Primate and Hominin Evolution
February 11
- Time was divided into geological eras known as epochs
Paleocene (65.5 – 55.8 MYA)
Climate: hotter, more humid than modern-day
Plesiadapaformes/Plesiadapids (Paleocene primate-like mammals)
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Size of shrew to small dog; likely solitary; nocturnal; quadrupedal; good sense of smell; diet of insects and seeds; was considered a primate because of teeth and limbs (adapted those for arboreal lifestyle)
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Argument (primate or not)
- They are not primates: ① No postorbital bar; ② Claws instead of nails; ③ Eyes placed on side of head; ④ Enlarged incisors Recently
- They ARE primates: origin of primates estimated 85 MYA, but no evidence past 65 MYA
Eocene (55.8 – 33.9 MYA)
Climate: began warm, but began to drop around 50 MYA
- Brain size: Eocene primates had relatively small brain size, which implies neither arboreality nor frugivory was responsible for large brain size of modern primates
Adapidae
- 100 – 6900 grams; diurnal and nocturnal; mainly arboreal quadrupeds; smaller ones ate mainly fruit and insects; larger ones ate more fruit and leaves
Omomyidae
- 45 – 2500 grams; diurnal and nocturnal; likely specialized leapers; teeth mainly adapted for eating insects and soft fruit, though some ate leaves
Oligocene (33.9 – 23.0 MYA)
Climate: Temperature initially static, increased at the end; increase in forests
Oligocene primates
- 3 Haplorhine features: fused frontal bone; full postorbital closure; fused mandibular symphasis
- 3 Taxonomic groups: Parapithecidae; Propliopithecidae; Platyrrhini
(Propliopithecidae)
South American primates
- In late Oligocene, primates begin to appear in fossil record of South America; origins unclear, but may have “rafted” over from Africa around 35 MYA
Miocene (23.0 – 5.3 MYA)
Climate: temperatures initially warm, before gradually decreasing
- First primate evolved in this period in Africa
Monkeys & apes (e.g., Proconsul), 23.0-16.0 MYA, Africa
In Early Miocene (23.0-16.0 MYA), confined to Africa
Ape-like catarrhines (e.g., Dryopithecus), 16.0-11.6 MYA, Europe and Asia
In Mid-Miocene (16.0-11.6 MYA), widespread and diverse in Europe and Asia
Apes (e.g., Sivapithecus), 11.6-5.3 MYA
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In Late Miocene (11.6-5.3 MYA) -
Apes became rarer as woodlands & forests replaced by drier and more open habitats
Pliocene (5.3 – 1.8 MYA)
Climate: fluctuations in global temperature
Fossil Cercopithecinae and fossil Colobinae
(phylogenetic relationships unresolved)
Transitional Forms (Apes: Humans);
- Modifications of postcranial skeleton for bipedal locomotion
- Shape and size of canines(犬齿), especially in males, changes so they aren’t pointy or blade-like. Reduction in level of sexual dimorphism in canine size
- Expansion of brain
Hominins
- Modern humans, chimpanzees, and fossil species more closely related to each other than to any other living species
- First hominin fossils was found in Africa
Morphological Trends in Hominin Evolution
Mosaic evolution - major evolutionary changes tend to take place in stages, not all at once; bipedalism; increased brain size; intelligence; relative vs absolute
- Quadrupedalism vs bipedalism - difference in body and skull shape (foramen magnum, knees, hallux, hands, pelvis)
- Changes in Hominin Brain Size: large increases beginning around 1.8 MYA, after very little variation from 3.3 – 1.8 MYA
- Ardipithecus ramidus & Ardipithecus kadabba: Middle Awash, Ethiopia
Ramidus: 4.4 MYA; Kadabba: 5.8-5.6 MYA
- Teeth and fragments of various upper and lower bones; both ape-like traits (thin enamel) and hominin-like traits (canines have reduced sexual dimorphism, bipedalism)
Australopithecines afarensis 3.6 MYA & Tanzania 4.2-3.0 MYA
- The first “Real” Humans: Australopithecus afarensis: Ethiopia (Hadar, Omo, and Fejej)
- Many specimens; complex morphology exhibiting some ape-like traits (sagittal crests) and hominin-like traits (valgus knee; indicative of bipedalism)
- Either one single, sexually dimorphic species or 2 species was find 3.6 MYA in Laetoli
- They emonstrate that early hominins were bipedal (big toes hardly diverged from the rest of the foot), unlike in chimpanzees; gait was “heel strike” followed by “foot fall”
Recent Discovery: Selam (peace)
- fossilized skull & skeletal remains of 3-year-old female. Dated to 3.2 MYA
- Hyoid bone: typical ape morphology
- Foot & Lower limb remains: bipedal locomotion;
- Scapula & Hand bones: gorilla-like scapula and long and curved manual phalanges
Other Australopithecines discovery
- Gracile Australopithecines: afarensis, africanus;
- Robust Australopithecines: boisei, robustus, aethiopicus
Australopithecus sediba: Malapa, South Africa around 1.98 MYA
Discovery of 9-year-old son of researcher; juvenile male (MH1) and adult female (MH2) [controversial]
- Brain: human-like in shape, yet < brain volumes in Homo;
- Hand: good for tree-climbing, and long thumb and short fingers (precision gripping);
- Pelvis: more human-like than ape-like;
- Conclusion: unique form of upright walking, not quite like that of humans, along with some degree of tree climbing