Chapter 11 From Hominoid to Hominin

Chapter 11 From Hominoid to Hominin - Chapter 11: From...

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Chapter 11: From Hominoid to Hominin - During the Miocene, the Earth’s temperature began to fall o The total amount of rain that fell each year declined o Rainfall became more seasonal, so there were several months each year when no rain fell o The tropical regions of Africa became drier, tropical forests shrank, and drier woodlands and grasslands expanded - Many of the Miocene ape lineages failed to adapt and became extinct o The chimp and gorilla lineages continued o The earliest hominins, our ancestors, were a few species that moved down from the trees and into the woodlands and savannas - The spread of woodland and savanna led to the evolution of the first hominins about 6 mya o Hominins appear in the fossil record starting 6 mya o Between 4 and 2 mya, the hominin lineage diversified They differed from the Miocene apes in two ways They walked upright Their teeth, skulls, and jaws changed - A number of shared derived characters distinguish modern humans from other living hominoids: bipedal locomotion, a larger brain, slower development, several features of dental morphology, and cultural adaptation o Hominins belong in our family but not our genus o Humans belong to the family Hominidae, which includes all of the great apes and the genus Homo o There are 5 traits that distinguish modern humans from contemporary apes We habitually walk bipedally Our dentition and jaw musculature are different from those of apes in a number of ways. We have a wide parabolic dental arcade, thick enamel, reduced canine teeth, and larger molars in relation to other teeth We have much larger brains in relation to our body size We develop slowly, with a long juvenile period We depend on elaborate, highly variable material and symbolic culture, transmitted in part through spoken language o Early hominins were bipedal and shared many dental features, so they are part of our subfamily But they are have different brains and different life histories, so they are not in our genus At the Beginning - The last common ancestor of humans and chimpanzees lived between 7 and 5 mya Ardipithecus - The genus Ardipithecus includes two species – A. ramidus and A. kadabba – and both have similarities to both humans and chimpanzees o Ardipithecus ramidus was found in Ethiopia and dated 4.4 mya
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o This species was a hominin The opening on the bottom of the skull through which the spinal cord passes, the foramen magnum, is located in the middle of the skull, like in humans In apes, it is located more towards the back of the skull This is associated with bipedalism, but it is not a definite indicator They have smaller, more incisorlike canine teeth that are not sharpened by the lower premolar Apes have relatively large canines that are sharpened by the first lower premolar It resembles humans in regards to teeth and arm bones It resembles apes in regards to molar size (they are smaller in relation to body size compared to other hominins), the enamel is thinner, and the canines are
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Chapter 11 From Hominoid to Hominin - Chapter 11: From...

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