NEW SKULL REMAINS OF PROCHELIDELLA BUITRERAENSIS FROM THE CANDELEROS FORMATION (CENOMANIAN) OF NEUQUÉN BASIN, PATAGONIA, ARGENTINA SHEDS LIGHT ON THE ANTERIOR ROSTRAL EVOLUTION IN CHELIDAE

MANIEL IGNACIO JORGE; DE LA FUENTE MARCELO SAUL; APESTEGUÍA SEBASTIÁN; KALUZA JONATAN

Simposio; Turtle Evolution Symposium 2021; 2021

New skull remains of Prochelidella buitreraensis were recovered from the Candeleros Formation(Cenomanian) exposed in the ?La Buitrera? locality (Río Negro Province, Argentina). These materials were sampled from the same level and outcrops as the holotype. The new specimen (MPCA PV 658) consists of an almost complete skull, a right lower jaw, four articulated cervical vertebrae, some hyoid apparatus bones, and several shell remains. The size of the new materials is similar to the holotype, with a 4 cm skull length. The skull is more complete than the holotype and allows us to describe and compare the rostral area, absent in the Prochelidella buitreraensis holotype. Besides, cervical vertebrae and carapace remains allow us to increase our knowledge about the anatomy of this species. MPCA PV 658 can be referred to Prochelidella sp. after a well-developed retropterygoideum foramen and a big area for muscle attachment over the basisphenoid. Additionally, the presence of nasals and prefrontals improve the knowledge of skull holotype (MPCA PV 307). The prefrontals in the new specimen of Prochelidella buitreraensis do not contact each other in the midline. A similar condition is observed in some South American extant chelids such as Mesoclemmys nasuta, Phrynops geoffroanus and Platemys platycephala. The nasal is a small bone that contacts the prefrontals posterolateral and forms the dorsal portion of the apertura narium externa. The contact between nasal and prefrontal is also recognized in some extant South American chelids (e.g., Acanthochelys macrocephala, Phrynops geoffroanus, and Platemys platycephala) but not in Mesoclemmys nasuta. Also, the size of thenasal bone differs from that observed in Platemys platycephala where it is bigger. The posteriormargin of the carapace is preserved as in other Prochelidella species. The eight costals contact each other along the dorsal and visceral surfaces, not allowing the visceral contact of the last neural with the suprapygal, contrary to the situation in Prochelidella cerrobarcinae. The cervical vertebrae exhibit the typical morphology of Chelidae centra (atlas biconcave, 2nd, 3rd, and 4th opisthocoelous). These new features improve the diagnosis of Prochelidella buitreraensis and provide a better understanding of the morphology of this key genus on the evolution of Chelidae.