1. Ch. 34:
Vertebrate Evolution
And Diversity

2. Intro:
A. Phylum Chordata has three subphylums:
1. Urochordates
2. Cephalochordates
3. Vertebrates
Four anatomical features that characterize
the phylum Chordata:
1. Notochord: Longitudinal, flexible rod
located between the digestive tube and
the nerve cord. It provides skeletal
support.

3.  In most vertebrates, the adult retains
only remnants of the embryonic notochord
(Humans = gelatinous material between
the disks of the vertebrae).
Dorsal, Hollow Nerve Cord:
-Develops from the ectoderm
-Develops into the brain and spinal cord
Pharyngeal Slits:
-Connect the pharynx, just posterior to
the mouth, to the outside of the animal.

4. -The pharyngeal slits and structures that
support them have become modified for
gas exchange (in aquatic vertebrates),
jaw support, digestion, hearing, and
other functions during vertebrate
evolution.

5. Tail: Has two purposes –
-Envelopes muscles and skeletal elements
-Propulsive force in aquatic species
Subphylum Urochordata: tunicates
1.Sessile, attached to rocks, docks, and boats
2.Live in colonies and some solitary

6. Food in seawater enters the animal through
siphon in mouth.
-Food passes through the slits into the
atrium and exits through the excurrent
siphon. Food is passed into the intestines.
-Cloaked in a tunic made of carbohydrate.

7. -The adult tunicate scarcely resembles a
chordate.
 No notochord, no nerve cord, no tail,
but the pharyngeal slits suggest a
link to other chordates.
-Larval form has all 4 characteristics of a

8. Subphylum Cephalochordata: Called
lancelets because of their bladelike shape.
Contains the 4 characteristics of chordates.
Few cm long and live with their posteriors
buried in the sand.

9. Lancelets are known as suspension
feeders: A mucous net secreted across the
pharyngeal slits traps tiny food particles in
the water. Food then enters the digestive
tube.

10. Relationship between Invertebrate Chordates
and Vertebrates:
1.Molecular evidence shows that the
cephalochordates are the vertebrates’
closest relatives.
Two stages in the evolution of vertebrates
from invertebrates:
-Urochordate  Cephalochordate
-Cephalochordate  Vertebrate

11. Introduction to Vertebrates:
Characteristics of Vertebrates:
1. Neural crest
2. Pronounced cephalization
3. Vertebral column
4. Closed circulatory system
Neural crest forms
skeletal and
cartilaginous
elements of the
cranium.

12. Jawless Vertebrates (Agnathans)
Two classes:
Class Myxini: Hagfishes; the most
primitive of living “vertebrates.”
-Marine
-Release gooey substance; glands can
produce slime to repulse predators
-Skeleton is made of cartilage

13. -Cartilaginous cranium (skull)
-Notochord
-Do not have vertebrae but are included in
subphylum Vertebrata as they belong to
the clade Craniata because they
represent an ancient branch of Craniata
that predates the origin of vertebral
column.

15. Class Cephalaspidomorphi: Lampreys
-Marine and freshwater
-Feeds by clamping its round mouth onto
live fish, sucking its blood. They are
called ectoparasites.
-Larvae live in freshwater streams and
then migrate to sea or lakes as they
mature.

16. Fishes and Amphibians: The first jawed
fishes, the placoderms (“plate skinned”)
gave rise to two extant groups, the
Chondrichthyes (cartilaginous fishes) and
Osteichthyes (bony fishes).
Jaws and paired fins were major
evolutionary breakthroughs in vertebrate
history.
-Jaws: enable the animal to grip food items
and slice them up.
-Paired fins: enable fish to maneuver
accurately while swimming.

17. Class Chondrichthyes: Sharks and rays
have cartilaginous skeletons.
-Carnivorous
-Well developed sense organs, powerful
muscles and predacious nature

18. -Can detect electrical fields generated by
the muscle contractions of nearby animals.
Lateral line system: Detect vibrations in
the water
-Internal fertilization:
Males have claspers on their pelvic fins
that transfer sperm into females.
Some sharks are oviparous: Lay eggs
that hatch outside the mother’s body.
Some sharks are ovoviviparous: Retain
the fertilized eggs in the oviduct; young
are nourished by the yolk in eggs and
after hatching, the babies are born.
Some sharks are viviparous: the young
develop within the uterus.

19. Class Osteichtheyes: Bony fishes broken
up into 3 other classes: ray-finned fishes,
lobe-finned fishes, and the lungfishes.
-Ossified endoskeleton with a hard matrix
of calcium phosphate.
-Skin is covered by flattened, bony scales.
-Glands in the skin secrete a mucus.

20. -Breath by drawing water over 4 to 5 pairs
of gills that are covered by the protective
operculum.
-Swim bladder: an air sac that helps
control the buoyancy of the fish.
In contrast to sharks, bony fishes can
conserve energy by remaining almost
motionless.

21. -Most are oviparous, reproducing externally
-Class Actinopterygii: Ray-finned fishes
Ex. Bass, trout, perch, tuna, and herring.

22. -Class Actinistia: Lobe-finned fishes
have muscular pectoral and pelvic fins
supported by extensions of the bony
skeleton.
Ex. Only extant lobe-finned fish is the
coelocanth.
Bottom dwellers that may have used their
muscular fins as aids to “walk” along the
bottom.

23. -Class Dipnoi: Lungfishes
-Live in the Southern Hemisphere
-Inhabit stagnant ponds and swamps,
surfacing to gulp air into lungs connected
to the pharynx of the digestive tract.
-Gills, which are the main organs for gas
exchange
-In dry seasons, lungfish can burrow into
the mud and aestivate.

24. Tetrapods evolved from specialized fishes
that inhabited shallow water.

25. -The earliest terresterial tetrapods,
amphibians benefited from an abundance
of food and relatively little competition.
 Great diversity of amphibians during
the early Carboniferous period, the
“age of amphibians.”

26. Class Amphibia: Salamanders, frogs, and
caecilians are the 3 extant amphibian
orders:
-Order Urodela: Salamanders
-Order Anura: Frogs - specialized for
moving on land, sticky tongue, camouflage,
skin secretes mucus (some poisonous).
-Order Apoda: Caecilians (legless,
burrowing amphibians) – nearly blind.

27. -Amphibian means “two lives,” as a reference
to the metamorphosis of frogs.
-Tadpoles are aquatic herbivores with gills
-Tadpole develops legs
-Gills disappear and are replaced by lungs
-Frogs are carnivorous

28. -Amphibians live in damp habitat
-Most amphibians rely on their moist skin
for gas exchange with their habitat.
-Some amphibians lack lungs and breath
exclusively through their skin.
-Eggs do not have shells and dehydrate
easily.

29. -Most have external fertilization.
-In some species, males and females carry
the fertilized eggs on their backs, in their
mouths, or even in their stomachs.
-Some are ovoviviparous or viviparous,
retaining the developing eggs in the female
reproductive tract until release as juveniles.

30. Amniotes: Mammals, birds, reptiles, turtles,
lizards, snakes, and crocodiles.
The evolution of the amniotic egg expanded
the success of vertebrates on land.
Amniotes also evolved waterproof skin and
the increase use of the rib cage to ventilate
the lungs.
The amniotic
egg enabled
terrestrial
vertebrates
to complete
their life
cycles entirely
on land

31. -Shell of the amniotic egg has several
extraembryonic membranes that
function in gas exchange, waste storage,
and the transfer of stored nutrients to
the embryo.
-Allantois: disposal sac
-Membrane of
allantois: functions
with the chorion
as a respiratory
organ.
-Amnion: fluid-filled
cavity that protects
the embryo from
dehydration.

32. -Chorion: exchanges gases between the
embryo and the surrounding air. O2 and
CO2 diffuse freely across the egg’s shell.
-Yolk sac: expands over the yolk; a stock-
pile of nutrients stored in egg. Blood
vessels in the yolk sac membrane transport
nutrients from the yolk into the embryo.

33. Three main groups of the amniotes:
1. Synapsida, 2. Anapsida, 3. Diapsida
All modern
amniotes
(birds &
mammals)
evolved
from
reptiles.

34. Reptilian heritage is evident in all amniotes:
1.Scales containing the protein keratin water-
proof the skin, preventing dehydration in
dry air.
2.Reptiles breath through lungs.
3.Fertilization occurs internally.
Reptiles are ectotherms: absorb external
heat rather than generating much of their
own.
 Advantage: Can survive on less than 10%
calories required by a mammal of
equivalent size.

35. Reptiles dominated the earth for more than
200 million years in two great waves:
1.The first major radiation occurred during
the early Permian and gave rise to the
three main evolutionary branches:
Synapsida, Anapsida, and Diapsida.
The second great radiation in the late
Triassic was marked by origin and
diversification of the dinosaurs on land
and the pterosaurs, or flying reptiles.
Dinosaurs:
1.Ornithischians which were mostly
herbivorous
2.Saurischians which included both
herbivorous and carnivorous dinosaurs
 Gave rise to birds

36. Debate whether or not dinosaurs were
endothermic.
 Some anatomical evidence
 Mesozoic climate was warm
 Dinosaurs that gave rise to birds were
endothermic
c.Dinosaurs went extinct in the late
Cretaceous period.
 Asteroid impact off the Yucatan
Penninsula of Mexico.
In the class of Reptila, there are four orders:
1.Testudines (turtles); 2. Sphenodontia
(tuataras); 3. Squamata (lizards and
snakes); and 4. Crocodilia (alligators and
crocodiles).

37. Testudines (turtles): protective shell;
some returned to the water, but come on
to land to lay eggs.

38. Sphenodontia (tuataras): Only one
species left living in New Zealand.
Squamata (lizards and snakes):
most diverse and numerous
-Lizards are relatively
small and hide in crevices.
-Snakes are carnivorous;
chemical sensors;
sensitive to ground vibrations;
some poisonous

39. Crocodilia (alligators and crocodiles):
among the largest reptiles.
-Spend most of their time in water breathing
air through their upturned nostrils.
-Live in the tropics and subtropics.

40. Birds began as feathered reptiles.
1.Chacteristics of birds:
Modified for flight:
-Bones that have an internal structure that
is honeycombed, making them strong but
light.

41. -Absence of some organs make the body
lighter. (Ex. Females have 1 ovary.)
-Toothless and grind their food in a
muscular gizzard near the stomach
-Excellent vision and coordination
-Large brains (proportionately, compared
to reptiles) allow for complex behaviors:
 Elaborate courtship rituals
-Wings have structure like a plane’s wings:

42. -Feathers function as insulation and are
also light for flight.
Birds evolved from the theropods which
were small, bipedal,
carnvirous
dinosaurs.
3. Ex. Archeopteryx:
Teeth and
clawed
forelimbs.

43. Modern Birds:
a.Flightless birds: Ratites
Ex. Emu, Ostrich, Kiwi

44. Carinates: birds capable of flying;
exhibit a great variety of feather colors,
beak and foot shapes, behaviors, and
flying styles.
-Nearly 60% of living bird species are in the order passeriformes, or perching birds.
Mammals diversified extensively in the wake
of the Cretaceous extinctions.
Characteristics of mammals:
-Mammary glands -Proportionately
-Hair Larger Brains
-Endothermic -Teeth with differing
-Live birth sizes
-Internal Fertilization

45. Three groups of mammals:
a. Monotremes: the playtpuses and the
echindas - are the only living mammals
that lay eggs.
-Babies suck milk from their mother’s
hair because the mothers lack nipples.

46. Marsupials: opossums, kangaroos,
bandicoots, and koalas
-Offspring are born very early in develop-
ment and in most species completes its
embryonic development while nursing
within a maternal pouch, the marsupium.

47. -Eutherian mammals
are placental. Here
is a figure that
shows how
convergent
evolution has
produced a number
of look-alikes
between marsupials
and eutherians due
to their similar
ecologial roles.

48. Eutherians (Placental): Have longer
periods of preganancy; complete their
development in the uterus. Ex. Deer,
mice, moles, squirrels, and wolves.
 Eutherians are closely related to
marsupials than monotremes. They
shared a common ancestor about
millions years ago.

51. Based on molecular data, there are four clades
among the eutherian orders.

52. IV. Primates and the evolution of homo sapiens.
Primate characteristics:
Grasping feet and hands–opposable thumb
Large brains and short jaws
Forward-looking eyes
Flat nails
Well-developed prenatal care
Complex social behavior
Two subgroups of primates:
Prosimians (lemurs,
lorises,
pottos,
and
tarsiers)

53. Anthropoids: Monkeys, apes, and humans
-The oldest known anthropoid
fossils, from
about 45 MYA
support the
hypothesis that
tarsiers are the
prosimians most
closed related
to anthropoids

54. New world monkeys: are arboreal (live
in trees) and have prehensile tails and
nostrils that open to the side
b.Old world monkeys: ground dwelling
lack prehensile tails and their nostrils open downward

55. Humans are just a small twig on the
vertebrate tree:
Paleoanthropology is the study of
human
evolution.
Hominoid:
refers to great
apes and
humans.
3.Hominid: refers
to humans and
close relatives.

56. Two main groups of hominids:
a. Australopithecines, which came first
and are all extinct.
b. The genus Homo, with all species
extinct except one: Homo sapiens.

57. 5 Major features of Human evolution:
-Brain size:
Hominoid brain volume 6 MYA =
cm3
Modern humans = 1,300 cm3
-Jaw shape:
Hominoid ancestors had prognathic jaws
(longer jaws). Shortening of the jaws
produced flatter faces with more
pronounced chins.
-Bipedal posture:
Upright posture and two-legged walking
associated with skeletal modifications.

58. -Reduced size differences between sexes:
“Sexual dimorphism” – Male gorillas and
orangutans weigh about twice as much
as females of their species. In humans,
the size differences are reduced: males
are 1.35 times heavier than females on
average.
-Some key changes in family structure:
Most ape species are not monogamous,
but in most human cultures, monogamy
is part of the social makeup. Newborn
human infants are dependent on their
mothers, and the duration of parental
care for offspring is much longer in
humans than in other apes.

59. The first humans:
-Ape-human split (5-7 mya)
-Australopithecus; “Lucy” (4.0 mya)
-Homo habilis; “Handy Man” (2.5 mya)
-Homo erectus; first to migrate (1.8 mya)
-Neanderthals (200,000 ya)
-Homo sapiens (1.0 mya?)

60. The origin of modern humans has two
hypothesis:
-Multiregional hypothesis:
fully modern humans
evolved in parallel from the local
populations of H. erectus.
Similarities between
the major groups is
due to occasional
interbreeding.

61. -”Out of Africa” replacement hypothesis:
All homo sapiens evolved from a second
major migration out of Africa that occurred
about 100,000 years ago. This migration
completely replaced
all the regional
populations of
Homo derived
from the first
hominid migrations
of H. erectus.