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From Lucy to Kadanuumuu: balanced analyses of Australopithecus afarensis assemblages confirm only moderate skeletal dimorphism.

Reno PL, Lovejoy CO - PeerJ (2015)

Bottom Line: In addition to a number of isolated specimens, the sample for this species includes two small associated skeletons (A.L. 288-1 or "Lucy" and A.L. 128/129) and a geologically contemporaneous death assemblage of several larger individuals (A.L. 333).These have driven both perceptions and quantitative analyses concluding that Au. afarensis was markedly dimorphic.Prevention of the dominance of a single specimen's contribution to calculations of multiple dimorphism estimates confirms that Au. afarensis was only moderately dimorphic.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Anthropology, The Pennsylvania State University , University Park, PA , USA.

ABSTRACT
Sexual dimorphism in body size is often used as a correlate of social and reproductive behavior in Australopithecus afarensis. In addition to a number of isolated specimens, the sample for this species includes two small associated skeletons (A.L. 288-1 or "Lucy" and A.L. 128/129) and a geologically contemporaneous death assemblage of several larger individuals (A.L. 333). These have driven both perceptions and quantitative analyses concluding that Au. afarensis was markedly dimorphic. The Template Method enables simultaneous evaluation of multiple skeletal sites, thereby greatly expanding sample size, and reveals that A. afarensis dimorphism was similar to that of modern humans. A new very large partial skeleton (KSD-VP-1/1 or "Kadanuumuu") can now also be used, like Lucy, as a template specimen. In addition, the recently developed Geometric Mean Method has been used to argue that Au. afarensis was equally or even more dimorphic than gorillas. However, in its previous application Lucy and A.L. 128/129 accounted for 10 of 11 estimates of female size. Here we directly compare the two methods and demonstrate that including multiple measurements from the same partial skeleton that falls at the margin of the species size range dramatically inflates dimorphism estimates. Prevention of the dominance of a single specimen's contribution to calculations of multiple dimorphism estimates confirms that Au. afarensis was only moderately dimorphic.

No MeSH data available.


Sampling procedure used to simulate the Template and Geometric Mean Methods in extant humans, chimpanzees and gorillas.
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fig-2: Sampling procedure used to simulate the Template and Geometric Mean Methods in extant humans, chimpanzees and gorillas.

Mentions: As the Au. afarensis BDI, CV and GMR statistics are computed from a combination of different variables which cannot be assumed to have the same variance, they cannot simply be compared to similar statistics computed using a more standard metric (e.g., actual FHD). Therefore, we conducted simulations of randomly generated samples with identical anatomical composition from species with known sexual dimorphism (Fig. 2 and Table S3). The chimpanzee, human, and gorilla samples used here are similar to those used previously (Reno et al., 2003; Reno et al., 2010) with the addition of three new metrics to maximize use of the Kadanuumuu template (Table 1). These three hominoids are appropriate reference taxa with which to judge Au. afarensis dimorphism, because they represent three of the four extant species most closely related to early hominids. In addition, with the exception of some ceropithecoids (i.e., Mandrillus (Setchell et al., 2001)) and possibly the extinct Miocene genus Lufengpithecus as indicated by postcanine dentition (Kelley & Xu, 1991) they essentially encompass the range of primate skeletal dimorphism (Smith & Jungers, 1997). Therefore, to determine where Au. afarensis falls within the spectrum of African hominoid dimorphism, we tested the hypotheses that its dimorphism is above minimally dimorphic chimpanzees, below extremely dimorphic gorillas, or compatible with moderately dimorphic humans.


From Lucy to Kadanuumuu: balanced analyses of Australopithecus afarensis assemblages confirm only moderate skeletal dimorphism.

Reno PL, Lovejoy CO - PeerJ (2015)

Sampling procedure used to simulate the Template and Geometric Mean Methods in extant humans, chimpanzees and gorillas.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4419524&req=5

fig-2: Sampling procedure used to simulate the Template and Geometric Mean Methods in extant humans, chimpanzees and gorillas.
Mentions: As the Au. afarensis BDI, CV and GMR statistics are computed from a combination of different variables which cannot be assumed to have the same variance, they cannot simply be compared to similar statistics computed using a more standard metric (e.g., actual FHD). Therefore, we conducted simulations of randomly generated samples with identical anatomical composition from species with known sexual dimorphism (Fig. 2 and Table S3). The chimpanzee, human, and gorilla samples used here are similar to those used previously (Reno et al., 2003; Reno et al., 2010) with the addition of three new metrics to maximize use of the Kadanuumuu template (Table 1). These three hominoids are appropriate reference taxa with which to judge Au. afarensis dimorphism, because they represent three of the four extant species most closely related to early hominids. In addition, with the exception of some ceropithecoids (i.e., Mandrillus (Setchell et al., 2001)) and possibly the extinct Miocene genus Lufengpithecus as indicated by postcanine dentition (Kelley & Xu, 1991) they essentially encompass the range of primate skeletal dimorphism (Smith & Jungers, 1997). Therefore, to determine where Au. afarensis falls within the spectrum of African hominoid dimorphism, we tested the hypotheses that its dimorphism is above minimally dimorphic chimpanzees, below extremely dimorphic gorillas, or compatible with moderately dimorphic humans.

Bottom Line: In addition to a number of isolated specimens, the sample for this species includes two small associated skeletons (A.L. 288-1 or "Lucy" and A.L. 128/129) and a geologically contemporaneous death assemblage of several larger individuals (A.L. 333).These have driven both perceptions and quantitative analyses concluding that Au. afarensis was markedly dimorphic.Prevention of the dominance of a single specimen's contribution to calculations of multiple dimorphism estimates confirms that Au. afarensis was only moderately dimorphic.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Anthropology, The Pennsylvania State University , University Park, PA , USA.

ABSTRACT
Sexual dimorphism in body size is often used as a correlate of social and reproductive behavior in Australopithecus afarensis. In addition to a number of isolated specimens, the sample for this species includes two small associated skeletons (A.L. 288-1 or "Lucy" and A.L. 128/129) and a geologically contemporaneous death assemblage of several larger individuals (A.L. 333). These have driven both perceptions and quantitative analyses concluding that Au. afarensis was markedly dimorphic. The Template Method enables simultaneous evaluation of multiple skeletal sites, thereby greatly expanding sample size, and reveals that A. afarensis dimorphism was similar to that of modern humans. A new very large partial skeleton (KSD-VP-1/1 or "Kadanuumuu") can now also be used, like Lucy, as a template specimen. In addition, the recently developed Geometric Mean Method has been used to argue that Au. afarensis was equally or even more dimorphic than gorillas. However, in its previous application Lucy and A.L. 128/129 accounted for 10 of 11 estimates of female size. Here we directly compare the two methods and demonstrate that including multiple measurements from the same partial skeleton that falls at the margin of the species size range dramatically inflates dimorphism estimates. Prevention of the dominance of a single specimen's contribution to calculations of multiple dimorphism estimates confirms that Au. afarensis was only moderately dimorphic.

No MeSH data available.