vertebrates

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Chapter 34
Vertebrates

• Overview: Half a Billion Years of Backbones
• By the end of the Cambrian period, some 540
million years ago
– An astonishing variety of animals inhabited
Earth’s oceans
• One of these types of animals
– Gave rise to vertebrates, one of the most
successful groups of animals

• The animals called vertebrates
– Get their name from vertebrae, the series of
bones that make up the backbone
Figure 34.1

• There are approximately 52,000 species of
vertebrates
– Which include the largest organisms ever to
live on the Earth

• Concept 34.1: Chordates have a notochord
and a dorsal, hollow nerve cord
• Vertebrates are a subphylum of the phylum
Chordata
• Chordates are bilaterian animals
– That belong to the clade of animals known as
Deuterostomia
• Two groups of invertebrate deuterostomes, the
urochordates and cephalochordates
– Are more closely related to vertebrates than to
invertebrates

• A hypothetical phylogeny of chordates
Chordates
Craniates
Vertebrates
Gnathostomes
Osteichthyans
Lobe-fins
Tetrapods
Amniotes
Milk
Amniotic egg
Legs
Lobed fins
Lungs or lung derivatives
Jaws, mineralized skeleton
Vertebral column
Head
Brain
Notochord
Ancestral deuterostome
Echinodermata
(sistergrouptochordates)
Urochordata
(tunicates)
Cephalochordata
(lancelets)
Myxini
(hagfishes)
Cephalaspidomorphi
(lampreys)
Chondrichthyes
(sharks,rays,chimaeras)
Actinopterygii
(ray-finnedfishes)
Actinistia
(coelacanths)
Dipnoi
(lungfishes)
Amphibia
(frogs,salamanders)
Reptilia
(turtles,snakes,
crocodiles,birds)
Mammalia
(mammals)
Figure 34.2

Derived Characters of Chordates
• All chordates share a set of derived characters
– Although some species possess some of these
traits only during embryonic development
Muscle
segments
Brain
Mouth
Anus
Dorsal,
hollow
nerve cord
Notochord
Muscular,
post-anal tail
Pharyngeal
slits or clefts
Figure 34.3

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

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

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
– Function as suspension-feeding structures in
many invertebrate chordates
– Are modified for gas exchange in aquatic
vertebrates
– Develop into parts of the ear, head, and neck
in terrestrial vertebrates

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

Tunicates
• Tunicates, subphylum Urochordata
– Belong to the deepest-branching lineage of
chordates
– Are marine suspension feeders commonly
called sea squirts

Figure 34.4c
• Tunicates most resemble chordates during
their larval stage
– Which may be as brief as a few minutes
Pharynx with slits
Notochord
Tail
Dorsal, hollow
nerve cord
Atrium
Stomach
Intestine
Excurrent
siphon
Incurrent
siphon
Muscle
segments
(c) A tunicate larva is a free-swimming but
nonfeeding “tadpole” in which all four
chief characters of chordates are evident.

• As an adult
– A tunicate draws in water through an incurrent
siphon, filtering food particles
(a) An adult tunicate, or
sea squirt, is a sessile
animal (photo is
approximately life-sized).
(b) In the adult, prominent
pharyngeal slits function
in suspension feeding,
but other chordate
characters are not obvious.
Tunic
Pharynx
with
numerous
slits
Atrium
Excurrent
siphon
Incurrent
siphon
to mouth
Stomach
Esophagus
Intestine
Anus
Excurrent
siphon
Figure 34.4a, b

Lancelets
• Lancelets, subphylum Cephalochordata
– Are named for their bladelike shape
Tentacle
Mouth
Pharyngeal slits
Atrium
Digestive tract
Atriopore
Segmental
muscles
Anus
Notochord
Dorsal, hollow
nerve cord
Tail
2 cm
Figure 34.5

• Lancelets are marine suspension feeders
– That retain the characteristics of the chordate
body plan as adults

Early Chordate Evolution
• The current life history of tunicates
– Probably does not reflect that of the ancestral
chordate

• Gene expression in lancelets
– Holds clues to the evolution of the vertebrate form
BF1
BF1
Otx
Otx Hox3
Hox3
Forebrain
Midbrain
Hindbrain
Nerve cord of lancelet
embryo
Brain of vertebrate embryo
(shown straightened)
Figure 34.6

• 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

Derived Characters of Craniates
• One feature unique to craniates
– Is the neural crest, a collection of cells that
appears near the dorsal margins of the closing
neural tube in an embryo
Notochord
(a) The neural crest consists of
bilateral bands of cells near
the margins of the embryonic
folds that form the neural tube.
(b) Neural crest cells migrate to
distant sites in the embryo.
Migrating neural
crest cells
Ectoderm
Ectoderm
Dorsal edges
of neural plate
Neural
crest
Neural
tube
Figure 34.7a, b

• Neural crest cells
– Give rise to a variety of structures, including
some of the bones and cartilage of the skull
(c) The cells give rise to some
of the anatomical structures
unique to vertebrates, including
some of the bones and cartilage
of the skull.
Figure 34.7c

The Origin of Craniates
• Craniates evolved at least 530 million years
ago
– During the Cambrian explosion

• The most primitive of the fossils
– Are those of the 3-cm-long Haikouella
Figure 34.8a
(a) Haikouella. Discovered in 1999 in
southern China, Haikouella had eyes
and a brain but lacked a skull, a
derived trait of craniates.

• In other Cambrian rocks
– Paleontologists have found fossils of even
more advanced chordates, such as
Haikouichthys
Figure 34.8b
(b) Haikouichthys. Haikouichthys had a
skull and thus is considered a true craniate.
5 mm

Hagfishes
• The least derived craniate lineage that still
survives
– Is class Myxini, the hagfishes
Figure 34.9
Slime glands

• Hagfishes are jawless marine craniates
– That have a cartilaginous skull and axial rod of
cartilage derived from the notochord
– That lack vertebrae

• Concept 34.3: Vertebrates are craniates that
have a backbone
• During the Cambrian period
– A lineage of craniates evolved into vertebrates

Derived Characters of Vertebrates
• Vertebrates have
– Vertebrae enclosing a spinal cord
– An elaborate skull
– Fin rays, in aquatic forms

Lampreys
• Lampreys, class Cephalaspidomorphi
– Represent the oldest living lineage of
vertebrates
– Have cartilaginous segments surrounding the
notochord and arching partly over the nerve
cord

• Lampreys are jawless vertebrates
– Inhabiting various marine and freshwater
habitats
Figure 34.10

Fossils of Early Vertebrates
• Conodonts were the first vertebrates
– With mineralized skeletal elements in their
mouth and pharynx
Dorsal view
of head
Dental
elementsFigure 34.11

• Armored, jawless vertebrates called
ostracoderms
– Had defensive plates of bone on their skin
Pteraspis
Pharyngolepis
Figure 34.12

Origins of Bone and Teeth
• Mineralization
– Appears to have originated with vertebrate
mouthparts
• The vertebrate endoskeleton
– Became fully mineralized much later

• Concept 34.4: Gnathostomes are vertebrates
that have jaws
• Today, jawless vertebrates
– Are far outnumbered by those with jaws

Derived Characters of Gnathostomes
• Gnathostomes have jaws
– That evolved from skeletal supports of the
pharyngeal slits
Mouth
Gill slits Cranium
Skeletal rods
Figure 34.13

• Other characters common to gnathostomes
include
– Enhanced sensory systems, including the
lateral line system
– An extensively mineralized endoskeleton
– Paired appendages

Fossil Gnathostomes
• The earliest gnathostomes in the fossil record
– Are an extinct lineage of armored vertebrates
called placoderms
Figure 34.14a
(a) Coccosteus, a placoderm

• Another group of jawed vertebrates called
acanthodians
– Radiated during the Devonian period
– Were closely related to the ancestors of
osteichthyans
Figure 34.14b
(b) Climatius, an acanthodian

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

• The largest and most diverse subclass of
Chondrichthyes
– Includes the sharks and rays
Figure 34.15a, b
Pectoral fins Pelvic fins
(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
their gaping mouth.

• A second subclass
– Is composed of a few dozen species of
ratfishes
Figure 34.15c
(c) Spotted ratfish (Hydrolagus colliei). Ratfishes,
or chimaeras, typically live at depths greater
than 80 m and feed on shrimps, molluscs,
and sea urchins. Some species have a poisonous
spine at the front of their dorsal fin.

• Most sharks
– Have a streamlined body and are swift
swimmers
– Have acute senses

Ray-Finned Fishes and Lobe-Fins
• The vast majority of vertebrates
– Belong to a clade of gnathostomes called
Osteichthyes

• 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

• Fishes breathe by drawing water over four or
five pairs of gills
– Located in chambers covered by a protective
bony flap called the operculum
Nostril
Brain
Spinal cord
Swim bladder
Dorsal fin Adipose fin
(characteristic of
trout)
Caudal
fin
Cut edge of
operculum Gills
Heart
Liver
Kidney
Stomach
Intestine
Gonad
Anus
Urinary
bladder
Lateral
line
Anal fin
Pelvic fin
Figure 34.16

Ray-Finned Fishes
• Class Actinopterygii, 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
(c) Sea horse (Hippocampus
ramulosus), unusual in
the animal kingdom in that
the male carries the young
during their embryonic
development
(d) Fine-spotted moray eel
(Gymnothorax dovii), a
predator that ambushes
prey from crevices in its
coral reef habitatFigure 34.17a–d

• The fins, supported mainly by long, flexible
rays
– Are modified for maneuvering, defense, and
other functions

Lobe-Fins
• The lobe-fins, class Sarcopterygii
– Have muscular and pectoral fins
– Include coelacanths, lungfishes, and tetrapods
Figure 34.18

• 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

Derived Characters of Tetrapods
• Tetrapods have some specific adaptations
– Four limbs and feet with digits
– Ears for detecting airborne sounds

The Origin of Tetrapods
• In one lineage of lobe-fins
– The fins became progressively more limb-like
while the rest of the body retained adaptations
for aquatic life
Tetrapod
limb
skeleton
Bones
supporting
gills
Figure 34.19

• Extraordinary fossil discoveries over the past
20 years
– Have allowed paleontologists to reconstruct
the origin of tetrapods
Figure 34.20
Amniotes
Amphibians
Greerpeton
Hynerpeton
lchthyostega
Acanthostega
Metaxygnathus
Elginerpeton
Eusthenopteron
Panderichthys
Lungfishes
Coelacanths
Ray-finned fishes
Paleozoic
Silurian Devonian Carboniferous Permian To
present
420 415 400 385 370 355 340 325 310 295 280 265
Millions of years ago

Amphibians
• Class Amphibia
– Is represented by about 4,800 species of
organisms
• Most amphibians
– Have moist skin that complements the lungs in
gas exchange

• Order Urodela
– Includes salamanders, which have tails
Figure 34.21a
(a) Order Urodela. Urodeles
(salamanders) retain their tail as adults.

• Order Anura
– Includes frogs and toads, which lack tails
Figure 34.21b
(b) Order Anura. Anurans, such as
this poison arrow frog, lack a tail as adults.

• Order Apoda
– Includes caecilians, which are legless and
resemble worms
Figure 34.21c
(c) Order Apoda. Apodans, or caecilians,
are legless, mainly burrowing amphibians.

• Amphibian means “two lives”
– A reference to the metamorphosis of an
aquatic larva into a terrestrial adult
Figure 34.22a–c
(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
would desiccate in air.
(b) The tadpole is
an aquatic
herbivore with
a fishlike tail and
internal gills.
(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

• A phylogeny of amniotes
Figure 34.23
Synapsids
Ancestral
amniote
Reptiles
Diapsids
Archosaurs
Saurischians
Lepidosaurs
Dinosaurs
Parareptiles
Turtles
Crocodilians
PterosaursOrnithischian
dinosaurs
Saurischian
dinosaursother
thanbirds
Birds
Plesiosaurs
Ichthyosaurs
Tuatara
Squamates
Mammals

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

• The extraembryonic membranes
– Have various functions
Figure 34.24
Shell
Albumen
Yolk (nutrients)
Amniotic cavity
with amniotic fluid
Embryo
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”).
Allantois. The allantois is a disposal
sac for certain metabolic wastes pro-
duced 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.
Extraembryonic membranes

• Amniotes also have other terrestrial
adaptations
– Such as relatively impermeable skin and the
ability to use the rib cage to ventilate the lungs

Early Amniotes
• Early amniotes
– Appeared in the Carboniferous period
– Included large herbivores and predators

Reptiles
• The reptile clade includes
– The tuatara, lizards, snakes, turtles,
crocodilians, birds, and the extinct dinosaurs

• Reptiles
– Have scales that create a waterproof barrier
– Lay shelled eggs on land
Figure 34.25

• 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

The Origin and Evolutionary Radiation of Reptiles
• The oldest reptilian fossils
– Date to about 300 million years ago
• The first major group of reptiles to emerge
– Were the parareptiles, which were mostly
large, stocky herbivores

• As parareptiles were dwindling
– The diapsids were diversifying
• The diapsids are composed of two main
lineages
– The lepidosaurs and the archosaurs

• The dinosaurs
– Diversified into a vast range of shapes and
sizes
– Included the long-necked giants called the
theropods

Figure 34.26
• Traditionally, dinosaurs were considered slow,
sluggish creatures
– But fossil discoveries and research have led to
the conclusion that dinosaurs were agile and
fast moving
• Paleontologists have also discovered signs of
parental care among dinosaurs

Lepidosaurs
• One surviving lineage of lepidosaurs
– Is represented by two species of lizard-like
reptiles called tuatara
Figure 34.27a (a) Tuatara (Sphenodon punctatus)

Figure 34.27b(b) Australian thorny devil
lizard (Moloch horridus)
• 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

• Snakes are legless lepidosaurs
– That evolved from lizards
Figure 34.27c
(c) Wagler’s pit viper (Tropidolaemus wagleri), a snake

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

• 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)

Alligators and Crocodiles
• Crocodilians
– Belong to an archosaur lineage that dates
back to the late Triassic
Figure 34.27e (e) American alligator (Alligator mississipiensis)

Birds
• Birds are archosaurs
– But almost every feature of their reptilian
anatomy has undergone modification in their
adaptation to flight

Derived Characters of Birds
• Many of the characters of birds
– Are adaptations that facilitate flight

• A bird’s most obvious adaptations for flight
– Are its wings and feathers
Figure 34.28a–c
(a) wing
(b) Bone structure
Finger 1
(c) Feather structure
Shaft
Barb
Barbule
Hook
Vane
Shaft
Forearm
Wrist
Palm
Finger 3
Finger 2

The Origin of Birds
• Birds probably descended from theropods
– A group of small, carnivorous dinosaurs

• By 150 million years ago
– Feathered theropods had evolved into birds
• Archaeopteryx
– Remains the oldest bird known
Figure 34.29
Toothed beak
Airfoil wing with
contour feathers
Long tail with
many vertebrae
Wing claw

Living Birds
• The ratites, order Struthioniformes
– Are all flightless
Figure 34.30a
(a) Emu. This ratite lives in Australia.

• The demands of flight
– Have rendered the general body form of many
flying birds similar to one another
Figure 34.30b–d
(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
to rest in place for long periods.

• Foot structure in bird feet
– Shows considerable variation
Figure 34.31
Grasping bird
(such as a
woodpecker)
Perching bird
(such as a
cardinal)
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

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

Early Evolution of Mammals
• Mammals evolved from synapsids
– In the late Triassic period

• The jaw was remodeled during the evolution of
mammals from nonmammalian synapsids
– And two of the bones that formerly made of the
jaw joint were incorporated into the
mammalian middle ear
Sound Sound
Jaw joint Jaw joint Key
Dentary
Angular
Squamosal
Articular
Quadrate
Dimetrodon Morganucodon
Dimetrodon Morganucodon
Eardrum
EardrumMiddle ear Middle earStapes Inner ear
Inner ear
Stapes
Incus (evolved
from quadrate)
Malleus (evolved
from articular)
(b) During the evolutionary remodeling of the mammalian skull, the quadrate and articular bones became incorporated
into the middle ear as two of the three bones that transmit sound from the eardrum to the inner ear. The steps in
this evolutionary remodeling are evident in a succession of fossils.
(a) The lower jaw of Dimetrodon is composed of several fused bones; two small bones, the quadrate
and articular, form part of the jaw joint. In Morganucodon, the lower jaw is reduced to a single bone,
the dentary, and the location of the jaw joint has shifted.
Figure 34.32a, b

• Living lineages of mammals originated in the
Jurassic
– But did not undergo a significant adaptive
radiation until after the Cretaceous

Monotremes
• Monotremes
– Are a small group of egg-laying mammals
consisting of echidnas and the platypus
Figure 34.33

Marsupials
• Marsupials
– Include opossums, kangaroos, and koalas

• 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
a) A young brushtail possum. The young of
marsupials are born very early in their
development. They finish their growth
while nursing from a nipple (in their
mother’s pouch in most species).

• In some species of marsupials, such as the
bandicoot
– The marsupium opens to the rear of the
mother’s body as opposed to the front, as in
other marsupials
Figure 34.34b
(b) Long-nosed bandicoot. Most bandicoots
are diggers and burrowers that eat mainly
insects but also some small vertebrates and
plant material. Their rear-opening pouch helps
protect the young from dirt as the mother digs.
Other marsupials, such as kangaroos, have a
pouch that opens to the front.

• In Australia, convergent evolution
– Has resulted in a diversity of marsupials that
resemble eutherians in other parts of the world
Figure 34.35
Marsupial mammals Eutherian mammals
Plantigale
Marsupial mole
Sugar glider
Wombat
Tasmanian devil
Kangaroo
Deer mouse
Mole
Woodchuck
Flying squirrel
Wolverine
Patagonian cavy

Eutherians (Placental Mammals)
• Compared to marsupials
– Eutherians have a longer period of pregnancy
• Young eutherians
– Complete their embryonic development within
a uterus, joined to the mother by the placenta

• Phylogenetic relationships of mammals
Figure 34.36
Ancestral mammal
Monotremes Marsupials Eutherians
Monotremata Marsupialia Xenarthra
Proboscidea Sirenia
Tubulidentata
Hyracoidea
Afrosoricida (golden
moles and tenrecs)
Macroscelidea
(elephant shrews)
Rodentia
Lagomorpha
Primates
Dermoptera
(flying lemurs)
Scandentia
(tree shrews)
Carnivora
Cetartiodactyla
Perissodactyla
Chiroptera
Eulipotyphla
Pholidota
(pangolins)
Possible phylogenetic tree of mammals.
All 20 extant orders of mammals are listed
at the top of the tree. Boldfaced orders
are explored on the facing page.
This diverse clade includes terrestrial
and marine mammals as well as bats,
the only flying mammals. A growing
body of evidence, including Eocene
fossils of whales with feet,
supports putting whales in
the same order (Cetartiodactyla)
as pigs, cows, and hippos.
This is the largest eutherian
clade. It includes the rodents,
which make up the largest
mammalian order by far, with
about 1,770 species. Humans
belong to the order Primates.
All members of this clade,
which underwent an adaptive
radiation in South America,
belong to the order Xenarthra.
One species, the nine-banded
armadillo, is found in the
southern United States.
This clade of eutherians evolved
in Africa when the continent
was isolated from other
landmasses. It includes
Earth’s largest living land
animal (the African elephant),
as well as species that weigh
less than 10 g.

• The major eutherian orders
Figure 34.36
ORDERS
AND EXAMPLES
MAIN
CHARACTERISTICS
Monotremata
Platypuses,
echidnas
Proboscidea
Elephants
Sirenia
Manatees,
dugongs
Cetartiodactyla
Artiodactyls
Sheep, pigs
cattle, deer,
giraffes
Lagomorpha
Rabbits,
hares, picas
Carnivora
Dogs, wolves,
bears, cats,
weasels, otters,
seals, walruses
Xenarthra
Sloths,
anteaters,
armadillos
Cetaceans
Whales,
dolphins,
porpoises
Echidna
African elephant
Manatee
Tamandua
Jackrabbit
Coyote
Bighorn sheep
Pacific white-
sided porpoise
Lay eggs; no
nipples; young
suck milk from
fur of mother
Long, muscular
trunk; thick,
loose skin; upper
incisors elongated
as tusks
Aquatic; finlike
forelimbs and
no hind limbs;
herbivorous
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
Sharp, pointed canine
teeth and molars for
shearing; carnivorous
Hooves with an
even number
of toes on each
foot; herbivorous
Aquatic; streamlined
body; paddle-like
forelimbs and no
hind limbs; thick
layer of insulating
blubber; carnivorous
Diet consists mainly
of insects and other
small invertebrates
Adapted for flight; broad
skinfold that extends
from elongated fingers
to body and legs;
carnivorous or
herbivorous
Hooves with an
odd number of toes
on each foot;
herbivorous
Opposable thumbs;
forward-facing eyes;
well-developed
cerebral cortex;
omnivorous
Chisel-like, continuously
growing incisors worn
down by gnawing;
herbivorous
Short legs; stumpy tail;
herbivorous; complex,
multichambered
stomach
Teeth consisting of
many thin tubes
cemented together;
eats ants and termites
Embryo completes
development in
pouch on mother
ORDERS
AND EXAMPLES
MAIN
CHARACTERISTICS
Marsupialia
Kangaroos,
opossums,
koalas
Tubulidentata
Aardvark
Hyracoidea
Hyraxes
Chiroptera
Bats
Primates
Lemurs,
monkeys,
apes,
humans
Perissodactyla
Horses,
zebras, tapirs,
rhinoceroses
Rodentia
Squirrels,
beavers, rats,
porcupines,
mice
Eulipotyphla
“Core insecti-
vores”: some
moles, some
shrews Star-nosed
mole
Frog-eating bat
Indian rhinoceros
Golden lion
tamarin
Red squirrel
Rock hyrax
Aardvark
Koala

Primates
• The mammalian order Primates include
– 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
• 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

Living Primates
• There are three main groups of living primates
– The lemurs of Madagascar and the lorises and
pottos of tropical Africa and southern Asia
Figure 34.37

– The tarsiers of Southeast Asia
– The anthropoids, which include monkeys and
hominids worldwide

• The oldest known anthropoid fossils, about 45
million years old
– Indicate that tarsiers are more closely related
to anthropoids
Figure 34.38
60
50
40
30
20
10
Millionsofyearsago
Ancestral primate
Lemurs,lorises,andpottos
Tarsiers
NewWorldmonkeys
OldWorldmonkeys
Gibbons
Orangutans
Gorillas
Chim-
panzees
Humans
Anthropoids
0

• The fossil record indicates that monkeys
– First appeared in the New World (South
America) during the Oligocene
• The first monkeys
– Evolved in the Old World (Africa and Asia)

• New World and Old World monkeys
– Underwent separate adaptive radiations during
their many millions of years of separation
Figure 34.39a, b
(a) New World monkeys, such as spider
monkeys (shown here), squirrel monkeys, and
capuchins, have a prehensile tail and nostrils
that open to the sides.
(b) Old World monkeys lack a prehensile tail, and their nostrils
open downward. This group includes macaques (shown here),
mandrills, baboons, and rhesus monkeys.

• The other group of anthropoids, the hominoids
– Consists of primates informally called apes
Figure 34.40a–e
(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.
(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.
(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.
(e) Bonobos are closely
related to chimpanzees
but are smaller. They
survive today only in the
African nation of Congo.

• Hominoids
– Diverged from Old World monkeys about 20–
25 million years ago

• Concept 34.8: Humans are bipedal hominoids
with a large brain
• Homo sapiens is about 160,000 years old
– Which is very young considering that life has
existed on Earth for at least 3.5 billion years

Derived Characters of Hominids
• A number of characters distinguish humans
from other hominoids
– Upright posture and bipedal locomotion
– Larger brains
– Language capabilities
– Symbolic thought
– The manufacture and use of complex tools
– Shortened jaw

The Earliest Humans
• The study of human origins
– Is known as paleoanthropology

• Paleoanthropologists have discovered fossils
of approximately 20 species of extinct
hominoids
– That are more closely related to humans than
to chimpanzees

• These species are known as hominids
Figure 34.41
Homo
sapiens
Homo
neanderthalensis
Homo
ergaster
?
Homo
erectus
Homo
habilis
Homo
rudolfensis
Paranthropus
robustus
Paranthropus
boisei
Australopithecus
garhi
Australopithecus
africanus
Australopithecus
afarensis
Kenyanthropus
platyops
Australopithecus
anamensis
Ardipithecus
ramidus
Orrorin tugenensis
Sahelanthropus
tchadensis
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0Millionsofyearsago

• Hominids originated in Africa
– Approximately 6–7 million years ago
• Early hominids
– Had a small brain, but probably walked upright,
exhibiting mosaic evolution

• Two common misconceptions of early
hominids include
– Thinking of them as chimpanzees
– Imagining human evolution as a ladder leading
directly to Homo sapiens

Australopiths
• Australopiths are a paraphyletic assemblage of
hominids
– That lived between 4 and 2 million years ago

• Some species walked fully erect
– And had human-like hands and teeth
Figure 34.42a–c
(a) Lucy, a 3.24-million-year-old skeleton,
represents the hominid species
Australopithecus afarensis.
(b) The Laetoli footprints, more than
3.5 million years old, confirm that
upright posture evolved quite early
in hominid history.
(c) An artist’s reconstruction of what
A. afarensis may have looked like.

Bipedalism
• Hominids began to walk long distances on two
legs
– About 1.9 million years ago

Tool Use
• The oldest evidence of tool use—cut marks on
animal bones
– Is 2.5 million years old

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”

• Homo ergaster
– Was the first fully bipedal, large-brained
hominid
– Existed between 1.9 and 1.6 million years
Figure 34.43

• Homo erectus
– Originated in Africa approximately 1.8 million
years ago
– Was the first hominid to leave Africa

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

Homo sapiens
• Homo sapiens
– Appeared in Africa at least 160,000 years ago
Figure 34.44

• The oldest fossils of Homo sapiens outside
Africa
– Date back about 50,000 years ago

• The rapid expansion of our species
– May have been preceded by changes to the
brain that made symbolic thought and other
cognitive innovations possible
Figure 34.45

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