Evidence of a chimpanzee-sized ancestor of humans but a gibbon-sized ancestor of apes

Grabowski, Mark; Jungers, William L.

doi:10.1038/s41467-017-00997-4

Cited by 28 publications

(24 citation statements)

References 72 publications

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“…If chimpanzee-like patterns of scaling existed in these earliest possible hominins, these results could mean that the larger body sizes found in some early australopiths (Pontzer, 2012;Grabowski et al, 2015;see also;Jungers et al, 2016;Masao et al, 2016) were already present in earlier taxa near the origins of our lineage. These results also point to a fairly large body mass for the last common ancestor of humans and chimpanzees, a conclusion that is consistent with the sizes of individual skeletal elements of late Miocene fragmentary fossils attributed to Sahelanthropus and earlier members of Ardipithecus (Haile-Selassie, 2001;Brunet et al, 2002) and a recent study using a different approach (Grabowski and Jungers, 2017). A common chimpanzeelike size has significant implications for the locomotor modes of the Pan-Homo last common ancestor, strongly arguing against small-bodied models (e.g., the hylobatidian model; Keith, 1923;Tuttle, 1981) and providing less support for an above-branch arboreal quadruped (Straus, 1949;Lovejoy, 2009).…”

Section: Resultssupporting

confidence: 86%

Body mass estimates of the earliest possible hominins and implications for the last common ancestor

Grabowski

Hatala

Jungers

2018

Journal of Human Evolution

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Many hypotheses regarding the paleobiology of the earliest possible hominins, Orrorin tugenensis and Ardipithecus ramidus, are dependent upon accurate body mass estimates for these taxa. While we have previously published body mass predictions for Orrorin and Ardipithecus, the accuracies of those estimates depend on the assumption that the postcranial skeletal dimensions and body masses of these taxa followed scaling patterns that were similar to those observed in modern humans. This assumption may not be correct because certain aspects of postcranial morphology in Orrorin and Ardipithecus differ from modern humans, and suggest that their overall body plans might be unique but more similar to modern non-human great apes than to modern humans. Here we present individual body mass predictions for O. tugenensis and Ar. ramidus assuming that they followed postcranial scaling patterns similar to those of chimpanzees. All estimates include individual prediction intervals as measures of uncertainty. In addition, we provide equations for predicting body mass from univariate postcranial measurements based on the largest sample (n = 25) yet compiled of common chimpanzee skeletons with known body masses, which is vital for calculating prediction intervals for individual fossils. Our results show that estimated body masses in Orrorin and Ardipithecus are generally larger when derived from a chimpanzee-like scaling pattern compared to estimates that assume a human-like pattern, though the prediction intervals of the two sets of estimates overlap. In addition, the more complete of the two known Orrorin femora has an overall scaling pattern that is more similar to common chimpanzees than to modern humans, supporting the application of a non-human great ape comparative model. Our new estimates fall near the male (Ardipithecus) average and in between the male and female averages (Orrorin) for wild-caught common chimpanzees. If a chimpanzee-like pattern of scaling between postcranial dimensions and body mass did exist in these earliest hominins, our results suggest the large body masses found in some early australopiths were already present in taxa near the origins of our lineage, and perhaps also in the Pan-Homo last common ancestor.

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Section: Resultssupporting

confidence: 86%

Body mass estimates of the earliest possible hominins and implications for the last common ancestor

Grabowski

Hatala

Jungers

2018

Journal of Human Evolution

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“…To test alternative hypotheses about the relationship between hand morphology and locomotor behavior, we reconstructed the adaptive landscape of primate hand evolution using phylogenetic comparative methods [( 38 , 39 ); see also ( 5 , 22 , 40 )]. These methods allow us to translate adaptive hypotheses into explicit evolutionary models tested against comparative data in a maximum likelihood framework.…”

Section: Resultsmentioning

confidence: 99%

Ardipithecus hand provides evidence that humans and chimpanzees evolved from an ancestor with suspensory adaptations

et al. 2021

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The morphology and positional behavior of the last common ancestor of humans and chimpanzees are critical for understanding the evolution of bipedalism. Early 20th century anatomical research supported the view that humans evolved from a suspensory ancestor bearing some resemblance to apes. However, the hand of the 4.4-million-year-old hominin Ardipithecus ramidus purportedly provides evidence that the hominin hand was derived from a more generalized form. Here, we use morphometric and phylogenetic comparative methods to show that Ardipithecus retains suspensory adapted hand morphologies shared with chimpanzees and bonobos. We identify an evolutionary shift in hand morphology between Ardipithecus and Australopithecus that renews questions about the coevolution of hominin manipulative capabilities and obligate bipedalism initially proposed by Darwin. Overall, our results suggest that early hominins evolved from an ancestor with a varied positional repertoire including suspension and vertical climbing, directly affecting the viable range of hypotheses for the origin of our lineage.

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“…Therefore, in evolutionary model comparison, the focus is on the number and arrangement of global phenotypic optima (θ) and their surrounding local optima (i.e., species means) rather than on individuals within species. Several recent studies have used modeling methods to test evolutionary hypotheses in paleoanthropology (Almécija et al, 2015; Grabowski and Jungers, 2017; Fernández et al, 2018).…”

Section: Methodsmentioning

confidence: 99%

The African ape-like foot of Ardipithecus ramidus and its implications for the origin of bipedalism

Prang

2019

eLife

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The ancestral condition from which humans evolved is critical for understanding the adaptive origin of bipedal locomotion. The 4.4 million-year-old hominin partial skeleton attributed to Ardipithecus ramidus preserves a foot that purportedly shares morphometric affinities with monkeys, but this interpretation remains controversial. Here I show that the foot of Ar. ramidus is most similar to living chimpanzee and gorilla species among a large sample of anthropoid primates. The foot morphology of Ar. ramidus suggests that the evolutionary precursor of hominin bipedalism was African ape-like terrestrial quadrupedalism and climbing. The elongation of the midfoot and phalangeal reduction in Ar. ramidus relative to the African apes is consistent with hypotheses of increased propulsive capabilities associated with an early form of bipedalism. This study provides evidence that the modern human foot was derived from an ancestral form adapted to terrestrial plantigrade quadrupedalism.

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Evidence of a chimpanzee-sized ancestor of humans but a gibbon-sized ancestor of apes

Cited by 28 publications

References 72 publications

Body mass estimates of the earliest possible hominins and implications for the last common ancestor

Body mass estimates of the earliest possible hominins and implications for the last common ancestor

Ardipithecus hand provides evidence that humans and chimpanzees evolved from an ancestor with suspensory adaptations

The African ape-like foot of Ardipithecus ramidus and its implications for the origin of bipedalism

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