AI Article Synopsis
- The study aimed to analyze the insertion sites of ligaments for the flexor digitorum muscles in the proximal phalanges of African apes and modern humans, focusing on differences in flexor ridge size based on behavior.
- Researchers used 3D models of phalanges from gorillas, chimpanzees, and humans to compare flexor ridge sizes within and between the species.
- Results showed that gorillas and chimpanzees have larger flexor ridges than humans, indicating adaptations related to hand use for locomotion, while humans exhibit unique flexor ridge patterns that support their precision gripping abilities.
Article Abstract
Objectives: The primary aim of this study was to describe the insertion sites of the ligaments holding the flexor digitorum profundus and superficialis muscles (flexor ridges) in proximal phalanges 2-5 of African apes and modern humans. To interpret differences in flexor ridge size based on general behavioral differences among taxa.
Materials And Methods: We analyzed 3D models of manual proximal phalanges 2-5 from 29 gorillas (Gorilla beringei and Gorilla gorilla), 30 chimpanzees (Pan troglodytes) and 36 recent modern humans. Flexor ridges (mm) were compared within and across genera.
Results: Gorillas and chimpanzees had larger flexor ridges for phalanges 2-4 than humans and this difference subsists when controlling for body size. Each genus had a unique insertion size pattern across the digits, with the most heterogeneous pattern found in chimpanzees, followed by humans, and lastly gorillas. These patterns corresponded strongly to the differences in the size of the phalanges within each genus, except for phalanx 5 in humans, which had a larger flexor ridge than expected.
Discussion: When comparing these genera, the flexor ridges signal differences between taxa that use their hands for manipulation and locomotion (gorillas and chimpanzees) and taxa that use them exclusively for manipulation (humans). This functional signal was also apparent in the PP5 of humans, whose larger FR may be indicating the high recruitment of this digit during forceful precision grip characteristic of humans.
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| http://dx.doi.org/10.1002/ajpa.24127 | DOI Listing |
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Cortical bone architecture of hominid intermediate phalanges reveals functional signals of locomotion and manipulation.
Am J Biol Anthropol
May 2024
Department of Human Origins, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany.
Objectives: Reconstruction of fossil hominin manual behaviors often relies on comparative analyses of extant hominid hands to understand the relationship between hand use and skeletal morphology. In this context, the intermediate phalanges remain understudied. Thus, here we investigate cortical bone morphology of the intermediate phalanges of extant hominids and compare it to the cortical structure of the proximal phalanges, to investigate the relationship between cortical bone structure and inferred loading during manual behaviors.
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