OBSERVATIONS ON NEW LATE PALEOZOIC BRITTLE STARS (ECHINODERMATA, OPHIUROIDEA) FROM NEW MEXICO AND TEXAS

Fossils of late Paleozoic ophiuroids are rare. Among Paleozoic ophiuroids, only the ophiurinids exhibit characters limited to post-Paleozoic groups. The exact relationship between ophiurinids and the post-Paleozoic fauna has not yet received detailed analysis in part due to the poverty of the fossil record. Discovery of two new late Paleozoic ophiurinid taxa provides new and valuable information on the morphological diversity of this group.

Specimens discussed include new taxa of ophiurinids from the Upper Mississippian Helms Formation, west Texas (three specimens), and the Mississippian Rancheria Formation in the San Andres Mountains, New Mexico (~30 specimen). In addition, we report the discovery of a single specimen of a member of the Furcasteridae from the Lower Permian Hueco Group in the Robledo Mountains, New Mexico.

The three specimens from the Upper Mississippian Helms Fm. exhibit features typical of ophiurinids including incipient radial shields, primary rosette, and ventral and dorsal arm ossicles. We recognize seven genera and eleven species of ophiurinids in the global fossil record. Of these, Archaeophiomusium is most similar to the new material from Texas. However, unlike Archaeophiomusium, the specimens have much larger ventral and dorsal arm ossicles, laterals that do not touch across the dorsal or ventral midline of the arm, and a different arrangement of dorsal disk plates.

Specimens from the Mississippian Rancheria Fm. display ambiguities and are difficult to interpret due to their small size. Apparently contradictory morphologies might be due to diagenetic alterations or suggestive of multiple species. Some of the better-preserved specimens exhibit stout laterals that touch across the proximal portion of the ventral surface of the arms, and well-developed oral shields, both characters found only in the ophiurinids.

The Permian specimen is poorly preserved but a large open mouth frame, slender, evenly-tapering arms, thin, hair-like vertical spines and overall form and shape are strongly reminiscent of members of the Furcasteridae. In combination with other reported occurrences of poorly preserved Permian Furcasteridae from Nevada and isolated ossicles from Germany, this record strengthens the view that this group, which first appeared in the Ordovician, survived into the Permian.