27lecturepresentation 160421162913

CAMPBELL BIOLOGY IN FOCUS
© 2014 Pearson Education, Inc.
Urry • Cain • Wasserman • Minorsky • Jackson • Reece
Lecture Presentations by
Kathleen Fitzpatrick and Nicole Tunbridge
27
The Rise of
Animal Diversity

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

Figure 27.1

 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
Concept 27.1: Animals originated more than
700 million years ago

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

Figure 27.2
(a) Dickinsonia
costata
(taxonomic affiliation
unknown)
2.5 cm
(b) The fossil
mollusc
Kimberella
1 cm

Figure 27.2a
(a) Dickinsonia
costata
(taxonomic affiliation
unknown)
2.5 cm

Figure 27.2b
(b) The fossil
mollusc
Kimberella
1 cm

Early-Diverging Animal Groups
 Sponges and cnidarians are two early-diverging
groups of animals

Figure 27.UN01
Other animal
groups
Sponges
Cnidarians

 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
Sponges

Figure 27.3
Water
flow
Pores
Choanocyte
Flagellum
Food particles
in mucus
Collar
Choanocyte
Phagocytosis of
food particles
Amoebocyte
Amoebocytes
Azure vase sponge
(Callyspongia plicifera)
Spicules

Figure 27.3a
Azure vase sponge
(Callyspongia plicifera)

 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

 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
Cnidarians

Video: Clownfish Anemone
Video: Coral Reef
Video: Hydra Budding
Video: Hydra Eating
Video: Jelly Swimming
Video: Thimble Jellies

Figure 27.4
(c) Anthozoa(a) Hydrozoa (b) Scyphozoa

Figure 27.4a
(a) Hydrozoa

Figure 27.4b
(b) Scyphozoa

Figure 27.4c
(c) Anthozoa

 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

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

 Strata formed during the Cambrian explosion contain
the oldest fossils of about half of all extant animal
phyla
Evolutionary Change in the Cambrian Explosion

Figure 27.5
Echinoderms
Sponges
Cnidarians
Chordates
Brachiopods
Annelids
Molluscs
Ediacaran
Arthropods
635
Cambrian
PALEOZOICPROTEROZOIC
605
Time (millions of years age)
575 545 515 485 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

Figure 27.6
Hallucigenia fossil
(530 mya)
1 cm

Figure 27.6a

Figure 27.6b
Hallucigenia fossil
(530 mya)
1 cm

 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

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

Figure 27.7
15 µm
(a) Valeria (800 mya):
roughly spherical, no
structural defenses,
soft-bodied
(b) Spiny acritarch
(575 mya): about five
times larger than
Valeria and covered in
hard spines
75 µm

Figure 27.7a
15 µm
(a) Valeria (800 mya):
roughly spherical, no
structural defenses,
soft-bodied

Figure 27.7b
(b) Spiny acritarch
(575 mya): about five
times larger than
Valeria and covered in
hard spines
75 µm

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

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

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

Figure 27.8
(b) Bilateral symmetry
(a) Radial symmetry

 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

 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

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

Figure 27.9
Digestive tract
(from endoderm)
Body covering
(from ectoderm)
Tissue layer
lining body cavity
and suspending
internal organs
(from mesoderm)
Body cavity

 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

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

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

Figure 27.10
ANCESTRAL
PROTIST
770 million
years ago
680 million
years ago
670 million
years ago
Arthropoda
Nematoda
Annelida
Mollusca
Brachiopoda
Ectoprocta
Rotifera
Platyhelminthes
Chordata
Echinodermata
Metazoa
Hemichordata
Cnidaria
Ctenophora
Porifera
EcdysozoaLophotrochozoa
Bilateria
Deuterostomia
Eumetazoa

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

Bilaterian Radiation I: Diverse Invertebrates
 Bilaterians have diversified into three major clades
 Lophotrochozoa
 Ecdysozoa
 Deuterostomia

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

Figure 27.11
Arthropoda
(1,000,000 species)
Nematoda
(25,000 species)
Annelida (16,500 species)
Mollusca
(93,000 species)
Ectoprocta
(4,500 species)
Ectoprocts
EcdysozoaLophotrochozoa
Echinodermata
(7,000 species)
Hemichordata
(85 species)
Deuterostomia
An octopus A roundworm
A web-building spider
(an arachnid)
Sea urchins and a
sea star
An acorn worm
A fireworm, a marine annelid

Figure 27.11a
Mollusca
(93,000 species)
Ectoprocta
(4,500 species)
Ectoprocts
Lophotrochozoa
An octopus

Figure 27.11aa
Ectoprocta
(4,500 species)
Ectoprocts

Figure 27.11ab
Mollusca
(93,000 species)
An octopus

Figure 27.11ac

Figure 27.11b
Arthropoda
(1,000,000 species)
Nematoda
(25,000 species)
Ecdysozoa
A roundworm
(an arachnid)

Figure 27.11ba
Nematoda
(25,000 species)
A roundworm

Figure 27.11bb
Arthropoda
(1,000,000 species)
(an arachnid)

Figure 27.11c
Echinodermata
(7,000 species
Hemichordata
(85 species)
Deuterostomia
Sea urchins and a
sea star
An acorn worm

Figure 27.11ca
Hemichordata
(85 species)
An acorn worm

Figure 27.11cb
Echinodermata
(7,000 species)
Sea urchins and a
sea star

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

 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

Figure 27.UN02
A fossil trilobite

 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

Figure 27.12
Red indicates regions
in which Ubx or
abd-A genes were
expressed.
Other
ecdysozoans
Arthropods
Onychophorans
Common ancestor
Origin of Ubx and
abd-A Hox genes?
Ant = antenna
J = jaws
L1–L15 = body segments
Experiment
Results

Figure 27.12a
Red indicates regions
in which Ubx or
abd-A genes were
expressed.
Ant = antenna
J = jaws
L1–L15 = body segments
Results

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

Figure 27.13

 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

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

Video: Clownfish Anemone
Video: Coral Reef
Video: Manta Ray
Video: Sea Horses

Figure 27.14
Muscle
segments
Notochord
Post-anal tail
Anus
Mouth
Dorsal, hollow nerve cord
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

Figure 27.15
(a) Lancelet (b) Tunicate

Figure 27.15a
(a) Lancelet

Figure 27.15b
(b) Tunicate

 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

The Rise of Vertebrates
 Early vertebrates were more efficient at capturing
food and evading predators than their ancestors
 The earliest vertebrates were conodonts, soft-
bodied, 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

Figure 27.16
Chondrichthyes ActinistiaActinopterygii
Myxini
Tetrapoda
Petromyzontida
Dipnoi
Chondrichthyes
(sharks, rays, chimaeras)
Actinistia
(coelacanths)
Actinopterygii
(ray-finned fishes)
Myxini
(hagfishes)
Tetrapoda
(amphibians,
reptiles,
mammals)
Petromyzontida
(lampreys)
Dipnoi
(lungfishes)
Limbs with digits
Lobed
fins
Lungs
or lung derivatives
Jaws,
mineralized
skeleton
Vertebral
column
Common
ancestor of
vertebrates
Tetrapods
Lobe-fins
Osteichthyans
Gnathostomes
Vertebrates

Figure 27.16a
Chondrichthyes
(sharks, rays, chimaeras)
Actinistia
(coelacanths)
Actinopterygii
(ray-finned fishes)
Myxini
(hagfishes)
Tetrapoda
(amphibians,
reptiles,
mammals)
Petromyzontida
(lampreys)
Dipnoi
(lungfishes)
Limbs with digits
Lobed
fins
Lungs
or lung derivatives
Jaws,
mineralized
skeleton
Vertebral
column
Common
ancestor of
vertebrates
Tetrapods
Lobe-fins
Osteichthyans
Gnathostomes
Vertebrates

Figure 27.16b
Chondrichthyes
ActinistiaActinopterygiiMyxini
Tetrapoda
Petromyzontida
Dipnoi

Figure 27.16ba
Myxini

Figure 27.16bb
Petromyzontida

Figure 27.16bba

Figure 27.16bbb

Figure 27.16bc
Chondrichthyes

Figure 27.16bd
Actinopterygii

Figure 27.16be
Actinistia

Figure 27.16bf
Dipnoi

Figure 27.16bg
Tetrapoda

 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

Figure 27.17
0.5 m

 Gnathostomes diverged into three surviving
lineages, chondrichthyans, ray-finned fishes, and
lobe-fins
 Humans and other terrestrial animals are included in
the lobe-fins

 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

 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

 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

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

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

 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

Figure 27.18
GREEN ALGA MARINE CRUSTACEAN AQUATIC LOBE-FIN
Derived (roots) N/A N/A
LAND PLANTS INSECTS
TERRESTRIAL
VERTEBRATES
N/A
Derived (lignin/stems)
Derived (vascular system)
Derived (cuticle)
Derived (stomata) Derived (tracheal system)
Ancestral
Ancestral
Ancestral
Ancestral
Derived
(amniotic egg/scales)
Ancestral
Ancestral
Ancestral (skeletal system)
Derived (limbs)
Ancestral
Anchoring
structure
Support
structure
Internal
transport
Muscle/
nerve cells
Protection
against
desiccation
Gas exchange
TERRESTRIAL
ORGANISM
CHARACTER
AQUATIC
ANCESTOR

Figure 27.18a
GREEN ALGA
Derived (roots)
LAND PLANTS
N/A
Derived (lignin/stems)
Derived (vascular system)
Derived (cuticle)
Derived (stomata)
Anchoring structure
Support structure
Internal transport
Muscle/nerve cells
Protection against
desiccation
Gas exchange
TERRESTRIAL
ORGANISM
CHARACTERAQUATIC
ANCESTOR

Figure 27.18b
Anchoring structure
Support structure
Internal transport
Muscle/nerve cells
Protection against
desiccation
Gas exchange
TERRESTRIAL
ORGANISM
CHARACTERAQUATIC
ANCESTOR
MARINE CRUSTACEAN
N/A
INSECTS
Derived (tracheal system)
Ancestral
Ancestral
Ancestral
Ancestral

Figure 27.18c
Anchoring structure
Support structure
Internal transport
Muscle/nerve cells
Protection against
desiccation
Gas exchange
TERRESTRIAL
ORGANISM
CHARACTERAQUATIC
ANCESTOR
AQUATIC LOBE-FIN
N/A
TERRESTRIAL
VERTEBRATES
Derived
(amniotic egg/scales)
Ancestral
Ancestral
Ancestral (skeletal system)
Derived (limbs)
Ancestral

Colonization of Land by Arthropods
 Terrestrial lineages have arisen in several different
arthropod groups, including millipedes, spiders,
crabs, and insects

General Characteristics of Arthropods
 The appendages of some living arthropods are
modified for functions such as walking, feeding,
sensory reception, reproduction, and defense

Figure 27.19
Cephalothorax
Swimming appen-
dages (one pair per
abdominal segment)
Abdomen
Antennae
(sensory
reception)
Thorax
Head
Pincer
(defense)
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

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

Figure 27.20
Lepidopterans
Hymenopterans Hemipterans

Figure 27.20a
Lepidopterans

Figure 27.20aa

Figure 27.20ab

Figure 27.20b
Hymenopterans

Figure 27.20c
Hemipterans

 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

 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

Figure 27.21

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

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

Figure 27.22
Fish
Characters
Neck
Shoulder bones
Head
Fin
Ulna
Flat skull
Eyes on top
of skull
Humerus
Ribs
Scales
Fin skeleton
Elbow
Radius
“Wrist”
Tetrapod
Characters
Scales
Fins
Gills and lungs
Neck
Ribs
Fin skeleton
Flat skull
Eyes on top of skull

Figure 27.22a
Neck
Shoulder bones
Head
Fin
Flat skull
Eyes on top
of skull

Figure 27.22b
Ribs

Figure 27.22c
Scales

Figure 27.22d
Ulna
Humerus
Fin skeleton
Elbow
Radius
“Wrist”

 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

Figure 27.23
Lungfishes
Eusthenopteron
Panderichthys
Tiktaalik
Acanthostega
Tulerpeton
Amphibians
Amniotes
Limbs
with digits
Silurian
PermianCarboniferousDevonian
PALEOZOIC
Key to
limb bones
Time (millions of years ago)
415 340355370385400 325 280295310 265 0
Ulna
Radius
Humerus

Figure 27.23a
Silurian
PALEOZOIC
Key to
limb bones
415 340355370385400 325 280295310 265 0
Ulna
Radius
Humerus
Lungfishes
Eusthenopteron
Panderichthys
Tiktaalik
Lobe-fins with limbs with digits

Figure 27.23b
Silurian
PALEOZOIC
Key to
limb bones
415 340355370385400 325 280295310 265 0
Ulna
Radius
Humerus
Acanthostega
Tulerpeton
Amphibians
Amniotes
Limbs
with digits

Amphibians
 Amphibians are represented by about 6,150 species
including salamanders, frogs, and caecilians
 Amphibians are restricted to moist areas within their
terrestrial habitats

Video: Marine Iguana
Video: Flapping Geese
Video: Snake Wrestling
Video: Soaring Hawk
Video: Swans Taking Flight
Video: Tortoise

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.

Figure 27.24a
Salamanders retain their tails as
adults.

Figure 27.24b
Frogs and toads lack tails as
adults.

Figure 27.24c
Caecilians have no legs and are
mainly burrowing animals.

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

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

Figure 27.25
Amniotic
cavity with
amniotic fluid Yolk
(nutrients)
Albumen
Yolk sac
Shell
ChorionAllantois
Amnion
Embryo
Extraembryonic membranes

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

 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

Figure 27.26
Tuataras
Squamates
Birds
Crocodilians
Turtles
†
Plesiosaurs
†
Pterosaurs
†
Ornithischian
dinosaurs
†
Saurischian
dinosaurs other
than birds
Crocodilians
Birds
Turtles
Tuataras
Squamates
Common
ancestor
of dinosaurs
Common
ancestor
of reptiles

Figure 27.26a
†
Plesiosaurs
†
Pterosaurs
†
Ornithischian
dinosaurs
†
Saurischian
dinosaurs other
than birds
Crocodilians
Birds
Turtles
Tuataras
Squamates
Common
ancestor
of dinosaurs
Common
ancestor
of reptiles

Figure 27.26b
Tuataras Squamates
Birds
Crocodilians
Turtles

Figure 27.26ba
Crocodilians

Figure 27.26bb
Birds

Figure 27.26bba

Figure 27.26bbb

Figure 27.26bc
Turtles

Figure 27.26bd
Tuataras

Figure 27.26be
Squamates

 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

 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

 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

Figure 27.27
Monotremes Marsupials
Eutherians

Figure 27.27a
Monotremes

Figure 27.27aa

Figure 27.27ab

Figure 27.27b
Marsupials

Figure 27.27c
Eutherians

Human Evolution
 Humans (Homo sapiens) are primates, nested within
a group informally called apes

Figure 27.28
New World monkeys
Old World monkeys
Humans
Chimpanzees
and bonobos
Gorillas
Orangutans
Gibbons
“Apes”

 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

 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

Figure 27.29

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

Ecological Effects of Animals
 The oceans of early Earth likely had very different
properties than the oceans of today

Figure 27.30
(b) Changes to ocean conditions by 530 mya
(a) Ocean conditions before 600 mya
Murky, poorly-mixed
Low oxygen
Cyanobacteria
Clear, well-mixed
High oxygen
Eukaryotic algae

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

 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
Terrestrial Ecosystems

Figure 27.31

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

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

Figure 27.32

 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

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

Figure 27.33
1960 1970 1980 1990 2000
Year
7.0
6.5
6.0
5.5
5.0
Ageatmaturity(years)

Figure 27.33a

 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

Figure 27.34
Workers on a mound of pearl
mussels killed to make buttons
(ca. 1919)
An endangered
Pacific island
land snail,
Partula suturalis
Recorded extinctions of animal
species
Other
invertebrates
Reptiles (excluding
birds)
Molluscs
Insects
Fishes
Birds
Mammals
Amphibians

Figure 27.34a
Recorded extinctions of animal species
Other
invertebrates
Reptiles (excluding
birds)
Molluscs
Insects
Fishes
Birds
Mammals
Amphibians

Figure 27.34b
An endangered
Pacific island
land snail,
Partula suturalis

Figure 27.43c
Workers on a mound of pearl
mussels killed to make buttons
(ca. 1919)

 The major threats imposed on species by human
activities include habitat loss, pollution, and
competition or predation by introduced, non-native
species

Figure 27.UN03
Southern
periwinkles
Northern
periwinkles
Southern Northern
Averagenumberof
periwinkleskilled
Source population of crab
6
4
2
0

Figure 27.UN04
Origin and
diversification
of dinosaurs365 mya:
Early land
animals
Diversification
of mammals
535–525 mya:
Cambrian explosion
560 mya:
Ediacaran animals
Millions of years age (mya)
Neo-
proterozoic Paleozoic
1,000
Era
542 251
Mesozoic
65.5
Ceno-
zoic
0

Figure 27.UN05

27lecturepresentation 160421162913

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