Stalked crinoids from Gan (Late Ypresian, southwestern France): exceptional stereom preservation, paleoecology and taxonomic affinities

Abstract

Exceptionally well-preserved ossicles of xenomorphic stalked crinoids (Echinodermata) were found into the Late Ypresian clay of the Tuilerie de Gan (Pyrénées-Atlantiques, southwestern France). Three kinds of columnal articulation correspond to three different genera, including the new genus Eocenocrinus. These columnals are attributed to Paraconocrinus romanensis, Democrinus londinensis and Eocenocrinus hessi n. gen., n. sp. Associated benthic fauna as well as columnal characters related to water depth confirm an increasing depth to an epibathyal environment as previously suggested by mollusk and foraminifer associations. Paraconocrinus romanensis associated with Democrinus londinensis mark the maximum water depth, which did not exceed 300 m. Distal columnal series with proximal roots of P. romanensis and D. londinensis were collected with their ossicles connected, indicating that these species lived on a muddy bottom. E. hessi n. gen., n. sp. is suspected to have been attached on hard substrate. Without diagenetic crystallizing, the crinoid stereom and its micro-biocorrosion appear as in extant specimens. We attribute to Eocenocrinus n. gen. large columnals previously described from northeastern Italy and recognize two species: E. bayani n. gen., n. sp. (Middle Lutetian) and E. didymus (Priabonian). E. hessi n. gen., n. sp. may represent the oldest known species in the family Phrynocrinidae.