Zoology Lecture 2 Outline Brief History of Animal Life A. Early Life on Earth B. Geological Time Scale 1. Paleozoic Era 2. Mesozoic Era 3. Cenozoic Era C. Major Milestones in Animal Evolution A. Early Life on Earth first life ~3.5 billion years ago prokaryotes → eukaryotes → simple multicellular organisms → animals, plants, fungi Oldest animal fossils: Ediacaran fossils ~600 million years (MY) old Fossil formation - mostly hard body parts preserved in deposited sediments - date fossils from age of rocks, comparison with corresponding strata in other locations B. Geological Time Scale Era Time Before Present ––-– 0 (present) –– Cenozoic –––––––––––––– –––– 65 MY ––-–Mesozoic –––––––––––––– ––– 250 MY ––-–– Paleozoic –––––––––––––– ––– 540 MY ––-–“Precambrian” C. Major Milestones 1. Cambrian Explosion - Cambrian Period, beginning of Paleozoic Era ~540 MYA - massive diversification of animal forms, nearly all major animal phyla represented Burgess Shale in B.C. Canada, fossils ~520 MY old Era Paleozoic Period *Permian Carboniferous *Devonian Silurian Ordovician *Cambrian Start End 290 MY → 250 MY* 350 MY 400 MY*
* know these periods and approximate dates
540 MY*
Early Paleozoic marked by diversification of marine invertebrates, early vertebrates - jawless fishes (ostracoderms) appear and diversify in Ordovician period - jawed fishes appear in Silurian/early Devonian period 2. Devonian Period “Age of Fishes” - diversification of jawed fishes - 3 major groups gave rise to modern fish classes: Chondrichthyes - cartilaginous fishes Actinopterygii - ray-finned fishes Sarcopterygii - lobe-finned fishes
- first amphibians (tetrapods) evolved from sarcopterygian fish (~360 MYA) - first insects Later Paleozoic Era: Carboniferous Period - diversification of amphibians, first reptiles Permian Period - mammal-like reptiles (therapsids) 3. Permian Extinction ~ 250 MYA - largest mass extinction in the fossil record > 90% of marine species and 70% of land vertebrates disappeared - mass extinctions likely caused by severe global environmental change, catastrophes - extinction events followed by new periods of diversification → adaptive radiation 4. Mesozoic Era - “Age of Reptiles” Era Mesozoic Period *Cretaceous *Jurassic *Triassic Start End 140 MY → 65 MY* 200 MY 250 MY*
- reptile groups diversified, became dominant land animals - dinosaurs evolved and diversified during Mesozoic, peak in Cretaceous period - continental drift begins - first mammals appear in Triassic period - first birds (Archaeopteryx) appear in late Jurassic 5. Cretaceous Extinction ~ 65 MYA - extinction of all dinosaurs (except birds) and many marine organisms - thought to have been caused by meteor or comet impact: Chicxulub crater 6. Cenozoic Era - “Age of Mammals” - also age of modern birds, insects, flowering plants Era Cenozoic Period *Quaternary *Tertiary Epochs Pleistocene, Holocene (5 epochs) Start End 2 MY* → present 65 MY*
Tertiary Period - diversification of mammals followed extinction of the dinosaurs - cooler, more variable climates favored mammals and birds: endotherms - evolutionary trends toward increasing size and specialization (e.g., horses, whales) - coevolution of insects and flowering plants - extensive grasslands appear ~ 25 MYA → evolution of large grazing mammals Quaternary Period Pleistocene - multiple ice ages, widespread glaciation in N. America & Eurasia - extinction of many large N.A. mammals, coincided with arrival of humans in N.A. Holocene - “Age of Humans” began ~ 10,000 years ago - high biological diversity, but declining rapidly in modern times - sixth mass extinction?