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A nimals, par t 3 BIO101 Fall 2011 Key Terms: Chordate Notocord Craniate Vertebrate Cranium Vertebrae Gills Operculum Cartilage Amniotes Ectotherm Endotherm Tetrapod Key Questions: • Why are you considered to be a chordate even though you don’t currently possess a notocord? • What key adaptations led to animals being less dependent on water? Lecture Outline: All vertebrates are chordates chordates all have a notocord: long flexible rod between digestive tube and nerve cord also, all chordates have a hollow nerve cord located dorsally some chordates aren’t vertebrates: lancelets and tunicates Craniates are chordates that have a head head typically contains the brain at the anterior end of the dorsal nerve cord, sensory organs and a skull (cranium) most craniates are vertebrates Vertebrates – Craniates with a backbone Vertebral Column – notocord gets replaced during development by bony or cartilaginous vertebrae Endoskeleton of cartilage or bone Much more diverse internal organs. notably the liver is unique to verts earliest verts resembled lampreys – jawless fishes Jawed Vertebrates -- jawbones evolved from bones supporting gill slits Cartilaginous fishes – sharks and rays endoskeleton is cartilage, not bone. This is a derived character – these creatures lost a bony skeleton Bony fishes – most fish have a bony skeleton that falls into several clades scales on surface are covered by slimy mucus to reduce drag still use gills to breath; have an operculum to move water across the gills Tetrapods – jawed vertebrates with four limbs. 360 MYA fins evolved into limbs and feet. Adaptive radiation from here to rich species diversity! 4 limbs is a major characteristic, but there are other subtler changes. more vertebrae; no gill slits likely evolved from lungfish that did well in oxygen-poor, shallow waters Amphibians. Greek for “two lives”. Lives terrestrially, reproduce in water. For example, frogs, toads, salamanders have true lungs, but inefficient. Air is pumped from mouth to lungs. Some air absorbed thru skin juvenile tadpoles have gills until metamorphosis Amniotes – tetrapods with desiccation-resistant eggs amniotic egg – four specialed membranes including the amnion generally have a shell may be hard or leathery to greatly slow water loss other key traits of amniotes include rib cage (to inflate lungs). more efficient so don’t need to breath thru skin thus, have desiccation-resistant skin water-conserving kidneys internal fertilization Reptiles – turtles, lizards, snakes, crocodiles, dinosaurs (and birds!) scaly skin to protect from dessication internal fertilization and eggs with shells are laid on land mostly ectothermic – absorb external heat to maintain internal temp exception: birds are endothermic – capable of maintaining internal temp via metabolism Mammals – milk-producing amniotes almost all are placental
