The Origin and Evolution of Vertebrates

1
Chapter 34
The Origin and Evolution of Vertebrates
2
Overview Half a Billion Years of Backbones

• Early in the Cambrian period, about 530 million
  years ago, an astonishing variety of invertebrate
  animals inhabited Earths oceans
• One type of animal gave rise to vertebrates, one
  of the most successful groups of animals
• The animals called vertebrates get their name
  from vertebrae, the series of bones that make up
  the backbone

3

• One lineage of vertebrates colonized land 365
  million years ago
• There are about 52,000 species of vertebrates,
  including the largest organisms ever to live on
  the Earth
• Vertebrates have great disparity, a wide range of
  differences within the group

4
Concept 34.1 Chordates have a notochord and a
dorsal, hollow nerve cord

• Chordates (phylum Chordata) are bilaterian
  animals that belong to the clade of animals known
  as Deuterostomia
• Chordates comprise all vertebrates and two groups
  of invertebrates, the urochordates and
  cephalochordates

5
Figure 34.2
Echinodermata
Cephalochordata
ANCESTRALDEUTEROSTOME
Chordates
Urochordata
Notochord
Myxini
Commonancestor ofchordates
Craniates
Petromyzontida
Head
Vertebrates
Chondrichthyes
Vertebral column
Actinopterygii
Gnathostomes
Jaws, mineralized skeleton
Actinistia
Osteichthyans
Lungs or lung derivatives
Lobe-fins
Dipnoi
Lobed fins
Amphibia
Tetrapods
Reptilia
Limbs with digits
Amniotes
Amniotic egg
Mammalia
Milk
6
Derived Characters of Chordates

• All chordates share a set of derived characters
• Some species have some of these traits only
  during embryonic development
• Four key characters of chordates
• Notochord
• Dorsal, hollow nerve cord
• Pharyngeal slits or clefts
• Muscular, post-anal tail

7
Figure 34.3
Dorsal,hollownerve cord
Musclesegments
Notochord
Mouth
Anus
Pharyngealslits or clefts
Muscular,post-anal tail
8
Notochord

• The notochord is a longitudinal, flexible rod
  between the digestive tube and nerve cord
• It provides skeletal support throughout most of
  the length of a chordate
• In most vertebrates, a more complex, jointed
  skeleton develops, and the adult retains only
  remnants of the embryonic notochord

9
Dorsal, Hollow Nerve Cord

• The nerve cord of a chordate embryo develops from
  a plate of ectoderm that rolls into a tube dorsal
  to the notochord
• The nerve cord develops into the central nervous
  system the brain and the spinal cord

10
Pharyngeal Slits or Clefts

• In most chordates, grooves in the pharynx called
  pharyngeal clefts develop into slits that open to
  the outside of the body
• Functions of pharyngeal slits
• Suspension-feeding structures in many
  invertebrate chordates
• Gas exchange in vertebrates (except vertebrates
  with limbs, the tetrapods)
• Develop into parts of the ear, head, and neck in
  tetrapods

11
Muscular, Post-Anal Tail

• Chordates have a tail posterior to the anus
• In many species, the tail is greatly reduced
  during embryonic development
• The tail contains skeletal elements and muscles
• It provides propelling force in many aquatic
  species

12
Lancelets

• Lancelets (Cephalochordata) are named for their
  bladelike shape
• They are marine suspension feeders that retain
  characteristics of the chordate body plan as
  adults

13
Figure 34.UN01
Cephalochordata
Urochordata
Myxini
Petromyzontida
Chondrichthyes
Actinopterygii
Actinistia
Dipnoi
Amphibia
Reptilia
Mammalia
14
Figure 34.4
Cirri
Mouth
Pharyngeal slits
Atrium
Digestive tract
Notochord
Atriopore
1 cm
Dorsal,hollownerve cord
Segmentalmuscles
Anus
Tail
15
Tunicates

• Tunicates (Urochordata) are more closely related
  to other chordates than are lancelets
• Tunicates most resemble chordates during their
  larval stage, which may last only a few minutes
• As an adult, a tunicate draws in water through an
  incurrent siphon, filtering food particles
• When attacked, tunicates, or sea squirts, shoot
  water through their excurrent siphon

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Figure 34.UN02
Cephalochordata
Urochordata
Myxini
Petromyzontida
Chondrichthyes
Actinopterygii
Actinistia
Dipnoi
Amphibia
Reptilia
Mammalia
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Figure 34.5
Incurrentsiphonto mouth
Water flow
Notochord
Dorsal, hollownerve cord
Excurrentsiphon
Tail
Excurrentsiphon
Excurrent siphon
Atrium
Incurrentsiphon
Musclesegments
Pharynxwithnumerousslits
Intestine
Anus
Stomach
Intestine
Tunic
Atrium
Esophagus
Stomach
Pharynx with slits
(a) Tunicate larva
(b) Adult tunicate
(c) Adult tunicate
18
Concept 34.2 Craniates are chordates that have a
head

• The origin of a head enabled chordates to
  coordinate more complex movement and feeding
  behaviors
• Craniates share some characteristics a skull,
  brain, eyes, and other sensory organs

19
Derived Characters of Craniates

• Craniates have two clusters of Hox genes
  lancelets and tunicates have only one cluster
• One feature unique to craniates is the neural
  crest, a collection of cells near the dorsal
  margins of the closing neural tube in an embryo
• Neural crest cells give rise to a variety of
  structures, including some of the bones and
  cartilage of the skull

20
Figure 34.7
21

• In aquatic craniates the pharyngeal clefts
  evolved into gill slits
• Craniates have a higher metabolism and are more
  muscular than tunicates and lancelets
• Craniates have a heart with at least two
  chambers, red blood cells with hemoglobin, and
  kidneys

22
Hagfishes

• The most basal group of craniates is Myxini, the
  hagfishes
• Hagfishes have a cartilaginous skull and axial
  rod of cartilage derived from the notochord, but
  lack jaws and vertebrae
• They have a small brain, eyes, ears, and
  tooth-like formations
• Hagfishes are marine most are bottom-dwelling
  scavengers

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Figure 34.UN03
Cephalochordata
Urochordata
Myxini
Petromyzontida
Chondrichthyes
Actinopterygii
Actinistia
Dipnoi
Amphibia
Reptilia
Mammalia
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Figure 34.9
Slime glands
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Concept 34.3 Vertebrates are craniates that have
a backbone

• During the Cambrian period, a lineage of
  craniates evolved into vertebrates
• Vertebrates became more efficient at capturing
  food and avoiding being eaten

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Lampreys

• Lampreys (Petromyzontida) represent the oldest
  living lineage of vertebrates
• They are jawless vertebrates that feed by
  clamping their mouth onto a live fish
• They inhabit various marine and freshwater
  habitats
• They have cartilaginous segments surrounding the
  notochord and arching partly over the nerve cord

27
Figure 34.UN04
Cephalochordata
Urochordata
Myxini
Petromyzontida
Chondrichthyes
Actinopterygii
Actinistia
Dipnoi
Amphibia
Reptilia
Mammalia
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Figure 34.10
29
Concept 34.4 Gnathostomes are vertebrates that
have jaws

• Today, jawed vertebrates, or gnathostomes,
  outnumber jawless vertebrates
• Gnathostomes include sharks and their relatives,
  ray-finned fishes, lobe-finned fishes,
  amphibians, reptiles (including birds), and
  mammals

30

• Other characters common to gnathostomes
• Genome duplication, including duplication of Hox
  genes
• An enlarged forebrain associated with enhanced
  smell and vision
• In aquatic gnathostomes, the lateral line system,
  which is sensitive to vibrations

31
Chondrichthyans (Sharks, Rays, and Their
Relatives)

• Chondrichthyans (Chondrichthyes) have a skeleton
  composed primarily of cartilage
• The largest and most diverse group of
  chondrichthyans includes the sharks, rays, and
  skates

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Figure 34.UN05
Cephalochordata
Urochordata
Myxini
Petromyzontida
Chondrichthyes
Actinopterygii
Actinistia
Dipnoi
Amphibia
Reptilia
Mammalia
33
Figure 34.15
Dorsal fins
Pectoralfins
Pelvic fins
(a) Blacktip reef shark (Carcharhinus
melanopterus)
(b) Southern stingray (Dasyatis americana)
(c) Spotted ratfish (Hydrolagus colliei)
34

• Shark eggs are fertilized internally but embryos
  can develop in different ways
• Oviparous Eggs hatch outside the mothers body
• Ovoviviparous The embryo develops within the
  uterus and is nourished by the egg yolk
• Viviparous The embryo develops within the uterus
  and is nourished through a yolk sac placenta from
  the mothers blood

35

• The reproductive tract, excretory system, and
  digestive tract empty into a common cloaca

36
Ray-Finned Fishes and Lobe-Fins

• The vast majority of vertebrates belong to a
  clade of gnathostomes called Osteichthyes
• Nearly all living osteichthyans have a bony
  endoskeleton
• Osteichthyans include the bony fish and tetrapods
• Aquatic osteichthyans are the vertebrates we
  informally call fishes

37
Figure 34.UN06
Cephalochordata
Urochordata
Myxini
Petromyzontida
Chondrichthyes
Actinopterygii
Actinistia
Dipnoi
Amphibia
Reptilia
Mammalia
38

• Most fishes breathe by drawing water over gills
  protected by an operculum
• Fishes control their buoyancy with an air sac
  known as a swim bladder
• Fishes have a lateral line system
• Most species are oviparous, but some have
  internal fertilization and birthing

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Figure 34.16
Swimbladder
Dorsal fin
Caudalfin
Spinal cord
Adipose fin
Brain
Nostril
Cutedge ofoperculum
Anal fin
Liver
Anus
Lateralline
Gonad
Gills
Stomach
Kidney
Pelvicfin
Intestine
Urinarybladder
Heart
40
Ray-Finned Fishes

• Actinopterygii, the ray-finned fishes, include
  nearly all the familiar aquatic osteichthyans
• Ray-finned fishes originated during the Silurian
  period (444 to 416 million years ago)
• The fins, supported mainly by long, flexible
  rays, are modified for maneuvering, defense, and
  other functions

41
Figure 34.17
Yellowfin tuna (Thunnus albacares)
Redlionfish(Pteroisvolitans)
Commonsea horse(Hippocampusramulosus)
Fine-spotted moray eel(Gymnothorax dovii)
42
Lobe-Fins

• The lobe-fins (Sarcopterygii) have muscular
  pelvic and pectoral fins
• Lobe-fins also originated in the Silurian period

43
Figure 34.18
5 cm
Lowerjaw
Scalycovering
Dorsal spine
44

• Three lineages survive and include coelacanths,
  lungfishes, and tetrapods
• Coelacanths were thought to have become extinct
  75 million years ago, but a living coelacanth was
  caught off the coast of South Africa in 1938

45
Figure 34.19
46
Concept 34.5 Tetrapods are gnathostomes that
have limbs

• One of the most significant events in vertebrate
  history was when the fins of some lobe-fins
  evolved into the limbs and feet of tetrapods

47
Derived Characters of Tetrapods

• Tetrapods have some specific adaptations
• Four limbs, and feet with digits
• A neck, which allows separate movement of the
  head
• Fusion of the pelvic girdle to the backbone
• The absence of gills (except some aquatic
  species)
• Ears for detecting airborne sounds

48
The Origin of Tetrapods

• Tiktaalik, nicknamed a fishapod, shows both
  fish and tetrapod characteristics
• It had
• Fins, gills, lungs, and scales
• Ribs to breathe air and support its body
• A neck
• Fins with the bone pattern of a tetrapod limb

49
Figure 34.20
TetrapodCharacters
FishCharacters
ScalesFinsGills andlungs
NeckRibsFin skeletonFlat skullEyes on topof
skull
Shoulder bones
Ribs
Scales
Neck
Head
Eyes on top of skull
Humerus
Ulna
Flat skull
Wrist
Elbow
Radius
Fin
Fin skeleton
50
Figure 34.21
Lungfishes
Eusthenopteron
Panderichthys
Tiktaalik
Acanthostega
Tulerpeton
Limbswith digits
Amphibians
Key tolimb bones
Ulna
Radius
Amniotes
Humerus
Silurian
PALEOZOIC
Carboniferous
Permian
Devonian
415
400
385
370
355
340
325
310
295
280
265
0
Time (millions of years ago)
51
Amphibians

• Amphibians (class Amphibia) are represented by
  about 6,150 species
• Order Urodela includes salamanders, which have
  tails

52
Figure 34.UN07
Cephalochordata
Urochordata
Myxini
Petromyzontida
Chondrichthyes
Actinopterygii
Actinistia
Dipnoi
Amphibia
Reptilia
Mammalia
53
Figure 34.22
(a) Order Urodela (salamanders)
(b)
OrderAnura(frogs)
Order Apoda(caecilians)
(c)
54

• Amphibian means both ways of life, referring to
  the metamorphosis of an aquatic larva into a
  terrestrial adult
• Most amphibians have moist skin that complements
  the lungs in gas exchange

55
Figure 34.23
(a) Tadpole
(b) During metamorphosis
(c) Mating adults
56

• Fertilization is external in most species, and
  the eggs require a moist environment
• In some species, males or females care for the
  eggs on their back, in their mouth, or in their
  stomach

57
Concept 34.6 Amniotes are tetrapods that have a
terrestrially adapted egg

• Amniotes are a group of tetrapods whose living
  members are the reptiles, including birds, and
  mammals

58
Figure 34.25
Parareptiles
Turtles
Crocodilians
Reptiles
Pterosaurs
Archosaurs
Ornithischiandinosaurs
Dinosaurs
Saurischian dinosaursother than birds
Diapsids
Saurischians
Birds
Plesiosaurs
ANCESTRALAMNIOTE
Ichthyosaurs
Tuataras
Lepidosaurs
Squamates
Mammals
Synapsids
59
Derived Characters of Amniotes

• Amniotes are named for the major derived
  character of the clade, the amniotic egg, which
  contains membranes that protect the embryo
• The extraembryonic membranes are the amnion,
  chorion, yolk sac, and allantois

60
Figure 34.26
Extraembryonic membranes
Chorion
Allantois
Amnion
Yolk sac
Embryo
Amniotic cavitywith amnioticfluid
Yolk(nutrients)
Shell
Albumen
61

• The amniotic eggs of most reptiles and some
  mammals have a shell
• Amniotes have other terrestrial adaptations, such
  as relatively impermeable skin and the ability to
  use the rib cage to ventilate the lungs

62
Reptiles

• The reptile clade includes the tuataras, lizards,
  snakes, turtles, crocodilians, birds, and some
  extinct groups
• Reptiles have scales that create a waterproof
  barrier
• Most reptiles lay shelled eggs on land

63
Figure 34.UN08
Cephalochordata
Urochordata
Myxini
Petromyzontida
Chondrichthyes
Actinopterygii
Actinistia
Dipnoi
Amphibia
Reptilia
Mammalia
64

• Most reptiles are ectothermic, absorbing external
  heat as the main source of body heat
• Birds are endothermic, capable of keeping the
  body warm through metabolism

65
Figure 34.29
(e) American alligator (Alligator
mississippiensis)
66
Derived Characters of Birds

• Many characters of birds are adaptations that
  facilitate flight
• The major adaptation is wings with keratin
  feathers
• Other adaptations include lack of a urinary
  bladder, females with only one ovary, small
  gonads, and loss of teeth

67
Figure 34.30
Finger 1
(b) Bone structure
Palm
(a) Wing
Finger 2
Forearm
Finger 3
Wrist
Shaft
Shaft
Barb
Vane
Barbule
Hook
(c) Feather structure
68

• Flight enhances hunting and scavenging, escape
  from terrestrial predators, and migration
• Flight requires a great expenditure of energy,
  acute vision, and fine muscle control

69
The Origin of Birds

• Birds probably descended from small theropods, a
  group of carnivorous dinosaurs
• Early feathers might have evolved for insulation,
  camouflage, or courtship display

70
Concept 34.7 Mammals are amniotes that have hair
and produce milk

• Mammals, class Mammalia, are represented by more
  than 5,300 species

71
Figure 34.UN09
Cephalochordata
Urochordata
Myxini
Petromyzontida
Chondrichthyes
Actinopterygii
Actinistia
Dipnoi
Amphibia
Reptilia
Mammalia
72
Derived Characters of Mammals

• Mammals have
• Mammary glands, which produce milk
• Hair
• A high metabolic rate, due to endothermy
• A larger brain than other vertebrates of
  equivalent size
• Differentiated teeth

73

• By the early Cretaceous, the three living
  lineages of mammals emerged monotremes,
  marsupials, and eutherians
• Mammals did not undergo a significant adaptive
  radiation until after the Cretaceous

74
Monotremes

• Monotremes are a small group of egg-laying
  mammals consisting of echidnas and the platypus

75
Figure 34.38
76
Marsupials

• Marsupials include opossums, kangaroos, and
  koalas
• The embryo develops within a placenta in the
  mothers uterus
• A marsupial is born very early in its development
• It completes its embryonic development while
  nursing in a maternal pouch called a marsupium

77
Figure 34.39
(a) A young brushtail possum
(b) Long-nosed bandicoot
78

• In Australia, convergent evolution has resulted
  in a diversity of marsupials that resemble the
  eutherians in other parts of the world

79
Figure 34.40
Eutherianmammals
Marsupialmammals
Plantigale
Deer mouse
Mole
Marsupial mole
Flyingsquirrel
Sugar glider
Wombat
Woodchuck
Wolverine
Tasmanian devil
Patagonian cavy
Kangaroo
80
Eutherians (Placental Mammals)

• Compared with marsupials, eutherians have a more
  complex placenta
• Young eutherians complete their embryonic
  development within a uterus, joined to the mother
  by the placenta
• Molecular and morphological data give conflicting
  dates on the diversification of eutherians

81
Figure 34.41a
Monotremes(5 species)
Monotremata
Marsupialia
Marsupials(324 species)
ANCESTRALMAMMAL
ProboscideaSireniaTubulidentataHyracoideaAfros
oricidaMacroscelidea
Eutherians(5,010 species)
Xenarthra
RodentiaLagomorphaPrimatesDermopteraScandentia
CarnivoraCetartiodactylaPerissodactylaChiropter
aEulipotyphiaPholidota
82
Figure 34.41b
Orders and Examples
Main Characteristics
Orders and Examples
Main Characteristics
Lay eggs no nipplesyoung suck milk fromfur of
mother
Completes embryonicdevelopment in pouchon
mothers body
Monotremata
Marsupialia
Platypuses,echidnas
Kangaroos,opossums,koalas
Echidna
Koala
Proboscidea
Long, muscular trunkthick, loose skin
upperincisors elongatedas tusks
Tubulidentata
Teeth consisting ofmany thin tubescemented
togethereats ants and termites
Elephants
Aardvarks
Aardvark
African elephant
Sirenia
Aquatic finlike fore-limbs and no hindlimbs
herbivorous
Hyracoidea
Short legs stumpytail herbivorouscomplex,
multi-chambered stomach
Manatees,dugongs
Hyraxes
Manatee
Rock hyrax
Xenarthra
Reduced teeth or noteeth herbivorous(sloths)
or carnivorous(anteaters, armadillos)
Rodentia
Chisel-like, continuouslygrowing incisors
worndown by gnawingherbivorous
Sloths,anteaters,armadillos
Squirrels,beavers, rats,porcupines,mice
Tamandua
Red squirrel
Lagomorpha
Chisel-like incisorshind legs longer
thanforelegs and adaptedfor running and
jumpingherbivorous
Primates
Opposable thumbsforward-facing
eyeswell-developed cerebralcortex omnivorous
Lemurs, monkeys,chimpanzees,gorillas, humans
Rabbits, hares,picas
Golden liontamarin
Jackrabbit
Sharp, pointed canineteeth and molars
forshearing carnivorous
Carnivora
Perissodactyla
Hooves with an oddnumber of toes oneach foot
herbivorous
Dogs, wolves,bears, cats,weasels,
otters,seals, walruses
Horses, zebras,tapirs,rhinoceroses
Coyote
Indian rhinoceros
Chiroptera
Adapted for flightbroad skinfold thatextends
from elongatedfingers to body andlegs
carnivorous orherbivorous
Hooves with an evennumber of toes on eachfoot
herbivorous
Cetartiodactyla
ArtiodactylsSheep, pigs,cattle, deer,giraffes
Bats
Frog-eating bat
Bighorn sheep
Aquatic streamlined body paddle-like
fore-limbs and no hind limbs thick layer of
insulating blubbercarnivorous
Cetaceans
Eulipotyphla
Eat mainly insectsand other smallinvertebrates
Whales,dolphins,porpoises
Coreinsectivoressome moles,some shrews
Star-nosedmole
Pacific white-sided porpoise
83
Figure 34.45
(a) Gibbon
(b) Orangutan
(c) Gorilla
(d) Chimpanzees
(e) Bonobos
84
Concept 34.8 Humans are mammals that have a
large brain and bipedal locomotion

• The species Homo sapiens is about 200,000 years
  old, which is very young, considering that life
  has existed on Earth for at least 3.5 billion
  years

85
Derived Characters of Humans

• A number of characters distinguish humans from
  other apes
• Upright posture and bipedal locomotion
• Larger brains capable of language, symbolic
  thought, artistic expression, the manufacture and
  use of complex tools
• Reduced jawbones and jaw muscles
• Shorter digestive tract

86
Figure 34.UN10
Description
Clade
Basal chordates marine suspension feeders
thatexhibit four key derived characters of
chordates
Cephalochordata(lancelets)
Marine suspension feeders larvae display
thederived traits of chordates
Urochordata(tunicates)
Jawless marine organisms have head that
includesa skull and brain, eyes, and other
sensory organs
Myxini(hagfishes andrelatives)
Chordates notochord dorsal, hollownerve cord
pharyngeal slits post-anal tail
Craniates two sets of Hoxgenes, neural crest
Petromyzontida(lampreys)
Jawless vertebrates typically feed by attaching
to alive fish and ingesting its blood
Gnathostomes hinged jaws, four sets of Hox genes
Chondrichthyes(sharks, rays,skates, ratfishes)
Aquatic gnathostomes have cartilaginous
skeleton,a derived trait formed by the reduction
of anancestral mineralized skeleton
Vertebrates Dix genes duplication,backbone of
vertebrae
Aquatic gnathostomes have bony skeleton
andmaneuverable fins supported by rays
Actinopterygii(ray-finned fishes)
Actinistia(coelacanths)
Ancient lineage of aquatic lobe-fins still
survivingin Indian Ocean
Osteichthyans bony skeleton
Dipnoi(lungfishes)
Freshwater lobe-fins with both lungs and gills
sistergroup of tetrapods
Lobe-fins muscular fins or limbs
Amphibia(salamanders,frogs, caecilians)
Have four limbs descended from modified fins
mosthave moist skin that functions in gas
exchange manylive both in water (as larvae) and
on land (as adults)
Tetrapods four limbs, neck, fusedpelvic girdle
Amniotes amniotic egg, rib cage ventilation
Reptilia(tuataras, lizardsand snakes,
turtles,crocodilians, birds)
One of two groups of living amniotes have
amnioticeggs and rib cage ventilation, key
adaptations for lifeon land
Mammalia(monotremes,marsupials,eutherians)
Evolved from synapsid ancestors include
egg-layingmonotremes (echidnas, platypus)
pouched marsupials(such as kangaroos, opossums)
and eutherians(placental mammals, such as
rodents, primates)