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– 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– 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– 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