Origins…
Amphibians to reptiles …
Devonian
410 – 360 mya
Carboniferous
360 – 286 mya
Permian
286 – 245 mya
‘The Age of Fishes’
(& First Tetrapods)
‘The Age of the
Giant Amphibians’
End of the Age of
the Giant
Amphibians
Origins and evolution of
the major groups…
Vertebrate Cladogram
The amniotic egg
Shared derived character of amniotes
Possible only with internal fertilization
Shell protects against desiccation
Reduces predation
Chorion
340
mya
(Amniotic egg)
(interface
with
mother)
(Four-limbed vertebrates)
(Animals with backbones)
Credit: Stanislav Traykov Jan 28, 2005
Early amniotes
Amnion
Amnion
(protection)
Fundamental Splits among the Amniotes
Allantois (waste
mgmt, gas
exchange)
Diverged ~ 340 mya
Small and lizard-like
Enlarged lungs
Nails/claws for burrowing
Loss of lateral line system
Relatively impervious skin to reduce water loss
Skull fenestrae are the synapomorphies that
distinguish these groups
Synapsids
Diapsids
Anapsids
Euryapsids
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Amniote Evolution
Rhipidistian
crossopterygian
lobe-finned fish
Synapsids
Amniote Evolution
Lepospondyls
Anapsids
Anthracosaurs
Diapsids
Rhipidistian
crossopterygian
lobe-finned fish
Euryapsids
Synapsids
Mammalia
Lepospondyls
Anapsids
Anthracosaurs
Diapsids
Euryapsids
Lepidosaurs
Chelonia?
(tuatara &squamates) Archosaurs
(birds & crocs)
?
Subclass Anapsida
stem reptiles
Lack fenestrae - Ancestral condition
Developed shells and attained huge sizes
(one turtle reached 6 m in length)
Eventually lead to the modern
chelonians — ancient reptiles
that have not changed much
since the Triassic.
Includes turtles and their
extinct relatives
What are turtles?
Because the anapsid condition is
ancestral, it gives no clue
to their relationship with extant reptiles
Both morphological and molecular analyses now suggest
that turtles may be nested within Diapsida
This would mean that the anapsid skulls of turtles may be
secondarily derived ?
Subclass Diapsida
Most species-rich group of amniotes
(>16,000 spp.)
Includes most extant reptiles
Enormous radiation of diapsids
in the Mesozoic (245 – 65 mya)
Only two groups are extant:
Lepidosaurs: Lizards, snakes,
tuatara and their extinct relatives
Archosaurs: Crocodylians, birds,
and their extinct relatives
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Subclass Diapsida
Lepidosauria
Two living orders:
Subclass Diapsida
Lepidosauria
Rhynocephalia (Tuatara)
Defining characters
Squamata (Lizards, snakes, amphisbaenids)
Subclass Diapsida
Archosauria
Transverse cloacal slit
Hemipenes
Ecdysis
The ‘Ruling Reptiles’
Originated ~ 250 mya in the Permian
Dominant terrestrial vertebrates in the Mesozoic Era
Descendants include crocodiles, birds and dinosaurs
Subclass Diapsida
Archosauria
Modifications of the skeleton allowing for diverse
locomotor specializations
Adaptations associated with
increased predatory efficiency
Microraptor
discovered
2003
Origins of flight
Archaeopteryx
First known
bird ~250 mya
Teeth set in sockets in the jaw bone
Forelimbs with sharp claws
The Age of the Reptiles - Mesozoic
245 – 65 mya (Triassic Jurassic Cretaceous periods)
Reptile-dominated trophic pyramid
Explosive radiation of flowering
plants, and the insects and small
reptiles that fed on them
Many medium- to large-sized semiaquatic herbivorous reptiles arose
Immense biomass of insect- and
plant-eating reptiles
Dominated by carnivorous species
130 mya
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End of the age of Reptiles (~65 mya): The KT (Cretaceous-Tertiary) event
Mass extinctions correlate with the occurrence of a 310-kmwide impact crater on the Yucatan Peninsula
70% of all species on earth went extinct
Legacies of the archosaurs….
The birds (~9,000 extant species)
Archosaurs also gave rise to the
Crocodylia
Originated ~200 mya
in the Triassic
Survive today in small
numbers
Only ~ 23 species
Amniote Evolution
Rhipidistian
crossopterygian
lobe-finned fish
Synapsids
Mammalia
Lepospondyls
Anapsids
Anthracosaurs
Diapsids
Euryapsids
Lepidosaurs
Chelonia?
(tuatara &squamates) Archosaurs
(birds & crocs)
?
4
Euryapsids
With a single dorsal opening on skull
Modified from the diapsid condition
Polyphyletic group
Highly successful and included many highly
derived aquatic forms, but none extant
Or are they?
Legend of Silver Lake
Actually, one Euryapsid plesiosaur
may still be extant…
Subclass Synapsida
Subclass Synapsida, with a
single opening on the side
of the skull
The ‘proto-mammals’ or
mammal-like reptiles
(technically not reptiles)
Originated 315 mya in
the Carboniferous
Eventually lead to the
modern mammals
Tetraceratops Oldest known therapsid (Permian)
First mammals
The first mammals appeared only shortly after
the dinosaurs (late Triassic).
1st 2/3 of their history, mammals were
numerous but relatively insignificant
Mostly nocturnal or arboreal shrew-like animals
Did not expand into a wide variety of
environments until
after the extinction
of the dinosaurs
5
Vertebrate Cladogram
340
mya
(Amniotic egg)
(Four-limbed vertebrates)
(Animals with backbones)
Credit: Stanislav Traykov Jan 28, 2005
Class Reptilia – 4 Orders
Testudines (Turtles) (300 spp)
Unifying characteristics
Squamata (Lizards and Snakes) (7,900 spp)
Crocodylia (Crocodylians) (23 spp)
Tetrapods - a few have secondarily lost their limbs
(snakes and glass lizards)
Shelled amniotic egg
Rhynocephalia (Tuatara)(2 spp)
Scales of epidermal origin made from keratin prevents water loss and slows dehydration rates
Three-chambered heart
encases the embryo in a fluid-filled container
frees reptiles from locating and using a moist habitat for
egg laying
more widespread than the amphibians, which are limited
by temperature and moisture
Other unifying characteristics
Atria
Ventricle
All reptiles except crocodilians have
a three-chambered heart
Despite having a single ventricle, oxygenated and
deoxygenated blood are largely kept separate
Because there is no septum, reptiles can adjust the
proportion of oxygenated blood that goes to the
body versus the lungs (intracardiac blood shunt)
Aids in heating and cooling
All have internal fertilization
accomplished by a copulatory
organ
penis or hemipenis:
outpocketing of the cloaca
(tuatara lack a copulatory
organ - mate by repressing
the cloaca)
6
Turtles
(Order Chelonia or Testudines) = 260 species
Only living anapsids = one of earliest reptile
lineages (little changed since the Triassic)
Protostega from ~ 60 mya
Turtles:Characteristics
A bony shell
completely
encloses internal
organs
Characterized by a
carapace, fused to
the vertebrae and
ribs, and joined to
the plastron.
Only head and tail
free
Other characteristics
Shell-associated Demography
Limbs, head, and
neck can be
drawn into shell
Extraordinary
armor
Implications:
great longevity,
high survival.
Other characteristics
No teeth, replaced by a keratinous beak as in birds.
All turtles are
oviparous with longterm sperm storage.
No parental care.
Dig nests with hind
feet on land
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Other characteristics
Highly mobile neck follows one of two patterns
Hidden necks: Cryptodira (suborder)
Side necks: Pleurodira (suborder)
Class Reptilia – 4 Orders
Testudines (Turtles) (300 spp)
Squamata (Lizards and Snakes) (7,900 spp)
Crocodylia (Crocodylians) (23 spp)
Rhynocephalia (Tuatara)(2 spp)
Squamates; the “scaly reptiles”
(Order Squamata)
Most diverse group of reptiles
(with > 7,900 species)
Lizards [Suborder Lacertilia]
Snakes [Suborders Serpentes or Ophidia]
Amphisbaenians [Suborder Amphisbaenia]
Squamates - Lizards
(Suborder: Lacertilia)
~3,000 species, 25 families
Range in size from 0.03-3 m
Most are small (80% are < 2 g) and insectivorous,
larger species are often herbivorous
Sphaerodactylus ariasae
Squamates - Lizards
(Suborder: Lacertilia)
Four limbs, but limb reduction or
loss in some groups
Squamates - Lizards
(Suborder: Lacertilia)
Most are oviparous, but some are
viviparous
External ear openings
Moveable eyelids
(unlike snakes)
Two species are venomous
(Gila monster, Mexican
bearded lizard)
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Squamates – Snakes
Snakes and feeding
(Suborder: Ophidia, Serpentes)
~2,300 species
No limbs, eyelids or external ear
(inner ear detects vibrations)
Have lost the sternum –
ribs extend the entire length
of the vertebral column
Left lung is reduced or absent,
organs elongate
All are carnivorous
Most take relatively large prey
Subdue by venom and/or constriction
Heat sensitive pits
Skull and jaws
exceedingly mobile
http://www.metacafe.com/watch/87916/snake_eating_an_egg/
Python eating a wallaby
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Squamates – Amphisbaenids
(Suborder: Amphisbaenia)
Amphisbaena = “to go both ways” named after
a mythical ant-eating serpent
with a head at each end
~ 135 species
Mostly legless –
burrow, eat inverts
Skin loose, scales in
annuli
Order Crocodylia
(crocodiles = 23 species – most are endangered)
Survivors (along with birds)
of the once-prevalent
group Archosauria thrived
during the Mesozoic
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Crocodylia
Crocodylia...
Bodies armored by sheets of abutting
osteoderms (plates of bone under the skin)
and covered by thick non-overlapping scales
Thecodont teeth (teeth set in bony sockets)
Teeth are replaced as often as once a month
Crocodylia
Secondary palate
A very advanced Four-chambered heart
Cogged valve allows blood to be shunted from the right side of
the heart to the systemic circulation, introducing deoxygenated
blood
Can re-route blood usually pumped into the lungs into other
parts of the body
Allows crocodiles to dive for several hours without surfacing to
breathe
When blood rich with carbon dioxide goes to the stomach
instead of the lungs, it can aid digestion
Crocodylia...
All build nests, either as mounds of
rotting vegetation (alligators,
caimans, and a few crocodiles) or in
friable soils (most crocodiles)
Females guard nests
and assist young
Allows crocodiles to breathe even when
submerged under water
Their internal nostrils open in the back of their throat,
where a part of the tongue called the "palatal valve"
closes off their respiratory
system. This way they can
open their mouths
underwater.
Most reptiles lack a
secondary palate
Rhynchocephalians (tuatara)
Sister group to the Squamates
Order: Rhynchocephalia
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Why are
Tuatara
Unique?
Rhyncocephalians
Rhyncocephalians: Characteristics
Lizard-like in body form
Series of spines on nape and back
tuatara = "spines on back” in Moari
Chisel-beaked upper jaw
overhanging the lower jaw.
Teeth fused to the jaw and
not replaced throughout life
Once a widespread group, but now just 2
species of the Genus Sphenodon on small
islands off New Zealand.
Most Rhynocephalians went extinct 70 mya
Rhynocephalians: Characteristics
Vestigial eye (parietal eye)
It has its own lens, cornea, retina with rod-like
structures and degenerated nerve connection to the
brain, possibly evolved from a real eye
Its function is unknown –
may be used for navigation,
thermoregulation, tracking
photoperiod
Tuatara
Long-lived, incubation of a year or more, sexual
maturity of a decade or more
Do not copulate – rub cloacas together
Origins of
reptiles…
End…
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