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<p>Cranial shape variation shows key patterns of evolution and adaptation. This study examines ecological and evolutionary influences on cranial size and shape in six species of bristly ground squirrels using geometric morphometric data from 61 landmarks digitized on 160 adult specimens from 76 localities, analyzed phylogenetically and combined with habitat and dietary data. Species significantly differed in skull size and shape. The low overlap in shape morphospace indicates a high diagnostic value of shape variables. As cranial size increased, the relative size of the braincase decreased, while most rostral bones elongated—aligning with established allometric patterns, including “craniofacial evolutionary allometry” (CREA) and Haller's Rule. Differences in diet and habitat preferences appear to disrupt some of the expected gracilization patterns predicted by CREA, with grass-eating species exhibiting distinct morphologies. Certain observed patterns, such as nasal lengthening and hypertrophied bullae, likely represent adaptations to arid environments. Dorsal skull shape more strongly reflects evolutionary relationships, whereas ventral skull shape is more influenced by ecological pressures. This study of Xerini skull diversity improves our understanding of ecological and evolutionary influences on rodent morphology in arid environments.</p>

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Ecological drivers of cranial evolution in bristly ground squirrels (tribe Xerini)

  • 期刊论文

  • 发表日期：

    2025年11月12日

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  • Bader H. Alhajeri

摘要

Cranial shape variation shows key patterns of evolution and adaptation. This study examines ecological and evolutionary influences on cranial size and shape in six species of bristly ground squirrels using geometric morphometric data from 61 landmarks digitized on 160 adult specimens from 76 localities, analyzed phylogenetically and combined with habitat and dietary data. Species significantly differed in skull size and shape. The low overlap in shape morphospace indicates a high diagnostic value of shape variables. As cranial size increased, the relative size of the braincase decreased, while most rostral bones elongated—aligning with established allometric patterns, including “craniofacial evolutionary allometry” (CREA) and Haller's Rule. Differences in diet and habitat preferences appear to disrupt some of the expected gracilization patterns predicted by CREA, with grass-eating species exhibiting distinct morphologies. Certain observed patterns, such as nasal lengthening and hypertrophied bullae, likely represent adaptations to arid environments. Dorsal skull shape more strongly reflects evolutionary relationships, whereas ventral skull shape is more influenced by ecological pressures. This study of Xerini skull diversity improves our understanding of ecological and evolutionary influences on rodent morphology in arid environments.