From the Oxfordian (Late Jurassic) of Savigna, Départment Du Jura, France
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Swiss J Palaeontol (2011) 130:69–89 DOI 10.1007/s13358-010-0008-x Asteroidea (Echinodermata) from the Oxfordian (Late Jurassic) of Savigna, De´partment du Jura, France Andrew Scott Gale Received: 25 May 2010 / Accepted: 20 September 2010 / Published online: 7 December 2010 Ó Akademie der Naturwissenschaften Schweiz (SCNAT) 2010 Abstract The asteroid fauna from the Late Oxfordian Introduction marls (bifurcatus Zone, stenocycloides Subzone) of Sav- igna includes 11 taxa, distributed between 8 families, of Much attention has been focused upon the rare finds of which 1 (Plumasteridae) is new. A goniasterid of distinc- articulated, beautifully preserved asteroid specimens. Such tive morphology, Hessaster longimarginalis, is described material is very important in our understanding of ancient as new, as is an asteriid, Savignasterias villieri. The faunas, as well demonstrated by Hans Hess’ thorough material was recovered by surface picking and processing description and illustration of the Schinznach fauna from over 1,000 kg of sediment, and includes 28 partial indi- the Hauptrogenstein (Bajocian) of Switzerland (Hess 1972) viduals and approximately 2,000 isolated ossicles in which documented the taxonomy and diversity of a excellent preservation, which show fine details of the Jurassic shallow marine echinoderm assemblage. However, stereom architecture and additionally allow ontogenetic it is unwise to rely entirely upon the infrequently found changes to be described. Detailed comparison with extant entire specimens, for two reasons. Firstly, they often reveal asteroids enables diverse ossicle types to be assigned pre- little, if any, detail of the internal skeletal structures of the cisely to individual taxa. The phylogenetic relationships of taxonomically important ambulacral groove and mouth individual fossil species with living taxa are determined frame ossicles, and secondly, they only represent a fraction using characters derived from numerous skeletal elements, of the real diversity of ancient asteroid assemblages. and it is shown that the benthopectinid and pterasterid Although dissociated asteroid ossicles have been col- species present in the Savigna fauna are basal to their lected and described for a long time (e.g. Desmoulins 1832; respective families. In comparison with other assemblages Goldfuss 1831), study has mostly concentrated upon the collected from Jurassic clay facies, the Savigna asteroid large and conspicuous marginal ossicles of astropectinids fauna is unusually diverse. Importantly, the fauna includes and goniasterids, and the enlarged abactinal and marginal elements typical of present day deep sea environments ossicles of families such as stauranderasterids and sphaer- (bathyal and abyssal), living abundantly in Oxfordian shelf asterids which can be readily collected in the field. Our seas of about 50 m depth. knowledge of the fossil record of these families is conse- quently relatively good, at least insofar as many genera and Keywords Asteroidea Á Oxfordian Á Jurassic Á French Jura species have been described. However, many asteroid taxa are themselves small, and consequently have very small ossicles, invisible to field collectors. Processing bulk sed- iment to concentrate residues, and picking asteroid ossicles from these residues, can provide very useful information on the diversity and occurrence of poorly known families, A. S. Gale (&) such as the Late Cretaceous pterasterids (Villier et al. School of Earth and Environmental Sciences, 2004a). University of Portsmouth, Burnaby Building, Burnaby Road, Portsmouth PO1 3QL, UK Asteroid skeletons are complex structures, including 11 e-mail: [email protected] major constructional skeletal elements, and diverse spine 70 A. S. Gale morphologies (Turner and Dearborne 1972). Consequently, d’Effingen (Enay 1966) are exposed in the banks of a small the ability to identify diverse ossicle types in the fossil state stream (Fig. 1a, locality 2a: N 46°26009.700, E 005°34055.100, and compare these with extant families requires a detailed 2b: N 46°26011.300, E 005°34058.200). The succession is comparative knowledge of the skeletal anatomy of extant continued downwards in a shallow excavation 50 m to the asteroid families. This work was pioneered by Blake southwest, immediately west of the Fe´tigny road (Fig. 1a, (1973), and continued using the SEM by Gale (in press). locality 1: N 46°26010.300, E 005°35004.800). The two suc- The asteroid skeleton, with its diverse and morphologically cessions can be correlated to make a composite outcrop of complex elements, is in some ways comparable with the nearly 15 m, comprising three thin marly limestones and vertebrate skeleton. It is therefore possible, with care, to intervening calcareous clays (Fig. 2). The Savigna expo- virtually reconstruct taxa from isolated ossicles of different sures are assigned to the stenocycloides Subzone of the types in exactly the same way as, say, a Pleistocene bifurcatus Zone, Late Oxfordian, dated to approximately mammal worker can confidently identify an extinct species 157–158 Ma. from a diversity of skeletal elements. It is always necessary The weathered surfaces of the clays are highly fossilif- to be cautious, especially when a number of closely related erous, with abundant columnal fragments of the crinoid species are present in an assemblage. Balanocrinus, zeillerid and acanthothyrid brachiopods, The description of asteroids from multiple skeletal ele- serpulids, pyritised nuclei of ammonites and diverse cal- ments has a number of advantages. Firstly, the amount of citic bivalves. The clay grade of the sediment, total bio- morphological information that can be obtained from a turbation, and lack of accumulations of coarser debris suite of ossicles is considerable, and allows very detailed suggest deposition below storm wave base (in excess of comparison with extant forms, permitting the reconstruc- 50 m; see Sahagian et al. 1996). The abundance of sus- tion of phylogenies. In this way, Gale (in press) was able to pension feeding crinoids, bivalves, serpulids and brachi- demonstrate that Oxfordian taxa based on ossicles, and pods would support a shallower rather than deeper related to extant benthopectinids and pterasterids, lack estimate, around 40–60 m. The high diversity and density critical skeletal characters present in all representatives of of benthos indicate an oxygenated palaeoenvironment, with the living families. They, therefore, represent basal mem- reasonable productivity. During the Oxfordian, the Jura bers of their respective groups. In turn, these features are was situated on a platform adjacent to the Helvetic Basin, directly related to specific life habits, and it can thus be on the north side of the Tethys spreading ridge (Ve´drine demonstrated, e.g., that Jurassic pterasterids did not possess and Strasser 2009; Fig. 1b herein). an abactinal canopy, and that benthopectinids lacked lon- gitudinal muscles in the arms (Gale in press). It has become evident over the past few years that Materials and methods marine clay deposits often contain well-preserved asteroid ossicles, and interest has been focused upon Jurassic clays. Calcareous clay was collected from a series of fossiliferous The most abundant and diverse fauna yet found is from the levels at Savigna, and dried in the sun. It was processed in a upper Oxfordian of Savigna, in the French Jura, originally clay machine (Ward 1981) using a 0.25 mm sieve, and the discovered by Hans Hess (1966). With the encouragement residue was dried, graded and picked and sorted into of Hans, I revisited the section in 2007, and have subse- ossicle types and taxa. Ossicles were cleaned using an quently collected and processed approximately 1 ton of ultrasonic tank, and mounted for SEM imaging. Ossicles material. This has yielded over 2,000 asteroid ossicles, were identified and assigned to taxa with reference to belonging to 12 taxa, 4 of which were described by Gale material of extant species (see Gale in press). For abbre- (in press). In this paper, I describe the remaining taxa viations, see Table 1. Museum abbreviations: BMNH, and review the entire fauna from both phylogenetic and Natural History Museum, London; CAMSM, Sedgwick palaeoecological perspectives. Museum, Cambridge, UK; Natural History Museum Basel, Switzerland, NMB. Abbreviations for morphological fea- tures follow Gale (in press) and are included in Table 1. Locality, stratigraphy and palaeoenvironment The village of Savigna is situated approximately 10 km Systematic palaeontology SSW of the town of Orgelet in the De´partment of Jura in eastern France (Fig. 1a). Approximately 500 m southwest Paxillosida PERRIER, 1884 of the church, 100 m to the north of the road to Fe´tigny, a Astropectinidae GRAY, 1840 series of natural exposures of Oxfordian calcareous clays Pentasteria VALETTE, 1929b and marly limestones belonging to the lower Couches Pentasteria (Pentasteria) longispina HESS, 1968 Asteroidea (Echinodermata) from the Oxfordian (Late Jurassic) of Savigna 71 Fig. 1 Location of Savigna section. a Present geography, b palaeogeographical map to show position of Jura Platform in the Oxfordian. After Ve´drine and Strasser (2009) Figs. 3a–h, 4a–e Type: Specimen figured by Hess (1968), NMB M 8748, 1968 Pentasteria (Pentasteria) longispina Hess, from the Late Oxfordian (bifurcatus Zone) of Scho¨fgraben, 607–614, figs. 1–3, pl. 1. Weissenstein. The species is well known from a slab 1975 Pentasteria (Pentasteria) longispina Hess, pl. 1, including 12 superbly preserved individuals,