The Crocodiles

ByDr. Girish Chandra

CROCODILIA

(The Higher Reptiles)

 

(Dr. Girish Chandra)

 

            The crocodiles belong to the family Crocodylidae, while alligators and caimans are placed in family Alligatoridae. The crocodile has a very long, narrow, V-shaped snout, while the alligator’s snout is wider and U-shaped. Because of the wide snout of the alligator it packs more crushing power to eat prey like turtles that constitute part of its diet. The narrow crocodile snout, although still very powerful, is not really suited for prey like turtles but is very versatile for fish and mammalian prey.

 

            Another physical difference between the crocodile and the alligator is that the crocodile’s upper and lower jaws are nearly the same width, so the teeth are exposed all along the jaw line in an interlocking pattern, even when the mouth is closed. They also have a large 4th tooth on the lower jaw that fits in the depressions in the upper jaw just behind the nostrils. An alligator, on the other hand, has a wider upper jaw, so when its mouth is closed the teeth in the lower jaw fit into sockets of the upper jaw. Only the teeth of the upper jaw are exposed along the lower jaw line. Crocodiles have a lighter olive brown colour, while alligators appear blackish. Both crocodiles and alligators have dotted sensory pits along the upper and lower jaws that look almost like beard stubble. They detect slight changes in water pressure, which is believed to help the animals locate their prey. These sensory pits are called Dermal Pressure Receptors. In terms of nesting, crocodiles lay their eggs in mud or sand nests near brackish water, while alligators make their nests out of mounds of vegetation surrounding freshwater.

 

            The crocodile’s biting force is more than 5,000 pounds per square inch compared to just 335 pounds per square inch for a rottweiler, 400 pounds for a large great white shark and 800-1000 pounds for a hyena. The jaws are opened by a very weak set of muscles.

 

            The largest recorded crocodile was a giant saltwater crocodile that measured at 8.6 metres and weighed 1,352 kilograms was shot in Australia, Queensland in 1957. The largest living crocodile known is 7.1 metres long saltwater crocodile recorded in Orissa, India. It lives in Bhitarkanika Wildlife Sanctuary and in June 2006, was entered in the Guinness Book of World Records. Adult males can reach sizes of up to 6 or 7 metres but in general, males over 5 m in length are extremely rare. Females are smaller, and do not normally exceed 3 m, with 2.5 m being considered very large.

 

Family CROCODYLIDAE

 

Genus CROCODYLUS

 

Crocodylus acutus, American Crocodile, in estuaries in Southern Florida, northwest South America and the Carrinbean. 6 m long.

Crocodylus cataphractus, Slender-snouted Crocodile (studies in DNA and morphology suggest that this species may be more basal than Crocodylus, and therefore belongs in its own genus, Mecistops)

Crocodylus intermedius, Orinoco Crocodile, in Amazon River of South America.

Crocodylus johnsoni, Freshwater Crocodile of Northern Australia.

Crocodylus mindorensis, Philippines Crocodile.

Crocodylus moreletii, Morelet’s Crocodile or Mexican Crocodile.

Crocodylus niloticus, Nile Crocodile or African Crocodile, 7 m long.

Crocodylus novaeguineae, New Guinea Crocodile, also occurs in parts of Philippines.

Crocodylus palustris, Mugger or Indian Crocodile of India, Bangladesh and Sri Lanka.

Crocodylus porosus, Saltwater Crocodile or Estuarine Crocodile, Southern Asia to Australia. 7 m long.

Crocodylus rhombifer, Cuban Crocodile.

Crocodylus siamensis, Siamese Crocodile.

 

Genus OSTEOLAEMUS

 

            Osteolaemus means “bony throat”, derived from osteon=bone + laimos=throat, referring to the extensive bony plates found in the neck and belly.

 

Osteolaemus tetraspis, The Dwarf Crocodile. The species name tetraspis=four shields, refers to the cluster of four bony plates (nuchal scales) on the back of the neck.

 It has the following 2 subspecies:

 

O. tetraspis tetraspis, found in western Africa.

O. tetraspis osborni, found in Congo (formerly Zaire). This species was formerly known as Osteoblepharon osborni.

 

Family ALLIGATORIDAE

 

Genus ALLIGATOR

 

            Alligators differ from crocodiles principally in having wider and shorter heads, with more obtuse snouts; in having the fourth, enlarged tooth of the under jaw received, not into an external notch, but into a pit formed for it within the upper one; in lacking a jagged fringe which appears on the hind legs and feet of the crocodile; in having the toes of the hind feet webbed not more than half way to the tips; and an intolerance to salinity, alligators strongly preferring fresh water, while crocodiles can tolerate salt water due to specialized glands for filtering out salt. In general, crocodiles tend to be more dangerous to humans than alligators.

 

Chinese Alligator (Alligator sinensis)

 

            It is smaller, about 5 ft long. Found along the lower Yangtze River in the provinces of Jiangsu, Zhejiang, and Anhui. Unlike the American Alligator, the Chinese Alligator is fully armored; even the belly is armored, which is a feature of only a few crocodilians.

 

American Alligator (Alligator mississippiensis)

 

            The American alligator is a large, semi-aquatic, armoured reptile that is related to crocodiles. Their body alone ranges from 6 – 14 feet long. Almost black in colour, the it has prominent eyes and nostrils with coarse scales over the entire body. It has a large, long head with visible upper teeth along the edge of the jaws. Its front feet have 5 toes, while rear feet have 4 toes that are webbed. American alligators are found from the southern Virginia-North Carolina border, along the Atlantic coast to Florida and along the Gulf of Mexico as far west as the Rio Grande in Texas.

 

Genus PALEOSUCHUS

 

Cuvier’s Dwarf Caiman (Paleosuchus palpebrosus)

 

            Paleosuchus means “ancient crocodile”, derived from palaios (Greek for “ancient”) + soukhos (Greek for “crocodile”), referring to the taxonomy and age of the genus.  palpebrosus means “bony eyelid”, derived from palpebra (Latin for “eyelid” or palpebrals) + osus (Latin for “full of”), referring to the bony plates (palpebrals) on the upper eyelids.  Found in freshwater in Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Paraguay, Peru, Surinam, Venezuela.

 

Smooth-fronted Caiman (Paleosuchus trigonatus)

 

            Paleosuchus trigonatus is found in both the Amazon and Orinoco river basins, within the forested regions surrounding shallow streams. Their range covers a wide area in South America, from Peru in the west to French Guiana in the east (Ross,1989; Britton, 2001). This species is found in and around cool, fast-flowing forest streams and rivers, often near waterfalls or rapids. Males of this species will grow to a length ranging from 1.7 to 2.3m, while females generally peak at 1.4 meters.

 

Genus CAIMAN

 

            Five species of the genus Caiman, which differs from the alligator by the absence of a bony septum between the nostrils, and the ventral armour is composed of overlapping bony scutes, each of which is formed of two parts united by a suture.

Some authorities further divide this genus into three, splitting off the smooth-fronted caimans into a genus Paleosuchus and the Black Caiman into Melanosuchus. Caimans tend to be more agile and crocodile-like in their movements, and have longer, sharper teeth than alligators. Varies according to species. All have wide, flat heads with rounded noses. Eyeline ridge is slightly more pronounced than in the closely related American alligator, Alligator mississippiensis. When mouth is closed, only teeth from upper jaw are visible.

            They are found in Southern Mexico & the remainder of the Central American countries through South America to the northeastern portion of Argentina. Chile is the only South American nation which caimans to not inhabit. Estuaries, swamps, lakes, streams, rivers, floodplains, and the surrounding terrestrial environment

 

Yacare Caiman, Caiman yacare

Spectacled Caiman, Caiman crocodilus

Rio Apaporis Caiman, C. c. apaporiensis

Brown Caiman, C. c. fuscus

Broad-snouted Caiman, Caiman latirostris

 

Genus MELANOSUCHUS

 

Black Caiman (Melanosuchus niger), found in Amazon grows to 5-6 m length.

 

            Melanosuchus niger is often associated with steep banks alongside slow-moving freshwater rivers, lakes, wetlands, black water swamps, and seasonally flooded areas of the Amazon. The Black Caiman retains its distinctive skin markings into adulthood: they display grey or brown banding on the lower jaw, and display white or yellowish bands on the sides of the body. Fish, such as piranhas and catfish, account for a large part of the adult Black Caiman’s diet, as do molluscs.

 

Family GAVIALIDAE

 

            G. gangeticus is probably the only living species in the Family.  Fossil and morphological data on Tomistoma schlegelii (false gharial) show closest resemblance to Crocodylidae. But recent molecular data show closer resemblance to G. gangeticus, causing some authors to place it in family Gavialidae.

 

Genus GAVIALIS

 

Gavialis gangeticus Gmelin

            Gavialis has been derived from the Hindi word ghariyal that refers to the ghara (Hindi for “pot”), which is a swelling around the nostrils of mature males. The species name, gangeticus means “of the River Ganges”, where it inhabits. The species is found in India, Myanmar (possibly extirpated), Nepal, Pakistan (close to being extirpated). They are found within the river systems of the Brahmaputra (Bhutan & India), the Indus (Pakistan), the Ganges (India & Nepal), and the Mahanadi (India), with small populations in the Kaladan and the Irrawaddy in Burma.

            Characteristic features include, elongated, narrow snout, similar only to the closely related False gharial, (Tomistoma schlegelii). The snout shape varies with the age of the saurian. The snout becomes progressively thinner the older the gharial gets. The bulbous growth on the tip of the male’s snout is called a ‘ghara’ (after the Indian word meaning ‘pot’), present in mature individuals. The bulbous growth is used for various activities, it is used to generate a resonant hum during vocalization, it acts as a visual lure for attracting females and it is also used to make bubbles which have been associated with the mating rituals of the species. The gharial has 27 to 29 upper and 25 or 26 lower teeth on each side.

Genus TOMISTOMA

Tomistoma schlegelii Muller

            Tomistoma means “sharp mouth”, referring to the slender shape of the jaws. schlegelii is named after the Dutch zoologist H. Schlegel (1804-1884) who is credited with its discovery. It is commonly called false Gharial. It is found in Indonesia (Sumatra, Kalimantan, Java, possibly Sulawesi), Malaysia (Malay Peninsula, Borneo) and possibly Vietnam. It occurs in freshwater lakes, rivers & swamps, where it is reported to make burrows and seems to prefer vegetative cover, floating mats of vegetation and slow-moving waterways. Characteristic features include, slender snout, not dissimilar to the gharial (Gavialis gangeticus), from which it derives its common name. Generally the colour is dark chocolate brown as a juvenile, with black banding on tail and body and dark blotches on jaws. Much of the juvenile colouration is retained in the adult. Maximum size attained is up to 5m (16 feet), although this species may potentially grow larger.

 

Reptiles (Classifying Animals)


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By (author): Sarah Wilkes

The Classifying Animals series welcomes readers to the world of classification, in which about 2 million different organisms have been identified and sorted into groups. This appealing and attractive book looks at the class of reptiles, and the orders, families and species within it. Find out about the characteristics that distinguish the reptiles in different groups and compare the differences in their life cycles. Discover the various ways in which reptiles have adapted to life in different climates and habitats on land and in water.
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