The ontogeny of knuckle‐walking and dorsal metacarpal ridge prominence in chimpanzees. Issue 1 (26th January 2022)

• Record Type: Journal Article
• Authors: Sarringhaus, Lauren; Mitani, John C.; MacLatchy, Laura M.
• Is Part Of: American journal of biological anthropology. Volume 178:Issue 1(2022)
• Page Start: 29
• Page End: 43
• Publication Date: 2022-01-26
• Subjects: digitigrade -- Gorilla -- locomotor development -- Papio -- quadrupedalism; Physical anthropology -- Periodicals; 599.9
• DOI: 10.1002/ajpa.24477
• Languages: English
• ISSNs: 2692-7691

Abstract

Abstract: Objectives: This study examines the sensitivity of the development of the dorsal metacarpal ridge (DMR) to the frequency of knuckle‐walking during ontogeny in chimpanzees, and compares the prevalence and prominence of the DMR in hominoids and baboons. Materials and Methods: We characterized the type and frequency of quadrupedalism of wild chimpanzees of different ages from the Ngogo community, Uganda. Using museum specimens, we quantified third metacarpal DMR angle and height in Pan individuals of different developmental stages, and in adult Gorilla, Pongo, Hylobates, and Papio . Results: When terrestrial, all quadrupedalism consisted of knuckle‐walking, although older individuals knuckle‐walked more than younger. The total amount of quadrupedalism engaged in by different age groups while arboreal was consistent; however, knuckle usage while arboreally quadrupedal increased with age. The DMR ridge did not emerge in Pan until older infancy, after the onset of knuckle‐walking, and reached prominence by the juvenile stage. The DMR angle increased significantly after juvenility but relative height did not. Adult Pan and Gorilla have more prevalent and prominent DMRs than Papio ; the DMR was rare in Pongo and absent in Hylobates . Discussion: The timing of development of the DMR in chimpanzees supports it as a knuckle walking character, as does its occurrence in gorillas, and virtual absence in suspensory orangutans and gibbons . The DMR in baboons differs in appearance and frequency from DMRs in African apes, and so differentiates knuckle‐walking from digitigrady in catarrhines. The relationship between the DMR and loading of a vertical hand while terrestrial deserves further study. Abstract : The DMR of Papio, Pan, and Gorilla in medial (top) and dorsal (bottom) view. When present in Papio, the DMR is two separate ridges angled to the lateral and medial side (blue arrows). The DMR of African apes ( Pan and Gorilla ) presents as a continuous ridge from the medial to lateral edge of the distal dorsal metacarpal (blue arrows)