INVERTEBRATE ZOOLOGY 



Geologic Chronology for North America 

 (Slightly modified from Lull) 



Eras 



Major divisions 



Periods 



Dominant life 



Psychozoic. 

 Coenozoic. . 



Mesozoio. 



Paleozoic. 



Late Proterozoic. . 

 Early Proterozoic. 



Archeozoic. 



Quaternary 

 Tertiary 



Late Mesozoic 

 Early Mesozoic 



Late Paleozoic or 

 Carboniferous 



Middle Paleozoic 



Early Paleozoic 



Algonkian 

 Neolaurentian 



Paleolaurcntian 



Glacial 

 Late Tertiary 

 Early Tertiary 

 Epi-Mesozoic 



interval 

 Cretaceous 



Comanchian 

 Jurassic 



Triassic 

 Epi-Paleozoic 



interval 

 Permian 



Pennsylvanian 



Mississippian 



Devonian 

 Silurian 



Ordovician 



Cambrian 



Age of man 



Age of mammals 

 Rise of archaic mammals 



Extreme specialization of 

 reptiles 



Rise of birds and flying 



reptiles 

 Rise of dinosaurs 

 Extinction of ancient life 



Rise of land vertebrates, 

 modern insects, and am- 

 monites 



Rise of insects and prim- 

 itive reptiles 



Rise of echinoderms and 

 sharks 



Rise of amphibia 



Rise of scorpions and lung 

 fishes 



Rise of corals, nautilids, 

 and armored fishes 



Rise of shelled animals and 

 dominance of trilobites 



Age of primitive marine 

 invertebrates, but very 

 few fossils known 



No fossils; probably only 

 single-celled organisms 



REPRODUCTION IN INVERTEBRATES 



Many of the early naturalists believed in spontaneous genera- 

 tion of life, that is, that non-living matter gives rise to living 

 organisms continuously. As early as the seventeenth century 

 Redi and some other leaders in science advanced evidences that 

 the more complex organisms cannot originate in this manner. 

 It is only within the past century, however, that the spontaneous 

 generation of the lower organisms was finally discredited and 

 disproved. That all life comes only from living things was only 

 then established as an axiom. Power of reproducing its like is 

 an inherent property of protoplasm which sharply differentiates 

 it from all lifeless matter. Though all forms of life possess this 



