Ulna curvature in Sahelanthropus, the StW 573 (“Little Foot”) Australopithecus, and other early hominins
MARC R. MEYER, ISABELLA FX. ARAIZA & SCOTT A. WILLIAMS
AAPA abstracts 2021
Discoveries of ulnae for early hominins such as the TM 266-01-050 Sahelanthropus tchadensis and the StW 573 (Little Foot) Australopithecus are welcome additions to the early hominin fossil record. Significant curvature of the ulna is a normal anatomic feature among extant apes and many early hominins that has been linked to locomotor behaviors involving the forearm. Here we employ elliptical Fourier shape analysis to quantify ulnar curvature in extant apes (n = 46), early hominins (n = 9), and Homo sapiens (n = 30) to better understand forearm functional morphology across the sample.
The significantly curved and gracile StW 573 ulna falls within the morphospace of Pongo, and well outside the distribution of H.sapiens the human clinical sample. Falling closest to the U.W.101-499 H.naledi and KNM-BK 66 H.erectus fossils, its high degree of midshaft curvature and gracility also distinguishes it from Pan, Gorilla, and the more robust and curved Sahelanthropus and Paranthropus fossils. The curvature of both the TM 266-01-050 and StW 573 is greater than observed in A.afarensis, A.sediba, and the KNM-WT 15000 H.erectus, which are all more similar to modern humans. We discuss the functional implications of forearm curvature across taxa, and also address whether the Little Foot ulna reflects traumatic bowing of the left forearm resulting from a childhood fall, as suggested by previous work.

littor...@gmail.com wrote:
> Ulna curvature in Sahelanthropus, the StW 573 (“Little Foot”) Australopithecus, and other early hominins
> MARC R. MEYER, ISABELLA FX. ARAIZA & SCOTT A. WILLIAMS
> AAPA abstracts 2021

<https://www.researchgate.net/publication/351120071_Ulna_curvature_in_Sahelanthropus_the_StW_573_Little_Foot_Australopithecus_and_other_early_hominins>

> Discoveries of ulnae for early hominins such as the TM 266-01-050 Sahelanthropus tchadensis and the StW 573 (Little Foot) Australopithecus are welcome additions to the early hominin fossil record. Significant curvature of the ulna is a normal anatomic feature among extant apes and many early hominins that has been linked to locomotor behaviors involving the forearm. Here we employ elliptical Fourier shape analysis to quantify ulnar curvature in extant apes (n = 46), early hominins (n = 9), and Homo sapiens (n = 30) to better understand forearm functional morphology across the sample.
> The significantly curved and gracile StW 573 ulna falls within the morphospace of Pongo, and well outside the distribution of H.sapiens the human clinical sample. Falling closest to the U.W.101-499 H.naledi and KNM-BK 66 H.erectus fossils, its high degree of midshaft curvature and gracility also distinguishes it from Pan, Gorilla, and the more robust and curved Sahelanthropus and Paranthropus fossils. The curvature of both the TM 266-01-050 and StW 573 is greater than observed in A.afarensis, A.sediba, and the KNM-WT 15000 H.erectus, which are all more similar to modern humans. We discuss the functional implications of forearm curvature across taxa, and also address whether the Little Foot ulna reflects traumatic bowing of the left forearm resulting from a childhood fall, as suggested by previous work.
>

"Sterrestrial African apes. So, I think it is safe to say that
Sahelanthropus was NOT
particularly suspensory."

"The Sahelanthropus shaft ulna displays a high degree of curvature and
proximal robusticity
as in the African great apes, signaling a forearm less adapted to
suspension, and more
toward elbow flexion as in Pan and Gorilla… and is likely a generalized
climbing adaptation."

"... …perhaps habitual pulling of plant resources from the ground which
requires dynamic
flexion, supination and pronation of the forelimb and countering ground forces
with the contralateral arm which are all activities associated with
significant ulna curvature."