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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)