There are 23 species of crocodilians classified into three families: crocodiles, alligators and caimans, and gharials. Crocodiles have long pointed snouts with the fourth lower tooth exposed, while alligators and caimans have broad, rounded snouts with the fourth lower tooth hidden. Gharials have extremely long, thin snouts lined with needle-like teeth adapted for catching fish.

1. Order Crocodilia

2. Order Crocodilia
There are 23 species in three families
A.Crocodiles

3. Order Crocodilia
There are 23 species in three families
A.Crocodiles
1.long pointed snout
2.4th
lower tooth is exposed

4. Order Crocodilia
There are 23 species in Three families
A.CrocodilesCrocodiles
1.long pointed snoutlong pointed snout
2.44thth
lower tooth is exposedlower tooth is exposed
B. Alligators and Caimans
1. broad, rounded snout
2. 4th
lower tooth is hidden

5. Order Crocodilia
There are 23 species in three families
CrocodilesCrocodiles
1.long pointed snoutlong pointed snout
2.44thth
lower tooth is exposedlower tooth is exposed
B. Alligators and CaimansAlligators and Caimans
1. broad, rounded snout1. broad, rounded snout
2. 42. 4thth
lower tooth is hiddenlower tooth is hidden
C. Gharials – long, thin snout lined with
needle-like teeth – adapted to catching fish.

7. Alligator

9. Gharial

10. Gharial
Convergent evolution with
Ichthyosaurs, Gars, and
Dolphins.

11. Gharial
Convergent evolution with
Ichthyosaurs, Gars, and
Dolphins. All have narrow
snouts lined with needle-
like teeth, but are
unrelated to each other.

12. Gharial
Convergent evolution with
Ichthyosaurs, Gars, and
Dolphins. All have narrow
snouts lined with needle-
like teeth, but are
unrelated to each other.
They evolved this trait
independently.

14. Crocodile

16. The position of all crocodilians’ eyes and
nostrils allow it to see above the water and
breathe while its entire body is submerged.

17. The ears are also positioned above the surface
of the water.

22. Crocodilians are the closest living ancestors to
birds.

23. Crocodilians are the closest living ancestors to
birds. There a several similar characterisitics
between the biology of the two.

24. Crocodilians are the closest living ancestors to
birds. There a several similar characterisitics
between the biology of the two.
1. Both have a four chambered heart.

25. Crocodilians are the closest living ancestors to
birds. There a several similar characterisitics
between the biology of the two.
1. Both have a four chambered heart.
2. Both deposit their eggs in nests.

26. Crocodilians are the closest living ancestors to
birds. There a several similar characterisitics
between the biology of the two.
1. Both have a four chambered heart.
2. Both deposit their eggs in nests.
3. Both provide extensive care for their young.

27. Most crocodiles dig nests in sandy river
shores where the sun warms the eggs
inside.

28. Most crocodiles dig nests in sandy river
shores where the sun warms the eggs
inside.
Alligators and Caimans build nests of mud
and vegetation.

29. Most crocodiles dig nests in sandy river
shores where the sun warms the eggs
inside.
Alligators and Caimans build nests of mud
and vegetation. Females climb onto the
nest and urinate on it to promote
decomposition of the vegetation.

30. Most crocodiles dig nests in sandy river
shores where the sun warms the eggs
inside.
Alligators and Caimans build nests of mud
and vegetation. Females climb onto the
nest and urinate on it to promote
decomposition of the vegetation.
Decomposition generates heat which
warms the eggs.

31. Gharials also nest in the sand along the shoreline
of the rivers in which they live.

32. Crocodilians range in size from five
feet; the Gold Dust Caiman of South
America, to 27 feet; the Saltwater
Crocodile or Indo-Pacific Crocodile.