REVISION OF THE FOSSIL RODENT ACAREMYS AMEGHINO (HYSTRICOGNATHI, OCTODONTOIDEA, ACAREMYIDAE) FROM THE MIOCENE OF PATAGONIA (ARGENTINA)

ARNAL MICHELLE; VUCETICH, MARÍA GUIOMAR

Jornada; REUNIÓN DE COMUNICACIONES DE LA ASOCIACIÓN PALEONTOLÓGICA ARGENTINA; 2013

Within South American rodents, the Acaremyidae is an independent fossil lineage of octodontoid represented in the late Oligocene?middle Miocene of Patagonia. The genus Acaremys is represented by six species recorded in the early Miocene which have not been re-studied since their original description. A morphological review and a phylogenetic analysis suggest that Acaremys is paraphyletic including all the originally described species. Three species are valid, Acaremys murinus Ameghino (type species), Acaremys major Scott, and Acaremys messor Ameghino. Acaremys karaikensis Ameghino is a junior synonym of Acaremys murinus. ?Acaremys? tricarinatus Ameghino is excluded from the genus, being closely related to Sciamys. The peculiar new species, Pseudoacaremys kramarzi, is closely related to ?Acaremys? tricarinatus and Sciamys. ?Acaremys? preminutus Bordasis excluded from the family, being closely related to the early Miocene octodontoid Protacaremys prior Ameghino, or the living octodontoids. The phylogenetic analysis demonstrated that Acaremyidae includes Platypittamys, Galileomys, Acaremys, Pseudoacaremys, and Sciamys. The evolutionary history of the superfamily suggests that the hypsodonty and the consequently occlusal simplification evolved, at least, twice within Octodontoidea: in Acaremyidae and in modern Octodontidae. Additionally, the cladistic analysis confirmed that most character ambiguities are due to missing data, not to a conflict between characters, and hence, it is essential to find better remains to elucidate the relationships among acaremyids.