BIOLOGY 1B Lecture 12: Evolution Lecture 12
12 Jun 2018
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Lecture 12
• Cenozoic mammal radiation: mass extinction event at end of cretaceous
o Lot of organisms went extinct
o When dinosaurs went extinct, mammals entered space and radiated
▪ Challenged by molecular data
▪ Radiation started way back in Mesozoic era long before cretaceous boundary
o Rapid radiation- fossil data
▪ Molecular data does not agree with fossil data
• Long fuse model; started in Mesozoic
• Primate evolution
o Tarsius: long legs to leap and escape predators and catch prey
o Hominidae (extant hominids): includes gorilla, pan, homo
▪ Closely related
▪ Orangutan
▪ Gorilla
▪ Pan (chimpanzee and bonobo)
▪ Human
• Hominini line includes everything more closely related to humans than to
chimps; includes missing links that are more closely related to us than chimps
including anything extinct
• Darwin knew humans most closely related to gorilla
o Missing links are small morphologically
▪ Australopithecus
• 4 ft tall; small people
• Darwin proposed that they were found in Africa because that’s where the
gorillas and chimps live
• Fossil record in Ethiopia to south Africa primarily
o Dry eroding landscapes and cavesites produce fossils
o Little fossils in central Africa
▪ Jungle and forested area has a lot more rainfall; not favorable for fossilization
• Hard to see fossils; plants eat fossils when fossils reach the surface of the earth
• Discovery of australopithecines
o Found the skull in south Africa- not a chimpanzee not a human but something in between
• Hominin phylogeny
o Record goes back 6 million years
• Sahelanthropus- 7-6 Ma
o Discovered in Chad
o Found remnants of skull
o Walked on 2 legs;
o Foramen magnum position: analyzed hole in skull that connects brain to spinal cord; positioned in
a way as evidence for bipedalism- walk on 2 legs; 4 legged creatures angle was different; 2 legged
more perpendicular- shows proof for being upright
o Chad was a wetland before not a desert
▪ Habitat reconstruction
▪ Found hippopotamus and aquatic fossils
▪ Dry uplands and swampy lowlands
• Ardipithecus (5.6-4.4 Ma)
o Most important early hominin
o Well documented
o Found complete skull
o Huge fangs; reduced compared to chimpanzees and gorillas; more like humans; not far off from
bonobo
o Long arms and big hands with curved phalanges
▪ Swinging action; lived in trees
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