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Coombs EJ, Knapp A, Park T, Bennion RF, McCurry MR, Lanzetti A, Boessenecker RW, McGowen MR. Drivers of morphological evolution in the toothed whale jaw. Curr Biol 2024; 34:273-285.e3. [PMID: 38118449 DOI: 10.1016/j.cub.2023.11.056] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2023] [Revised: 11/20/2023] [Accepted: 11/27/2023] [Indexed: 12/22/2023]
Abstract
Toothed whales (odontocetes) emit high-frequency underwater sounds (echolocate)-an extreme and unique innovation allowing them to sense their prey and environment. Their highly specialized mandible (lower jaw) allows high-frequency sounds to be transmitted back to the inner ear. Echolocation is evident in the earliest toothed whales, but little research has focused on the evolution of mandibular form regarding this unique adaptation. Here, we use a high-density, three-dimensional geometric morphometric analysis of 100 living and extinct cetacean species spanning their ∼50-million-year evolutionary history. Our analyses demonstrate that most shape variation is found in the relative length of the jaw and the mandibular symphysis. The greatest morphological diversity was obtained during two periods of rapid evolution: the initial evolution of archaeocetes (stem whales) in the early to mid-Eocene as they adapted to an aquatic lifestyle, representing one of the most extreme adaptive transitions known, and later on in the mid-Oligocene odontocetes as they became increasingly specialized for a range of diets facilitated by increasingly refined echolocation. Low disparity in the posterior mandible suggests the shape of the acoustic window, which receives sound, has remained conservative since the advent of directional hearing in the aquatic archaeocetes, even as the earliest odontocetes began to receive sounds from echolocation. Diet, echolocation, feeding method, and dentition type strongly influence mandible shape. Unlike in the toothed whale cranium, we found no significant asymmetry in the mandible. We suggest that a combination of refined echolocation and associated dietary specializations have driven morphology and disparity in the toothed whale mandible.
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Affiliation(s)
- Ellen J Coombs
- Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, 10th St & Constitution Ave NW, Washington, DC 20560, USA; Department of Life Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, UK.
| | - Andrew Knapp
- Department of Life Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, UK; University College London, Gower Street, London WC1E 6BT, UK
| | - Travis Park
- Department of Life Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, UK; School of Biological Sciences, Monash University, Clayton, VIC 3800, Australia
| | - Rebecca F Bennion
- Evolution & Diversity Dynamics Lab, Department of Geology, University of Liege, 4000 Liege, Belgium; O.D. Earth and History of Life, Royal Belgian Institute of Natural Sciences, 1000 Brussels, Belgium
| | - Matthew R McCurry
- Australian Museum Research Institute, 1 William Street, Sydney, NSW 2010, Australia; Earth & Sustainability Science Research Centre, School of Biological, Earth and Environmental Sciences (BEES), University of New South Wales, Kensington, NSW 2052, Australia; Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560, USA
| | - Agnese Lanzetti
- Department of Life Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, UK; School of Geography, Earth, and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
| | - Robert W Boessenecker
- University of California Museum of Paleontology, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Michael R McGowen
- Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, 10th St & Constitution Ave NW, Washington, DC 20560, USA
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Fostowicz-Frelik Ł, Tseng ZJ. The mammalian skull: development, structure and function. Philos Trans R Soc Lond B Biol Sci 2023; 378:20220077. [PMID: 37183895 PMCID: PMC10184243 DOI: 10.1098/rstb.2022.0077] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/16/2023] Open
Abstract
The mammalian skull is an informative and versatile study system critical to research efforts across the broad spectrum of molecular, cellular, organismal and evolutionary sciences. The amount of knowledge concerning mammalian skull continues to grow exponentially, fuelled by the advent of new research methods and new material. Computed microtomography, including X-ray imaging using synchrotron radiation, proved to be an important tool for the descriptive and quantitative analysis of cranial anatomy. A major conceptual change, namely combining genetics and development with evolution into 'evo-devo' studies, also contributed to our knowledge of the mammalian skull enormously. These advances, coupled with novel techniques now allow researchers to integrate the process of cranial development with data from the fossil record, which is also augmented by seminal discoveries from Africa, Asia and both Americas. However, for decades, there has been no comprehensive source covering fundamental aspects of this vibrant field of evolutionary biology. To address this gap, we offer in this theme issue a balanced mix of research papers and reviews from leading experts in the field and a younger generation of scientists from five continents. This article is part of the theme issue 'The mammalian skull: development, structure and function'.
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Affiliation(s)
- Łucja Fostowicz-Frelik
- Department of Organismal Biology and Anatomy, University of Chicago, Chicago, IL 60637, USA
- Institute of Paleobiology, Polish Academy of Sciences, 00-818 Warsaw, Poland
| | - Z Jack Tseng
- Department of Integrative Biology, University of California, Berkeley, CA 94720-3200, USA
- University of California Museum of Paleontology, Berkeley, CA 94720, USA
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