Wonky whales: the evolution of cranial asymmetry in cetaceans
Wonky whales: the evolution of cranial asymmetry in cetaceans
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DOI：
10.1186/s12915-020-00805-4
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发表时间：
2020-07-10
期刊：
影响因子：
5.4
通讯作者：
Goswami, Anjali
中科院分区：
文献类型：
--
作者：
Coombs, Ellen J.;Clavel, Julien;Goswami, Anjali
与大多数哺乳动物不同，齿鲸（Odontoceti）头骨的鼻和面部区域缺乏对称性。这种不对称性被假设与回声定位有关，这可能是在最早的分叉齿鲸类中进化而来的。早期的鲸类动物（鲸鱼、海豚和鼠海豚），如古鲸，即原鲸类和基龙科，有不对称的喙，但目前还不清楚鼻面不对称是在古鲸向现代鲸鱼过渡的过程中进化而来的。我们使用三维几何形态测量学和系统发育比较方法，重建了5000万年来162个现存和灭绝的鲸类头骨的不对称性。结果在古人类中，喙部、鳞部、轭部和眶部普遍存在不对称现象，可能反映了骨的变形。齿鲸类的不对称性在鼻面区域占主导地位。须鲸的对称性与陆地上的偶蹄类动物（如牛）相似。第一个显着的转变，不对称发生在干齿鲸科Xacrophidae在早渐新世。不对称性的进一步增加发生在渐新世晚期的physeteroids，渐新世晚期/中新世早期的Squalodelphinidae和Platanistidae，以及中新世晚期/上新世早期的Monodontidae。在渐新世中晚期发现了齿鲸头骨不对称性的快速变化，这是一个快速进化和多样化的时期。在神秘生物和古生物中，没有发现不对称性的高概率增加或跳跃。出乎意料的是，没有增加的不对称性恢复内的高度不对称zipphiids，这可能是由于极端的，不对称的形状，在这些类群的前上颌骨嵴不被单独的地标。结论：现存鲸鱼的早期祖先几乎没有颅骨不对称，可能无法进行回声定位。古鲸类的喙部显示出高度的不对称性，这可能与方向性听觉有关，而这在早期的新鲸类中已经消失了，新鲸类是现存鲸类的最新共同祖先。鼻面不对称在渐新世早期成为齿鲸类头骨的一个重要特征，在现存的分类群中达到了最高水平。独立的进化制度重建的odontocetes生活在声学复杂的环境中，这表明这些壁龛施加强大的选择性压力回声定位能力，从而增加颅骨的不对称性。
Background Unlike most mammals, toothed whale (Odontoceti) skulls lack symmetry in the nasal and facial (nasofacial) region. This asymmetry is hypothesised to relate to echolocation, which may have evolved in the earliest diverging odontocetes. Early cetaceans (whales, dolphins, and porpoises) such as archaeocetes, namely the protocetids and basilosaurids, have asymmetric rostra, but it is unclear when nasofacial asymmetry evolved during the transition from archaeocetes to modern whales. We used three-dimensional geometric morphometrics and phylogenetic comparative methods to reconstruct the evolution of asymmetry in the skulls of 162 living and extinct cetaceans over 50 million years. Results In archaeocetes, we found asymmetry is prevalent in the rostrum and also in the squamosal, jugal, and orbit, possibly reflecting preservational deformation. Asymmetry in odontocetes is predominant in the nasofacial region. Mysticetes (baleen whales) show symmetry similar to terrestrial artiodactyls such as bovines. The first significant shift in asymmetry occurred in the stem odontocete family Xenorophidae during the Early Oligocene. Further increases in asymmetry occur in the physeteroids in the Late Oligocene, Squalodelphinidae and Platanistidae in the Late Oligocene/Early Miocene, and in the Monodontidae in the Late Miocene/Early Pliocene. Additional episodes of rapid change in odontocete skull asymmetry were found in the Mid-Late Oligocene, a period of rapid evolution and diversification. No high-probability increases or jumps in asymmetry were found in mysticetes or archaeocetes. Unexpectedly, no increases in asymmetry were recovered within the highly asymmetric ziphiids, which may result from the extreme, asymmetric shape of premaxillary crests in these taxa not being captured by landmarks alone. Conclusions Early ancestors of living whales had little cranial asymmetry and likely were not able to echolocate. Archaeocetes display high levels of asymmetry in the rostrum, potentially related to directional hearing, which is lost in early neocetes-the taxon including the most recent common ancestor of living cetaceans. Nasofacial asymmetry becomes a significant feature of Odontoceti skulls in the Early Oligocene, reaching its highest levels in extant taxa. Separate evolutionary regimes are reconstructed for odontocetes living in acoustically complex environments, suggesting that these niches impose strong selective pressure on echolocation ability and thus increased cranial asymmetry.