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With all of the evidence from the previously mentioned gradual speciation, anatomy and physiology, embryology, and fossil record it can be said that crocodilians are very similar. Not only are modern crocodilians similar to other modern crocodilians, but they are also very similar to ancient crocodilians. At any point in history, crocodilians have showed tremendous similarities with each other . All of this evidence leads to the conclusion of decent with modification.

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The order of crocodilia has show stabilizing natural selection since the time of the dinosaurs. With immigration, adaptive radiation, divergent evolution, and gradual speciation all slowly changing crocodilia and limiting its resources and changing the environment that is beneficial, not everyone can survive. Stabilizing natural selection shows the benefits of being average.If a crocodile is too small then it will not need very much food but it could easily be preyed upon. If a crocodile is too big then it will not be preyed upon but if there is not very much food it will starve. Therefore the most average will survive the best.

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Physical Characteristics:
- Cold-blooded
- Sex is determined by the level of hormones in the egg that is determined by the temperature of the egg
- They are Diaspids
- They have a secondary palate
- Cerebral Cortex

Behavioral  Characteristics:
- Crocodiles are solitary organisms, spending most of their time alone or in small groups
- Territorial by nature protecting basking spots and nests
- Protect their young until they can take care of themselves
- The presences of the cerebral cortex makes the crocodile the most vocal type of reptile

Habitat Requirements
- An aquatic habitat because crocodiles have a semi-aquatic lifestyle
- Because crocodiles are cold blooded they need a warm habitat to maintain a healthy body temperature
- Sufficient amount of territory to sleep, hunt, and breed in

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Classification:
Kingdom - Animalia
Phylum - Chordata
Class - Reptilia
Order - Crocodilia
Family - Alligatordae
Genus - Alligator
Species -  A. mississippiensis

Habitat:
American Alligators live in wetland areas, such as swamps, in south eastern America. The American Alligator create alligator hole, which are small ponds that store water during the dry season. These alligator holes provide protection for birds because the predators of the birds will not enter the alligator holes.

Physical Characteristics
The upper jaws of the American Alligator overlap the lower jaws and the teeth of the lower jaws are contained in small holes in the upper jaw when the alligators mouth is closed. The average length of the American Alligator is 15 feet and the average weight is 999 pounds.

Behavioral Characteristics:
American Alligators use a variety of vocalizations to speak to other alligators, either declaring territory or to threaten other alligators. American Alligators are apex predators and their hunting patterns are determined by availability of food, age, and temperature. American Alligators are known for using branches and leaves to cover their heads to trick birds into landing and becoming prey.

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Classification:
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Crocodilia
Family: Crocodylidae
Genus: Crocodylus
Species: C. johnsoni

Habitat:
The Australian Freshwater Crocodile lives in western and northern Australia, living in wetlands, rivers, and streams. Many Freshwater Crocodiles live in Kakadu National Park because it is far away from the territory of the Saltwater Crocodiles.

Physical Characteristics:
Australian Freshwater Crocodiles are unexpectedly small comparatively to other crocodiles, only measuring to be around 10 feet at the longest but averaging at around 8 feet. The body color is light brown with darker bands on the body and tail which tend to be broken up near the neck. Some individuals possess distinct bands or speckling on the snout.

Behavioral Characteristics:
Like the American Alligator, the Australian Freshwater Crocodile lives in gator holes and provides care for its young until they can take care of themselves. The Australian Freshwater Crocodile rarely eats during the dry season but begins mating as the dry season begins.

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Classification:
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Crocodilia
Family: Gavialidae
Genus: Gavialis
Species: G. gangeticus

Habitat:

The Indian Gharial is found around India, Nepal and Pakistan. Only an estimated 235 Indian Gharial are left in the world. The majority of Indian Gharials live in rivers, tributaries, and National Parks. The Indian Gharial lives a mostly aquatic life.

Physical Characteristics:
Because the Indian Gharial spends most of its time in the water it has weak and short legs but has a very well developed tail used for swimming and attacking prey.Indian Gharial are unique because of their long slender snout. This is because they primarily eat fish.

Behavioral Characteristics:
Indian Gharial live in small groups and hunt both at night and during the day. They slide onto small islands in order to bask but spend most of their time thermoregulating in the water.

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By Looking at the chart of the three exemplary organisms of crocodilia, you can see how similar they actually are. The comparison of the American Alligator, Australian Freshwater Crocodile, and Indian Gharial shows that the three only have differences in the last three divisions of classification. Concluding from this how the different species can proved to be similar through Taxonomy.

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The Embryonic development of the American Crocodile, Australian Freshwater Crocodile and the Indian Gharial are very similar for the majority of the development, but begin to change near the end of development. Through the embryonic development the examples all develop limbs, eyes, and snout at the same time, but after the development of major characteristics the embryos become unique to their species. The first time this is apparent is in the development of the snout at 5 weeks. The teeth and shape of the snout are different throughout all of the examples in this embryonic stage. Although they develop differently the timing is still the same

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Crocodilia have been for the most part unchanged since the time of the dinosaurs but this does not mean that they are the same as they were millions of years ago. The comparison of fossils between extinct and living members of crocodilia can show how they have evolved. By comparing modern day and ancient crocodiles you will observe many differences in the shape, size, and structure of the skeleton. These changes can help explain what might have happened to cause the changes like the considerable decrease in size from the Dienosuchus to the American alligator because of the decrease in oxygen on Earth that allowed everything to grow exponentially.

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Permian 290 mya

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Cretaceous 112 mya

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Cretacious 80 mya

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Triassic 240 mya

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Jurassic 183 mya

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The chromosomes of crocodilia compared to the majority of all other chromosomes is unique because of the process in which the sex of a crocodile is determined. This process that is not well understood begins to show how evolution has occurred. The process might by at risk because of the climate changes that sway the ratio of male to female possibly making the process unable to be understood. The actual structure of the chromosomes show additional similarities in the species.

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The Chromosomal Structure of both the American Alligator and the Australian Freshwater Crocodile show additional similarities. The first similarity is the amount of chromosomes. Both examples have the same amount of chromosomes being a huge similarity. Secondly the size and shape of the chromosomes are similar.

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Anatomy:
The anatomy of crocodilia has stayed quite constant for the whole of its evolution, the main changes being in the skull. The skull of crocodilia has changed frequently throughout its evolution. Beginning with the Proterosuchidae, it is evident that the skull is unique. The Proterosuchidae has large nostrils and an upper jaw that is much longer than the lower jaw. The Pelagosaurus has a much narrower and longer snout, similar to the Indian Gharial. The Sarcosuchus has a wide skull but slender snout for its size. Finally, the Deinosuchs has a large, wide snout. The differences between all of these skulls shows how they evolved throughout time and adapted to their environment.

Physiology:
Crocodilia all have the same basic physical features as many other organisms. Having hind legs and forearms as well as a tail are common physical structures shared by many organisms. The use for these structures, however, may vary between organisms. The tail of an alligator is used to propel it through the water and jump out of the water in order to catch prey, while a monkey uses its tail to balance itself and help it swing through trees. The forearms of a crocodile are used to walk around on land and dig nests to lay eggs in. The forearms of a bird, however, are used to fly. The differences in the use of these structures show how organisms adapt to their environment.

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The differences between species of crocodilia have been a result of gradual speciation. The crocodilia have been alive since the dinosaurs and have not been drastically changed since then. Sticking to the same general shape, habitat and behavior. This can only be the result of gradual speciation. Over time their were small changes in the environment and they were slowly changed to better adapt to their environment but there were no major changes for millions of years. The Australian Saltwater Crocodile is a current example of gradual speciation. The Freshwater Crocodiles are slowly being pushed into saltier environments because of the loss of freshwater. This will make the Freshwater Crocodiles use their barely functioning salt glands. Slowly these glands will become more effective and the Freshwater Crocodile will no longer be freshwater.

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Because of the solitary nature of crocodilia, small groups or individuals are often left in a competition for territory and food. This causes the population to constantly be migrating in search for a better place to live because there is so much competition. It is too hard for a small group or individual to find a stable place to stay in and live so they are forced to move on and search for a place to live constantly. This creates stabilizing natural selection because the gene pool was already very diverse but no extreme was beneficial to evolution.

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Crocodilia have constantly been going through divergent evolution. Because of the constant competition for food and resources in the population of crocodilia, parts of the population are forced to break off and move to a new area with different resources and a new environment. When pushed to this new environment, the crocodilians are forced to adapt and become accustomed to their new environment. This process repeats over and over again as more changes occur. However this is a very slow process and explains why crocodilia have very little differences.

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Adaptive Radiation can be found throughout the history of crocodilia and can be proven with the small changes in different species in crocodilia. Because of the slow process of divergent evolution and gradual speciation, the crocodilia order remains, for the most part, unchanged. The small changes that do occur, however, are proof of adaptive radiation. The crocodilia order is constantly migrating because of competition for resources. When migrating, the species has to adapt to their new environment, and so you get the small changes between species of crocodilia. Examples include the slender snout of the Indian Gharial and the wide snout of the American Crocodile.