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

PAZOS, PABLO J.; GIACHETTI, LUCIANA M.; FERNÁNDEZ, DIANA E.; STÖHR, SABINE; THUY, BEN; PÉREZ, DAMIÁN E.; COMERIO, MARCOS

Congreso; 5th International Paleontological Congress; 2018

Previous findings 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 Neuquén Basin, Patagonia, Argentina. These are the first remains of ophiuroids for the Mesozoic of South America. The specimens have a disc diameter of 3.5 mm, and very 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 differs 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 rst remains of Ophiopetra described from the Southern Hemisphere. It is also the rst post-Jurassic record of the genus worldwide.