Amniote Relationships
turtles
mammals
?
Synapsida
lizards,
snakes,
birds,
crocs
Diapsida
Anapsida
Reptilia
Amniota
Reptilian Ancestor
Mesosuarus
freshwater dwelling “reptile”
Reptilia
General characteristics of reptiles (not all of these are shared derived characters)
• amniotic egg
• internal fertilization
• pulmonary respiration
• single occipital condyle*
• two sacral vertebrae with ribs
• epidermal scales
* knob of bone at back of skull that articulates with the first vertebrae
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Modern Reptile Diversity
• 7,500 species
• About 6,800 of these are lizards and snakes
• All continents except Antarctica
Amniote Relationships
mammals
turtles
lizards,
snakes,
birds,
crocs
Diapsida
Anapsida
Synapsida
Reptilia
Amniota
Reptile Relationships
Class Reptilia
Subclass Anapsida - turtles
Subclass Diapsida - diapsids
Superorder Lepidosauria - lepidosaurs
Order Rhyncocephalia - tuataras
Order Squamata - lizards and snakes
Superorder Archosauria - “ruling reptiles”
Order Crocodylia - crocodilians
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Diversity of Modern Reptiles
?
snakes and lizards
crocodilians
turtles
Relationships Among Modern Reptiles
turtles
snakes,
lizards
crocs
Reptile Diversity
Reproduction
All reptiles have internal fertilization. Why?
• Male turtles and crocodilans have a penis that lies in the floor of the cloaca
• Tuataras lack an intromittent organ. How is fertilization achieved?
• Snakes and lizards paired hemipenes that are formed from the rear of the cloaca
snake hemipenes
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Reptile Diversity
Reproduction
Reptile Diversity
Reproduction
Retention of eggs and live birth
• Most reptiles are oviparous and lecithotrophic
• There are a few viviparous lecithotrophic snakes/lizards
and even fewer viviparous placentotrophic snakes/lizards
 Six families of snakes/lizards are entirely oviparous
 Seven families of snakes/lizards are entirely
viviparous
 Fifteen have both
• All turtles and crocodilians are oviparous
Reptile Diversity
Reproduction
Costs of viviparity:
• production limited to one clutch per season
• clutch size is lower because of space limitations
• gravid (pregnant) females are more vulnerable to
predators
Viviparity may have evolved in association with cold climates
because embryos retained in a thermoregulating female are
warmer and develop faster than embryos developing in nests
on the ground. This results in earlier hatching which has
obvious benefits in cold climates with a short summer.
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Reptile Diversity
Parental Care
Reproduction
• absent in turtles
• found in all crocodilians with both parents involved. Takes
three forms: defense of nest (females), opening nest and
aiding young in hatching, transporting young to water.
• approximately 100 species of squamates (=snakes & lizards)
have parental care. Takes three forms: egg brooding, defense
of nest site, and egg brooding with thermogenesis.
Reptile Diversity
Reproduction
Sex Determination
In most animals the sex of offspring is determined by which
sex chromosomes they inherit. This is known as genotypic
sex determination (GSD). All amphibians, snakes, and
some lizards have GSD.
X
Y
Reptile Diversity
Reproduction
Sex Determination
However, the sex of some lizards, most turtles, and all crocs and tuataras
is determined by the incubation temperature of the nest. This is called
temperature dependent sex determination (TSD). There are three major
patterns of TSD.
A. Males at high temps
B. Males at low temps
C. Males at intermediate temps
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Reptile Diversity
Reproduction
Asexuality
Parthenogenesis is the only form of
asexuality known in reptiles. It has been
reported in 30 species of squamates,
mostly geckos, lacertids, and teiids (all
lizards) and blind snakes (a group of small,
sightless, primitive snakes).
Subclass Anapsida
The Shell
• Of all living reptiles, turtles are most recognizable because of
the shell. The turtle shell is made up of the carapace (top) and
the plastron (bottom). Both are bone covered with keratinized
scutes or leathery skin.
Subclass Anapsida
The Shell
The CARAPACE is composed of 10 trunk vertebrae and the
associated, widened ribs. Dermal bone fills in the spaces
between the ribs. The extent of this filling, and thus the
“completeness” of the shell varies among families.
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Subclass Anapsida
The Shell
The PLASTRON is composed of unique “abdominal ribs” and
the expanded pectoral girdle. This results in a unique situation
in which the ribs are external to the girdles (pelvic and pectoral)
as opposed to almost all other tetrapods in which the opposite
spatial arrangement is true.
Subclass Anapsida
Shared Derived Characters
• shell
• no teeth
• skull with large otic notch to support tympanum
• presence of trochlea, a ridge of bone over which the jaw
adductor muscles pass
• loss of pineal foramen
Subclass Anapsida
Size Range:
10 cm
2.5 m and 1,000 kg
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Subclass Anapsida
Systematics and Classification
Order Testudinata - living turtles
Suborder Pleurodira - side-neck turtles
Suborder Cryptodira - hidden-neck turtles
Subclass Anapsida
Diversity
Suborder Pleurodira - side-neck turtles
• 3 families
• about 75 species
• southern hemisphere
Podocnemis unifilis
Chelodina mccordi
Subclass Anapsida
Diversity
Suborder Cryptodira - hidden-neck turtles
• 10 families
• about 200 species
• worldwide
snapping and big-head turtles
Macrochelys temminckii
Platysternon megacephalum
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Subclass Anapsida
Diversity
Suborder Cryptodira - hidden-neck turtles
sea turtles
Dermochelys coriacea
Eretmochelys imbricata
Subclass Anapsida
Diversity
Suborder Cryptodira - hidden-neck turtles
pond turtles
Clemmys guttata
Rhinoclemmys punctularia
Subclass Anapsida
Diversity
Suborder Cryptodira - hidden-neck turtles
tortoises
Testudo sp.
Geochelone radiata
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Subclass Anapsida
Diversity
Suborder Cryptodira - hidden-neck turtles
softshells
Apalone spinifera
Cycloderma frenatum
Subclass Anapsida
Diversity
Suborder Cryptodira - hidden-neck turtles
pignose turtle
Central American river turtle
Carettochelys insculpta
Dermatemys mawii
Subclass Anapsida
Diversity
Suborder Cryptodira - hidden-neck turtles
mud and musk turtles
Kinosternon carinatum
Staurotypus salvinii
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Subclass Anapsida
Evolutionary Trends
• aquatic habit (esp. locomotion) e.g. sea turtles
• terrestrial habit e.g. tortoises
• bottom dwelling e.g. softshells
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