"The pectoral girdle of StW 573 (‘Little Foot’) and its implications for shoulder evolution in the Hominina" by Kristian J Carlson

Article

The pectoral girdle of StW 573 (‘Little Foot’) and its implications for shoulder evolution in the Hominina

Journal of Human Evolution (2021)

Kristian J Carlson, University of Southern California
David J Green, Campbell University School of Osteopathic Medicine
Tea Jashashvili, University of Southern California
Travis R Pickering, University of Wisconsin-Madison
Jason L Heaton, Birmingham-Southern College
Amelie Beaudet, University of the Witwatersrand, Johannesburg
Dominic Stratford, University of the Witwatersrand, Johannesburg
Robin Crompton, University of Liverpool
Kathleen Kuman, University of the Witwatersrand, Johannesburg
Laurent Bruxelles, French National Centre for Scientific Research
Ronald J Clarke, University of the Witwatersrand, Johannesburg

Link

Abstract
The ca. 3.67 Ma adult skeleton known as ‘Little Foot’ (StW 573), recovered from Sterkfontein Member 2
breccia in the Silberberg Grotto, is remarkable for its morphology and completeness. Preservation of
clavicles and scapulae, including essentially complete right-side elements, offers opportunities to assess
morphological and functional aspects of a nearly complete Australopithecus pectoral girdle. Here we
describe the StW 573 pectoral girdle and offer quantitative comparisons to those of extant hominoids
and selected homininans. The StW 573 pectoral girdle combines features intermediate between those of
humans and other apes: a long and curved clavicle, suggesting a relatively dorsally positioned scapula;
an enlarged and uniquely proportioned supraspinous fossa; a relatively cranially oriented glenoid fossa;
and ape-like reinforcement of the axillary margin by a stout ventral bar. StW 573 scapulae are as follows:
smaller than those of some homininans (i.e., KSD-VP-1/1 and KNM-ER 47000A), larger than others (i.e.,
A.L. 288-1, Sts 7, and MH2), and most similar in size to another australopith from Sterkfontein, StW 431.
Moreover, StW 573 and StW 431 exhibit similar structural features along their axillary margins and
inferior angles. As the StW573 pectoral girdle (e.g., scapular configuration) has a greater affinity to that of
apesdGorilla in particulardrather than modern humans, we suggest that the StW 573 morphological
pattern appears to reflect adaptations to arboreal behaviors, especially those with the hand positioned
above the head, more than human-like manipulatory capabilities. When compared with less complete
pectoral girdles from middle/late Miocene apes and that of the penecontemporaneous KSD-VP-1/1
(Australopithecus afarensis), and mindful of consensus views on the adaptiveness of arboreal positional
behaviors soliciting abducted glenohumeral joints in early Pliocene taxa, we propose that the StW 573
pectoral girdle is a reasonable model for hypothesizing pectoral girdle configuration of the crown
hominin last common ancestor.

Keywords

Clavicle,
Scapula,
Upper limb,
Australopithecus,
Sterkfontein,
Locomotion

Disciplines

Publication Date

Spring April 20, 2021

DOI

https://doi.org/10.1016/j.jhevol.2021.102983

Citation Information

Kristian J Carlson, David J Green, Tea Jashashvili, Travis R Pickering, et al.. "The pectoral girdle of StW 573 (‘Little Foot’) and its implications for shoulder evolution in the Hominina" Journal of Human Evolution (2021) p. 102983
Available at: http://works.bepress.com/david-j-green/62/