Class Reptilia – Amniote Origins and
Nonavian Reptiles
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With the reptile group(s) we see better adaptation to
a terrestrial existence.
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1) shelled amniotic egg
2) tough, dry and scaly skin
3) efficient jaws for crushing and gripping prey
4) efficient circulatory system with a higher blood
pressure
5) internal fertilization using some form of copulatory
organ
6) better developed lungs
7) better body support; more efficient limbs
8) more complex nervous systems
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The Amniotic Egg
The liquid environment needed for the
eggs/embryo of amphibians has been enclosed
within the amniotic egg
 No longer a necessity to breed in water
 Amniotic egg consists of 4 extraembryonic
membranes; the amnion, yolk sac, allantois,
and the chorion all surrounded by a protective,
porous shell.
 Ancestral reptiles gave rise to the monophyletic
group of the Amniota which include modern
reptiles, birds, and mammals
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Figure 18_04
Skull Structures of Reptilian Groups
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Evolutionary development within the late
Carboniferous gave rise to 3 major groups of
amniotes based upon skull structure
Anapsids – no temporal opening behind
orbits; gave rise to turtles
 Diapsids – 2 temporal openings behind orbit;
gave rise to modern reptilian groups and
birds
 Synapsids – 1 temporal opening behind orbit;
gave rise to modern mammals
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Paraphyly of Reptilians
Class Reptilia is a paraphyletic group; does
not include birds (Aves) within the clade of
Reptilia although birds are the direct
descendants of reptiles
 Crocodilians and birds share a more recent
common ancestor (along with dinosaurs) and
represent the Archosauria
 Lepidosauria represents the snakes, lizards,
tuataras, and worm lizards
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Figure 18_01
Order Testudines - turtles
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Anapsid group having diverged early in the evolutionary history
of the reptilian group
Possess distinctive shells
 Long-lived adapted to terrestrial (tortoises typically), semiaquatic, aquatic, and marine existence (sea turtles)
 Lack teeth
 All are oviparous and bury eggs on land (including aquatic and
sea turtles
 No specific distinction between the words turtle, tortoise, and
terrapin; tortoise and terrapin generally refers to terrestrial
types and turtles to aquatic types
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Diapsid groups – Lizards (Order Squamata)
Highly diversified and successfully adapted for walking,
running, climbing, swimming, and burrowing; common
groups are geckos, iguanas, skinks, monitors, and
chameleons
 Differentiated from snakes by:
 2 pair of legs (although a few are legless)
 Fused lower jaw halves
 Movable eyelids
 External ears
 Absense of fangs
 The Amphisbaenia are the worm lizards well adapted for
burrowing
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Diapsid groups - Snakes
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Completely legless (python and boa groups
possess vestigial limbs) and elongated
Kinetic skull allowing for swallowing of prey
whole
Many possess Jacobson’s organs to detect
prey
Pit vipers possess infrared sensors
Some venomous and with fangs (rear-fanged
vs. front-fanged types)
Diapsid groups – Tuataras Order Sphenodonta
Ancient, relic lizard like species found in
New Zealand
 Possess diapsid skull like that of ancient
ancestors and a median parietal “third
eye”
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Diapsid groups – Order Crocodilia
Only extant reptilian representatives of the
archosauria that gave rise to dinosaurs and birds
 Large skulls with powerful jaws
 Secondary palate
 Most complex social behavior of any reptilians
(mating and reproductive behavior)
 High nest temps produce males, low temps produce
females (opposite in turtles)
 Alligator common to Florida; North American
crocodile in South Florida also
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