32 animaldiversity text

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Nutritional Mode• Animals are heterotrophs

– That ingest their food

An Introduction to Animal Diversity

Cell Structure and Specialization

Animals are multicellular eukaryotesTheir cells lack cell walls


• Their bodies are held together

– By structural proteins such as collagen

• Nervous tissue and muscle tissue

– Are unique to animals


Reproduction and Development

• Most animals reproduce sexually

– With the diploid stage usually dominating the life cycle

• After a sperm fertilizes an egg

– The zygote undergoes cleavage, leading to the formation of a blastula

• The blastula undergoes gastrulation

– Resulting in the formation of embryonic tissue layers and a gastrula


Zygote

Cleavage

Eight-cell stage

Cleavage

Blastula Cross section of blastula

Blastocoel

Blastocoel

Gastrula Gastrulation

Endoderm

Ectoderm

Blastopore

• Early embryonic development in animals

Figure 32.2

In most animals, cleavage results in theformation of a multicellular stage called a blastula.The blastula of many animals is a hollow ball of cells.

3

The endoderm ofthe archenteron de-

velops into the tissuelining the animal’s

digestive tract.

6

The blind pouchformed by gastru-

lation, calledthe archenteron,

opens to the outsidevia the blastopore.

5

Most animals also undergo gastrulation, a rearrangement of the embryo in which one end of the embryo folds inward, expands, and eventually fills the blastocoel, producing layers of embryonic tissues: the ectoderm (outer layer) and the endoderm (inner layer).

4

Only one cleavagestage–the eight-cellembryo–is shown here.

2 The zygote of an animal undergoes a succession of mitotic cell divisions called cleavage.

1


• All animals, and only animals

– Have Hox genes that regulate the development of body form

• Although the Hox family of genes has been highly conserved

– It can produce a wide diversity of animal morphology


• The common ancestor of living animals

– May have lived 1.2 billion–800 million years ago

– May have resembled modern choanoflagellates, protists that are the closest living relatives of animals

Figure 32.3

Single cell

Stalk


– Was probably itself a colonial, flagellated protist

Figure 32.4

Colonial protist,an aggregate ofidentical cells

Hollow sphere of unspecialized cells (shown in cross section)

Beginning of cell specialization

Infolding Gastrula-like “protoanimal”

Somatic cells Digestivecavity

Reproductive cells


• Animals can be characterized by “body plans”

• One way in which zoologists categorize the diversity of animals

– Is according to general features of morphology and development

• A group of animal species

– That share the same level of organizational complexity is known as a grade


• The set of morphological and developmental traits that define a grade

– Are generally integrated into a functional whole referred to as a body plan


Symmetry

• Some animals have radial symmetry

– Like in a flower pot

Figure 32.7a

Radial symmetry. The parts of a radial animal, such as a sea anemone (phylum Cnidaria), radiate from the center. Any imaginary slice through the central axis divides the animal into mirror images.

(a)


• Some animals exhibit bilateral symmetry

– Or two-sided symmetry

Figure 32.7b

Bilateral symmetry. A bilateral animal, such as a lobster (phylum Arthropoda), has a left side and a right side. Only one imaginary cut divides the animal into mirror-image halves.

(b)


• Bilaterally symmetrical animals have

– A dorsal (top) side and a ventral (bottom) side

– A right and left side

– Anterior (head) and posterior (tail) ends

– Cephalization, the development of a head


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


• Animal embryos

– Form germ layers, embryonic tissues, including ectoderm, endoderm, and mesoderm

• Diploblastic animals

– Have two germ layers

• Triploblastic animals

– Have three germ layers


Body Cavities

• In triploblastic animals

– A body cavity may be present or absent


• A true body cavity

– Is called a coelom and is derived from mesoderm

Figure 32.8a

Coelom

Body covering(from ectoderm)

Digestive tract(from endoderm)

Tissue layerlining coelomand suspendinginternal organs(from mesoderm)

Coelomate. Coelomates such as annelids have a true coelom, a body cavity completely lined by tissue derived from mesoderm.

(a)


• A pseudocoelom

– Is a body cavity derived from the blastocoel, rather than from mesoderm

Figure 32.8b

PseudocoelomMuscle layer(from mesoderm)

Body covering(from ectoderm)

Digestive tract(from ectoderm)

Pseudocoelomate. Pseudocoelomates such as nematodes have a body cavity only partially lined by tissue derived from mesoderm.

(b)


• Organisms without body cavities

– Are considered acoelomates

Figure 32.8c

Body covering(from ectoderm) Tissue-

filled region(from mesoderm)

Digestive tract(from endoderm)

Acoelomate. Acoelomates such as flatworms lack a body cavity between the digestive tract and outer body wall.

(c)


Protostome and Deuterostome Development

• Based on certain features seen in early development

– Many animals can be categorized as having one of two developmental modes: protostome development or deuterostome development


Cleavage

• In protostome development

– Cleavage is spiral and determinate

• In deuterostome development

– Cleavage is radial and indeterminate

Figure 32.9a

Protostome development(examples: molluscs, annelids,

arthropods)

Deuterostome development(examples: echinoderms,

chordates)

Eight-cell stage Eight-cell stage

Spiral and determinate Radial and indeterminate

(a) Cleavage. In general, protostomedevelopment begins with spiral, determinate cleavage.Deuterostome development is characterized by radial, indeterminate cleavage.


Coelom Formation


– The splitting of the initially solid masses of mesoderm to form the coelomic cavity is called schizocoelous development


– Formation of the body cavity is described as enterocoelous development

Figure 32.9b

Archenteron

Blastopore MesodermCoelom

BlastoporeMesoderm

Schizocoelous: solidmasses of mesodermsplit and form coelom

Enterocoelous:folds of archenteronform coelom

Coelom (b) Coelom formation. Coelom formation begins in the gastrula stage. In protostome development, the coelom forms from splits in the mesoderm (schizocoelous development). In deuterostome development, the coelom forms from mesodermal outpocketings of the archenteron (enterocoelous development).


Fate of the Blastopore


– The blastopore becomes the mouth


– The blastopore becomes the anus

Figure 32.9c

Anus

Anus

Mouth

Mouth

Mouth developsfrom blastopore

Anus developsfrom blastopore

Digestive tube


• Leading hypotheses agree on major features of the animal phylogenetic tree

• Zoologists currently recognize about 35 animal phyla

• The current debate in animal systematics

– Has led to the development of two phylogenetic hypotheses, but others exist as well


• One hypothesis of animal phylogeny based mainly on morphological and developmental comparisons

Figure 32.10

Po

rife

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Cn

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ora

Ph

oro

nid

a

Ect

op

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rmat

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Ch

ord

ata

Pla

tyh

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inth

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An

nel

ida

Art

hro

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da

Ro

tife

ra

Ne

me

rte

a

Ne

ma

tod

a

“Radiata” Deuterostomia Protostomia

Bilateria

Eumetazoa

Metazoa

Ancestral colonialflagellate


• One hypothesis of animal phylogeny based mainly on molecular data

Figure 32.11

Ca

lcar

ea

Sili

care

a

Cte

no

ph

ora

Cn

ida

ria

Ech

ino

de

rmat

a

Ch

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Art

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da

“Radiata”

“Porifera” Deuterostomia Lophotrochozoa Ecdysozoa

Bilateria

Eumetazoa

Metazoa

Ancestral colonialflagellate


Points of Agreement

• All animals share a common ancestor

• Sponges are basal animals

• Eumetazoa is a clade of animals with true tissues


• Most animal phyla belong to the clade Bilateria

• Vertebrates and some other phyla belong to the clade Deuterostomia


Disagreement over the Bilaterians

• The morphology-based tree

– Divides the bilaterians into two clades: deuterostomes and protostomes

• In contrast, several recent molecular studies

– Generally assign two sister taxa to the protostomes rather than one: the ecdysozoans and the lophotrochozoans


• Ecdysozoans share a common characteristic

– They shed their exoskeletons through a process called ecdysis

Figure 32.12


• Lophotrochozoans share a common characteristic

– Called the lophophore, a feeding structure

• Other phyla

– Go through a distinct larval stage called a trochophore larva

Figure 32.13a, b

Apical tuftof cilia

Mouth

Anus(a) An ectoproct, a lophophorate (b) Structure of trochophore larva


Future Directions in Animal Systematics

• Phylogenetic studies based on larger databases

– Will likely provide further insights into animal evolutionary history


Invertebrates

– Are animals that lack a backbone

– Account for 95% of known animal species

Ancestral colonialchoanoflagellate

Eumetazoa

Bilateria

Deuterostomia

Po

rife

ra

Cn

ida

ria

Oth

er

bila

teria

ns

(incl

ud

ing

Ne

ma

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a,

Art

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da

,M

ollu

sca

, a

nd

An

ne

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)

Ech

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Ch

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ata

Figure 33.2


Sponges• Sponges are sessile and have a porous body and

choanocytes

• Sponges, phylum Porifera

– Live in both fresh and marine waters

– Lack true tissues and organs

• Choanocytes, flagellated collar cells

– Generate a water current through the sponge and ingest suspended food

• Most sponges are hermaphrodites

– Meaning that each individual functions as both male and female


• Sponges are suspension feeders

– Capturing food particles suspended in the water that passes through their body

Azure vase sponge (Callyspongia plicifera)

Osculum

Spicules

Waterflow

Flagellum

CollarFood particlesin mucus

Choanocyte

Phagocytosis offood particles Amoebocyte

Choanocytes. The spongocoel is lined with feeding cells called choanocytes. By beating flagella, the choanocytes create a current that draws water in through the porocytes.

Spongocoel. Water passing through porocytes

enters a cavity called the spongocoel.

Porocytes. Water enters the epidermis through

channels formed by porocytes, doughnut-shaped cells that span the body wall.

Epidermis. The outer layer consists of tightly

packed epidermal cells.

Mesohyl. The wall of this simple sponge consists of

two layers of cells separatedby a gelatinous matrix, themesohyl (“middle matter”).

The movement of the choanocyte flagella also draws water through its collar of fingerlike projections. Food particles are trapped in the mucus coating the projections, engulfed by phagocytosis, and either digested or transferred to amoebocytes.

Amoebocyte. Amoebocytes transport nutrients to other cells ofthe sponge body and also produce materials for skeletal fibers (spicules).

5

6

7

4

3

2

1

Figure 33.4


Cnidarians

• Cnidarians

– Have diversified into a wide range of both sessile and floating forms including jellies, corals, and hydras

– But still exhibit a relatively simple diploblastic, radial body plan

• The basic body plan of a cnidarian

– Is a sac with a central digestive compartment, the gastrovascular cavity

• A single opening

– Functions as both mouth and anus


• There are two variations on this body plan

– The sessile polyp and the floating medusa

Mouth/anus

TentacleGastrovascularcavity

Gastrodermis

Mesoglea

Epidermis

Tentacle

Bodystalk

Mouth/anus

MedusaPolyp

Figure 33.5


Tentacle

“Trigger”

Nematocyst

Coiled thread

DischargeOf thread

Cnidocyte

Prey

Figure 33.6

• Cnidarians are carnivores

– That use tentacles to capture prey

• The tentacles are armed with cnidocytes

– Unique cells that function in defense and the capture of prey


– The phylum Cnidaria is divided into four major classes: Hydrozoa, Scyphozoa, Cubozoa, and Anthozoa

(a) These colonial polyps are members of class Hydrozoa.

(b) Many species of jellies (classScyphozoa), including thespecies pictured here, are bioluminescent. The largest scyphozoans have tentaclesmore than 100 m long dangling from a bell-shaped body up to 2 m in diameter.

(c) The sea wasp (Chironex fleckeri) is a member of class Cubozoa. Its poison,which can subdue fish andother large prey, is more potent than cobra venom.

(d) Sea anemones and othermembers of class Anthozoaexist only as polyps.

Figure 33.7a–d


Hydrozoans

• Most hydrozoans

– Alternate between polyp and medusa forms

Feeding polyp

Reproductivepolyp

Medusabud

ASEXUALREPRODUCTION(BUDDING)

GonadMedusa

MEIOSIS

FERTILIZATION

SEXUALREPRODUCTION Egg Sperm

Developingpolyp

Portion ofa colonyof polyps

Maturepolyp

Planula(larva) Key

Haploid (n)Diploid (2n)1 mm

Zygote

Figure 33.8

A colony ofinterconnected

polyps (inset,LM) results

from asexualreproductionby budding.

1

Some of the colony’s polyps, equipped with tentacles, are specialized for feeding.

2 Other polyps, specialized for reproduction, lack tentacles and produce tiny medusae by asexual budding.

3

The medusae swim off, grow, and reproduce sexually.

4

The zygote develops into a solid ciliated larva called a planula.5 The planula eventually settles

and develops into a new polyp.6


Scyphozoans

• In the class Scyphozoa

– Jellies (medusae) are the prevalent form of the life cycle

• In the class Cubozoa, which includes box jellies and sea wasps

– The medusa is box-shaped and has complex eyes

• Class Anthozoa includes the corals and sea anemones

– Which occur only as polyps


bilateral symmetry

• Most animals have bilateral symmetry

• The vast majority of animal species belong to the clade Bilateria

– Which consists of animals with bilateral symmetry and triploblastic development


Flatworms

• Members of phylum Platyhelminthes

– Live in marine, freshwater, and damp terrestrial habitats

– Are flattened dorsoventrally and have a gastrovascular cavity

• Although flatworms undergo triploblastic development

– They are acoelomates

– Flatworms are divided into four classes


• Turbellarians

– Are nearly all free-living and mostly marine

• The best-known turbellarians, commonly called planarians

– Have light-sensitive eyespots and centralized nerve nets

Pharynx. The mouth is at thetip of a muscular pharynx thatextends from the animal’sventral side. Digestive juicesare spilled onto prey, and thepharynx sucks small pieces offood into the gastrovascularcavity, where digestion continues.

Digestion is completed withinthe cells lining the gastro-vascular cavity, which hasthree branches, each withfine subbranches that pro-vide an extensive surface area.

Undigested wastesare egestedthrough the mouth.

Ganglia. Located at the anterior endof the worm, near the main sourcesof sensory input, is a pair of ganglia,dense clusters of nerve cells.

Ventral nerve cords. Fromthe ganglia, a pair ofventral nerve cords runsthe length of the body.

Gastrovascularcavity

Eyespots

Figure 33.10


Monogeneans and Trematode

• Monogeneans and trematodes

– Live as parasites in or on other animals

– Parasitize a wide range of hosts

These larvae penetratethe skin and blood vessels of humans working in irrigated fields contaminated with infected human feces.

Asexual reproduction within a snail results in another type of motilelarva, which escapes from the snail host.

Blood flukes reproduce sexually in the human host. The fertilized eggs exit the host in feces.

The eggs develop in water into ciliated larvae. These larvaeinfect snails, the intermediate hosts.

Snail host

1 mm

Female

Male

52

3

4

Figure 33.11

Mature flukes live in the blood vessels of the human intestine. A female fluke fits into a groove running the length of the larger male’s body, as shown in the light micrograph at right.

1

Trematodes that parasitize humans

Spend part of their lives in snail hosts

Most monogeneansAre parasites of fish


Tapeworm

• Tapeworms

– Are also parasitic and lack a digestive system

Proglottids withreproductive structures

200 µm

HooksSucker

Scolex

Figure 33.12


Rotifers

• Rotifers, phylum Rotifera

– Are tiny animals that inhabit fresh water, the ocean, and damp soil

• Rotifers are smaller than many protists

– But are truly multicellular and have specialized organ systems

0.1 mmFigure 33.13


• Rotifers have an alimentary canal

– A digestive tube with a separate mouth and anus that lies within a fluid-filled pseudocoelom

• Rotifers reproduce by parthenogenesis

– In which females produce more females from unfertilized eggs


Lophophorates: Ectoprocts, Phoronids, and Brachiopods

• Lophophorates have a lophophore

– A horseshoe-shaped, suspension-feeding organ bearing ciliated tentacles

• Ectoprocts

– Are colonial animals that superficially resemble plants

• Phoronids

– Are tube-dwelling marine worms ranging from 1 mm to 50 cm in length

• Brachiopods superficially resemble clams and other hinge-shelled molluscs

– But the two halves of the shell are dorsal and ventral rather than lateral, as in clams


Nemerteans

• Members of phylum Nemertea

– Are commonly called proboscis worms or ribbon worms

• The nemerteans unique proboscis

– Is used for defense and prey capture

– Is extended by a fluid-filled sac

• Nemerteans also have a closed circulatory system

– In which the blood is contained in vessels distinct from fluid in the body cavity

Figure 33.15


Molluscs

• Molluscs have a muscular foot, a visceral mass, and a mantle

• Phylum Mollusca

– Includes snails and slugs, oysters and clams, and octopuses and squids

• Most molluscs are marine

– Though some inhabit fresh water and some are terrestrial

• Molluscs are soft-bodied animals

– But most are protected by a hard shell


Visceral mass

Mantle

Foot

Coelom Intestine

Gonads

Mantlecavity

Anus

Gill

Nervecords Esophagus

Stomach

ShellRadula

Mouth

Mouth

Nephridium. Excretory organs called nephridia remove metabolic wastes from the hemolymph.

Heart. Most molluscs have an open circulatory system. The dorsally located heart pumps circulatory fluid called hemolymph through arteries into sinuses (body spaces). The organs of the mollusc are thus continually bathed in hemolymph.

The long digestive tract is coiled in the visceral mass.

Radula. The mouth region in many mollusc species contains a rasp-like feeding organ called a radula. This belt of backward-curved teeth slides back and forth, scraping and scooping like a backhoe.

The nervous system consists

of a nerve ring around the

esophagus, from which nerve

cords extend.

Figure 33.16


• Most molluscs have separate sexes

– With gonads located in the visceral mass

• The life cycle of many molluscs

– Includes a ciliated larval stage called a trochophore

There are four major classes of molluscs


Chitons

• Class Polyplacophora is composed of the chitons

– Oval-shaped marine animals encased in an armor of eight dorsal plates

Figure 33.17


Gastropods

• About three-quarters of all living species of molluscs

– Belong to class Gastropoda

A land snail (a)

A sea slug. Nudibranchs, or sea slugs, lost their shell during their evolution.

(b)Figure 33.18a, b

Most gastropodsAre marine, but there are also many freshwater and terrestrial speciesPossess a single, spiraled shell

Slugs lack a shellOr have a reduced shell


• The most distinctive characteristic of this class

– Is a developmental process known as torsion, which causes the animal’s anus and mantle to end up above its head

Anus

Mantlecavity

StomachIntestine

Mouth

Figure 33.19


Bivalves

• Molluscs of class Bivalvia

– Include many species of clams, oysters, mussels, and scallops

– Have a shell divided into two halves

Figure 33.20


• The mantle cavity of a bivalve

– Contains gills that are used for feeding as well as gas exchange

Hinge areaGut Coelom

Heart

Adductormuscle

AnusExcurrentsiphon

Waterflow

IncurrentsiphonGill

Mantlecavity

Foot

Palp

Mouth

Shell

Mantle

Figure 33.21


Cephalopods

• Class Cephalopoda includes squids and octopuses

– Carnivores with beak-like jaws surrounded by tentacles of their modified foot

• Most octopuses

– Creep along the sea floor in search of prey

• Squids use their siphon

– To fire a jet of water, which allows them to swim very quickly


`

• One small group of shelled cephalopods

– The nautiluses, survives today

Figure 33.22c(c) Chambered nautiluses are the only living

cephalopods with an external shell.


Annelids

• Annelids are segmented worms

• Annelids

– Have bodies composed of a series of fused rings

– The phylum Annelida is divided into three classes


Oligochaetes

• Oligochaetes (class Oligochaeta)

– Are named for their relatively sparse chaetae, or bristles made of chitin

– Include the earthworms and a variety of aquatic species

• Members of class Polychaeta

– Possess paddlelike parapodia that function as gills and aid in locomotion

• Members of class Hirudinea

– Are blood-sucking parasites, such as leeches


• Earthworms eat their way through the soil, extracting nutrients as the soil moves through the alimentary canal

– Which helps till the earth, making earthworms valuable to farmers


• Anatomy of an earthworm

MouthSubpharyngealganglion

Pharynx EsophagusCrop

Gizzard

Intestine

Metanephridium

Ventralvessel

Nervecords

Nephrostome

Intestine

Dorsalvessel

Longitudinalmuscle

Circularmuscle

Epidermis Cuticle

Septum(partitionbetweensegments)

Anus

Each segment is surrounded by longitudinal muscle, which in turn is surrounded by circular muscle. Earthworms coordinate the contraction of these two sets of muscles to move (see Figure 49.25). These muscles work against the noncompressible coelomic fluid, which acts as a hydrostatic skeleton.

Coelom. The coelom of the earthworm is partitioned by septa.

Metanephridium. Each segment of the worm contains a pair of excretory tubes, called metanephridia, with ciliated funnels, called nephrostomes. The metanephridia remove wastes from the blood and coelomic fluid through exterior pores.

Tiny blood vessels are abundant in the earthworm’s skin, which functions as its respiratory organ. The blood contains oxygen-carryinghemoglobin.

Ventral nerve cords with segmental ganglia. The nerve cords penetrate the septa and run the length of the animal, as do the digestive tract and longitudinal blood vessels.

The circulatory system, a network of vessels, is closed. The dorsal and ventral vessels are linked by segmental pairs of vessels. The dorsal vessel and five pairs of vessels that circle the esophagus of an earthworm are muscular and pump blood through the circulatory system.

Cerebral ganglia. The earthworm nervous system features a brain-like pair of cerebral ganglia above and

in front of the pharynx. A ring of nerves around the pharynx connects to a subpharyngeal ganglion, from which a fused

pair of nerve cords runs posteriorly.

Chaetae. Each segment has four pairs of

chaetae, bristles that provide traction for

burrowing.

Many of the internal structures are repeated within each segment of

the earthworm.

Giant Australian earthworm

Clitellum

Table 33.23


Nematodes

• Nematodes are nonsegmented pseudocoelomates covered by a tough cuticle

• Among the most widespread of all animals, nematodes, or roundworms

– Are found in most aquatic habitats, in the soil, in moist tissues of plants, and in the body fluids and tissues of animals

• Some species of nematodes

– Are important parasites of plants and animals


• The cylindrical bodies of nematodes (phylum Nematoda)

– Are covered by a tough coat called a cuticle

25 µmFigure 33.26


Arthropods

• Arthropods are segmented coelomates that have an exoskeleton and jointed appendages

• 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


General Characteristics of Arthropods

• The diversity and success of arthropods

– Are largely related to their segmentation, hard exoskeleton, and jointed appendages

Antennae(sensoryreception)

Head Thorax

Swimmingappendages

Walking legs

Mouthparts (feeding)Pincer (defense)

AbdomenCephalothorax

Figure 33.29

Figure 33.28


• The body of an arthropod

– Is completely covered by the cuticle, an exoskeleton made of chitin

• When an arthropod grows

– It molts its exoskeleton in a process called ecdysis

• Arthropods have an open circulatory system

– In which fluid called hemolymph is circulated into the spaces surrounding the tissues and organs

• A variety of organs specialized for gas exchange

– Have evolved in arthropods


Cheliceriforms

• Cheliceriforms, subphylum Cheliceriformes

– Are named for clawlike feeding appendages called chelicerae

– Include spiders, ticks, mites, scorpions, and horseshoe crabs

• Most of the marine cheliceriforms are extinct

– But some species survive today, including the horseshoe crabs

Figure 33.30


Scorpions have pedipalps that are pincers specialized for defense and the capture of food. The tip of the tail bears a poisonous stinger.

(a) Dust mites are ubiquitous scavengers in human dwellings but are harmless except to those people who are allergic to them (colorized SEM).

(b) Web-building spiders are generally most active during the daytime.

(c)

50 µm

Figure 33.31a–c

• Most modern cheliceriforms are arachnids

– A group that includes spiders, scorpions, ticks, and mites


• Arachnids have an abdomen and a cephalothorax

– Which has six pairs of appendages, the most anterior of which are the chelicerae

Digestivegland

Intestine

HeartStomach

Brain

Eyes

Poisongland

PedipalpChelicera

Book lung

Spermreceptacle

Gonopore(exit for eggs)Silk gland

Spinnerets

Anus

Ovary

Figure 33.32


Myriapods

• Millipedes, class Diplopoda

– Have a large number of legs

• Each trunk segment

– Has two pairs of legs

• Centipedes, class Chilopoda

– Are carnivores with jaw-like mandibles

– Have one pair of legs per trunk segment

Figure 33.33

Figure 33.34


Insects

• Subphylum Hexapoda, insects and their relatives

– Are more species-rich than all other forms of life combined

– Live in almost every terrestrial habitat and in fresh water


• The internal anatomy of an insect

– Includes several complex organ systems

Compound eye

Antennae

Anus

Vagina

OvaryDorsalartery Crop

Abdomen Thorax Head

The insect body has three regions: head, thorax, and abdomen. The segmentation of the thorax and abdomen are obvious, but the segments that form the head are fused.

Heart. The insect heart drives hemolymph through an open circulatory system.

Cerebral ganglion. The two nerve cords meet in the head, where the ganglia of several anterior segments are fused into a cerebral ganglion (brain). The antennae, eyes, and other sense organs are concentrated on the head.

Tracheal tubes. Gas exchange in insects is accomplished by a tracheal system of branched, chitin-lined tubes that infiltrate the body and carry oxygen directly to cells. The tracheal system opens to the outside of the body through spiracles, pores that can control air flow and water loss by opening or closing.

Nerve cords. The insect nervous system consists of a pair of ventral nerve cords with several segmental ganglia.

Insect mouthparts are formed from several pairs of modified appendages. The mouthparts include mandibles, which grasshoppers use for chewing. In other insects, mouthparts are specialized for lapping, piercing, or sucking.

Malpighian tubules. Metabolic wastes are

removed from the hemolymph by excretory organs called Malpighian

tubules, which are out-pocketings of the

digestive tract.

Figure 33.35


• Flight is obviously 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


• Many insects

– Undergo metamorphosis during their development

• In incomplete metamorphosis, the young, called nymphs

– Resemble adults but are smaller and go through a series of molts until they reach full size

• Insects with complete metamorphosis

– Have larval stages specialized for eating and growing that are known by such names as maggot, grub, or caterpillar

• The larval stage

– Looks entirely different from the adult stage


• Metamorphosis from the larval stage to the adult stage

– Occurs during a pupal stage

Larva (caterpillar)(a)(b) Pupa

(c) Pupa(d) Emerging adult

(e) AdultFigure 33.6a–e


• Insects are classified into about 26 ordersORDER

Blattodea 4,000 Cockroaches have a dorsoventrally flattened body, with legs modified for rapid running. Forewings, when present, areleathery, whereas hind wings are fanlike. Fewer than 40 cock-roach species live in houses; the rest exploit habitats ranging from tropical forest floors to caves and deserts.

Beetles comprise the most species-rich order of insects. They have two pairs of wings, one of which is thick and leathery, theother membranous. They have an armored exoskeleton andmouthparts adapted for biting and chewing. Beetles undergocomplete metamorphosis.

Earwigs are generally nocturnal scavengers. While some species are wingless, others have two pairs of wings, one of which is thick and leathery, the other membranous. Earwigshave biting mouthparts and large posterior pincers. They un-dergo incomplete metamorphosis.

Dipterans have one pair of wings; the second pair has become modified into balancing organs called halteres. Their head islarge and mobile; their mouthparts are adapted for sucking,piercing, or lapping. Dipterans undergo complete metamorpho-sis. Flies and mosquitoes are among the best-known dipterans, which live as scavengers, predators, and parasites.

Hemipterans are so-called “true bugs,” including bed bugs, assassin bugs, and chinch bugs. (Insects in other orders aresometimes erroneously called bugs.) Hemipterans have two pairs of wings, one pair partly leathery, the other membranous.They have piercing or sucking mouthparts and undergoincomplete metamorphosis.

Ants, bees, and wasps are generally highly social insects. Theyhave two pairs of membranous wings, a mobile head, and chewing or sucking mouthparts. The females of many species have a posterior stinging organ. Hymenopterans undergo com-plete metamorphosis.

Termites are widespread social insects that produce enormous colonies. It has been estimated that there are 700 kg oftermites for every person on Earth! Some termites have twopairs of membranous wings, while others are wingless. They feed on wood with the aid of microbial symbionts carried in specialized chambers in their hindgut.

Coleoptera 350,000

Dermaptera 1,200

Diptera 151,000

Hemiptera 85,000

Hymenoptera 125,000

Isoptera 2,000

APPROXIMATENUMBER OF

SPECIESMAIN CHARACTERISTICS EXAMPLES

Germancockroach

Japanesebeetle

Earwig

Horsefly

Leaf-Footedbug

Cicada-killer wasp

Termite

Figure 33.37

Lepidoptera 120,000 Butterflies and moths are among the best-known insects. They have two pairs of wings covered with tiny scales. To feed, theyuncoil a long proboscis. Most feed on nectar, but some species feed on other substances, including animal blood or tears.

Odonata5,000 Dragonflies and damselflies have two pairs of large, membran-

ous wings. They have an elongated abdomen, large, compound eyes, and chewing mouthparts. They undergo incomplete meta-morphosis and are active predators.

Orthoptera 13,000 Grasshoppers, crickets, and their relatives are mostly herbi-vorous. They have large hind legs adapted for jumping, twopairs of wings (one leathery, one membranous), and biting or chewing mouthparts. Males commonly make courtship sounds by rubbing together body parts, such as a ridge on their hind leg. Orthopterans undergo incomplete metamorphosis.

Phasmida 2,600 Stick insects and leaf insects are exquisite mimics of plants. The eggs of some species even mimic seeds of the plants on which the Insects live. Their body is cylindrical or flattened dorsoventrally. They lack forewings but have fanlike hind wings. Their mouthparts are adapted for biting or chewing.

Phthiraptera 2,400 Commonly called sucking lice, these insects spend their entire life as an ectoparasite feeding on the hair or feathers of a singlehost. Their legs, equipped with clawlike tarsi, are adapted forclinging to their hosts. They lack wings and have reduced eyes.Sucking lice undergo incomplete metamorphosis.

Siphonaptera 2,400 Fleas are bloodsucking ectoparasites on birds and mammals. Their body is wingless and laterally compressed. Their legs are modified for clinging to their hosts and for long-distance jumping. They undergo complete metamorphosis.

Thysanura 450 Silverfish are small, wingless insects with a flattened body and reduced eyes. They live in leaf litter or under bark. They can also infest buildings, where they can become pests.

Trichoptera 7,100 The larvae of caddisflies live in streams, where they make houses from sand grains, wood fragments, or other material held to-gether by silk. Adults have two pairs of hairy wings and chewingor lapping mouthparts. They undergo complete metamorphosis.

Swallowtailbutterfly

Dragonfly

Katydid

Stick insect

HumanBodylouse

Flea

Silverfish

Caddisfly

ORDERAPPROXIMATE

NUMBER OFSPECIES

MAIN CHARACTERISTICS EXAMPLE

Figure 33.37


Crustaceans

• While arachnids and insects thrive on land

– Crustaceans, for the most part, have remained in marine and freshwater environments

• Crustaceans, subphylum Crustacea

– Typically have biramous, branched, appendages that are extensively specialized for feeding and locomotion


• Decapods are all relatively large crustaceans

– And include lobsters, crabs, crayfish, and shrimp

Ghost crabs (genus Ocypode) live on sandy ocean beaches worldwide. Primarily nocturnal, they take shelter in burrows during the day.

(a)

Figure 33.38a

Planktonic crustaceans include many species of copepods

Which are among the most numerous of all animals

Planktonic crustaceans known as krill are consumed in vast quantities by whales. (b)

Figure 33.38b


• Barnacles are a group of mostly sessile crustaceans

– Whose cuticle is hardened into a shell

The jointed appendages projecting from the shellsof these barnacles capture organisms and organic particles suspended inthe water.

(c)

Figure 33.38c


• Echinoderms and chordates are deuterostomes

• At first glance, sea stars and other echinoderms, phylum Echinodermata

– May seem to have little in common with phylum Chordata, which includes the vertebrates

• Chordates and echinoderms share characteristics of deuterostomes

– Radial cleavage

– Development of the coelom from the archenteron

– Formation of the mouth at the end of the embryo opposite the blastopore


Echinoderms

• Sea stars and most other echinoderms

– Are slow-moving or sessile marine animals

• A thin, bumpy or spiny skin

– Covers an endoskeleton of hard calcareous plates

• The radial anatomy of many echinoderms

– Evolved secondarily from the bilateral symmetry of ancestors

– Living echinoderms are divided into six classes


• Unique to echinoderms is a water vascular system

– A network of hydraulic canals branching into tube feet that function in locomotion, feeding, and gas exchange

StomachAnus

Ringcanal

Gonads

AmpullaPodium

Radialnerve

Tubefeet

Spine

Gills

A short digestive tract runs from the mouth on the bottom of the central disk to the anus on top of the disk.

The surface of a sea star is covered by spines that help defend against predators, as well as by small gills that provide gas exchange.

Madreporite. Water can flow in or out of the water vascular system into the surrounding water through the madreporite.

Branching from each radial canal are hundreds of hollow, muscular tube feet filled with fluid. Each tube foot consists of a bulb-like ampulla and suckered podium (foot portion). When the ampulla squeezes, it forces water into the podium and makes it expand. The podium then contacts the substrate. When the muscles in the wall of the podiumcontract, they force water back into the ampulla, making the podium shorten and bend.

Radial canal. The water vascular system consists of a ring canal in the central disk and five radial canals, each running in a groove down the entire length of an arm.

Digestive glands secrete digestive juices and aid in

the absorption and storage of nutrients.

Central disk. The central disk has a nerve ring and

nerve cords radiating from the ring into the arms.

Figure 33.39


Sea Stars

• Sea stars, class Asteroidea

– Have multiple arms radiating from a central disk

• The undersurfaces of the arms

– Bear tube feet, each of which can act like a suction disk

• Brittle stars have a distinct central disk

– And long, flexible arms

(a) A sea star (class Asteroidea)Figure 33.40a

(b) A brittle star

(class Ophiuro

idea)

Figure 33.40b


Sea Urchins and Sand Dollars

• Sea urchins and sand dollars have no arms

– But they do have five rows of tube feet that function in movement

• Sea lilies

– Live attached to the substrate by a stalk

• Feather stars

– Crawl about using their long, flexible arms

(c) A sea urchin (class

Echinoidea)

Figure 33.40c


Sea Cucumbers

• Sea cucumbers

– Upon first inspection do not look much like other echinoderms

– Lack spines, and their endoskeleton is much reduced

• Sea daisies were discovered in 1986

– And only two species are known

(e) A sea cucumber

(class Holothuroi

dea)

Figure 33.40e

(f) A sea daisy (class

Concentricycloidea)

Figure 33.40f


Chordates

• Chordates

– Phylum Chordata

– Consists of two subphyla of invertebrates as well as the hagfishes and the vertebrates

– Shares many features of embryonic development with echinoderms


Vertebrates

• Chordates have a notochord and a dorsal, hollow nerve cord

• Vertebrates are a subphylum of the phylum Chordata

• Chordates are bilaterian animals

– That belong to the clade of animals known as Deuterostomia

• Two groups of invertebrate deuterostomes, the urochordates and cephalochordates

– Are more closely related to vertebrates than to invertebrates


Derived Characters of Chordates

• All chordates share a set of derived characters

– Although some species possess some of these traits only during embryonic development

Musclesegments

Brain

Mouth

Anus

Dorsal,hollow

nerve cord

Notochord

Muscular,post-anal tail

Pharyngealslits or clefts

Figure 34.3


Notochord

• The notochord

– Is a longitudinal, flexible rod located between the digestive tube and the nerve cord

– Provides skeletal support throughout most of the length of a chordate

• In most vertebrates, a more complex, jointed skeleton develops

– And the adult retains only remnants of the embryonic notochord


Dorsal, Hollow Nerve Cord

• The nerve cord of a chordate embryo

– Develops from a plate of ectoderm that rolls into a tube dorsal to the notochord

– Develops into the central nervous system: the brain and the spinal cord


Pharyngeal Slits or Clefts

• In most chordates, grooves in the pharynx called pharyngeal clefts

– Develop into slits that open to the outside of the body

• These pharyngeal slits

– Function as suspension-feeding structures in many invertebrate chordates

– Are modified for gas exchange in aquatic vertebrates

– Develop into parts of the ear, head, and neck in terrestrial vertebrates


Muscular, Post-Anal Tail

• Chordates have a tail extending posterior to the anus

– Although in many species it is lost during embryonic development

• The chordate tail contains skeletal elements and muscles

– And it provides much of the propelling force in many aquatic species


Tunicates

• Tunicates, subphylum Urochordata

– Belong to the deepest-branching lineage of chordates

– Are marine suspension feeders commonly called sea squirts

• Tunicates most resemble chordates during their larval stage

– Which may be as brief as a few minutes


Lancelets

• Lancelets, subphylum Cephalochordata

– Are named for their bladelike shape

• Lancelets are marine suspension feeders

– That retain the characteristics of the chordate body plan as adults Tentacle

Mouth

Pharyngeal slitsAtrium

Digestive tract

AtrioporeSegmentalmuscles

Anus

Notochord

Dorsal, hollownerve cord

Tail

2 cm

Figure 34.5


Hagfishes

• The least derived craniate lineage that still survives

– Is class Myxini, the hagfishes

• Hagfishes are jawless marine craniates

– That have a cartilaginous skull and axial rod of cartilage derived from the notochord

– That lack vertebrae

Figure 34.9

Slime glands


Derived Characters of Vertebrates

• Vertebrates have

– Vertebrae enclosing a spinal cord

– An elaborate skull

– Fin rays, in aquatic forms


Lampreys

• Lampreys, class Cephalaspidomorphi

– Represent the oldest living lineage of vertebrates

– Have cartilaginous segments surrounding the notochord and arching partly over the nerve cord

• Lampreys are jawless vertebrates

– Inhabiting various marine and freshwater habitats


• Gnathostomes are vertebrates that have jaws

• Today, jawless vertebrates

– Are far outnumbered by those with jaws

• Other characters common to gnathostomes include

– Enhanced sensory systems, including the lateral line system

– An extensively mineralized endoskeleton

– Paired appendages


Chondrichthyans (Sharks, Rays, and Their Relatives)

• Members of class Chondrichthyes

– Have a skeleton that is composed primarily of cartilage

• The cartilaginous skeleton

– Evolved secondarily from an ancestral mineralized skeleton

• Most sharks

– Have a streamlined body and are swift swimmers

– Have acute senses


Ray-Finned Fishes and Lobe-Fins

• The vast majority of vertebrates

– Belong to a clade of gnathostomes called Osteichthyes

• Nearly all living osteichthyans

– Have a bony endoskeleton

• Aquatic osteichthyans

– Are the vertebrates we informally call fishes

– Control their buoyancy with an air sac known as a swim bladder


• Fishes breathe by drawing water over four or five pairs of gills

– Located in chambers covered by a protective bony flap called the operculum

Nostril Brain

Spinal cordSwim bladder

Dorsal fin Adipose fin(characteristic oftrout)

Caudal fin

Cut edge of operculum Gills

HeartLiver

KidneyStomach

Intestine

GonadAnus

Urinary bladder

Lateral line

Anal fin

Pelvic finFigure 34.16


Ray-Finned Fishes

• Class Actinopterygii, the ray-finned fishes

– Includes nearly all the familiar aquatic osteichthyans

(a) Yellowfin tuna (Thunnus albacares), a fast-swimming, schooling fish that is an important commercial fish worldwide

(b) Clownfish (Amphiprion ocellaris), a mutualistic symbiont of sea anemones

(c) Sea horse (Hippocampus ramulosus), unusual in the animal kingdom in that the male carries the young during their embryonic development

(d) Fine-spotted moray eel (Gymnothorax dovii), a predator that ambushes prey from crevices in its coral reef habitatFigure 34.17a–d


• The fins, supported mainly by long, flexible rays

– Are modified for maneuvering, defense, and other functions

• The lobe-fins, class Sarcopterygii

– Have muscular and pectoral fins

– Include coelacanths, lungfishes, and tetrapods


• Concept 34.5: Tetrapods are gnathostomes that have limbs and feet

• 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

Figure 34.18


Derived Characters of Tetrapods

• Tetrapods have some specific adaptations

– Four limbs and feet with digits

– Ears for detecting airborne sounds

• In one lineage of lobe-fins

– The fins became progressively more limb-like while the rest of the body retained adaptations for aquatic life

Tetrapodlimbskeleton

Bonessupportinggills

Figure 34.19


Amphibians

• Class Amphibia

– Is represented by about 4,800 species of organisms

• Most amphibians

– Have moist skin that complements the lungs in gas exchange

• Order Urodela

– Includes salamanders, which have tails

• Order Anura

– Includes frogs and toads, which lack tails

• Order Apoda

– Includes caecilians, which are legless and resemble worms


• Amphibian means “two lives”

– A reference to the metamorphosis of an aquatic larva into a terrestrial adult

Figure 34.22a–c

(a) The male grasps the female, stimulating her to release eggs. The eggs are laid and fertilized in water. They have a jelly coat but lack a shell and would desiccate in air.

(b) The tadpole is an aquatic herbivore witha fishlike tail and internal gills.

(c) During metamorphosis, the gills and tail are resorbed, andwalking legs develop.


• Amniotes are tetrapods that have a terrestrially adapted egg

• Amniotes are a group of tetrapods

– Whose living members are the reptiles, including birds, and the mammals


• The extraembryonic membranes

– Have various functions

Figure 34.24Shell

Albumen

Yolk (nutrients)

Amniotic cavitywith amniotic fluid

Embryo

Yolk sac. The yolk sac contains the yolk, a stockpile of nutrients. Blood vessels in the yolk sac membrane transport nutrients from the yolk into the embryo. Other nutrients are stored in the albumen (“egg white”).

Allantois. The allantois is a disposalsac for certain metabolic wastes pro-duced by the embryo. The membraneof the allantois also functions withthe chorion as a respiratory organ.

Amnion. The amnion protectsthe embryo in a fluid-filled cavity that cushions againstmechanical shock.

Chorion. The chorion and the membrane of the allantois exchange gases between the embryo and the air. Oxygen and carbon dioxide diffuse freely across the shell.

Extraembryonic membranes


• Amniotes also have other terrestrial adaptations

– Such as relatively impermeable skin and the ability to use the rib cage to ventilate the lungs


Reptiles• The reptile clade includes

– The tuatara, lizards, snakes, turtles, crocodilians, birds, and the extinct dinosaurs

• Reptiles

– Have scales that create a waterproof barrier

– 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


Figure 34.26

• Traditionally, dinosaurs were considered slow, sluggish creatures

– But fossil discoveries and research have led to the conclusion that dinosaurs were agile and fast moving

• Paleontologists have also discovered signs of parental care among dinosaurs


Lepidosaurs

• One surviving lineage of lepidosaurs

– Is represented by two species of lizard-like reptiles called tuatara

• The other major living lineage of lepidosaurs

– Are the squamates, the lizards and snakes

• Lizards

– Are the most numerous and diverse reptiles, apart from birds

• Snakes are legless lepidosaurs

– That are thought to have evolved from lizards

Figure 34.27a

(a) Tuatara (Sphenodon punctatus)

Figure 34.27b

(b) Australian thorny devil lizard (Moloch horridus)


Turtles

• Turtles

– Are the most distinctive group of reptiles alive today

• Some turtles have adapted to deserts

– And others live entirely in ponds and rivers

• All turtles have a boxlike shell

– Made of upper and lower shields that are fused to the vertebrae, clavicles, and ribs


Alligators and Crocodiles

• Crocodilians

– Belong to an archosaur lineage that dates back to the late Triassic

Figure 34.27e (e) American alligator (Alligator mississipiensis)


Birds

• Birds are archosaurs

– But almost every feature of their reptilian anatomy has undergone modification in their adaptation to flight

• Many of the characters of birds

– Are adaptations that facilitate flight


• A bird’s most obvious adaptations for flight

– Are its wings and feathers

Figure 34.28a–c

(a) wing

(b) Bone structure

Finger 1

(c) Feather structure

Shaft

BarbBarbule

Hook

Vane

Shaft

ForearmWrist

Palm

Finger 3

Finger 2


• By 150 million years ago

– Feathered theropods had evolved into birds

• Archaeopteryx

– Remains the oldest bird known

Figure 34.29

Toothed beak

Airfoil wing with contour feathers

Long tail with many vertebrae

Wing claw


Living Birds

• The ratites, order Struthioniformes

– Are all flightless

Figure 34.30a

(a) Emu. This ratite lives in Australia.


• Foot structure in bird feet

– Shows considerable variation

Figure 34.31

Grasping bird (such as a woodpecker)

Perching bird (such as a cardinal)

Raptor(such as a bald eagle)

Swimming bird(such as a duck)


Mammals

• Mammals are amniotes that have hair and produce milk

• Mammals, class Mammalia

– Are represented by more than 5,000 species


Derived Characters of Mammals

• Mammary glands, which produce milk

– Are a distinctively mammalian character

• Hair is another mammalian characteristic

• Mammals generally have a larger brain

– Than other vertebrates of equivalent size


Monotremes

• Monotremes

– Are a small group of egg-laying mammals consisting of echidnas and the platypus

Figure 34.33


Marsupials

• Marsupials

– Include opossums, kangaroos, and koalas

• A marsupial is born very early in its development

– And completes its embryonic development while nursing within a maternal pouch called a marsupium

Figure 34.34a

(a) A young brushtail possum. The young of marsupials are born very early in their development. They finish their growth while nursing from a nipple (in their mother’s pouch in most species).


• In some species of marsupials, such as the bandicoot

– The marsupium opens to the rear of the mother’s body as opposed to the front, as in other marsupials

Figure 34.34b

(b) Long-nosed bandicoot. Most bandicoots are diggers and burrowers that eat mainly insects but also some small vertebrates andplant material. Their rear-opening pouch helps protect the young from dirt as the mother digs. Other marsupials, such as kangaroos, have a pouch that opens to the front.


• In Australia, convergent evolution

– Has resulted in a diversity of marsupials that resemble eutherians in other parts of the world

• Compared to marsupials

– Eutherians have a longer period of pregnancy

• Young eutherians

– Complete their embryonic development within a uterus, joined to the mother by the placenta

Figure 34.35

Marsupial mammals Eutherian mammals

Plantigale

Marsupial mole

Sugar glider

Wombat

Tasmanian devil

Kangaroo

Deer mouse

Mole

Woodchuck

Flying squirrel

Wolverine

Patagonian cavy


• The major eutherian orders

Figure 34.36

ORDERSAND EXAMPLES

MAIN CHARACTERISTICS

Monotremata Platypuses, echidnas

Proboscidea Elephants

SireniaManatees,dugongs

CetartiodactylaArtiodactylsSheep, pigs cattle, deer,giraffes

Lagomorpha Rabbits, hares, picas

Carnivora Dogs, wolves,bears, cats, weasels, otters,seals, walruses

Xenarthra Sloths, anteaters,armadillos

CetaceansWhales,dolphins,porpoises

Echidna

African elephant

Manatee

Tamandua

Jackrabbit

Coyote

Bighorn sheep

Pacific white-sided porpoise

Lay eggs; nonipples; young suck milk fromfur of mother

Long, musculartrunk; thick, loose skin; upper incisors elongated as tusks

Aquatic; finlikeforelimbs and no hind limbs; herbivorous

Reduced teeth orno teeth; herbivorous(sloths) or carnivorous (anteaters, armadillos)

Chisel-like incisors; hind legs longer than forelegs and adapted for running and jumping

Sharp, pointed canineteeth and molars for shearing; carnivorous

Hooves with an even number of toes on each foot; herbivorous

Aquatic; streamlinedbody; paddle-like forelimbs and no hind limbs; thicklayer of insulating blubber; carnivorous

Diet consists mainly of insects and other small invertebrates

Adapted for flight; broad skinfold that extends from elongated fingers to body and legs; carnivorous or herbivorous

Hooves with an odd number of toeson each foot; herbivorous

Opposable thumbs; forward-facing eyes; well-developed cerebral cortex; omnivorous

Chisel-like, continuously growing incisors worn down by gnawing;herbivorous

Short legs; stumpy tail; herbivorous; complex, multichamberedstomach

Teeth consisting of many thin tubes cemented together; eats ants and termites

Embryo completes development in pouch on mother

ORDERSAND EXAMPLES

MAIN CHARACTERISTICS

MarsupialiaKangaroos,opossums,koalas

TubulidentataAardvark

HyracoideaHyraxes

ChiropteraBats

PrimatesLemurs,monkeys,apes,humans

PerissodactylaHorses,zebras, tapirs,rhinoceroses

RodentiaSquirrels,beavers, rats, porcupines,mice

Eulipotyphla“Core insecti-vores”: some moles, some shrews Star-nosed

mole

Frog-eating bat

Indian rhinoceros

Golden lion tamarin

Red squirrel

Rock hyrax

Aardvark

Koala


Primates• The mammalian order Primates include

– Lemurs, tarsiers, monkeys, and apes

• Humans are members of the ape group

• Most primates

– Have hands and feet adapted for grasping

• Primates also have

– A large brain and short jaws

– Forward-looking eyes close together on the face, providing depth perception

– Well-developed parental care and complex social behavior

– A fully opposable thumb


• New World and Old World monkeys

– Underwent separate adaptive radiations during their many millions of years of separation

Figure 34.39a, b

(a) New World monkeys, such as spider monkeys (shown here), squirrel monkeys, and capuchins, have a prehensile tail and nostrils that open to the sides.

(b) Old World monkeys lack a prehensile tail, and their nostrils open downward. This group includes macaques (shown here), mandrills, baboons, and rhesus monkeys.


• The other group of anthropoids, the hominoids

– Consists of primates informally called apes

Figure 34.40a–e

(a) Gibbons, such as this Muller's gibbon, are found only in southeastern Asia. Their very long arms and fingers are adaptations for brachiation.

(b) Orangutans are shy, solitary apes that live in the rain forests of Sumatra and Borneo. They spend most of their time in trees; note the foot adapted for grasping and the opposable thumb.

(c) Gorillas are the largest apes: some males are almost 2 m tall and weigh about 200 kg. Found only in Africa, these herbivores usually live in groups of up to about 20 individuals.

(d) Chimpanzees live in tropical Africa. They feed and sleep in trees but also spend a great deal of time on the ground. Chimpanzees are intelligent, communicative, and social.

(e) Bonobos are closely related to chimpanzees but are smaller. They survive today only in the African nation of Congo.


• Humans are bipedal hominoids with a large brain

• Homo sapiens is about 160,000 years old

– Which is very young considering that life has existed on Earth for at least 3.5 billion years


Derived Characters of Hominids

• A number of characters distinguish humans from other hominoids

– Upright posture and bipedal locomotion

– Larger brains

– Language capabilities

– Symbolic thought

– The manufacture and use of complex tools

– Shortened jaw


The Earliest Humans

• The study of human origins

– Is known as paleoanthropology


• These species are known as hominids

Figure 34.41

Homosapiens

Homoneanderthalensis

Homoergaster

?

Homoerectus

Homohabilis

Homorudolfensis

Paranthropusrobustus

Paranthropusboisei

Australopithecusgarhi

Australopithecusafricanus

Australopithecusafarensis

Kenyanthropusplatyops

Australopithecusanamensis

Ardipithecusramidus

Orrorin tugenensis

Sahelanthropustchadensis

7.0

6.5

6.0

5.5

5.0

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0M

illio

ns o

f yea

rs a

go


Early Homo

• The earliest fossils that paleoanthropologists place in our genus Homo

– Are those of the species Homo habilis, ranging in age from about 2.4 to 1.6 million years

• Stone tools have been found with H. habilis

– Giving this species its name, which means “handy man”


• Homo ergaster

– Was the first fully bipedal, large-brained hominid

– Existed between 1.9 and 1.6 million years

Figure 34.43


• Homo erectus

– Originated in Africa approximately 1.8 million years ago

– Was the first hominid to leave Africa


Neanderthals

• Neanderthals, Homo neanderthalensis

– Lived in Europe and the Near East from 200,000 to 30,000 years ago

– Were large, thick-browed hominids

– Became extinct a few thousand years after the arrival of Homo sapiens in Europe


Homo sapiens

• Homo sapiens

– Appeared in Africa at least 160,000 years ago

Figure 34.44

The oldest fossils of Homo sapiens outside Africa

Date back about 50,000 years ago


• The rapid expansion of our species

– May have been preceded by changes to the brain that made symbolic thought and other cognitive innovations possible

Figure 34.45

32 animaldiversity text

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