Chapter 25 Animal Evolution – The Chordatesclasspages.warnerpacific.edu/SRamos/BIO102 lectures...•Dinosaurs are a reptile group –Birds branched off from a dinosaur lineage during

© Cengage Learning 2016

Chapter 25

Animal Evolution

– The Chordates


25.1 Very Early Birds

• Archaeopteryx

– First early bird fossil discovered

– Lived about 150 million years ago

• Sinosauropteryx prima

– First fossil of this species discovered in 1994 in

China

– Feathered dinosaur

– Supports theory that birds descended from

dinosaurs


25.2 Chordate Traits and Evolutionary

Trends

• Chordates

– Group of bilaterally symmetrical, coelomate

animals

– Have a complete digestive system and a closed

circulatory system

• Chordate traits

– Stiff, flexible connective tissue (notochord)

– Hollow nerve cord runs parallel to notochord

– Gill slits

– Muscular tail


Chordate Traits and Evolutionary

Trends

• Invertebrate chordates

– Lancelets

• Fish-shaped body

• Adults are about five centimeters long

• Live in sediment

• Filter food particles out of the water

– Tunicates

• Only larvae have typical chordate traits

• Undergo metamorphosis into barrel-shaped adult

• Suck in water through a tube to get nutrients


pharynx with gill slits

dorsal nerve cord

notochord

tail that extends beyond the anus

single eyespot

anus

© 2013 Cengage Learning


A Free-swimming tunicate larva with all the defining chordate traits.

water flows in

2 cm

postanal taildorsal nerve cord notochor d

(A, B left) From Russell/Wolfe/Hertz/Starr. Biology, 1e. © 2008 Cengage Learning, Inc.; (B right) Ethan Daniels/Shutterstock.

water flows out

pharynx with

gill slits

secreted

“tunic”

B Adult tunicate. The only defining chordate trait it retains is the pharynx

with gill slits. The species in the photo is sessile as an adult.

pharynx with gill slits


Chordate Traits and Evolutionary

Trends

• Most chordates are vertebrates

• Endoskeleton

– Internal skeleton

• First vertebrates: fishes that sucked up food

– Later, jaws evolved

• New feeding strategies emerged


Chordates

Vertebrates

Tetrapods

Amniotes

ancestral chordate

6 Amniote eggs

© 2016 Cengage Learning

Jawless Cartilaginous Ray-finned Lobe-finned Reptiles

Lancelets Tunicates fishes fishes fishes fishes Amphibians (with birds) Mammals

1 Backbone

2 Jaws

3 Swim bladder or lung(s)

4 Bony appendages

5 Four limbs


25.3 Jawless Fishes

• Fishes

– First vertebrate lineage to evolve

– Most fully aquatic of vertebrates

– Rely on gills for oxygen exchange

• Earliest jawless fish fossil dates to 530

million years ago

• Two lineages survive to the present

– Lampreys

– Hagfishes


Jawless Fishes

• Some lampreys are parasites of fish

• Hagfishes are marine bottom feeders

– Feed on worms and carcasses on the seafloor

– About 60 species of Hagfish exist

• Frightened hagfish emits a compound that

combines with water to form a gelatinous

slime

• Harvested for their skin

– “Eel skin” belts and wallets actually made of

hagfish skin


25.4 Evolution of Jawed Fishes

• First jawed vertebrates evolved 420 million

years ago

• Jaws evolved from gill arches

– Skeletal elements that support gills

• Jawed fishes: first animals with scales

• Scales

– Hard, flattened structures that cover the skin

• Most jawed fishes have movable paired fins


supporting

structure

for gill slits

gill slits

jaw, derived from support structure

location of spiracle

(modified gill slit)

jaw© 2016 Cengage Learning

jaw support


jaw

location of spiracle

(modified gill slit)

jaw support

jaw, derived

from support

structure

supporting

structure for

gill slits

gill slits

Stepped Art


Evolution of Jawed Fishes

• Placoderms

– Lived during the Devonian period

– Bony armor covered their head and neck

– No teeth, but instead, sharp bony plates

– Some were very large

• Acanthodians

– Arose during the same time period as

placoderms

– Centimeters long

– No bony armor



25.5 Modern Jawed Fishes

• Cartilaginous fishes

– Mostly marine fishes with a cartilage skeleton

– Jaws include teeth that grow in rows

• Teeth are continually shed and replaced

– Separate sexes

– Eggs develop in an egg case inside the

mother’s body

• Ruptures to release young into the environment

– Cloaca functions in reproduction and to remove

wastes


Modern Jawed Fishes

• Sharks

– Some are predators

– Some are scavengers that suck up

invertebrates

– Others strain plankton from seawater

• Rays

– Flattened body with large pectoral fins

– Feed by filtering out plankton

– Barbed venomous tail defends against

predators


Bony Fishes

• Lineages of bony fishes

– Ray-finned fishes

– Lobe-finned fishes

• Bone replaces cartilage in the adult skeleton

• Gill slits hidden beneath gill cover

• Ray-finned fishes have thin, membranous

fins

– Swim bladder (sac) volume can be adjusted to

affect buoyancy


Bony Fishes

• Lobe-finned fishes have thick, fleshy fins

– Bones support the inside of the fins

• Two lineages of lobe-finned fishes

– Marine coelacanths

• Thought to be extinct until 1938, when a living

coelacanth found in the Indian Ocean

– Freshwater lungfishes

• Have lungs

• Oxygen diffuses from the lungs into the blood


ovary

anus intestine stomach liver heart gills

B Anatomy of a perch. The swim bladder allows

the fish to adjust its buoyancy (its tendency to float).

kidneyswim bladder

brain

nerve cord

A Goldfish (a type of carp). Note the flexible fins

supported by thin rays. As in most bony fishes, a bony

cover hides the gills.(A) Ultrachock/Shutterstock.com; (B) © 2016 Cengage Learning


25.6 Amphibians – First Tetrapods on

Land

• Amphibians

– Scaleless, land-dwelling vertebrates

– Typically breed in the water

– First tetrapods

– Evolved from fishes about 395 million years ago

• Changes supporting the move to land

– Skeletal changes

– Lungs became larger and more complex

– Eyelids evolved to keep eyes from drying out


Amphibians – First Tetrapods on Land

• Modern amphibians

– Carnivores

• Eat insects and worms

• Examples of modern amphibians

– Salamanders

– Caecilians

– Frogs

– Toads

• Frogs and toads undergo metamorphosis


1 Fish (Eusthenopteron) with bony fins.

3

1

left, © Cengage Learning; right #1 & 3, © P. E. Ahlberg; right #2, Illustration by © Kalliopi Monoyios

3 Early amphibian (Icthyostega) with well-developed ribs, and thick limbs with distinct digits.

2 Fish (Tiktaalik) with sturdier weight-bearing pectoral fins, wristlike bones, and enlarged ribs.

2


Amphibians – First Tetrapods on Land

• Amphibian diversity declining

– Thin, scaleless skin makes them more

susceptible to parasites, pathogens, and

pollutants

– Habitat loss: another influencing factor


25.7 Amniote Evolution

• Amniotes

– Live their lives entirely on land

– Adapted to life in dry places

– Have lungs, and a waterproof skin

– Separate sexes

– Produce eggs in which young are hatched

• Reptile clade includes:

– Turtles, lizards, snakes, crocodilians, and birds


Amniote Evolution

• Dinosaurs are a reptile group

– Birds branched off from a dinosaur lineage

during the Jurassic

– Dinosaurs became extinct by the end of the

Cretaceous

• Endotherms

– Maintain body temperature by adjusting

metabolic heat production

• Ectotherms

– Body temperature varies with the environment


25.8 Nonbird Reptiles

• Lizards and snakes

– Most diverse group of modern reptiles

– About 9,000 species exist

– Covered with overlapping scales

– Periodically shed their skin

• Komodo dragon

– Largest lizard

– Venomous bite

• All snakes are predators with teeth


Nonbird Reptiles

• Turtles

– 300 species

– Bony, keratin-covered shell attached to skeleton

– Toothless

– Freshwater turtles eat fishes and invertebrates

– Land turtles (tortoises) eat plants

• Crocodilians

– Predators that spend much of their time in water

– Have a four-chambered heart, like birds


25.9 Birds – The Feathered Ones

• Feathers

– Filamentous keratin structures derived from

scales

• Feather functions

– Help birds maintain temperature

• Slow the loss of metabolic heat

– Helps keep bird dry by shedding water

– Color plays a role in courtship

– Play a role in flight


Birds – The Feathered Ones

• Most birds are surprisingly lightweight

– Helps them become airborne

– No bladder or teeth

• Bird has a much larger brain than a lizard

– Flying requires coordination and good eyesight

• Reproduction

– Fertilization occurs through the cloaca

– Female lays eggs with nutrients which sustain

the embryo


Avian Diversity

• 10,000 living bird species

– About half are perching birds

• Examples: jays, sparrows, starlings, robins, and

cardinals

• Hummingbirds

– 450 species

– Capable of flying backwards

• Many birds make a seasonal migration

• Penguins and ratite birds cannot fly

– Emus, ostriches, kiwis, rheas, cassowaries


25.10 Mammals – Milk Makers

• Females produce milk to nourish offspring

• Mammals have hair or fur made of keratin

• Endotherms

• Four-chambered heart

• Larger skull and brain for their body size

than other vertebrates

• Lower jaw consists of a single bone

• Four different types of teeth

– Incisors, canines, premolars, and molars


Mammalian Origins and Diversification

• Two branches split from the amniote lineage

– One branch gave rise to reptiles and birds

– One branch (synapsids) gave rise to mammals

• Therapsids (snynapsid subgroup of

mammals)

– Became dominant creatures on land by the end

of the Permian

– Largest extinction event known occurred 250

million years ago

• 70 percent of land species disappeared


Mammalian Origins and Diversification

• Cynodonts survived the extinction event

– Endotherms with insulating fur or hair

– Gave rise to mammals during the Jurassic

• Three surviving mammal lineages

– Monotremes

• Egg-laying mammals

– Marsupials

• Pouched mammals

– Placental mammals

• Placenta transfers nutrients to growing embryo


25.11 Modern Mammalian Diversity

• Monotremes

– Five species: four are echidnas (spiny

anteaters) and the platypus

• Marsupials

– 300 species live in Australia and surrounding

islands

– Examples: kangaroos, koalas, Tasmanian

devils

– 100 species live in Central and South America

– Opossum lives in North America



B North

American

oppossum with

its young.

Jack Dermid

© iStockphoto.com/Craig Dingle

A Kangaroowith a juvenile

in its pouch.


Modern Mammalian Diversity

• Placental mammals

– Encompass 5,000 species

– Dominant mammals in land habitats

– Only mammals that live in seas

– 40 percent are classified as rodents

• Rodent teeth specialized for gnawing

– Bats have 1,200 species

• Only mammals capable of sustained flight

– Moles and shrews

• Adapted to burrowing


Chiroptera (bats)

Carnivora (dogs, cats, bears,

weasels, seals, and walruses)

Cetacea (dolphins, whales)

Perissodactyla

(odd-toed mammals: horses, zebras, rhinos)

Primates (lemurs, monkeys, apes, humans)

Chiroptera (bats)

Rodentia (rats,

mice, squirrels, porcupines)

Soricomorpha

(moles and shrews)

Clockwise from top left, © Abel Tumik/Shutterstock.com; © Kirsanov/ Shutterstock.com; © Maxim Kulko/Shutterstock.com; © Vishnevskiy Vasily/Shut- terstock.com; © Eric Isselée/Shutterstock.com; © prapass/Shutterstock.com; © olly/Shutterstock.com; © Vishnevskiy Vasily/Shutterstock.com.

Artiodactyla (even-toed

mammals: deer, cattle, goats, pigs, hippos)


Modern Mammalian Diversity

• Placental mammals (cont’d.)

– Whales and dolphins

• Adapted to life in the sea

– Carnivora

• Examples: dogs, cats, bears, wolves, foxes, weasels,

seals, sea lions, and walruses

– Cetaceans

• Large mammalian grazers

• Diet of plant material

– Primates

• Includes humans


Points to Ponder

• Are all chordates vertebrates? Are all

vertebrates chordates?

• Were dinosaurs more similar to birds or

reptiles?

• Why is it necessary for amphibians to

produce very large amounts of eggs?

Chapter 25 Animal Evolution – The Chordatesclasspages.warnerpacific.edu/SRamos/BIO102 lectures...•Dinosaurs are a reptile group –Birds branched off from a dinosaur lineage during

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