Reached point of

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Last day - surveying diversity of chordates
(about 51,000 spp.?)
Reached point of evolution of limbs with
feet Tetrapods
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Tetrapoda - the tetrapods
Tetrapods have feet with digits, transfer
muscular forces to ground
Pelvic girdle fused to vertebral column,
allowing transfer of forces to body
No pharyngeal clefts in adults, ears adapted
for airborne sounds
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Class Amphibia
Present day amphibians are highly specialized
groups not necessarily very similar to early
tetrapods
- most dependent on H2O at least part of life,
or in moist habitats
- moist skin important for gas exchange, some
lack lungs
- skin may also be toxic to varying degrees
Cobalt Poison Dart Frog
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Amphibian dual life - metamorphosis - most
species breed, develop as larvae in fresh water
but typically terrestrial as adults
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Eastern Red-backed Salamander
Southern Gastric Brooding Frog
Exceptions to standard life cycle fairly
numerous, sometimes bizarre
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Order Urodela - Salamanders

• About 500 spp., many in eastern US
• - some entirely aquatic, but often live on land
  as adults, or sometimes throughout life

Spotted Salamander
On land, most walk with side-to-side
bending of body, may resemble
movement of early terrestrial tetrapods.
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Order Anura Frogs and Toads
By far largest order, w. 4,500 spp., worldwide
except many ocean islands, cold climates
- specialized for hopping on land (legs,
urostyle) but swim well too
- catch insects with sticky tongue (attached
in front)
American Toad
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Golden Mantella
Many species toxic, may have aposematic
coloration (warning colors, easy to recognize
learn)
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Order Apoda - Caecilians

• About 170 species, legless nearly blind
• - reduction of legs evolved secondarily

- superficially resemble big earthworms,
most burrow in moist soil in tropical
forests - some South American spp. live in
ponds streams
Bannan Caecilian
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A Chordate Phylogenetic Tree
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The Amniotes

• Amniota consists of mammals, turtles,
  crocodilians, birds, tuataras squamates
  (lizards snakes), plus many extinct groups

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Amniotic Egg - major derived trait
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Amniotic egg allowed life completely on
land - shell retains water, but allows gas
exchange
Great Tinamou eggs
Eggs of birds calcareous, of most reptiles
more leathery
Leatherback Turtle hatching
- most mammals have lost shell retain egg
in uterus
echidna puggle
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• Other amniote traits...
• evolved less permeable skin with keratin
  scales
• (lost in mammals only on legs of birds)
• lungs almost exclusively for respiration
• increasing use of rib cage to ventilate lungs

- adopted more elevated stance than earlier
tetrapods
Komodo Dragon
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An Amniote Phylogenetic Tree
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Class Testudinia - Turtles
Highly distinctive group - shell formed by bony
shields fused to vertebrae, ribs, clavicles,
covered with horny scutes
Green Sea Turtle
- About 300 species, most associated with
water but some in arid areas
- respiration in water aided by cloaca or
pharynx
- relationships uncertain
Ornate Box Turtle
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Class Crocodilia - Crocodilians
Part of group known as archosaurs, early
crocodilians were small terrestrial -
Cretaceous crocs up to 12 m, modern spp. 1-6 m
- 23 species in tropical warm regions - top
predators, but also good parents
Nile Crocodile
Siamese Crocodile
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Class Aves - Birds
Another group of archosaurs, closest living
relative of dinosaurs - thought by most to be
descended from theropod dinosaurs (though
some skeptics remain...)
Archaeopteryx from Jurassic (about 150
MYA) - has feathers (defining feature of
birds), but also teeth, many tail tail
vertebrae, etc.
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Currently, most diverse terrestrial vertebrates
(about 9800 spp.) - found virtually anywhere
on planet
Often abundant conspicuous (because diurnal,
use use vocal visual signals)
Emperor Penguin
Ostrich
Rainbow Lorikeet
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Success of birds probably largely due to superior
flight abilities Peregrine Falcon over 200
mph in dives, some birds in level flight 60
mph?
Flight allows safety from terrestrial predators,
fast efficient transport, ability to use
scattered resources (short-term or
seasonally)
Brown-backed Needletail
Peregrine Falcon
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Many features of birds related to flight
lightweight flexible feathers w. interlocking
flat vanes hollow quill
- bipedalism, large flight muscles, wings acting
as effective airfoils propellers, hollow
bones air sacs
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Other avian features also related to flight lack
of teeth, possession of gizzard (muscular
grinding stomach), excellent vision, small
size
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Why birds are better than mammals...
Higher metabolism - maintain body temperatures
around 40º C enables greater speed
power, faster nerve transmission, activity
at cold temperatures
More efficient respiration - lungs with one-way
flow, maximizes O2 exchange
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Live longer than most mammals of same size
Birds are even smarter than (non-human)
mammals (arguably...)
New Caledonian Crow
African Grey Parrot (Alex)
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Next groups on another major branch
Lepidosaurs
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Class Rhynchocephalia - Tuataras
Only 2 surviving species of group common in
Mesozoic, found in New Zealand (now basically
on offshore islands - due to introduced rats)
Common Tuatara
- resemble lizards, but many unspecialized
anatomical traits (diapsid skull,
gastralia, parietal eye)
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Class Squamata Lizards and Snakes
Squamates are quite diverse numerous
almost 5,100 lizard spp. and 3,150 snakes -
most numerous in tropical warm temperate
areas
Gila Monster
Lizards are not monophyletic if snakes
excluded - snakes evolved from lizards
related to monitor lizards
Coral Snake
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Most lizards small (to 16 mm), though Komodo
Dragon to 3 m - small species
insectivorous, large spp. often herbivores
Jaragua Sphaero
Chameleons highly specialized w. prehensile
tail, long sticky tongue, independently
swivelling eyes, etc.
Green Iguana
Usambara Three- horned Chameleon
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Snakes range from tiny (10 cm) burrowers to
constrictors near 10m - all? carnivorous, but
only 500 venomous?
- flexible connections in skull mandibles
important for swallowing large diameter prey
Reticulated Python ( minor celebrities)
Common Egg-eating Snake
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Grass Snake
Snakes and some lizards sample odors w.
tongue, then contact paired vomeronasal
organs in roof of mouth - may detect odor
gradient?
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Final group - a little familiar...
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Class Mammalia - the Mammals
A moderately diverse successful group - about
5400 spp. - averages larger than most
vertebrates, but 2300 rodents 1100 bats,
so most quite small
Humpback Whale
Little Brown Bat
Red-backed Vole
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Lineage leading to mammals - the Synapsida -
branched off from other amniotes early, but not
considered mammals yet
- later stages included the therapsids before
true mammals evolved in the Triassic or
Jurassic
Dicynodon, a therapsid
Dimetrodon, a synapsid
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Mammalian characters include hair (may be
sparse!), mammary glands for nursing young,
endothermy, four-chambered heart muscular
diaphragm
- varied dentition is important in feeding
ecological specialization
Manatee
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Mammalian jaw evolution Dimetrodon is early
synapsid Morganucodon is more mammalian
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Monotremes
Monotremes - the platypus 4 spp. of echidnas -
only living mammals that lay eggs Reptile-like
egg contains enough yolk to nourish the
developing embryo. Monotremes have hair, and
females produce milk in specialized glands After
hatching, baby sucks milk from mothers fur
because she lacks nipples
Platypus
Short- beaked Echidna
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Marsupials
Marsupials include opossums, kangaroos,
bandicoots, koalas, etc. Unlike monotremes,
marsupials have higher metabolic rate, nipples
that produce milk, give birth to live
young. Marsupials born very early in development
, in most spp., completes development while
nursing in maternal pouch, the marsupium Marsupial
s existed worldwide in Mesozoic but now are
restricted to Australia the Americas
Koala
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Newborn kangaroo in marsupium
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Convergent evolution between marsupial
and eutherian mammals
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Eutherian Mammals
Compared to marsupials, eutherian mammals
(placentals) have longer gestation period
(pregnancy) Young eutherians complete embryonic
development in uterus, joined to mother by
placenta Eutherians often called placental
mammals - placentas are more complex than
marsupials, provide more intimate long-lasting
association between mother and young
Cougar
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A Phylogenetic Tree for Mammals