Reconstructing phylogeny of the hornless rhinoceros Aceratheriinae

Abstract

This study presents the first phylogenetic analysis focused on the Subfamily Aceratheriinae to date, with 391 characters coded from 43 taxa at the species level. We added 77 newly defined and 33 revised characteristics, including features of the skull, teeth, and postcranial bones. In the present analysis, the tribe Teleoceratini, as well as the tribe Aceratheriini, was reclassified within Aceratheriinae, however, the traditionally established monophyly of each tribe was decomposed. Combined with detailed morphological comparisons, we reconstructed the phylogeny of Aceratheriinae and revised the diagnosis of Aceratheriinae. The reported skull and teeth specimens of Turkanatherium from the late Early Miocene indicate that it is not an acerathere and has been placed as a basal rhinocerotid. The Aceratheriinae has undergone evolutionary adaptation several times during the early stage of evolution, and several genera from the Oligocene to the Early Miocene have been reconstructed as early diverging taxa, such as Molassitherium, Protaceratherium, Plesiaceratherium and Chilotheridium; Aprotodon and Mesaceratherium from the Late Oligocene to the Early Miocene were united as the earliest divergent clade of Aceratheriinae; meanwhile, due to the limited materials, the phylogenies of Floridaceras and Dromoceratherium are unstable in this analysis, and both have been tentatively considered as the early diverging clades of Aceratheriinae. Alicornops was reclassified a member of Teleoceratini. Aceratheriini and Teleoceratini have been redefined as two highly specialized groups. Furthermore, Aceratheriini has been divided into two/three clades based on the difference in the skull outlines and the occlusal patterns of the cheek teeth.