V SEMSTER ZOOLOGY 
                                                              GEOLOGICAL TIME SCALE 
                                                                                     
                                                                                     
                        Era              Period          Epoch              Million                                 Organisms evolved 
                                                                             Years 
                   Coenozoic          Quaternary  Holocene                  0.01-0           Dominance of man. Domestication of animals and 
                                                                                             agriculture. Modern genera and species evolved. 
                                                                                             Last ice age 30-40 thousand years ago. Woolly 
                                                                                             mammoth extinct. 
                                                      Pleistocene           1.5-0.1          Mass extinction. Huge floods. Ice age. Many large 
                                                                                             mammals extinct. Mastodons and woolly mammoth 
                                                                                             extinct. Prehistoric man evolved. Cave paintings.  
                                      Tertiary        Pliocene               6-1.5           Dry climate. Oceans shrink. Mammals increase 
                                                                                             specialization. Mountains rise. First hominids 
                                                                                             appear. First orchids.  
                                                      Miocene                23-6            Ice age. First man-like apes. Evolution of apes, 
                                                                                             monkeys, horse, elephant. Radiation of grazing 
                                                                                             mammals. Huge grasslands. All grass subfamilies 
                                                                                             distinct.  
                                                      Oligocene              37-23           Archaic mammals attain their maximum diversity. 
                                                                                             Creodonts (archaic carnivores) appear. First apes. 
                                                                                             Origin of grasslands.  
                                                      Eocene                 53-37           Forests of monocotyledons and flowering plants 
                                                                                             appear. Ancestors of horse, camel, elephant appear. 
                                                                                             First bats.  
                                                      Paleocene              65-53           Climate warm. Vegetation abounds. Ancestors of 
                                                                                             most modern mammals appear.  Insectivores 
                                                                                             abundant. First grasses, Rhododendrons, whales 
                                                                                             and rodents.  
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              Mesozoic      Cretaceous                               Mass extinction. 60% of tetrapod families extinct. 
                                                        135-65       Himalayas, Andes, Alps arise. Dinosaurs and 
                                                                     Ammonites extinct. First monocotyledons. First 
                                                                     marsupials and placental mammals (Pantotheres). 
                                                                     First flowering plants. Climate cool. Angiosperms 
                                                                     radiate.  
                            Jurassic                    205-135      First bird, Archaeopteryx. Dominance of dinosaurs. 
                                                                     Earliest mammals. Dicotyledons and conifers 
                                                                     common. Continents become high. Origin of insect 
                                                                     pollinators.  
                            Triassic                    250-205      Mass extinction. 80% of tetrapod families extinct. 
                                                                     Continental drift begins. Arid conditions. 
                                                                     Gymnosperms dominate. First dinosaurs. Mammal-
                                                                     like reptiles. First teleosts, first crocodiles and first 
                                                                     flying reptiles.  
              Palaeozoic    Permian                     290-250      Mass extinction. 70% of tetrapod families extinct. 
                                                                     Single land mass, Pangaea and single ocean. 
                                                                     Continents rise. Glaciations set in. Expansion of 
                                                                     reptiles, origin of Cotylosauria and Therapsida. Last 
                                                                     trilobites.  
                            Carbonife-  Pennsylva-        290        Warm and humid climate. Swamps abundant. First 
                            rous        nian                         modern soils. First reptiles. Sharks abundant. First 
                                                                     mammal-like reptiles. Earthworms. 
                                        Mississipp-                  Forests of ferns and gymnosperms. Foraminiferans 
                                        ian               350        and shell-crushing sharks abound. First winged 
                                                                     insects. Radiation of amphibians. Little seasonal 
                                                                     variations.  
                            Devonian                    410-350      Mass extinction. Arid climate. First gymnosperm 
                                                                     forests. First amphibians (Labyrinthodonts). First 
                                                                     spiders. Dominance of fishes. First ferns. First 
                                                                     vascular plants. First insects.  
                            Silurian                    440-410      Algae dominate. Land plants definite. Trilobites 
                                                                     decline. First scorpions and millipedes appear. First 
                                                                     fishes, ostracoderms and placoderms appear. 
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                             Ordovician                  510-438      Land submerged. Warm climate. Algae abound. 
                                                                      Plants invade land. First corals. First vertebrates. 
                                                                      Cephalopods and snails. First Agnatha. 
                             Cambrian                    600-510      Mass extinction. Mild climate. Marine algae. Many 
                                                                      invertebrates. Trilobites. Brachiopods. Sponges. 
                                                                      Molluscs. Explosion after mass extinction. 
               Proterozoic                              3,500-600     Primitive aquatic algae and fungi. Annelid burrows. 
                                                                      Protozoa. Oxygenation of atmosphere. Prokaryote 
                                                                      radiation. Skeleton of sponges. 
               Archeozoic                              4,600-3,500    Calcareous deposits by algae. Origin of life. Fossils 
                                                                      of cyanobacteria.  
               Solar                                   5,000-4,600    Formation of Solar system. Strong solar wind. 
                                                                      Formation of primitive atmosphere on earth. 
               Cosmic                                  20,000-5,000   Big Bang and matter synthesis. 
              
             
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