The Vertebrate Genealogy

What is a chordate? There are 4 anatomical structures that appear during some point during the animal’s lifetime: 1. Notochord – long flexible tube between the gut and the nerve cord - becomes gelatinous material between vertebrae in humans 2. Dorsal, hollow nerve cord – becomes CNS 3. Pharyngeal slits 4. Muscular postanal tail – most chordates have a tail that extends beyond the anus

What is a chordate?

Survey of Vertebrate Classes Fishes: Agnatha, Chondrichthyes, Osteichthyes Tetrapods: Amphibia, Reptilia, Aves, Mammalia Amniotes: Reptilia, Aves, Mammalia Have a shelled water-retaining egg

Class Agnatha Sample organisms: Hagfishes, lampreys Jawless vertebrates Feed by sucking blood after clamping onto prey or by scavenging Do not have paired appendages

Class Chondrichthyes Sample organisms: sharks and rays Cartilaginous fishes – have relatively flexible skeletons made of cartilage rather than bone Most sharks are carnivorous and have acute senses

Class Osteichthyes Bony fishes Have hard skeletons (due to ossification) Sample organisms: perch, trout Breathe by drawing water over 4-5 pairs of gills covered by operculum (protective flap) Most bony fishes are oviparous Females lays large numbers of eggs, fertilization occurs externally

Class Osteichthyes

Class Amphibia The first vertebrates (tetrapods) on land Amphibians must deposit their shell-less eggs in water Sample organisms: frogs & salamanders Amphibian = “two lives” Tadpole – larval stage Metamorphosis occurs Frog – legs develop Salamanders – have tails Frogs – do not have tails

The Amniotic Egg The amniotic egg is a reproductive adaptation that allowed terrestrial vertebrates to complete their life cycles on land The shell prevents the egg from drying out 4 layers of protection: Amnion – prevents dehydration, cushions shocks Yolk Sac – stockpile of nutrients Allantois – disposal sac for certain metabolic wastes Chorion – gas exchange

Class Reptilia Sample organisms: lizards, snakes, turtles, crocodiles Reptiles have scales made of keratin that cover their skin Obtain oxygen with their lungs Fertilization occurs internally Most reptiles lay amniotic eggs on land Ectotherms – body temperature fluctuates with the environment

Class Aves Birds are tetrapods with feathers Their forelimbs are modified as wings Sample organisms: owl, sparrow, penguin, eagles Lay amniotic eggs Endothermic – regulate their own body temps. Anatomy adapted for flight Form & function

Class Mammalia Mammals have hair Endothermic Mammary glands that produce milk Most mammals are born, not hatched Three major groups: Monotremes – lay eggs platypuses, echidnas Marsupials – complete development in a maternal pouch Kangaroos, koalas, opossums Placental mammals – complete development within the uterus, joined to the mother by the placenta Sheep, bats, elephants, humans