Wonky whales: the evolution of cranial asymmetry in cetaceans

International audience 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, dolphi...

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Bibliographic Details
Published in:BMC Biology
Main Authors: Coombs, Ellen, Clavel, Julien, Park, Travis, Churchill, Morgan, Goswami, Anjali
Other Authors: Department of Genetics, Evolution and Environment, University College of London London (UCL), Laboratoire d'Ecologie des Hydrosystèmes Naturels et Anthropisés (LEHNA), Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-École Nationale des Travaux Publics de l'État (ENTPE)-Centre National de la Recherche Scientifique (CNRS), The Natural History Museum London (NHM), University of Wisconsin Oshkosh (UWO)
Format: Article in Journal/Newspaper
Language:English
Published: HAL CCSD 2020
Subjects:
Trait evolution
Asymmetry
Cetaceans
Morphometrics
Macroevolution
[SDV.BA.ZV]Life Sciences [q-bio]/Animal biology/Vertebrate Zoology
[SDV.BID.EVO]Life Sciences [q-bio]/Biodiversity/Populations and Evolution [q-bio.PE]
[SDU.STU.PG]Sciences of the Universe [physics]/Earth Sciences/Paleontology
baleen whales
toothed whale
Online Access:https://hal-univ-lyon1.archives-ouvertes.fr/hal-02907425
https://hal-univ-lyon1.archives-ouvertes.fr/hal-02907425/document
https://hal-univ-lyon1.archives-ouvertes.fr/hal-02907425/file/8-Coombs%20et%20al%202020.pdf
https://doi.org/10.1186/s12915-020-00805-4
Description
Summary:International audience 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 ...

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