Tags

Type your tag names separated by a space and hit enter

Wonky whales: the evolution of cranial asymmetry in cetaceans.
BMC Biol. 2020 Jul 10; 18(1):86.BB

Abstract

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.

Authors+Show Affiliations

Genetics, Evolution, and Environment Department, University College London, Gower Street, London, WC1E 6BT, UK. ellen.coombs.14@ucl.ac.uk. Department of Life Sciences, Natural History Museum, London, Cromwell Road, London, SW7 5BD, UK. ellen.coombs.14@ucl.ac.uk.Univ Lyon, Université Claude Bernard Lyon 1, CNRS, ENTPE, UMR 5023 LEHNA, F-69622, Villeurbanne, France.Department of Life Sciences, Natural History Museum, London, Cromwell Road, London, SW7 5BD, UK. Department of Earth Sciences, University of Oxford, Oxford, OX1 3AN, UK.Department of Biology, University of Wisconsin-Oshkosh, Oshkosh, WI, 54901, USA.Genetics, Evolution, and Environment Department, University College London, Gower Street, London, WC1E 6BT, UK. Department of Life Sciences, Natural History Museum, London, Cromwell Road, London, SW7 5BD, UK. Department of Earth Sciences, University College London, Gower Street, London, WC1E 6BT, UK.

Pub Type(s)

Journal Article

Language

eng

PubMed ID

32646447

Citation

Coombs, Ellen J., et al. "Wonky Whales: the Evolution of Cranial Asymmetry in Cetaceans." BMC Biology, vol. 18, no. 1, 2020, p. 86.
Coombs EJ, Clavel J, Park T, et al. Wonky whales: the evolution of cranial asymmetry in cetaceans. BMC Biol. 2020;18(1):86.
Coombs, E. J., Clavel, J., Park, T., Churchill, M., & Goswami, A. (2020). Wonky whales: the evolution of cranial asymmetry in cetaceans. BMC Biology, 18(1), 86. https://doi.org/10.1186/s12915-020-00805-4
Coombs EJ, et al. Wonky Whales: the Evolution of Cranial Asymmetry in Cetaceans. BMC Biol. 2020 Jul 10;18(1):86. PubMed PMID: 32646447.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Wonky whales: the evolution of cranial asymmetry in cetaceans. AU - Coombs,Ellen J, AU - Clavel,Julien, AU - Park,Travis, AU - Churchill,Morgan, AU - Goswami,Anjali, Y1 - 2020/07/10/ PY - 2020/05/04/received PY - 2020/06/01/accepted PY - 2020/7/11/entrez PY - 2020/7/11/pubmed PY - 2020/7/11/medline KW - Asymmetry KW - Cetaceans KW - Macroevolution KW - Morphometrics KW - Trait evolution SP - 86 EP - 86 JF - BMC biology JO - BMC Biol. VL - 18 IS - 1 N2 - 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. SN - 1741-7007 UR - https://www.unboundmedicine.com/medline/citation/32646447/Wonky_whales:_the_evolution_of_cranial_asymmetry_in_cetaceans L2 - https://bmcbiol.biomedcentral.com/articles/10.1186/s12915-020-00805-4 DB - PRIME DP - Unbound Medicine ER -
Try the Free App:
Prime PubMed app for iOS iPhone iPad
Prime PubMed app for Android
Prime PubMed is provided
free to individuals by:
Unbound Medicine.