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4/6/11
Chordata
•  Finally, a
phylum to call
our own.
•  Deuterostomes
•  Includes three
invertebrate
lineages
Chordata
•  Defined by
characters that each
appears at some
stage in a chordate’s
life, often
embryologically
Chordata
•  notochord longitudinal, flexible
rod that serves as
an internal skeleton,
or axis of support.
(replaced by bony
segments in adult
vertebrates)
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Chordata
•  dorsal hollow
neural tube located above
notochord, develops
as tube from
ectoderm
Chordata
•  pharyngeal gill
slits
–  posterior to mouth
(pharynx) pharyngeal
slits function in filter
feeding
–  modified for
respiration (gills) in
vertebrates
Chordata
•  post anal tail muscular, functions
in locomotion
(aquatic, marine)
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Chordata
•  Probably evolved from
larval form of
deuterostome that
evolved sexual
maturity and could
therefore reproduce
•  PAEDOMORPHOSIS
Invertebrate Chordates
•  Paraphyletic
•  Display some
plesiomorphic
(ancestral) traits
•  Display some
apomorphic
(uniquely derived)
traits
Cephalochordata: Lancelets
• 
• 
Diverged from rest of
Chordata ~520 mya
Simple, fusiform body
retaining all 4 basic chordate
characteristics
–  What are these?
• 
• 
• 
Small (1-2 cm) shallow
marine filter feeders, usually
buried tail-first in sand with
oral cavity protruding.
Chevron-shaped muscle
segments (myomeres) flex
notochord for locomotion.
Is this an ancestral Chordata?
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Urochordata: Tunicates
•  Also sea squirts &
sea pork (?)
•  Larva is freeswimming filter
feeder, possesses
all four basic
chordate characters
•  Life stage often as
short as a few
minutes
Urochordata: Tunicates
•  But adult undergoes
radical metamorphosis
•  Becomes sessile, loses
notochord, neural tube,
and tail
•  Pharynx is reduced
•  Outer, epidermal wall or
“tunic” surrounds the
adult
Myxini: Hagfishes
•  Last clade of
invertebrates
•  First group of
Chordata with a
head
•  Monophyletic group
Craniata
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Craniata
•  Craniata
–  Brain at anterior end of
dorsal nerve cord
–  Eyes and other sensory
organs concentrated
–  Skull as enclosure
•  Neural crest
–  Cells that appear near
dorsal margins of closing
neural tube
–  Migrate to become a
variety of structures:
•  teeth, much of skull, inner
layer of skin of facial
region, many neurons,
other important cells
–  Has been called the fourth
germ layer
Myxini: Hagfishes
•  Only extant animals which
have a skull and not a
vertebral column
•  World’s most disgusting
animal?
•  Enter both living and dead
fish (through openings),
feeding on the insides
•  Can exude copious
amounts of slime as
defensive mechanism
•  Will tie themselves in
knots for defense or
offense
Vertebrata: Animals with a backbone
•  Most successful
group of chordates
•  Originated 513-542
mya
•  First fossils part of
Cambrian Explosion
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Vertebrata
•  Evolutionary trend:
Notochord replaced by
bony segments:
vertebrae
•  Some lineages notochord
still prominent, vertebrae
just cartilaginous
projections
•  Others (e.g. us),
notochord only remnant
as part of intervertebral
discs
Vertebrata
•  BONE
•  Specialized tissue
unique to vertebrates,
forming an
endoskeleton
•  Can be cartilage (e.g.
lampreys), collagenbased cartilage (e.g.
sharks & rays), or hard
matrix of calcium
phosphate (e.g. us)
Vertebrata: Major Events
•  Jaws
•  Mineralized
skeleton
•  Radiation of fish
and paired
appendages
•  Tetrapod invasion
of land
•  Amniotic egg
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Agnathans: Jawless vertebrates
•  Include extinct
Ostracoderms
(oldest known
vertebrates)
•  Include extant
lampreys
(Petromyzontida)
Lampreys
•  Only extant jawless
vertebrates
•  Larvae filter feeders in
freshwater
•  Adults parasitic in freshwater
or marine (catadromous)
•  Skeleton is cartilage without
collagen
•  Notochord is prominent axial
skeleton, vertebrae are
cartilaginous pipe around
notochord.
Relationships of the hagfishes
•  Are jawless fishes
monophyletic?
•  What do these two
alternatives say
about the evolution
of the backbone?
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Relationships of the hagfishes
Heimberg, A.M. et al. 2010. microRNAs reveal the interrelationships of hagfish, lampreys, and
gnathostomes and the nature of the ancestral vertebrate. PNAS 107: 19379-19383.
GNATHOSTOMES: vertebrates with jaws
•  The vast majority
of Vertebrates
•  470 mya
•  Paired fins and tail
allowed effective
swimming
•  Jaws enhanced
predation
GNATHOSTOMES: vertebrates with jaws
•  Jaws evolved from
modifications of
pharyngeal bars
•  Mechanism to increase
efficiency of buccal pump
•  Move water through
pharynx
•  Secondarily, jaws gave
vertebrates the life of a
predator
•  Teeth from modified
dermal scales
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GNATHOSTOMES: vertebrates with jaws
•  Placodermi earliest jawed
fish
•  Dermal armor
pronounced; true paired
appendages (pectoral
and pelvic) in most
•  Typically 1 m or less;
some very large (10 m); all
predaceous
•  Most diverse in Devonian,
extinct by end of
Paleozoic
Modern Fish
•  Chondrichthyes
–  Sharks, skates, rays
•  Osteichthyes
–  Bony fish
–  Actinopterygii
•  Ray-finned fishes
–  Sarcopterygii
•  Lobe-finned fishes
and Tetrapods
Chondrichthyes
•  Sharks, skates, rays
(elasmobranchs); chimaera
(holocephalans)
•  Skeleton made of cartilage
•  Internal fertilization: males
possess claspers
(specialized structures of
pelvic fins)
–  Oviparous
–  Ovoviviparous
–  Viviparous
•  External gill slits open, not
covered
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Osteichthyes: Bony “fish”
•  Clade includes
Tetrapods!
•  Ray-finned fishes
make up most of
“fish” diversity
•  Lobe-finned fish
gave rise to
tetrapods
Osteichthyes: Bony “fish”
•  Ancestrally:
•  Operculum: bony flap
covering the gills
externally
•  Swim bladder:
modification of
pharyngeal pouch, gas
filled, regulates
buoyancy
•  Homologous with
lungs?
Actinopterygii: Ray-finned
fishes
•  Ray-finned fishes
make up most of
“fish” diversity
•  Most diverse group
of vertebrates
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Actinopterygii: Ray-finned
fishes
•  Pectoral and pelvic
fins: webs of skin
supported by bony
or horny spines
("rays")
•  Typical fish
Sarcopterygii: Lobe-finned
“fishes”
•  Includes Tetrapods
•  Two lineages of
truly aquatic forms
Sarcopterygii: Lobe-finned
“fishes”
•  Fin bases bony,
fleshy, robust,
surrounded by thick
layer of muscle
•  Not rayed.
Coelocanth
limb
Lungfish
Tetrapod
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Sarcopterygii: Lobe-finned
“fishes”
•  Aquatic forms never
particularly diverse,
two extant lineages:
–  Actinistians
(Coelocanth)
–  Dipnoians
(Lungfish)
Coelocanth
Lungfish
•  But gave rise to
tetrapods
Tetrapod
Tetrapods and the Transition to Land
•  The fleshy, robust pectoral
and pelvic fins preadapted the lobe-finned
fishes to moving in a
terrestrial environment.
•  Why is this a challenge?
•  Used lungs to breathe air
in low oxygen water.
•  Another pre-adaptation.
•  The transition to land did
not come out of nowhere.
Tetrapods and the Transition to Land
•  Tetrapods: Four feet
•  In place of pectoral fins,
have limbs that can support
weight on land
•  Have digits that allow
transmission of force to
ground when walking
•  First appear in midDevonian (~380 mya)
•  Transition to tetrapod is
gradual, no abrupt transition
(including in limbs)
Acanthostega: Limbs with digits BUT…
•  Limbs too weak to support weight on land
•  Tail with fin
•  Bones supporting gills
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Key Transformations in the Evolution
of Tetrapods
•  Well-developed girdles
(shoulder & pelvic) and
limbs
•  Adaptations for
respiration
–  Loss of operculum
–  Loss of internal gills
–  Increased branching
of lungs
•  Cranial-cervical joint
–  Head moves
independently of axial
skeleton
Key Transformations in the
Evolution of Tetrapods
•  Story of evolution of
tetrapods is, like
________________,
the story of
increased
terrestriality
•  Least terrestrial
extant Tetrapoda
are the Class
Amphibia
Amphibians
•  Amphibians
traditionally defined
as all Tetrapods
without amniotic egg
(later)
•  Extant members
monophyletic
•  Extinct members
paraphyletic
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Amphibians
•  Early amphibians
diverse small to
large (4m)
•  Generalized
tetrapods with low,
sprawling posture
•  Most extinct by end
of Paleozoic
Modern Amphibians: Lissamphibia
• 
• 
• 
Little resemblance to Paleozoic
forms
First appear in early Mesozoic
Generally terrestrial & aquatic
lifestyle
–  Smooth, mucus-covered skin
–  Various means of gas exchange
(gills, lungs, skin)
–  But some have adaptations that
permit complete terrestriality
–  Unshelled eggs dehydrate quickly in
dry air
–  Larval stage to brooding to viviparity
to direct development
Anura: Frogs & Toads
•  5420 species
•  Specialized morphology for
hopping
•  Adults are tailless
•  From 10 mm to 300 mm
•  Worldwide distribution
•  External fertilization
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Urodela: Salamanders & Newts
•  ~550 species, northern
hemisphere & northern
South America
•  Generalized tetrapod
morphology
•  2.7 cm to 1.8 m
•  Paedomorphosis common
•  External fertilization
Apoda: Caecilians
•  Secondarily limbless
•  Highly adapted to
burrowing
–  Strong skull, pointed
snout
–  Unique muscular
adaptations
•  Pan-tropical
•  Internal fertilization
Amniota and the Amniote egg
•  Sister group to modern
amphibians
•  Tetrapods with
amniotic egg
•  Reptiles & mammals
•  Increased adaptation to
dry land
•  Monophyletic group
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Amniota and the Amniote egg
•  Amniotic egg can be
deposited on dry land:
resistant to desiccation
•  Extraembryonic
membranes
–  Amnion: surrounds embryo,
provides mechanical
protection
–  Allantois: receives metabolic
wastes
–  Chorion: gas exchange
–  Calcareous or leathery shell
(plesiomorphic, what has lost
this?)
Amniota: Terrestriality
•  Amniotic egg
•  Negative pressure inhalation
–  Rib cage ventilation
–  More efficient than positive pressure inhalation
(amphibians)
•  Keratinized skin: less permeable
•  Internal fertilization
–  Oviparity: most reptiles, all birds, some mammals
–  Ovoviviparity: some reptiles
–  Viviparity: most mammal
Amniote Diversity
•  Two main extant lineages
1.  Mammals (derived
Synapsids)
2.  Reptiles
1.  Chelonia (turtles)
2.  Archosaurs (crocodilians +
birds)
3.  Lepidosaurs (tuataras,
snakes, lizards)
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Reptiles: Testudines
•  Turtles: 307 known species
•  First fossils ~210 mya
•  Terrestrial, freshwater,
marine
•  Carapace (dorsal) and
plastron (ventral)
–  Derived from ribs
•  Head retraction evolved
twice
Reptiles: Testudines
•  Sister-group to
remaining Reptilia
•  Lack openings in the
skull near the temple
•  Anapsida (without
arch)
Reptiles:
Diaspids
•  Distinguished by two
ancestral skull openings
(temporal fenestrae)
posteriorly above and
below the eye
•  Include Lepidosaurs and
Archosaurs
•  Differ in numerous details
of skull morphology.
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Lepidosauria
•  Reptiles with overlapping
scales
•  Ectothermic
–  Derive metabolic heat from
environment
•  Sphenodontia
–  Tuataras only living
examples (2 species)
–  Part of a lineage that
flourished ~200mya
–  Now found only on islands
off of New Zealand
•  Squamata
Lepidosauria
•  Reptiles with overlapping
scales
•  Ectothermic
–  Derive metabolic heat from
environment
•  Sphenodontia
–  Tuataras only living
examples (2 species)
–  Part of a lineage that
flourished ~200mya
–  Now found only on islands
off of New Zealand
–  Why might their
conservation be so
important?
•  Squamata
Lepidosauria
•  Reptiles with overlapping
scales
•  Sphenodontia
•  Squamata
–  Lizards & Snakes
–  ~7,800 species
–  Ectothermic
•  Derive body heat from
environment
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Lepidosauria
•  Reptiles with overlapping
scales
•  Sphenodontia
•  Squamata
–  Lizards & Snakes
–  ~7,800 species
–  Ectothermic
•  Derive body heat from
environment
–  Snakes derived lizards
–  One of four legless
lineages of lizards
–  Ancestry betrayed by
vestigial limbs in early
diverging snake groups
Archosauria
•  Sister group to
Lepidosauria
•  Includes:
– 
– 
– 
– 
Crocodilia
Pterosauria† *#
Ornithischia† *
Saurischia *
•  Including Aves*#
–  † = extinct
–  * = Dinosauria
–  # = powered flight (2 or 4
origins)
Archosauria: CROCODILIA
•  23 species survive today
•  Most have long snouts with
numerous pointed teeth
•  Nesting behavior and parental
care (synapomorphy of
Archosauria?)
•  In general, have legs splayed
somewhat to the sides,
however they can pull the legs
inward and gallop, can move
quite fast if the need arises.
•  Ectothermic
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Archosauria: PTEROSAURIA
•  Non-bird Dinosauria extinct
by end of Mesozoic
•  What event?
•  Pterosaurs:
–  First vertebrates with
powered flight
–  25 cm to 10 m wingspan
•  First evidence of
endothermy?
–  Maintain body temperature
using metabolic energy
Archosauria: ORNITHISCHIA
•  Bird-hip dinosaurs
–  (although birds derived
from lizard-hip
dinosaurs)
•  Herbivores
•  Extinct 65 mya
•  Considerable
evidence of nesting
behavior.
•  Endothermic?
Archosauria: SAURISCHIA
•  Lizard-hip dinosaurs
•  Two lineages
•  Sauropods: Long-necked
herbivores
•  Theropods: Bipedal,
primarily carnivorous
•  Only one lineage survived
K-T extinction
•  Extant lineage has
nesting behavior and is
endothermic
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Living Dinosaurs
•  Derived
Saurischians
descended from
same lineage as
T. rex
(Coelurosauria)
•  BIRDS: Class
Aves
AVES: Birds
•  ~10,000 species:
most diverse tetrapod
vertebrates
•  5 cm bee
hummingbird to 2.7 m
ostrich
•  Inhabit ecosystems
from Antarctic to
Arctic
•  Diverse feeding habits
linked with diverse
beak morphology
Modern Birds
• 
• 
• 
• 
• 
• 
Feathers
Lightweight but strong skeleton
Beak with no teeth
Hard-shelled eggs
High metabolic rate
Four-chambered heart
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Modern Birds
•  All of these intimately
associated with
evolution of flight
•  Flight is plesiomorphic
for modern birds
•  Large flight muscles
attached to keeled
sternum
•  Forelimb modified as
aerofoil (wing)
Modern Birds
•  Flight lost in some lineages
•  Including Ratites
–  Ostriches, Rheas, Cassowaries,
Emus, Kiwis, Moas†, Elephant
Birds†
–  No flight muscle attachment
(keel)
•  Including Penguins
–  Flight muscles adapted for
swimming
•  Flightlessness evolved
approximately 50 times in
numerous island forms, 27 of
which have gone extinct with
colonization by Europeans
The Evolution of
Flight
•  Birds are derived
Coelurosauria (bipedal
predatory archosaurs)
•  So, how did flight
evolve?
•  Recently discovered
(1990s) fossils in China
show that feathers
evolved well before flight
•  Why evolve a branched,
3-dimensional scale?
Sinosauropteryx with primitive
hollow hair-like feathers
Reconstructed Deinonychus
based on fossilized feathers
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The Evolution of
Flight
• 
First fossil with evidence of
mechanical properties of flight is
Archaeopteryx
–  Flight feathers indistinguishable
from modern birds
–  Probably not powerful flier,
probably downstroke glider
–  Braincase & inner ear
synapomorphies with modern
birds
• 
But many plesiomorphic
characters
–  Sharp teeth
–  Forefingers with claws
–  Long, bony tail
Summary: Reptilia
•  Dominated terrestrial environments in Mesozoic
•  Currently represented by lineages in three major
groups:
–  Testudines: Turtles
–  Lepidosaurs: Tuataras, lizards, snakes
–  Archosaurs: Crocodiles, birds
•  Sister group to Synapsida, currently represented by
Mammalia
Synapsids
•  Single fenestration in
temporal region of skull
•  Diverged from Reptilia
~300 mya
•  Gradual transition in skull
morphology
–  Increased control over jaws
–  Specialized teeth
–  Transition in hinge of jaw (to
squamosal hinge) and
evolution of inner ear (from
articular-quadrate hinge)
–  (see Fig. 25.6 & 34.31 in
textbook)
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The Origin of
Mammals
•  First true mammals appear
during the Jurassic
•  True mammals:
•  Hair
•  Mammary glands & sweat
glands
•  Deciduous, heterodont
dentition
•  Three middle ear ossicles
(incus, malleus, stapes)
The Origin of Mammals
•  Three extant groups
present by early
Cretaceous
–  Monotremes
–  Marsupials
–  Eutherians
•  ALL endothermic
•  Adaptive radiation after
K-T extinction event
•  From 30-40mm
bumblebee bat to 33m
blue whale
Mammalian Diversity
Reptilia
• 
Three extant clades
distinguished by
reproductive modes
1.  Monotremes =
Protheria
2.  Marsupials =
Metatheria
3.  Placentals =
Eutheria
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Mammalian Diversity
• 
Three extant clades
distinguished by
reproductive modes
1.  Monotremes/
Protherians
– 
– 
– 
Platypus & Echidna
Australia, New Guinea
(fossils in Argentina)
Five species
1. Monotremes/ Protherians
•  Share numerous
plesiomorphic traits with
Reptilia:
•  Lay eggs
•  Urinary, defecatory, and
reproductive systems all
open into a single duct, the
cloaca
•  Lack nipples
•  Legs to side rather than
underneath
1. Monotremes/ Protherians
•  Why are they
mammals?
•  What are the
synapomorphic traits
that they must have?
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1. Monotremes/ Protherians
•  Also have numerous
synapomorphies of their own
•  Leg bears a spur in the ankle
region
–  Non-functional in echidnas
–  Powerful venom in male
platypus
•  Capable of electroreception
•  Adults lack teeth
Marsupials: Metatheria
• 
• 
• 
Kangaroos & wallabies1,
wombats2, koalas3, bandicoots &
bilbies4, Tasmanian devils5,
thylacines6, possums7,
opossums8
234 species in Australasia
100 species in Americas
2
1
3
4
5
8
7
6
Marsupials: Metatheria
• 
• 
• 
• 
• 
Distinctive pouch (marsupium), in
which females carry their young
through early infancy
Give birth at a very early stage of
development (about 4–5 weeks)
Why might this be adaptive?
Newborn crawls up the body of the
mother and attaches itself to a nipple
(in marsupium)
Have specialized sex orifices
–  Cloaca is single urinary and
defecatory tract
–  Females with two vaginas, male with
two-pronged penis; only function is
sperm reception and discharge
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Marsupials:
Metatheria
•  Fossils present in ALL
continents (North American
origin)
•  Declined as Eutherians
diversified
•  Why dominant in
Australasia?
•  Numerous convergent forms
with Eutherians
•  Numerous forms extinct only
60,000-15,000 ybp
Placentals: Eutheria
•  Embryo attaches itself to the
uterus via a large placenta via
which the mother supplies food
and oxygen and removes waste
products.
•  Pregnancy is relatively long and
the young are fairly welldeveloped at birth.
Placentals: Eutheria
•  No longer a cloaca
•  Separate urinary
and defecatory tract
•  But sexual orifice
shared with urinary
tract in both males
and females
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Eutherians:
Four clades
with ~20
orders
Clade I: Afrotheria
•  Golden moles5 & tenrecs8,
elephant shrews3,
aardvarks1, hyraxes6,
elephants7 and
manatees2,4
•  Includes largest land
animal and some not-solarge relatives
•  Believed to have
originated in Africa when
the continent was isolated
from other continents
–  Contradicts with some fossil
evidence
Clade I: Afrotheria
•  Originally grouped based on
DNA sequences
•  Possible synapomorphies:
–  Movable snout
–  Testicondy (lack of a
scrotum in males)
–  Descended testicle and
scrotum ancestral for
Mammalia
–  Why would the scrotum
have evolved in the first
place?
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Clade II:
Xenarthra
•  Sloths, Anteaters,
Armadillos
•  Originated in
South America
•  Colonized North
America in Great
American
Interchange
~3mya
Clade III: Euarchontoglires
• 
• 
First subclades: Glires
Rodentia (rodents)
–  Mice, rats, squirrels,
chipmunks, gophers,
porcupines, beavers,
hamsters, gerbils, guinea
pigs, degus, chinchillas,
prairie dogs, and
groundhogs, capybaras
–  By far, most diverse order of
mammals
–  Rodents and bats only
Eutherian orders with
species endemic to
Australia
• 
Lagomorpha
–  Rabbits, hares, picas
Clade III: Euarchontoglires
• 
• 
Second subclades:
Euarchonta
Scandentia
• 
Dermoptera
• 
Primates
–  Tree shrews
–  Flying lemurs
–  Lemurs, the Aye-aye,
lorids, galagos, tarsiers,
monkeys, and apes
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Clade IV: Laurasiatheria
•  Hypothesis: evolved on the supercontinent of
Laurasia, after it split from Gondwana when
Pangaea broke up
•  Based on DNA
sequence data
•  Fits well with
zoogeography
(distribution of
fossils and extant
lineages)
•  Six main orders
Clade IV: Laurasiatheria
•  Eulipotyphia
–  Hedgehogs, shrews,
moles
–  Insectivorous
•  Chiroptera
–  Bats
–  Forelimbs are
developed as wings
–  Only mammals
naturally capable of
flight
–  Only terrestrial
mammals found on
oceanic islands
Clade IV: Laurasiatheria
•  Carnivora
–  Dogs & foxes,
skunks, weasels,
raccoons, bears,
seals, cats,
mongooses,
hyenas, civets
–  Most diverse in size
–  Predaceous
•  Pholidota
–  Pangolins
•  Perissodactyla
–  Horses, tapirs,
rhinos
–  Odd-toed ungulates
–  Hind gut fermenters
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Clade IV: Laurasiatheria
•  Cetartiodactyla
•  Consists of what had been
two orders:
•  Artiodactyla
–  Even-toed ungulates
•  Cetacea
–  Whales, dolphins, porpoises
•  But whales sister-taxon to
Hippos
•  Originally grouped based on
DNA sequence data
•  Fossil evidence supporting
hypothesis, as is some
morphology
Clade 4: Laurasiatheria
Clade 4: Laurasiatheria
Tragulidae: Mouse deer
Moschidae:
Musk deer
Cervidae: Deer
Bovidae: Antelope, Cattle, Bison, Sheep, Goats
Giraffidae: Giraffes & Okapis
Antilocapridae:
Pronghorns
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4/6/11
Mammalian Phylogeny
•  Transition to internalization of egg
•  Many orders of Eutheria were present at
K-T extinction event
•  Underwent tremendous diversification in
species and in body form into the open
niches formed by the extinction of most
dinosaur lineages
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