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CHAPTER 35
LECTURE
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Vertebrates
Chapter 35
Phylum Chordata
• Chordates are deuterostome coelomates
• Nearest relatives are echinoderms (the only other
deuterostomes)
• Fishes, amphibians, reptiles, birds, and mammals
3
4 Features
1. Nerve cord
2. Notochord
– May be replaced
by vertebral
column
3. Pharyngeal slits
– Pharyngeal
pouches present in
all vertebrate
embryos
4. Postanal tail
4
• All chordates have all
four of these
characteristics at some
time in their lives
• Other characteristics also
distinguish chordates
– Chordate muscles are
arranged in segmented
blocks called somites
– Most chordates have an
internal skeleton against
which the muscles work
5
6
Phylum Chordata can be divided into three
subphyla
1. Urochordata
Nonvertebrates
2. Cephalochordata
3. Vertebrata
7
Subphylum Urochordata
• Tunicates and salps are marine animals
• Larvae are tadpolelike and have notochord
and nerve cord
– Are free-swimming but do not feed
• Adults typically lose the tail and notochord
– Are immobile filter-feeders
– Many secrete a tunic (cellulose sac) that
surrounds the animal
8
9
10
Subphylum
Cephalochordata
•
•
•
•
•
•
Lancelets are scaleless chordates
Notochord persists throughout animal’s life
Spend most of their time partly buried
Have no distinguishable head
Feed on plankton using cilia-generated currents
Closest relatives to vertebrates
11
Subphylum Vertebrata
• Vertebrates are chordates with a spinal
column
• Distinguished from nonvertebrates by
– Vertebral column – Encloses and protects the
dorsal nerve cord
– Head – Distinct and well-differentiated
possessing sensory organs
12
• Vertebrates also have
• Neural crest – unique group of embryonic cells
that forms many vertebrate structures
• Internal organs – liver, kidneys, endocrine
glands, heart, and closed circulatory system
• Endoskeleton – made of cartilage or bone
– Makes possible great size and extraordinary
movement
13
14
• The first vertebrates appeared in the
oceans about 545 MYA
– Mouth at one end, fin at the other
• Jawed fishes soon became dominant
• Amphibians invaded the land
• Reptiles replaced them as the dominant
land vertebrates
• Birds and mammals became dominant
after Cretaceous mass extinction
15
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Myxini
(hagfish)
Cephalaspidomorphi
(lampreys)
Chondrichthyes
(cartilaginous fishes)
Actinopterygii
(ray-finned fishes)
Sarcopterygii
(lobe-finned fishes)
Amphibia
(amphibians)
Mammalia
(mammals)
Mammary glands,
4-chambered heart,
hair , synapsid skull
Testudines
(turtles)
Lepidosauria
(lizards, snakes,
tuataras)
Crocodilia
(crocodiles,
alligators)
Anapsid skull,
bony shell
Diapsid
skull
Aves
(birds)
Feathers
Skull with
two additional
openings
Amniotic egg
Rayed fins
Vertebral column
Jaws, two pairs
of appendages
Lobed fins
Legs with
multiple digits
Internal
bony skeleton
Head with 3 pairs of sense organs
Chordate ancestor
• Fish and reptiles are paraphyletic
16
Fishes
• Most diverse vertebrate group
• Over half of all vertebrates
• Provided the evolutionary base for invasion
of land by amphibians
17
• Fishes have the following characteristics
1. Vertebral column
•
Hagfish and lamprey exceptions
2. Jaws and paired appendages
•
Hagfish and lamprey exceptions
3. Internal gills
4. Single-loop blood circulation
5. Nutritional deficiencies
•
Inability has been inherited by all their vertebrate
descendants
18
19
History of the Fishes
• The first fishes had mouths with no jaws
– Agnatha extant as hagfish (class Myxini) and
lampreys (class Cephalaspidomorphi)
– Ostracoderms are now extinct
• The development of jaws occurred in the
late Silurian period
– Jaws evolved from the anterior gill arches that
were made of cartilage
20
History of the Fishes
21
• Armored fishes (placoderms) and spiny
fishes both had jaws
– Spiny fish were common during early
Devonian – replacing ostracoderms
• Cartilage skeleton but skin had small plates of bone
• Extinct at close of Permian
– Placoderms became common in late Devonian
• Jaw more improved than spiny fishes’
– Upper jaw fused to the skull and the skull hinged on the
shoulder
• Extinct by end of period
22
• At the end of the Devonian period,
essentially all of these pioneer vertebrates
disappeared, replaced by sharks and bony
fishes in one of several mass extinctions
• Sharks and bony fishes first evolved in the
early Devonian, 400 MYA
• Jaw was improved even further allowing
the mouth to open much wider than was
previously possible
23
Aves
Crocodilia
Lepidosauria
Testudines
Mammalia
Amphibia
Sarcopterygii
Actinopterygii
Chondrichtyes
Cephalaspidomorphi
Class
Chondrichthyes
Mixini
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• Sharks, skates, rays
• Became the dominant sea predators in the
Carboniferous period (360–280 MYA)
• Cartilage skeleton “calcified” with granules
of calcium carbonate
– Light, strong skeleton
24
• Sharks were among the first vertebrates to
develop teeth
– Evolved from rough scales on mouth’s skin
– Easily lost but continuously replaced
• Sharks (and bony fishes) have a fully developed
lateral line system
– Series of sensory organs under the skin that detects
changes in pressure waves
25
• Reproduction in sharks differs from that of
other fishes
– Eggs are fertilized internally
– Most pups are born alive
• A few species do lay fertilized eggs
• Sharks have long gestation periods and
relatively few offspring
– Therefore, are not able to recover quickly
from population declines
26
Aves
Crocodilia
Lepidosauria
Testudines
Mammalia
Amphibia
Sarcopterygii
Actinopterygii
Chondrichtyes
Cephalaspidomorphi
Bony fishes
Mixini
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• Evolved at the same time as sharks about
400 MYA
– However, they adopted a heavy internal
skeleton made completely of bone
• Bony fishes are the most species-rich
group of all vertebrates (> 30,000 living
species)
• Significant adaptations include swim
bladder and gill cover
27
• Swim bladder
– Gas-filled sac that allows bony fishes to
regulate their buoyant density
– In most modern fish, filled and drained with
gases internally
• Gill cover
– Hard plate, the operculum, covers gills
– Flexing plate permits water pumping over gills
– Efficient bellows system when stationary
28
• Gases are
taken from the
blood, and the
gas gland
secretes the
gases into the
swim bladder;
gas is released
from the
bladder by a
muscular
valve, the oval
body
29
Two Major Groups of Bony Fishes
• Ray-finned fishes (class Actinopterygii)
– Parallel bony rays support and stiffen each fin
– There are no muscles within the fins
• Lobe-finned fishes (class Sarcopterygii)
– Have paired fins that consist of a long fleshy
muscular lobe
– Supported by central core of bones with fully
articulated joints
– Almost certainly the amphibian ancestors
30
31
Class Amphibia
• First vertebrates to walk on land
• Direct descendants of fishes
32
• 5 distinguishing amphibian features
Legs – adaptation to life on land
Lungs
Cutaneous respiration – supplement lungs
Pulmonary veins – separate pulmonary
circuit allows higher pressure blood to
tissues
5. Partially divided heart – improves separation
of pulmonary and systemic circuits
1.
2.
3.
4.
33
• Successful invasion of land by vertebrates
required several adaptations
– Legs to support body’s weight
– Lungs to extract oxygen from air
– Redesigned heart and circulatory system to
drive larger muscles
– Reproduction still in water to prevent egg
drying
– System to prevent whole body desiccation
34
Ichthyostega
• Amphibians evolved from lobe-finned fish
• Ichthyostega was one of the first
amphibians
• Sturdy forelegs, flipper-shaped hindlimbs
– Moved like a seal
• Long, broad, overlapping ribs form solid
cage for lungs and heart
35
Tiktaalik
• In 2006, a transitional fossil was found
between fish and Ichthyostega
• Had gills and scales like a fish, but a neck
like an amphibian
• Shoulder, forearm, and wrist bones were
like those of amphibians, but at the end of
the limb was a lobed fin, rather than the
toes of an amphibian
36
37
3 Modern Amphibian groups
•
•
•
•
5,670 species in 37 different families
Order Anura (“without tail”)
Order Caudata (“visible tail”)
Order Apoda (“without legs”)
38
Order Anura (frogs and toads)
• Frogs have smooth, moist skin and long legs
– Most live in or near water, aquatic tadpole stage
before metamorphosis into adult
• Toads have bumpy, dry skin and short legs
– Most live in dry environments
– Not a monophyletic group
• Eggs laid in water – lack watertight membranes
– Eggs fertilized externally
– Tadpole – swimming larval form
– Gradual metamorphosis into adult form
39
• Order Caudata (salamanders)
– Have long bodies, tails, and smooth, moist
skin
– Live in moist places
– Eggs are fertilized internally – sperm packet
– Larvae similar to adults
• Order Apoda (caecilians)
– Tropical, burrowing amphibians
– Legless with small eyes and jaws with teeth
– Fertilization is internal
40
Aves
Crocodilia
Lepidosauria
Testudines
Mammalia
Amphibia
Sarcopterygii
Actinopterygii
Chondrichthyes
Cephalaspidomorphi
Class
Reptilia
Mixini
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• Over 7000 living species
• All living reptiles exhibit three key features
1. Amniotic eggs, which are watertight
2. Dry skin, which covers body and prevents
water loss
3. Thoracic breathing, which increases lung
capacity
41
• Reptiles, birds, and mammals are
amniotes
• The amniotic egg has four membranes
– Chorion
• Outermost layer, allows gas exchange
– Amnion
• Encases embryo in fluid-filled cavity
– Yolk sac
• Provides food
– Allantois
• Contains excreted wastes from embryo
42
43
• Reptiles dominated earth for 250 million
years
• Reptiles are distinguished by the number
of holes on side of the skull behind eye
orbit
– 0 (anapsids), 1 (synapsids), 2 (diapsids)
44
• The synapsids rose to
dominance first
• Pelycosaurs
– First land vertebrates to kill
beasts their own size
• Therapsids
– Replaced them about 250
MYA
– May have been endotherms
– “Mammal-like reptile
– Most became extinct 170 MYA
– One group survived and has
living descendants today – the
mammals
45
History of Reptiles
A number of different diapsids occurred in
the Triassic period (248–213 MYA)
46
• Therapsids were replaced
by diapsids about 230 MYA
• Archosaurs were the first
land vertebrates to be
bipedal
– Gave to rise crocodiles,
pterosaurs, dinosaurs, and
birds
• Dinosaurs dominated for
over 150 million years
– Became extinct 65 MYA
• Except bird descendents
– Asteroid’s impact
47
• Modern reptiles developed two important
characteristics
– Internal fertilization
• Sperm fertilizes egg before protective membranes
are formed
– Improved circulation
• Oxygen is provided to the body more efficiently
• Septum in heart extended to create partial wall
– Crocodiles, birds, and mammals have completely divided
4-chambered heart
48
49
• All living reptiles are ectothermic
– Obtain heat from external sources
– Regulate body temperature by moving in and
out of sunlight
– Compare to endothermic animals that
generate their own heat internally
50
• There are four surviving orders of reptiles
– Chelonia (turtles and tortoises)
– Rhynchocephalia (tuataras)
– Squamata (lizards and snakes)
– Crocodylia (crocodiles and alligators)
• About 7000 species
• Reptiles occur worldwide except in the
coldest regions, where it is impossible for
ectotherms to survive
51
Order Chelonia
• Differ from all other reptiles because their bodies
are encased within a protective shell
– Carapace (dorsal) and plastron (ventral)
• Tortoises are terrestrial while turtles are mostly
aquatic
• Both lack teeth but have sharp beaks
• Marine turtles must return to land to lay eggs
52
Order
Rhynchocephalia
• Contains only two species of tuataras
• Large, lizardlike animals about half a
meter long
• Only found on islands near New Zealand
• Parietal eye
– Eye with lens and retina concealed under
layer of scales on top of head
53
Order Squamata
• A characteristic of this order is
the presence of paired
copulatory organs in the male
• Snakes – 3000 species
– Lack limbs, movable eyelids,
and external ears
• Lizards – 3800 species
– Many have ability to regenerate
lost tails
54
Order Crocodylia
• 25 species of large, primarily aquatic
carnivorous reptiles
• Crocodiles
– Typically nocturnal
– Tropical and subtropical regions
• Alligators – only 2 species
• Bodies well adapted to stealth hunting
– Eyes on top of head, nostrils on top of snout,
enormous mouth, strong necks
55
• Crocodiles resemble birds far more than
they do other living reptiles
– Build nests and care for their young
– Have a 4-chambered heart
56
Class Aves
• Birds are the most diverse of all terrestrial
vertebrates
– 28 orders, 166 families, about 8600 species
• Success lies in unique structure – feather
Aves
Crocodilia
Lepidosauria
Testudines
Mammalia
Amphibia
Sarcopterygii
Actinopterygii
Chondrichthyes
Cephalaspidomorphi
Mixini
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57
• Birds still retain many reptilian traits
– Amniotic eggs and scales on legs
– Lack teeth and tails of reptiles
• Two major distinguishing traits
– Feathers
• Modified scales of keratin
• Provide lift for flight and conserve heat
– Flight skeleton
• Bones are thin and hollow
• Many are fused for rigidity – anchor strong flight
muscles
58
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Hooks
Barb
Barbule
Shaft
Quill
• Feathers developed from reptile scales
• Linked structures provide continuous
surface and a sturdy but flexible shape
59
• Archaeopteryx is the first known bird
– Had skull with teeth, long reptilian tail
– Feathers on wings and tail
– Forelimbs nearly identical to those of
theropods
• Feather probably evolved for insulation
60
• Most paleontologists agree that birds are the
direct descendants of theropod dinosaurs
61
• Confuciornis
– A few million years later, diversity
of birds
– Toothed birds with the hollow
bones and breastbones necessary
for sustained flight
• Birds exhibit three
evolutionary novelties
1. Feathers
2. Hollow bones
3. Physiological mechanisms for
flight
62
Modern Birds
• 28 orders of birds
– Most ancient birds are flightless – like ostrich
– Ducks, geese, and waterfowl next
– Passeriformes comprise 60% of species today
63
• Adaptations for flight
1. Efficient respiration
• Air passes all the way through lungs in a
single direction
2. Efficient circulation
• 4-chambered heart so muscles receive fully
oxygenated blood
• Rapid heartbeat
3. Endothermy
• Body temperature (40–42oC) permits
higher metabolic rate
64
Class Mammalia
• There are about 4500 species of mammals
– Lowest number among 5 vertebrate classes
– 3200 species are rodents, bats, shrews, or moles
Aves
Crocodilia
Lepidosauria
Testudines
Mammalia
Amphibia
Sarcopterygii
Actinopterygii
Chondrichthyes
Cephalaspidomorphi
Mixini
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65
• 2 fundamentally mammalian traits
1. Hair
• Long, keratin-rich filaments that extend from hair
follicles
• Insulation, camouflage, sensory structure
2. Mammary glands
• Females possess mammary glands that secrete
milk
66
• Other notable features of mammals
– Endothermy depends on higher metabolic
rate
• 4-chambered heart
• Respiration using diaphragm
– Placenta in most mammals
• Specialized organ that brings fetal and maternal
blood into close contact
67
68
• The mammalian lineage also gave rise to
several adaptations in some groups
1.Specialized teeth
– Different types of teeth are highly specialized
to match particular eating habits
– Contrast carnivore teeth to herbivore teeth
69
70
2. Digestion of plants
– Herbivorous mammals rely on mutualistic
partnerships with bacteria for cellulose
breakdown
3. Development of hooves and horns
– Hooves are specialized keratin pads
– Horns are bone surrounded by keratin
– Antlers are made of bone, not keratin
71
4. Flying mammals: Bats
– Only mammals capable of powered flight
– Wing is a leathery membrane of skin and
muscle stretched over 4 finger bones
– Navigate in the dark by echolocation
72
History of Mammals
• Mammals have been around since the
time of the dinosaurs, about 220 MYA
– Tiny, shrewlike, insect-eating, tree-dwelling
creatures
– May have been nocturnal – large eye sockets
• Mammals reached their maximum
diversity in the Tertiary period (65–2 MYA)
– After mass extinction of dinosaurs
– Decline in the total number of mammalian
species over last 15 million years
73
2 Subclasses of Mammals
1. Prototheria (most primitive)
– Lay shelled eggs
– Only living group is the monotremes
2. Theria
– Viviparous – young are born alive
– Two living groups
• Marsupials or pouched mammals
• Placental mammals
74
Monotremes
• Lay shelled eggs
• Like reptiles have single
opening (cloaca) for feces,
urine, and reproduction
• Lack well developed
nipples
• Only three living species
– Duck-billed platypus
– 2 echidna species
75
Marsupials
• Major difference is pattern of
embryonic development
– Short-lived placenta
– After birth, it crawls into marsupial
pouch, latches onto nipple, and
continues to develop
• Kangaroo – isolation of Australia
• Opossum – only North American
marsupial
76
Placental Mammals
• Produce a true placenta that
nourishes embryo throughout
its development
– Forms from both fetal and
maternal tissue
– Young undergo a considerable
period of development before
they are born
• Includes most living mammals
77
Evolution of Primates
• Primates are the mammals that gave rise
to our own species
• Evolved two features that allowed them to
succeed in an arboreal environment
1. Grasping fingers and toes
• First digit (thumb) is opposable in many
2. Binocular vision
• Eyes are shifted toward the front of the face
• Lets brain judge distances precisely
78
• About 40 MYA, the
earliest primates split into
two groups
1.Prosimians
– Only a few survive today
– Lemurs, lorises and
tarsiers
– Large eyes with increased
visual acuity
– Most are nocturnal
2.Anthropoids
79
• Anthropoids
– Include monkeys, apes, and humans
– Almost all diurnal
• Changes in eye design include color vision
– Expanded brain
– Live in groups with complex social
interactions
• Care for young for extended period
• Long period of learning and brain development
80
• 30 MYA
– New World monkeys migrated to South
America
• All arboreal; many have prehensile tail
– Old World monkeys and hominids remained in
Africa
• No prehensile tails
81
• Hominoids include
– Apes
• Gibbon, orangutan, gorilla, and chimpanzee
• Larger brains than monkeys and lack tails
• Paraphyletic group – some more closely related to
hominids
– Hominids
• Humans
• Soon after the gorilla lineage diverged, the
common ancestor of all hominids split off from the
chimpanzee line to begin the evolutionary journey
leading to humans
82
83
Apes vs. Hominids
• The common ancestor of apes and
hominids is thought to have been an
arboreal climber
– Hominids became bipedal, walking upright
– Apes evolved knuckle-walking
• Differences related to bipedal locomotion
– Human vertebral column is more curved
– Spinal cord exits from bottom of skull
– Humans carry much of the body’s weight on
the lower limbs
84
Early Hominids
• Genus Homo
– 3–7 species (depending)
• Genus Australopithecus
– 7 species
– Older and smaller-brained
• Several even older lineages
• In every case where the fossils allow a
determination, the hominids are bipedal,
the hallmark of hominid evolution
85
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Australopithecus
afarensis
Australopithecus
robustus
Homo habilis
Homo floresiensis
Homo sapiens sapiens
Homo sapiens
sapiens
Homo neanderthalensis
Homo heidelbergensis
Homo floresiensis
Homo erectus
Homo ergaster
Homo habilis
Australopithecus africanus
Australopithecus afarensis
Australopithecus anamensis
Australopithecus boisei
Ardipithecus ramidus
Australopithecus robustus
Sahelanthropus tchadensis
7.5
7
6.5
6
5.5
5
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
Millions of Years Ago (MYA)
86
Australopithecines
• Our knowledge is based on hundreds of
fossils found in Africa
• Characteristics
– Weighed about 18 kg
– About 1 m tall
– Hominid dentition
– Brains no larger than those of apes
– Walked upright
87
Bipedalism
• Seems to have evolved as
australopithecines left forests for
grasslands and open woodland
• African fossils demonstrate that
bipedalism extended back 4 MYA
• Substantial brain expansion, on the other
hand, did not appear until about 2 MYA
• Why bipedalism evolved is still a matter of
controversy
88
Genus Homo
• The first humans evolved from
australopithecine ancestors about 2 MYA
• Thought to be Australopithecus afarensis
• In the 1960s, hominid bones were found
near stone tools in Africa
– Early human was called Homo habilis
– It closely resembled Australopithecus, but had
larger brain
89
Homo floresiensis
• In 2004, a new human species was
discovered in the tiny Indonesian Island of
Flores
• Youngest fossils only 15,000 years old!
• H. floresiensis had a diminutive stature
• Coexisted with and preyed on a miniature
species of elephant (now extinct)
• Believed to be more closely-related to H.
erectus than to H. sapiens
90
• Small size may be an example of “island
dwarfism”
91
Modern Humans
• Modern humans first appeared in Africa
about 600,000 years ago
• Three species are thought to have evolved
– Homo heidelbergensis (oldest)
• Coexisted with H. erectus
– Homo neanderthalensis
• Shorter and stockier than modern humans
– Homo sapiens (“wise man”)
• Some lump all 3 into H. sapiens
92
• Neanderthals, Homo neanderthalensis
–
–
–
–
Made diverse tools
Took care of sick and buried dead
First evidence of symbolic thinking
They abruptly disappeared about 34,000 years ago
• Suddenly replaced by Cro-Magnons
–
–
–
–
2 species did not interbreed
Complex social organization
Elaborate cave paintings
Thought to have had full language capabilities
93
94
Homo sapiens
• Only surviving hominid
• Progressive increase in brain size
– Effective making and use of tools
– Refined and extended conceptual thought
– Use of symbolic language
• Extensive cultural experience
– We change and mold our world rather than
change evolutionarily in response to the
environment
95
Human Races
• Human beings differentiated in their traits
as they have spread throughout the world
• All humans are capable of mating with one
another and producing fertile offspring
• Humans are visually oriented;
consequently, we have relied on visual
cues – primarily skin color – to define
races
• Constant gene flow has prevented
96
subspecies of humans from forming
• Groupings based on overall genetic
similarity are different from those based on
skin color or other visual features
97