CT-informed skull osteology of Palaeolagus haydeni (Mammalia: Lagomorpha)

Lagomorpha is a clade of herbivorous mammals nested within Euarchontoglires, one of the major placental groups represented today. It comprises two extant families with markedly different body plans: the long-eared and long-limbed Leporidae (hares and rabbits) and the short-eared and short-limbed Ochotonidae (pikas). These two lagomorph lineages diverged probably during the latest Eocene/early Oligocene, but it is unclear whether the last common ancestor of crown lagomorphs was more leporid- or more ochotonid-like in morphology. Palaeolagus, an early lagomorph dominant in western North America from the late Eocene to Oligocene is of particular importance for addressing this controversy. Here, we present new and comprehensive data on the cranial anatomy of Palaeolagus haydeni, the type species for the genus, based on micro-computed tomography (μCT). Our μCT data allow us to confirm, revise and score for the very first time the states of several leporid-like and ochotonid-like characters in the skull of Palaeolagus. This mixed cranial architecture differentiates Palaeolagus from the crown groups of Lagomorpha and supports its phylogenetic status as a stem taxon.兔形目（Lagomorpha）是隶属于真灵长总目（Euarchontoglires）的植食性哺乳动物演化支，而真灵长总目是现今现存的主要胎盘类群之一。该类群包含两个躯体构型差异显著的现生科：具有长耳、长肢的兔科（Leporidae，包含野兔与家兔），以及短耳、短肢的鼠兔科（Ochotonidae，包含鼠兔）。这两支兔形类群的分化时间大致处于始新世末期至渐新世早期，但目前仍无法确定冠群兔形类的最近共同祖先在形态特征上更接近兔科还是鼠兔科。古兔属（Palaeolagus）是始新世晚期至渐新世时期北美西部占据优势的早期兔形类群，其对于解决这一学术争议具有至关重要的研究价值。本文基于显微计算机断层扫描（μCT）技术，报道了该属模式种哈氏古兔（Palaeolagus haydeni）的颅骨解剖学全新且全面的研究数据。本次研究的μCT数据首次完成了古兔颅骨中多项类兔科、类鼠兔科特征状态的确认、修订与编码。这种混合的颅骨构型将古兔与兔形目冠群区分开来，同时支持其作为兔形目茎类群的系统发育地位。