Taxonomic analysis of the 1rst ophiuroid remains for the Mesozoic of South America: the youngest record of the extinct genus Ophiopetra Hess

PAZOS P.J.; GIACHETTI, L.; FERNÁNDEZ D. E.; STOHR, S.; THUY, B.; PEREZ, D.; COMERIO M.

Congreso; V Congreso Internacional de Paleontologia; 2018

Previous ndings of articulated and/or nearly complete brittle stars in South America are restricted to Devonian, Permian and Cenozoic specimens. In this work ophiuroids are described from the Neuquen Basin, Patagonia, Argentina. These are the rst remains of ophiuroids for the Mesozoic of South America. The specimens have a disc diameter of 3.5 mm, and ve long and slender arms that are 3 times longer than the disc diameter. The stout lateral arm plates exhibited by the specimens are similar to what is found in Ophiodoris Koehler and Ophioplax Lyman, recently included in the family Ophionereididae. However, the disc ornamentation diers from both genera: both sides of the disc are densely covered with granules. We therefore place these specimens in the extinct genus Ophiopetra Hess, also taking into account similarities in the overall shape of the lateral arm plates. The specimens belong to a new species but are poorly preserved. A new name is not introduced, as it would be based on an incomplete diagnosis. At the moment, Ophiopetra is considered an ophiolepidid. In the context of the latest progress in ophiuroid systematics, and thanks to new insights on the spine articulation microstructure of Ophiopetra lithographica found by this study, a transfer of Ophiopetra to the family Ophionereididae within the order Amphilepidida is proposed. This material expands the palaeogeographic record of this genus, since it represents the first remains of Ophiopetra described from the Southern Hemisphere. It is also the first post-Jurassic record of the genus worldwide.