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 Crocodiles (Crocodylia) are much closer related to birds than to other reptiles or amphibians. Their existence mounts back to the Triasic age, i.e. some 230 million years ago. Their maximum diversification took place during the Cretacic to the Cenozoic era. Since this last era the crocodile order started to decline. Thus from the 14 families that are known thanks to fossil records only 3 families remain nowadays: the crocodilidos (genus Crocodylus, Osteolaemus and Tomistoma) the alligators (genus Melanosuchus, Alligator, Paleosuchus and Caiman) and the gaviálidos (genus Gavialis).
Up to today 23 species have survived. Three of these are found in Mexican territory: the swamp crocodile (Crocodylus moreletii), the caiman (Caiman crocodilus chiapasius , Common o Dusky Caiman) and the river crocodile (Crocodylus acutus, American Crocodile). What has been most pointed out, at least towards the end of the 19 th century, has been the existence of the Northamerican alligator (Alligator mississippiensis ) in the northern zone of Tamaulipas, specifically around the mouth of the Rio Bravo river.
Banderas Bay is only inhabited by the river crocodile which is the largest of the 3 species that dwell in our country. It can measure up to a length of between 5 and 7 meters , however the biggest observed specimen reaches around 4 meters .
 Its body is covered by plates or shields with highly elevated keels. They have a notably pointed and long muzzle, in which the 4 th tooth of the jaw is always visible even when the mouth is kept closed. In addition the muzzle has a subtle protuberance in front of the eyes. Its general coloring is a pale grey with some greenish or yellowish tint.
Its back legs are clapped (its toes are united by interdigital membranes and by the way the back legs only have 4 toes), a feature that is used in order to change direction while swimming, given that the propulsion is generated by its tail. The nasal orifices, located in the upper part of the muzzle, remain air-tight closed thanks to a valve.
At the moment of immersion, which lasts several minutes (up to 1 hour approximately), the crocodile closes the valves of the nasal orifices, plugs the eardrums with the skin folding and the eyes are protected by their transparent eyelids. There is no sexual dimorphism in the specie. At the base of the tail you can see the rump which is longitudinal, contrary to what ocurres in other reptiles.
The females place their eggs in hollow-out holes in the sand or in mud mixed with fallen (up to 60 eggs per nest) which upon fermenting contributes to the incubation as a consequence of the rising of the temperature which is the determining factor for the sex in the organisms that develop inside the eggs (normally 28°C to 33°C are necessary for the eggs to be fertile, temperatures from 28°C to 31°C and from 33°C to 34°C produce females, temperatures from 31°C to 33°C produce males). It has been observed that this crocodile digs several false or trial nests close to the definite one and it is believed that the same place is used for repeated occasions. The adults, especially the females, develop a maternal caring behavior in order to protect and watch over the nest as well as to carry the offspring in their muzzle to the water.
 It lives in the estuaries and rivers; however it may also occupy water areas in golf courses and urban areas. Sometimes it is seen ploughing the seawaters or sunbathing on the beach. It is the only American crocodile with an ample distribution, since it is found from southern Florida to the Caribbean Islands . On Mexico 's west coast it usually lives starting at the southern half of Veracruz up to Quintana Roo. On the same Atlantic Coast it is found from Belize as far as Venezuela and Colombia . On the Mexican Pacific coast it is located from the Fuerte river in the state of Sinaloa up to the Suchiate river in the state of Chiapas . Likewise, it penetrates into the country up to 110 km from the coast through the basin of the Grijalva and Usumacinta rivers.
They are carnivorous predators. The young individuals consume huge quantities of insects and others in vertebras: the adults hunt amphibians, birds, big crustaceans, mammals and swimming they chase fish in order to catch it.
I will speak in general about the other 2 species of crocodiles that live in the country: the swamp crocodile and the caiman. The size of the first one does not exceed a length of 3 meters . It is a smaller and less audacious species than the river crocodile. Its color is brown with yellowish spots. Its muzzle is somewhat shorter and broader than that of the river crocodile. In addition its eyes are bigger and bulging. It is distributed from the center of Tamaulipas to the peninsula of Yucatan and the interior of Chiapas , Belize and the Peten region in Guatemala . It feeds on fish, frogs, birds and small mammals; however its chief attribute is that it dedicates time to the nest's caretaking.
With regard to the caiman, it is the smallest species of the crocodiles that inhabit the country, reaching a length of 2 meters . Its color is yellow or dark with numerous black spots. The morphological characteristics coincide with those of the other 2 crocodiles, with the exception that their muzzle is shorter and broader and they also have a kind of horn over their eyes. For that reason it is also called the caiman of the eye-glasses. The teeth of the upper jaw are not visible when the animal closes its muzzle, except for the individual adults since their 4 th tooth usually perforates the border of the upper jaw. It lives in the rivers and swamps of Oaxaca and Chiapas . In contrast to the other 2 species, both parents of this specie take care of the nest.
All three species are protected by the Mexican authorities. In addition public and private institutions in the whole country investigate their natural population, protecting them and breeding them in captivity.
Prof. Fabio Cupul
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