Vertebrate Evolution and Diversity Biology 351 Python vs. Alligator Python consuming deer.

Vertebrate Evolution

First Step: Notochord is Replaced by Vertebrae

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

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 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)

Chondrichthyes (Cartilage Fish) endoskeleton made of cartilage most are fast predators and extremely agile large sensory arrays (eyes, olfaction, taste, lateral line, magnetic sense) gills individually exit oral cavity

Sharks and Rays Silky shark Great White Blue Spotted Ray Sting Ray

Primitive Osteichthyian From Primitive Jawed Fish Primitive Osteichthyian Actinopterygii Air bladder (accessory resp organ) Bony skeleton Decrease bony armor Fin rays bony scales Ray Finned Fish Connection from air bladder to pharynx lost in most (bouyancy) Well developed fin rays No internal nares Gave rise to teleosts (modern bony fish) Most have an operculum

Osteichthyes –bony fish

From Primitive Jawed Fish Sacrcopterygian Internal nares Flesh lobed fins Air bladder = lungs Cosmoid scales Dipnoi: Lungfish Fin structure different from amhibians Actinistia: Coelocanths Rhipidistian Deep sea rhipidistian Bladder filled with fat Sarcopterygian with improved pectoral and pelvic bone structure for walking on bottom; less fin rays

Fin Rayed vs. Flesh Lobed Fish

Lissamphibia From Flesh Lobed Fish (Sacrcopterygii Rhipidistian) 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 Lissamphibia Modern Amphibians No scales Thin keratinized skin Gave rise to modern amphibians

Tiktaalik

Amphibians includes salamanders, newts and frogs must return to water to mate and/or lay eggs

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

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

Mammals mammary glands hair Egg-laying Pouched Placental