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Mitchell DR, Sherratt E, Weisbecker V. Facing the facts: adaptive trade-offs along body size ranges determine mammalian craniofacial scaling. Biol Rev Camb Philos Soc 2024; 99:496-524. [PMID: 38029779 DOI: 10.1111/brv.13032] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2023] [Revised: 11/12/2023] [Accepted: 11/14/2023] [Indexed: 12/01/2023]
Abstract
The mammalian cranium (skull without lower jaw) is representative of mammalian diversity and is thus of particular interest to mammalian biologists across disciplines. One widely retrieved pattern accompanying mammalian cranial diversification is referred to as 'craniofacial evolutionary allometry' (CREA). This posits that adults of larger species, in a group of closely related mammals, tend to have relatively longer faces and smaller braincases. However, no process has been officially suggested to explain this pattern, there are many apparent exceptions, and its predictions potentially conflict with well-established biomechanical principles. Understanding the mechanisms behind CREA and causes for deviations from the pattern therefore has tremendous potential to explain allometry and diversification of the mammalian cranium. Here, we propose an amended framework to characterise the CREA pattern more clearly, in that 'longer faces' can arise through several kinds of evolutionary change, including elongation of the rostrum, retraction of the jaw muscles, or a more narrow or shallow skull, which all result in a generalised gracilisation of the facial skeleton with increased size. We define a standardised workflow to test for the presence of the pattern, using allometric shape predictions derived from geometric morphometrics analysis, and apply this to 22 mammalian families including marsupials, rabbits, rodents, bats, carnivores, antelopes, and whales. Our results show that increasing facial gracility with size is common, but not necessarily as ubiquitous as previously suggested. To address the mechanistic basis for this variation, we then review cranial adaptations for harder biting. These dictate that a more gracile cranium in larger species must represent a structural sacrifice in the ability to produce or withstand harder bites, relative to size. This leads us to propose that facial gracilisation in larger species is often a product of bite force allometry and phylogenetic niche conservatism, where more closely related species tend to exhibit more similar feeding ecology and biting behaviours and, therefore, absolute (size-independent) bite force requirements. Since larger species can produce the same absolute bite forces as smaller species with less effort, we propose that relaxed bite force demands can permit facial gracility in response to bone optimisation and alternative selection pressures. Thus, mammalian facial scaling represents an adaptive by-product of the shifting importance of selective pressures occurring with increased size. A reverse pattern of facial 'shortening' can accordingly also be found, and is retrieved in several cases here, where larger species incorporate novel feeding behaviours involving greater bite forces. We discuss multiple exceptions to a bite force-mediated influence on facial proportions across mammals which lead us to argue that ecomorphological specialisation of the cranium is likely to be the primary driver of facial scaling patterns, with some developmental constraints as possible secondary factors. A potential for larger species to have a wider range of cranial functions when less constrained by bite force demands might also explain why selection for larger sizes seems to be prevalent in some mammalian clades. The interplay between adaptation and constraint across size ranges thus presents an interesting consideration for a mechanistically grounded investigation of mammalian cranial allometry.
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Affiliation(s)
- D Rex Mitchell
- College of Science and Engineering, Flinders University, GPO Box 2100, Adelaide, South Australia, 5001, Australia
- Australian Research Council Centre of Excellence for Australian Biodiversity and Heritage, Wollongong, New South Wales, 2522, Australia
| | - Emma Sherratt
- School of Biological Sciences, The University of Adelaide, Adelaide, South Australia, 5005, Australia
- South Australian Museum, Adelaide, South Australia, 5000, Australia
| | - Vera Weisbecker
- College of Science and Engineering, Flinders University, GPO Box 2100, Adelaide, South Australia, 5001, Australia
- Australian Research Council Centre of Excellence for Australian Biodiversity and Heritage, Wollongong, New South Wales, 2522, Australia
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Balcarcel AM, Geiger M, Sánchez-Villagra MR. Cranial form differences in goats by breed and domestic status. Sci Rep 2024; 14:917. [PMID: 38195639 PMCID: PMC10776561 DOI: 10.1038/s41598-023-50357-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2023] [Accepted: 12/19/2023] [Indexed: 01/11/2024] Open
Abstract
Domestic goats (Capra hircus) are globally represented by over 300 breeds, making them a useful model for investigating patterns of morphological change related to domestication. However, they have been little studied, likely due to their poor representation in museum collections and the difficulty in obtaining truly wild goat (Capra aegagrus, the bezoar) samples. Similar studies on other species reveal that domestication correlates with craniofacial alterations in domestics, which are non-uniform and often species-specific. Here, we use three-dimensional geometric morphometric methods (3DGMM) to describe and quantify cranial shape variation in wild (n = 21) versus domestic (n = 54) goats. We find that mean cranial shapes differ significantly between wild and domestic goats as well as between certain breeds. The detected differences are lower in magnitude than those reported for other domestic groups, possibly explained by the fewer directions of artificial selection in goat breeding, and their low global genetic diversity compared to other livestock. We also find tooth-row length reduction in the domestics, suggestive of rostral shortening-a prediction of the "domestication syndrome" (DS). The goat model thus expands the array-and combinations of-morphological changes observed under domestication, notably detecting alterations to the calvarium form which could be related to the ~ 15% brain size reduction previously reported for domestic compared to wild goats. The global success of domestic goats is due more to their ability to survive in a variety of harsh environments than to systematized human management. Nonetheless, their domestication has resulted in a clear disruption from the wild cranial form, suggesting that even low-intensity selection can lead to significant morphological changes under domestication.
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Affiliation(s)
- A M Balcarcel
- Department of Paleontology, University of Zurich, Karl-Schmid-Str. 4, 8006, Zurich, Switzerland.
| | - M Geiger
- Naturmuseum St.Gallen, Rorschacher Strasse 263, 9016, St.Gallen, Switzerland
| | - M R Sánchez-Villagra
- Department of Paleontology, University of Zurich, Karl-Schmid-Str. 4, 8006, Zurich, Switzerland
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Goswami A, Noirault E, Coombs EJ, Clavel J, Fabre AC, Halliday TJD, Churchill M, Curtis A, Watanabe A, Simmons NB, Beatty BL, Geisler JH, Fox DL, Felice RN. Developmental origin underlies evolutionary rate variation across the placental skull. Philos Trans R Soc Lond B Biol Sci 2023; 378:20220083. [PMID: 37183904 PMCID: PMC10184245 DOI: 10.1098/rstb.2022.0083] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/16/2023] Open
Abstract
The placental skull has evolved into myriad forms, from longirostrine whales to globular primates, and with a diverse array of appendages from antlers to tusks. This disparity has recently been studied from the perspective of the whole skull, but the skull is composed of numerous elements that have distinct developmental origins and varied functions. Here, we assess the evolution of the skull's major skeletal elements, decomposed into 17 individual regions. Using a high-dimensional morphometric approach for a dataset of 322 living and extinct eutherians (placental mammals and their stem relatives), we quantify patterns of variation and estimate phylogenetic, allometric and ecological signal across the skull. We further compare rates of evolution across ecological categories and ordinal-level clades and reconstruct rates of evolution along lineages and through time to assess whether developmental origin or function discriminate the evolutionary trajectories of individual cranial elements. Our results demonstrate distinct macroevolutionary patterns across cranial elements that reflect the ecological adaptations of major clades. Elements derived from neural crest show the fastest rates of evolution, but ecological signal is equally pronounced in bones derived from neural crest and paraxial mesoderm, suggesting that developmental origin may influence evolutionary tempo, but not capacity for specialisation. This article is part of the theme issue 'The mammalian skull: development, structure and function'.
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Affiliation(s)
- Anjali Goswami
- Department of Life Sciences, Natural History Museum, London SW7 5BD, UK
- Department of Genetics, Evolution, and Environment, University College London, London WC1E 6BT, UK
| | - Eve Noirault
- Department of Life Sciences, Natural History Museum, London SW7 5BD, UK
| | - Ellen J Coombs
- Department of Life Sciences, Natural History Museum, London SW7 5BD, UK
- Department of Genetics, Evolution, and Environment, University College London, London WC1E 6BT, UK
- Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20013, USA
| | - Julien Clavel
- Université Lyon, Université Claude Bernard Lyon 1, CNRS, ENTPE, UMR 5023 LEHNA, 69622 Villeurbanne, France
| | - Anne-Claire Fabre
- Department of Life Sciences, Natural History Museum, London SW7 5BD, UK
- Naturhistorisches Museum Bern, 3005 Bern, Switzerland
- Institute of Ecology and Evolution, University of Bern, 3012 Bern, Switzerland
| | - Thomas J D Halliday
- Department of Life Sciences, Natural History Museum, London SW7 5BD, UK
- School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham B15 2TT, UK
| | - Morgan Churchill
- Department of Biology, University of Wisconsin Oshkosh, Oshkosh, WI 54901, USA
| | - Abigail Curtis
- Department of Biology, University of Washington, Seattle, WA 98195, USA
| | - Akinobu Watanabe
- Department of Life Sciences, Natural History Museum, London SW7 5BD, UK
- Department of Anatomy, College of Osteopathic Medicine, New York Institute of Technology, Old Westbury, NY 11568, USA
- Division of Paleontology, American Museum of Natural History, New York, NY 10024, USA
| | - Nancy B Simmons
- Department of Mammalogy, Division of Vertebrate Zoology, American Museum of Natural History, New York, NY 10024, USA
| | - Brian L Beatty
- Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20013, USA
- Department of Anatomy, College of Osteopathic Medicine, New York Institute of Technology, Old Westbury, NY 11568, USA
| | - Jonathan H Geisler
- Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20013, USA
- Department of Anatomy, College of Osteopathic Medicine, New York Institute of Technology, Old Westbury, NY 11568, USA
| | - David L Fox
- Department of Earth and Environmental Sciences, University of Minnesota, Minneapolis, MN 55455, USA
| | - Ryan N Felice
- Department of Life Sciences, Natural History Museum, London SW7 5BD, UK
- Department of Genetics, Evolution, and Environment, University College London, London WC1E 6BT, UK
- Centre for Integrative Anatomy, Department of Cell and Developmental Biology, University College London, London WC1E 6BT, UK
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