A new elasmothere genus and species from the middle Miocene of Tongxin, Ningxia, China, and its phylogenetic relationship

The elasmotheres were well diversified and widespread throughout the Neogene in Eurasia and East Africa. Here we report a new elasmothere genus and species, <i>Tongxinotherium latirhinum</i> gen. et sp. nov., from the Zhang’enbao Formation (middle Miocene) of Tongxin, Ningxia, China. The new genus is characterized by a broad and thick nasal bone, the ‘U’-shaped nasal notch located at the level of P3, the anterior margin of the orbit situated at the level of M2, subhypsodont teeth covered and filled by plentiful cement, slightly developed enamel foldings, expanded protocone with anterior and posterior constrictions, the middle valley and posterior valley closed on the premolars, protoloph separated from the ectoloph on P2, and buccal and lingual cingula present on premolars, but absent on molars. A phylogenetic analysis reveals that <i>Tongxinotherium latirhinum</i> gen. et sp. nov. is more derived than the early elasmotheres, and more primitive than <i>Iranotherium</i> and <i>Ningxiatherium</i>, bridging a morphological and stratigraphical gap between them. The discovery of new material improves the morphological characteristics of the early elasmotheres’ horns and increases the diversity of the middle Miocene elasmotheres. http://zoobank.org/urn:lsid:zoobank.org:pub:7DF2F57F-38DD-4FBF-B3DF-57AADD510131

板齿犀类（elasmothere）曾具有高度的分类多样性，且在新近纪时期广泛分布于欧亚大陆与东非地区。本文报道了产自中国宁夏同心县中新世中期张恩堡组的板齿犀科新属新种——宽鼻同心犀（<i>Tongxinotherium latirhinum</i> gen. et sp. nov.）。该新属的鉴别特征包括：鼻骨宽硕厚实；“U”形鼻切迹位于P3齿位水平；眶前缘处于M2齿位水平；牙齿为亚高齿型，被大量白垩质覆盖并充填；釉质褶皱不甚发育；原尖扩张且具前后收缩痕；前臼齿的中谷与后谷完全闭合；P2上的原脊与外脊相互分离；前臼齿具颊侧与舌侧齿带，而臼齿则无齿带分布。系统发育分析结果表明，宽鼻同心犀（<i>Tongxinotherium latirhinum</i> gen. et sp. nov.）相较于早期板齿犀类更为衍化，却又较伊朗犀（<i>Iranotherium</i>）与宁夏犀（<i>Ningxiatherium</i>）更为原始，填补了二者在形态学与地层学上的演化空白。该新材料的发现完善了早期板齿犀类角部的形态学特征，并丰富了中新世中期板齿犀类的物种多样性。标本注册链接：http://zoobank.org/urn:lsid:zoobank.org:pub:7DF2F57F-38DD-4FBF-B3DF-57AADD510131