Vertebrates

Phylum Chordata 4 basic characteristics: Notochord – supporting rod dorsally located, below the nerve cord, replaced by vertebral column in most chordates Nerve cord – anterior portion becomes brain, rest spinal cord Pharyngeal pouches – only seen during embryonic development, gills in aquatic vertebrates. In humans, 1st pair = auditory tubes, 2nd = tonsils, 3 and 4th pair = thyroid and parathyroid Postanal tail – in embryo if not in adult

Nonvertebrate chordates Notochord persists in adults Lancelets marine, few centimeters long retain 4 chordate characteristics as adult Sea squirts (tunicates) live on ocean floor squirt water in defense Retain gills as adult

Vertebrates At some stage in life history, have all four chordate characteristics Living endoskeleton with vertebral column Closed circulatory system Paired appendages Efficient respiration and excretory High degree of cephalization

Fishes Evolution Jawless – agnathans, lamprey jaws Cartilaginous – sharks, stingrays Bony - Lobe finned – coelacanths, thought to give rise to amphibians Ray finned – soldier fish, lionfish, seahorse, swordfish

Fish Characteristics Aquatic ectotherms – depend on environment to regulate body temp Skin covered with scales Fins for swimming Single loop cardiovascular pathway, 2 chambered heart Breath with gills Lay eggs Swim bladder seen in bony fish, buoyancy

Amphibians Live on both land and water 3 main groups Salamanders and newts –elongated bodies, long tails Frogs and toads - tailless Caecilians – legless, sometimes sightless, worm shaped

Amphibian characteristics Usually tetrapod – 4 legged Usually lungs in adults Metamorphosis Smooth and moist skin 3 chambered heart Ectothermy Most lay eggs in water

Reptiles Amniotic egg evolves Extraembryonic membranes – protect the embryo, remove nitrogenous wastes and provide the embryo with oxygen, food and water Crocodiles and alligators, turtles, lizards, snakes, amphisbaenians (worm lizards) and tuataras

Reptile characteristics Usually tetrapods Lungs with expandable rib cage Leathery-sheled amniotic egg – allows for movement to land Dry, scaly skin that is impermeable to water Ectotherms – can lay in sun to maintain a warm body temperature

Birds - Aves Some fly, some do not Usually classified according to beak and foot type Efficient nervous, respiratory, and circulatory systems.

Bird characteristics Feathers Hard shelled amniotic egg 4 chambered heart Usually wings for flying Air sac endothermy

Mammals - development Monotremes – mammals have a cloaca and lay hard shelled amniote eggs Duckbill platypus and spiny anteater Marsupials – begin development inside the female body and born in a very immature condition, move to pouch and attach to nipple Kangaroo, koala, wombat Placental mammals – Eutherians - dependent on the placenta (organ of exchange between maternal blood and fetal blood) Long dependency on the parents

Mammal characteristics Body hair Differentiated teeth Well-developed brain Usually live births and newborn dependency Mammary glands Endothermy Internal development