evolution of animals - waterford mott...

CHAPTERS 18 & 19: ANIMAL EVOLUTION AND DIVERSITY

Honors Biology 2012

ANIMALS

Eukaryotic, multicellular heterotrophs whose cells lack cell walls

Most animal cells are diploid

Haploid gametes fuse to form a zygote

Most animals have a blastula, gastrula, and larval stage

Egg

Meiosis

1

8

7

6

5

4

3

2

Sperm

Zygote (fertilized egg)

Eight-cell stage Adult

Metamorphosis

Blastula (cross section) Digestive

tract

Larva Ectoderm

Endoderm

Internal sac Later gastrula (cross section)

Future mesoderm

Early gastrula (cross section)

Haploid (n) Diploid (2n)

Key

Fig. 18.1

EVOLUTION OF ANIMALSAbout 550 million years ago Cambrian explosion produced many animal fauna (adaptive radiation)

Ecological causes: Evolution of hard body coverings led to complex predator-prey relationships

Geological Causes: Atmospheric O2 reached high enough concentration to support metabolism of active animals

Genetic causes: Variations in Hox genes produced diversity

1 2 3 4 5 Colonial protist, an aggregate of identical cells

Hollow sphere of unspecial- ized cells

Reproductive cells

Beginning of cell specialization

Infolding Gastrula-like “proto-animal”

Somatic cells

Digestive cavity

Fig. 18.2

1

2

3

BODY PLANS

Radial symmetry - any slice through the central axis divides the animal into mirror image halves

Bilateral symmetry - have mirror image right and left sides, distinct head and tail, and a back (dorsal) and belly (ventral) surface

Body plans vary in organization of tissues

Sponges lack true tissues

Tissue layers organized into ectoderm, endoderm, and mesoderm

Top

Bottom

Anterior end

Dorsal surface

Ventral surface

Posterior end

BODY PLANS

Body cavities (coeloms)

No coelom (ex. flatworms)

Pseudocoelom - partially lined with mesoderm tissue

True coelom - completely lined by mesoderm tissue

Digestive sac (from endoderm)

Body covering (from ectoderm)

Tissue-filled region (from mesoderm)


Muscle layer (from mesoderm)

Digestive tract (from endoderm)

Pseudocoelom

Coelom

Digestive tract (from endoderm)


Tissue layer lining coelom and suspending internal organs (from mesoderm)

Fig. 18.3

PHYLOGENETIC TREES

Hypothesis for the evolutionary history of the groups involved

Based on comparative morphology

Ancestral colonial protist

No true tissues

Radial symmetry

True tissues

Bilateral symmetry

Eum

etazoans Bilaterians

Protostom

es D

euterostomes

Sponges

Cnidarians

Echinoderms

Chordates

Flatworms

Molluscs

Annelids

Arthropods

Nematodes Fig. 18.4

4

5

6

INVERTEBRATE DIVERSITY

Phylum Porifera (sponges) - no true tissues

Suspension feeders - filter food particles from water

Sessile - cannot escape from predators

Phylum Cnidaria (Cnidarians) - have two tissue layers (epidermis and inner cell layer)

Use tentacles to capture prey and push them into their mouths

Radial symmetry

Polyp and medusa stages

Pores

Amoebocyte

Skeletal fiber

Central cavity

Choanocyte in contact with an amoebocyte

Flagella

Water flow

Choanocyte

Tentacle

Prey

“Trigger”

Discharge of thread

Cnidocyte

Coiled thread

Capsule (nematocyst)

Figs. 18.5 &

18.6


Phylum Platyhelminthes (flatworms) - simplest bilateral animals

Planarians have heads with light-sensitive eyespots

Flukes and tapeworms are parasitic flatworms

Phylum Nematoda (roundworms) - bilateral symmetry and three tissue layers

Units with reproductive structures

Scolex (anterior end)

Hooks Sucker

Gastrovascular cavity

Mouth

Nerve cords

Eyespots

Nervous tissue clusters

Bilateral symmetry


Phylum Mollusca (molluscs) - have a true coelom and a circulatory system

Gastropods - largest group of molluscs (include snails and slugs)

Bivalves - shells divided into two halves (clams, oysters, mussels, and scallops)

Cephalopods - have large brains and sense organs including image-focusing eyes

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8

9


Phylum Annelida (annelids) - have a closed circulatory system; nervous system with a simple brain and nerve cord; true coelom

Earthworms

Polychaetes - largest group

Leeches


Phylum Arthropoda (arthropods) - segmented bodies, exoskeleton, jointed appendages, open circulatory system

Includes crayfish, lobsters, crabs, barnacles, spiders, ticks, and insects

Cephalothorax Abdomen

Head Thorax

Antennae (sensory reception)

Swimming appendages

Pincer (defense) Mouthparts (feeding)

Walking legs

A scorpion (about 8 cm long)

A black widow spider (about 1 cm wide) A dust mite

(about 420 µ m long)


Insects

70% of all animal species

Successful because of jointed appendages, exoskeleton, flight, waterproof cuticle

Some undergo a complete metamorphosis

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11

12


Phylum Echinodermata (echinoderms) - slow-moving and sessile, radial symmetry, water vascular system, exoskeleton

Phylum Chordata (chordates) - dorsal, hollow nerve cord

Tunicates and lancelets use pharyngeal slits for suspension feeding

Anus

Spines

Stomach

Canals

Tube feet

Excurrent siphon

Adult (about 3 cm high)

Post-anal tail

Dorsal, hollow nerve cord

Pharyngeal slits

Mouth

Larva

Notochord

Muscle segments

Mouth

Head

Pharynx

Pharyngeal slits

Digestive tract

Water exit Segmental muscles

Anus

Notochord

Dorsal, hollow nerve cord

Post-anal tail

Ancestral colonial protist

No true tissues

True tissues

Radial symmetry

Eum

etazoans Bilaterians

Bilateral symmetry

Ecdysozoans

Lophotrochozoans D

euterostomes

Sponges

Cnidarians

Echinoderms

Chordates

Flatworms

Molluscs

Annelids

Arthropods

Nematodes

Ancestral chordate

Brain

Head

Vertebral column

Jaws

Lungs or lung derivatives

Lobed fins

Legs

Amniotic egg

Milk Mammals

Reptiles

Amphibians

Lobe-fins

Ray-finned fishes

Sharks, rays

Lampreys

Hagfishes

Lancelets

Tunicates Chordates

Craniates Vertebrates

Jawed vertebrates

Tetrapods

Am

niotes

VERTEBRATE DIVERSITYAll contained within Phylum Chordata

Hagfish and lampreys

Craniates that lack a hinged jaw and paired fins

Hagfish only have the notochord for support, but lampreys have a notochord and rudimentary vertebral structures (vertebrates)

Hagfish produce slime as an antipredator defense

Lampreys are parasites that penetrate the sides of fish

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VERTEBRATE DIVERSITY

Some vertebrate features arose 470 million years ago

Paired fins and tails and hinged jaws

Jaws arose from a modification of the pharyngeal gill slits that were used for trapping suspended food particles

Gill slits

Skeletal rods

Skull

Mouth

Hinged jaw

VERTEBRATE DIVERSITY: JAWED FISH

Class Chondrichthyes (sharks and rays)

Flexible skeleton made of cartilage

Electrosensors on the heads of sharks heads help them locate prey

Rays are adapted for life on the bottom of the sea with flat bodies and eyes on the tops of their heads

Lobe-fins

Have muscular pelvic and pectoral fins supported by rod-shaped bones

Gill openings

VERTEBRATE DIVERSITY: JAWED FISH

Ray-finned fish

Have an internal skeleton reinforced with CaPO3

Have flattened scales covered with mucus

Buoyant swim bladder (derived from ancestral lung)

Includes more than 27,000 species

Gills Bony skeleton Dorsal fin

Anal fin Swim bladder

Pelvic fin Heart Pectoral fin

Operculum

Rainbow trout, a ray-fin

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VERTEBRATE DIVERSITY: TETRAPODS

Lobe-fin fish gave rise to the tetrapods (jawed vertebrates with limbs and feet

Scientists have collected fossils of many transitional forms

Devonian Carboniferous

Time known to exist

Eusthenopteron

Pandericthys

Tiktaalik

Acanthostega

Ichthyostega

Tetrapod with no gills, limbs better-adapted

for bearing weight

420 400 380 360 340 320 300 280 260 0 Millions of years ago

Bones supporting gills

Tetrapod limb skeleton

VERTEBRATE DIVERSITY: AMPHIBIANS

Class Amphibia (frogs, salamanders, and caecilians) - First tetrapods to be able to move on land (most have tadpole larvae)

Salamanders walk on land with side-to-side bending

Frogs hop with powerful hind legs

Caecilians are blind and legless (burrow in tropical soil)

VERTEBRATE DIVERSITY: REPTILES

Reptiles (including birds) and mammals are amniotes

Amniotic egg provides a specialized membrane that protects the embryo

Reptiles (lizards, snakes, turtles, crocodilians, and birds)

Terrestrial adaptations include scales that are waterproofed with keratin

Ectothemic - must absorb heat from the environment (most reptiles)

Endothemic - use metabolism to produce heat (birds)

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VERTEBRATE DIVERSITY: REPTILES (BIRDS)

Birds evolved from two-legged dinosaurs called theropods

Archaeopteryx - oldest bird (150 million years ago) with feathered wings

Birds are reptiles with feathers, endothermic metabolism, and adaptations for flight

Flight adaptations: loss of teeth, feathers with hollow shafts, strong and light bones

Flight is costly in terms of metabolism

Wing claw (like dinosaur)

Feathers

Teeth (like dinosaur)

Long tail with many vertebrae (like dinosaur)

VERTEBRATE DIVERSITY: MAMMALS

Mammals are endothermic amniotes with hair and mammary glands

Generally have larger relative brain size

Generally have a long period parental care

First mammals arose 200 million years ago as nocturnal insectivores

Marsupials diverged from eutherians (placental mammals) 180 million years ago

Underwent adaptive radiation after the Cretaceous extinction

VERTEBRATE DIVERSITY: MAMMALS

Monotremes - egg-laying mammals (ex. duck-billed platypus)

Only mammals whose embryos are not nourished by a placenta within the uterus

Marsupials - have a brief gestation and give birth to tiny, embryonic offspring

Offspring complete development attached to mother’s nipple in a pouch or marsupium

Eutherians - give birth to fully developed young

Commonly referred to as placental mammals because their placentas are more complex than marsupial placentas

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VERTEBRATE DIVERSITY: PRIMATES

Includes lemurs, tarsiers, monkeys, and apes

Adaptations include: shoulder and hip joints that allow for climbing, grasping hands, forward pointing eyes (allows for better depth perception)

Phylogenetic trees show primates are composed of three groups:

1st group - lorises, lemurs, and pottos

2nd group - tarsiers (small, nocturnal tree-dwellers with flat faces and large eyes)

3rd group - anthropoids (monkeys, apes, and humans)

Large brains, rely more on eyesight, have opposable thumbs

VERTEBRATE DIVERSITY: PRIMATES (HOMINOIDS)

Often called apes

Include gibbons, orangutans, gorillas, chimpanzees, and humans

Have relatively large brain size and high degrees of social organization

Gibbons are the only fully arboreal apes

Orangutans are shy and solitary and live in trees and on land

Gorillas (largest of the apes) are fully terrestrial

Chimpanzees are able to make use of tools

Diverged from a common ancestor with humans between 5 and 7 million years ago (share 99% of their genes)

VERTEBRATE DIVERSITY: PRIMATES (HOMINIDS)

Oldest hominid discovered was Sakelanthopus tchadensis (lived 6-7 million years ago)

Adaptation of hominids

Bipedalism (arose about 4 million years ago)

Homo habilis - fossils found with stone tools (2.4 million years ago)

Homo ergaster - more sophisticated stone tools, long legs for long-distance walking (1.6-1.9 million years ago)

Homo erectus - first to leave Africa

Australopithecus anamensis

Australopithecus afarensis

Australopithecus africanus

Paranthropus boisei

Paranthropus robustus

Homo ergaster

?

Homo sapiens

Homo neanderthalensis

Homo erectus

Homo habilis

Kenyanthropus platyops

Ardipithecus ramidus

Sahelanthropus tchadensis

Orrorin tugenensis

Mill

ions

of y

ears

ago

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.5

5.5

5.0

4.0

6.0

7.0

6.5

Ancient footprints

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VERTEBRATE DIVERSITY: PRIMATES (HOMINIDS)

Neanderthals - lived in Europe until about 30,000-40,000 years ago

Brain was smaller but the same shape as human

Diverged from human ancestors about 500,000 years ago

Mitochondrial DNA analysis shows that all living humans inherited their mitochondrial DNA from a woman who lived 160,000-200,000 years ago in Africa

Approximate range of Neanderthals

>35,000 years ago 30,000–35,000 years ago <30,000 years ago

Key

Europe

Africa

Neander Valley

Original discovery

Atlantic Ocean

Black Sea

Mediterranean Sea

North America

South America

Australia

Asia

Europe

Africa

100,000 BP

40,000 BP

50–60,000 BP

>40,000 BP (50–60,000?)

15–35,000 BP

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