Vertebrate Diversity

Phylum Chordata Bilateral Deuterostomes 4 characteristics Dorsal, hollow nerve cord Central nervous system Notochord Supports nerve cord, reduced in many vertebrates Pharyngeal slits Filter feeding, gills, parts of ear Post-anal tail

Chordates Lancelets Tunicates Muscle structure similar to fish in chevron shape Tunicates Only larval stage has chordate characteristics 9 hox genes instead of 13 like vertebrates Research on genetic control of brain and nerve formation

Craniates Head with brain, eyes, nerves Characteristics Neural crest becomes teeth and some nerves Pharyngeal slits become gills Muscular digestive system to support higher metabolism

Craniates Hagfishes Brain and partial skull No jaws or vertebrae Marine scavangers Slime glands to avoid being eaten

Vertebrates Backbone made of vertebrae Lampreys- no jaws Parasites of fish Problems for Great Lakes

Gnathostomes Have jaws Aquatic species have lateral line systems Sensitive to changes in water pressure Fossil gnathostomes: placoderms Armored fish Dunkleosteus: 10m long

Chondrichthyes Sharks and rays Reduced calcification of bones is derived Denser than water Oil filled liver to reduce density Suspension feeders or active predators

Chondrichthyes Rays Bottoms dwellers Predators Enhanced pectoral fin

Chondrichthyes Sharks Acute senses for predatory lifestyle Detect electric fields No eardrums, entire body receives sounds waves

Osteichthyes “bony fish” Paraphyletic without tetrapods For now, just the aquatic variety Operculum covering gills Swim bladder Evolved from lungs Scales

Bony Fish: Ray Fins Most of fish Fins supported by bony rays Evolved in freshwater and then moved to the sea Some still make this transition during life

Bony Fish: Lobe Fins Pectoral and pelvis fins have rod shaped bone surrounded by muscle. Used muscular fins to walk on land in swampy areas Only three lineages remain

Bony Fish: Lobe Fins Coelacanths Lungfishes Thought to be extinct until 1999 Lungfishes Only six species Gills and lungs to gulp air When ponds dry up, can estivate in the mud Tetrapods (next section of notes)

Tetrapods Gnathostomes with 4 limbs

Amphibians Salamanders, frogs and caecilians “double life” But not in salamanders and caecilians Damp habitats Exchange gas across skin External fertilization Some carry fertilized eggs on back

Amniotes Tetrapods with a terrestrially adapted egg Amniotic egg Amnion- fluid filled cavity to protect against physical shock Chorion- exchange gases Yolk sac- stockpile of nutrients Allantois- waste products Covered in shell or remains in mother’s body Rib cage to enhance breathing through lungs

Reptiles: Traits Scales containing keratin Shelled eggs Internal fertilization Ectothermic Derive body heat from surroundings EXCEPT birds Diapsids

Reptile Diversity Lepidosaurs Tuataras Squamates Snakes Lizards

Reptiles: Turtles Distinctive because of shield Fused to the ribs and vertebrae May be most closely related to crocodiles

Alligators and Crocodiles Appeared during Triassic Some were as big as 12m long

Reptiles: Birds Most characters are derived for function in flying Wings and feathers Efficient lungs Acute vision Larger brain Lighter bones

Mammals Amniotes that have hair and produce milk

Mammals: Diversity Monotremes Marsupials Eutherians Australia and New Guinea Platypus and echidnas Lay eggs Marsupials Give birth to live young early in development Offspring continue to develop in pouch Eutherians Offspring are born well developed