If evolution has occurred, then the features of modern crocodiles developed over time. Modern crocodiles would not have always existed and other lineages may have developed traits which make them similar to crocodiles. The variation which occurs within a lineage could be significant.


If the creationism model is correct, then modern crocodiles have always existed. If there are multiple "kinds" of crocodile, then their classification should be easy given that each kind is completely unrelated to every other. Signficant variation are not expected within a kind.


If intelligent design is correct, then it should not be possible to evolve the adaptations of modern crocodiles over a series of steps. These adaptations should appear in an "all-or-none" fashion. If crocodilian design is truly intelligent, it should not need continual reworking to adapt separate lineages for survival. It is unexpected that similar changes would have to be independently introduced into ancestral design.

There is not one "design" for a crocodile-like body plan. The early archosaurs were somewhat similar to crocodiles.


Unrelated groups, such as phytosaurs, champosaurs, and (to a lesser degree) some lizards and the theropod dinosaur Baryonx developed a crocodile-like form.
Dracocena paragauyensis


The crocodilian body plan does not seem to have been "designed" for any one specific lifestyle.
While most modern crocodiles have more of a sprawling gait (although they can hold their bodies erect when they run), the earliest crocodiles walked erect.

Some possessed very gracile bodies.
Grasilisuchus, the earliest known crocodile, was a bipedal archosaur about 30 cm long.


Some of the selecosuchians of the Upper Cretaceous were probably fully terrestrial. Different groups of crocodiles became marine including the teleosaurs of the Late Triassic, thalattosauchians of the Early Jurassic, pholidosaurs of the Late Jurassic, and the dryosaurs of the Late Cretaceous. Not all developed equivalent levels of adaptations for aquatic life. For example, thalattosuchians were much more modified than were teleosaurs, which were more modified for aquatic life than pholidosaurs (Iordansky, 1973; Romer, 1956).
marine crocodiles
While some crocodilians (such as the modern gharial) seem to be highly specialized to preying on fish with their long, narrow jaws and fine teeth, similar adaptations have evolved in other groups including mesosuchians, Permian mesosaurs, Triassic phytosaurs, and Mesozoic through Tertiary champosaurs. Fossil gharials are known which possessed a more typical body plan (Iordansky, 1973).. Other modern crocodiles which feed on fish (such as the African slender-snouted crocodile, the Australian freshwater crocodile, and the false gharial) may also possess narrow snouts (Halliday, 1987).

Reptiles not closely related to dinosaurs, such as champosaurs and phytosaurs, also evolved slender snouts.


Two different lineages of crocodilians (a Tertiary alligator and an alligator-like eusuchian of the Cretaceous) developed elongated "duck-bills" which may have been adaptations for mud feeding.
In gavials and some marine mesosuchians, the nasal bones were reduced and no longer contacted the premaxillary bone (Iordansky, 1973; Romer, 1956). Teeth have varied in crocodilians. Terrestrial family Goniopholidae had blunt teeth for crushing. Libycosuchus almost toothless. Members of Barusuchidae had fewer teeth and they were almost tusklike (Neil, 1971)

Many other modifications evolved within crocodile groups. Thalattosaur limbs were modified into paddles and the tails formed prominent fins. A family of elongate sea crocodiles Metriorhynchidae had more paddle like limbs and occurred in the deeper ocean Notosuchians possessed a very short snout. Ceratosuchus horned alligator with two blunt horns over eye; from Paleocene of Colorado. The amplification of ancestral osteoderms to include bony eyelids occurred several times in crocodile lineages and as a result, crocodiles have varied in the amount of dermal armor they possessed. The position of the eyes was modified in several crocodilian lineages. (Iordansky, 1973; Neil, 1971; Romer, 1956).


Although the hard palate of mammals is part of the complex suite of characters needed for endothermy and the hard palate of crocodiles is a component of the design which allows for feeding without the risk of drowning, fossil evidence shows how both these structures developed over time.The elongated hard palate was variable in crocodilians and its most advanced state evolved gradually. The internal naris was originally bounded by the maxillary bones in protosuchians, later by the palatine bones in mesosuchians and their relatives, and finally the pterygoid bones in advanced eusuchians. As a result, over time the hard palate lengthened and the internal nares moved farther posteriorly (Iordansky, 1973).
Size varied significantly in crocodiles. Many of the earliest crocodiles were small, measuring a meter or less. Species of the family Theriosuchidae could measure less than an meter and some members of Atoposauridae under a foot long (Neil, 1971; Romer, 1956). Among mesosuchians, Deinosuchus measured 17m and had a head which measured 2 meters.


Among eusuchians, Sarcosuchus and a Tertiary gavial measured 13 to 17 meters. Stomatosuchus had a head which measured 2 meters. Purussaurus, known from the Amazon 8 million years ago, stood 8 feet tall, measured 39 feet long and weighed 10-12,000 kg.