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Chapter 34
Vertebrates
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Overview:
• The animals called vertebrates
– Get their name from vertebrae, the series of
bones that make up the backbone
Figure 34.1
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Concept 34.1: Derived Characters of Chordates
• All chordates share a set of derived characters
– Although some species possess some of these
traits only during embryonic development
Dorsal,
hollow
nerve cord
Muscle
segments
Brain
Notochord
Mouth
Anus
Muscular,
post-anal tail
Figure 34.3
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Pharyngeal
slits or clefts
Notochord
• The notochord
– Is a longitudinal, flexible rod located between
the digestive tube and the nerve cord
– Provides skeletal support throughout most of
the length of a chordate
• In most vertebrates, a more complex, jointed
skeleton develops
– And the adult retains only remnants of the
embryonic notochord
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Dorsal, Hollow Nerve Cord
• The nerve cord of a chordate embryo
– Develops from a plate of ectoderm that rolls
into a tube dorsal to the notochord
– Develops into the central nervous system: the
brain and the spinal cord
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Pharyngeal Slits or Clefts
• In most chordates, grooves in the pharynx
called pharyngeal clefts
– Develop into slits that open to the outside of
the body
• These pharyngeal slits
– Are modified for gas exchange in aquatic
vertebrates
– Develop into parts of the ear, head, and neck
in terrestrial vertebrates
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Muscular, Post-Anal Tail
• Chordates have a tail extending posterior to the
anus
– Although in many species it is lost during
embryonic development
• The chordate tail contains skeletal elements
and muscles
– And it provides much of the propelling force in
many aquatic species
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Concept 34.2:
• Craniates are chordates that have a head
• The origin of a head
– Opened up a completely new way of feeding
for chordates: active predation
• Craniates share some common characteristics
– A skull, brain, eyes, and other sensory organs
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Concept 34.3:
• Vertebrates are craniates that have a backbone
• Vertebrates have
– Vertebrae enclosing a spinal cord
– An elaborate skull
– Fin rays, in aquatic forms
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Lampreys
• Lampreys, class Cephalaspidomorphi
– Represent the oldest living lineage of
vertebrates
– Have cartilaginous segments surrounding the
notochord and arching partly over the nerve
cord
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• Lampreys are jawless vertebrates
– Inhabiting various marine and freshwater
habitats
Figure 34.10
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Concept 34.4:
• Gnathostomes are vertebrates that have jaws
• Today, jawless vertebrates
– Are far outnumbered by those with jaws
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• Other characters common to gnathostomes
include
– Enhanced sensory systems, including the
lateral line system
– An extensively mineralized endoskeleton
– Paired appendages
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Chondrichthyans (Sharks, Rays, and Their Relatives)
• Members of class Chondrichthyes
– Have a skeleton that is composed primarily of
cartilage
• The cartilaginous skeleton
– Evolved secondarily from an ancestral
mineralized skeleton
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• The largest and most diverse subclass of
Chondrichthyes
– Includes the sharks and rays
(a) Blacktip reef shark (Carcharhinus melanopterus).
Fast swimmers with acute senses, sharks have
paired pectoral and pelvic fins.
(b) Southern stingray (Dasyatis americana).
Most rays are flattened bottom-dwellers that
crush molluscs and crustaceans for food. Some
rays cruise in open water and scoop food into
Figure 34.15a, b their gaping mouth.
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Pectoral fins
Pelvic fins
Ray-Finned Fishes and Lobe-Fins
• The vast majority of vertebrates
– Belong to a clade of gnathostomes called
Osteichthyes
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• Nearly all living osteichthyans
– Have a bony endoskeleton
• Aquatic osteichthyans
– Are the vertebrates we informally call fishes
– Control their buoyancy with an air sac known
as a swim bladder
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• Fishes breathe by drawing water over four or
five pairs of gills
Dorsal fin
Swim bladder
Nostril
Spinal cord
Brain
Cut edge of
operculum Gills
Heart
Figure 34.16
Gonad
Urinary
Anus bladder
Liver
Kidney
Stomach Pelvic fin
Intestine
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Adipose fin
(characteristic of
trout)
Caudal
fin
Anal fin
Lateral
line
Ray-Finned Fishes
• The ray-finned fishes includes nearly all the
familiar aquatic osteichthyans
(a) Yellowfin tuna (Thunnus
albacares), a fast-swimming,
schooling fish that is an important
commercial fish worldwide
(b) Clownfish (Amphiprion
ocellaris), a mutualistic
symbiont of sea anemones
Figure 34.17a–d
(c) Sea horse (Hippocampus
ramulosus), unusual in
the animal kingdom in that
the male carries the young
during their embryonic
development
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(d) Fine-spotted moray eel
(Gymnothorax dovii), a
predator that ambushes
prey from crevices in its
coral reef habitat
• The fins, supported mainly by long, flexible
rays
– Are modified for maneuvering, defense, and
other functions
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Lobe-Fins
• The lobe-fins
– Have muscle covering bones of their pelvic
and pectoral fins
– Include coelacanths, lungfishes, and tetrapods
Figure 34.18
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Concept 34.5:
• Tetrapods are gnathostomes that have limbs
and feet
• One of the most significant events in vertebrate
history
– Was when the fins of some lobe-fins evolved
into the limbs and feet of tetrapods
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Derived Characters of Tetrapods
• Tetrapods have some specific adaptations
– Four limbs and feet with digits
– Ears for detecting airborne sounds
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Amphibians
• Amphibians are represented by about 4,800
species of organisms
• Most amphibians
– Have moist skin that complements the lungs in
gas exchange
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Amphibians
• Includes salamanders, which have tails
(a) salamanders retain their tail as adults.
Figure 34.21a
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Amphibians
• Includes frogs and toads, which lack tails as
adults
Figure 34.21b
(b) poison arrow frog
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Amphibians
• Includes caecilians, which are legless and
resemble worms
(c) Caecilians, mainly burrowing amphibians.
Figure 34.21c
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Amphibians
• Amphibian means “two lives”
– A reference to the metamorphosis of an
aquatic larva into a terrestrial adult
(b) The tadpole is
an aquatic
herbivore with
a fishlike tail and
internal gills.
(a) The male grasps the female, stimulating her to
release eggs. The eggs are laid and fertilized in
water. They have a jelly coat but lack a shell and
Figure 34.22a–c would desiccate in air.
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(c) During metamorphosis, the
gills and tail are resorbed, and
walking legs develop.
Concept 34.6:
• Amniotes are tetrapods that have a terrestrially
adapted egg
• Amniotes are a group of tetrapods
– Whose living members are the reptiles,
including birds, and the mammals
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Derived Characters of Amniotes
• Amniotes are named for the major derived
character of the clade, the amniotic egg
– Which contains specialized membranes that
protect the embryo
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• The extraembryonic membranes have various
functions
Extraembryonic membranes
Allantois. The allantois is a disposal
sac for certain metabolic wastes produced by the embryo. The membrane
of the allantois also functions with
the chorion as a respiratory organ.
Amnion. The amnion protects
the embryo in a fluid-filled
cavity that cushions against
mechanical shock.
Chorion. The chorion and the membrane of the
allantois exchange gases between the embryo
and the air. Oxygen and carbon dioxide diffuse
freely across the shell.
Yolk sac. The yolk sac contains the
yolk, a stockpile of nutrients. Blood
vessels in the yolk sac membrane transport
nutrients from the yolk into the embryo.
Other nutrients are stored in the albumen (“egg white”).
Embryo
Amniotic cavity
with amniotic fluid
Yolk (nutrients)
Albumen
Shell
Figure 34.24
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• Amniotes also have other terrestrial
adaptations
– Such as relatively impermeable skin and the
ability to use the rib cage to ventilate the lungs
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Reptiles
• The reptile clade includes
– The tuatara, lizards, snakes, turtles,
crocodilians, birds, and the extinct dinosaurs
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• Reptiles
– Have scales that create a waterproof barrier
– Lay shelled eggs on land
Figure 34.25
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• Most reptiles are ectothermic
– Absorbing external heat as the main source of
body heat
• Birds are endothermic
– Capable of keeping the body warm through
metabolism
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The Origin and Evolutionary Radiation of Reptiles
• One surviving lineage of lepidosaurs
– Is represented by two species of lizard-like
reptiles called tuatara
Figure 34.27a
(a) Tuatara (Sphenodon punctatus)
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• The other major living lineage of lepidosaurs
– Are the squamates, the lizards and snakes
• Lizards
– Are the most numerous and diverse reptiles,
apart from birds
Figure 34.27b
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(b) Australian thorny devil
lizard (Moloch horridus)
• Snakes are legless lepidosaurs
– That evolved from lizards
(c) Wagler’s pit viper (Tropidolaemus wagleri), a snake
Figure 34.27c
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Turtles
• Turtles
– Are the most distinctive group of reptiles alive
today
• Some turtles have adapted to deserts
– And others live entirely in ponds and rivers
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• All turtles have a boxlike shell
– Made of upper and lower shields that are fused
to the vertebrae, clavicles, and ribs
Figure 34.27d (d) Eastern box turtle (Terrapene carolina carolina)
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Alligators and Crocodiles
• Crocodilians
– Belong to a lineage that dates back about 200
million years
Figure 34.27e (e) American alligator (Alligator mississipiensis)
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Birds
• Birds are archosaurs
– But almost every feature of their reptilian
anatomy has undergone modification in their
adaptation to flight
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Derived Characters of Birds
• A bird’s most obvious adaptations for flight
– Are its wings and feathers
Finger 1
(b) Bone structure
Palm
(a) wing
Finger 2
Forearm
Wrist
Finger 3
Shaft
Vane
Shaft
Figure 34.28a–c
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Barb
Barbule
Hook
(c) Feather structure
Living Birds
• The ratites, order Struthioniformes
– Are all flightless
(a) Emu. This ratite lives in Australia.
Figure 34.30a
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• The demands of flight
– Have rendered the general body form of many
flying birds similar to one another
(b) Mallards. Like many bird species,
the mallard exhibits pronounced color
differences between the sexes.
(c) Laysan albatrosses. Like most birds,
Laysan albatrosses have specific
mating behaviors, such as this
courtship ritual.
(d) Barn swallows. The barn swallow is a member of
the order Passeriformes. Species in this order are
called perching birds because the toes of their feet
can lock around a branch or wire, enabling the bird
Figure 34.30b–d
to rest in place for long periods.
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• Foot structure in bird feet
– Shows considerable variation
Perching bird
(such as a
cardinal)
Grasping bird
(such as a
woodpecker)
Figure 34.31
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Raptor
(such as a
bald eagle)
Swimming bird
(such as a duck)
Concept 34.7:
• Mammals are amniotes that have hair and
produce milk
• Mammals, class Mammalia
– Are represented by more than 5,000 species
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Derived Characters of Mammals
• Mammary glands, which produce milk are a
distinctively mammalian character
• Hair is another mammalian characteristic
• Mammals generally have a larger brain than other
vertebrates of equivalent size
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Monotremes
• Monotremes
– Are a small group of egg-laying mammals
consisting of echidnas and the platypus
Figure 34.33
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Marsupials
• Marsupials
– Include opossums, kangaroos, and koalas
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• A marsupial is born very early in its
development
– And completes its embryonic development
while nursing within a maternal pouch called a
marsupium
Figure 34.34a
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(a) A young brushtail possum.
Eutherians (Placental Mammals)
• Compared to marsupials
– Eutherians have a longer period of pregnancy
• Eutherians
– Complete their embryonic development within
a uterus, joined to the mother by the placenta
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The major eutherian orders
MAIN
CHARACTERISTICS
ORDERS
AND EXAMPLES
Lay eggs; no
nipples; young
suck milk from
fur of mother
Monotremata
Platypuses,
echidnas
ORDERS
AND EXAMPLES
Proboscidea
Elephants
Koala
Long, muscular
trunk; thick,
loose skin; upper
incisors elongated
as tusks
Tubulidentata
Aardvark
African elephant
Teeth consisting of
many thin tubes
cemented together;
eats ants and termites
Aardvark
Aquatic; finlike
forelimbs and
no hind limbs;
herbivorous
Sirenia
Manatees,
dugongs
Embryo completes
development in
pouch on mother
Marsupialia
Kangaroos,
opossums,
koalas
Echidna
MAIN
CHARACTERISTICS
Hyracoidea
Hyraxes
Rock hyrax
Short legs; stumpy tail;
herbivorous; complex,
multichambered
stomach
Manatee
Xenarthra
Sloths,
anteaters,
armadillos
Reduced teeth or
no teeth; herbivorous
(sloths) or carnivorous
(anteaters,
armadillos)
Rodentia
Squirrels,
beavers, rats,
porcupines,
mice
Chisel-like, continuously
growing incisors worn
down by gnawing;
herbivorous
Red squirrel
Tamandua
Lagomorpha
Rabbits,
hares, picas
Chisel-like incisors;
hind legs longer than
forelegs and adapted
for running and
jumping
Primates
Lemurs,
monkeys,
apes,
humans
Golden lion
tamarin
Jackrabbit
Carnivora
Dogs, wolves,
bears, cats,
weasels, otters,
seals, walruses
Sharp, pointed canine
teeth and molars for
shearing; carnivorous
Perissodactyla
Horses,
zebras, tapirs,
rhinoceroses
Hooves with an
even number
of toes on each
foot; herbivorous
Chiroptera
Bats
Frog-eating bat
Bighorn sheep
Cetaceans
Whales,
dolphins,
porpoises
Figure 34.36
Pacific whitesided porpoise
Hooves with an
odd number of toes
on each foot;
herbivorous
Indian rhinoceros
Coyote
Cetartiodactyla
Artiodactyls
Sheep, pigs
cattle, deer,
giraffes
Opposable thumbs;
forward-facing eyes;
well-developed
cerebral cortex;
omnivorous
Aquatic; streamlined
body; paddle-like
forelimbs and no
hind limbs; thick
layer of insulating
blubber; carnivorous
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Eulipotyphla
“Core insectivores”: some
moles, some
shrews
Adapted for flight; broad
skinfold that extends
from elongated fingers
to body and legs;
carnivorous or
herbivorous
Diet consists mainly
of insects and other
small invertebrates
Star-nosed
mole
Primates
• The mammalian order
Primates include
– Lemurs, tarsiers, monkeys,
and apes
• Humans are members of the
ape group
Figure 34.37 Lemurs
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Derived Characters of Primates
• Most primates
– Have hands and feet adapted for grasping
• Primates also have
– A large brain and short jaws
– Forward-looking eyes close together on the
face, providing depth perception
– Well-developed parental care and complex
social behavior
– A fully opposable thumb
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Hominoids (Apes)
(a) Gibbons, such as this Muller's gibbon, are
found only in southeastern Asia. Their very
long arms and fingers are adaptations for
brachiation.
(b) Orangutans are shy, solitary apes that live in the rain
forests of Sumatra and Borneo. They spend most of
their time in trees; note the foot adapted for grasping
and the opposable thumb.
Figure 34.40a–e
(d) Chimpanzees live in tropical Africa. They
feed and sleep in trees but also spend a
great deal of time on the ground. Chimpanzees
are intelligent, communicative, and social.
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(e) Bonobos are closely
related to chimpanzees
but are smaller. They
survive today only in the
African nation of Congo.
(c) Gorillas are the largest apes: some
males are almost 2 m tall and weigh
about 200 kg. Found only in Africa, these
herbivores usually live in groups of up to
about 20 individuals.
Concept 34.8:
• Humans are bipedal hominoids with a large
brain
• Homo sapiens is about 160,000 years old
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Derived Characters of Hominids
• A number of characters distinguish humans
from other hominoids
– Upright posture and bipedal locomotion
– Larger brains
– Language capabilities
– The manufacture and use of complex tools
– Shortened jaw
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The Earliest Humans
• The study of human origins
– Is known as paleoanthropology
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Hominids
Paranthropus
robustus
0
Paranthropus
boisei
0.5
1.0
Millions of years ago
2.5
3.0
3.5
Kenyanthropus
platyops
Australopithecus
garhi
5.0
Homo
Homo
rudolfensis habilis
Ardipithecus
ramidus
Australopithecus
afarensis
5.5
6.0
6.5
Figure 34.41
7.0
Homo
erectus
Australopithecus
anamensis
4.0
4.5
Homo
?
ergaster
Australopithecus
africanus
1.5
2.0
Homo
Homo
neanderthalensis sapiens
Orrorin tugenensis
Sahelanthropus
tchadensis
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• Hominids originated in Africa
– Approximately 6–7 million years ago
• Early hominids
– Had a small brain, but probably walked upright,
exhibiting mosaic evolution
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Early Homo
• The earliest fossils that paleoanthropologists
place in our genus Homo
– Are those of the species Homo habilis, ranging
in age from about 2.4 to 1.6 million years
• Stone tools have been found with H. habilis
– Giving this species its name, which means
“handy man”
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• Homo ergaster
– Was the first fully bipedal, large-brained
hominid
– Existed between 1.9 and 1.6 million years
Figure 34.43
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• Homo erectus
– Originated in Africa approximately 1.8 million
years ago
– Was the first hominid to leave Africa
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Neanderthals
• Neanderthals, Homo neanderthalensis
– Lived in Europe and the Near East from
200,000 to 30,000 years ago
– Were large, thick-browed hominids
– Became extinct a few thousand years after the
arrival of Homo sapiens in Europe
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Homo sapiens
• Homo sapiens
– Appeared in Africa at least 160,000 years ago
Figure 34.44
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