CHAPTER 20 HISTORY OF THE VERTEBRATES. THE PALEOZOIC ERA Scientists divide the earth’s past into...
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Transcript of CHAPTER 20 HISTORY OF THE VERTEBRATES. THE PALEOZOIC ERA Scientists divide the earth’s past into...
CHAPTER 20
HISTORY OF THE VERTEBRATES
THE PALEOZOIC ERA
• Scientists divide the earth’s past into different time periods.• Large blocks of time
are called eras.• Eras are divided
into blocks of time called periods.
• Some periods are divided into epochs, which in turn can be divided into ages.
Paleozoic EraPrecambrian
Devonian CarboniferousSecond massextinction
SilurianOrdovicianFirst massextinction
Fourth massextinction
Cretaceous
Jurassic
Permian Triassic
Cretaceous
NowCenozoic EraTertiary
Cambrian
400 M.Y.A.500 M.Y.A. 450 M.Y.A.
300 M.Y.A.350 M.Y.A.400 M.Y.A.
300 M.Y.A.
200 M.Y.A.
100 M.Y.A. 3.5 M.Y.A.50 M.Y.A.
100 M.Y.A.150 M.Y.A.
200 M.Y.A.250 M.Y.A.
600 M.Y.A. 500 M.Y.A.550 M.Y.A.
Mesozoic Era
Fifth massextinction
Third massextinction
THE PALEOZOIC ERA
• Virtually all of the animals that survive at the present time originated in the sea at the beginning of the Paleozoic era.• The diversification of animal life began soon
after the Cambrian period (545490 M.Y.A.).• Some Cambrian animals, such as trilobites,
have no surviving close relatives.• The first vertebrates evolved about 500 M.Y.A.
THE PALEOZOIC ERA
• While most of the animal phyla that evolved in the Cambrian remained marine, a few phyla have successfully invaded land.• Fungi and plants were the first terrestrial
organisms, appearing over 500 M.Y.A.• Arthropods were the first terrestrial animals,
invading land about 410 M.Y.A.
THE PALEOZOIC ERA
• Vertebrates invaded the land during the Carboniferous period (360280 M.Y.A.).• Amphibians were
the first terrestrial vertebrates, followed by the reptiles, which were successful and dominant.
THE PALEOZOIC ERA
• Mass extinctions are particularly sharp declines in species diversity.• Five mass extinctions
have occurred.• The most drastic
occurred during the last ten million years of the Permian period, the end of the Paleozoic era.• An estimated 96% of
all species of marine animals became extinct.
• The most well-studied extinction occurred at the end of the Cretaceous period (65 M.Y.A.).• Probably triggered by a large asteroid hitting the earth.• Dinosaurs went extinct at this time.
THE PALEOZOIC ERA
• Mass extinctions left vacant many ecological opportunities.• Extinctions are often followed by rapid evolution
among the relatively few species that survived.
THE PALEOZOIC ERA
• We are currently experiencing a sixth mass extinction event.• The number of species is declining at a rapid
rate due to human activity.• Some predict that as many as 25% of all
species will become extinct in the near future.
THE MESOZOIC ERA
• The Mesozoic era (248–65 M.Y.A.) has traditionally been divided into three periods:• Triassic• Jurassic• Cretaceous
• During the Jurassic period, the supercontinent of Pangaea began to break up, sea levels were rising, and the world’s climate became warmer and wetter.
http://youtu.be/cQVoSyVu9rk
THE MESOZOIC ERA
• The Mesozoic era (248–65 M.Y.A.) was a time of intensive evolution of terrestrial plants and animals.• Reptiles continued their
success and diversified greatly.
• The flowering plants evolved in the early Cretaceous.
• From reptile ancestors, dinosaurs, mammals, and birds evolved.
THE MESOZOIC ERA
• Dinosaurs and mammals appeared at about the same time, 200–220 M.Y.A.• But the dinosaurs filled the evolutionary niche
for large animals.• For over 150 million years, dinosaurs were the
dominant land vertebrates.
THE MESOZOIC ERA
• About 65 M.Y.A., at the end of the Cretaceous period, dinosaurs disappeared.• This loss included flying
reptiles (pterosaurs) and the great marine reptiles.
• Mammals occupied the niches left open by the loss of the dinosaurs.
THE MESOZOIC ERA
• Many explanations have been advanced to explain the demise of the dinosaurs.• The most widely accepted, proposed by Luis W.
Alvarez, blames an asteroid impact.• Iridium is an element rare on earth but
abundant in meteorites.• A layer of iridium is abundant in many parts of
the world in a layer of sediment that dates to the end of the Cretaceous period.
THE CENOZOIC ERA
• Early in the Cenozoic era (65 M.Y.A. to present), the climate was relatively warm compared to today’s colder and drier climate.• The first half of the era was very warm with
jungle-like forests at the poles.• A gradual cooling caused ice caps to form
at the poles.
THE CENOZOIC ERA
• This was followed by a series of glaciations, the most recent ending about 10,000 years ago.• Many very large mammals
evolved during the ice ages, including:• Mastodons, mammoths,
saber-toothed tigers, and cave bears.
MammothsAlthough only two species of elephants survivetoday, the elephant family was far more diverseduring the late Tertiary. Many were cold-adaptedmammoths with fur.
Giant ground slothsMegatherium was a giant 6-meter groundsloth that weighed 3 tons and was as largeas a modern elephant.
Irish elkNeither Irish nor an elk (it is a kind of deer),Megaloceros as the largest deer that ever lived, withantlers spanning nearly 4 meters. Seen in French cavepaintings, they survived until at least 7,700 years ago.
Cave bearsNumerous in the ice ages, this enormousvegetarian bear slept through the winterin large groups.
SOME GROUPS OF EXTINCT ANIMALSTABLE 20.1
Saber-tooth catsThe jaws of these large, lionlike catsopened an incredible 120 degreesto allow the animal to drive its hugeupper pair of saber teeth into prey.
FISHES DOMINATE THE SEA
• A series of key evolutionary advances allowed vertebrates first to conquer the sea and then the land.
• About half of all vertebrates are fishes.• Fishes provide the evolutionary base for the
invasion by land by amphibians.
VERTEBRATE FAMILY TREE
0
Tim
e (m
illio
ns
of
year
s ag
o)
Mammals
Birds
Reptiles
Amphibians
Modern bonyfishes
Cartilaginousfishes
Jawlessfishes
(two classes)
Primitive reptiles(extinct)
Primitive amphibians(extinct)Acanthodians
(extinct)
Ostracoderms(extinct)
Placoderms(extinct)
Chordate ancestor
Ordovician(490–438)
Silurian(438–408)
Devonian(408–360)
Carboniferous(360–280)
Permian(280–248)
Quaternary(2–Present)
Tertiary(65–2)
Cretaceous(144–65)
Jurassic(213–144)
Triassic(248–213)
100
200
300
400
500
FISHES DOMINATE THE SEA
• All fishes have four important characteristics in common:• Gills are used to extract dissolved
oxygen from water.• Vertebral column - all fishes have
an internal skeleton with a spine.
• Single-loop blood circulation - blood is pumped in a single loop, from the heart to the gills, then to the body, then back to the heart.
• Nutritional deficiencies:• Fishes are unable to synthesize some amino acids and
must consume them in their diet.• This trait has been inherited by all of their vertebrate
descendants.A
mp
hib
ian
s
Fis
h
Rep
tile
s
Bir
ds
Mam
ma
ls
Chordate ancestor
FISHES DOMINATE THE SEA
• The first fishes were jawless ostracoderms that appeared in the sea about 500 M.Y.A.• Agnathans are the
only jawless fishes found today.• They include
hagfish and lampreys.
FISHES DOMINATE THE SEA
• Jawed fishes appeared around 410 M.Y.A.• Jaws evolved from the frontmost of a series of
cartilaginous arch supports that reinforced the tissue between gill slits.
Skull Anterior gill arches
Gill slits
FISHES DOMINATE THE SEA
• The earliest jawed fishes had spines (acanthodians) or heavy armor (placoderms), and some reached enormous sizes.
FISHES DOMINATE THE SEA
• Sharks and bony fishes appeared about 400 M.Y.A. and shared the seas with spiny fish and placoderms for 150 million years.
• Eventually, the less maneuverable spiny fish and placoderms went extinct.
• Sharks and bony fish have dominated the seas for the last 250 million years.
FISHES DOMINATE THE SEA
• Sharks, along with skates and rays, belong to the class Chondrichthyes.• Sharks have a flexible skeleton made of
cartilage and are fast and maneuverable swimmers.
• There are 750 species in this class today.
FISHES DOMINATE THE SEA
• While some are filter feeders, most sharks are predators and have a mouth armed with rows of sharp teeth.
• Sharks also have many special sensory adaptations that suit their predatory life.
FISHES DOMINATE THE SEA
• Bony fishes have a heavier internal skeleton made of bone.• But they achieve
maneuverability through the aid of a swim bladder, a gas-filled sac that allows fish to regulate their buoyancy.• Sharks gain buoyancy
with oil in their livers, but they must keep swimming to counteract their denser-than-water bodies.
Muscularvalve
Toheart
Dorsal aorta
Gasgland
Swim bladder
FISHES DOMINATE THE SEA
• Bony fishes comprise the class Osteichthyes.• Some bony fishes are lobe-finned (subclass
Sarcopterygii).• This group includes the ancestors of the first
tetrapods (four-legged animals).
FISHES DOMINATE THE SEA
• Other bony fishes are ray-finned (subclass Actinopterygii).• This group includes the vast majority of
today’s fishes.• Bony fishes are the most successful of all
fishes, indeed of all vertebrates – nearly 30,000 species.
FISHES DOMINATE THE SEA
• Bony fishes have several adaptations that have helped make them such evolutionary successes:• Lateral line system
• A special sensory system that enables fish to detect changes in water pressure.
• Also present in sharks.• Operculum
• A bony covering on top of the opening of the gills.
• This allows the fish to ventilate the gills while remaining stationary.
AMPHIBIANS INVADE THE LAND
• The amphibians include frogs, salamanders, and caecilians.• They were the first
terrestrial vertebrates and evolved from the lobe-finned fishes.
Am
ph
ibia
ns
Fis
h
Rep
tile
s
Bir
ds
Mam
mal
s
Chordate ancestor
1
2
3
Lobe-finned Fish
Tiktaalik
Early Amphibian
Humerus
Pelvis
Tibia
Fibula
FemurUlna
Shoulder
Radius
Radius
Shoulder
Ulna
Humerus
Pelvis
Shoulder
Tibia
Femur
Humerus
Ulna RadiusFibula
• A fossil of the genus Tiktaalik (discovered in 2006) exhibited limb morphology that was transitional between fish and amphibians.
AMPHIBIANS INVADE THE LAND
• Amphibians have five key characteristics that allowed them to invade land successfully:
• legs• lungs• cutaneous respiration• pulmonary veins• partially divided heart
AMPHIBIANS INVADE THE LAND
• Amphibians were the dominant land vertebrates for 100 million years.• By the mid-Permian
period, fully terrestrial groups of amphibians had evolved, some very large and with extensive body armor.
AMPHIBIANS INVADE THE LAND
• The amphibians of today must reproduce in water and are not completely terrestrial.
• Approximately 4,850 species exist today in the class Amphibia.
REPTILES CONQUER THE LAND
• Reptiles are more fully terrestrial than amphibians.
• All living reptiles share the following fundamental characteristics:• Amniotic egg
• This innovation is a watertight environment that offers the embryo protection against drying out.
• Dry skin• Reptiles are covered by scales
or armor in order to prevent drying out.
• Thoracic breathing• Reptiles increase their lung
capacity by expanding their chest cavity when breathing in air.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Am
ph
ibia
ns
Fis
h
Rep
tile
s
Bir
ds
Mam
mal
s
Chordate ancestor
THE WATERTIGHT EGG
Chorion
Leathery skinEmbryo
Yolk sac
AllantoisAmnion
REPTILES CONQUER THE LAND
• Today some 7,000 species of reptiles belong to the class Reptilia.
• Reptiles improved on the evolutionary innovations of amphibians to terrestrial life.– Reptilian legs were arranged to better support
body weight and to facilitate more efficient locomotion.
– Lungs and heart became more efficient in reptiles than in amphibians.
REPTILES CONQUER THE LAND
• Reptiles evolved around 300 million years ago; three lineages formed:• In one lineage, predatory reptiles called the
pelycosaurs evolved and were dominant for 50 million years; therapsids replaced the pelycosaurs as the dominant land vertebrate, and one group eventually gave rise to the mammals.
REPTILES CONQUER THE LAND
• A second lineage gave rise to the ancestors of turtles.
REPTILES CONQUER THE LAND
• A third lineage gave rise around 230 M.Y.A. to the ancestors of snakes, lizards, and tuataras, to marine reptiles (ichthyosaurs and plesiosaurs), and to the archosaurs.
REPTILES CONQUER THE LAND
• Early archosaurs resembled crocodiles, but later forms called thecodonts were the first reptiles to be bipedal.
REPTILES CONQUER THE LAND
• Early archosaurs gave rise to four groups: • Dinosaurs, many of which grew to immense
sizes• Crocodiles, which have changed little• Pterosaurs, the flying reptiles• Birds
• Dinosaurs were the most successful of all land vertebrates but became extinct around 65 million years ago, along with the marine reptiles and pterosaurs.
BIRDS MASTER THE AIR
• Birds evolved from bipedal dinosaurs about 150 M.Y.A.• They only became
common after the pterosaurs became extinct.
Am
ph
ibia
ns
Fis
h
Rep
tile
s
Bir
ds
Mam
mal
s
Chordate ancestor
BIRDS MASTER THE AIR
• Many scientists consider birds to be feathered dinosaurs, given their similarity in so many respects to dinosaurs.
BIRDS MASTER THE AIR
• Modern birds lack teeth and have only vestigial tails.
• They retain many reptilian characteristics• Birds lay amniotic eggs (but with hard shells).• Birds have reptilian scales on their feet and
lower legs.
BIRDS MASTER THE AIR
• Birds are different than reptiles in that they have:• Feathers
• Derived from reptilian scales but adapted for flight.
• Flight skeleton• The bones of birds are
thin and hollow, reducing weight while providing enhanced points for flight muscle attachment.
Barbules
Quill
Shaft
HooksBarb
Shaft
BIRDS MASTER THE AIR
• Birds are endothermic• Their high body
temperatures enhance metabolism, satisfying the large energy requirements of flight.
• The oldest bird of which there is a clear fossil is Archaeopteryx.
• There are about 8,600 species of birds in the class Aves today.
MAMMALS ADAPT TO COLDER TIMES
• Mammals evolved about 220 M.Y.A. and belong to the class Mammalia.• Members of this
class share three key characteristics:• Mammary glands
• Hair• Middle ear
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Am
ph
ibia
ns
Fis
h
Rep
tile
s
Bir
ds
Mam
mal
s
Chordate ancestor
MAMMALS ADAPT TO COLDER TIMES
• The first mammals evolved from therapsids.
• Early mammals were small shrewlike creatures.• They lived
inconspicuously in an age dominated by dinosaurs.
MAMMALS ADAPT TO COLDER TIMES
• Mammals were a minor group during the time of the dinosaurs, but rapidly diversified when dinosaurs and many other land and marine animals became extinct 65 M.Y.A.
• Over 4,500 species of mammals exist now, half of them rodents, and one-quarter of them bats.
MAMMALS ADAPT TO COLDER TIMES
• Modern mammals have a number of characteristics that make them successful.• Endothermy allows for mammals to be active
at any time of day or night and to colonize harsh environments.
• Teeth type varies in mammals, which have heterodont dentition, allowing specialization to eating habits.
• Hooves help with locomotion in running mammals; hooves, claws, and fingernails are made of keratin; horns are composed of a bony core surrounded by a sheath of compacted keratin.
MAMMALS ADAPT TO COLDER TIMES
• Placenta is an adaptation for nourishing developing young that will be born live.
PlacentaChorion
Embryo
Uterus
Amnion
Yolksac
Umbilicalcord
MAMMALS ADAPT TO COLDER TIMES
• Today’s mammals include.• Monotremes
• Egg-laying mammals
• Marsupials• Pouched mammals
• Placental mammals