Systematics and stratigraphic range of the hegetotheriids Hegetotheriopsis sulcatus and Prohegetotherium sculptum (Mammalia, Notoungulata)

KRAMARZ, A.; BOND, M.

JOURNAL OF SYSTEMATIC PALAEONTOLOGY

CAMBRIDGE UNIV PRESS

Lugar: Cambridge; Año: 2016

1477-2019

Hegetotheriidae is one of the most advanced clades within the endemicSouth American placental Order Notoungulata. The species Hegetotheriopsissulcatus Kramarz & Paz,2013 differs from all other known hegetotheriids in having a peculiarcombination of cranial and dental features, some of them shared withArchaeohyracidae (sister group of Hegetotheriidae). A previous cladisticsanalysis supported H. sulcatus as theearliest diverging hegetotheriid. Nevertheless, a more recent analysis, basedon a different data matrix, concluded that this species is an advanced formwithin the family, the little known Prohegetotheriumsculptum Ameghino, 1897 (late Oligocene) being the basal-most taxon. Wepresent here a revision of the concept and the content of P. sculptum based on the re-examination of the type specimens. We findthat they exhibit several dental and cranial characters not recognized in allprevious studies; we conclude that no specimen other than the types can beassigned to P. sculptum, and all the synonymiespreviously proposed (i.e. P.shumwayi and P. crassus) areunfounded. A new cladistic analysis, combining characters from the twoaforementioned analyses, confirms the position of H. sulcatus as the earliest diverging hegetotheriid. The taxon wasoriginally described on remains from early Miocene deposits in central andNorthern Patagonia (Sarmiento, Chichinales, and Cerro Bandera formations). Herewe report new materials from late Oligocene levels at Cabeza Blanca (centralPatagonia), and reassign others previously attributed to Prohegetotherium from presumably equivalent levels at QuebradaFiera (central West Argentina). These remains extend the occurrence of H. sulcatus back to the Late Oligocene,and fill and important gap of the early record of Hegetotheriidae.