Seventeen specimens representing three of the four asterozoan classes (Stenuroidea, Asteroidea, Ophiuroidea) are recorded from Ordovician and Silurian strata of the western United States and northwest France; only the Somasteroidea is not represented. New taxa are: the stenuroids Lopidiaster jamisoni nov. gen. and sp. and Lehmannaster spinosus nov. gen. and sp.; the asteroids Meturaster belli nov. gen. and sp., Petraster crozonensis nov. sp., and Schuchertia sprinklei, nov. sp.; Lepidactis? sp. also is recognized. The Ophiuroidea is represented by Stenaster sp., Protaster sp., and an arm tip is of unknown familial and generic affinities. Class level assignments of all specimens are clear, and all but Lopidiaster are similar to earlier-known representatives of their respective classes; phylogenetic differentiation within the subphylum was well-established early in the Paleozoic. Ordovician asterozoans are both geographically widely distributed and morphologically clearly separable from modern asterozoans, yet overall structural similarities favor ecologic roles paralleling those known today.
- United States
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