Transcript Document
What features the vertebrates? • Four features define chordates – A notochord – A dorsal hollow nerve cord – A pharynx with gill slits – A tail extending past the anus • All features form in embryos – May or may not persist in adults Invertebrate chordates • Ancestors • Tunicates and lancelets (marine filter-feeders) • Adult and larva Craniates • Another ancestor • Chordates with a braincase of cartilage or bone – Hagfish (jawless fish): Simplest modern craniate Vertebrate evolution • Key innovations laid the foundation for adaptive radiations of vertebrates – Vertebral column of cartilaginous or bony segments – Jaws evolved in predatory fishes – Gills evolved in water, then lungs for dry land – Paired fins were a starting point for other limbs Jawed fishes • Jawed fishes – Cartilaginous fishes (sharks and rays) – Bony fishes • Gills present – Not free • Body plans adapted to life in water – Streamlined shape reduces drag – Swim bladder (in bony fishes) adjusts buoyancy Bony fishes • The most diverse vertebrates – Lungfishes – Lobe-finned fishes (coelacanth) – Ray-finned fishes Amphibians • Frogs, toads, and salamanders – Carnivorous vertebrates – First to evolve from aquatic Devonian tetrapods – Adapted to life on land (lungs, 3-chambered heart) – Nearly all return to the water to reproduce Vanishing amphibians • Many amphibians now face extinction due to pollution and habitat loss Amniotes • First vertebrates able to complete their life cycle on dry land – Water-conserving skin and kidneys – Amniote eggs (four membranes) – Active life-styles Some amniote groups • Sauropsids – Reptiles (including extinct dinosaurs) and birds • Anapsids – Turtles • Synapsids – Modern mammals and mammal-like species Modern reptiles • Major Groups – Turtles (shell attached to skeleton) – Lizards (the most diverse reptiles) – Snakes (limbless) – Tuataras (some amphibianlike traits; third eye) – Crocodilians (closest relatives of birds) Reptile characteristics • General characteristics – Live on land or in water – Cold-blooded – Have a cloaca (opening for wastes and reproduction) – Eggs are fertilized in the body, usually laid on land Birds • Birds are the only modern animals with feathers • Birds are warm-blooded amniotes Adaptations for flight and migration • Feathers, lightweight bones, and highly efficient respiratory and circulatory systems Mammals • Animals with hair, females that nourish young with milk from mammary glands, a single lower jawbone and four kinds of teeth Modern mammals • Three major lineages – Egg-laying mammals (monotremes) – Pouched mammals (marsupials) – Placental mammals (eutherians), the most diverse and widespread mammals Primate evolution • Key trends – Better daytime vision – Upright walking (bipedalism) – More refined hand movements – Smaller teeth – Bigger brains – Social complexity (extended parental care; culture evolved in some lineages)