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CHAPTER
19
The Evolution of Vertebrate Diversity
Chapter Objectives
Opening Essay
Describe the difficulties of classifying the duck-billed platypus.
Vertebrate Evolution and Diversity
19.1
19.2–19.8
19.4
19.8
Describe the key derived traits of the chordates and the chordate subgroups.
Describe the characteristics of and distinguish between each of the following
vertebrate groups: hagfishes, lampreys, chondrichthyans, ray-finned fishes,
lobe-finned fishes, amphibians, reptiles, birds, and mammals.
Describe the transitional species that occupy the range between fishes and
amphibians in evolutionary history.
Distinguish between monotremes, marsupials, and placental mammals. Provide
examples of each.
Primate Diversity
19.9
Compare the three main groups of living primates. List their characteristics and
describe their evolutionary relationships.
19.10 Distinguish between monkeys and apes. Compare the different groups of apes
to each other and to humans.
Hominin Evolution
19.11 Describe the evidence that suggests that hominins did not evolve in a straight
line leading directly to our species.
19.12 Describe the evidence that suggests when upright posture and large brains first
evolved in humans.
19.13 Describe the evolution of larger brain size in hominins.
19.14 Describe the relationships between Neanderthals and modern humans. Describe
the evidence that suggests that all modern humans share a common ancestor
that lived 160,000–200,000 years ago.
19.15 Describe the unusual characteristics of the newly discovered Homo floresiensis.
19.16 Describe the adaptive advantages of darker skin in humans living near the
equator but lighter skin in humans living in northern latitudes.
19.17 Explain why the total number of animal species alive today remains an
estimate.
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Lecture Outline
I. Introduction
A. The duck-billed platypus is a strange animal and hard to classify. It has
1. a furry body,
2. bill and webbed feet that look like a duck, and
3. mammary glands that produce milk for its young.
4. In addition, it lays eggs!
II. Vertebrate Evolution and Diversity
A. 19.1 Derived characters define the major clades of chordates
1. Biologists have developed hypotheses for the evolution of chordate groups using
a. anatomical,
b. molecular, and
c. fossil evidence.
2. Figure 19.1
a. illustrates a current view of the major clades of chordates and
b. lists some of the derived characters that define the clades.
B. 19.2 Hagfishes and lampreys lack hinged jaws
1. Hagfishes and lampreys
a. are craniates,
b. have a notochord, but
c. lack hinged jaws and paired fins.
2. Lampreys but not hagfishes have rudimentary vertebral structures. Thus,
a. lampreys are vertebrates but
b. hagfishes are not vertebrates.
3. Hagfishes are deep-sea scavengers that produce slime as an antipredator defense.
4. Lamprey adults are parasites that penetrate the sides of fishes with their rasping
tongues.
5. Larval lampreys
a. resemble lancelets and
b. are suspension feeders that live in freshwater streams, where they feed, buried in
sediment.
C. 19.3 Jawed vertebrates with gills and paired fins include sharks, ray-finned fishes, and
lobe-finned fishes
1. Jawed vertebrates
a. appeared in the fossil record about 470 million years ago and
b. quickly diversified using their paired fins and tail to chase a wide variety of prey.
2. Jaws may have evolved by modifications of skeletal supports of the anterior pharyngeal (gill) slits.
3. The remaining gill slits remained as sites of gas exchange.
4. Three lineages of jawed fishes with gills and paired fins that are commonly called
fishes:
a. chrondrichthyans—sharks and rays,
b. ray-finned fishes—tuna, trout, and goldfish, and
c. lobe-finned fishes—coelacanths and lungfishes.
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CHAPTER 19
The Evolution of Vertebrate Diversity
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5. Chondrichthyans have
a. a flexible skeleton made of cartilage,
b. electrosensors on their heads, and
c. a lateral line system that helps them locate prey.
d. Most sharks are fast-swimming predators, with sharp vision and a keen sense of
smell.
e. Most rays are adapted for life on the bottom, with dorsoventrally flattened bodies
and eyes on the top of their heads.
6. Ray-finned fishes have
a. an internal skeleton reinforced with a hard matrix of calcium phosphate,
b. flattened scales covered with mucus,
c. an operculum that covers a chamber of gills, and
d. a buoyant swim bladder (derived from an ancestral lung).
7. With more than 27,000 species, ray-finned fishes are the most diverse group of
vertebrates.
8. Lobe-fins have muscular pelvic and pectoral fins that are supported by rod-shaped
bones.
9. Today, three lineages of lobe-fins survive:
a. coelacanths, living deep in the oceans, were once thought to be extinct,
b. lungfishes, which can gulp air into lungs, inhabit stagnant waters in the Southern
Hemisphere, and
c. tetrapods, adapted to life on land, include terrestrial vertebrates.
D. 19.4 EVOLUTION CONNECTION: New fossil discoveries are filling in the gaps of tetrapod evolution
1. During the late Devonian, a line of lobe-finned fishes gave rise to tetrapods, jawed
vertebrates with limbs and feet that can support weight on land.
2. Adapting to life on land was a key event in vertebrate history.
3. All subsequent groups are descendants of these early land-dwellers.
4. Like plants, vertebrates faced obstacles on land in regard to
a. gas exchange,
b. water conservation,
c. structural support,
d. a means of locomotion,
e. adapting sensory organs that worked well in water but not on land, and
f. reproduction.
E. 19.5 Amphibians are tetrapods—vertebrates with two pairs of limbs
1. Amphibians
a. include salamanders, frogs, and caecilians,
b. use their moist skins to supplement their lungs for gas exchange,
c. often have poison glands in their skins,
d. usually return to standing water to reproduce,
e. undergo metamorphosis from a larval stage to the adult form, and
f. were the first tetrapods able to move on land.
F. 19.6 Reptiles are amniotes—tetrapods with a terrestrially adapted egg
1. Reptiles (including birds) and mammals are amniotes.
2. The major derived character of this clade is an amniotic egg with four internal
membranes.
a. The amnion is a fluid-filled sac surrounding the embryo.
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b. The yolk sac contains a rich store of nutrients for the developing embryo.
c. The allantois also helps dispose of metabolic waste.
d. The chorion (and allantois) enable the embryo to obtain oxygen from the air and
dispose of carbon dioxide.
3. Reptiles
a. include lizards, snakes, turtles, crocodilians, birds, and extinct dinosaurs,
b. have a skin covered with scales and waterproofed with keratin,
c. obtain most of their oxygen using lungs, and
d. are ectothermic, absorbing external heat rather than generating much of their own.
G. 19.7 Birds are feathered reptiles with adaptations for flight
1. Most birds can fly, and nearly every part of their bodies reflect adaptations that
enhance flight.
a. The forelimbs have been remodeled as feather-covered wings that act as airfoils.
b. Large flight muscles anchored to a central ridge along the breastbone provide power.
c. Many features help reduce weight for flight:
i. Present-day birds lack teeth.
ii. The tail is supported by only a few small vertebrae.
iii. Feathers have hollow shafts.
iv. Their bones have a honeycombed structure that makes them strong but light.
2. Flight is very costly, and present-day birds have a high rate of metabolism.
3. Unlike other living reptiles, birds are endothermic, using heat generated by metabolism to maintain a warm, steady body temperature.
4. Birds have relatively large brains and display complex behaviors. They have
a. acute senses,
b. fine muscle control, and
c. excellent eyesight.
5. Birds evolved from a lineage of small, two-legged dinosaurs called theropods.
a. Archaeopteryx is the oldest, most primitive known bird (150 million years old),
with feathered wings.
b. It resembled a small bipedal dinosaur, with teeth, wing claws, and a long tail with
many vertebrae.
H. 19.8 Mammals are amniotes that have hair and produce milk
1. Mammals are endothermic amniotes with
a. hair, which insulates their bodies, and
b. mammary glands, which produce milk.
2. Mammals have efficient respiratory and circulatory systems that support their high
rate of metabolism.
3. Mammalian teeth are differentiated for many kinds of diets.
4. Monotremes are egg-laying mammals. Living monotremes include
a. the duck-billed platypus and
b. echidnas.
5. Unlike monotremes, the embryos of marsupials and eutherians are nurtured by a
placenta, in which nutrients from the mother’s blood diffuse into the embryo’s blood.
6. Marsupials have a brief gestation and give birth to tiny, embryonic offspring that
complete development while attached to the mother’s nipples.
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7. Eutherians are mammals that bear fully developed live young. They are commonly
called placental mammals because their placentas are more complex than those of
marsupials.
8. The first true mammals arose 200 million years ago and were probably small,
nocturnal insectivores.
a. Monotremes are the oldest lineage of mammals.
b. Marsupials diverged from eutherians (placental mammals) about 180 million years
ago.
c. Mammals underwent an adaptive radiation following the Cretaceous extinction of
dinosaurs, giving rise to large terrestrial carnivores and herbivores, bats, and aquatic
whales and porpoises.
III. Primate Diversity
A. 19.9 The human story begins with our primate heritage
1. The mammalian order Primates includes the lemurs, tarsiers, monkeys, and apes.
a. Primates probably arose as small arboreal mammals before 65 million years ago,
when dinosaurs still dominated the planet.
2. Many primate characters are arboreal adaptations.
a. Shoulder and hip joints allow climbing and brachiation.
b. Grasping hands and feet are highly mobile and flexible.
c. Sensitive hands and feet aid in manipulation.
d. A short snout and forward-pointing eyes enhance depth perception.
3. A phylogenetic tree shows that all primates are divided into three groups:
a. lemurs, lorises, and pottos,
b. tarsiers, and
c. anthropoids, including monkeys and apes with a fully opposable thumb, in which
the tip of all four fingers can touch the thumb.
4. Monkeys do not constitute a monophyletic group.
a. Old World monkeys (Africa and Asia)
i. probably evolved first,
ii. lacked a prehensile tail, and
iii. have nostrils that open downward.
b. New World monkeys have
i. a prehensile tail and
ii. nostrils that are wide open and farther apart.
B. 19.10 Humans and four other groups of apes are classified as anthropoids
1. In addition to monkeys, the anthropoid group includes apes: gibbons, orangutans,
gorillas, chimpanzees (and bonobos), and humans.
2. Apes
a. lack a tail and
b. have relatively long arms and short legs,
c. have relatively larger brains with respect to size, and
d. more flexible behavior.
3. Gorillas, chimpanzees, and humans have a high degree of social organization.
4. Nonhuman apes
a. live only in Africa and Southeast Asia, in tropical rain forests and
b. have a smaller geographic range than monkeys.
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5. Gibbons are
a. monogamous and
b. the only fully arboreal apes.
6. Orangutans are
a. shy,
b. solitary, and
c. live in rain-forest trees and the forest floor.
7. Gorillas are
a. the largest of the apes and
b. fully terrestrial.
8. Chimpanzees make and use tools.
9. Humans and chimpanzees
a. are closely related,
b. share 99% of their genes, and
c. diverged from a common ancestor between 5 and 7 million years ago.
IV. Hominin Evolution
A. 19.11 The hominin branch of the primate tree includes species that coexisted
1. Paleoanthropology is the study of human origins and evolution, the brief history
since the divergence of human and chimpanzee lineages.
2. Paleoanthropologists have unearthed
a. about 20 species of extinct hominins, species that are more closely related to
humans than to chimpanzees, and
b. thousands of hominin fossils.
3. Figure 19.11 presents some of the known hominins.
4. The oldest hominin yet discovered, Sahelanthropus tchadensis, lived about 7 to 6
million years ago.
5. The fossil record suggests that hominin diversity increased dramatically between 4 to
2 million years ago.
B. 19.12 Australopiths were bipedal and had small brains
1. Unlike chimpanzees, humans
a. walk upright and
b. have larger brains.
2. Bipedalism arose millions of years before larger brain size. Evidence of bipedalism
includes
a. 3.6-million-year-old upright-walking homin footprints and
b. fossil skeletons.
C. 19.13 Larger brains mark the evolution of Homo
1. Australopiths had such small brains (400–450 cc) that they were too small to be members of Homo.
2. Homo habilis (2.4–1.6 million years ago) had a brain size of 510–690 cc. Their fossils
are found with stone tools.
3. Homo ergaster (1.9–1.6 million years ago) had a brain size ranging from 750–850 cc.
Their
a. fossils are found with more sophisticated stone tools and
b. long, slender legs were adapted for long-distance walking.
4. Homo sapiens has a brain size of around 1300 cc.
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5. Homo erectus
a. had a brain volume of around 940 cc and
b. was the first hominin to leave Africa.
6. The oldest known fossils of hominins outside of Africa are about 1.8 million years old.
7. Homo neanderthalensis, commonly called Neanderthals
a. lived in Europe from about 350,000 to 28,000 years ago when they went extinct,
b. had brains as large as modern humans, and
c. hunted big game with tools made of stone and wood.
8. How are Neanderthals related to modern humans?
a. An analysis of mtDNA isolated from Neanderthal bones suggests that they were a
distinct species from modern humans.
b. The last common ancestor between humans and Neanderthals lived about 500,000
years ago.
D. 19.14 From origins in Africa, Homo sapiens spread around the world
1. Analysis of mtDNA and Y chromosomes suggest that all living humans
a. inherited their mtDNA from a woman who lived 160,000–200,000 years ago and
b. diverged from a common African ancestor.
2. Our species emerged from Africa in one or more waves, migrating to Asia 50,000–
60,000 years ago and then to Europe, Southeast Asia, and Australia.
3. The capacity for creativity and symbolic thought may have spurred human evolution.
E. 19.15 Who were the “hobbits”?
1. Fossils of small hominins named Homo floresiensis that were found in Indonesia are
controversial. The 2004 discovery of the nearly complete skeleton was of a hominin
that
a. was about 1 meter tall,
b. had a chimp-sized brain, and
c. had a skull that displayed some humanlike traits.
2. Scientists are trying to determine their relationship to other hominins.
F. 19.16 EVOLUTION CONNECTION: Human skin color reflects adaptations to varying
amounts of sunlight
1. Human skin color varies geographically, likely as a result of natural selection.
2. Natural selection may have selected for the competing abilities of skin to
a. block UV radiation, which degrades folate, and
b. absorb UV radiation to synthesize vitamin D.
c. Folate is vital for fetal development and spermatogenesis.
d. Vitamin D is essential for proper bone development.
G. 19.17 CONNECTION: Our knowledge of animal diversity is far from complete
1. Thousands of new species of organisms are discovered each year.
2. The pace of discovery has recently increased due to
a. better access to remote areas and
b. new mapping technologies.
Key Terms
amniote
amniotic egg
amphibian
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anthropoid
birds
chondrichthyan
INSTRUCTOR GUIDE FOR CAMPBELL BIOLOGY: CONCEPTS & CONNECTIONS
craniate
ectothermic
endothermic
Copyright © 2012 Pearson Education, Inc.
eutherian
hominins
lateral line system
lobe-fins
mammal
marsupial
monotreme
operculum
opposable thumb
paleoanthropology
placenta
placental mammal
ray-finned fish
reptile
swim bladder
tetrapod
vertebra (plural, vertebrae)
vertebral column
vertebrate
Word Roots
amphi- = both; -bio = life (amphibian: a type of vertebrate that inhabits both aquatic and terrestrial
habitats)
anthro- = human; -oid = likeness (anthropoid: a member of the primate group including apes and
monkeys, all of which resemble humans in certain characteristics)
australo- = southern; -pithekos = ape (australopith: one of the first hominins)
chondr- = cartilaginous; -ichthy = fish (chondrichthyan: the group of fish that have cartilaginous
skeletons, including sharks and rays)
chord- = a string (chordates: the group of organisms that possess a notochord and other characteristics at some point in their lives)
crani- = the skull (craniate: a chordate with a head)
ecto- = outside; -therm = heat (ectotherm: an animal that warms itself mainly by absorbing heat
from its surroundings)
endo- = inner; -therm = heat (endotherm: an animal that derives most of its body heat from its
own metabolism)
eu- = good (eutherian: one of the mammals whose young complete their embryonic development
within the uterus, joined to the mother by the placenta)
homin- = man (hominin: species that are more closely related to humans than to chimpanzees)
later- = side (lateral line system: a row of sensory organs along each side of a fish’s body that is
sensitive to changes in water pressure)
marsupi- = a bag, pouch (marsupial: a mammal, such as a koala, kangaroo, or opossum, whose
young complete their embryonic development inside a maternal pouch called the marsupium)
mono- = one (monotreme: an egg-laying mammal, such as the duck-billed platypus)
opercul- = a covering, lid (operculum: a protective flap that covers the gills of fishes)
paleo- = ancient; anthrop- = man; -ology = the science of (paleoanthropology: the study of
human origins and evolution)
tetra- = four; -podi = foot (tetrapod: a vertebrate with two pairs of limbs, such as a mammal,
amphibian, or reptile)
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