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Ch. 34: Vertebrates
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Concept 34.1: Chordates have a notochord and
a dorsal, hollow nerve cord
 Chordates (phylum Chordata) are bilaterian animals that
belong to the clade of animals known as Deuterostomia
 Chordates comprise all vertebrates and two groups of
invertebrates, the urochordates and cephalochordates
 All chordates share a set of derived characters
 Some species have some of these traits only during
embryonic development
 Four key characters of chordates
 Notochord
 Dorsal, hollow nerve cord
 Pharyngeal slits or clefts
 Post anal tail
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Figure 34.2
Echinodermata
ANCESTRAL
DEUTEROSTOME
Chordates
Cephalochordata
Urochordata
Notochord
Common ancestor
of chordates
Vertebrates
Myxini
Petromyzontida
Jaws, mineralized skeleton
Lobe-fins
Actinistia
Lungs or lung derivatives
Dipnoi
Lobed fins
Amniotic egg
Mammalia
Milk
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Amniotes
Reptilia
Limbs with digits
Tetrapods
Amphibia
Osteichthyans
Actinopterygii
Gnathostomes
Chondrichthyes
Vertebrae
 The notochord is a longitudinal, flexible rod between
the digestive tube and nerve cord that 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 (For example, it is the gelatinous
material of the disks between the vertebrae in humans)
• The dorsal hollow nerve cord of a chordate embryo
develops from a plate of ectoderm that rolls into a tube
dorsal to the notochord. The nerve cord develops into
the central nervous system: the brain and the spinal
cord-- other animal phyla have solid nerve cords,
usually located ventrally
• Chordates have a tail posterior to the anus. The tail
contains skeletal elements and muscles. In many
species, the tail is greatly reduced during embryonic
development. It provides propelling force in many
aquatic species
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• In most chordates, grooves in the pharynx called
pharyngeal clefts develop into slits that open to the
outside of the body
• Functions of pharyngeal slits include:
• Suspension-feeding structures in many invertebrate
chordates
• Gas exchange in vertebrates (except vertebrates with
limbs, the tetrapods). Gill slits allow water that enters
the mouth to exit without continuing through the
entire digestive system
• Develop into parts of the ear, head, and neck in
tetrapods
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Figure 34.3
Notochord
Dorsal, hollow nerve cord
Muscle
segments
Mouth
Anus
Post-anal tail
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Pharyngeal slits or clefts
Lancelets (Cephalochordata) are named for
their bladelike shape
They are marine suspension feeders that retain
characteristics of the chordate body plan as
adults
They live with their posterior end buried in the
sand and the anterior end exposed for feeding
but frequently leaves its burrow to swim to a new
location.
●Rather than a full-fledged brain, lancelets have
only a slightly swollen tip on
the anterior end of the dorsal
Cirri
nerve cord.
1 cm
●
Notochord
Mouth
Dorsal, hollow
nerve cord
Pharyngeal slits
Atrium
Digestive tract
Atriopore
Segmental
muscles
Anus
Tail
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Tunicates (sea squirts) (Urochordata) are more closely related to other
chordates than are lancelets
Tunicates most resemble chordates during their larval stage, which may
last only a few minutes
Tunicates undergo a radical metamorphosis to form a sessile adult with
few chordate characteristics. Its tail and notochord are resorbed, its
nervous system degenerates, and its organs rotate 90 degrees.
As an adult, a tunicate draws in water through an incurrent siphon,
filtering food particles
When attacked, tunicates, or “sea squirts,” shoot water through their
excurrent siphon
Water flow
Notochord
Incurrent
siphon
to mouth
Excurrent
siphon
Dorsal, hollow
nerve cord
Tail
Excurrent
siphon
Incurrent
siphon
Muscle
segments
Intestine
Stomach
Atrium
Pharynx with slits
(a) A tunicate larva
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Excurrent
siphon
Anus
Intestine
Esophagus
Atrium
Pharynx
with
numerous
slits
Tunic
Stomach
(b) An adult tunicate
(c) An adult tunicate
Derived Characters of Vertebrates
 Vertebrates have two or more sets of Hox genes; lancelets
and tunicates have only one cluster
• Vertebrates have the following derived characters
•
•
•
•
•
•
•
Vertebrae enclosing a spinal cord
An elaborate skull
Complete digestive system
Large coelom,
Separate sexes and sexual reproduction are usual
Kidneys are the excretory organs
Aquatic vertebrates also have a number of adaptations
associated with faster swimming, including fins stiffened by fin
rays and a more efficient gas exchange system in the gills.
 A skeletal system and complex nervous system have
allowed vertebrates efficiency at both capturing food and
evading predators
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Hagfishes and Lampreys
 Fossil evidence shows that the earliest vertebrates lacked
jaws
 Only two lineages of jawless vertebrates remain today: the
hagfishes and the lampreys
 Members of these groups lack a backbone but do have
rudimentary vertebrae
 Together, the hagfishes and lampreys form a clade of living
jawless vertebrates, the cyclostomes
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Hagfishes
 Hagfishes (Myxini) are jawless vertebrates that have a
cartilaginous skull, reduced vertebrae, and a flexible rod of
cartilage derived from the notochord
 They have a small brain, eyes, ears, and tooth-like
formations
 Hagfishes are marine; most are bottom-dwelling
scavengers
Slime
glands
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Lampreys
• Lampreys (Petromyzontida) are parasites that feed by
clamping their mouth onto a live fish. They use their rasping
tongues to penetrate the skin of their fish prey and to ingest
the prey’s blood.
• Lampreys larvae resemble lancelets and live as suspensionfeeders in streams for years before migrating to the sea or
lakes as adults.
 They inhabit various marine and freshwater habitats
 They have cartilaginous segments surrounding the notochord
and arching partly over the nerve cord
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Gnathostomes are vertebrates that have jaws
Gnathostomes include sharks and their relatives, ray-finned
fishes, lobe-finned fishes, amphibians, reptiles (including birds),
and mammals
Gill slits
Cranium
Skeletal
rods
Modified
skeletal rods
The jaws are hypothesized to have evolved by modification of
skeletal rods that supported the pharyngeal (gill) slits
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 Other characters common to gnathostomes
 Genome duplication, including duplication of Hox
genes
 An enlarged forebrain associated with enhanced
smell and vision
 In aquatic gnathostomes, the lateral line system,
which is sensitive to vibrations
 Three lineages of jawed vertebrates survive today:
chondrichthyans, ray-finned fishes, and lobe-fins
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Chondrichthyans (Sharks, Rays, and Their
Relatives)
• Chondrichthyans (Chondrichthyes) have a skeleton
composed primarily of cartilage
• The largest and most diverse group of chondrichthyans
includes the sharks, rays, and skates
• A second subclass is composed of a few dozen species of
ratfishes, or chimaeras
• In most species, parts of the skeleton are impregnated by
calcium. Traces of bone can be found in living
chondrichthyes, in their scales, at the base of their teeth and
(in some sharks) in a thin layer on the surface of their
vertebrae.
• All have well-developed jaws and paired fins.
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Figure 34.14
Dorsal fins
Pectoral fins
Pelvic fins
(a) Blacktip reef shark
(Carcharhinus melanopterus)
(c) Spotted ratfish (Hydrolagus colliei)
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(b) Southern stingray (Dasyatis americana)
Rays:
●
●
●
Most rays are flattened bottom dwellers that crush molluscs and
crustaceans in their jaws.
The enlarged pectoral fins of rays are used like wings to propel
the animal through the water.
The tail of many rays is whiplike and may bear venomous barbs
for defense against threats.
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 Sharks have a streamlined body and are swift swimmers
 The largest sharks are suspension feeders, but most are
carnivores
 Has several rows of teeth that gradually move to the
front of the mouth as old teeth are lost
 Sharks have a short digestive tract with a ridge called the
spiral valve to increase the digestive surface area
 Sharks have acute senses including sight, smell, and the
ability to detect electrical fields from nearby animals as well
as a lateral line system-- a row of microscopic organs
sensitive to low-frequency vibrations
• The dorsal fins provide stabilization
• The reproductive tract, excretory system, and digestive
tract empty into a common cloaca
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 Shark eggs are fertilized internally but embryos
can develop in different ways
 Oviparous: Eggs hatch outside the mother’s body
 Ovoviviparous: The embryo develops within the
uterus and is nourished by the egg yolk
 Viviparous: The embryo develops within the uterus
and is nourished through a yolk sac placenta from
the mother’s blood
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Osteichthes: Ray-Finned Fishes and Lobe-Fins
 Nearly all living osteichthyans have a bony endoskeleton
 Osteichthyans include the bony fishes and tetrapods
 Most fishes breathe by drawing water over gills protected by an
operculum
 Fishes control their buoyancy with an air sac known as a swim
bladder. The positive buoyancy provided by air counters the
negative buoyancy of the tissues, enabling many fishes to be
neutrally buoyant and remain suspended in the water.
• The skin of bony fishes is often covered with thin, flattened bony
scales that differ in structure from the toothlike scales of sharks.
• Glands in the skin secrete mucus that reduces drag in
swimming.
 Fishes have a lateral line system
 Most species are oviparous, but some have internal fertilization
and birthing
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Ray-Finned Fishes
 Actinopterygii, the ray-finned fishes, include nearly all the
familiar aquatic osteichthyans
 Ray-finned fishes originated during the Silurian period (444 to
416 million years ago)
 The fins, supported mainly by long, flexible rays, are modified for
maneuvering, defense, and other functions
Lobe-Finned Fish
 The lobe-fins (Sarcopterygii) have muscular pelvic and pectoral
fins that they use to swim and “walk” underwater across the
substrate
 Three lineages survive and include coelacanths, lungfishes, and
tetrapods
 Coelacanths were thought to have become extinct 75 million
years ago, but a living coelacanth was caught off the coast of
Africa
in 1938
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Pearson Education,
Inc.
▼
Figure 34.16
Red
lionfish
(Pterois
volitans)
Yellowfin tuna (Thunnus albacares)
▼
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▼
▼
Figure 34.18 A coelacanth (Latimeria),
a lobe finned fish
Common sea
horse,
(Hippocampus
ramulosus)
Fine-spotted
moray eel,
(Gymnothorax
dovii)
Figure 34.15
Cut edge
of operculum
Swim
Spinal cord bladder
Dorsal fin
Brain
Adipose fin
(characteristic
of trout)
Caudal
fin
Nostril
Anal fin
Gills
Kidney
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Liver
Heart
Stomach
Anus
Gonad
Pelvic
Intestine
fin
Lateral line
Urinary
bladder
Concept 34.4: Tetrapods are gnathostomes that
have limbs
 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
Derived Characters of Tetrapods
 Tetrapods have some specific adaptations
 Four limbs, and feet with digits
 A neck, which allows separate movement of the head
 Fusion of the pelvic girdle to the backbone
 The absence of gills (except some aquatic species)
 Ears for detecting airborne sounds
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Amphibians: (class Amphibia)
 Amphibians are represented by about 6,150 species
 Order Anura includes frogs and toads, which lack tails. They
have powerful hind legs for locomotion on land. Frogs with
leathery skin are called “toads”
 Order Apoda includes caecilians, which are legless, nearly
blind, and resemble worms
 Order Urodela includes salamanders, which have tails. Some
are aquatic, but others live on land as adults or throughout life
Paedomorphosis, the retention of juvenile features in sexually
mature organisms, is common in aquatic species
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Figure 34.21
(b) Order Anura
(a) Order Urodela
(c) Order Apoda
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•Most amphibians have moist skin that complements the lungs
in gas exchange
•Tadpoles are usually aquatic herbivores with gills and a lateral
line system, and they swim by undulating their tails. The larvae
of salamanders and caecilians look like adults. During
metamorphosis, lungs replace gills.
•Adult frogs and toads are carnivorous hunters with a more
terrestrial habitat. Salamanders and caecilian larvae are also
carnivorous.
•There are some strictly aquatic, and some strictly terrestrial
frogs, salamanders, and caecilians. Some terrestrial species
lack lungs entirely and breathe exclusively through their skin
and oral cavity
•Amphibian populations have been declining in recent decades
 The causes include a disease-causing chytrid fungus, habitat
loss, climate change, and pollution
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• Amphibian means “both ways of life,” referring to the
metamorphosis of an aquatic larva into a terrestrial adult
• Many amphibians display social behavior, especially
during the mating season.
• It is the male that calls as they defend territory or attract
mates
• Fertilization is external in most species, and the eggs
require a moist environment
• In some species, males or
females care for the eggs on
their back, in their mouth, or
in their stomach
• Tadpoles are herbivores that
lack legs
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Figure 34.22
(a) The tadpole
(b) During metamorphosis
(c) The adults return to water to mate.
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Concept 34.5: Amniotes are tetrapods that have
a terrestrially adapted egg
 Amniotes are a group of tetrapods whose living members are
the reptiles, including birds, and mammals
 Amniotes are named for the major derived character of the
clade, the amniotic egg, which contains membranes that
protect the embryo
 The amniotic egg was a key adaptation to life on land
 The amniotic eggs of most reptiles and some mammals have a
shell
 The extraembryonic membranes are the amnion (shockabsorbing protection), chorion (gas exchange), yolk sac (stored
food), and allantois (waste storage)
 Amniotes 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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Figure 34.25
Extraembryonic membranes
Allantois
Chorion
Amniotic cavity
with amniotic fluid
Embryo
Yolk
(nutrients)
Albumen
Shell
Amnion
Yolk sac
Extraembryonic membranes
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Reptiles
 The reptile clade includes the tuataras, lizards, snakes,
turtles, crocodilians, birds, and some extinct groups
 Reptiles have scales that create a waterproof barrier
 Most reptiles lay shelled eggs on land and obtain oxygen
through lungs
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Figure 34.28
(a) Eastern box turtle (Terrapene carolina
carolina)
(d) Wagler’s pit viper
(b) Tuatara (Sphenodon punctatus)
(Tropidolaemus wagleri)
(c) Australian thorny
devil lizard
(Moloch horridus)
(e) American alligator (Alligator
mississippiensis)
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 Most reptiles are ectothermic, absorbing external
heat as the main source of body heat
 Ectotherms regulate their body temperature
through behavioral adaptations such as basking in
the sun when cool or seeking shade when hot
 Birds are endothermic, capable of maintaining
body temperature through metabolism
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 There are two main living reptilian lineages: the
lepidosaurs and the archosaurs
 Living lepidosaurs include tuataras, lizards, and snakes.
Squamates (the name of their order) are the most numerous and
diverse reptiles, apart from birds
 The archosaur lineage produced the crocodilians, (as well
as the extinct pterosaurs, the first tetrapods to exhibit
flight, and dinosaurs, including the theropods, from which
birds are descended)
 Fossil discoveries and research have led to the conclusion
that many dinosaurs were agile and fast moving, exhibited
signs of parental care for offspring, and some anatomical
evidence supports the hypothesis that at least some
dinosaurs were endotherms
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Turtles
• It is still uncertain exactly where turtle fit evolutionarily.
• All turtles have a boxlike shell made of upper (carapace)
and lower shields (plastron) that are fused to the vertebrae,
clavicles, and ribs
• Some turtles have adapted to deserts and others live entirely
in ponds and rivers
 The largest turtles live in the sea
 Many species of sea turtles are endangered by accidental
capture in fishing nets or development of beaches where
they lay eggs
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Lizards
 Characteristics:
 Most lizards have dry, scaly skin.
 Four legs, clawed feet, and a long tail, sometimes weak to
break off when grabbed by a predator
 A short neck
 External ear opening.
 Movable eyelids
 Fat is stored in the tail
 Some lizards eat bugs and spiders. Others eat plants,
small animals, or even other lizards.
 Lizards have jaws with teeth. They also have teeth on the
roof of their mouth.
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Snakes
 Snakes are legless lepidosaurs that evolved from lizards
 Snakes are carnivorous, and have adaptations to aid in
capture and consumption of prey including
 Chemical sensors- are sensitive to ground vibrations.
 Heat-detecting organs- and the flicking tongue fans odors
toward olfactory organs on the roof of the mouth.
 Venom- while not all are venomous, those that are inject
their venom through a pair of sharp, hollow or grooved teeth
 Loosely articulated jawbones and elastic skin enable most
snakes to swallow prey larger than the diameter of the
snake itself.
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Crocodilians
 Crocodilians (alligators and crocodiles) belong to an
archosaur lineage that dates back to the late Triassic
 Living crocodilians are restricted to warm regions
 Crocodilians (alligators and crocodiles) spend most of their
time in water, breathing air through upturned nostrils.
 Crocodilians are confined to the tropics and subtropics,
have narrower snouts than crocodiles and have teeth on
the outside of the mouth when closed.
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Birds
 Birds are archosaurs, but almost every feature of their
reptilian anatomy has undergone modification in their
adaptation to flight
●
One adaptation to reduce weight is the absence of some
organs. For instance, females have only one ovary. Other
adaptations include lack of a urinary bladder, small gonads,
and loss of teeth
●
The bones are air-filled and honeycombed to reduce weight
without sacrificing much strength.
●
A bird’s feathers, made of the protein keratin, have a hollow,
air-filled shaft that is light and strong.
●
Power for flapping the wings comes from contractions of the
pectoral muscles, anchored to a keel on the sternum.
• Flight enhances hunting and scavenging, escape from
terrestrial predators, and migration.
• Flying requires a great expenditure of energy with an active
metabolism.
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Figure 34.29
•Early feathers might have
evolved for insulation,
camouflage, or courtship display
Finger 1
(b) Bone structure
Palm
Finger 2
(a) Wing
Finger 3
Forearm
Vane
Shaft
Wrist
Shaft
Barb
Barbule
Hook
(c) Feather structure
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●
●
●
●
●
Birds are endothermic, using their own metabolic heat to
maintain a constant body temperature.
Efficient respiratory and circulatory systems with a fourchambered heart keep tissues well supplied with oxygen and
nutrients.
The lungs have tiny tubes leading to and from elastic air sacs
that help dissipate heat and reduce body density.
Modern birds are toothless and grind their food in a muscular
gizzard near the stomach.
The beak/ feet of birds is very adaptable, taking on a great
variety of shapes for different diets / habitats.
Birds have excellent vision and coordination, supported by
well-developed areas of the brain.
• During the breeding season, birds engage in elaborate
courtship rituals. After eggs are laid, the avian embryo is
kept warm through brooding by the mother, father, or both,
depending on the species.
●
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Living Birds
• Several groups of birds are flightless- the best known are:
• The ratites, order Struthioniformes: ostriches, kiwi,
and emus-- all lack keels and large pectoral muscles
• Penguins, order Sphenisciformes: pectoral muscles
used to swim and “wings” are flippers
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The demands of flight have rendered the
general body form of many flying birds
similar to one another
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Mammals are amniotes that have hair and
produce milk
• Mammals, Class Mammalia has more than 5,300 species
• Mammals have
• Mammary glands, which produce milk
• Hair made of keratin
• A high metabolic rate, due to endothermy
• A larger brain than other vertebrates of equivalent size
• Differentiated teeth
• Muscular diaphragm and four-chambered heart
• Longer periods of parental involvement allow for longer
time periods for offspring to learn from parents
There are three living lineages of mammals: monotremes,
marsupials, and eutherians
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Figure 34.38
www.duke.edu
Monotremes are a small
group of egg-laying
mammals consisting of
echidnas and the platypus
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Marsupials
 Marsupials include opossums, kangaroos, and koalas
 The embryo develops within a placenta in the mother’s
uterus
 A marsupial is born very early in its development
 It completes its embryonic development while nursing in a
maternal pouch called a marsupium
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Figure 34.39
animals.howstuffworks.com
animal-wildlife.blogspot.com
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(a) A young brushtail possum
(b) Long-nosed bandicoot
Figure 34.40a
Monotremes
(5 species)
Marsupials
(324 species)
ANCESTRAL
MAMMAL
Monotremata
Marsupialia
Eutherians
(5,010 species)
Proboscidea
Sirenia
Tubulidentata
Hyracoidea
Afrosoricida
Macroscelidea
Xenarthra
Rodentia
Lagomorpha
Primates
Dermoptera
Scandentia
Carnivora
Cetartiodactyla
Perissodactyla
Chiroptera
Eulipotyphla
Pholidota
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Eutherians (Placental Mammals)
 Compared with marsupials, eutherians have a
more complex placenta
 Young eutherians complete their embryonic
development within a uterus, joined to the mother
by the placenta
 Molecular and morphological data give conflicting
dates on the diversification of eutherians
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Figure 34.39
Marsupial mammals Eutherian mammals
In Australia,
convergent evolution
has resulted in a
diversity of marsupials
that resemble the
eutherians in other
parts of the world
Plantigale
Deer mouse
Marsupial
mole
Mole
Sugar
glider
Wombat
Tasmanian
devil
Kangaroo
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Flying
squirrel
Woodchuck
Wolverine
Patagonian
cavy
Figure 34.40ba
Orders and Examples
Main Characteristics
Lay eggs; no nipples;
young suck milk from
fur of mother
Monotremata
Platypuses,
echidnas
Echidna
Marsupialia
Kangaroos,
opossums,
koalas
Completes embryonic
development in pouch
on mother’s body
Koala
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Figure 34.40bb
Orders and Examples
Main Characteristics
Long, muscular trunk;
thick, loose skin; upper
incisors elongated
as tusks
Proboscidea
Elephants
African elephant
Aquatic; finlike forelimbs and no hind
limbs; herbivorous
Sirenia
Manatees,
dugongs
Manatee
Teeth consisting of
many thin tubes
cemented together;
eats ants and termites
Tubulidentata
Aardvarks
Aardvark
Hyracoidea
Hyraxes
Rock hyrax
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Short legs; stumpy
tail; herbivorous;
complex, multichambered stomach
Figure 34.40bc
Orders and Examples
Xenarthra
Sloths,
anteaters,
armadillos
Tamandua
Lagomorpha
Rabbits, hares,
picas
Jackrabbit
Main Characteristics
Reduced teeth or no
teeth; herbivorous
(sloths) or carnivorous
(anteaters, armadillos)
Chisel-like incisors;
hind legs longer than
forelegs and adapted
for running and jumping; herbivorous
Rodentia
Squirrels,
beavers,
rats, porcupines,
mice
Red squirrel
Chisel-like, continuously
growing incisors worn
down by gnawing;
herbivorous
Primates
Lemurs, monkeys,
chimpanzees,
gorillas, humans
Golden lion
tamarin
Opposable thumbs;
forward-facing eyes;
well-developed cerebral
cortex; omnivorous
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Figure 34.40bd
Orders and Examples
Carnivora
Dogs, wolves,
bears, cats,
weasels, otters,
seals, walruses
Main Characteristics
Sharp, pointed canine
teeth and molars for
shearing; carnivorous
Coyote
Cetartiodactyla
Hooves with an even
Artiodactyls:
number of toes on each
sheep, pigs,
foot; herbivorous
cattle, deer,
Bighorn sheep
giraffes
Aquatic; streamlined
Cetaceans:
body; paddle-like
whales,
forelimbs and no hind
dolphins,
limbs; thick layer of
porpoises Pacific whiteinsulating blubber;
sided porpoise carnivorous
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Figure 34.40be
Orders and Examples
Main Characteristics
Perissodactyla
Hooves with an odd
Horses, zebras,
number of toes on
tapirs,
each foot; herbivorous
rhinoceroses
Indian
rhinoceros
Chiroptera
Bats
Adapted for flight;
broad skinfold that
extends from elongated
fingers to body and
Frog-eating bat legs; carnivorous or
herbivorous
Eulipotyphla
“Core
insectivores”:
some moles,
some shrews
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Eat mainly insects
and other small
invertebrates
Star-nosed
mole
Primates
 The mammalian order Primates includes lemurs, tarsiers,
monkeys, and apes
 Humans are members of the ape group
Derived Characters of Primates
 Most primates have hands and feet adapted for grasping,
and flat nails
 A large brain and short jaws
 Forward-looking eyes close together on the face, providing
depth perception
 Complex social behavior and parental care
 A fully opposable thumb (in monkeys and apes)
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Figure 34.42
Lemurs, lorises,
and bush babies
ANCESTRAL
PRIMATE
Tarsiers
Old World monkeys
Gibbons
There are three main
groups of living primates
 Lemurs, lorises, and bush
babies
 Tarsiers
 Anthropoids (monkeys and
apes)
70
60 50 40 30 20 10
Time (millions of years ago)
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Orangutans
Gorillas
Chimpanzees
and bonobos
Humans
0
Anthropoids
New World monkeys
Apes and Monkeys
●
●
●
●
●
Monkeys are found in Africa, Asia, and South America.
The Old World and New World monkeys underwent separate
adaptive radiations.
All New World monkeys are arboreal, have flat noses open to the
sides, prehensile tails, thumbs in a scissorlike grip with the index
finger (spider monkeys lack thumbs), and males are more
involved.
Old World monkeys tolerate a much wider range of habitats from
forest to desert, have downfacing narrow noses, no prehensile
tails, sitting pads around tail region, fully prehensile thumbs, and
male involvement is rare.
Most monkeys in both groups are diurnal, and usually live in
bands held together by social behavior.
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Figure 34.43
(a) New World monkey:
spider monkey
(b) Old World monkey:
macaque
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 The other group of anthropoids consists of primates
informally called apes
 In addition to monkeys, the anthropoid suborder also
includes four genera of apes: Hylobates (gibbons), Pongo
(orangutans), Gorilla (gorillas), and Pan (chimpanzees and
bonobos) and humans
 This group includes gibbons, orangutans, gorillas,
chimpanzees, bonobos, and humans
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Figure 34.44
(a) Gibbon
(b) Orangutan
(c) Gorilla
(d) Chimpanzees
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(e) Bonobos
Derived Characters of Humans
 A number of characters distinguish humans from other apes
 Upright posture and bipedal locomotion
 Larger brains capable of language, symbolic thought,
artistic expression, the manufacture / use of complex tools
 Reduced jawbones and jaw muscles
 Shorter digestive tract
 The human and chimpanzee genomes are 99% identical.
Changes in regulatory genes can have large effects
 Hominins and chimpanzees shared a common ancestor
 Hominin evolution included many branches or coexisting
species, though only humans survive today
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