Cenozoic terrestrial vertebrate body size variation (Cope's & Bergmann's rules) + owl and hawk tarsometatarsal morphology for prey carrying
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Ben Creisler
Dec 22, 2025, 5:38:15 PM12/22/25
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Ben Creisler
Non-dino papers not yet mentioned:
Qinfeng Guo, Hong Qian & Jian Zhang (2025)
Body size variation of world's living terrestrial vertebrates in the Cenozoic
Journal of Systematics and Evolution (advance online publication)
doi: https://doi.org/10.1111/jse.70038
https://onlinelibrary.wiley.com/doi/10.1111/jse.70038
Body size is among the key subjects in macroecology and macroevolution with important implications for conservation. Two major rules have been proposed to explain how body size changes over evolutionary time (Cope's rule) and across temperature gradients (Bergmann's rule). To date, however, the applicability of both rules to global terrestrial vertebrates (tetrapod) remains elusive. Here, using the newly available data, we comparatively examined the temporal variation in species body size of the world's extant tetrapod species (tetrapoda as a whole) and of each class, amphibians (Amphibia), reptiles (Reptilia), mammals (Mammalia), and birds (Aves), through the Cenozoic Era. When all four classes were considered together, the species' body size had increased over time and was negatively correlated with global surface temperature. However, separate analyses on each of the four classes showed that reptiles and mammals tended to support Cope's rule, while birds and amphibians did not. Also, we found no clear difference in temporal body size variation between endothermic and ectothermic species. Overall, the support for Bergmann's rule was much stronger than that for Cope's rule. Future research using more complete and compatible body size data from fossils is needed to better understand how species' body size evolves over time and across space.
Alexander D. Clark, Linnea L. Lungstrom, Samantha J. Clark & Mark W. Westneat (2025)
Biomechanics of raptorial dorsiflexion and tensile material properties of the m. tibialis cranialis tendon in the hindlimbs of hawks and owls
Journal of Experimental Biology 228 (23): jeb251052.
doi: https://doi.org/10.1242/jeb.251052
https://journals.biologists.com/jeb/article/228/23/jeb251052/370076/Biomechanics-of-raptorial-dorsiflexion-and-tensile
Skeletal morphology and tendon properties reveal the underlying systems that facilitate movement and, ultimately, behavior in animals. Of all terrestrial vertebrates, birds are the most diverse in terms of species. Birds often interact with their prey via the hindlimbs, making these portions of the body rich in ecomorphological information. The m. tibialis cranialis is the primary dorsiflexor of the ankle, and in raptorial birds, this muscle critically aids in both prey acquisition and transport. Here, we assessed the biomechanical implications of tarsometatarsal morphology and the tensile properties of the m. tibialis cranialis tendon among accipitrids and strigids to assess potential differences in prey acquisition strategies and load capacities. Examination of tarsometatarsal morphology reveals significantly more robust and much more distally positioned insertion points for the m. tibialis cranialis in strigids, resulting in comparatively increased mechanical advantage. Though acquisition strategies among focal raptorial birds differed, results of tensile properties indicate no significant differences in mass-specific load-carrying capabilities. However, results suggest that strigids only require approximately half the torque required by accipitrids to lift a given resistance, even when adjusting for mass categories. The elastic modulus of m. tibialis cranialis tendons was low across examined birds, ranging from 17.2 to 128 MPa. Our central conclusions are that tarsometatarsal morphology indicates differences in mechanical lever arm advantage between the two groups, and that hindlimb tendons of arboreal birds of prey are relatively elastic, with significantly lower moduli than those of cursorial birds and mammals, suggesting functional roles in shock absorption and strain energy storage during lifting and transport of prey.
===
Qinfeng Guo, Hong Qian & Jian Zhang (2025)
Body size variation of world's living terrestrial vertebrates in the Cenozoic
Journal of Systematics and Evolution (advance online publication)
doi: https://doi.org/10.1111/jse.70038
https://onlinelibrary.wiley.com/doi/10.1111/jse.70038
Body size is among the key subjects in macroecology and macroevolution with important implications for conservation. Two major rules have been proposed to explain how body size changes over evolutionary time (Cope's rule) and across temperature gradients (Bergmann's rule). To date, however, the applicability of both rules to global terrestrial vertebrates (tetrapod) remains elusive. Here, using the newly available data, we comparatively examined the temporal variation in species body size of the world's extant tetrapod species (tetrapoda as a whole) and of each class, amphibians (Amphibia), reptiles (Reptilia), mammals (Mammalia), and birds (Aves), through the Cenozoic Era. When all four classes were considered together, the species' body size had increased over time and was negatively correlated with global surface temperature. However, separate analyses on each of the four classes showed that reptiles and mammals tended to support Cope's rule, while birds and amphibians did not. Also, we found no clear difference in temporal body size variation between endothermic and ectothermic species. Overall, the support for Bergmann's rule was much stronger than that for Cope's rule. Future research using more complete and compatible body size data from fossils is needed to better understand how species' body size evolves over time and across space.
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Free pdf:
Alexander D. Clark, Linnea L. Lungstrom, Samantha J. Clark & Mark W. Westneat (2025)
Biomechanics of raptorial dorsiflexion and tensile material properties of the m. tibialis cranialis tendon in the hindlimbs of hawks and owls
Journal of Experimental Biology 228 (23): jeb251052.
doi: https://doi.org/10.1242/jeb.251052
https://journals.biologists.com/jeb/article/228/23/jeb251052/370076/Biomechanics-of-raptorial-dorsiflexion-and-tensile
Skeletal morphology and tendon properties reveal the underlying systems that facilitate movement and, ultimately, behavior in animals. Of all terrestrial vertebrates, birds are the most diverse in terms of species. Birds often interact with their prey via the hindlimbs, making these portions of the body rich in ecomorphological information. The m. tibialis cranialis is the primary dorsiflexor of the ankle, and in raptorial birds, this muscle critically aids in both prey acquisition and transport. Here, we assessed the biomechanical implications of tarsometatarsal morphology and the tensile properties of the m. tibialis cranialis tendon among accipitrids and strigids to assess potential differences in prey acquisition strategies and load capacities. Examination of tarsometatarsal morphology reveals significantly more robust and much more distally positioned insertion points for the m. tibialis cranialis in strigids, resulting in comparatively increased mechanical advantage. Though acquisition strategies among focal raptorial birds differed, results of tensile properties indicate no significant differences in mass-specific load-carrying capabilities. However, results suggest that strigids only require approximately half the torque required by accipitrids to lift a given resistance, even when adjusting for mass categories. The elastic modulus of m. tibialis cranialis tendons was low across examined birds, ranging from 17.2 to 128 MPa. Our central conclusions are that tarsometatarsal morphology indicates differences in mechanical lever arm advantage between the two groups, and that hindlimb tendons of arboreal birds of prey are relatively elastic, with significantly lower moduli than those of cursorial birds and mammals, suggesting functional roles in shock absorption and strain energy storage during lifting and transport of prey.
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