© Cengage Learning 2016
Chapter 25
Animal Evolution
– The Chordates
© Cengage Learning 2016
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
© Cengage Learning 2016
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
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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
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pharynx with gill slits
dorsal nerve cord
notochord
tail that extends beyond the anus
single eyespot
anus
© 2013 Cengage Learning
© Cengage Learning 2016
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
© Cengage Learning 2016
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
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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
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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
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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
© Cengage Learning 2016
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
© Cengage Learning 2016
supporting
structure
for gill slits
gill slits
jaw, derived from support structure
location of spiracle
(modified gill slit)
jaw© 2016 Cengage Learning
jaw support
© Cengage Learning 2016
jaw
location of spiracle
(modified gill slit)
jaw support
jaw, derived
from support
structure
supporting
structure for
gill slits
gill slits
Stepped Art
© Cengage Learning 2016
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
© Cengage Learning 2016
© Cengage Learning 2016
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
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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
© Cengage Learning 2016
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
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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
© Cengage Learning 2016
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
© Cengage Learning 2016
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
© Cengage Learning 2016
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
© Cengage Learning 2016
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
© Cengage Learning 2016
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
© Cengage Learning 2016
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
© Cengage Learning 2016
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
© Cengage Learning 2016
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
© Cengage Learning 2016
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
© Cengage Learning 2016
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
© Cengage Learning 2016
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
© Cengage Learning 2016
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
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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
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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
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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
© Cengage Learning 2016
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
© Cengage Learning 2016
© Cengage Learning 2016
B North
American
oppossum with
its young.
Jack Dermid
© iStockphoto.com/Craig Dingle
A Kangaroowith a juvenile
in its pouch.
© Cengage Learning 2016
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
© Cengage Learning 2016
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)
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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
© Cengage Learning 2016
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?