SEA STARS FROM MIDDLE JURASSIC LAGERSTATTE OF LA VOULTE-SUR-RHONE (ARDECHE, FRANCE)

摘要

The Callovian Lagerst_tte of La Voulte-sur-Rh_ne represents deep (bathyal) environments at the bottom of a submarine rocky slope. Three sea star body fossils partially replaced with pyrite were collected from clay beds. A small, stellate specimen is assigned to Terminaster cancriformis, a species already known from Jurassic clay deposits of Germany, Switzerland and England. The morphology of Terminaster illustrates mostly plesiomorphic features for post-Paleozoic sea stars, and the genus may be considered either as a paedomorphic Zoroasteridae or a stem group Forcipu_latacea. Two specimens of a large multiarmed sea star are assigned to Decacuminaster n. gen. solaris n. sp., characterized by a lack of abactinal plates and an axial skeleton typical of the Velatida. The two genera Xandarodaster and Plesias_tropecten are close to Decacuminaster and must be transferred to the Velatida. In modern oceans, the association of a multiarmed Velatida and a zoroasterid-like species would be typical of bathyal/abyssal environments, which suggests that these groups explored deep sea environments early in their history.