Contours of the hominoid lateral tibial condyle with implications for Australopithecus

Jason Organ, Carol V. Ward

Research output: Contribution to journalArticle

35 Citations (Scopus)

Abstract

Tibial condyle shape is alleged to vary among fossil tibiae attributed to Australopithecus, and has been argued to reflect functional differences of the knee. Convex anteroposterior curvature of the lateral tibial condyle in A. africanus has been interpreted to indicate a more chimpanzee-like locomotor repertoire than the flatter lateral tibial condyles of A. afarensis (Berger and Tobias, 1996, J. Hum. Evol. 30, 343). Alternatively, Latimer, Ohman, and Lovejoy (1987, Am. J. Phys. Anthropol. 74, 155) have suggested that in response to increased transarticular loads accompanied by larger body mass, joints should become flatter as size increases, both within and among species, so that the variation observed among hominin fossils reflects size alone rather than functional differences. In this study, three-dimensional surface areas of the lateral tibial condyle of humans, chimpanzees, and gorillas were computed using a Digibot II (Digibotics) laser scanner and the DataSculpt v.4.6 engineering software package to evaluate joint surface contours, and compared to two-dimensional surface area and arc and chord length measurements of the anteroposterior and mediolateral axes. Extant species measurements were then compared to those of A. afarensis (A.L. 129-1b, A.L. 288-1aq, A.L. 333x-26, A.L. 333-42) and A. africanus (Stw 514a). Results do not support the hypothesis that A. afarensis and A. africanus differ in condylar topology. They also do not support the hypothesis that joint surfaces become flatter with increased transarticular load accompanying increased body size, as curvature of the lateral tibial condyle in anteroposterior and mediolateral planes is not negatively allometric. However, femoral condylar shape is not included in this study, which may better reflect joint surface responses to increased body size. Finally, there is no basis from this study to reconstruct differences in locomotor behavior among fossil hominin taxa based on lateral tibial condyle morphology.

Original languageEnglish (US)
Pages (from-to)113-127
Number of pages15
JournalJournal of Human Evolution
Volume51
Issue number2
DOIs
StatePublished - Aug 2006
Externally publishedYes

Fingerprint

Hominidae
fossils
fossil
Pan troglodytes
curvature
body size
surface area
Gorilla
knees
scanners
thighs
engineering
scanner
tibia
joints (animal)
topology
body mass
lasers
laser
software

Keywords

  • Allometry
  • Hominin
  • Joint curvature
  • Reduced major axis
  • Variation

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics

Cite this

Contours of the hominoid lateral tibial condyle with implications for Australopithecus. / Organ, Jason; Ward, Carol V.

In: Journal of Human Evolution, Vol. 51, No. 2, 08.2006, p. 113-127.

Research output: Contribution to journalArticle

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abstract = "Tibial condyle shape is alleged to vary among fossil tibiae attributed to Australopithecus, and has been argued to reflect functional differences of the knee. Convex anteroposterior curvature of the lateral tibial condyle in A. africanus has been interpreted to indicate a more chimpanzee-like locomotor repertoire than the flatter lateral tibial condyles of A. afarensis (Berger and Tobias, 1996, J. Hum. Evol. 30, 343). Alternatively, Latimer, Ohman, and Lovejoy (1987, Am. J. Phys. Anthropol. 74, 155) have suggested that in response to increased transarticular loads accompanied by larger body mass, joints should become flatter as size increases, both within and among species, so that the variation observed among hominin fossils reflects size alone rather than functional differences. In this study, three-dimensional surface areas of the lateral tibial condyle of humans, chimpanzees, and gorillas were computed using a Digibot II (Digibotics) laser scanner and the DataSculpt v.4.6 engineering software package to evaluate joint surface contours, and compared to two-dimensional surface area and arc and chord length measurements of the anteroposterior and mediolateral axes. Extant species measurements were then compared to those of A. afarensis (A.L. 129-1b, A.L. 288-1aq, A.L. 333x-26, A.L. 333-42) and A. africanus (Stw 514a). Results do not support the hypothesis that A. afarensis and A. africanus differ in condylar topology. They also do not support the hypothesis that joint surfaces become flatter with increased transarticular load accompanying increased body size, as curvature of the lateral tibial condyle in anteroposterior and mediolateral planes is not negatively allometric. However, femoral condylar shape is not included in this study, which may better reflect joint surface responses to increased body size. Finally, there is no basis from this study to reconstruct differences in locomotor behavior among fossil hominin taxa based on lateral tibial condyle morphology.",
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