Evolution of <i>Protanancus</i> (Proboscidea, Mammalia) in East Asia

<div><p>ABSTRACT—</p><p>Interspecific competition and species replacement explain many evolutionary successions, but these processes are difficult to test. According to recent paleontological research, amebelodontines were predominant proboscideans in faunas of the early to middle Miocene of East Asia. In addition to the abundant <i>Platybelodon</i>, other amebelodontines are known, but they have been largely neglected by researchers. Here we describe two species of <i>Protanancus</i>, <i>Pr. tobieni</i> and <i>Pr. brevirostris</i>, sp. nov., from China. The former was present during the middle Miocene in Tongxin and Qin’an and was previously attributed to <i>Amebelodon</i> or <i>Serbelodon</i>; the latter was present during the early Miocene in the Linxia Basin. Cladistic analysis indicates that the two species appear to represent primitive members of <i>Protanancus</i>. However, the phylogenetic relationship among <i>Protanancus</i>, <i>Platybelodon</i>, and <i>Amebelodon</i> remains unresolved because of their strong parallel evolution. Our study suggests intensive competition between <i>Protanancus</i> and <i>Platybelodon</i> based on similarities in their mandibular morphologies and dental microwear patterns, with the former genus disappearing from East Asia by the late middle Miocene. This scenario is supported by a mechanical model, in which lower tusks with dentinal tubules, as occur in <i>Platybelodon</i>, show greater resistance to the adverse effects of both a heavy load and abrasion than those with concentric laminae, present in <i>Protanancus</i>. The model aids in interpreting the evolution of the inner structure of the lower tusks of amebelodontines, which may have provided a competitive advantages for these species.</p><p>http://zoobank.org/urn:lsid:zoobank.org:pub:4D33BD71-CB05-4058-B9DD-337060B0B7CB</p><p>SUPPLEMENTAL DATA——Supplemental materials are available for this article for free at www.tandfonline.com/UJVP </p>