Download chapter 34 the vertebrates

CHAPTER 34
THE
VERTEBRATES
Prepared by
Brenda Leady, University of Toledo
Copyright (c) The McGraw-Hill
Companies, Inc. Permission required
for reproduction or display.
1
Phylum Chordata
Subphylum Urochordata – tunicates
 Subphylum Cephalochordata – lancelets
 Subphylum Vertebrata – vertebrates

 48,000
species
 Range in size from tiny fish to huge whales
 Occupy all of Earth’s biomes
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Craniates

1.
2.

2 defining characteristics compared to
nonvertebrate chordates
Cranium - protective bony or
cartilaginous housing
Neural crest - embryonic cells that will
disperse throughout the embryo
contributing to the development of the
skeleton, nerves, jaws, and teeth
Also, at least 2 Hox clusters
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4
Class Myxini




Hagfish
Jawless, finless,
marine fish that lack
vertebrae
Essentially blind with
a keen sense of smell
Copious amounts of
slime
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Vertebrates

1.
2.
3.
All chordate and craniate characteristics plus
Vertebral column - notochord is replaced by a
bony or cartilaginous column of interlocking
vertebrae
Endoskeleton of cartilage or bone – most also
have two pairs of appendages
Internal organs - liver, kidneys, endocrine
glands, and a heart with at least two chambers


Liver unique to vertebrates
Heart, kidneys, and endocrine system are more
complex than analogous structures in other taxa
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The fish
Key innovation in vertebrate evolution is
hinged jaw
 Developed first in fish
 Agnathans – jawless
 Gnathostomes – jawed with 2 additional
Hox clusters

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Class Cephalaspidomorphi






Lampreys
Mack hinged jaw and true appendages
Do possess a notochord and rudimentary
vertebral column
One of the most primitive groups of vertebrates
Found in marine and freshwater
Marine lampreys parasitic as adults
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

Hinged jaws developed from the pharnygeal
arches
Descent with modification
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Class Chondricthyes
Cartilaginous fish
 Sharks, skates, rays
 Skelton composed of flexible cartilage

 Derived

not ancestral character
Sharks among earliest fish to develop
teeth
 Not
set into jaw
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Denser than water – swim to maintain
buoyancy and breathing
 2 chambered heart – single circulation
 Powerful sense of smell
 Lateral line – pressure wave detection
 Internal fertilization

– lay eggs
 Ovoviparous – egg retained in female, no
placenta
 Viviparous – eggs develop in uterus, placenta
nourishes young
 Oviparous
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Bony fish

3 living classes
Actinopterygii – ray-finned fish
 Actinistia – coelacanths
 Dipnoi – lungfish


3 features different from Chondricthyes
Bony skeleton
2. Operculum covers gills
3. Swim bladder for buoyancy
1.
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
Actinopterygii – ray-finned fish
 Includes
all bony fish but coelocanths and
lungfish
 Fins supported by thin, bony, flexible rays
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
Actinistia – coelacanths
 Believed
extinct until 1938
 Special joint in skull gives powerful bite
 Instead of vertebral column has hollow
notochord filled with oil-like fluid
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
Dipnoi – lungfish
3
genera with 6 species
 Live in oxygen-poor freshwater
 Both gills and lungs
 Will drown if unable to breathe air
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Tetrapods
Transition to land meant adaptations to
prevent desiccation and locomotion and
reproduction on land possible
 Sturdy lobe-finned fishes became fishes
with four limbs
 Vertebral column strengthened, hip and
shoulder bones braced against backbone
 Relatively simple changes in gene
expression, especially Hox genes

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




Transitional taxa
Acanthostega –
retained adaptations
for aquatic life – stem
species
Species increasingly
fed on land but tied to
water for reproduction
Vertebral column and
hip and shoulder
bones grew even
sturdier
Evolution of rib cage
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Davis, Capecchi, and Colleagues Showed a
Genetic-Developmental Explanation for Limb Length
in Tetrapods
Specific Hox genes are responsible for
determining limb formation in mice
 Mutations in the genes HoxA-11 and HoxD11 resulted in the loss of the radius, ulna,
and some of the carpals
 Relatively simple mutations can control
relatively large changes in limb
development

Amphibians
Successfully invaded land but must return
to water to reproduce
 Buccal pumping to force air into lungs
 Skin can absorb oxygen
 3 chambered heart
 Fertilization external
 Larval stages aquatic
 Metamorphosis regulated by thyroid
hormones

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
Order Anura – frog and toads
 Nearly
90% of amphibians
 Carnivorous adults, herbivorous larva

Order Caudata – salamanders
 Paedomorphosis
– adult has larval
characteristics

Order Gymnophiona – caecilians
 Legless,
nearly blind tropical
 Secondarily legless
 Uterine milk nourishes young inside mother’s
body
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Amniotes
Critical innovation was the development of
a shelled egg that sheltered the embryo
from desiccating conditions on land
 Amniotic egg broke tie to water

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
1.
2.
3.
4.
4 extraembryonic
membranes
Amnion – protects
embryo in
amniotic cavity
Yolk sac – yolk
Allantois –
disposal of wastes
Chorion – with
allantois for gas
exchange
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
Other key innovations
 Desiccation
resistant skin
 Thoracic breathing – negative pressure sucks
air in
 Water-conserving kidneys – concentrate
waste prior to elimination
 Internal fertilization
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Reptiles
Classification under revision
 One class or four?
 Class Testudines
 Class Lepidosauria
 Class Crocodilia
 Class Aves

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Class Testudines





Turtles, tortoises and
terrapins
Virtually unchanged
for 200 million years
Hard protective shell
In most, vertebrae
and ribs fused to shell
Lack teeth but have
sharp beak
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Class Lepidosauria



Lizards and snakes
Kinetic skull with
extremely mobile
joints
Lizards have
moveable eyelids and
external ears while
snakes do not
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Class Crocodilia





Crocodiles and alligators
Essentially unchanged for 200 million years
4 chambered heart
Teeth in sockets
Care for young
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Dinosaurs



Class Ornithischia – bird-hipped dinosaurs
Class Saurischia – lizard-hipped dinosaurs
Legs of dinosaurs were positioned directly under
the body
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The Differentiation of Scales, Feathers, and
Fur May Be Caused by Simple Changes in
Developmental Pathways
Epithelial appendages (scales, feathers, hair,
fur) look different but share similarities in
initial development
 All originate as epithelial placodes
 Timing and expression of regulatory
molecules determines the appendage that
develops in the dermal layer


Archaeopteryx lithographica
 Except


for feathers very similar to dinosaurs
Caudipteryx zoui
Confuciusornis sanctus
 Completely
feathered, lacking bony tail and toothed jaw
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Class Aves

1.
2.
4 features unique to birds (for flight)
Feathers- modified scales keep birds
warm and enable flight
Lightweight skeleton – thin, hollow,
honeycombed

3.
4.
Sternum to anchor flight muscles, no teeth
Air sacs – very efficient breathing
Reduction of organs – single ovary, no
urinary bladder
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Double circulation with 4 chambered heart
 Acute vision
 Most carnivores
 Eggs brooded
 Complex courtship
 28 orders, 9600 species

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Mammals
Evolved from amniote ancestors earlier
than birds
 Appeared about 220 mya
 After dinosaur extinction mammals
flourished
 Range of sizes and body forms
unmatched

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
Distinguishing characters
 Mammary
glands secrete milk
 All mammals have (more or less) hair
 Only vertebrates with specialized teeth
 Skull
Single lower jaw bone
 3 inner ear bones
 Pinnae, external ears
 Brain enlarged in large skull

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
Some but not all mammals
 Digest
plants using symbiotic bacteria
 Horns and antlers
Horns – bony outgrowth of skull
 Antlers – entirely of bone

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
Subclass Prototheria – Order
Monotremata
 Platypus
and echidna lay eggs, lack placenta,
poorly developed nipples

Subclass Metatheria – marsupials
7
orders
 Once widespread, now confined mostly to
Australia
 Opossum found in North America
 Very undeveloped young must make it to
marsupium to finish development
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
Subclass Eutheria
 Placental
mammals
 Prolonged gestation
 Placenta provides nourishment
 18 orders
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Primates
Primarily tree-dwelling species
 Evolved about 85 mya
 Defining characteristics

 Grasping
hands with opposable thumbs
 Large brain
 Some digits have flat nails (not claws)
 Binocular vision
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
Prosimians
 Bush
babies, lemurs, pottos, tarsiers
 Generally nocturnal and smaller-brained

Anthropoids
 Monkeys

Tails, monkeys cannot swing from branch to
branch
– gibbons, gorillas, orangutans,
chimpanzees and humans
 Hominoids
No tails, can swing branch to branch
 Family Hylobatidae – lesser apes or gibbons
 Family Hominidae – greater apes

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Humans
Related to chimpanzees and apes but not
descended from them
 All hominoids shared a common ancestor
 6 mya lineage leading to humans
separated from other primates
 1 or 2 hominid species coexisting at one
time

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Bipedalism resulted in many changes –
spine sits underneath skull, broader pelvis,
lower limbs larger
 Australopithecines – widespread, at least
6 species, relatively small, facial structure
and brain size similar to chimp
 Homo – increased brain size, stone tools

 Homo
sapiens 3,000 years ago
 Taller, lighter-weight, slightly smaller brain
capacity than H. neanderthalensis
 Out of Africa hypothesis supported over
multiregional hypothesis
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