Evolution of Multicellular Life• Precambrian - all periods before

the Paleozoic era – 90% of Earth’s History– fossil evidence is contained in

stromatolites • layers of bacteria and algae • Oxygen revolution

– Endosymbionts• Leads to multicellular animals

• Paleozoic Era• invertebrates Cambrian period

– Explosion of life!– trilobites is the most common index

fossil ~500 million years ago – Aquatic based

Paleozoic Era• Cambrian…Cambrian explosion• Ordovician & Silurian

– First vertebrates resembling suckerfish– First transition to land of both plants and animals

• Devonian… “Age of Fishes”– Insects and terrestrial arthropods appear– Massive increase in the diversity of bony fishes

• Sharks appear

• Carboniferous & Permian– Reptiles develop and start laying eggs– The animals and plants now inhabit the continents

• Mass extinction marks the end of the period– 95% of the aquatic animals dissapear

Mesozoic Era “Age of Reptiles”• Triassic

– Dominated by the survivors of the mass extinction

– First dinosaurs appear– First mammals appear

• Jurassic– Dominated by dinosaurs– First birds apear

• Cretaceous– Still dominated by reptiles (Dinosaurs)– Plants are now diverse with seed producing

flowering plants (fruit)– Turtles & crocodiles appear

• Mass extinction marks the end of the period

Cenozoic Era “Age of Mammals”• Tertiary

– Whales and Dolphins evolved– Grasses and flowering plants prompted the

development of insects and grazing animals

– Climate is warm and mild• Quaternary

– Ice ages force the movement of animals and drops the level of the oceans

– Mammoths– Early ancestors of humans arrive ~4.5 mil

years ago– Homo sapiens ~ 200,000 years ago in Africa

• Mass Extinction coming?

Cenozoic• Diversity of life

– Holocene… Historical time begins (.01mil yrs)– Pleistocene… Ice Ages… Humans appear

(1.8mil yrs)– Pliocene… Origin of genus Homo (5.3mil yrs)– Miocene… Continued radiation of species

(23mil yrs)• Apelike ancestors of humans

– Oligocene… Origin of primate groups (33.9mil yrs)

– Eocene… Angiosperms dominate (55.8mil yrs)

– Paleocene… massive radiation of mammals, birds, & insects (65.5mil yrs)