Although the Crocodyliformes have been around about 220 million years, the extant crocodilians of today have their roots in the Late Cretaceous, or around 65-70 million years ago. Twenty-three extant species have been described, and they all fall into three extant superfamilies.
General Anatomy:
(A) Dorsal view (B) Ventral view of skull (C) Lateral view (D) Jaw |
The bodies of extant crocodilians are adapted to a semiaquatic or aquatic life. Their tails are laterally compressed and make them efficient swimmers. The eyes are positioned on the top of the head, allowing the body to be concealed beneath the water while searching for prey.
Crocodilians have long, robust snouts, which are necessary for their strictly carnivorous diet. The actual shape of the snout can provide information about what type of diet the particular croc species consumes: a more slender snout indicates a fish diet, while a heavier snout would indicate a diet of food items which require more crushing power.
The skull of a crocodilian displays a good example of the diapsid condition. The subtemporal and supratemporal fenestra can easily be seen when looking at the skull.
The skull of a crocodilian displays a good example of the diapsid condition. The subtemporal and supratemporal fenestra can easily be seen when looking at the skull.
Left to Right: Gharial, Caiman, Alligator. Note the differences among the snouts. |
Crocodylian "penis" |
Crocs have internal fertilization and direct development, which takes place inside a cleidoic egg. The "penis" of a crocodilian extends from the anterior wall of the cloaca. By slightly dissecting into the cloaca, we can determine is a specimen is a male or female.
In addition, crocodilians exhibit parental care in the form of nest building and guarding. Females also help the young to hatch out of their eggs and continue to guard the new hatchlings until they are larger.
Crocodilian Superfamilies:
There are three Superfamilies within Crocodylia: Gavialoidea, Alligatoroidea, and Crocodyloidea.
Gavialoidea: Gavialidae
Gharial. Note the placement of the teeth and the presence of the boss. (1) |
Alligatoroidea: Alligatoridae
Caiman |
Crocodyloidea: Crocodylidae
Crocodylus. (2) |
Crocodilian Phylogeny:
The exact phylogeny of crocodilians is up for debate at the moment. Molecular data suggests that the family Alligatoridae is sister to all other crocodilians; however, morphological data points to Gavialis (from the family Gavilidae) as the sister to all other crocodilians.
Stay tuned for our next adventure in Biology of the Reptilia, when we take over the Cleveland Natural History Museum!
KG & MH
Citations:
(1) http://www.crocodilenepal.org/images/croc1.jpg
(2) http://www.worldofstock.com/slides/NAN6572.jpg
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