1.
Vertebrates Evolution

2.
Phylum Chordata
• Vertebrates are a subphylum
of the phylum Chordata
• This lecture will build up to
vertebrates and mammals by
moving through the Chordata
Phylum, from the most
inclusive traits and simpliest
organisms to the to most
specific traits and complex
organisms

3.
Phylum
Chordata
• This phylum
includes
– All vertebrates
– Urochordata
(tunicates)
– Cephalochordata
(lancelets)
– Myxini (hagfish)

4.
Characteristics of Chordates
Many appear only during embryonic
development
1. Notochord - Chordates named for
this structure; a long flexible rod
that appears during embryonic
development (some adults retain
it)
• Provides skeletal support
• Most adults retain only a
remnant of this
• In humans it becomes the
gelatinous disks between our
vertebrae

5.
Characteristics of Chordates
Many appear only during embryonic
development
2. A dorsal, hollow nerve cord - forms
from a plate of ectoderm that rolls into a
hollow tube; develops into the central
nervous system

6.
Characteristics of Chordates
Many appear only during embryonic
development
3. Pharyngeal clefts -
grooves that
separate a series of
pouches along the
sides of the pharynx.
• Usually develop into slits that
allow water to enter and exit the
mouth without going through the
digestive tract
• Become gill slits in fish or
become part of the ear in
terrestrial animals

7.
Characteristics of Chordates
Many appear only during embryonic
development
4. A muscular tail posterior to the anus
Many adults lose this during embryonic
development

8.
Invertebrate Chordates
• 2 subphyla -
Urochordata
(tunicates) and
Cephalochordata
(lancelets)
• Think of these 2
groups as simpler
versions of
vertebrates
• Tunicates - most primitive; like
other chordates during larval
stage, lose chordate traits as
adults

9.
Craniates
• Chordates that have a
head
• Most ancient of these
are the hagfish
• Hagfish are marine,
bottom dwelling
scavengers
• No vertebrae
• Do have a skull made
of cartilage

10.
Vertebrates
• Craniates with a backbone
• Evolved during the Cambrian when
some Craniates developed
• more complex nervous systems
• more complex skeletons
• more extensive skull
• backbone composed of vertebrae that
encloses the spinal cord

11.
Vertebrates
• Lampreys are the oldest
line of vertebrates
• Marine or freshwater
• Cartilage pipe surrounds
the notochord
• No jaws - have a rasping
mouth that bores holes in
the sides of fish - live on
the blood of their host

12.
Gnathostomes
• Vertebrates with
jaws
– Evolved from the
pharyngeal slits
– 2 major classes:
• Class
Chondrichtyes
• Class
Osteichthyes

13.
Gnathostomes - Class
Chrondrichythyans
• Sharks, rays, and their relatives
• Flexible endoskeletons made of
cartilage
• Streamlined bodies
• Will sink if they stop swimming
because they are denser than
water
• Have changed little over 300
million years of evolution

14.
Shark Reproduction
• Eggs fertilized internally
• Some are oviparous - lay
eggs that hatch outside the
body
• Some are ovoviviparous -
fertilized eggs stay in body,
hatch in uterus
• Some are viviparous - baby
develops inside the uterus
and gets nutrients there
Horn shark
egg case

15.
Gnathostomes - Class
Osteichthyes
• The bony fishes
• Most numerous of all the
vertebrate groups
• 2 main classes
– The ray-finned fish
– The lobe fin fish
• Includes lungfish - freshwater, air
gulpers
• Have an ossified (bony)
endoskeleton
• Covered in scales
• Have a swim bladder - air sac
that controls buoyancy
Most fish ray finned

16.
Tetrapods -
Gnathostomes
with limbs & feet
• Evolution of limbs and
feet from fins ~ 360
mya
• Loss of gill slits
• Fusion of pelvic bones
to backbone
• All of these adaptations
lost or altered in
various groups of
tetrapods

17.
Tetrapods - Class Amphibia
• Includes salamanders, frogs, and caecilians
• Still closely tied to water
• Rely on skin for gas exchange with environment
• Not all have legs
• Some have an aquatic larval stage with a terrestrial adult
life
• Eggs do not have a shell
• External fertilization
• Complex social behavior

18.
Tetrapods -
Amniotes
• Tetrapods with a
terrestrial
adapted, amniotic
egg
• Consists of
mammals and
reptiles (including
birds)

19.
Tetrapods - Amniotes
• Evolution of the amniotic egg very important for life on land
– Shell retains water
– Now animals can live away from water
– Amniotic eggs have an extramembryonic membrane that functions in
gas exchange, waste disposal, and transport of nutrients to embryo

20.
Tetrapods - Reptiles
• Have scales that contain
keratin
– No longer breath through skin
like amphibians
• Get oxygen through lungs
• Lay eggs on land
• Internal fertilization
• Most are ectothermic -
control body temp with
behavior, not metabolism

21.
Tetrapods - Reptiles
• Extinct reptiles include:
– Dinosaurs (land dwelling)
– Pterosaurs (flying)
– Plesiosaurs (marine)
• Modern reptiles include:
– Turtles
– Tuataras
– Lizards
– Snakes
– Alligators
– Crocodiles
tuatara
brown basilisk
Giant Galapagos

22.
Tetrapods - Birds
• Lay amniotic eggs (like reptiles)
• Have keratin containing scales on
their legs (like reptiles)
• Endotherms - maintain a warm
internal body temp
• 4-chambered heart
• High metabolism
• Larger brains than reptiles

23.
Tetrapods - Birds
• Most have bodies
adapted for flights
– Light, hollow bones
– Relatively few organs
– Wings
– Feathers

24.
Amniotes -
Mammals
• Amniotes that have hair
and produce milk from
mammary glands
• Endothermic
• Most born, not hatched
• All have internal
fertilization
• Large brains
• Teeth

25.
Mammals
• 3 groups:
– Monotremes - egg laying, have
hair, produce milk, playpuses,
spiny anteaters
– Marsupials - give birth to embryo,
completes development in a pouch
while nursing, wombats,
kangaroos, Tasmanian devils
– Placental mammals (eutherians) -
longer pregnancy, deer, mice,
tigers, primates

26.
Mammals - primates
• All have
– hands & feet that grasp
– Large brains
– Short jaws
– Forward-looking eyes
– Flat nails
– Well-developed parental care
– Complex social behavior

27.
Mammals - primates
• 3 subgroups
– Lemurs, lorisese,
pottos
– Tarsiers
– Anthropoids
(monkeys, apes,
humans) lemurs
tarsier
ape

28.
Mammals - humans
• Increase brain volume
• Shorter jaw
• Less of a size difference between the
sexes
• Different family structures
Jane Goodall
Diane Fossey

29.
Quick Check
For each new clade,
list the primary feature
that separates it from
the clade before it.