Vertebrate Evolution and Diversity Biology 201 Python vs

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

Vertebrate Evolution

First Step: Notochord is Replaced by Vertebrae

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

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

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

From Ostracoderm ancestor Primitive Jawed 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) • Switch to predation • Jaws and teeth • Gills respiratory only • Decrease armor for speed • Increase sense organs • Paired fins • gave rise to all fish

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

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

Osteichthyes –bony fish

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

Fin Rayed vs. Flesh Lobed Fish

From Flesh Lobed Fish Labyrinthodont Modern Amphibians • No scales • Thin keratinized skin • Gave rise to modern amphibians • 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

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

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 Mammal-like reptile Mammals • Endothermic • Three ear ossicles: mallus, incus and stapes • Large brain, Hair, Mammary glands Monotremes • Lay eggs • No nipples • Echidna and platypus Eutherians Metatherians • Marsupials • Young born live but premature • Complete development in pouch attached to nipple • Placental mammals with long gestations

Mammals • mammary glands • hair Egg-laying Pouched Placental