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Evolution And History Of Crocodiles

Crocodiles are large semi-aquatic reptiles inhabiting the tropics in Africa, Asia, the Americas, and Australia. All current members of the order Crocodilia, including extinct taxa such as the gharial and false gharial (family Gavialidae), alligators, and caimans (family Alligatoridae), are frequently referred to as crocodiles.

The first crocodilians, reptiles, originally arose about 320 million years ago. The amphibians, a diverse group of animals at the time, were the immediate ancestors of reptiles. The gharial is easy to detect due to its short snout, whereas crocodiles and alligators have more subtle physical characteristics. These features could also be seen in the crocodile fossils.

Quick Facts

  • The size, shape, behavior, and ecology of different crocodile species vary somewhat.
  • Despite having a similar appearance, crocodiles, alligators, and gharials come from different biological families. 
  • The shape and musculature of their jaws, which tended to be much more prominent and powerful, set the first crocodiles apart from the first dinosaurs.
  • Crocodiles continue to change, and they do so more quickly than at any other point in their family's scaly history.
  • The name "crocodile" derives from the Ancient Greek "lizard" (krokódilos).
  • Crocodylians, which include alligators, crocodiles, and gharials today, had a common ancestor in the Cretaceous, some 95 million years ago.
Crocodile Fossil


The crocodilian shape has evolved to suit an amphibious lifestyle. The large, muscular tail and elongated body make it ideal for swimming quickly. The highest points on the head are the external apertures, eyes, and ear openings. Even when the remainder of the head and body are submerged, these vital sense organs are still above the water's surface. At the point of the muzzle, an elevated area has two nostril openings near one another. Membrane flaps may cover these apertures to keep water out when the animal dives. One can explore such features after getting a specimen from crocodile fossils.

The interior nostril openings, or choanae, are situated at the extreme posterior end of the palate and are connected to the outer nostril openings by a lengthy bone-enclosed nasal channel. A membrane flap in front of the choanae serves as the posterior closure of the mouth cavity. Because of this, the crocodile can breathe even with its mouth open when submerged. Crocodiles, like many nocturnal animals, have vertical, slit-shaped pupils in their eyes that close in intense light and broaden in the dark, regulating the amount of light that enters. The tapetum lucidum, located on the back wall of the eye, reflects incoming light, making the most of the limited amount of nighttime light. 

The nictitating membrane, a thin, translucent eyelid, can be dragged across the eye from the inner corner. At the same time, the lids are open, in addition to the protection offered by the upper and lower eyelids. Underwater, the sensitive ocular surface is shielded, yet some degree of vision is still available. In contrast to other modern reptiles, the crocodile's ears feature a moveable, external membrane flap that shields the ears from the water. The ability to smell is well-developed; the egg may even use it before it hatches.


Alligators and crocodiles have six different ways to move around. These include swimming, diving, belly-crawling, high-walking, galloping, and floating. They are well suited for swimming, where their motion seems effortless and flowing. But these crocodilians appear cumbersome and sluggish on land. The amount of air in a crocodile's lungs determines where it is in the water—above, below, or underwater. The crocodile can adjust its buoyancy by changing the amount of air in its lungs. To dive, for instance, a crocodile exhales air from its lungs, which causes its body to drop into the water. The "float," which can be either horizontal or vertical, is the standard crocodilian swimming stance.

Skin Pattern

Large, rectangular horny plates are organized consistently in longitudinal and transverse rows on the upper surfaces of the back and tail. A longitudinal ridge, or keel, can be found on most dorsal plates. Osteoderms, bony structures of the same size, are located beneath these plates. All species, except one, have this arrangement; the estuarine crocodile's bone plates are smaller. Scales with a regular pattern cover the entire underside of the crocodile; these scales are smaller than those on the top surface. These scales are rectangular, completely smooth, and hardly ever have any bone.

Caimans belonging to the genera Melanosuchus, Caiman, and Paleosuchus are an exception to this rule because they have bony surface plates on the lower side. The vaginal, anal, and urogenital openings are located in the cloaca, which extends lengthwise within the body. On the bottom of the body, an oval region covered in microscopic scales surrounds the cloaca. The attachment of the hind legs at the base of the tail is slightly posterior to the location of the cloacal vent. These features are visible in crocodile fossils, explaining the evaluation of crocodiles. 

Evolution And Taxonomy

There was an explosion of various reptile body forms between 320 and 220 million years ago; some were big, some were little, and some dominated the land surfaces while others dominated the sea. The "Age of Reptiles" had begun, and reptiles would live in abundance for the next 155 million years. Most known reptiles from that period appeared in the fossil record about 65 million years ago, when the group abruptly experienced mass extinction.

About 200 million years ago, the first distinctly recognizable crocodilian fossils were discovered (Suborders Protosuchia and Sphenosuchia). A terrestrial crocodilian appeared soon after the first archosaurs ("Ruling Reptiles") but before they underwent significant radiation (Orthosuchus). Before they began to colonize the seas, lakes, and swamps, all crocodilians were likely terrestrial for at least 20 million years. 

The Mesosuchians encompassed terrestrial and marine forms and were the largest group of early crocodilians. Flippers were used instead of feet by marine Mesosuchians, and their laterally compressed tails resembled those of sharks. However, specialized, predatory Mesosaurs lived on land and had long, serrated teeth. Although most Mesosuchians vanished 65 million years ago, a few persisted in Australia for about a million years before becoming extinct.

Therefore, two crocodiles with comparable skull forms might not be related. Instead, since they feed on prey and inhabit comparable habitats, distantly related crocodiles converge on the same skull designs, with various species repeating several skull types. 

History Of Life And Reproduction

Crocodiles have existed for 240 million years; they predated the earliest dinosaurs by 25 million years and the first birds and mammals by 100 million years. 230 million years ago, crocodiles could grow to 40 feet in length. About 200 million years ago, a mysterious calamity towards the close of the Triassic period wiped out the majority of crurotarsans. Dinosaurs gained control when their rivals drove from the area. Remains are still found in such areas in the form of crocodile fossil and other body parts. In the seas, enormous swimming predators like plesiosaurs had also evolved during the same period, leaving little place for outsiders. The crocodiles that persisted evolved into a variety of new forms, but eventually, they could only live in rivers, swamps, and marshes, where their descendants still exist today.

Crocodilians either build their nests in mounds or holes. They create a mound out of vegetation, usually made of sand, and place their eggs in the center, or they dig a hole and bury their eggs there. Only the remnant population of American crocodiles in Florida appears to employ mounds and holes; in all other nations, the species only nests in holes.  

Event Of Extinction

When habitat degradation became a problem, it made the recovery of those populations even more difficult for some species and regions where the crocodile populations had not yet recovered from the hunting of the early 1900s. For those, the residual populations are modest and dispersed over limited habitat patches. 

Due to habitat degradation, poaching, bycatch in fishing gear, and river damming, more than half of all crocodilians face extinction. If we lost these endangered species, we would lose the variety of ecological functions they play, with unknown and potentially disastrous ecological repercussions. 


Crocodiles have long captivated people throughout history with their amazing behavioral patterns. A crocodile replaces lost teeth as soon as possible. According to the San Diego Zoo, these reptiles can have 8,000 teeth removed throughout their lifetime. Crocs don't perspire. They open their mouths in a technique known as "mouth gaping," which is similar to panting, to stay cool. When someone apologizes dishonestly, they are said to be "crying crocodile tears."

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