Transcript Chapter 15 - McGraw Hill Higher Education

Essentials of
The Living World
First Edition
GEORGE B. JOHNSON
15
Evolution of Animals
PowerPoint® Lectures prepared by Johnny El-Rady
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15.1 General Features of Animals
All animals are multicellular heterotrophs
They all require oxygen for respiration
Animals are diverse in form
There are ~ 10 million living species
Only ~ 54,000 are vertebrates (possessing a backbone)
The rest are invertebrates (lacking a backbone)
There are about 36 phyla
Most occur in the sea
Three phyla dominate life on land
Arthropoda; Mollusca; Chordata
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Animals lack cell walls
They are usually quite flexible
Animals are mobile
They move more rapidly and in more complex ways than
members of other kingdoms
Most animals reproduce sexually
An animal develops from a zygote by a characteristic
process of embryonic development
Morula  Blastula  Gastrula
Details vary widely between phyla
Provide clues to evolutionary relatedness
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Fig. 15.2
Evolutionary
trends
among the
animals
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15.2 Sponges and Cnidarians:
The Simplest Animals
The Kingdom Animalia consists of two subkingdoms
Parazoa
Animals that lack symmetry and possess
neither tissues nor organs
1 phylum: Porifera (sponges)
Eumetazoa
Animals that have symmetry and in most cases
tissues and organs
About 35 phyla
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Sponges
Sponges are the simplest animals
Bodies consist of little more than masses of specialized
cells embedded in a gel-like matrix
The adult sponge is shaped like a vase
It is anchored in place on the seafloor
Fig. 15.3
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Sponges are perforated by tiny holes
Basis of the phylum name Porifera
Unique flagellated cells called choanocytes or
collar cells, line the body cavity of the sponge
Beating of the flagella draws water in through the
pores and drives it through the cavity
The sponge is a ”filter-feeder”
The choanocytes of sponges very closely resemble
a kind of protist called choanoflagellates
These may be the ancestors of all animals
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Cnidarians
The structure of eumetazoans is much more
complex than that of sponges
Radially symmetric eumetazoans form two distinct
embryonic layers
An outer ectoderm  epidermis
An inner endoderm  gastrodermis
A jelly-like layer called the mesoglea forms
between the epidermis and gastrodermis
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Cnidarians
There are two radially symmetric phyla
Together, they are called Radiata
1. Cnidaria
Hydra
Fig. 15.4
2. Ctenophora
A minor phylum that includes the comb jellies
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Cnidarians
A major evolutionary innovation among the
radiates is extracellular digestion of food
In radiates, digestion begins in the
gastrovascular cavity
Cnidarians are carnivores that capture their prey
with tentacles
Bear unique stinging cells called cnidocytes
Contain a small but powerful harpoon called a
nematocyst
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Cnidarians have two basic body forms
Medusae
Free-floating,
gelatinous and often
umbrella-shaped
Polyps
Cylindrical, pipeshaped and usually
attached to a rock
Fig. 15.5
Cnidarians may exist exclusively as either/or
Others alternate between the two phases
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15.3 The Advent of Bilateral Symmetry
Radiates are radially
symmetrical
Have a regular arrangement
of parts around a central axis
All other eumetazoans are
bilaterally symmetrical
Have right and left halves
that are mirror images
Fig. 15.6
Dorsal (top) vs.
Ventral (bottom)
Anterior (front) vs.
Posterior (back)
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Bilaterally symmetrical animals have evolved a
definite head end, a process called cephalization
Solid worms are the simplest of all bilaterally
symmetrical animals
Nervous system
Ectoderm
Mesoderm
Endoderm
Lack internal
cavities, except
for digestive tract
Acoelomate
+
Fig. 15.7
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Flatworms
Members of Platyhelminthes
Planaria
The largest phylum of solid worms
Simplest animals in which
organs occur
Some species are free-living
Most species are parasitic
Tapeworms
Fig. 15.8a
Flukes
Many require two or more hosts
to complete their life cycle
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Flatworms
Have incomplete gut with only one opening
Cannot eat, digest and excrete food simultaneously
Have an excretory system consisting of a network
of tubules running throughout the body
Have a simple nervous system
Lack a circulatory system
Most are hermaphroditic
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15.4 The Advent of a Body Cavity
The evolution of an internal body cavity was
important for three reasons
Circulation
Rapid passage of material
Movement
Muscle-driven body movement
Organ function
Little deformation by surrounding muscles
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Three kinds of body plans
Fig. 15.9
Acoelomates
Have no body cavity
Pseudocoelomates
Have body cavity between
mesoderm and endoderm
Pseudocoel
Coelomates
Have body cavity entirely
within mesoderm
Coelom
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Pseudocoelomates
There are seven phyla
The pseudocoel serves as a hydrostatic skeleton
Gains rigidity from being filled with fluid under pressure
Therefore muscles can work against this “skeleton”
Lack a defined circulatory system
Two important phyla
Cilia aid in feeding
and locomotion
Nematoda
Fig. 15.10
Rotifera
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Phylum Nematoda: The Roundworms
Nematodes are bilaterally symmetrical, cylindrical,
unsegmented worms
Covered by a thick, flexible cuticle
Mouth is equipped with piercing organs called stylets
Food passes through the mouth by the sucking
action of the pharynx
Lack flagella or cilia
Reproduction is sexual
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Phylum Nematoda: The Roundworms
Caenorhabditis elegans
Only animal whose complete cellular anatomy is
known
First animal whose genome was fully sequenced
Trichinella sp.
Cause trichinosis
Acquired from pigs
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Mollusks
The bulk of the animal kingdom consists of
coelomates
A major advantage of the coelomate body plan is
that it allows mesoderm–endoderm contact
In pseudocoelomates, the body cavity limits
developmental interaction between the tissues
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Mollusks
Only major phylum of coelomates without a
segmented body
The second largest animal phylum, after Arthropods
The body consists of three distinct parts
Head-foot; Visceral mass; Mantle
Gills capture O2 from water and release CO2
The radula is a rasping, tongue-like organ
Used to scrape algae off rocks
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The three major groups
of mollusks
Fig. 15.11
Gastropods
Snails and slugs
Bivalves
Clams, oysters and
scallops
Cephalopods
Octopuses and squids
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Annelids
Segmentation is the building of a body from a series
of similar segments
It offers evolutionary flexibility
Small change in existing segment can produce
a new segment with a different function
The first segmented animals to evolve were the
annelid worms, phylum Annelida
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Most annelid species are marine
About one-third are terrestrial
Representative annelids
Fig. 15.12
Earthworm
Shiny bristle
worm
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The basic body plan is a tube within a tube
Three characteristics
Repeated segments
Separate segments able to expand or contract
independently
Specialized segments
Front segments contain the worm’s sensory organs
Connections
Materials and information pass through partitions in
the segments
Segmentation underlies the body organization of all
complex coelomate animals
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Arthropods
Arthropods belong to
the phylum Arthropoda
The most successful of
all animal groups
2/3rd of all named species
80% of all arthropods are
insects
Scientists estimate that a
quintillion insects are
Fig. 15.13
alive at any one time
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All arthropods have jointed appendages
They have a rigid external skeleton made up of chitin
This exoskeleton protects the animals and provides sites
for muscle attachment
It is brittle, so its thickness limits arthropod body size
Arthropod bodies are
segmented
Most larval stages
have many segments
These fuse into
functional groups
in the adult
Fig. 15.14
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Major kinds of arthropods
Arachnids (spiders, ticks, mites)
Crustaceans (lobsters, crabs, shrimps)
Centipedes and millipedes
Insects
Fig. 15.15
Beetle
Flea
Honeybee
Grasshoppers
Moth
Dragonfly
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15.5 Redesigning the Embryo
In the coelomates there are two different
developmental patterns
In protostomes, the mouth develops from or near
the blastopore
The anus (if present) develops later from
another region of the embryo
In deuterostomes, the anus develops from or near
the blastopore
The mouth develops later from another region
of the embryo
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Fig. 15.16
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Fig. 15.16
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Deuterostomes differ from protostomes in three
other fundamental embryological features
1. Cleavage pattern
In protostomes, the egg cleaves spirally
In deuterostomes, the egg cleaves radially
2. Developmental fate of cells
In protostomes, the cells are committed even early on
In deuterostomes, the commitment occurs later
3. Origination of coelom
In protostomes, it forms directly from the mesoderm
In deuterostomes, it forms indirectly via the archenteron
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Echinoderms
Echinoderms belong to the phylum Echinodermata
They have an endoskeleton composed of hard
calcium-rich ossicles that are often fused
They consist of about 6,000 living marine species
Sand dollar
Feather star
Sea urchin
Sea star
Fig. 15.17
Sea cucumber
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Echinoderms are bilaterally symmetrical as larvae
But they become radially symmetrical as adults
This could be an environmental adaptation
Adults have a five-part body plan
The key evolutionary innovation is the development
of a water vascular system
A fluid-filled system with a central ring canal and
five radial canals
Thousands of tiny, hollow tube feet extend
from each radial canal
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Chordates
Chordates are members of the phylum Chordata
They are deuterostomes that employ a truly internal
endoskeleton
Chordates are quite diverse
Lancelets
Tunicate
Fig. 15.18
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Distinguishing features of chordates
1. Notochord
A stiff, but flexible rod, that forms beneath the nerve cord
2. Nerve cord
A single dorsal nerve to which other nerves are attached
3. Pharyngeal slits
A series of slits behind the mouth into the pharynx
4. Postanal tail
A tail that extends beyond the anus
All chordates have all four of these at some time in
their life
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Vertebrates
With the exception of tunicates and lancelets, all
chordates are vertebrates
Distinguishing features of vertebrates
1. Backbone
A bony vertebral column replaces the notochord
2. Head
Well-differentiated, with skull and brain
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Vertebrates
All vertebrates have an internal skeleton made of
bone and cartilage against which the muscles work
This makes possible great size and movement
Lion
Fig. 15.18c
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15.6 Overview of Vertebrate Evolution
The Earth’s past is divided into large blocks of time
called eras
Subdivided into periods
Subdivided into epochs
Subdivided into ages
Virtually all of the surviving animal groups originated
in the sea at the beginning of the Paleozoic Era
During or soon after the Cambrian period (545490 mya)
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15.6 Overview of Vertebrate Evolution
The Cambrian period was a period of experimentation
with different body forms and ways of life
Some led to contemporary animal phyla
Trilobites appear to be the ancestors of
horseshoe crabs
Others failed and became extinct
Ammonites
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15.6 Overview of Vertebrate Evolution
The first vertebrates evolved around 470 mya in
the oceans
Fishes without jaws
Invasion of the land
First – fungi and plants (around 500 mya)
Second – arthropods (around 410 mya)
Third – vertebrates (360-280 mya)
Amphibians were the first to live on land
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Mass extinctions are particularly sharp declines in
species diversity
Create vacant niches, allowing rapid evolution
Five have occurred
The most dramatic is the third
Occurred at the end of the Paleozoic era
Estimated 96% of all marine species became extinct
The most famous and well-studied is the fourth
Occurred in the Mesozoic era
Dinosaurs became extinct
We are living during the fifth
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15.7 Fishes Dominate the Sea
Fishes constitute about half of all vertebrates
They are are the most diverse and successful
group of vertebrates
They provided the evolutionary base for
invasion of land by amphibians
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Fig. 15.19 Vertebrate family tree
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Characteristics of Fishes
Fishes vary in size, shape, color and appearance
However, they all share these four characteristics
1. Gills
Used to extract dissolved oxygen gas from water
2. Vertebral column
An internal skeleton with a spine surrounding the
dorsal nerve cord
3. Single-loop blood circulation
Blood flow: Heart  Gills  Body  Heart again
4. Nutritional deficiencies
Inability to synthesize the aromatic amino acids
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The earliest fishes were jawless and toothless
Sucked up small food particles from ocean floor
Agnathans survive today as hagfish and parasitic
lampreys
These fishes were eventually replaced by larger,
heavier, jawed fishes that were predators
Jaws seem to have evolved from cartilage arch supports
The heavier, jawed fish were in turn replaced by
faster fishes
Sharks and bony fishes
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Sharks
The Class Chondrichthyes adopted a light skeleton
made up of strong, flexible cartilage
Skates and rays are
flattened sharks that
are bottom-dwellers
Have the most
advanced fish
reproduction system
Galápagos shark
Fig. 15.20
Shark eggs are fertilized internally
About 40% lay fertilized eggs
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Bony Fishes
The Class Osteichthyes adopted a heavy internal
skeleton made of bone
Serves as base for
attachment of strong
muscles
Fig. 15.21
Regulation of buoyant
density occurs via a
swim bladder
By adjusting the
amount of gas in it,
fish rise up or down
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Bony Fishes
The most successful of all vertebrates
Of the ~ 30,800 species of living fishes, ~30,000
are bony fishes
Lateral line system
Detects changes in water pressure
Operculum
Covers gills
Its flexing pumps water over the gills
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15.8 Amphibians and Reptiles
Invade the Land
Amphibians are direct descendants of fishes
They are the first vertebrate to walk on land
They include
Frogs
Salamanders
Caecilians
Fig. 15.22
Red-eyed tree frog
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Characteristics of Amphibians
1. Legs
Found in frogs and salamanders, but not in Caecilians
Fig. 15.23 Evolution of legs
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Characteristics of Amphibians
2. Lungs
Provide a more efficient means of respiration than gills
3. Cutaneous respiration
Respiration directly across the skin supplements the use
of lungs
4. Pulmonary veins
Two large veins that return aerated blood to the heart for
repumping
5. Partially divided heart
Separates the blood circulation into two separate paths
Pulmonary and systemic
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History of Amphibians
Amphibians were the dominant land vertebrates for
100 million years
At their peak, 40 families existed
Only two of these families survived the Age of Dinosaurs
About 4,850 species of amphibians exist today
Class Amphibia
Order Anura (frogs)
Order Urodela (salamanders)
Order Apoda (caecilians)
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Reptiles
Reptiles replaced amphibians as the dominant
terrestrial vertebrates
There are ~ 7,000 species of living reptiles
Among the most important reptile characteristics
are:
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1. Amniotic egg
Watertight egg
Contains four membranes
Chorion: Allows O2 entry
Amnion: Fluid-filled cavity
Yolk sac: Provides food
Allantois: Excretes waste
2. Dry skin
Fig. 15.24
Covers body and prevents water loss
3. Thoracic breathing
Increases lung capacity
Plus, leg arrangement to better support body weight
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15.9 Birds Master the Air
Birds evolved from small bipedal dinosaurs about
150 mya
Birds still retain many reptilian characteristics
1. They lay amniotic eggs
2. They have reptilian scales on feet and lower legs
So what distinguishes birds from living reptiles?
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1. Feathers
Derived from reptilian
scales
Lightweight and easily
replaced when damaged
Fig. 15.25
2. Flight skeleton
Bones are thin and hollow
Have a keeled breastbone
(the wishbone)
Have a fused collarbone
Birds, like mammals, are endothermic
However, they maintain body temperatures much higher
than most mammals
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History of Birds
The oldest bird fossil is
that of Archaeopteryx
Had teeth and solid
bones
By the early Cretaceous
period, a diverse array
of birds had evolved
Fig. 15.26
About 8,600 species of birds exist today
Class Aves
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15.10 Mammals Adapt to Colder Times
Mammals (class Mammalia) evolved about 220 mya
They share three characteristics with mammals
today
1. Mammary glands
Females have mammary glands which produce milk
2. Hair
Keratin-made filaments that provide insulation
3. Middle ear
Three middle ear bones that amplify vibration
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History of Mammals
They have been around since the time of dinosaurs
The first mammals were tiny shrew-like creatures
Lived in trees chasing insects
Over 4,500 species of mammals exist today
Almost one-quarter are bats!
There are only 233 known species of primates
Humans evolved less than 2 mya
There have been at least three species
Only Homo sapiens is alive today!
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Other Characteristics of Modern Mammals
Endothermy
Allows colonization of severe environments
Depends on
1. More efficient blood circulation
Provided by the four-chambered heart
2. More efficient breathing
Provided by the diaphragm
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Other Characteristics of Modern Mammals
Placenta
Characteristic of
most mammals
Brings the bloodstream
of mother and fetus into
close contact
The two don’t mix
Fig. 15.27
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Other Characteristics of Modern Mammals
Teeth
Reptiles have homodont dentition
Teeth are all the same
Mammals have heterodont dentition
Teeth are of different types specialized for different
feeding types
Hooves and horns
Keratin is the structural building material in claws,
hooves, and horns
Hooves are specialized keratin pads on the toes of
horses, cows and other running mammals
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Today’s Mammals
Monotremes: Egg laying mammals
The only living examples
Duck-billed platypus
Two species of echidna
(spiny anteater)
Echidna
Have reptilians and
mammalian features
Fig. 15.28a
Females lack well-developed nipples
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Today’s Mammals
Marsupials: Pouched mammals
Fertilized egg is surrounded
by chorion and amniotic
membranes, but no shell
The embryo is nourished by
an abundant yolk
After embryo is born, it crawls
into the marsupial pouch
It latches onto a nipple and
continues its development
Kangaroo
Fig. 15.28b
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Today’s Mammals
Placental mammals
Produce a true placenta
Nourishes the embryo
throughout its entire
development
The placenta forms
from both fetal and
maternal tissue
Lion
Fig. 15.28c
Most species living today are in this group
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