Lecture 9: Hominin Evolution and Bipedalism
Early Primate Evolution
- First primates
- Prosiman radiation (one species that diversifies into many species to fill in empty niches.
- Example lemurs and lorises)
- First Anthropoids (ancestor of early apes and humans)
- Anthropoid radiation
- First Hominoids (humans and extinct human ancestors)
- Hominoid radiation widespread distribution
Miocene Hominoid distribution
- Hominin Evolution Overview
- Hominin vs. Hominid
A group (superfamily Hominoidea) that includes humans, their fossil ancestors, and the great apes. Are more closely related to the ape/human group than the old world monkeys. They have large bodies (chimp size or bigger it's a trend for primates to get larger). Most of them are so derived and specialised to an adapted niche that they're not likely to be an ancestor to a hominoid.
- Hominins are a family (Hominidae) that includes humans and their fossil ancestors. Homo sapiens are the only remaining species left. Same term as hominid, which is just a larger group.
- Mosaic meaning evolution occurred in steps, not all at once.
- Bipedal locomotion: first step. The number one trait for a hominin is habitual bipedal walking.
- Brain encephalization (brain to body size ratio): a gradual process, where different parts of the brain got bigger.
- Cultural behaviour (seen via tools where they used sticks and fibers before stone tools).
- Hominins are always bioculturally adapting.
Hominin bipedalism - habital and obligate
- Many thing have to change before becoming bipedal.
- The ability of bipedalism makes walking more effiecient. The animal can now walk longer distances using less energy, and now has the ability to use both hands for other things while walking.
Anatomical indicators of bipedalism
- Cranium - foramen magnum
- Vertabal column (spine) - if the spine is curved to support more weight and placed right below the head, acting like a shock absorber.
- Pelvis - basin shaped to support more weight.
- Hind limb
- Femur/ knee
- Foot: big toes line up to support weight.
- The first human ancestors lived in forest/woodland areas, not complete grasslands because they still climbed trees and could only walk short distances.
Overview of Early Hominins
Possible Hominins (6.0+ - 4.4mya)
- Sahelanthropus tchadensis
- Orrorin tugenensis
- Ardipithicus (ramidus)
Australopiths (4.2 - 1.2mya)
- The longest lived hominins ever, found only in Africa. They're all fully bipedal, have small brains, low brain to body mass ratio, projecting snouts, big feet (especially in the back) and are sexually dimorphic.
- Australopithecus aferensis (4-3mya). Best known for: Lucy who was found in Hadar, 'first family,' Selam and Laetoli footprints. An early group when many other species were in existence.
- Later derived Australopiths (3.2-1.2mya). Numerous species including: graciles: A. africanus and robusts (Pranthropus): P. aethiopicus, P. boisei, P. robustus. Called robust because they were robust in the jaw, needing big muscles to chew tough plant foods, although they ate nuts, seeds, stems and some meat.
- Australopithecus sediba (2mya). Found in South Africa, and has a mixture of Australopiths and Homo features. Page 220-221.