This order consists of Crocodiles, Alligators, & Caimans, Gharials. Their distribution is world wide in tropics & sub tropic zones living in fresh water, brackish water & sometimes may even move to the sea. Only crocodiles are present in Sri Lanka. It includes two species which lives in estuarine & fresh water. They are modern representatives, adapted for a special type of amphibious life. Crocodiles are predators & superficially lizard like forms showing many differences. Crocodilians differ from all other reptiles in having certain advanced characteristics, such as
- thecodont teeth set in sockets
- lungs in pleural cavities
- muscular diaphragm, analogous to that of mammals
- a relatively complete bony palate
- simple but grooved copulatory organs in mails
- completely divided four chambered hear
Crocodiles have highly keratinized skin with thick rectangular scutes hinged by softer skin. Underlying these scutes are plates of dermal bones. The tail acts as the defensive & attacking organ. It’s strong & very powerful. Surface area of it is increased by the presence of the vertical spines. The tail is also flattened from side to side which helps them to swim. The limbs & the partly webbed feet help them when moving slowly in water as well as land.
Their morphology gives the ability to remain invisible in water with only the nostrils & eyes above the water level. This helps them to catch prey under water. Ears are covered by flaps of skin. The eyes are at the dorsal position. They have very sensitive hearing & eyesight. The long snout has a midline near the tip & provided with valves. The snout is triangular or rounded. Halves of the lower jaws are not fused up to the 8th tooth. The 4th tooth of the lower jaw fits in to a notch in the side of the upper jaw. To separate the food passage from the air passage, a second palate has developed in the internal nares far back to the throat region. This is an adaptation for keeping the mouth open under water & approach close to a prey to grasp it with its jaws & drag it under water. Some forms have divided nasal aperture. Nasal bone & snout are turned upwards from front.
Crocodiles are oviparous & eggs are buried under heaps of rubbish, so the decaying of vegetation heat helps it to hatch. The opening of cloaca is vertical & clitoris occurs in females.
Killing of crocodiles & trading in crocodile skins are banned in Sri Lanka under the Fauna Protection Ordinance.