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 in central-west Argentina (Mendoza Province). It was the subject of paleontological studies in the first half of the 20th century and its interest has sporadically continued since. New systematic field work revealed novel material, such as a complete skull (IANIGLA-PV 29) from the Río Seco de la Última 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 distal border of M3, convergence of maxillary bones at the level of the P3/P4 embrasure, flat snout, very protruding orbits, round outline of premaxillary area in palatal view, and small diastemata between I3-C and C-P1). Other differences (lack of sagittal crest) could be the result of an important intraspecific variation if co-specificity were demonstrated. A CT scan revealed the presence of an orbitotemporal canal in the latero-ventral aspect of the piriform lobe cast, below the rhinal fissure, and the V2 leaving the skull through the sphenorbital fissure, as in all other litopterns that we have studied. IANIGLA-PV 29 body mass was estimated to be about 400 kg. The phylogenetic analysis failed to satisfactory resolve the position of IANIGLA-PV 29, which may be a consequence of intraspecific variation. When monophyly is forced Huayqueriana is nested among macraucheniines, as the stem taxon of a clade formed by Macrauchenia and other Pliocene and late Miocene taxa.