Crocodile

CROCODYLIA

Our planet is home to 24 species of crocodiles, to be found in the Americas, Africa, Australia and Asia. They are the largest reptiles on earth today and their size varies from 1.50 meters to over 6 meters . Thick scales protect their skin. They are carnivorous and water-dependent. Their strong jaws can stand up to 1350 pounds of pressure per cm2, their conical teeth being  used to puncture and retain prey. Crocodiles lay eggs, that is they are oviparous and are the only reptiles to emit a range of sounds that permits them to communicate with one another. Throughout history crocodiles have generated both fascination  and fear.

SENSES

Crocodiles are well adapted to aquatic environments: their nostrils, ears and eyes are grouped together at the top of the skull. They can therefore remain still on the lookout in the water, almost invisible but still fully alert. Their eyes are able to detect color and are covered by three eyelids. They have good night vision, but, strangely, have relatively poor vision underwater. A transparent lid protects the eye of the crocodile while underwater and a muscle hermetically seals the nostrils. The ears, which are located behind the eyes, are well protected by a large scale. The senses of hearing and smell are also well developed in crocodiles.

SUNBATHING

Crocodiles greatly appreciate warm temperatures. The warmth enables them to store energy, however if temperatures exceed 35C, they seek refreshment in the water or in the shade. Another way of regulating their body temperature is by holding their mouth open. Temperature is especially important for crocodiles. Temperatures ranging from between 27 and 33 degrees Celsius promote good digestion, faster growth and infection-free healing if they are injured. Conversely extremely hot (42C) or cold (5C) conditions may lead to death.

MOVEMENT

Crocodiles are amphibian animals and above all excellent swimmers. They flatten out their body and legs and use their powerful tails to “slide ” into the water. Their webbed hind legs allow them to stabilize themselves, change direction or to slow down in the water. However, on land, they move at an average speed of only 3 km/h and get tired very quickly. Some species however can reach top speeds of about 18 km/h but only over very short distances.

COMMUNICATION

They are the only reptiles that emit a range of sounds enabling communication between the members of the species: the young call their mothers, some grumble when they cut across each other. Adults are very sensitive and react aggressively to distress calls from a newborn. During courtship, alligators emit a low intensity cry, audible over several meters and resembling the sound of a cough. Most often it is possible to observe them communicating through jaw clapping. Both vocalizations and posture express an individual’s social status. For example, a crocodile swimming on the surface of the water shows off his dominance over weaker crocodiles.

REPRODUCTION

The females are the ones that initiate courtship, not hesitating to mate with several males. Mating always takes place in the water. It is possible then to observe many courtship rituals such as vocalizations, swimming in a circle, straddling, rubbing heads and producing bubbles. They are oviparous and females lay their eggs in the sand or in a mounded nest made from plant material. The number of eggs laid by a female varies between species but ranges from 10 to 90. Females do not cover the eggs but stay near them in order to protect them. The eggs incubate at temperatures of between 27ºC and 34ºC. The incubation period is also species-dependent and ranges from 60 to 100 days. The hatchlings  measure 20-30 cm and weigh 50-80 g. It is known today that the incubation temperature influences the determination of the sex of future crocodilian offspring (For example in alligators and caimans, cold temperatures result in a greater percentage of females). Eggs and hatchlings are often predated upon, even by other crocodilians.

Small crocodiles in the egg have a protuberance at the end of their jaws, which allows them to break the very solid egg shell. Sometimes, when the first egg is laid, the protuberance has not calcified, and the little crocodile consequently dies of suffocation in its egg.

ALLIGATORIDAE

Alligators and caimans are species of crocodilians making up the family Alligatoridae. Today, there are only two species of true alligators; A. mississippiensis in the southeastern United States and small A. sinensis in the Yangtze River in China. The name “alligatoridae” is derived from the Spanish word “lagarto”, which means “the lizard”. In Central and South America, the alligator family is represented by five species of caiman, which differs from the alligator by the absence of a bony septum between the nostrils, and the ventral amour, which is composed of overlapping bony scutes. Caimans tend to be more agile and crocodile-like in their movements, and have longer, sharper teeth than alligators.

CROCODYLIDAE

Crocodiles are aquatic reptiles of the order  of  aquatic  crocodilians. They belong to the family of crocodilians and  live in much of tropical Africa but rarely in Asia, the Americas or Australia. They tend to inhabit  slow-moving rivers and feed on a wide variety  of  both living and dead mammals  and  fish. Some  species,  especially  the  Saltwater crocodile of Australia and  some Pacific  islands, on occasions venture out  far into the sea.

GAVIALIDAE

The family Gavialidae was  designated by the British military physician and zoologist, Andrew Adams  (1827-1882).  This  family  includes  only  one  genus with a single extant species, the Ganges gavial, Gavialis  gangeticus. Formerly considered to belong to the same genus, the False gharial (or Schlegel gharial) is  now  included  in  the list of Crocodylidae under the scientific name of Tomistoma schlegelii. There are still doubts concerning its systematic position.

The Crocodilians of the world

The family of crocodilians encompasses 3 genera and 24 species

§  Crocodylidae

o   Crocodylus acutus — crocodile américain.

o   Crocodylus cataphractus — faux-gavial d’Afrique ou crocodile à nuque cuirassée.

o   Crocodylus intermedius — crocodile de l’Orénoque.

o   Crocodylus johnstoni — crocodile de Johnston.

o   Crocodylus mindorensis — crocodile des Philippines.

o   Crocodylus moreletii — crocodile de Morelet ou crocodile d’Amérique centrale.

o   Crocodylus niloticus — crocodile du Nil.

o   Crocodylus suchus — crocodile du Sahara.

o   Crocodylus novaeguineae — crocodile de Nouvelle-Guinée.

o   Crocodylus palustris — crocodile des marais.

o   Crocodylus porosus — crocodile à double crête ou crocodile de mer.

o   Crocodylus rhombifer — crocodile de Cuba.

o   Crocodylus siamensis — crocodile du Siam.

o   Osteolaemus tetraspis — crocodile nain ou crocodile à front large

§  Alligatoridae

o   Alligator sinensis — alligator de Chine.

o   Alligator mississipiensis — alligator américain

o   Caïman crocodilus — Caïman à lunettes

o   Caiman yacaré — Caïman yacaré

o   Caiman latirostris — Caïman à large museau

o   Melanosuchus niger — Caïman noir

o   Paleosuchus palpebrosus — Caïman nain de Cuvier

o   Paleosuchus trigonatus — Caïman de Schneider

§  Gavialidae

o   Gavialis gangeticus — gavial du Gange

o   Tomistoma schlegelii — faux-gavial de Malaisie.