Li Lüzhou, Li Qiang, Lu Xiaoyu, Ni Xijun
Key Laboratory of Vertebrate Evolution and Human Origins of Chinese Academy of Sciences, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing, China.
University of Chinese Academy of Sciences, Beijing, China.
PeerJ. 2017 May 16;5:e3311. doi: 10.7717/peerj.3311. eCollection 2017.
The Early to Late Oligocene is the earliest known beaver genus from Eurasia. Although many species of this genus have been described, these species are defined based on very fragmentary specimens. from the Early Oligocene Irtysh River Formation in northwestern Xinjiang, China is one of the earliest-known members of . This species is defined on a single maxillary fragment. We revise the diagnosis of and the genus , based on newly discovered specimens from the Irtysh River Formation. The dental morphology of is very similar to other early castorids. The caudal palatine foramen of is situated in the maxillary-palatine suture. This is a feature generally accept as diagnostic character for the castorids. On the other hand, has two upper premolars, a rudimentarily developed sciuromorph-like zygomatic plate, and a relatively large protrogomorph-like infraorbital foramen. Some previous researchers suggested that is a junior synonym of , while other took it as a valid genus. Our morphological comparison and phylogenetic analysis suggest that differs from and is a valid genus. We also suggest that , , . , , , and " aff. " should be referred to . is the earliest and most basal beaver. The origin place of and castorids is uncertain. The Early Oligocene radiation of castorids probably is propelled by the global climate change during the Eocene-Oligocene transition.
早渐新世到晚渐新世的[具体名称未明确，暂译为某属]是已知最早来自欧亚大陆的河狸属。尽管已描述了该属的许多物种，但这些物种是基于非常破碎的标本定义的。来自中国新疆西北部早渐新世额尔齐斯河组的[具体名称未明确，暂译为某物种]是该属已知最早的成员之一。这个物种是根据一块单一的上颌骨碎片定义的。我们基于从额尔齐斯河组新发现的标本，对[具体名称未明确，暂译为某物种]和该属进行了修订诊断。[具体名称未明确，暂译为某物种]的牙齿形态与其他早期河狸科动物非常相似。[具体名称未明确，暂译为某物种]的腭后孔位于上颌骨与腭骨的缝合处。这是一个通常被认为是河狸科动物诊断特征的特征。另一方面，[具体名称未明确，暂译为某物种]有两颗上前臼齿，一个发育不全的松鼠型颧板，以及一个相对较大的原兽型眶下孔。一些先前的研究人员认为[具体名称未明确，暂译为某物种]是[另一具体名称未明确，暂译为某物种]的次同物异名，而其他人则将其视为一个有效的属。我们的形态学比较和系统发育分析表明，[具体名称未明确，暂译为某物种]与[另一具体名称未明确，暂译为某物种]不同，是一个有效的属。我们还建议，[多个具体名称未明确，暂译为某几个物种]应归入[具体名称未明确，暂译为某属]。[具体名称未明确，暂译为某属]是最早且最基干的河狸。[具体名称未明确，暂译为某属]和河狸科动物的起源地尚不确定。渐新世早期河狸科动物的辐射可能是由始新世 - 渐新世过渡期间的全球气候变化推动的。
