ADDITIONS TO THE KNOWLEDGE OF ASTRAPOTHERICULUS(MAMMALIA, ASTRAPOTHERIA): CRANIODENTAL ANATOMY, DIVERSITY AND DISTRIBUTION.

ADDITIONS TO THE KNOWLEDGE OF ASTRAPOTHERICULUS(MAMMALIA, ASTRAPOTHERIA): CRANIODENTAL ANATOMY, DIVERSITY AND DISTRIBUTION. Astrapothericulus Ameghino is the taxon which typifies the Astrapothericulan beds (Early Miocene, central Patagonia). Although so far it is poorly known. it was distinguished from other Oligo-Miocene astrapotheres by its comparatively smaller size and by having less specialized mandibular and dental features. The dentition is herein redescribed and compared based oil new and abundant materials. and the first cranial remain positively referred to the genotypic species Astroapothericulus iheringi is described. The check teeth are lower crowned than in Astrapotherium magnum (Santaerucian), the basal cingula are broader and more prominent, and the p4 hypoflexid is absent or very Superficial, as in Parastrapotherium (Deseadan-Colhuehuapian). The canines can be small and rooted or large rootless tusks, which is herein interpreted as dimorphic variations. The skull and jaw exhibit supposedly primitive characters in relation to Astrapotherium and Parastrapotherium (e.g. less retracted nasals, larger anterior orbits, mandible with shorter, narrower and more concave symphysis). However, recent phylogenetic analyses concluded that these are autapomorphic reversions. Astrapothericulus would have differentiated from all ancestor with much larger size, structurally close to Astrapotherium, and the mentioned characters, presumably paedomorphic, would be associated to a secondary reduction of body size as a result of a heterochronic processes. Of the described species, only Astrapothericulus iheringi (=Astrapothericulus hebelatum) and Astrapothericulus emarginatus Ameghino(=Astrapothericulus peninsulatus) are herein interpreted as valid. The genus also occurs in levels of Colhuehuapian age and in the upper levels of the Pinturas Formation bearing typical Santacrucian fauna, and consequently its distribution exceeds chronologically, Astrapothericulan fauna bearing beds.