About the systematic status of an old and forgotten specimen of terror bird (Phorusrhacidae: Mesembriornithinae) from the Miocene of Northwestern Argentina

VEZZOSI, R.I.; NORIEGA, J.I.

Diamante

Congreso; 9th International Meeting of the Society of Avian Paleontology and Evolution; 2016

CICYTTP-CONICET, Society of Avian Paleontology and Evolution

A new record of a mid-large sized terror bird from northwestern Argentina is reported based on associated and fragmentary hind limb elements of a single specimen. The latter (MUFYCA 305) belongs to old collections of the Museo Florentino y Carlos Ameghino (Instituto de Fisiografía y Geología) of Rosario city, Argentina, which had remained unstudied since its finding during the Forties. The original label of its collector (F. López Méndez) states that the specimen comes from Yocavil valley (Catamarca Province) at east of Loma Rica locality near Andalhuala, from the ?Araucanense medio? levels. Although this stratigraphic provenance does not follow current nomenclature, the bearing fossil horizon can be correlated with lower levels of the Andalhuala Formation, i.e., sediments of late Miocene age (Huayquerian SALMA or Tortonian Global Stage/Age). The preserved fossil materials include the distal end of a femur with both condyles and part of the sulcus patellaris, the proximal end of a right tarsometatarsus, the distal end of a left tarsometatarsus without the fourth trochlea, and several fragments of shaft of both hindlimbs. After an exhaustive comparison of anatomical characters (e.g. morphology of hypotarsus) and morphometric analysis, the specimen is assigned to Mesembriornis cf. M. incertus (Rovereto 1914) by showing a triangular asymmetric hypotarsus and a distally widened third tarsometatarsal trochlea. Both diagnostic morphologies define the clade Mesembriornithinae within the family Phorusrhacidae. It is noteworthy that some dimensions of the specimen presented herein exceed those known for mesembriornithines, being very close to analogue measures in patagornithine taxa. It will be necessary to find more complete materials to infer if such differences are due to intraspecific variations or they merit the erection of a new species Mesembrionis.