1. General Organisation and
Affinities
of
crocodilia

2. Introduction
The order crocodilia contain 25 species
which closely resemble each other.
Member of crocodilian ,appeared about 250
million year ago in early triassic period and
diversified during Mesozoic era.
All the species of alligators, caimans,
crocodiles, and gharial together are known as
“crocodilians.”

3. Distribution and Habit and Habitat
Crocodilians are found mainly in lowlands in the
tropic region .Found in south eastern ,united states .
They are aquatic animal lives in fresh water even in
sea water.
They are carnivores feed on fish, crustaceans,
molluscs ,birds and mammals.

4. External Features
Their body is long cylindrical and depressed and
head elongated into a flat snout with nostril at
the tip.
Limbs are pentadactyle,clawed and webbed.
Massive tail is laterally compressed forming a
powerful moving appendages.
Crocodilus porosus

5. Distinction Of Crocodylus,Alligator and
Gavialis
Variation in Head
shapes
Alligator
Crocodylus Gavialis

6. Integument and Exoskeleton
Skin is thick, leathery with Horney scutes,those
on back and belly rectangular and supported by
dermal bony plates.
Tail bears dorsally a crest of broad plates,
doubled in basal half but single in distal half.

7. Endoskeleton
Skull diapsid.
Quadrate immovable
No parental foramen.
A pseudopalate present.
Ribs bicephalous .Abdominal ribs present.

8. Digestive organ
The stomach is two chambered
one part is muscular known as Gizzard having
gastrolith.
Second part is smaller and glandular pyloric chamber.

9. Organ of Respiration
The lungs are well developed.
Lies in thorax serve by trachea.
Separated from abdominal cavity by a non
muscular
diaphragm .

10. Organ of Circulation
Completely four chambered heart.
Interventricular septum is completely divided
into right and left ventricle.
Presence of small
foramen Of panizza

11. Urinogenital system
Presence of metanepric kidney but crocodilian
do not have bladder.
Development and Reproduction
Sexes are seperated.
Males with mesian,erectile,grooved penis.
All crocodilians are oviparous.
Parental care present.
Usually 7to 95 eggs are laid depending on species.

12. Affinites
 Presence of abdominal ribs.
 Presence of pro-atlas.
 Fusion of caudal ribs with vertebrae.
Affinite with Dinosaurs
Diapsid condition of the skull.
Uncinated process of ribs .
Dentition is thecodont .
Absence of clavical.
Affinite with Chelonian
Fixed quadrates bone.
Male have penis
Affinite with Sphenodon

13. Affinites with Lacertilia
Pro-atlas present.
Chevron bone present.
Presence of pecten.
Copulatory organ present .
Affinites with Aves and Mammales
Lungs in pleural cavities seperated by a muscular diaphragm.
Completely four chambered heart.