Chapter 11: Animal Diversification
Visibility in motion
Lectures by Mark Manteuffel, St. Louis Community College
Learning Goals




Define an animal and the key distinctions
that divide the species.
Define and describe the invertebrates,
including sponges, cnidarians, flatworms,
mollusks, arthropods and echinoderms.
Define and describe vertebrates and their
evolution.
Define and describe the terrestrial vertebrates,
including amphibians, birds, and mammals.
Animals are just
one branch of
the Eukarya
domain.
11.1 What is an animal?
Three Key Characteristics
Take-home message 11.1
Animals are organisms that share three
characteristics:
1) All of them can move during at least one
stage of development.
2) All of them eat other organisms.
3) All of them are multicellular.
11.2 There are no “higher” or
“lower” species.
• The fact that a species exists means
it can do the things all organisms
must do:
 find food
 escape predators
 reproduce
Take-home message 11.2
• From an evolutionary perspective, it is
inappropriate to view any species as
“higher” or “lower.”
Take-home message 11.2
• Certain adaptations have led to the rapid
and extensive diversification of particular
groups of species.
• Of the approximately 36 animal phyla, 9
phyla account for more than 99% of all
described animal species.
11.3 Four key distinctions
divide the animals.
1) Does the animal have specialized
cells that form defined tissues?
2) Does the animal develop with radial
symmetry or bilateral symmetry?
A body structured like a pie
or
A body with a left and right side,
which are mirror images
3) During gut development, does the
mouth or anus form first?
Protostomes
and
Deuterostomes
4) Does growth occur by molting or
by adding to the animal’s body in
a continuous manner?
Four key distinctions divide the animals
1) Does the animal have specialized cells that
form defined tissues?
2) Does the animal develop with radial
symmetry or bilateral symmetry?
3) During gut development, does the mouth or
anus form first?
4) Does growth occur by molting or by adding
to the animal’s body in a continuous
manner?
Take-home message 11.3
 The
animals probably originated from an
ancestral protist.
 Four key distinctions divide the extant
animals into monophyletic groups:
1) tissue or not
2) radial or bilateral symmetry
3) protostome or deuterostome development
4) growth through molting or through
continuous addition to the body
Invertebrates—
animals without
a backbone—
are the most
diverse group of
animals.
11.4
Sponges are
animals that
lack tissues
and organs.
Sponges are hermaphrodites
• Each individual contains both male and
female reproductive organs
• Sponges can also reproduce asexually
Q
Is your kitchen
sponge an animal?
Is it alive?
Take-home message 11.4
• Sponges are among the simplest of the
animal lineages.
• A sponge consists of a hollow tube with
pores in its wall; it has no tissues or
organs.
Take-home message 11.4
• Sponges reproduce sexually (by producing
eggs and sperm) and asexually (by
budding).
• The fertilized eggs grow into freeswimming larvae that settle and develop
into sessile, filter-feeding adult sponges.
11.5 Jellyfish and other
cnidarians are among the most
poisonous animals in the world.
Cnidarians
 Two
types of cnidarian bodies:
• a sessile polyp
• a free-floating medusa.
 Reproduce
both sexually and asexually
 Carnivores
that use cnidocysts
• stinging cells
3 Major Groups of Cnidarians
• Corals
• Sea anemones
• Jellyfishes
The Corals
• Small soft-bodied polyps living in large
colonial groups
• Secrete calcium carbonate
• Stinging tentacles surrounding a mouth
• Sexual and asexual reproduction
How is global warming affecting
the coral reefs of the world?
The Sea Anemones
• Resemble flowers
• Free-swimming larval stage
• Adult stage settles
– But may crawl slowly
The Jellyfishes
• Range tremendously in size
• Some species deadly
Take-home message 11.5
 Corals,
sea anemones, and jellyfishes are
radially symmetrical animals with defined
tissues, in the phylum Cnidaria.
 All
cnidarians are carnivores and use
specialized stinging cells located in their
tentacles to capture prey.
11.6 Flatworms, roundworms, and
segmented worms come in all
shapes and sizes.
The
Flatworms
The
Roundworms
The
Segmented
Worms
(Annelids)
Annelids: Polychaetes
 Marine
worms
 “Many
bristles”
 Some
are burrowing
 Some
are tube dwelling
Annelids: Earthworms
 “Few
 Bulk
bristles”
feeders
• consume particles of soil and organic material
 Castings
are valued by gardeners
Annelids: Leeches
 The
saliva of blood-sucking leeches
contains an anticoagulant substance that
prevents blood from clotting.
 Not
all leeches are blood suckers.
• More than half the species of leeches are
predators.
Take-home message 11.6
 Worms
are found in several different phyla
and are not a monophyletic group.
 All
are bilaterally symmetrical protostomes
with defined tissues.
 The
flatworms and segmented worms
(annelids) do not molt; the roundworms
do.
Take-home message 11.6
 Flatworms
include parasitic flukes and
tapeworms, many of which infect humans.
 Many
roundworms are parasites of plants
or animals and are responsible for several
widespread human diseases.
 Earthworms
are annelids that play an
important role in recycling dead plant
material.
11.7 Most mollusks live in shells.
Gastropods
 Snails
and slugs are called gastropod
mollusks.
 “Belly
 Found
foot”
in both aquatic and terrestrial
environments, snails and slugs account for
three-quarters of all mollusks.
Bivalve Mollusks
 Clams,
scallops, oysters, and mussels have
a pair of shells that clamp together.
 Roughly
8000 species of bivalve—most of
them live in the ocean.
 All
are filter feeders.
Cephalopods
Take-home message 11.7
 Mollusks
are protostome invertebrates that
do not molt.
 They
are the second most diverse phylum
of animals and include snails and slugs,
clams and oysters, and squids and
octopuses.
Take-home message 11.7
 Most
mollusks have a shell for protection,
a mantle of tissue that wraps around their
body, and a specialized tongue called a
radula.
11.8 Are some animals
smarter than others?
Are octopuses smart?
Take-home message 11.8

The predatory behavior of octopuses involves
exploration and manipulation.

These behaviors are considered as intelligent by
humans, but the concept of intelligence cannot be
applied objectively to other species.

Rather, species should be viewed as having
evolved in response to the selective forces at work
in their own particular niches.
11.9 Arthropods are the most
diverse group of all animals.
Arthropods make up about 75%
of the animal species on earth.
• The arthropod phylum is so large that,
even if we excluded all the insects—the
most diverse arthropod group—it would
still contain more species than any other
phylum.
Millipedes and Centipedes
• Long, segmented bodies that seem almost
worm-like
– jointed legs
– hard exoskeletons
• They live among fallen leaves.
• Millipedes feed on decaying plant material
• Centipedes are predators.
Chelicerates
• ~ 60,000 species
• Includes four horseshoe crab species and
the arachnids, land-dwelling arthropods
that include spiders, scorpions, mites, and
ticks.
Crustaceans
• ~ 52,000 species
• They all have one feature in common:
– five pairs of appendages extending from the
head.
• Most species are aquatic
– but the wood lice are terrestrial
Insects
• The most diverse group of arthropods.
• Three pairs of walking legs
– and most also have one or two pairs of wings
extending from the thorax.
• Abound in nearly all terrestrial habitats
• Wings, the ability to fly, and the
developmental process of metamorphosis
– Have led to their great diversification
Take-home message 11.9
 The
arthropods are protostome
invertebrates, and with nearly one million
species (and probably at least as many
more yet to be identified), they
outnumber all other forms of life in
species diversity.
Take-home message 11.9
• Centipedes are predators with fangs that
inject venom, and millipedes are herbivores
that feed on dead plant material.
• Spiders and scorpions are predatory
arthropods that eat insects and,
occasionally, small vertebrates.
Take-home message 11.9
• Lobsters, crabs, shrimp, and barnacles are
predatory marine crustaceans.
• Insects, with adaptations that include the
ability to fly and metamorphosis, are the
most diverse group of arthropods.
11.10 THIS IS HOW WE DO IT
How many species are there
on earth?
How many species of
beetles are there in one
species of tree?
How is the number of beetle
species in one tree species
related to the number of all
insect species in all types of
trees?
“I would hope someone will
challenge these figures with
more data.”
Unfortunately, this isn’t an
answer to our original
question.
What types of species are
the most difficult to
estimate (or count)?
Take-home message 11.10
• Determining how many distinct species
there on earth has long been a challenge
for biologists.
Take-home message 11.10
• By counting the exact number of beetle
species in one species of tropical tree,
• then estimating several parameters that
can be used to extrapolate this number to
the number of species of all arthropods
across the entire tropics,
• it is possible to make headway on this
challenge.
Take-home message 11.10
• Initial estimates using this method
suggest there may be many more species
on earth than previously believed.
11.11 Flight and metamorphosis
produced the greatest adaptive
radiation ever.
Mammals get bigger and
bigger the more they eat.
Why don’t insects?
Metamorphosis
• Complete
• Incomplete
Take-home message 11.11
 The
arthropods are protostome
invertebrates, and with nearly one million
species (and probably at least as many
more yet to be identified), they
outnumber all other forms of life in
species diversity.
Take-home message 11.11
• The ability to fly and the developmental
process of metamorphosis as a means of
overcoming the constraints of having a
rugged exoskeleton have contributed to
the enormous ecological diversity of
insects.
Take-home message 11.11
• The life cycle of most insects includes a
larval stage that is devoted to feeding and
growth, a pupal stage during which
metamorphosis occurs, and an adult stage
in which the insect reproduces.
11.12 Echinoderms are
vertebrates’ closest invertebrate
relatives
And include sea stars, sea urchins, and sand
dollars
Echinoderms do not have a brain.
• Their nervous system consists of a central
ring of nerves
• Branches extend into each appendage
• Tube feet
Take-home message 11.12
 Because
they are deuterostomes (as are
vertebrates), echinoderms are the
invertebrates that are the closest
evolutionary relatives to the vertebrates
(and other chordates).
 Their
aquatic larvae are bilaterally
symmetrical and share some anatomical
features with chordates, but adult
echinoderms are radially symmetrical.
The phylum
Chordata includes
vertebrates,
animals with a
backbone.
11.13 All vertebrates are
members of the phylum Chordata.
Four distinct features of chordates:
The Notochord

A rod of tissue extending from the head to
the tail

Stiffens the body when muscles contract
during locomotion

In advanced chordates
• present only in early embryos
• replaced by the vertebral column (backbone)
A Dorsal Hollow Nerve Cord
 Extends
from head to tail
 In
vertebrates, forms the central nervous
system (spinal cord and brain)
 In
other animals, lies in lower portion of
ventral part of body (and is solid instead
of hollow)
Pharyngeal Slits
 Pharyngeal
region
• the area between the back of the mouth and
the top of the throat
 Pharyngeal
slits are present in the
embryos of all chordates.
 Originally
used for breathing and feeding
A Post-Anal Tail
 extends
back beyond the end of the trunk
Phylum Chordata
• The Tunicates
• The Lancelets
• The Vertebrates
The Tunicates
• subphylum Urochordata
• ~ 2,000 species
• Invertebrate marine animals
• Filter feeders
The Lancelets
• subphylum Cephalochordata
• ~ 20 species
• Invertebrate animals
• Live in coastal waters
– are also filter feeders
The Vertebrates: The Most
Diverse Subphylum of Chordates
Vertebrates differ from the other
chordates in two important ways:
1. They have a backbone
2. They have a head
Take-home message 11.13
All chordates have four characteristic
structures:
1)
2)
3)
4)
a notochord
a dorsal hollow nerve cord
pharyngeal gills slits
a post-anal tail
Take-home message 11.13
 The
three subphyla of chordates are
superficially very different, but are united
by possessing these four structures at
some stage of their life cycle.
11.14 The evolution of jaws and
fins gave rise to the vast diversity
of vertebrate species.
The evolution of fins
paralleled the evolution of
jaws because the two
structures work together.
Fins get you to the organism you are
going to eat.
Jaws capture and kill it.
Take-home message 11.14
 The
development of two structures in
fishes—fins and jaws—set the stage for
the enormous diversity of modern
vertebrates.
11.15 The movement onto land
required lungs, a rigid backbone,
four legs, and eggs that resist
drying.
Q
Where did legs and lungs
come from?
Take-home message 11.15
• Four adaptations were important in the
transition of life from water to land:
• fins were modified into limbs,
• vertebrae were modified to transmit the body
weight through the limbs to the ground,
• the site of gas exchange was transferred from
gills and swim bladders to lungs,
• and terrestrial vertebrate eggs with membranes
and a shell resisted drying out
All terrestrial vertebrates are
tetrapods.
Amniotes and non-amniotes
11.16 Amphibians live a double life.
Take-home message 11.16
 Amphibians
are terrestrial vertebrates, but
the adults of most species still lay eggs in
water.
 The
eggs hatch into aquatic juveniles.
11.17 Birds are reptiles in
which feathers evolved.
Feathers
Take-home message 11.17
 Birds
are a branch of the reptile lineage
but, unlike other reptiles, possess feathers
and can generate body heat.
 The complex anatomical and physiological
systems that we see in extant animals,
such as feathers and endothermy in birds,
are the products of hundreds of millions of
years of step-by-step changes that began
with simple structures.
Take-home message 11.17
 Feathers
were originally colorful
structures, possibly used for behavioral
displays;
 additional
functions such as insulation and
flight evolved later.
11.18 Mammals are animals that
have hair and produce milk.
Are all mammals viviparous?
 Viviparity—giving
than laying eggs
 Monotremes
milk.
birth to babies rather
lay eggs, but also produce
Take-home message 11.18
 Hair
and mammary glands are defining
characteristics of mammals.
 Monotremes
 Marsupial
are egg-laying mammals.
mammals give birth after a
short period of development in the uterus,
and the newborn completes its
development in the mother’s pouch.
Take-home message 11.18
 Placental
mammals have a placenta that
provides oxygen and nutrients to the fetus
as it undergoes a longer development in
the uterus.
11.19 Humans tried out
different lifestyles.
Chimpanzee and
Modern Human Lineages
 Separated
only 5 or 6 million years ago
Humans differ from chimpanzees in
three major anatomical characteristics:
 Humans
are bipedal.
 Humans
are bigger than chimpanzees.
 Humans
have a brain that is about three
times the size of the brain of a
chimpanzee.
What are the advantages of
walking on two feet rather than
four?
Take-home message 11.19
 Humans’
forward-looking eyes, hands and
feet with ten fingers and ten toes, and
shoulder and elbow joints that allow the
arms to rotate are characteristics retained
from our arboreal ancestors.
Take-home message 11.19
 The
early ancestors of humans left the
trees and took up life on the ground,
where they walked on two legs.
11.20 How did we get here?
The past 200,000 years of human evolution
Were there ever two species of
humans alive at the same time?
If so, what happened?
Neandertals,
Homo neanderthalensis
 About
the same size as modern humans
 More
robust and muscular
 Lived
in organized groups
 Probably
hunted large mammals
The Indo-Australian Archipelago
 Homo
erectus
 Homo
floresiensis
What happened to the 3
other human species?
• Neandertals became extinct ~30,000
years ago.
• H. erectus ~27,000 years ago.
• H. floresiensis ~12,000 years ago.
Take-home message 11.20
humans (Homo sapiens) evolved
in Africa between 200,000 years ago
 Modern
 All
living humans are descended from that
evolutionary radiation.
Take-home message 11.20
 About
60,000 years ago, a small group of
modern humans moved out of Africa, and
the descendants of this group ultimately
populated Europe, Asia, and the Americas.
• Three other species of humans were living
at this time, all of which became extinct
between 30,000 and 12,000 years ago,
after modern humans had spread into the
areas where they were living.