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What features the vertebrates?
Four features define chordates
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A notochord
A dorsal hollow nerve cord
A pharynx with gill slits
A tail extending past the anus
All features form in embryos
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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
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Hagfish (jawless fish): Simplest modern craniate
Vertebrate evolution
Key innovations laid the foundation for adaptive radiations of vertebrates
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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
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Cartilaginous fishes (sharks and rays)
Bony fishes
Gills present
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Not free
Body plans adapted to life in water
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Streamlined shape reduces drag
Swim bladder (in bony fishes) adjusts buoyancy
Bony fishes
The most diverse vertebrates
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Lungfishes
Lobe-finned fishes (coelacanth)
Ray-finned fishes
Amphibians
Frogs, toads, and salamanders
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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
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Water-conserving skin and kidneys
Amniote eggs (four membranes)
Active life-styles
Some amniote groups
Sauropsids
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Reptiles (including extinct dinosaurs) and birds
Anapsids
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Turtles
Synapsids
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Modern mammals and mammal-like species
Modern reptiles
Major Groups
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Turtles (shell attached to skeleton)
Lizards (the most diverse reptiles)
Snakes (limbless)
Tuataras (some amphibian-like traits; third eye)
Crocodilians (closest relatives of birds)
Reptile characteristics
General characteristics
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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
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Egg-laying mammals (monotremes)
Pouched mammals (marsupials)
Placental mammals (eutherians), the most diverse and widespread mammals
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Primate evolution
Key trends
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Better daytime vision
Upright walking (bipedalism)
More refined hand movements
Smaller teeth
Bigger brains
Social complexity (extended parental care; culture evolved in some lineages)