THE HUMERUS OF PROTEROTHERRIIDAE (MAMMALIA, LITOPTERNA) AND ITS SYSTEMATIC USEFULNESS: THE CASE OF “PROTEROTHERIUM BERROI” KRAGLIEVICH, 1930 --- Preprint doi: 10.5710/AMGH.10.12.2017.3148

Andrea Corona, Daniel Perea, Martín Ubilla

Abstract


The Proterotheriidae Ameghino, 1889 constitute a group of small-medium native South American ungulates with high diversity in Early Miocene and Late Miocene (Santacrucian and Huayquerian SALMAs). Recent studies demonstrated the wide dental variability useful in the discrimination of species. The aim of this work is to analyze the humerus as a postcranial element usually found in no association with cranial remains and evaluate (qualitatively and quantitatively) its systematic usefulness. We use as a specific case study the only know specimen (a distal fragment of a humerus) of “Proterotherium berroi” Kraglievich, 1930, re-describing and re-illustrating it. We performed a principal components analysis (PCA) that resulted in 2 principal components, explaining 86% of the variance. The PCA shows a clear differentiation of the largest species (Diadiaphorus majusculus and Anisolophus floweri) from the other species (an intermediate group, consisting of "Proterotherium" – Tetramerorhinus – Eoauchenia – Proterotheriidae indet., and then, the smallest Thoatherium minusculum). This study allowed establishing that although there are slight morphological differences in the distal epiphysis of the humeri of Proterotheriidae, they mostly correspond to gradual changes in characters with continuous variation, not linked to any particular taxonomic entity. Accordingly, these are not enough to assure a generic or specific determination, except Eoauchenia. Instead, the differences in humeri size are considerable and they could be used as a criterion for discriminating Diadiaphorus – Anisolophus, to which the largest specimens would belong. We consider “P. berroi” a probable synonym of Neolicaphrium recens, but we ratify that a reliable systematic determination is only possible if it is based on cranial or dental remains.

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