Kraatz Brian, Sherratt Emma
Department of Anatomy, Western University of Health Sciences , United States.
Department of Evolution, Ecology and Genetics, Research School of Biology, The Australian National University , Canberra, ACT , Australia.
PeerJ. 2016 Sep 22;4:e2453. doi: 10.7717/peerj.2453. eCollection 2016.
The skull of leporids (rabbits and hares) is highly transformed, typified by pronounced arching of the dorsal skull and ventral flexion of the facial region (i.e., facial tilt). Previous studies show that locomotor behavior influences aspects of cranial shape in leporids, and here we use an extensive 3D geometric morphometrics dataset to further explore what influences leporid cranial diversity. Facial tilt angle, a trait that strongly correlates with locomotor mode, significantly predicts the cranial shape variation captured by the primary axis of cranial shape space, and describes a small proportion (13.2%) of overall cranial shape variation in the clade. However, locomotor mode does not correlate with overall cranial shape variation in the clade, because there are two district morphologies of generalist species, and saltators and cursorial species have similar morphologies. Cranial shape changes due to phyletic size change (evolutionary allometry) also describes a small proportion (12.5%) of cranial shape variation in the clade, but this is largely driven by the smallest living leporid, the pygmy rabbit (Brachylagus idahoensis). By integrating phylogenetic history with our geometric morphometric data, we show that the leporid cranium exhibits weak phylogenetic signal and substantial homoplasy. Though these results make it difficult to reconstruct what the 'ancestral' leporid skull looked like, the fossil records suggest that dorsal arching and facial tilt could have occurred before the origin of the crown group. Lastly, our study highlights the diversity of cranial variation in crown leporids, and highlights a need for additional phylogenetic work that includes stem (fossil) leporids and includes morphological data that captures the transformed morphology of rabbits and hares.
兔形目动物（兔子和野兔）的头骨高度特化，其典型特征是头骨背侧明显拱起以及面部区域腹侧弯曲（即面部倾斜）。先前的研究表明，运动行为会影响兔形目动物颅骨形状的某些方面，在此我们使用一个广泛的三维几何形态测量数据集，进一步探究影响兔形目动物颅骨多样性的因素。面部倾斜角是一种与运动模式密切相关的特征，它能显著预测颅骨形状空间主轴线所捕捉到的颅骨形状变化，并且在该类群的整体颅骨形状变化中占比很小（13.2%）。然而，运动模式与该类群的整体颅骨形状变化并无关联，因为存在两种不同的泛化物种形态，且跳跃型和奔跑型物种具有相似的形态。由于系统发育大小变化（进化异速生长）导致的颅骨形状变化在该类群的颅骨形状变化中也占比很小（12.5%），但这在很大程度上是由现存最小的兔形目动物——侏兔（Brachylagus idahoensis）所驱动的。通过将系统发育历史与我们的几何形态测量数据相结合，我们发现兔形目动物的颅骨呈现出较弱的系统发育信号和大量的同塑性。尽管这些结果使得难以重建“祖先”兔形目动物的头骨模样，但化石记录表明，背侧拱起和面部倾斜可能在冠群起源之前就已出现。最后，我们的研究强调了冠群兔形目动物颅骨变化的多样性，并突出了开展更多系统发育研究的必要性，这些研究应包括基部（化石）兔形目动物，并纳入能够捕捉兔子和野兔特化形态的形态学数据。
