Crinoids from the Middle Jurassic (Bajocian–Lower Callovian) of Ardèche, France

Abstract

Several Middle Jurassic outcrops in the Ardeche Department near La Voulte-sur-Rhone and St-Etienne-de-Boulogne are rich in the remains of crinoids, but these were known from surface collections only and were not described using present standards of systematics. This paper brings the taxonomic status of the previously described crinoids up to date, reassesses the systematic position of some of the species based on cups and describes new forms. Sampling and washing of bulk material from the Lower Bathonian of the La Pouza locality yielded nearly 100,000 crinoid ossicles. Among them are rare comatulids with the following recognized as new: Andymetragalei n. g., n. sp., Palaeocomaster messingi n. sp., Singillatimetra inordinata n. g., n. sp. and Solanocrinitesvoultensis n. sp. These forms supplement the meagre record of Middle Jurassic comatulids and indicate that this group radiated well before the Late Jurassic. The Cyrtocrinida constitute the bulk of the crinoids and they are dominated by Cyrtocrinus praenutans n. sp. from which nearly all parts of the skeleton are described in their morphological variability. The La Pouza site furnished the additional new cyrtocrinids, Praetetracrinus bathonicus n. sp. and Phyllocrinusvoultensis n. sp. The material also includes numerous remains of the isocrinids Isocrinus dumortieri (de Loriol), Balanocrinus dumortieride Loriol, Balanocrinus pacomeide Loriol and Balanocrinus inornatus (d’Orbigny), which are described in some detail, including brachials. From the Upper Bajocian–Lower Bathonian locality of Pont des Etoiles, Pentacrinites ausichi n. sp. and the cyrtocrinid Scutellacrinus tenuis n. g., n. sp. are new to science. The results demonstrate that the Middle Jurassic crinoids from the Ardeche are one of the important and diverse Mesozoic crinoid faunas. Some forms bridge the gap between the Early Jurassic and the Late Jurassic hardground faunas of cyrtocrinids. Cyrtocrinus praenutans n. sp., a form similar to Cyrtocrinus nutans (Goldfuss) from the Oxfordian, is described as a separate species despite some overlapping phenotypic variability of cups and columnals. Pathological deformations on all types of ossicles of C. praenutans n. sp. are ascribed to the epizoan commensal Oichnus paraboloides Bromley. Different species are dominant at the different Bathonian localities, namely C. praenutans n. sp. at La Pouza and Phyllocrinus fenestratus (Dumortier) and Lonchocrinus dumortieri (de Loriol) at La Clapouze. Preservation and rock formation of the Upper Bajocian–Lower Bathonian Isocrinus nicoleti (Thurmann) at Pont des Etoiles suggests that this form lived in rather shallow and turbulent water. The dominance of cyrtocrinids and the presence of all growth stages and parts of the skeleton at La Pouza and La Clapouze suggest a deeper palaeoenvironment, with some transport of the ossicles.