A new sphenodontid (Lepidosauria) from the Cretaceous of Chubut Province and the distribution of the eilenodontines

APESTEGUÍA, S. Y CARBALLIDO, J. L.

Neuquén

Congreso; III Congreso Latinoamericano de Paleontología de Vertebrados; 2008

CEPALB

Sphenodontians are a group of lepidosaurs well known from Late Triassic to Early Cretaceous deposits of most of the world, but represented today by two sole species barely surviving at New Zealand. Discoveries during the last 10 years depicted an unexpected abundance and diversity of sphenodontids for the Late Cretaceous of South America (e.g., Simón and Kellner 2003; Apesteguía and Novas, 2003; Martinelli and Forasiepi, 2004; Apesteguía, 2005). However, most remains come from the Neuquén basin and its eastern extensions, providing a rich but strongly biased panorama. Here we report a new sphenodontid from Cretaceous beds of the the Cañadón Asfalto Basin in Chubut Province. The fossil comes from a new locality in the Bayo Overo Member of the Cerro Barcino Formation, regarded as Cenomanian in age by Proserpio (1987). The locality also provided remains of titanosauriforms, carcharodontosaurids and crocodyliform teeth. The sphenodontid here reported (MPEF-PV 3166) is composed by a partially eroded skull with attached jaws belonging to an adult specimen. A phylogenetic analysis was performed using a data matrix of 67 characters (8 of them traded as additive) and 17 terminal taxa. MPEF-PV 3166 belongs to Opisthodontia for the following unambiguous synapomorphies: weak and squared coronoid process, absence of caniniform teeth or dental regionalization and the presence of anteromedial dental flanges. MPEF-PV 3166 can be included in Kaikaifilusaurus for its extremely large anteromedial flanges. However, the new material clearly differs from other Kaikaifilusaurus species in an extremely small size, tall jaw teeth with a high anteroventral angle, a dense dental packing, and the shape of the nasal process of the premaxilla. The new taxon not only increases the morphological variation among eilenodontines (Apesteguía, 2002) but also shows a dwarfing process among the most gigantic known sphenodontids. Additionally, this finding extends the elilenodontine distribution southwards, and supports the biostratigraphical utility of eilenodontines for Cretaceous red beds on different basins.