Vertebrate Evolution and Diversity Biology 201 Python consuming deer. Python vs. Alligator

Vertebrate Evolution

First Step: Notochord is Replaced by Vertebrae

Ostracoderms Stem vertebrate Dermal bony armor Jawless, free swimming, filter feeder No paired fins Cephalization present Agnathans Jawless fish cyclostomes Reduction in armor Stem Vertebrate From jawless filter feeding chordate

Agnathans (jawless fish) –first vertebrates Ostracoderms –armored jawless fish -extinct most were filter feeders, may have been able to filter sand

Notochord with some skeletal plates parasitize other fish Hagfish Living Jawless Fish

Primitive Jawed Fish Switch to predation Jaws and teeth Gills respiratory only Decrease armor for speed Increase sense organs Paired fins gave rise to all fish Placoderms -extinct Armor reduced (some to bony scales) Paired fins Cartilage skeleton Some with claspers May have given rise to Chondrichthyes -Cartilage Fish (sharks and rays) From Ostracoderm ancestor

Chondrichthyes (Cartilage Fish) endoskeleton made of cartilage most are fast predators and extremely agile large sensory arrays gills individually exit oral cavity

Primitive Bony Fish Air bladder Bony skeleton Decrease bony armor Fin rays bony scales Ray Finned Fish From Primitive Jawed Fish Well developed fin rays No internal nares Gave rise to teleosts (modern bony fish) Most have an operculum

Osteichthyes –bony fish

Sacrcopterygian Internal nares Flesh lobed fins Air bladder Rhipidistian Sarcopterygian with improved pectoral and pelvic bone structure for walking on bottom; less fin rays Coelocanths Deep sea rhipidistian Bladder filled with fat Lungfish

Fin Rayed vs. Flesh Lobed Fish

Labyrinthodont Stem amphibian Inwardly folded enamel teeth Limbs with digits Lateral line First ear bones Rayed tail Some keratinized skin Need water to reprod. Flattened skull Modern Amphibians No scales Thin keratinized skin Gave rise to modern amphibians From Flesh Lobed Fish

Amphibians includes salamanders, newts and frogs must returns to water to mate and lay eggs

Cotylosaurs Turtles Carapace and plastron composed of bone and covered by scales Anapsid skull Highly mobile neck Diapsids Synapsids Two temporal fenestrae Improved erect posture Gave rise to all other reptiles and birds Lizards, snakes Archosaurs Dinosaurs and crocodilians Single, lower temporal fenestra Canine tooth regulated body temperature leads to mammals Ex: dimetrodon Homiothermic, feathers Birds Stem reptile (anapsid) amniote egg Keratinized scales Skin impervious to water Separate pulmonary and systemic circulation Lateral movement of neck Digits tipped with claws

Amniotic Egg extra-embryonic membranes Amnion –bring pond to embryo Yolk sac – food storage Allantois –waste storage Chorion –contact with ext. environment hard outer shell impermeable to water adapted for dry environment

Reptiles Adapted for Land –amniotic egg –scales –more upright posture –hearing

Birds descendents of Archosaurs feathers homeothermic

Synapsids Therapsids Enlarged canine teeth More upright stance Heterodonts may have been homeothermic Mammals Endothermic Three ear ossicles: mallus, incus and stapes Large brain, Hair, Mammary glands Monotremes Metatherians Eutherians Lay eggs No nipples Echidna and platypus Marsupials Young born live but premature Complete development in pouch attached to nipple Placental mammals with long gestations Mammal-like reptile

mammary glands hair Mammals Egg-laying Pouched Placental