An exceptional skull of Huayqueriana (Litopterna, Macraucheniidae) from the late Miocene of Mendoza, Argentina

FORASIEPI, ANALÍA M.; SCHMIDT, GABRIELA I.; HERNANDEZ DEL PINO, S.; MACPHEE, R.

Diamante, Entre Ríos

Jornada; XXIX Jornadas Argentinas de Paleontología de Vertebrados; 2015

Asociación Paleontológica Argentina

The Huayquerías Formation (late Miocene, Huayquerian Age) is exposed incentral-west Argentina (Mendoza Province). It was the subject ofpaleontological studies in the first half of the 20th century and its interesthas sporadically continued since. New systematic field work revealed novelmaterial, such as a complete skull (IANIGLA-PV 29) from the Río Seco de laÚltima Aguada, referred to Huayqueriana cf. H. cristata (Rovereto) (Litopterna,Macraucheniidae). IANIGLA-PV 29 shares some non-exclusive features with H.cristata (similar size, rostral border of the orbit almost level with distalborder of M3, convergence of maxillary bones at the level of the P3/P4embrasure, flat snout, very protruding orbits, round outline of premaxillaryarea in palatal view, and small diastemata between I3-C and C-P1). Otherdifferences (lack of sagittal crest) could be the result of an importantintraspecific variation if co-specificity were demonstrated. A CT scan revealedthe presence of an orbitotemporal canal in the latero-ventral aspect of thepiriform lobe cast, below the rhinal fissure, and the V2 leaving the skullthrough the sphenorbital fissure, as in all other litopterns that we havestudied. IANIGLA-PV 29 body mass was estimated to be about 400 kg. The phylogeneticanalysis failed to satisfactory resolve the position of IANIGLA-PV 29, whichmay be a consequence of intraspecific variation. When monophyly is forcedHuayqueriana is nested among macraucheniines, as the stem taxon of a cladeformed by Macrauchenia and other Pliocene and late Miocene taxa.