eprintid: 10106493 rev_number: 12 eprint_status: archive userid: 608 dir: disk0/10/10/64/93 datestamp: 2020-07-31 13:23:43 lastmod: 2020-07-31 13:23:43 status_changed: 2020-07-31 13:23:43 type: article metadata_visibility: show creators_name: Coombs, EJ creators_name: Clavel, J creators_name: Park, T creators_name: Churchill, M creators_name: Goswami, A title: Wonky whales: the evolution of cranial asymmetry in cetaceans ispublished: pub divisions: UCL divisions: A01 divisions: B02 divisions: C08 divisions: D09 keywords: Asymmetry, Cetaceans, Macroevolution, Morphometrics, Trait evolution note: This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. 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. date: 2020-07-10 date_type: published official_url: https://doi.org/10.1186/s12915-020-00805-4 oa_status: green full_text_type: pub pmcid: PMC7350770 language: eng primo: open primo_central: open_green verified: verified_manual elements_id: 1798916 doi: 10.1186/s12915-020-00805-4 pii: 10.1186/s12915-020-00805-4 lyricists_name: Coombs, Ellen lyricists_id: EJCOO82 actors_name: Austen, Jennifer actors_id: JAUST66 actors_role: owner full_text_status: public publication: BMC Biology volume: 18 article_number: 86 event_location: England citation: Coombs, EJ; Clavel, J; Park, T; Churchill, M; Goswami, A; (2020) Wonky whales: the evolution of cranial asymmetry in cetaceans. BMC Biology , 18 , Article 86. 10.1186/s12915-020-00805-4 <https://doi.org/10.1186/s12915-020-00805-4>. Green open access document_url: https://discovery.ucl.ac.uk/id/eprint/10106493/1/s12915-020-00805-4.pdf