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Bipedalism evolved well before the large human brain or the development of stone tools. [39] Bipedal specializations are found in Australopithecus fossils from 4.2 to 3.9 million years ago and recent studies have suggested that obligate bipedal hominid species were present as early as 7 million years ago.
Ape skeletons. A display at the Museum of Zoology, University of Cambridge.From left to right: Bornean orangutan, two western gorillas, chimpanzee, human. The evolution of human bipedalism, which began in primates approximately four million years ago, [1] or as early as seven million years ago with Sahelanthropus, [2] [3] or approximately twelve million years ago with Danuvius guggenmosi, has ...
In contrast, obligate bipedalism is where walking or running on two legs is the primary method of locomotion. Facultative bipedalism has been observed in several families of lizards and multiple species of primates, including sifakas, capuchin monkeys, baboons, gibbons, gorillas, bonobos and chimpanzees.
Analysis of the Laetoli footprints indicated the characteristics of obligate bipedalism: pronounced heel strike from deep impressions, lateral transmission of force from the heel to the base of the lateral metatarsal, a well-developed medial longitudinal arch, adducted big toe, and a deep impression for the big toe commensurate with toe-off.
Pachycephalosaurs, or "thick-headed reptiles", have primitive features that include basally small sized bodies, obligate bipedalism, and simple teeth with one row in operation at a time that are replaced as they are worn down. As they evolved, pachycephalosaurs evolved much thicker and advanced skull roofs including dome forms with horn-like ...
The post-cranial remains of australopithecines show they were adapted to bipedal locomotion, but did not walk identically to humans. They had a forearm to upper arm ratio similar to the Golden Ratio [ 15 ] [ 16 ] – greater than other hominins.
While Homo habilis was certainly bipedal, its long arms are indicative of an arboreal adaptation. [60] Homo erectus had longer legs and shorter arms, revealing a transition to obligate terrestriality, though it remains unclear how this change in relative leg length might have been an advantage. [61]
In addition to bipedal locomotion, the reduced strength of the pelvic floor due to a wider maternal pelvis also leads to fitness detriments in the mother pressuring the birth canal to remain relatively narrow. [3] [4] This idea was widely accepted when first published in 1960, but has since been criticized by other scientists. [5]