Animals: The Vertebrates Chapter 26. Something Old, Something New Every animal is a combination of traits Every animal is a combination of traits Some.

Animals: The Animals: The VertebratesVertebrates

Chapter 26Chapter 26

Something Old, Something Old, Something NewSomething New

Every animal is a combination of Every animal is a combination of traitstraits

Some traits are conserved from Some traits are conserved from remote ancestors remote ancestors

Other traits are unique to its branch Other traits are unique to its branch of the family treeof the family tree

Chordate FeaturesChordate Features

Deuterostomes Deuterostomes

All share four features:All share four features:

– Notochord supports bodyNotochord supports body

– Nervous system develops from dorsal Nervous system develops from dorsal nerve cordnerve cord

– Embryos have pharynx with slitsEmbryos have pharynx with slits

– Embryos have tail that extends past Embryos have tail that extends past anusanus

Chordate GroupsChordate Groups

Urochordata Urochordata

– Salps and tunicatesSalps and tunicates

Cephalochordata Cephalochordata

– Lancelets Lancelets

CraniatesCraniates

– Fishes, amphibians, reptiles, birds, Fishes, amphibians, reptiles, birds,

mammalsmammals

Tunicates (Urochordates)Tunicates (Urochordates) Larva is free-swimming Larva is free-swimming Adult is sessile and baglike with no coelomAdult is sessile and baglike with no coelom Both stages are filter feedersBoth stages are filter feeders Pharynx serves in both feeding and Pharynx serves in both feeding and

respirationrespiration

Tunicate Life Tunicate Life HistoryHistory

Larva Larva undergoes undergoes metamorphosimetamorphosis to adult forms to adult form

nerve cord notochord

gutTunicate larva

oral opening

atrial opening

pharynx with gill slits

Tunicate adult

pharynx

Figure 26.3Page 446

Lancelets Lancelets (Cephalochordates)(Cephalochordates)

Fish-shaped filter feedersFish-shaped filter feeders Simple brainSimple brain Segmented muscles Segmented muscles Chordate characteristics of adult:Chordate characteristics of adult:

– Notochord lies under dorsal nerve cordNotochord lies under dorsal nerve cord– Pharynx has gill slitsPharynx has gill slits– Tail extends past anusTail extends past anus

Lancelet Body PlanLancelet Body Plan

dorsal, tubular nerve cord

notochord

pharynx with gill slits tail extending past anus

anuspore of atrial cavity

hindgut

gonadaorta

midgut

segmented muscles

tentaclelike structures

around mouth

Figure Figure 26.4a26.4a

Page 447Page 447

Early CraniatesEarly Craniates

Reconstruction of one of the earliest known craniates

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• Brain inside Brain inside chamber of chamber of cartilage or bonecartilage or bone

• Arose before 530 Arose before 530 million years agomillion years ago

• Resemble Resemble lancelets, lamprey lancelets, lamprey larvalarva

Figure 26.4Page 447

Trends in the Evolution Trends in the Evolution of Vertebratesof Vertebrates

Shift from notochord to vertebral columnShift from notochord to vertebral column

Nerve cord expanded into brainNerve cord expanded into brain

Evolution of jawsEvolution of jaws

Paired fins evolved, gave rise to limbsPaired fins evolved, gave rise to limbs

Gills evolved, gave rise to lungsGills evolved, gave rise to lungs

Evolution of Evolution of JawsJaws

First fishes First fishes

lacked jaws lacked jaws

Jaws are Jaws are

modifications of modifications of

anterior gill anterior gill

supportssupportsFigure 26.5Page 448

supporting structures

gill slit

jaw

spiracle jaw support

jaw

Early jawless

fish(agnathan)

Early jawed fish

(placoderm)

Modern jawed fish

(shark)

Existing Jawless FishesExisting Jawless Fishes

Cylindrical bodyCylindrical body

Cartilaginous Cartilaginous

skeletonskeleton

No paired finsNo paired fins

gill openings (seven pairs)Lamprey

Hagfish

tentacles gill slits (twelve pairs) mucous glands

Jawed FishesJawed Fishes

Most diverse and numerous group Most diverse and numerous group

of vertebratesof vertebrates

Two classes:Two classes:

– Chondrichthyes (cartilaginous fishes)Chondrichthyes (cartilaginous fishes)

– Osteichthyes (bony fishes)Osteichthyes (bony fishes)

Cartilaginous Fishes: Cartilaginous Fishes: Class ChondrichthyesClass Chondrichthyes Most are marine Most are marine

predatorspredators

Cartilaginous skeletonCartilaginous skeleton

Main groups:Main groups:

– Skates and raysSkates and rays

– SharksSharks

– Chimaeras (ratfishes)Chimaeras (ratfishes)

Bony Fishes: Bony Fishes: Class OsteichthyesClass Osteichthyes

Includes 96 percent of Includes 96 percent of

living fish speciesliving fish species

Three subclasses:Three subclasses:

– Ray-finned fishesRay-finned fishes

– Lobe-finned fishesLobe-finned fishes

– Lung fishesLung fishes

Body Plan of a Bony Body Plan of a Bony FishFish

muscle segments

fin supports

brain

olfactory bulb

heart

liver

gallbladderstomach

intestineswim bladderkidney

anus

urinary bladder

Figure 26.9bPage 451

Lobe-Finned FishesLobe-Finned Fishes

CoelocanthsCoelocanths

Lunglike sacs do not Lunglike sacs do not function in gas exchangefunction in gas exchange

LungfishesLungfishes

Have gills and one lung or a pair Have gills and one lung or a pair

Must surface to gulp air Must surface to gulp air

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Figure 26.9fPage 451

Early AmphibiansEarly Amphibians

Fishlike skull Fishlike skull

and tail and tail

Four limbs Four limbs

with digitswith digits

Short neck Short neck Acanthostega

Ichthyostega

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Figure 26.10aPage 452

Modern AmphibiansModern Amphibians

All require water at some stage in All require water at some stage in

the life cycle; most lay eggs in waterthe life cycle; most lay eggs in water

Lungs are less efficient than those of Lungs are less efficient than those of

other vertebratesother vertebrates

Skin serves as respiratory organSkin serves as respiratory organ

From Fins to LimbsFrom Fins to Limbs

Genetic enhancer controls genes Genetic enhancer controls genes involved in formation of digits on involved in formation of digits on limb boneslimb bones

Change in a single master gene can Change in a single master gene can drastically alter morphologydrastically alter morphology

Living Amphibian Groups Living Amphibian Groups

Frogs and toadsFrogs and toads

SalamandersSalamanders

CaeciliansCaecilians

Rise of AmniotesRise of Amniotes

Arose during CarboniferousArose during Carboniferous

Adaptations to life on landAdaptations to life on land

– Tough, scaly skinTough, scaly skin

– Internal fertilizationInternal fertilization

– Amniote eggsAmniote eggs

– Water-conserving kidneysWater-conserving kidneys

Adaptive RadiationAdaptive Radiation

Produced numerous lineagesProduced numerous lineages

Extinct groups include:Extinct groups include:

– Therapsids (ancestors of Therapsids (ancestors of

mammals)mammals)

– Marine plesiosaurs & ichthyosaursMarine plesiosaurs & ichthyosaurs

– Dinosaurs and pterosaursDinosaurs and pterosaurs

Living ReptilesLiving Reptiles

Not a monophyletic groupNot a monophyletic group

CrocodiliansCrocodilians

TurtlesTurtles

TuatarasTuataras

Snakes and lizardsSnakes and lizards

Evolutionary History of Evolutionary History of AmniotesAmniotes

lizards

snakes

tuataras

birds

archosaurs

dinosaurs

pterosaurs

crocodilians

ichthyosaurs

plesiosaurs

turtles

synapsids

therapsidsanapsids

(mammals)

stem reptiles

Paleozoic era Mesozoic eraCarboniferous Permian Triassic Jurassic Cretaceous

Figure 26.14Page 455

Crocodile Body PlanCrocodile Body Plan

Figure Figure 26.13c26.13c

Page 454Page 454

snout

olfactory lobe

spinal cord

vertebral column

gonad

kidney

cloaca

intestine

stomach

liver

heart

esophagus

hindbrain, midbrain, forebrain

Turtles Turtles

Armorlike shell Armorlike shell Horny plates instead of Horny plates instead of

teethteeth Lay eggs on landLay eggs on land

Figure 26.15Page 456

Lizards and SnakesLizards and Snakes

Largest order (95 Largest order (95 percent of living reptiles)percent of living reptiles)

Most lizards are Most lizards are insectivores with small insectivores with small peglike teeth peglike teeth

All snakes are carnivores All snakes are carnivores with highly movable with highly movable jawsjaws

hollow fang

venom gland

Figure 26.15dPage 457

TuatarasTuataras

Only two living speciesOnly two living species

Live on islands off coast of New Live on islands off coast of New

ZealandZealand

Look like lizards, but resemble Look like lizards, but resemble

amphibians in some aspects of amphibians in some aspects of

their brain and in their way of their brain and in their way of

walkingwalking

Birds Birds

Diverged from small theropod Diverged from small theropod

dinosaurs during the Mesozoicdinosaurs during the Mesozoic

Feathers are a unique traitFeathers are a unique trait

– Derived from reptilian scalesDerived from reptilian scales

– Serve in insulation and flightServe in insulation and flight

Amniote EggAmniote Egg

yolk sac embryo

chorion

amnion

albumin

hardened shell

allantois

Figure 26.16aPage 458

Adapted for FlightAdapted for Flight

Four-chambered Four-chambered heartheart

Highly efficient Highly efficient respiratory systemrespiratory system

Lightweight bones Lightweight bones with air spaceswith air spaces

Powerful muscles Powerful muscles attach to the keel attach to the keel

Figure 26.17Page 458

Mammals: Phylum Mammals: Phylum MammaliaMammalia

HairHair Mammary Mammary

glandsglands Distinctive teethDistinctive teeth Highly Highly

developed braindeveloped brain Extended care Extended care

for the youngfor the youngFigure 26.19c

Page 460

Mammal Origins & RadiationMammal Origins & Radiation

During Triassic, synapsids gave rise to During Triassic, synapsids gave rise to therapsids (ancestors of mammals)therapsids (ancestors of mammals)

By Jurassic, mouselike therians had By Jurassic, mouselike therians had evolved evolved

Therians coexisted with dinosaurs Therians coexisted with dinosaurs through Cretaceousthrough Cretaceous

Radiated after dinosaur extinction Radiated after dinosaur extinction

Three Mammalian LineagesThree Mammalian Lineages

MonotremesMonotremes– Egg-laying mammals Egg-laying mammals

MarsupialsMarsupials– Pouched mammalsPouched mammals

EutheriansEutherians– Placental mammalsPlacental mammals

Role of Geologic ChangeRole of Geologic Change

Monotremes and marsupials evolved Monotremes and marsupials evolved while Pangea was intactwhile Pangea was intact

Placental mammals evolved after Placental mammals evolved after what would become Australia had what would become Australia had split offsplit off

No placental mammals in AustraliaNo placental mammals in Australia Elsewhere, placental mammals Elsewhere, placental mammals

replaced most marsupials replaced most marsupials

Living MonotremesLiving Monotremes

Three speciesThree species

– Duck-billed platypus Duck-billed platypus

– Two kinds of spiny Two kinds of spiny

anteater anteater

All lay eggsAll lay eggs

Living MarsupialsLiving Marsupials

Most of the 260 species are native Most of the 260 species are native to Australia and nearby islandsto Australia and nearby islands

Only the opossums are found in Only the opossums are found in North AmericaNorth America

Young are born in an undeveloped Young are born in an undeveloped state and complete development state and complete development in a permanent pouch on mother in a permanent pouch on mother

Living Placental MammalsLiving Placental Mammals

Most diverse mammalian groupMost diverse mammalian group Young develop in mother’s uterusYoung develop in mother’s uterus Placenta composed of maternal and fetal Placenta composed of maternal and fetal

tissues; nourishes fetus, delivers oxygen, tissues; nourishes fetus, delivers oxygen, and removes wastesand removes wastes

Placental mammals develop more quickly Placental mammals develop more quickly than marsupials than marsupials

Earliest PrimatesEarliest Primates

Primates evolved more than 60 million Primates evolved more than 60 million

years ago during the Paleoceneyears ago during the Paleocene

First primates resembled tree shrewsFirst primates resembled tree shrews

– Long snoutsLong snouts

– Poor daytime visionPoor daytime vision

From Primates to HumansFrom Primates to Humans

““Uniquely” human traits Uniquely” human traits

evolved through evolved through

modification of traits that modification of traits that

evolved earlier, evolved earlier,

in ancestral formsin ancestral forms

HominoidsHominoids

Apes, humans, and extinct species of Apes, humans, and extinct species of their lineagestheir lineages

In biochemistry and body form, humans In biochemistry and body form, humans are closer to apes than to monkeysare closer to apes than to monkeys

HominidsHominids– Subgroup that includes humans and Subgroup that includes humans and

extinct humanlike speciesextinct humanlike species

Trends in Lineage Trends in Lineage Leading to HumansLeading to Humans

Less reliance on smell, more on visionLess reliance on smell, more on vision

Skeletal changes to allow bipedalismSkeletal changes to allow bipedalism

Modifications of hand allow fine Modifications of hand allow fine

movementsmovements

Bow-shaped jaw and smaller teethBow-shaped jaw and smaller teeth

Longer lifespan and period of dependency Longer lifespan and period of dependency

Adaptations to anAdaptations to anArboreal LifestyleArboreal Lifestyle

Better daytime visionBetter daytime vision

Shorter snoutShorter snout

Larger brain Larger brain

Forward-directed eyesForward-directed eyes

Capacity for grasping Capacity for grasping

motionsmotions

The First HominoidsThe First Hominoids

Appeared during MioceneAppeared during Miocene

Arose in Central AfricaArose in Central Africa

Spread through Africa, Asia, EuropeSpread through Africa, Asia, Europe

Climate was changing, becoming Climate was changing, becoming

cooler and driercooler and drier

The First HominidsThe First Hominids

Sahelanthropus tchadensis Sahelanthropus tchadensis arose 6-7 million years agoarose 6-7 million years ago Bipedal australopiths evolved during Miocene into PlioceneBipedal australopiths evolved during Miocene into Pliocene

Exact relationships are not knownExact relationships are not known

A. anamensisA. afarensis A. africanus

A. garhiA. boisei A. robustus

Homo HabilisHomo Habilis 1.9-1.6 million years ago1.9-1.6 million years ago

May have been May have been

the first member the first member

of genusof genus

Lived in Lived in

woodlands of woodlands of

eastern and eastern and

southern Africasouthern AfricaH. habilis

Figure 26.31Page 468

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Homo erectusHomo erectus22 million-53,000? years agomillion-53,000? years ago

Evolved in Africa Evolved in Africa

Migrated into Europe and Asia Migrated into Europe and Asia

Larger brain than Larger brain than H. habilisH. habilis

Creative toolmakerCreative toolmaker

Built fires and used furs for Built fires and used furs for

clothingclothing

Homo sapiensHomo sapiens

Modern man evolved by 100,000 Modern man evolved by 100,000 years agoyears ago

Compared to Compared to Homo erectus:Homo erectus:– Smaller teeth and jawsSmaller teeth and jaws– ChinChin– Smaller facial bonesSmaller facial bones– Larger-volume brain caseLarger-volume brain case

NeanderthalsNeanderthals

Early humans that lived in Europe and Early humans that lived in Europe and Near EastNear East

Massively built, with large brainsMassively built, with large brains Disappeared when Disappeared when H. sapiensH. sapiens

appearedappeared DNA evidence suggests that they did DNA evidence suggests that they did

not contribute to modern European not contribute to modern European populationspopulations

Earliest Fossils Are African Earliest Fossils Are African

Africa appears to be the cradle of Africa appears to be the cradle of

human evolutionhuman evolution

No human fossils older than 2 million No human fossils older than 2 million

years exist anywhere but Africayears exist anywhere but Africa

Homo erectusHomo erectus left Africa in waves left Africa in waves

from 2 million to 500,000 years agofrom 2 million to 500,000 years ago

Where Did Where Did H. sapiensH. sapiens Arise? Arise?

Two hypotheses:Two hypotheses:

– Multiregional modelMultiregional model

– African emergence modelAfrican emergence model

Both attempt to address Both attempt to address

biochemical and fossil evidencebiochemical and fossil evidence

Multiregional ModelMultiregional Model

Argues that Argues that H. erectusH. erectus migrated to many migrated to many locations by about 1 million years agolocations by about 1 million years ago

Geographically separated populations Geographically separated populations gave rise to phenotypically different gave rise to phenotypically different races of races of H. sapiensH. sapiens in different locations in different locations

Gene flow prevented races from Gene flow prevented races from becoming speciesbecoming species

African Emergence ModelAfrican Emergence Model

Argues that Argues that H. sapiensH. sapiens arose in sub- arose in sub-Saharan AfricaSaharan Africa

H. sapiensH. sapiens migrated out of Africa and migrated out of Africa and into regions where into regions where H. erectusH. erectus had had preceded thempreceded them

Only after leaving Africa did Only after leaving Africa did phenotypic differences arisephenotypic differences arise

Genetic Distance DataGenetic Distance Data

NEW GUINEA, AUSTRALIA

PACIFIC ISLANDS

SOUTHEAST ASIA

ARCTIC, NORTHEAST ASIA

NORTH, SOUTH AMERICA

NORTHEAST ASIA

EUROPE, MIDDLE EAST

AFRICA

0.2 0.1 0

Genetic distance (percent)Figure 26.37

Page 471