Morphological and ecological diversity of Amebelodontidae (Proboscidea, Mammalia) revealed by a Miocene fossil accumulation of an upper-tuskless proboscidean

Amebelodontidae is the most taxonomically and morphologically diverse group of proboscideans. However, relative to the morphological variation of the mandible and mandibular tusks, ecological and phylogenetic differentiations within Amebelodontidae have been largely debated. Here we evaluate a middle Miocene fossil accumulation of a new amebelodontid, <i>Aphanobelodon zhaoi</i> gen. et sp. nov. This species lacks upper tusks, which is unique in elephantiforms. The mandible and mandibular tusk morphologies of <i>A. zhaoi</i> are similar to those of the genus <i>Platybelodon</i>, which is the typical representative of one of the two main amebelodontid branches (the other branch is represented by <i>Amebelodon</i>). We suggest that <i>Amebelodon</i> potentially used its mandible and mandibular tusks to dig for food in relatively hard substrates; whereas <i>Platybelodon</i> is more specialized and possibly used its mandibular tusks for cutting soft vegetation. <i>Aphanobelodon zhaoi</i> morphology indicates that it is an offshoot of the platybelodont clade within Amebelodontidae, because it has primitive undifferentiated states of the mandible and mandibular tusks. Cladistic analysis indicates that <i>Aphanobelodon</i>, <i>Platybelodon</i> and <i>Torynobelodon</i> comprise a monophyletic group within Amebelodontidae. This study enhances our knowledge regarding proboscidean evolutionary history in terms of morphology, taxonomy and biology. http://zoobank.org/urn:lsid:zoobank.org:pub:8F30BAC7-4245-4952-BFCF-884E3DB839F6

嵌齿象科（Amebelodontidae）是分类学与形态学多样性最为丰富的长鼻类（proboscideans）类群。然而相较于下颌骨与下颌象牙的形态变异，嵌齿象科内部的生态分化与系统发育关系长期存在广泛争议。
本研究针对一件产自中中新世的新属新种化石埋藏群——赵氏隐嵌齿象（<i>Aphanobelodon zhaoi</i> gen. et sp. nov.）展开分析。该物种不具有上颌象牙，这在象形类（elephantiforms）中极为独特。赵氏隐嵌齿象的下颌骨与下颌象牙形态与铲齿象属（<i>Platybelodon</i>）高度相似，而铲齿象属是嵌齿象科两大主要分支之一的典型代表，另一分支以嵌齿象属（<i>Amebelodon</i>）为代表。
我们推测，嵌齿象属（<i>Amebelodon</i>）可能借助下颌骨与下颌象牙在相对坚硬的基质中挖掘食物；而铲齿象属（<i>Platybelodon</i>）特化程度更高，或通过下颌象牙切割柔软的植被。
赵氏隐嵌齿象的形态特征表明，其属于嵌齿象科内铲齿象演化支的一个演化分支，因其下颌骨与下颌象牙保留了原始的未分化状态。支序分析结果显示，隐嵌齿象属（<i>Aphanobelodon</i>）、铲齿象属（<i>Platybelodon</i>）与托里嵌齿象属（<i>Torynobelodon</i>）共同构成嵌齿象科内的一个单系群。
本研究从形态学、分类学与生物学维度，深化了我们对长鼻类演化历史的认知。
http://zoobank.org/urn:lsid:zoobank.org:pub:8F30BAC7-4245-4952-BFCF-884E3DB839F6