Download Origins of reptiles

Amphibians
to reptiles …
Origins and evolution of
the major groups…
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Origins…
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
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Vertebrate Cladogram
340
mya
(Amniotic egg)
(Four-limbed vertebrates)
(Animals with backbones)
Credit: Stanislav Traykov Jan 28, 2005
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The amniotic egg
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Shared derived character of amniotes
Possible only with internal fertilization
Shell protects against desiccation

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Laying in terrestrial environments
Allantois (waste
mgmt, gas
exchange)
Reduces predation
Chorion
(encloses
embryo,
interface
with
mother)
Amnion
Amnion
(protection)
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Early amniotes
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Diverged ~ 340 mya
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Middle of Age of Amphibs
Small and lizard-like
Nails/claws for burrowing
Skin relatively impervious to reduce water loss
Enlarged lungs
Amniotic egg
Exploited the opportunity of aridity
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Amniote Evolution
Rhipidistian
crossopterygian
lobe-finned fish
Synapsids
Lepospondyls
“Anapsids”
Anthracosaurs
Diapsids
Euryapsids
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Fundamental splits among the Amniotes

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
Lepospondyls
“Anapsids”
Anthracosaurs
Diapsids
Lepidosaurs
(tuatara & squamates)
Mammalia
Chelonia
Euryapsids
?
Archosaurs
(birds & crocs)
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Class Reptilia – 4 Orders
 Anapsids:
 Testudines (Turtles) (~300 spp)
 Diapsids:
 Squamata (Lizards and Snakes) (~7,900 spp)
 Crocodylia (Crocodylians) (23 spp)
 Rhynchocephalia (Tuatara)(2-3 spp)
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Unifying characteristics
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Tetrapods - a few have secondarily lost their limbs
(snakes and glass lizards)
Shelled amniotic egg
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encases the embryo in a fluid-filled container
frees reptiles from locating and using a moist habitat for
egg laying
Scales of epidermal origin made from keratin prevents water loss and slows dehydration rates

more widespread than the amphibians, which are limited
by temperature and moisture
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Reptile skin …scales, scutes, and
osteoderms
Three-chambered heart
Atria
Ventricle
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All reptiles except crocodilians have
a three-chambered heart
Ridges still help oxygenated and deoxygenated
blood stay separate
= thermal flexibility
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can adjust the proportion of oxygenated blood that goes
to the body versus the lungs (intracardiac blood shunt)
Aids in heating and cooling
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Other unifying characteristics

All have internal fertilization
accomplished by a copulatory
organ
 Penis (turtles and crocs)
 Hemipenes (lizards and
snakes): paired
outpocketings of the cloaca
 Tuatara lack a copulatory
organ - mate by repressing
the cloaca

Why? Timing with egg
shelling
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Amniote Evolution
Rhipidistian
crossopterygian
lobe-finned fish
Synapsids
Lepospondyls
“Anapsids”
Anthracosaurs
Diapsids
Euryapsids
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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 251-199MYBP)
 Includes turtles and their
extinct relatives
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What are turtles?
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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 ?
?
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Three hypotheses of turtle origins
Lyson et al. (2013) Evolutionary
origin of the turtle shell. Current
Biology 23:1113-1119.
Gastralia = dermal
bones of ventral body
wall still found in crocs –
not associated with
vertebra = became
plastron?
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Archelon, Late Cretaceous
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Turtles
(Order Chelonia or Testudines) = ~300 species

Only living “anapsids” = one of earliest reptile
lineages (little changed since the Triassic)
Protostega from ~ 60 mya
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Figure 1.5 The body forms of
turtles reflect their habits and
habitats
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Turtles characteristics
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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
Outer layer =
keratin / “living”
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Shell-associated Demography
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Limbs, head, and
neck can be
drawn into shell
Extraordinary
armor
Implications:
great longevity,
high survival.
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Other characteristics
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No teeth, replaced by a keratinous beak as in birds.
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Other characteristics
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All turtles are
oviparous with longterm sperm storage.
No parental care.
Dig nests with hind
feet on land
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Other characteristics
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Highly mobile neck follows one of two patterns
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Hidden necks: Cryptodira (suborder)
Side necks: Pleurodira (suborder)
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Fang sheng – Buddhist
practice of releasing captive
animals, motivated by
compassion
Turtle remedies
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Distinct in public appreciation = birds
Freshwater turtles and land tortoises are used for
food and ancient medicinal remedies in China
Thought to cure cancer and prevent aging
Turtles in
Native
American
mythology
“…in the ancient
days of creation,
the world was all
water and the only
living creatures
dwelt upon the back
of a huge
tortoise…Then crayfish obtained
mud from the bottom of the
ocean….From the mud the earth
was built upon the back of the
tortoise.”
Turtles
“ A well-known scientist (some say it was
Bertrand Russell) once gave a public lecture
on astronomy. He described how the earth
orbits around the sun and how the sun, in turn,
orbits around the center of a vast collection of
stars called our galaxy. At the end of the
lecture, a little old lady at the back of the room
got up and said: "What you have told us is
rubbish. The world is really a flat plate
supported on the back of a giant tortoise." The
scientist gave a superior smile before replying,
"What is the tortoise standing on?" "You're
very clever, young man, very clever," said the
old lady. "But it's turtles all the way down!“
Stephen Hawking, A Brief History of Time
Amniote Evolution
Rhipidistian
crossopterygian
lobe-finned fish
Synapsids
Lepospondyls
“Anapsids”
Anthracosaurs
Diapsids
Euryapsids
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Subclass Diapsida
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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:
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Lepidosaurs: Lizards, snakes,
tuatara and their extinct relatives
Archosaurs: Crocodylians, birds,
and their extinct relatives
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
Diapsida
Subclass Lepidosauria (scaly lizards) (versus
Archosauria – crocs and birds)
Two living orders:
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Rhynchocephalia (Tuatara)

Squamata (Lizards, snakes, amphisbaenids)
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Subclass Diapsida
Lepidosauria
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Defining characters
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Transverse cloacal slit
Hemipenes
Ecdysis
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Hemipenes of squamates
Reptile skin (vs amphibian skin)
and shedding
Subclass Diapsida / Lepidosauria
Order: Rhynchocephalia
Rhynchocephalians ("beak head”) or Tuatara
(“spines on back”)
Sister group to the Squamates
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Why are
Tuatara
“so special”?
Order “Rhynchocephalia”
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Rhynchocephalians: Characteristics
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Lizard-like in body form
Series of spines on nape and back
tuatara = "spines on back” in Maori
Chisel-beaked upper jaw
overhanging the lower jaw.
Teeth fused to the jaw and
not replaced throughout life
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Rhynchocephalians: Characteristics
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Vestigial eye (parietal eye)
Has its own lens, cornea, retina with rod-like
structures and degenerated nerve connection to the
brain
Possibly evolved from a real eye
Used for navigation,
thermoregulation, tracking
photoperiod?
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Tuatara
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Long-lived, incubation of a year or more, sexual
maturity of a decade or more
Do not copulate – rub cloacas together
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Rhynchocephalians
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Once a widespread group, but now just 2-3
species of the genus Sphenodon on small islands
off New Zealand.
Most Rhynchocephalians went extinct 70
MYA
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Figure 4.6 Rhynchocephalia
Tuatara, the Keeper of the Knowledge,
guards the trails of the mind and spirit
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To here
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Order “Rhynchocephalia”
Subclass Lepidosauria
Order “Squamata”
Subclass Archosauria
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Squamates; the “scaly reptiles”
(Order Squamata)
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Most diverse group of reptiles
(with > 7,900 species)
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Lizards [Suborder Lacertilia]
Snakes [Suborders Serpentes or Ophidia]
Amphisbaenians [Suborder Amphisbaenia]
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Squamates – True 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
Size range:
Sphaerodactylus ariasae
Squamates – true lizards
(Suborder: Lacertilia)
External ear openings
Moveable eyelids
(unlike snakes)
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Four limbs, but limb reduction or loss in
some groups…all Lerista spp. (Aust. skinks)
Squamates - Lizards (Suborder: Lacertilia)
Most are oviparous, but some are
viviparous
Two species are venomous
(Gila monster, Mexican
beaded lizard)
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caudal autotomy
Intravertebral tail autotomy
(> 50% families)
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Unreliability: “She’s a chameleon…”
Squamates – Snakes
(Suborder: Ophidia, Serpentes)
Squamates – Snakes
(Suborder: Ophidia, Serpentes)
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~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
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Snakes and feeding
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All are carnivorous
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Most take relatively large prey
Subdue by venom and/or constriction
Heat sensitive pits
Skull and jaws
exceedingly mobile
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Python eating a wallaby
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Many snakes have infrared-sensitive organs
Many snakes have infraredsensitive organs
When God learned of the Serpent’s
role, he placed a curse on the snake…
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God cursed the snake "above every beast of the
field" and commanded that "upon your belly you
shall crawl, and dust you shall eat all the days of
your life." (Gen 3:14)
Roots in evolution
In honor of Asclepius, a particular type of non-venomous
snake was often used in ancient Greek healing rituals…
https://en.wikipedia.org/wiki/Rod_of_Ascle
pius
Gadsden flag – revolutionary war
origins
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Originally had 13 rattles
Jefferson’s original
Squamates – Amphisbaenids
(Suborder: Amphisbaenia)
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Amphisbaena = “to go both ways” named after
a mythical ant-eating serpent
with a head at each end
Move like accordions – backward
or forward
~ 180 species
Oviparous
Morphology for burrowing
Mostly legless –
burrow, eat inverts
Skin loose, scales in
annuli
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Prolific burrowers:
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Bipes spp. – “Mexican mole lizards” or
“ajolotes”
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Subclass Diapsida
Archosauria
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The ‘Ruling Reptiles’
Originated ~ 250 mya in the Permian
Dominant terrestrial vertebrates in the Mesozoic Era
Descendants include crocodiles, birds and dinosaurs
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Subclass Diapsida
Archosauria
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Modifications of the skeleton allowing for diverse
locomotor specializations
Adaptations associated with
increased predatory efficiency
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Teeth set in sockets in the jaw bone
Forelimbs with sharp claws
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The Age of the Reptiles - Mesozoic
245 – 65 mya (Triassic, Jurassic, Cretaceous periods)
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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
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End of the age of Reptiles (~65 mya): The KT (Cretaceous-Tertiary) event
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Mass extinctions correlate with the occurrence of a 310-kmwide impact crater on the Yucatan Peninsula
70% of all species on earth went extinct
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Legacies of the archosaurs….
The birds (~10,000 extant species: Class
Aves or Neornithes)
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Microraptor
discovered
2003
Origins of flight
Archaeopteryx
First known
bird ~250 mya
130 mya
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Class Aves
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Archosaurs also gave rise to the
Crocodylia
 Originated ~200 mya
in the Triassic
 Survive today in small
numbers
 Only ~ 23 species
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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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Figure 1.6 Crocodylians’ jaws
provide information about their
food habits
Crocodylia
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Thecodont teeth (teeth set in bony sockets)
Teeth are replaced as often as once a month
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Crocodylia...
Bodies armored by sheets of abutting
osteoderms (plates of bone under the skin)
and covered by thick non-overlapping scales
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Crocodylia
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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
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Secondary palate
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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
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Crocodylia...
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All build nests, either as mounds of
rotting vegetation (alligators,
caimans, and a few crocodiles) or in
friable soils (most crocodiles)
Parents guard nests
and assist young
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Crocodiles in mythology
 In Egypt the reptile was equated
with the crocodile-headed "Sebek"
who symbolized viscous passions,
deceit, treachery and hypocrisy
“crocodile tears”
Amniote Evolution
Rhipidistian
crossopterygian
lobe-finned fish
Synapsids
Mammalia
Lepospondyls
Anapsids
Anthracosaurs
Diapsids
Euryapsids
Lepidosaurs
Chelonia?
(tuatara &squamates) Archosaurs
(birds & crocs)
?
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Euryapsids
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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?
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Actually, one Euryapsid plesiosaur
may still be extant…
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Legend of Silver Lake
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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
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Tetraceratops Oldest known therapsid (Permian)
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First mammals
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The first mammals appeared only shortly after
the early archosaurs (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 early archosaurs
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Definitions
of Reptilia
Origins of
reptiles
End…
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crocodile complaint # 303068
Alligator in the park
might eat the kids
Hey mister city manager
city parks are for people
Parks guy tells the manager
No alligator in the park
I looked myself
It's a crocodile
Crocodile in the park
might eat the kids
Call Channel 7
then tell the Mayor
State biologist tells the city
crocodiles are protected
Here's a useful brochure
"Living with crocodiles"
- Philip Stoddardit's