Ocean Planet & The Great Migration Life in the Paleozoic Ocean Planet & The Great Migration
Late Middle Paleozoic Early 543-248 Myr
Vertebrate Evolution From Pikaia to Cheney
Phylum Chordata Including Subphylum Vertebrata Notochord Nerve cord Pharyngeal gill slits Vertebrates Vertebral column replaces notochord & skull encloses brain
Phylogeny Reminder Fish --> Amphibians --> Reptiles --> Mammals
Think in terms of common ancestors and speciation
Fish Phylogeny
Fish: Jawless Fish (Agnatha) Cephalasphid Early Paleozoic ostracoderms. (A) Thelodus, (B) Pteraspis, (C) Jamoytius, and (D) Hemicyclaspis, drawn to the same scale.
Modern Agnatha: Sea Lamprey
Origin of Jaws
Fish: Armored Fish (Placoderms) Dunkleosteus Bothriolepis Extinct
Fish: Armored Fish (Acanthodians) Armor - a form of phosphorus storage? Extinct Acanthodes
Fish: Chondrichthyes (Cartilaginous Fish)
Modern Chondrichthyes (Sharks & Rays)
Fish: Osteichthyes (Bony Fish)
Osteichthyes: Ray Fined Subclass: Actinopterygii Rays
Ray Finned Fish Sturgeon Longnose Gar
Ray Finned Fish: Teleosts Weedy Sea Dragon 96% of today’s fish Zebrafish
Osteichthyes: Lobe Finned Subclass: Sarcopterygii
Lobe Finned Fish Coelacanth
Lobe Finned Fish Lungfish Eusthenopteron
The Great Migration (Silurian/Devonian) Plants, Insects, Vertebrates (Tetrapods)
Amphibians
Amphibians Wood Frog Eggs
Lobe Fins to Amphibians
Acanthostega (Upper Devonian)
Ichthyostega (Upper Devonian)
Advantages to Moving onto Land Lots of light for photosynthesis Easy access to oxygen and carbon dioxide Less competition Rich source of nutrients an (eventually) food Fewer predators
Challenges to Moving onto Land Conserving water - not drying out Obtaining & circulating water, food & gases Overcoming gravity Reproduction Exposure to UV
Vertebrate Solutions Conserving water - not drying out Obtaining & circulating water, food & gases Overcoming gravity Reproduction Exposure to UV Leathery skin & scales 3 or 4 chambered heart Modified skeletal arrangement Internal Fertilization & Amniotic Egg
Amniotic Egg Encloses embryo in water Regulates oxygen.carbon dioxide exchange Amniotic Egg Food Collects wastes = Freedom from Oceans
Permian Reptile Egg
Modern Reptile Skin
The Amniotes Classified based on skull structure Diapsids (Includes lizards, dinosaurs & birds)) The Amniotes Classified based on skull structure Synapsids (Includes mammals) Anapsids (Includes turtles)
Amniote Cladogram About 300 Myr
Anapsids & Diapsids (True Reptiles) Early Permian - Labidosaurus
Anapsids & Diapsids (True Reptiles)
Early Synapsids (Mammal-Like Reptiles)
Pelycosaurs (Sail Fins) Temperature control? Dimetrodon
Therapsids (Permian Synapsids) Dicynodonts Cynodont
More on Synapsid, Mammal, and Reptile Evolution in the Mesozoic…