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Friday, September 11, 2015

Early hominins were small than previously thought

J Hum Evol. 2015 Aug;85:75-93. doi: 10.1016/j.jhevol.2015.05.005.
Epub 2015 Jun 17.

Body mass estimates of hominin fossils and the evolution of human body
size.
Grabowski M, Hatala KG, Jungers WL, Richmond BG.

Abstract

Body size directly influences an animal's place in the natural world,
including its energy requirements, home range size, relative brain size,
locomotion, diet, life history, and behavior. Thus, an understanding of
the biology of extinct organisms, including species in our own lineage,
requires accurate estimates of body size. Since the last major review of
hominin body size based on postcranial morphology over 20 years ago, new
fossils have been discovered, species attributions have been clarified,
and methods improved. Here, we present the most comprehensive and
thoroughly vetted set of individual fossil hominin body mass predictions
to date, and estimation equations based on a large (n = 220) sample of
modern humans of known body masses. We also present species averages
based exclusively on fossils with reliable taxonomic attributions,
estimates of species averages by sex, and a metric for levels of sexual
dimorphism. Finally, we identify individual traits that appear to be the
most reliable for mass estimation for each fossil species, for use when
only one measurement is available for a fossil. Our results show that
many early hominins were generally smaller-bodied than previously
thought, an outcome likely due to larger estimates in previous studies
resulting from the use of large-bodied modern human reference samples.
Current evidence indicates that modern human-like large size first
appeared by at least 3-3.5 Ma in some Australopithecus afarensis
individuals. Our results challenge an evolutionary model arguing that
body size increased from Australopithecus to early Homo. Instead, we
show that there is no reliable evidence that the body size of
non-erectus early Homo differed from that of australopiths, and confirm
that Homo erectus evolved larger average body size than earlier
hominins. 



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