Revision of Parastrapotherium (Mammalia, Astrapotheria) and other Deseadan astrapotheres of Patagonia

摘要

Parastrapotherium Ameghino, 1895 is one of the most characteristic faunal elements of the Deseadan South American Land Mammal Age (Late Oligocene) of Patagonia, and seven species have been described for that Age. The genus was traditionally differentiated from Astrapotherium by its giant size and by having a higher number of upper and lower premolars. The revision of the dentition of Parastrapotherium revealed that this genus has only one more lower premolar than Astrapotherium. Other differential features are: lower crowned cheek teeth, cingulum absent at base of labial fold in all upper cheek teeth, upper premolars with labial fold less prominent and with broader base, crown of lower incisors proportionally more robust and buccolingually broader, lower molars with bunoid "pillar", lingual cingulum absent at the base of metaconid, and lower cheek teeth with very superficial labial flexid. Of the described Deseadan species, P. holmbergi and P. martiale Ameghino are herein interpreted as valid. The validity of P. ephebicum Ameghino is uncertain. Astrapotherium voghti Mercerat is valid and herein provisionally transferred to Parastrapotherium. Liarthrus copei Ameghino, previously considered as synonym of P. holmbergi, should be kept in a separate genus. The phylogenetic relationships of Parastrapotherium are still uncertain, because it has some features suggesting uruguaytheriine affinities (lower molar cingulum absent at the base of metaconid and very superficial labial flexids), whereas the dental formula and the degree of hypsodonty suggest a very basal position among the Oligocene - Miocene astrapotheres. Cladistic analysis is pending on further additional studies on the still poorly known Astraponotus and other astrapotheriids.