Roedores chinchilloideos (Hystricognathi) de la Formación Pinturas, Mioceno temprano-medio de la provincia de Santa Cruz, Argentina
. The chinchilloid rodents are represented in the
Pinturas Formation (Ameghino’s Atrapothericulan beds) by at least three species of the genus Perimys (P.
intermedius sp. nov., P. erutus and Perimys sp.) and by one species of Prolagostomus. Perimys
intermedius is only known from this unit. It can be distinguished from other species by having cheek teeth
with narrower laminae with straight margins, wider hypoflexus and hypoflexid, lingual flexid only in m3,
enamel reduced on the labial wall of the M3, completely absent on the labial wall of M1 and M2, and on
the lingual wall of the m1 and m2. Variable size of the dentition is a result of ontogeny, as in other
euhypsodont species. Based on this criterion and on morphological characters of the dentition, P. erutus
Ameghino 1887 is considered as the senior synonym of the following: P. diminutus, P. reflexus, P.
angulatus, P. procerus and P. scalaris. The specimens of Prolagostomus from the Pinturas Formation
show a dentition with an intermediate evolutionary condition between the Colhuehuapian and Deseadan
chinchillids and the Santacrucian species of the genus Prolagostomus.
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