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CAMPBELL BIOLOGY IN FOCUS
Urry • Cain • Wasserman • Minorsky • Jackson • Reece
27
The Rise of
Animal Diversity
Lecture Presentations by
Kathleen Fitzpatrick and Nicole Tunbridge
© 2014 Pearson Education, Inc.
Overview: Life Becomes Dangerous
 Most animals are mobile and use traits such as
strength, speed, toxins, or camouflage to detect,
capture, and eat other organisms
 For example, the chameleon captures insect prey with
its long, sticky, fast-moving tongue
© 2014 Pearson Education, Inc.
Figure 27.1
© 2014 Pearson Education, Inc.
Concept 27.1: Animals originated more than
700 million years ago
 Current evidence indicates that animals evolved
from single-celled eukaryotes similar to present-day
choanoflagellates
 More than 1.3 million animal species have been
named to date; the actual number of species is
estimated to be nearly 8 million
© 2014 Pearson Education, Inc.
Fossil and Molecular Evidence
 Fossil biochemical evidence and molecular clock
studies date the common ancestor of all living
animals to the period between 700 and 770 million
years ago
 Early members of the animal fossil record include
the Ediacaran biota, which dates from about 560
million years ago
© 2014 Pearson Education, Inc.
Figure 27.2
(a) Dickinsonia
2.5 cm
costata
(taxonomic affiliation
unknown)
(b) The fossil
mollusc
Kimberella
© 2014 Pearson Education, Inc.
1 cm
Figure 27.2a
(a) Dickinsonia
2.5 cm
costata
(taxonomic affiliation
unknown)
© 2014 Pearson Education, Inc.
Figure 27.2b
(b) The fossil
mollusc
Kimberella
© 2014 Pearson Education, Inc.
1 cm
Early-Diverging Animal Groups
 Sponges and cnidarians are two early-diverging
groups of animals
© 2014 Pearson Education, Inc.
Figure 27.UN01
Sponges
Cnidarians
Other animal
groups
© 2014 Pearson Education, Inc.
Sponges
 Animals in the phylum Porifera are known informally
as sponges
 Sponges are filter feeders, capturing food particles
suspended in the water that passes through their
body
 Water is drawn through pores into a central cavity
and out through an opening at the top
 Sponges lack true tissues, groups of cells that
function as a unit
© 2014 Pearson Education, Inc.
Figure 27.3
Collar
Food particles
Choanocyte
in mucus
Flagellum
Choanocyte
Phagocytosis of
food particles
Amoebocyte
Pores
Spicules
Water
flow
Amoebocytes
Azure vase sponge
(Callyspongia plicifera)
© 2014 Pearson Education, Inc.
Figure 27.3a
Azure vase sponge
(Callyspongia plicifera)
© 2014 Pearson Education, Inc.
 Choanocytes, flagellated collar cells, generate a
water current through the sponge and ingest
suspended food
 Morphological similarities between choanocytes and
choanoflagellates are consistent with the hypothesis
that animals evolved from a choanoflagellate-like
ancestor
 Amoebocytes are mobile cells that play roles in
digestion and structure
© 2014 Pearson Education, Inc.
Cnidarians
 Like most animals, members of the phylum Cnidaria
have true tissues
 Cnidarians are one of the oldest groups of animals,
dating back to 680 million years ago
 Cnidarians have diversified into a wide range of both
sessile and motile forms, including hydrozoans,
jellies, and sea anemones
© 2014 Pearson Education, Inc.
Video: Clownfish Anemone
Video: Coral Reef
Video: Hydra Budding
Video: Hydra Eating
Video: Jelly Swimming
Video: Thimble Jellies
© 2014 Pearson Education, Inc.
Figure 27.4
(a) Hydrozoa
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(b) Scyphozoa
(c) Anthozoa
Figure 27.4a
(a) Hydrozoa
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Figure 27.4b
(b) Scyphozoa
© 2014 Pearson Education, Inc.
Figure 27.4c
(c) Anthozoa
© 2014 Pearson Education, Inc.
 The basic body plan of a cnidarian is a sac with a
central digestive compartment, the gastrovascular
cavity
 A single opening functions as mouth and anus
 Cnidarians are carnivores that use tentacles to
capture prey
 Cnidarians have no brain, but instead have a
noncentralized nerve net associated with sensory
structures distributed throughout the body
© 2014 Pearson Education, Inc.
Concept 27.2: The diversity of large animals
increased dramatically during the “Cambrian
explosion”
 The Cambrian explosion (535 to 525 million years
ago) marks the earliest fossil appearance of many
major groups of living animals
© 2014 Pearson Education, Inc.
Evolutionary Change in the Cambrian Explosion
 Strata formed during the Cambrian explosion contain
the oldest fossils of about half of all extant animal
phyla
© 2014 Pearson Education, Inc.
Figure 27.5
Sponges
Cnidarians
Echinoderms
Chordates
Brachiopods
Annelids
Molluscs
Arthropods
PROTEROZOIC
Ediacaran
635
© 2014 Pearson Education, Inc.
PALEOZOIC
Cambrian
545
515
605
575
Time (millions of years age)
485 0
 Fossils from the Cambrian period include the first
hard, mineralized skeletons
 Most fossils from this period are of bilaterians, a
clade whose members have a complete digestive
tract and a bilaterally symmetric form
© 2014 Pearson Education, Inc.
Figure 27.6
1 cm
Hallucigenia fossil
(530 mya)
© 2014 Pearson Education, Inc.
Figure 27.6a
© 2014 Pearson Education, Inc.
Figure 27.6b
1 cm
Hallucigenia fossil
(530 mya)
© 2014 Pearson Education, Inc.
 There are several hypotheses regarding the cause
of the Cambrian explosion and decline of Ediacaran
biota
 New predator-prey relationships
 A rise in atmospheric oxygen
 The evolution of the Hox gene complex
© 2014 Pearson Education, Inc.
Dating the Origin of Bilaterians
 Molecular clock estimates date the bilaterians to
100 million years earlier than the oldest fossil, which
lived 560 million years ago
 The appearance of larger, well-defended eukaryotes
635–542 million years ago indicates that bilaterian
predators may have originated by that time
© 2014 Pearson Education, Inc.
Figure 27.7
15 m
(a) Valeria (800 mya):
roughly spherical, no
structural defenses,
soft-bodied
© 2014 Pearson Education, Inc.
75 m
(b) Spiny acritarch
(575 mya): about five
times larger than
Valeria and covered in
hard spines
Figure 27.7a
15 m
(a) Valeria (800 mya):
roughly spherical, no
structural defenses,
soft-bodied
© 2014 Pearson Education, Inc.
Figure 27.7b
75 m
(b) Spiny acritarch
(575 mya): about five
times larger than
Valeria and covered in
hard spines
© 2014 Pearson Education, Inc.
Concept 27.3: Diverse animal groups radiated in
aquatic environments
 Animals in the early Cambrian oceans were very
diverse in morphology, way of life, and taxonomic
affiliation
© 2014 Pearson Education, Inc.
Animal Body Plans
 Zoologists sometimes categorize animals according
to a body plan, a set of morphological and
developmental traits
 There are three important aspects of animal body
plans
 Symmetry
 Tissues
 Body cavities
© 2014 Pearson Education, Inc.
Symmetry
 Animals can be categorized according to the
symmetry of their bodies or lack of it
 Some animals have radial symmetry, with no front
and back or left and right
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Figure 27.8
(a) Radial symmetry
(b) Bilateral symmetry
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 Two-sided symmetry is called bilateral symmetry
 Bilaterally symmetrical animals have
 A dorsal (top) side and a ventral (bottom) side
 A right and left side
 Anterior (head) and posterior (tail) ends
 Many also have sensory equipment
concentrated in the anterior end, including a
brain in the head
© 2014 Pearson Education, Inc.
 Radial animals are often sessile or planktonic
(drifting or weakly swimming)
 Bilateral animals often move actively and have a
central nervous system enabling coordinated
movement
© 2014 Pearson Education, Inc.
Tissues
 Animal body plans also vary according to the
organization of the animal’s tissues
 Tissues are collections of specialized cells isolated
from other tissues by membranous layers
 During development, three germ layers give rise to
the tissues and organs of the animal embryo
© 2014 Pearson Education, Inc.
Figure 27.9
Body cavity
Body covering
(from ectoderm)
Digestive tract
(from endoderm)
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Tissue layer
lining body cavity
and suspending
internal organs
(from mesoderm)
 Ectoderm is the germ layer covering the embryo’s
surface
 Endoderm is the innermost germ layer and lines
the developing digestive tube, called the
archenteron
 Cnidarians have only these two germ layers
 Mesoderm is a third germ layer that fills the space
between the ectoderm and the endoderm in all
bilaterally symmetric animals
© 2014 Pearson Education, Inc.
Body Cavities
 Most bilaterians possess a body cavity (coelom), a
fluid- or air-filled space between the digestive tract
and the outer body wall
 The body cavity may
 Cushion suspended organs
 Act as a hydrostatic skeleton
 Enable internal organs to move independently of the
body wall
© 2014 Pearson Education, Inc.
The Diversification of Animals
 Zoologists recognize about three dozen animal
phyla
 Phylogenies now combine molecular data from
multiple sources with morphological data to
determine the relationships among animal phyla
Video: C. Elegans Crawling
Video: Earthworm Locomotion
Video: Echinoderm Tubefeet
Video: Nudibranchs
Video: Rotifer
© 2014 Pearson Education, Inc.
Figure 27.10
Porifera
Metazoa
Cnidaria
Deuterostomia
770 million
years ago
Eumetazoa
ANCESTRAL
PROTIST
Ctenophora
680 million
years ago
Echinodermata
Chordata
Lophotrochozoa
Bilateria
670 million
years ago
Hemichordata
Ecdysozoa
© 2014 Pearson Education, Inc.
Platyhelminthes
Rotifera
Ectoprocta
Brachiopoda
Mollusca
Annelida
Nematoda
Arthropoda
The following points are reflected in the animal
phylogeny
1. All animals share a common ancestor
2. Sponges are basal animals
3. Eumetazoa is a clade of animals (eumetazoans) with
true tissues
4. Most animal phyla belong to the clade Bilateria and are
called bilaterians
5. Most animals are invertebrates, lacking a backbone;
Chordata is the only phylum that includes vertebrates,
animals with a backbone
© 2014 Pearson Education, Inc.
Bilaterian Radiation I: Diverse Invertebrates
 Bilaterians have diversified into three major clades
 Lophotrochozoa
 Ecdysozoa
 Deuterostomia
© 2014 Pearson Education, Inc.
An Overview of Invertebrate Diversity
 Bilaterian invertebrates account for 95% of known
animal species
 They are morphologically diverse and occupy almost
every habitat on Earth
 This morphological diversity is mirrored by extensive
taxonomic diversity
 The vast majority of invertebrate species belong to
the Lophotrochozoa and Ecdysozoa; a few belong to
the Deuterostomia
© 2014 Pearson Education, Inc.
Figure 27.11
Lophotrochozoa
Ectoprocta
(4,500 species)
Ecdysozoa
Mollusca
(93,000 species)
Nematoda
(25,000 species)
An octopus
A roundworm
Arthropoda
(1,000,000 species)
Annelida (16,500 species)
Ectoprocts
A web-building spider
(an arachnid)
Deuterostomia
A fireworm, a marine annelid
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Hemichordata
(85 species)
An acorn worm
Echinodermata
(7,000 species)
Sea urchins and a
sea star
Figure 27.11a
Lophotrochozoa
Ectoprocta
(4,500 species)
Mollusca
(93,000 species)
An octopus
Annelida (16,500 species)
Ectoprocts
A fireworm, a marine annelid
© 2014 Pearson Education, Inc.
Figure 27.11aa
Ectoprocta
(4,500 species)
Ectoprocts
© 2014 Pearson Education, Inc.
Figure 27.11ab
Mollusca
(93,000 species)
An octopus
© 2014 Pearson Education, Inc.
Figure 27.11ac
Annelida (16,500 species)
A fireworm, a marine annelid
© 2014 Pearson Education, Inc.
Figure 27.11b
Ecdysozoa
Nematoda
(25,000 species)
Arthropoda
(1,000,000 species)
A roundworm
A web-building spider
(an arachnid)
© 2014 Pearson Education, Inc.
Figure 27.11ba
Nematoda
(25,000 species)
A roundworm
© 2014 Pearson Education, Inc.
Figure 27.11bb
Arthropoda
(1,000,000 species)
A web-building spider
(an arachnid)
© 2014 Pearson Education, Inc.
Figure 27.11c
Deuterostomia
Hemichordata
(85 species)
An acorn worm
© 2014 Pearson Education, Inc.
Echinodermata
(7,000 species
Sea urchins and a
sea star
Figure 27.11ca
Hemichordata
(85 species)
An acorn worm
© 2014 Pearson Education, Inc.
Figure 27.11cb
Echinodermata
(7,000 species)
Sea urchins and a
sea star
© 2014 Pearson Education, Inc.
Arthropod Origins
 Two out of every three known species of animals
are arthropods
 Members of the phylum Arthropoda are found in
nearly all habitats of the biosphere
© 2014 Pearson Education, Inc.
 The arthropod body plan consists of a segmented
body, hard exoskeleton, and jointed appendages
 This body plan dates to the Cambrian explosion
(535–525 million years ago)
 Early arthropods show little variation from segment
to segment
© 2014 Pearson Education, Inc.
Figure 27.UN02
A fossil trilobite
© 2014 Pearson Education, Inc.
 Arthropod evolution is characterized by a decrease
in the number of segments and an increase in
appendage specialization
 These changes may have been caused by changes
in Hox gene sequence or regulation
© 2014 Pearson Education, Inc.
Figure 27.12
Experiment
Origin of Ubx and
abd-A Hox genes?
Other
ecdysozoans
Arthropods
Common ancestor
Onychophorans
Results
Red indicates regions
in which Ubx or
abd-A genes were
expressed.
Ant  antenna
J  jaws
L1–L15  body segments
© 2014 Pearson Education, Inc.
Figure 27.12a
Results
Red indicates regions
in which Ubx or
abd-A genes were
expressed.
Ant  antenna
J  jaws
L1–L15  body segments
© 2014 Pearson Education, Inc.
Bilaterian Radiation II: Aquatic Vertebrates
 The appearance of large predatory animals and the
explosive radiation of bilaterian invertebrates
radically altered life in the oceans
 One type of animal gave rise to vertebrates, one of
the most successful groups of animals
© 2014 Pearson Education, Inc.
Figure 27.13
© 2014 Pearson Education, Inc.
 The animals called vertebrates get their name from
vertebrae, the series of bones that make up the
backbone
 Vertebrates are members of phylum Chordata
 Chordates are bilaterian animals that belong to the
clade of animals known as Deuterostomia
© 2014 Pearson Education, Inc.
Early Chordate Evolution
 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, a flexible rod providing support
 Dorsal, hollow nerve cord
 Pharyngeal slits or pharyngeal clefts, which function
in filter feeding, as gills, or as parts of the head
 Muscular, post-anal tail
© 2014 Pearson Education, Inc.
Video: Clownfish Anemone
Video: Coral Reef
Video: Manta Ray
Video: Sea Horses
© 2014 Pearson Education, Inc.
Figure 27.14
Notochord
Dorsal, hollow nerve cord
Muscle
segments
Mouth
Anus
Post-anal tail
© 2014 Pearson Education, Inc.
Pharyngeal slits or clefts
 Lancelets are a basal group of extant, blade-shaped
animals that closely resemble the idealized chordate
 Tunicates are another early diverging chordate
group, but they only display key chordate traits
during their larval stage
 The ancestral chordate may have looked similar to a
lancelet
© 2014 Pearson Education, Inc.
Figure 27.15
(a) Lancelet
© 2014 Pearson Education, Inc.
(b) Tunicate
Figure 27.15a
(a) Lancelet
© 2014 Pearson Education, Inc.
Figure 27.15b
(b) Tunicate
© 2014 Pearson Education, Inc.
 In addition to the features of all chordates, early
vertebrates had a backbone and a well-defined head
with sensory organs and a skull
 Fossils representing the transition to vertebrates
formed during the Cambrian explosion
© 2014 Pearson Education, Inc.
The Rise of Vertebrates
 Early vertebrates were more efficient at capturing
food and evading predators than their ancestors
 The earliest vertebrates were conodonts, softbodied, jawless animals that hunted prey using a set
of barbed hooks in their mouth
 There are only two extant lineages of jawless
vertebrates, the hagfishes and lampreys
© 2014 Pearson Education, Inc.
Figure 27.16
Common
ancestor of
vertebrates
Vertebrates
Myxini
(hagfishes)
Petromyzontida
(lampreys)
Chondrichthyes
© 2014 Pearson Education, Inc.
Dipnoi
(lungfishes)
Tetrapoda
(amphibians,
reptiles,
mammals)
Osteichthyans
Limbs with digits
Actinistia
(coelacanths)
Myxini
Dipnoi
Tetrapods
Lobed
fins
Actinopterygii
(ray-finned fishes)
Lobe-fins
Jaws,
mineralized
skeleton
Lungs
or lung derivatives
Gnathostomes
Chondrichthyes
(sharks, rays, chimaeras)
Vertebral
column
Actinopterygii
Petromyzontida
Actinistia
Tetrapoda
Figure 27.16a
Common
ancestor of
vertebrates
Vertebrates
Myxini
(hagfishes)
Petromyzontida
(lampreys)
© 2014 Pearson Education, Inc.
Tetrapoda
(amphibians,
reptiles,
mammals)
Osteichthyans
Limbs with digits
Dipnoi
(lungfishes)
Tetrapods
Lobed
fins
Actinistia
(coelacanths)
Lobe-fins
Jaws,
mineralized
skeleton
Lungs
or lung derivatives
Actinopterygii
(ray-finned fishes)
Gnathostomes
Chondrichthyes
(sharks, rays, chimaeras)
Vertebral
column
Figure 27.16b
Myxini
Actinopterygii
Actinistia
Petromyzontida
Dipnoi
Tetrapoda
Chondrichthyes
© 2014 Pearson Education, Inc.
Figure 27.16ba
Myxini
© 2014 Pearson Education, Inc.
Figure 27.16bb
Petromyzontida
© 2014 Pearson Education, Inc.
Figure 27.16bba
© 2014 Pearson Education, Inc.
Figure 27.16bbb
© 2014 Pearson Education, Inc.
Figure 27.16bc
Chondrichthyes
© 2014 Pearson Education, Inc.
Figure 27.16bd
Actinopterygii
© 2014 Pearson Education, Inc.
Figure 27.16be
Actinistia
© 2014 Pearson Education, Inc.
Figure 27.16bf
Dipnoi
© 2014 Pearson Education, Inc.
Figure 27.16bg
Tetrapoda
© 2014 Pearson Education, Inc.
 Today, jawed vertebrates, or gnathostomes,
outnumber jawless vertebrates
 Early gnathostome success is likely due to
adaptations for predation including paired fins and
tails for efficient swimming and jaws for grasping
prey
Video: Lobster Mouth Parts
© 2014 Pearson Education, Inc.
Figure 27.17
0.5 m
© 2014 Pearson Education, Inc.
 Gnathostomes diverged into three surviving
lineages, chondrichthyans, ray-finned fishes, and
lobe-fins
 Humans and other terrestrial animals are included in
the lobe-fins
© 2014 Pearson Education, Inc.
 Chondrichthyans include sharks, rays, and their
relatives
 The skeletons of chondrichthyans are composed
primarily of cartilage
 This group includes some of the largest and most
successful vertebrate predators
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 Ray-finned fishes include nearly all the familiar
aquatic osteichthyans
 The vast majority of vertebrates belong to the clade
of gnathostomes called Osteichthyes
 Nearly all living osteichthyans have a bony
endoskeleton
© 2014 Pearson Education, Inc.
 Lobe-fins are the other major lineage of
osteichthyans
 A key derived trait in the lobe-fins is the presence of
rod-shaped bones surrounded by a thick layer of
muscle in their pectoral and pelvic fins
 Three lineages survive: the coelacanths, lungfishes,
and tetrapods, terrestrial vertebrates with limbs and
digits
© 2014 Pearson Education, Inc.
Concept 27.4: Several animal groups had
features facilitating their colonization of land
 Some bilaterian animals colonized land following
the Cambrian explosion, causing profound changes
in terrestrial communities
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Early Land Animals
 Members of many animal groups made the transition
to terrestrial life
 Arthropods were among the first animals to colonize
the land about 450 million years ago
 Vertebrates colonized land 365 million years ago
© 2014 Pearson Education, Inc.
 The evolutionary changes that accompanied the
transition to terrestrial life were much less extensive
in animals than in plants
Video: Bee Pollinating
Video: Butterfly Emerging
© 2014 Pearson Education, Inc.
Figure 27.18
MARINE CRUSTACEAN
AQUATIC LOBE-FIN
AQUATIC
ANCESTOR
GREEN ALGA
Derived (roots)
N/A
N/A
Support
structure
Derived (lignin/stems)
Ancestral
Ancestral (skeletal system)
Derived (limbs)
Internal
transport
Derived (vascular system)
Ancestral
Ancestral
Muscle/
nerve cells
N/A
Ancestral
Ancestral
Protection
against
desiccation
Derived (cuticle)
Ancestral
Derived
(amniotic egg/scales)
Derived (stomata)
Derived (tracheal system)
Ancestral
CHARACTER
Anchoring
structure
TERRESTRIAL
ORGANISM
Gas exchange
LAND PLANTS
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INSECTS
TERRESTRIAL
VERTEBRATES
Figure 27.18a
AQUATIC
ANCESTOR
GREEN ALGA
CHARACTER
Anchoring structure Derived (roots)
Support structure
Derived (lignin/stems)
Internal transport
Derived (vascular system)
Muscle/nerve cells
N/A
Protection against
desiccation
Derived (cuticle)
TERRESTRIAL
ORGANISM
Gas exchange
© 2014 Pearson Education, Inc.
Derived (stomata)
LAND PLANTS
Figure 27.18b
AQUATIC
ANCESTOR
MARINE CRUSTACEAN
CHARACTER
Anchoring structure N/A
Support structure
Ancestral
Internal transport
Ancestral
Muscle/nerve cells
Ancestral
Protection against
desiccation
Ancestral
TERRESTRIAL
ORGANISM
Gas exchange
© 2014 Pearson Education, Inc.
Derived (tracheal system)
INSECTS
Figure 27.18c
CHARACTER
AQUATIC
ANCESTOR
AQUATIC LOBE-FIN
Anchoring structure N/A
Support structure Ancestral (skeletal system)
Derived (limbs)
Internal transport
Ancestral
Muscle/nerve cells
Ancestral
Protection against
desiccation
Derived
(amniotic egg/scales)
TERRESTRIAL
ORGANISM
Gas exchange
© 2014 Pearson Education, Inc.
Ancestral
TERRESTRIAL
VERTEBRATES
Colonization of Land by Arthropods
 Terrestrial lineages have arisen in several different
arthropod groups, including millipedes, spiders,
crabs, and insects
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General Characteristics of Arthropods
 The appendages of some living arthropods are
modified for functions such as walking, feeding,
sensory reception, reproduction, and defense
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Figure 27.19
Cephalothorax
Antennae
(sensory
reception)
Abdomen
Thorax
Head
Swimming appendages (one pair per
abdominal segment)
Pincer
(defense)
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Mouthparts
(feeding)
Walking legs
 The body of an arthropod is completely covered by
the cuticle, an exoskeleton made of layers of protein
and the polysaccharide chitin
 The exoskeleton provides structural support and
protection from physical harm and desiccation
 A variety of organs specialized for gas exchange
have evolved in arthropods
© 2014 Pearson Education, Inc.
Insects
 The insects and their relatives include more species
than all other forms of life combined
 They live in almost every terrestrial habitat and in
fresh water
© 2014 Pearson Education, Inc.
Figure 27.20
Lepidopterans
Hymenopterans
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Hemipterans
Figure 27.20a
Lepidopterans
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Figure 27.20aa
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Figure 27.20ab
© 2014 Pearson Education, Inc.
Figure 27.20b
Hymenopterans
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Figure 27.20c
Hemipterans
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 Insects diversified several times following the
evolution of flight, adaptation to feeding on
gymnosperms, and the expansion of angiosperms
 Insect and plant diversity declined during the
Cretaceous extinction, but has been increasing in
the 65 million years since
© 2014 Pearson Education, Inc.
 Flight is one key to the great success of insects
 An animal that can fly can escape predators, find
food, and disperse to new habitats much faster than
organisms that can only crawl
© 2014 Pearson Education, Inc.
Figure 27.21
© 2014 Pearson Education, Inc.
Terrestrial Vertebrates
 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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The Origin of Tetrapods
 Tiktaalik, nicknamed a “fishapod,” shows both fish
and tetrapod characteristics
 It had
 Fins, gills, lungs, and scales
 Ribs to breathe air and support its body
 A neck and shoulders
 Fins with the bone pattern of a tetrapod limb
© 2014 Pearson Education, Inc.
Figure 27.22
Fish
Characters
Scales
Fins
Gills and lungs
Tetrapod
Characters
Neck
Ribs
Fin skeleton
Flat skull
Eyes on top of skull
Shoulder bones
Neck
Ribs
Head
Scales
Eyes on top
of skull
Flat skull
Humerus
Ulna
“Wrist”
Fin
Elbow
Radius
Fin skeleton
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Figure 27.22a
Shoulder bones
Neck
Head
Eyes on top
of skull
Flat skull
Fin
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Figure 27.22b
Ribs
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Figure 27.22c
Scales
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Figure 27.22d
Humerus
Ulna
“Wrist”
Elbow
Radius
Fin skeleton
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 Tiktaalik could most likely prop itself on its fins, but
not walk
 Fins became progressively more limb-like over
evolutionary time, leading to the first appearance of
tetrapods 365 million years ago
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Figure 27.23
Lungfishes
Eusthenopteron
Panderichthys
Tiktaalik
Acanthostega
Limbs
with digits
Tulerpeton
Amphibians
Key to
limb bones
Ulna
Radius
Humerus
Amniotes
Silurian
Devonian
PALEOZOIC
Carboniferous
Permian
415 400 385 370 355 340 325 310 295 280 265 0
Time (millions of years ago)
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Figure 27.23a
Lungfishes
Eusthenopteron
Panderichthys
Tiktaalik
Lobe-fins with limbs with digits
Silurian
Devonian
PALEOZOIC
Carboniferous
Permian
415 400 385 370 355 340 325 310 295 280 265 0
Time (millions of years ago)
© 2014 Pearson Education, Inc.
Key to
limb bones
Ulna
Radius
Humerus
Figure 27.23b
Acanthostega
Limbs
with digits
Tulerpeton
Key to
limb bones
Ulna
Radius
Humerus
Amphibians
Amniotes
Silurian
Devonian
PALEOZOIC
Carboniferous
Permian
415 400 385 370 355 340 325 310 295 280 265 0
Time (millions of years ago)
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Amphibians
 Amphibians are represented by about 6,150 species
including salamanders, frogs, and caecilians
 Amphibians are restricted to moist areas within their
terrestrial habitats
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Video: Marine Iguana
Video: Flapping Geese
Video: Snake Wrestling
Video: Soaring Hawk
Video: Swans Taking Flight
Video: Tortoise
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Figure 27.24
Salamanders
retain their tails
as adults.
Caecilians have
no legs and are
mainly burrowing
animals.
Frogs and toads
lack tails as adults.
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Figure 27.24a
Salamanders retain their tails as
adults.
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Figure 27.24b
Frogs and toads lack tails as
adults.
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Figure 27.24c
Caecilians have no legs and are
mainly burrowing animals.
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Terrestrial Adaptations in Amniotes
 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 extraembryonic membranes are the amnion,
chorion, yolk sac, and allantois
 The amniotic eggs of most reptiles and some
mammals have a shell
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Video: Bat Licking
Video: Bat Pollinating
Video: Chimp Agonistic
Video: Chimp Cracking Nut
Video: Gibbon Brachiating
Video: Sea Lion
Video: Shark Eating Seal
Video: Wolves Agonistic
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Figure 27.25
Extraembryonic membranes
Amnion
Allantois
Chorion
Yolk sac
Embryo
Amniotic
cavity with
amniotic fluid
Shell
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Yolk
(nutrients)
Albumen
The Origin and Radiation of Amniotes
 Living amphibians and amniotes split from a
common ancestor about 350 million years ago
 Early amniotes were more tolerant of dry conditions
than early tetrapods
 The earliest amniotes were small predators with
sharp teeth and long jaws
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 Reptiles are one of two living lineages of amniotes
 Members of the reptile clade includes the tuataras,
lizards, snakes, turtles, crocodilians, birds, and
some extinct groups
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Figure 27.26
†
Plesiosaurs
Crocodilians
†
Pterosaurs
†
Turtles
Ornithischian
dinosaurs
Common
ancestor
of reptiles
†
Common
ancestor
of dinosaurs
Saurischian
dinosaurs other
than birds
Birds
Turtles
Tuataras
Squamates
Squamates
Crocodilians
Birds
Tuataras
© 2014 Pearson Education, Inc.
Figure 27.26a
†
Plesiosaurs
Crocodilians
†
Pterosaurs
†
Ornithischian
dinosaurs
Common
ancestor
of reptiles
†
Common
ancestor
of dinosaurs
Saurischian
dinosaurs other
than birds
Birds
Turtles
Tuataras
Squamates
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Figure 27.26b
Crocodilians
Tuataras
Squamates
Birds
Turtles
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Figure 27.26ba
Crocodilians
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Figure 27.26bb
Birds
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Figure 27.26bba
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Figure 27.26bbb
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Figure 27.26bc
Turtles
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Figure 27.26bd
Tuataras
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Figure 27.26be
Squamates
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 Reptiles have scales that create a waterproof barrier
 Most reptiles lay shelled eggs on land
 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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 Mammals are the other extant lineage of amniotes
 There are many distinctive traits of mammals
including
 Mammary glands that produce milk
 Hair
 A fat layer under the skin
 A high metabolic rate, due to endothermy
 Differentiated teeth
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 The first true mammals evolved from synapsids
and arose about 180 million years ago
 By 140 million years ago, the three living lineages
of mammals had emerged
 Monotremes, egg-laying mammals
 Marsupials, mammals with a pouch
 Eutherians, placental mammals
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Figure 27.27
Monotremes
Eutherians
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Marsupials
Figure 27.27a
Monotremes
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Figure 27.27aa
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Figure 27.27ab
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Figure 27.27b
Marsupials
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Figure 27.27c
Eutherians
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Human Evolution
 Humans (Homo sapiens) are primates, nested within
a group informally called apes
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Figure 27.28
New World monkeys
Old World monkeys
Gibbons
“Apes”
Orangutans
Gorillas
Chimpanzees
and bonobos
Humans
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 A number of characters distinguish humans from
other apes
 Upright posture and bipedal locomotion
 Larger brains capable of language, symbolic thought,
artistic expression, and the use of complex tools
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 The evolution of bipedalism preceded the evolution
of increased brain size in early human ancestors
 Brain size, body size, and tool use increased over
time in Homo species
 Modern humans, H. sapiens, originated in Africa
about 200,000 years ago and colonized the rest of
the world from there
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Figure 27.29
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Concept 27.5: Animals have transformed
ecosystems and altered the course of evolution
 The rise of animals from a microbe-only world
affected all aspects of ecological communities, in
the sea and on land
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Ecological Effects of Animals
 The oceans of early Earth likely had very different
properties than the oceans of today
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Figure 27.30
Murky, poorly-mixed
Low oxygen
Cyanobacteria
(a) Ocean conditions before 600 mya
Clear, well-mixed
High oxygen
Eukaryotic algae
(b) Changes to ocean conditions by 530 mya
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Marine Ecosystems
 The rise of filter-feeding animals likely caused the
decline of cyanobacteria and other suspended
particles in the oceans during the early Cambrian
 This resulted in a shift to algae as the dominant
producers and changed the feeding relationships in
marine ecosystems
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Terrestrial Ecosystems
 Terrestrial ecosystems were transformed with the
move of animals to land
 Herbivores, such as the lesser snow goose, can
improve the growth of plants at low population sizes
through additions of nutrient-rich wastes
 At high population sizes herbivores can defoliate
large tracts of land
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Figure 27.31
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Evolutionary Effects of Animals
 The origin of mobile, heterotrophic animals with a
complete digestive tract drove some species to
extinction and initiated ongoing “arms races”
between bilaterian predators and prey
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Evolutionary Radiations
 Two species that interact can exert strong,
reciprocal selective pressures on one another
 For example, flower form can be influenced by the
structure of its pollinators’ mouth parts, and vice
versa
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Figure 27.32
© 2014 Pearson Education, Inc.
 Reciprocal selection pressures can also occur
when the origin of new species in one group
stimulates further radiation in another group
 For example, the origin of a new group of
animals provides new food sources for parasites,
resulting in radiations in parasite groups
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Human Impacts on Evolution
 Humans have made large changes to the
environment that have altered the selective
pressures faced by many species
 For example, human targeting of large fish for
harvesting has led to the reduction in age and size at
which individuals reach sexual maturity
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Figure 27.33
Age at maturity (years)
7.0
6.5
6.0
5.5
5.0
1960
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1970
1980
Year
1990
2000
Figure 27.33a
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 Rapid species declines over the past 400 years
indicate that human activities may be driving a sixth
mass extinction
 Molluscs, including pearl mussels, have suffered
the greatest impact of human-caused extinctions
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Figure 27.34
Other
invertebrates
An endangered
Pacific island
land snail,
Partula suturalis
Molluscs
Insects
Fishes
Birds
Amphibians
Mammals
Reptiles (excluding
birds)
Recorded extinctions of animal
species
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Workers on a mound of pearl
mussels killed to make buttons
(ca. 1919)
Figure 27.34a
Other
invertebrates
Molluscs
Insects
Fishes
Birds
Amphibians
Mammals
Reptiles (excluding
birds)
Recorded extinctions of animal species
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Figure 27.34b
An endangered
Pacific island
land snail,
Partula suturalis
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Figure 27.43c
Workers on a mound of pearl
mussels killed to make buttons
(ca. 1919)
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 The major threats imposed on species by human
activities include habitat loss, pollution, and
competition or predation by introduced, non-native
species
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Average number of
periwinkles killed
Figure 27.UN03
6
4
2
Southern
periwinkles
0
Northern
periwinkles
Northern
Southern
Source population of crab
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Figure 27.UN04
535–525 mya:
Cambrian explosion
560 mya:
Ediacaran animals
365 mya:
Early land
animals
Origin and
diversification
of dinosaurs
Diversification
of mammals
Era
Neoproterozoic
1,000
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Paleozoic
542
251
Millions of years age (mya)
Mesozoic
Cenozoic
65.5
0
Figure 27.UN05
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