The reptiles

Asma Thebo
PH.D ZOOLOGY (CONT…)

 • Cold-Blooded
• Regulate their body temperature using the
environment
• Can survive both on land and in water
• Most lay eggs
• Most have scales, none have hair or fur
• All lack external ears.
Four main groups of reptiles
• Crocodiles
• Lizards
• Turtles
• Snakes
Asma Thebo (Department of STE) Asma Thebo (Department of STE)

 EVOLUTIONARY PERSPECTIVE (reptos, to creep)
 Reptiles were the first vertebrates that possess amniotic
eggs. Amniotic eggs have extra embroynic membranes.
These membranes performs the following functions:
1. They Protect the embryo from dessication.
2. These support the embryo like cushion.
3. These membranes promote gas transfer.
4. These membranes remove the waste materials.

 The amnioitic eggs of reptiles and
birds also have following parts:
 1. Shells: Birds and reptiles have
hard or leathery shell. This shell
protects the developing embryo.
 2. Albumin: The albumen cushions
the embryo. It also provides
moisture and nutrients to the embno.
 3. Yolk: The yolk supplies food to
the embryo.

 All these features are adaptations for development on land.
 The amniotic egg is the major synapomorphy
(distinguishing characteristic). It distinguishes the reptiles,
birds, and mammals from nonaminote vertebrates.
 The amniotic egg has played an important role in success
of vertebrate in terrestrial habitats.
 Thus the members of this class flourished on land. Living
reptiles are turtles.
 lizards, snakes, worm lizards. crocodilians and the tuatara.

 CLADISTIC METHOD
 Cladistic taxonomic methods have reexamined and reinterpreted the amniotic
lineage.
 Cladistics believes that the amniotic lineage is monophyletic. The birds and the
mammals have a common ancestor with the reptiles.
 It is the rule of the cladistic analysis that animals with most recent common
ancestor must be placed in a particular taxon. Birds and mammals have
common ancestor with reptiles.
 But traditional classification does not include birds and mammals in class
Reptilia.
 According to cladistic interpretations, birds should be classified as “reptiles”
with dinosaurs. Similarly, cladistic interpretations also develop close
relationship between mammals and ancient synapsid reptiles
Asma Thebo (Department of STE)

 Evolutionary systematics
 1.Evolutionary systematists disagree that these cladistic interpretation.
These explain that the birds and mammals have important
morphological, behavioral and ecological characteristics.
 For example, feathers and endothermy in the birds, hair, mammary
glands and endothermy in mammals.
 These characteristics suggest that birds and mammals should be
placed in separate classes. Evolutionary systematists take them as
important characters. They conclude that these characteristics have
great importance in the taxonomy of these groups.

 Class Reptilia includes many diverse species that are
classified into four living clades.
 Reptilia includes four living clades:
1. Crocodilia (crocodiles and alligators),
2. Sphenodontia (tuataras),
3. Squamata (lizards and snakes), and
4. Testudines (turtles).
These are the 25 species of Crocodilia, 2 species of
Sphenodontia, approximately 9,200 Squamata species, and
the Testudines, with about 325 species.

 2. Sphenodontia (“wedge tooth”) arose in
the Mesozoic era and includes only one
living genus, Tuatara, comprising two
species that are found in New Zealand
(Figure 2).
 Tuataras measure up to 80 centimeters and
weigh about 1 kilogram. Although quite
lizard-like in gross appearance, several
unique features of the skull and jaws
clearly define them and distinguish the
group from the squamates.

 3. Squamata (“scaly”) arose in the late
Permian, and extant species include lizards
and snakes. Both are found on all continents
except Antarctica.
 Lizards and snakes are most closely related to
tuataras, both groups having evolved from a
lepidosaurian ancestor. Squamata is the
largest extant clade of reptiles
 Lizard species range in size from chameleons
and geckos, which are a few centimeters in
length, to the Komodo dragon, which is about
3 meters in length. Most lizards are
carnivorous, but some large species, such as
iguanas, are herbivores.

 3. Squamata Snakes are thought to have
descended from either burrowing lizards or
aquatic lizards over 100 million years ago
 . Snakes comprise about 3,000 species and
are found on every continent except
Antarctica.
 They range in size from 10 centimeter-long
thread snakes to 10 meter-long pythons and
anacondas. All snakes are carnivorous and eat
small animals, birds, eggs, fish, and insects.
Their specializations all point to snakes
having evolved to feed on relatively large
prey (even though some current species have
reversed this trend).

 4. Testudines
 Turtles are members of the
clade Testudines (“having a shell”).
 Turtles are characterized by a bony or
cartilaginous shell. The shell consists of the
ventral surface called the plastron and the
dorsal surface called the carapace, which
develops from the ribs.
 Turtles arose approximately 200 million
years ago, predating crocodiles, lizards,
and snakes..

 4. Testudines
 Similar to other reptiles, turtles are
ectotherms. They lay eggs on land, although
many species live in or near water.
 None exhibit parental care. Turtles range in
size from the speckled padloper tortoise at 8
centimeters (3.1 inches) to the leatherback
sea turtle at 200 centimeters (over 6 feet).
 The term “turtle” is sometimes used to
describe only those species of Testudines
that live in the sea, with the terms “tortoise”
and “terrapin” used to refer to species that
live on land and in fresh water, respectively.

The reptiles

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