Primate Evolution/Evolution of Man
Learning Objectives
The evolution of Primates is important because it leads to the development of Man.
Characteristics of Primates:
- opposable thumb
- post orbital ridges
- binocular vision
- grasping hand
- rotating forearm
- structurally generalized form (no special adaptations such as tusks)
Primates first appear 48 million years ago. Evolutionary trends in primate development/evolution of man include:
expansion of brain
shortened snout
mobility of fingers and toes
complex social behavior
more upright stature
The primate taxonomic classification:
Order Primata:
Sub Order Prosimian: primitive, nocturnal, includes tarsiers and lemurs
Sub Order Anthropoidea: diurnal, all other primates
SuperFamily New World Monkeys: all tree dwellers, prehensile tail, include howlers, spider, tamarins
SuperFamily Old World Monkeys: tree and ground dwellers, include mandrills, baboons, macque
SuperFamily Hominoids: apes, man and his ancestors
Family Pliopithecidea: extinct
Family Oreopithecidea: extinct
Family Pongidae: great apes, include oragutangs, chimpanzees and gorillas
Family Hominid: man and his ancestors
Genus Australopithecus: ancestors to man, coexisted with genus Homo, extinct
Genus Homo: several species extinct, modern man coexisted with some of these
Time line for evolution:
48 mya: Primates split off from mammals
40 mya: Prosimians split from Anthropoids
Fossil Specimen: Proconsul 25 mya (Hominoid)
25 mya: Anthropoids split into Super Family New World, Old World and Hominoid
Fossil Specimen: Ramapithecus 12 mya, common ancestor to both Hominids and Pongidae
6-8 mya: Hominids and Pongidae split, known not from fossil evidence but protein studies
Ramapithecus: short body with long limbs; thick teeth and large canines. Ramapithecus was about the size of a baboon and is believed to have been predominantly vegetarian. Several species of Ramapithecus existed and they were successfully adapted to living in a woodland environment. Ramapithecus is thought to ba a common ancestor for both the hominids and the pongidae (great apes).
Hominids: Scientists map the proteins of different organisms to determine how different or alike these organisms are from one another. From this type of study it is believed that hominids first developed (split with great apes) about 6-8 mya. Unfortunately there are very few rock sequences that date from this time period and therefore no fossil hominid from this time period has been found. The "missing link" is still missing.
| Why did hominids develop at all?
Traditional view: the use of tools and upright stature developed simultaneously. This led to an expansion of the brain. Therefore the evolutionary response to tool use was bipedalism and brain expansion.
New view: if hominid development is examined as any other animal a new idea for hominid development emerges. The environment was changing from woodlands to grasslands. This caused a change in both diet and habitat. Therefore the evolutionary response to a change in environment (diet and habitat) is bipedalism and tool use.
Evidence: earliest tools date from ~2.5 - 3 mya yet bipedalism dates from 3.5 mya.
*Modern "knuckle walk" of gorillas did not evolve until AFTER they split with hominids* |
A partial skull exists from 4.4 mya. It is intriguing because the jaw is very ape like yet the teeth are hominid like.
Genus Australopithecus:
Australopithecus Afarensis: 3.5 mya, "Lucy", first undisputed hominid fossil. Brain 1/3 the size of modern humans (~400cc cranial capacity), 3-4 ft tall, bipedal with long arms, jaw jutted forward. Afarensis lived in open grasslands.
Australopithecus Africanus: 2-3 mya, cranial capacity ~450cc, it is believed from brain size and head position (not enough room to accommodate a voice box) that neither Afarensis or Africanus was capable of articulated speech. Teeth changing, front teeth are becoming smaller.
Australopithecus Robustus: 1.5 -2 mya, overall possessed a heavier build, face flatter and a bony crest ran along the top of the skull. This crest is believed to have been an anchor for strong jaw muscles. Very large molars, cranial capacity ~530cc.
Australopithecus Bosei (Zinjanthropus Man): 1.5 -2 mya, largest of the hominids he was similar to robustus only slightly larger in size. Cranial capacity ~530 cc. Some paleontologists suggest that Robustus and Bosei are an example of sexual dimorphism* in hominids. *sexual dimorphism is the characteristic of a species where the male is larger than the female.
Australopithecus species used rudimentary tools... bones were used but not shaped.
Genus Homo:
This genus coexisted with the Australopithecines.
Homo Habilis: 2 mya, cranial capacity ~680cc. The face was ape like but the back teeth more narrow than Australopithecus. Brain casts suggest rudimentary speech. Big brow ridges and a flat skull. Used primitive stone tools.
Homo Erectus: 1.5 mya. Some famous skeletons "Java Man" and "Peking Man" believed to be Homo Erectus skeletons. Cranial capacity ~1000cc, the first to have radiated out of Africa. Teeth smaller but skull still not modern. Lower anatomy very similar to modern mans. (Thigh bone identical) Asian skulls thicker and appear to have numerous healed fractures.
Homo Sapien Archaic: 500,000 - 250,000 ya, transition form between Homo Erectus and Homo Sapien Neanderthalensis, big brows, teeth getting smaller and brain getting bigger.
Homo Sapien Neanderthalensis: 250,000 - 125,000 ya, disappear 30 - 40,000 ya. Brain size is the same as modern humans, big brows, short in stature and stocky. Specialized bone and stone tools, burials, cave dwelling.
Homo Sapien Sapien: (Cro Magnon) Modern humans after ~35,000. Speech developed, art (cave paintings), extensive bone and stone tools, hunters of big game, domesticate animals after ~15,000 ya.
