JAW MUSCLE RECONSTRUCTION OF THE PSITTACIFORM NANDAYUS VOROHUENSIS (LATE PLIOCENE, PAMPEAN REGION, ARGENTINA)

CARRIL, J.; DEGRANGE, F.J.; TAMBUSSI, C.P.

Córdoba

Congreso; Reunión de Comunicaciones de la Asociación Paleontológica Argentina; 2013

Asociación Paleontológica Argentina

Parrot skulls are highly derived among birds, featuring some novelties like the presence of an ossified suborbital arch (SOA) and two exclusive muscles associated with large adduction forces: the ethmomandibularis (EM) and pseudomasseter (PM). The aim of this work is to verify the presence of these apomorphies and other jaw muscles in the holotype of Nandayus vorohuensis (MLP 94-IV-1-1). We assume that some gross osteological features allow (limited) muscle reconstruction and the dissection in extant close relatives (e.g., Myiopsitta) can be used as comparative models. The SOA is absent, the EM insertion is located in a conspicuous cranio-medial mandible bulge and the PM attachs in the distal half of the lateral processus suborbitalis. Regarding other jaw muscles we inferred: the m. adductor mandibulae externus profundus origin in a shallow and cranio-caudally extended fossa temporalis and on the dorsal aspect of the processus zygomaticus; the wide insertion of the m. adductor mandibulae externus superficialis at the level of the processus coronoideus in the lateral aspect of the mandible; part of the origin of the m. pterygoideus dorsalis occupying the entire dorsal aspect of the large palatine and its insertion site in the medial and caudal aspect of the mandible; the insertion of the m. adductor mandibulae posterior visible on the medial aspect of the mandible; and the broad origin of the m. depressor mandibulae at the exoccipital region. Precise muscle reconstructions represent key evidences that strengthen any phylogenetic, paleobiological and paleoecological study. This research contributes in these fields.