© 2010 Pearson Education, Inc. The Evolution of Animals The Origins of Animal Diversity Major invertebrate Phyla Vertebrate Evolution and Diversity The

© 2010 Pearson Education, Inc.

The Evolution of Animals

The Origins of Animal Diversity

Major invertebrate Phyla

Vertebrate Evolution and Diversity

The Human Ancestry

Figure 17.00


– Some scientists think that these bones represent pygmies of a previously unknown human species, named Homo floresiensis.

– Other scientists suggest that the bones are from diseased Homo sapiens.


THE ORIGINS OF ANIMAL DIVERSITY

– Animal life began in Precambrian seas with the evolution of multicellular creatures that ate other organisms.


What Is an Animal?– Animals are:

• Eukaryotic

• Multicellular

• Heterotrophic organisms that obtain nutrients by ingestion

• Able to digest their food within their bodies

– Animal cells lack the cell walls that provide strong support in the bodies of plants and fungi.


Figure 17.1


– Most animals have:• Muscle cells • Nerve cells that control the muscles• Are diploid• Reproduce sexually• Proceed through a series of typically similar developmental

stages

MEIOSIS

Sperm

Egg

Adult

Key

FERTILIZATION

MITOSIS

Eight-cell stage

Internal sac

Digestive tract

Larva

METAMORPHOSIS

Haploid (n)

Diploid (2n)

Outer cell layer(ectoderm)

Later gastrula(cross section)

Future middlelayer of cells(mesoderm)

Inner cell layer(endoderm)

Early gastrula(cross section)

Blastula(cross section)

Zygote(fertilized egg)

Figure 17.2-8


Early Animals and the Cambrian Explosion

– Animals probably evolved from a colonial flagellated protist that lived in Precambrian seas about 600–700 million years ago.

Reproductive cells

Digestivecavity

Figure 17.3-5


– At the beginning of the Cambrian period, 542 million years ago, animals underwent a rapid diversification.

– During a span of about 15 million years:• All major animal body plans we see today evolved• Many of these animals seem bizarre

Figure 17.4


– What ignited the Cambrian explosion?• One hypothesis emphasizes increasingly complex

predator-prey relationships that led to diverse adaptations to feed, move, and provide protection.

• Another hypothesis, studying evolution and development, called evo-devo, focuses on the evolution of genes that control the development of animal forms.


Animal Phylogeny– Biologists categorize animals by:

• General features of body structure• More recently, using genetic data

– One major branch point distinguishes sponges from all other animals because, unlike more complex animals, sponges lack true tissues.

Ancestralprotist

No true tissues

Radial symmetry

Tissues

Bilateral symmetry

Sponges

Cnidarians

Molluscs

Flatworms

Annelids

Roundworms

Arthropods

Echinoderms

Chordates

Figure 17.5


– A second major evolutionary split is based on body symmetry.

• Radial symmetry refers to animals that are identical all around a central axis.

• Bilateral symmetry exists where there is only one way to split the animal into equal halves.

Radial symmetry. Parts radiate from the center, so any slicethrough the central axis divides into mirror images.

Bilateral symmetry. Only one slice can divide left and rightsides into mirror-image halves.

Figure 17.6


– Animals also vary according to the presence and type of body cavity, a fluid-filled space separating the digestive tract from the outer body wall.

– There are differences in how the body cavity forms.• If the body cavity is not completely lined by tissue derived from mesoderm, it is a pseudocoelom.• A true coelom is completely lined by tissue derived from mesoderm.

(a) No body cavity

(b) Pseudocoelom

(c) True coelom

Body covering(from ectoderm)

Tissue-filledregion (frommesoderm)



Musclelayer (frommesoderm)

Tissue layer liningcoelom andsuspendinginternal organs(from mesoderm)

Digestive tract(from endoderm)



Pseudocoelom

Coelom

Figure 17.7


MAJOR INVERTEBRATE PHYLA– Invertebrates:

• Are animals without backbones• Represent 95% of the animal kingdom


Sponges– Sponges represent multiple phyla.– Sponges include sessile animals that lack true tissues and that were once believed to be plants.– The body of a sponge resembles a sac perforated with holes.– Choanocyte cells draw water through the walls of the sponge where food is collected.

Choanocyte(feeding cell)

Waterflow

Skeletalfiber

Centralcavity

Choanocytein contactwith anamoebocyte

Amoebocyte

Flagella

Pores

Figure 17.8


Cnidarians– Cnidarians (phylum Cnidaria) are characterized by:

• The presence of “true” body tissues • Radial symmetry • Tentacles with stinging cells

– The basic body plan of a cnidarian is a sac with a gastrovascular cavity, a central digestive compartment with only one opening.

– The body plan has two variations:

• The sessile polyp – not able to move about• The floating medusa – the “mobile stage”

– Cnidarians are carnivores that use tentacles, armed with cnidocytes (“stinging cells”), to capture prey.

Mouth/anus

Tentacle

Polyp form

Gastrovascularcavity

Coral Hydra

Sea anemone

Gastrovascularcavity

Mouth/anusTentacle

Medusa form

JellyFigure 17.9

Tentacle

Trigger

Capsule

Cnidocyte

Dischargeof thread

Prey

Coiledthread

Figure 17.10


Molluscs– Molluscs (phylum Mollusca) are represented by soft-bodied animals,

usually protected by a hard shell.

– Many molluscs feed by using a file-like organ called a radula to scrape up food.

– The body of a mollusc has three main parts:

• A muscular foot used for movement

• A visceral mass housing most of the internal organs

• A mantle, which secretes the shell if present

– The three major groups of molluscs are:

• Gastropods, protected by a single, spiraled shell

• Bivalves, with a shell divided into two halves hinged together

• And cephalopods

– Typically lacking an external shell

– Built for speed and agility

Visceral mass

Reproductiveorgans

Digestivetract

Mantlecavity

Nervecords

Digestivetract

Coelom

Radula

Radula

Kidney Heart

Shell

Mouth

Mouth

Anus

Gill

Foot

Mantle

Figure 17.11

Gastropods

Snail (spiraled shell)

Sea slug (no shell)Figure 17.12a

Bivalves(hinged shell)

ScallopFigure 17.12b

Cephalopods(large brain and tentacles)

Octopus Squid

Figure 17.12c


Flatworms– Flatworms (phylum Platyhelminthes) are the

simplest bilateral animals.– Have “true” tissues– Flatworms include forms that are:

• Parasites or• Free-living in marine, freshwater, or damp habitats

– The gastrovascular cavity of flatworms• Is highly branched • Provides an extensive surface area for absorption of

nutrients

Digestive tract(gastrovascularcavity)

Nerve cords

Mouth

Eyespots (detect light)

Nervous tissue clusters(simple brain)

Planarian

Bilateral symmetry

Figure 17.13a


Annelids– Annelids (phylum Annelida) have:

• Body segmentation, a subdivision of the body along its length into a series of repeated parts

• A coelom• A complete digestive tract with

– Two openings, a mouth and anus– One-way movement of food

– The three main groups of annelids are:• Earthworms, which eat their way through soil• Polychaetes, marine worms with segmental

appendages for movement and gas exchange• Leeches, typically free-living carnivores but with

some bloodsucking forms

Mouth

Brain

Coelom

Nerve cord

Blood vesselsWaste disposal organ

Anus

Accessoryhearts

Mainheart

Digestivetract

Segmentwalls

Figure 17.15

Earthworms Polychaetes Leeches

MAJOR GROUPS OF ANNELIDS

Christmas tree wormGiant Australian earthworm European freshwater leech

Figure 17.14


Roundworms– Roundworms (phylum Nematoda) are:

• Cylindrical in shape, tapered at both ends• The most diverse and widespread of all animals

– Roundworms (also called nematodes) are:• Important decomposers • Dangerous parasites in plants, humans, and other

animals

(a) A free-livingroundworm

(b) Parasiticroundworms in pork

(c) Canine heartInfected with parasiticroundworms

Figure 17.16


Arthropods– Arthropods (phylum Arthropoda) are named for their

jointed appendages.– There are about one million arthropod species identified,

mostly insects.– Arthropods are a very diverse and successful group,

occurring in nearly all habitats in the biosphere.– There are four main groups of arthropods. Insects,

crustaceans, arachnids (spiders) and millipedes and centipedes

– Arthropods are segmented animals with specialized segments and appendages for an efficient division of labor among body regions. This allows for their great success as a phylum.

MAJOR GROUPS OF ARTHROPODS

Arachnids

Crustaceans

Millipedes and Centipedes

Insects

Figure 17.17


– The body of arthropods is completely covered by an exoskeleton, an external skeleton that provides:

• Protection • Points of attachment for the muscles that move appendages

AbdomenCephalothorax

(head and thorax)

Swimmingappendage

Antenna(sensory reception)

Eyes onmovable stalks

Mouthparts (feeding)

Walking leg

Walking legs

Figure 17.18

an arthropod of the large, mainly aquatic group Crustacea, such as a crab, lobster, shrimp, or barnacle.


– Arachnids:• Live on land• Usually have four pairs of walking legs and a

specialized pair of feeding appendages• Include spiders, scorpions, ticks, and mites

Arachnids

Two feedingappendages

Leg (four pairs)

Black widow spider Wood tick

Dust miteScorpion

Figure 17.19


– Crustaceans:• Are nearly all aquatic

• Have multiple pairs of specialized appendages

• Include crabs, lobsters, crayfish, shrimps, and barnacles

Crustaceans

Two feedingappendages Leg (three or more pairs)

Antennae

BarnaclesCrayfish

Pill bugShrimp

Crab

Figure 17.20


– Millipedes and centipedes have similar segments over most of the body.

– Millipedes:• Eat decaying plant matter • Have two pairs of short legs per body segment

– Centipedes:• Are terrestrial carnivores with poison claws • Have one pair of short legs per body segment

Millipedes and Centipedes

One pair of legs per segment

Two pairs of legsper segment

Millipede Centipede

Figure 17.21


– Insects typically have a three-part body:• Head• Thorax• Abdomen

– The insect head usually bears:• A pair of sensory antennae • A pair of eyes

– The mouthparts are adapted for particular kinds of eating.

– Flight is one key to the great success of insects.

Insect Anatomy

Antenna

Head Thorax Abdomen

Eye

Mouthparts

Figure 17.22


– Insects outnumber all other forms of life combined.

– Insects live in:• Almost every terrestrial habitat • Freshwater• The air

Insect Diversity

Banded OrangeHeliconian

PrayingmantisGiraffe weevil

Yellow jacket wasp Leaf beetle

Leaf roller

Peacock katydid

Longhorn beetleFigure 17.23


– Many insects undergo metamorphosis in their development.– Young insects may:

• Appear to be smaller forms of the adult or• Change from a larval form to something much different as an adult

The larva (caterpillar) spendsits time eating and growing,molting as it grows.

After several molts, thelarva becomes a pupaencased in a cocoon.

Within the pupa, the larval organs breakdown and adult organs develop fromcells that were dormant in the larva.

Finally, the adult emergesfrom the cocoon.

The butterfly flies off and reproduces, nourished mainlyby calories stored when it was a caterpillar.

Figure 17.24-5

Monarch butterflies

Figure 17.24a


Echinoderms– Echinoderms (phylum Echinodermata):

• Lack body segments• Typically show radial symmetry as adults but bilateral

symmetry as larvae • Have an endoskeleton• Have a water vascular system that facilitates

movement and gas exchange

– Echinoderms are a very diverse group.

Sea star

Sea urchin

Sea cucumber Sand dollar

Tube feet

Figure 17.25


VERTEBRATE EVOLUTION AND DIVERSITY

– Vertebrates have unique endoskeletons composed of:

• A cranium (skull) • A backbone made of a series of bones called

vertebrae

Vertebra

Cranium(protects brain)

Figure 17.26


Characteristics of Chordates– Chordates (phylum Chordata) all share four key

features that appear in the embryo and sometimes the adult:

• A dorsal, hollow nerve cord• A notochord• Pharyngeal slits• A post-anal tail

• A lancelet is an invertebrate chordate

Muscle segments

Notochord

Dorsal,

hollow

nerve cord

Pharyngeal

slits

Brain

Mouth

Anus

Post-anal

tail

Figure 17.27


– Another chordate characteristic is body segmentation, apparent in the:

• Backbone of vertebrates • Segmental muscles of all chordates


– Chordates consists of three groups of invertebrates:• Lancelets are bladelike animals without a cranium.• Tunicates, or sea squirts, also lack a cranium.• Hagfishes are eel-like forms that have a cranium.

– All other chordates are vertebrates.

Mouth

Tail

Lancelet Tunicates

Figure 17.28


– An overview of chordate and vertebrate evolution

Ancestralchordate

Tunicates

Lancelets

Hagfishes

Lampreys

Cartilaginousfishes

Bony fishes

Amphibians

Reptiles

Mammals

Ch

ord

ate

s

Ve

rteb

rate

s

Te

trap

od

sAm

nio

tes

Figure 17.29


Fishes– The first vertebrates were aquatic and probably evolved

during the early Cambrian period, about 542 million years ago. They:

• Lacked jaws • Are represented today by hagfishes

(a) Hagfish (inset: slime)

Figure 17.30a


– Lampreys:• Are vertebrates• Have a cranium• But lack jaws

(b) Lamprey (inset: mouth)Figure 17.30b


– The two major groups of living fishes are the:• Cartilaginous fishes (sharks and rays) with a flexible

skeleton made of cartilage

(c) Shark, a cartilaginous fish

Lateral line

Figure 17.30c


• And bony fishes with a skeleton reinforced by hard calcium salts

– Bony fishes include:• Ray-finned fishes• Lungfishes• Lobe-finned fishes

(d) Bony fish

Lateral line

Operculum

Figure 17.30d

(a) Hagfish(inset: slime)

(b) Lamprey(inset: mouth)

(c) Shark, acartilaginous fish

(d) Bony fish

Lateral line

Operculum

Figure 17.30


– Cartilaginous and bony fishes have a lateral line system that detects minor vibrations in the water.

– To provide lift off the bottom:• Cartilaginous fish must swim but

• Bony fish have swim bladders, gas-filled sacs that make them buoyant


Amphibians– Amphibians:

• Exhibit a mixture of aquatic and terrestrial adaptations• Usually need water to reproduce• Typically undergo metamorphosis from an aquatic

larva to a terrestrial adult

(a) Tadpole and adult golden palm tree frog

(b) Frogs and salamanders: the two major groups of amphibians

Red-eyed tree frog Texas barred tiger salamander

Figure 17.31


– Amphibians:• Were the first vertebrates to colonize land • Descended from fishes that had lungs and fins with muscles

Lobe-finned fish

Early amphibianFigure 17.32


– Terrestrial vertebrates are collectively called tetrapods, which means “four feet.”

– Tetrapods include:• Amphibians• Reptiles• Mammals


Reptiles– Reptiles (including birds) and mammals are amniotes,

which produce amniotic eggs that consist of a fluid-filled shell inside of which the embryo develops.


– Reptiles include:• Snakes• Lizards• Turtles• Crocodiles• Alligators• Birds


– Reptile adaptations to living on land include:• Amniotic eggs • Scaled, waterproof skin

Video: Galápagos Tortoise

Snake

Crocodile

Lizard

Turtle

Dinosaur

Birds

Figure 17.33


– Nonbird reptiles are ectotherms, sometimes referred to as “cold-blooded,” which means that they obtain their body heat from the environment.

– A nonbird reptile can survive on less than 10% of the calories required by a bird or mammal of equivalent size.

– Dinosaurs were the largest animals ever to live on land.


Birds– Recent genetic evidence shows that birds

evolved from a lineage of small, two-legged dinosaurs during the great reptilian radiation of the Mesozoic era.

– Birds have many adaptations that make them lighter in flight:

• Honeycombed bones• One instead of two ovaries• A beak instead of teeth

– Unlike other reptiles, birds are endotherms, maintaining a warmer and steady body temperature.


– Birds wings adapted for flight are airfoils, powered by breast muscles anchored to a keel-like breastbone.

Lower air pressure

Higher air pressure

Airfoil

Figure 17.34


Mammals– The first true mammals:

• Arose about 200 million years ago • Were probably small, nocturnal insect-eaters

– Most mammals are terrestrial although dolphins, porpoises, and whales are totally aquatic.

– Mammalian hallmarks are:• Hair • Mammary glands that produce milk, which nourishes the young

– There are three major groups of mammals:• Monotremes, egg-laying mammals• Marsupials, pouched mammals with a placenta• And eutherians, placental mammals

MAJOR GROUPS OF MAMMALS

Monotremes(hatched from eggs)

Marsupials(embryonic at birth)

Eutherians(fully developed at birth)

Echidna adultand egg Kangaroo newborn and mother

Wildebeest newbornand mother

Figure 17.35


– Eutherian placentas provide more intimate and long-lasting association between the mother and her developing young than do marsupial placentas.


THE HUMAN ANCESTRY– Humans are primates, the mammalian group

that also includes:• Lorises• Pottos• Lemurs• Tarsiers• Monkeys• Apes

Ancestralprimate

Lemurs, lorises,and pottos

Tarsiers

New World monkeys

Old World monkeys

Gibbons

Orangutans

Gorillas

Chimpanzees

Humans

An

thro

po

ids

Mo

nk

ey

sA

pe

s

Figure 17.36


– Primates evolved from insect-eating mammals during the late Cretaceous period.– Primates are distinguished by characteristics that were shaped by the demands of living in trees. These characteristics include:

• Limber shoulder joints

• Eyes in front of the face

• Excellent eye-hand coordination

• Extensive parental care

The Evolution of Primates


– Taxonomists divide the primates into three main groups:– The first group of primates includes:

• Lorises• Pottos• Lemurs• Tarsiers form the second group.

– The third group, anthropoids, includes:• Monkeys

Ring-tailed lemurFigure 17.37a

TarsierFigure 17.37b

Patas monkey (Old World monkey)Figure 17.37d

Black spider monkey(New World monkey)

Figure 17.37c


• Hominoids, the ape relatives of humans


• And humans

Ring-tailedlemur

Tarsier

Black spider monkey(New World monkey)

Patas monkey (Old World monkey)

Gorilla (ape)

Gibbon (ape)

Chimpanzee (ape)

Orangutan (ape)

HumanFigure 17.37


The Emergence of Humankind– Humans and chimpanzees have shared a common

African ancestry for all but the last 5–7 million years.


Some Common Misconceptions– Chimpanzees and humans represent two divergent

branches of the anthropoid tree that each evolved from a common, less specialized ancestor.

– Our ancestors were not chimpanzees or any other modern apes.


– Human evolution is not a ladder with a parade of fossil hominids (members of the human family) leading directly to modern humans.

– Instead, human evolution is more like a multibranched bush than a ladder.

– At times in hominid history, several different human species coexisted.

Ardipithecusramidus

Australopithecusafarensis

Australopithecusafricanus

Paranthropusrobustus

Paranthropusboisei

Homoneanderthalensis

Homosapiens

Homohabilis

Homo erectus

?M

illi

on

s o

f y

ea

rs a

go

6.0

5.0

5.5

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0

Figure 17.38


– Upright posture and an enlarged brain appeared at separate times during human evolution.

– Different human features evolved at different rates.

– Upright posture was the first human characteristic to evolve.


Australopithecus and the Antiquity of Bipedalism

– Before there was the genus Homo, several hominid species of the genus Australopithecus walked the African savanna.

– Fossil evidence pushes bipedalism in A. afarensis back to at least 4 million years ago.

(a) Australopithecusafarensis skeleton

(b) Ancient footprints (c) Model of anAustralopithecusafarensis male

Figure 17.39


Homo Habilis and the Evolution of Inventive Minds

– Homo habilis, “handy-man”:• Had a larger brain, intermediate in size between

Australopithecus and modern humans• Walked upright• Made stone tools that enhanced hunting, gathering,

and scavenging on the African savanna

Homo Erectus and the Global Dispersal of Humanity

– Homo erectus was the first species to extend humanity’s range from Africa to other continents.

– The global dispersal began about 1.8 million years ago.



– Homo erectus:• Was taller than H. habilis• Had a larger brain• Gave rise to Neanderthals

Tunicates

Lancelets

Hagfishes

Lampreys

Cartilaginous fishes

Bony fishes

Amphibians

Reptiles

MammalsFigure 17.UN11

Ancestralprotist

True tissues

Bilateral symmetry

Sponges

Cnidarians

Molluscs

Flatworms

Annelids

Roundworms

Arthropods

Echinoderms

Chordates

Figure 17.UN15

Ancestralchordate

Tunicates

Lancelets

Hagfishes

Lampreys

Cartilaginousfishes

Bony fishes

Amphibians

Reptiles

Mammals

Ch

ord

ate

s

Ve

rteb

rate

s

Te

trap

od

s

Am

nio

tes

Figure 17.UN16

Gastropods Bivalves Cephalopods

MOLLUSCS

Figure 17.UN19

Arachnids

ARTHROPODS

Crustaceans InsectsMillipedesand Centipedes

Figure 17.UN20

Monotremes

MAMMALS

Marsupials Eutherians

Figure 17.UN21

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© 2010 Pearson Education, Inc. The Evolution of Animals The Origins of Animal Diversity Major invertebrate Phyla Vertebrate Evolution and Diversity The