Department of Biology, University of Wisconsin Oshkosh, Oshkosh Wisconsin 54901.
Department of Anatomy, College of Osteopathic Medicine, New York Institute of Technology, Old Westbury, New York 11568.
Evolution. 2018 May;72(5):1092-1108. doi: 10.1111/evo.13480. Epub 2018 Apr 25.
Odontocete (echolocating whale) skulls exhibit extreme posterior displacement and overlapping of facial bones, here referred to as retrograde cranial telescoping. To examine retrograde cranial telescoping across 40 million years of whale evolution, we collected 3D scans of whale skulls spanning odontocete evolution. We used a sliding semilandmark morphometric approach with Procrustes superimposition and PCA to capture and describe the morphological variation present in the facial region, followed by Ancestral Character State Reconstruction (ACSR) and evolutionary model fitting on significant components to determine how retrograde cranial telescoping evolved. The first PC score explains the majority of variation associated with telescoping and reflects the posterior migration of the external nares and premaxilla alongside expansion of the maxilla and frontal. The earliest diverging fossil odontocetes were found to exhibit a lesser degree of cranial telescoping than later diverging but contemporary whale taxa. Major shifts in PC scores and centroid size are identified at the base of Odontoceti, and early burst and punctuated equilibrium models best fit the evolution of retrograde telescoping. This indicates that the Oligocene was a period of unusually high diversity and evolution in whale skull morphology, with little subsequent evolution in telescoping.
齿鲸（回声定位鲸）的头骨表现出极度的后向位移和面部骨骼的重叠，这里称为逆行颅伸缩。为了研究 4000 万年鲸类进化过程中的逆行颅伸缩，我们收集了跨越齿鲸进化的鲸头骨的 3D 扫描。我们使用滑动半标志形态计量方法进行 Procrustes 叠加和 PCA，以捕捉和描述面部区域存在的形态变化，然后进行祖先特征状态重建（ACSR）和显著成分的进化模型拟合，以确定逆行颅伸缩是如何进化的。第一主成分解释了与伸缩相关的大部分变化，反映了外鼻孔和前颌骨的向后迁移，同时上颌骨和额骨的扩张。最早分化的化石齿鲸比后来分化但同时代的鲸类具有较小程度的颅伸缩。在齿鲸的基部，PC 分数和质心大小的主要变化被识别出来，早期爆发和间断平衡模型最适合逆行伸缩的进化。这表明，渐新世是鲸头骨形态异常高多样性和进化的时期，随后在伸缩方面的进化很少。
