals are differentiated, although only in Afraster are three stout proximal superomarginals of each arm involved. In Afraster, and to a lesser extent, Tarsaster, the ossicles are broad and shield-like, and in both, only the first superomarginals are differentiated. Differentiation is weak in Anteliaster, Pedicellaster and Hydrasterias, all of which have comparatively numerous dorsal ossicles. Ambulacral ossicles of Afraster are like those of the living pedicellasterids, especially those of Ampheraster and Hydrasterias. Hydrasterias and some Ampheraster are six-armed. In none of the living genera are the dorsal ossicles (i. e., above the marginals) clearly differentiated and arranged in comparatively few robust rows, as they are in Afraster (although rows in Tarsasterand Ampheraster are distinct). Dorsals of Ampheraster, except for the carinals, tend


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to be irregular in arrangement, and irregular and cruciform in shape, rather than in well-defined rows. Those of Anteliaster and especially Hydrasterias are irregular in arrangement and delicate in form. There are m a n y rows of rather uniform ossicles in Pedicellaster and Tarsaster (and to a lesser extent, Anteliaster), and ossicles are not as stout as in Afraster (specimens of radius u n d e r about 20 m m have few ossicular rows, but size alone w o u l d serve to separate these individuals). The m a n y rows of comparatively stout ossicles of the Jurassic genus Derrnaster are also unlike the arrangement f o u n d in Afraster (H~ss 1972). A m o n g asteriids with the more typical, four rows of podial pores described by HESS (1972) and BEAIiE (1990), Afraster dorsal ossicle arrangement is perhaps m o s t like that of Germanasterias BLAKE, although shape of the dorsal ossicles is different, and there is no clear indication of pedicellariae in Afraster.

Acknowledgements DBB is, as always, indebted to D. L. PAWSON, C. AHERN, and the authorities of the U.S. National Museum for their kind hospitality and access to collections under their care. S. G. thanks Prof. J. M. GONZALEZ DONOSO (University of Mfilaga, Spain) for assistance with the identification of planktic foraminifera and Mrs. M. L. DUARTEMORAIS(University of Luanda, Angola) for bringing her attention to the geological map issued by TOTAL. RuDo VON COSEL kindly prepared the German-language abstract.

References BLAKE,D.B. 1990. Henangian Asteriidae (Echinodermata: Asteroidea) from southern Germany; taxonomy, phylogeny and life habits. - Pal~iontologische Zeitschrift 64: 103-123, Stuttgart. BLAKE,D.B. & ZINSMEISTER, W.J. 1988. Eocene asteroids (Echinodermata) from Seymour Island, Antarctic Peninsula. - [In:] FELDMANN, R. M. & WOODBURNE, M. O. (eds.) - Geology and Paleontology of Seymour Island, Antarctic Peninsula. - Geological Society of America Memoir 169: 489-498, Boulder/Co. BROGNON, G.P. & VERRIER, G. 1966. Oil and geology in Cuanza Basin of Angola. - American Association of Petroleum Geologists Bulletin 50: 108-158, Tulsa/Ok. CARON, M. 1985. Cretaceous planktic Foraminifera. - [In:] BOLL1, H. M.; SAUNDERS,J. B. & PERCHNIELSEN, K. (eds.) Plankton Stratigraphy: 17-86, Cambridge Earth Science Series, Cambridge (Cambridge University Press). CLARK, A.M. & DOWNEY, M. E. 1992. Starfishes of the Atlantic. - 794 pp. London (Chapman & Hall). FISHER, W.K. 1928. Asteroidea of the North Pacific and adjacent waters. - United States National Museum Bulletin 76: 1-161. HESS, H. 1972. Eine Echinodermen-Fauna aus dem Mittleren Dogger des Aargauer Juras. - Schweizerische Pal~iontologische Abhandlungen 92: 1-88, Basel. ROBASZYNSKI,E & CARON, M. 1979. Atlas de Foraminif~res planctoniques du Cr&ac6 moyen. - Cahiers de Micropal~ontologie 1: 1-185; 2: 1-181, Paris. ROBASZYNSKI,E; CARON, M.; GONZALEZDONOSO, J. M. & WONDERS, A. 1984, Atlas of Late Cretaceous globotruncanids. - Revue de Micropal~ontologie 26: 145-305, Paris. SmAL, J. 1955. Notes micropal~ontologiques Nord-Africaines. 1. du C~nomanien au Santonien, zones et limites en faci& p~lagiques. - Comptes Rendus sommaires de la Soci&~ G6ologique de France 1955(8): 157-160, Paris. TOTAL Compagnie Angolaise des P&roles and S O N A N G O L , 1987. Carte g~ologique du Bassin du Kwanza, Angola, 1:250 000. Luanda. Eingangdes Manuskriptes am 9. April 1995; Annahme durch die Schriftleitung am 21. Juni 1995.