Ch 25 Vertebrate Diversity
25.1 Vertebrate Origins
• Chordates share four features at some stage
of development.
– notochord
– hollow nerve cord
– pharyngeal slits
– tail
• Most chordates lose some or all of these
characteristics in adulthood.
• An endoskeleton allows
vertebrates to grow to large
sizes.
– internal
– made of bone or cartilage
• An endoskeleton can be
divided into four parts
–
–
–
–
braincase (cranium)
Vertebrae
Bones
gill arches (in fish and some
amphibians)
• There are seven classes of vertebrates.
– Agnatha are jawless fish.
– Cartilaginous and bony fish are characterized
by the presence of jaws.
– Amphibians are characterized by the
presence of four limbs.
– Reptiles, birds, and mammals are
characterized by the presence of an amnion.
– Birds are characterized by the presence of
feathers.
– Mammals are characterized by the presence
of hair.
• Tunicates may be the closest relatives to
vertebrates.
• The first recognizable vertebrates were
jawless fish.
• Two groups of jawless fish still exist today.
– Lampreys
– hagfish
25.2 Fish Diversity
• Dominant verts are fish
• Have gills and paired fins
• Fish use specialized organs called gills to
breathe underwater.
– sheets of thick, frilly tissue filled with capillaries
– take in dissolved oxygen from water, release
carbon dioxide
water
flow
• Countercurrent flow is the
opposite movement of water
against the flow of blood in the
fish’s gills.
• Fins are surfaces that project
from a fish’s body.
– keep fish stable
– redirect water around fish as it
swims
– help fish maneuver in water
• All fish have a lateral line system.
– sensory system
– sensitive to small changes in water
movement
• Jaws developed from gill arches
located around the pharynx.
• Jaws gave vertebrates a huge
advantage as predators.
• Cartilaginous fish and bony fish
are still in existence.
• Cartilaginous fish have
skeletons made of cartilage.
• Cartilaginous fish include the
Holocephali and
Elasmobranchs.
– Holocephali include ratfish, a
small group of deep-sea fish.
– Elasmobranchs include
sharks, rays, and skates.
• Bony fish have skeletons made of bone.
– operculum protects a bony fish’s gills
– movements of operculum help bony fish move
water over gills
25.3 A closer look at boney fishes
• Ray-finned fish have fins
supported by a fan-shaped
array of bones.
– embedded in a thin layer of skin
and connective tissue
– light, collapsible, and easy to
move
• Ray-finned fish have a variety
of body plans.
• long torpedo-shaped bodies
(barracuda)
• Ray-finned fish have a
variety of body plans.
• flattened bodies (plaice)
• Ray-finned fish have a
variety of body plans.
• elaborate camouflage (sea dragon)
• A swim bladder helps a fish float
higher or lower in the water.
• Some ray-finned fish have both lungs and
gills.
– can breathe air and survive out of water for
several hours at a time
– example: bichir found in West Africa
• Lobe-fins are paired pectoral and pelvic fins
that are round in shape.
– not as maneuverable as ray-fins
– able to support weight
• Only seven species of lobe-finned fish
exist today.
– Coelacanths
– lungfish
25.4 Amphibians
• Tetrapods are vertebrates
that have four limbs.
• Vertebrates that lack four
limbs evolved from limbed
ancestors.
• Amphibians are animals that
can live both on land and in
water.
• A number of
adaptations allow
amphibians to live
on land.
– large shoulder and
hip bones
– mobile, muscular
tongue
– middle ear
– breathe through skin
or with gills or lungs
• Amphibians use many
strategies to keep their eggs
wet.
–
–
–
–
lay eggs directly in water
lay eggs on moist ground
wrap eggs in leaves
brood eggs in pockets
on the female’s back
• Tadpoles are aquatic larvae
of frogs.
• During metamorphosis,
tadpoles develop into their
adult form.
• Not all amphibians undergo
metamorphosis.
• Amphibians are divided into 3 groups
• Salamanders have a long body, four
walking limbs, and a tail.
• There are over 300 species of
salamanders.
• Frogs are the largest amphibian group
and include toads.
• There are over 3000 species of frogs.
• Glands in the skin of frogs and toads
contain poisons that help to protect
them from predators.
• Caecilians are legless, burrowing,
tropical amphibians.
• There are 160 species of caecilians.
25.5 Vertebrates on land
• Reptiles, birds, and
mammals are adapted for
life on land.
• Amniotes are specialized Amnion
Protects
and
surrounds
to maintain moisture.
the
– An amniote develops inside
a thin, tough, membranous
sac as an embryo or fetus.
embryo
• Several characteristics help amniotes prevent
water loss.
– keratin forms a hydrophobic layer
– larger size of kidneys and intestines increases
water absorption
• The amniotic egg is an almost completely
waterproof container.
– prevents embryo from drying out as it develops
– each egg represents a large investment of energy
• Not all amniotes lay eggs.
– reptiles such as garter snakes
retain their eggs
– most mammals develop inside
the mother’s reproductive tract
• The placenta is a membranous
organ that develops in female
mammals during pregnancy.
– lines the uterine wall and
partially envelops the fetus
– carries nutrients from mother to
embryo and removes wastes