1. Reptiles originated from primitive labyrinthodont amphibians during the Carboniferous period and underwent two major periods of adaptive radiation - in the Paleozoic and Mesozoic eras. 2. During the Mesozoic era, reptiles dominated land, sea and air, represented by 16 orders, including dinosaurs, pterosaurs, marine reptiles and the ancestors of modern crocodiles and birds. 3. Transitional fossils like Archaeopteryx provide evidence that birds evolved from reptiles with feathers and wishbones evolving among traits shared with modern avians.

1. Priyanka Rani Majumdar
Lecturer
Dept. of FIMS
NSTU

2. Class Reptilia
• L. repere, creeping
• Terrestrial tetrapods
• Cold blooded, limbs 2 pairs; Skin dry and devoid of glands
• Respiration by lungs
• Covered by ectodermal horny scales or bony plates
• Body divisible into head, neck, trunk and tail
• Heart usually 2-3chambered except crocodiles
• Amniote (shelled) egg with extra-embryonic membranes (gas
exchange, waste storage, nutrient transfer)
• Fertilization internal. Mostly oviparous
e.g. snake, crocodiles, turtles

3. Classification
 Reptiles are grouped into approximately 16 orders of which only
4 are living.
 On the basis of absence or presence of certain openings
through the posterolateral or temporal region of the skull
I. Subclass Anapsida
II. Subclass Euryapsida
III.Subclass Parapsida
IV.Subclass Synapsida
V. Subclass Diapsida

5. Order 1. Chelonia or Testudinata
Gr., chelone, turtle; L., testudo, turtle
 Body short, broad and oval
 Limbs clawed and webbed, paddle-like
 Body encased in a firm shell of dorsal carapace and ventral plastron,
made of dermal bony plates
 Thoracic vertebrae and ribs usually fused to carapace
 Teeth absent. Jaws with horny sheaths.
e.g. Chelone, Testudo
Subclass 1. Anapsida
Primitive reptiles with a solid skull roof. No
temporal openings

6. Subclass 2. Euryapsida (extinct)
Skull with a single dorso-lateral temporal opening on either
side bounded below by postorbital and squamosal bones
Subclass 3. Parapsida (extinct)
Skull with a single dorso-lateral temporal opening on either
side bounded below by the supratemporal and postfrontal
bones.
Subclass 4. Synapsida (extinct)
Skull with a single dorso-lateral temporal opening on either
side bounded above by postorbital and squamosal bones

7. Subclass 5. Diapsida
 Skull with two temporal openings on either side separated by
the bar of postorbital and squamosal bones
Order 2. Rhynchocephalia
L., rhynchos-snout and Gr., kephale-head
 Body small,elongated and lizard-like
 Limbs pentadactyle, clawed and burrowing
 Exoskeleton of granualar scales and a mid dorsal row of spine
 Skull diapsid
 Teeth acrodont i.e. attached on the top surface of the jaw bone
 Cloacal aperture transverse
 No copulatory organ in male
e.g. Sphenodon punctatum (Tuatara)

8. Order 3. Squamata
L., squama-scale
 Small to medium, elongated
 Limbs clawed, absent in snakes and few lizards
 Exoskeleton of horny epidermal scales, shields and spines
 Teeth acrodont or pleurodont i.e. on the inner side and upper
side of the jawbone
 Cloacal aperture transverse
 Male with eversible double copulatory organs (Hemipenes)
 Divided into two suborder-Lacertilia and Ophidia
e.g. Lizards and snakes

10. Order 4. Crocodilia
Gr., Krokodeilos- Crocodile
 Large-sized, carnivorous and aquatic reptiles
 Limbs short but powerful, clawed and webbed
 Skin thick with scales, bony plates and scutes
 Teeth numerous, thecodont, lodged in sockets
 Cloacal aperture is a longitudinal slit
 Male with a median, erectile, grooved copulatory
organ (penis)
e.g. Crocodylus, Gavialis, Alligator

12. Sphenodon punctatum (Tuatara)
 It is a single living species under the order Rhynchocephalia, commonly called
Tuatara, found only in New Zealand.
 It is referred to as a living fossil because it has retained many primitive
characteristics of stem reptiles i.e. Anapsida
 It is burrowing, carnivorous and nocturnal in habits
 Lives in small holes or burrows in rocks associated with petrels or in water.
 Feeds largely on small invertebrates (worms, insects, spiders, molluscs), fish,
gecko
 During the day it basks in the sun to raise its body temperature
 It lays about 10 eggs with white egg shells in spring in holes in ground which
require more than a year to develop and hatch
 Life span in captivity is 50 years

14. Lacertilia Ophidia
Body elongated, lizard-like Body slender, narrow, snake-like
Limbs and girdles usually well-developed Usually absent, vestigial hindlimbs and pelvic
girdle in boa, python etc.
Eyelids movable. Nictitating membranes
present
Eyelids fixed. Nictitating membranes absent
Ear openings and tympanum present Auditory openings and tympanum absent
Mouth non-expansible because two rami of
mandible firmly united
Mouth expansible because mandibular rami
joined by an elastic ligament and can be widely
separated during swallowing of large prey
Tongue rarely notched or extensile Tongue slender, bifid and extensile
The ventral side of the body is covered by
the small scales
The ventral side of the snake’s body is covered
by the large shields

16. Crocodiles Alligators Gavials or Gharials
Crocodiles or true Crocodiles are
included in the family
Crocodylidae and subfamily
Crocodylinae
An alligator is a crocodilian of the
family Alligatoridae
Gavials or Gharials is a crocodilian of
the family Gavialidae
More aggressive. Dangerous to man Less aggressive. Attack man in self-
defense if provoked
They can eat only fish because of
narrow throat. They also known as
the fish-eating crocodile
Moderately long and V-shaped
snouts
Short broad and U-shaped snouts Very long and slender for their
piscivorous diet
The upper and lower jaws of
crocodiles have same width.
An alligator’s upper jaw is wider than
its lower jaw
The upper and lower jaws of Gavials
have same width.
When mouth is closed, Many
interlocking teeth are visible
When mouth is closed, only the top
teeth are visible
When mouth is closed, Many
interlocking teeth are visible
males growing much larger and more
rapidly than females
Male and female alligators can be
hard to tell apart visually
Sexes of gavials are separated easily
by the presence of bulbous growth on
the tip of the mature male’s snout
which is looking as like as earthen pot
known locally as 'ghara'
Crocodiles can move by ‘belly-run’
and ‘high walk’ where the body is
raised clear of the ground
Crocodiles can move by ‘belly-run’
and ‘high walk’ but cannot walk on
their hind legs for long distances
do not have the ability to raise the
body off the ground or to produce the
"high-walk" and can only move in a
forward "sliding" motion on land

20. Turtle Tortoise
Mostly aquatic, especially in seawater Terrestrial
Streamlined carapace The carapace of tortoise is rounded and
domed
A turtle cannot retract their heads and
flippers into their shells
They can completely retract their heads
and legs into their shells
They have webbed feet and the feet
become long flippers in the case of sea
turtles
They have short, thick and stumpy feet for
walking and their feet have claws for
digging
They are good swimmers They aren’t good swimmers
They are heavy and cannot lift their
bodies off the ground when crawling
They can lift their bodies off the ground
when crawling
Mainly omnivorous Mainly herbivorous

22. Origin of Reptiles
 The primitive reptiles originated from some primitive labyrinthodont amphibia in
the beginning of Carboniferous period
 About 250 years ago, some labyrinthodont amphibians gradually took on
reptilian characteristics, which are called stem reptiles.
 These reptiles are belong to the order Cotylosauria of the subclass Anapsida
 Seymouria, one of the members of the Cotylosauria found in the Texas,
perhaps 250 million years ago
 Seymouria is a connecting link between labyrinthodontia and Cotylosauria
because the structure of Seymouria was intermediate between the amphibians
of that time and the early reptiles

23. Resemblance of Seymouria with the amphibia
 Skull is flat
 An intertemporal bone is present
 Teeth are labyrinthine and also found on vomers and palentines
 Neck is short
Resemblance of Seymouria with the reptilian
 Limbs are muscular and arise mid-ventrally
 Skull is anapsid
 Pelvic girdle is attached to vertebral column by sacral vertebrae

24. Adaptive radiation
Adaptation or adaptive radiation is a evolutionary
process in which organisms diversify rapidly into a
multitude of new forms, as a result of natural selection
so that it adjusts to new or altered environmental
conditions or able to live in its habitat or habitats.
Adaptation may cause either the gain of a new feature,
or the loss of an ancestral feature for the competition for
food and living space
The adaptive radiation of reptiles took place twice, first
in the Palaeozoic and secondly in the Mesozoic

25. Palaeozoic radiation:
 The ancestral reptiles or cotylosaurs multiplied rapidly all
ecological niches
 Their radiation involved adaptations to different methods of
locomotion and feeding
 The synapsida- Pelycosauria and Theromorpha were similar to
cotylosaurs.
 Later Therapsida which had different dentition and improved
locomotion as nearly like as mammals

27. Mesozoic radiation:
 The ancestral cotylosaurs had disappeared at the end of the palaeozoic, but
their descendants produced a second and bigger radiation during Mesozoic
 Throughout the Mesozoic era, the reptiles dominated not only the land but also
the sea and the air.
 The Mesozoic era is called as the age of reptiles
 The reptiles ruled the earth over a great span of time, about 130 million years
 The extinct reptiles are represented by as many as 16 orders- one led to the
birds, one to the mammals and four to the modern reptiles
 Mesozoic reptiles were disappeared at the beginning of the Cenozoic era,
leaving behind the representatives of only 4 living orders.

28. Euryapsid line:
The euryapsids or Plesiosaurs were large, marine, turtle-like, heavy-
bodied and long-necked creatures and fish-eaters which were extinct
towards the end of the Cretaceous
Parapsid line:
As like as Euryapsida, another marine blind alley was fish-like or porpoise
like Ichthyosaurs

29. Diapsid line:
 Divided into two branches-Lepidosauria and Archosauria
 Lepidosauria were probably ancestor of the modern Squamata (snakes
and lizards) and Rhynchocephalia (Tuatara)
 Archosauria were the ruling reptiles of the Mesozoic era and represented
the extinct Pterosauria, the extinct Dinosaurs and the modern
Crocodilia and the modern birds
 Pterosauria were the extinct flying reptiles which are the ancestors of the
modern birds

30. Transitional fossils
Many fossils show a clear transition
from one species, or group, to
another.
Archaeopteryx was found in
Germany in 1861. It share many
characteristics with both reptiles
(such as a long, bony tail and conical
teeth) and birds (such as feathers
and a wishbone).
Archaeopteryx suggest that birds
were evolved from animals like
reptiles.
Archaeopteryx

31. Dinosaurs:
 At the end of Triassic, Thecodontia, the early descendants of
Archosauria, gave rise the dinosaurs which means terrible lizards
 Subdivided into two orders depending on the structure of their
pelvis-Saurischia and Ornithischia.

33. Adaptive radiation in reptiles

35. Convergent evolution is the process whereby organisms not
closely related (not monophyletic), independently evolve
similar traits i.e. analogous structures as a result of having to
adapt to similar environments or ecological niches.
Divergent evolution is the evolutionary process in which a
single ancestral species evolves into different forms or new
species which occupy into different or isolated habitats or
environments

36. Convergent evolution Divergent evolution
Species are unrelated Species are closely related
Different ancestor Common ancestor
Converge to produce analogous
structures (common usage)
Diverge to produce homologous
structures (Same structure)
Species appearance becomes more
similar over time
Species appearance becomes more
different over time
e.g. wings in birds, insects and bats e.g. Pentadactyl limb structure