Crocodiles and False Gharials (Crocodylidae)
Crocodiles and false gharials
Medium-sized to very large, egg-laying, aquatic reptiles characterized by well-toothed jaws and dorsal armor
5–20 ft (1.5–6.1 m) total length
Number of genera, species
3 genera; 14 species
Marshes, rivers, streams, lakes, and creeks
Critically Endangered: 3 species; Endangered: 2 species; Vulnerable: 3 species; Lower Risk/Conservation Dependent: 1 species; Data Deficient: 1 species
North and South America, Africa, Asia, and Australia
Evolution and systematics
Centers of abundance for the Crocodylidae are South America (four species), and the Indo-Pacific region (six species), although the family is postulated to have radiated from Africa in the Miocene epoch. Studies on the physiology of crocodiles have revealed that all species are able to concentrate and excrete salt, and this feature may well have aided in further speciation via transoceanic migrations. Some adaptations for continued survival of the Crocodylidae are the position of the eyes and nostrils, parental care, and their cost-effective metabolisms, but they are capable of immense speed on land or in water when necessary. Morphological and molecular data support a close relationship between Crocodylus and Osteolaemus. In addition, the Indo-Pacific crocodilians (Crocodylus palustris, C. porosus, C. siamensis, C. novaeguineae, C. mindorensis, and C. johnstonii) are closely related. In the past, subspecies status has been proposed for both Crocodylus palustris and Crocodylus niloticus, but these were not recognized as of 2002. The addition of a new species to the family Crocodylidae, the Borneo crocodile (Crocodylus raninus,), has also not been recognized scientifically, pending further investigation. The New World species (Crocodylus acutus, C. intermedius, C. moreletii, and C. rhombifer) are a monophylectic assemblage, that is, they share a common ancestor. Two subfamilies are recognized: Crocodylinae, containing two genera and 12 species; and Tomistominae, containing one genus and two species.
Crocodiles range from the small (6.2 ft [1.9 m] total length) West African dwarf crocodile (Osteolaemus tetraspis) to the huge (20 ft [6.1 m] total length) saltwater crocodile (Crocodylus porosus). Crocodiles are characterized by smaller, weak front limbs and strong hind limbs with webbed toes. Dorsal scales backed by osteoderms form heavy armor plating on neck and back. All crocodiles are elongate with snout-vent length almost equal to tail length. The tail is strongly muscled and flattened for swimming. Other adaptations for aquatic life include nostril and ear valves, a nictitating membrane to cover the eye, and a glottal valve in the throat. Crocodiles have effective visual, auditory, and olfactory systems. Crocodile teeth are replaced throughout life. Crocodiles can live for 70–80 years.
Crocodiles are found in the tropical regions of the world, although two species, the American crocodile (Crocodylus acutus) and the mugger crocodile (Crocodylus palustris) also occur in the subtropics. There are four species in the Americas, three in Africa, and seven in the Asia and Pacific region.
Although some species of crocodiles, such as the mugger crocodile and Nile crocodile (Crocodylus niloticus,) are highly adaptable and can live well in a variety of aquatic habitats, others such as the Malayan gharial (Tomistoma schlegelii) and the West African dwarf crocodile are restricted to forested, swampy areas. Deep water is a prime requisite for safety and security from drought, but some species live in places where the water dries up annually. In these habitats, crocodiles excavate deep tunnels to wait out inhospitable weather conditions. Crocodiles have found niches in habitats including hill
streams, large rivers, marshes, ponds, lakes, canals, reservoirs, as well as saline habitats such as mangrove creeks and saltpans.
Crocodiles are mainly nocturnal hunters and scavengers. They raise their body temperatures by hauling themselves out of the water and basking in the sun, usually both morning and evening. Crocodiles often appear torpid while they are in fact in a state of readiness to either flee or attack. Crocodiles are variably vocal. Adult males may bellow to establish dominance. All size classes will growl and hiss when intimidated. Hatchlings grunt to each other and will squawk loudly if caught. There is evidence that they also communicate via ultrasound.
Feeding ecology and diet
Crocodiles are opportunistic feeders and their diet includes a huge range of both invertebrates and vertebrates. The young are agile and will jump to catch dragonflies and flying termites. The bulk of their diet is insects and spiders. As the young grow, they prey on crabs, fish, frogs, reptiles, birds, and mammals. Crocodiles are active hunters that stalk prey both above and below water. Most species eat carrion, even leaving the safety of the water to feed on a carcass. All species have teeth and jaws designed for seizing, tearing, and crushing rather than chewing. Some species, like the Malayan gharial, Johnstone's crocodile (Crocodylus johnstonii), and African slender-snouted crocodile (Crocodylus cataphractus) have narrow jaws and very sharp teeth specially adapted to catch fish. Sensory pores in and around the mouth help crocodiles find prey under water. Several species of crocodiles have been seen to herd fish to shore with their bodies, sometimes communally. Crocodiles play a vital role at the apex (top) of the aquatic food chain. They control predators on commercially important fishes and keep the habitat clean as part-time scavengers.
Crocodiles are territorial. Males are larger than females and will defend territories and compete for mates. Males mate with as many females as possible during the fixed breeding seasons. Crocodiles use a variety of social signals, especially at mating time. These include jawslaps, roaring, dominance, and subordination displays. Females initiate courtship in some species.
All crocodiles lay eggs. Females lay their eggs 40–70 days after mating. The incubation period depends on nest temperature
and is typically 60–90 days. The sex of the developing embryo is determined by temperature; in general, higher temperatures produce males and lower temperatures result in females.
Five species of crocodiles dig holes in the sand, earth, or gravel embankments above the high-water line to lay their eggs. The hole is L-shaped and as deep as the length of the female's hind limbs, which are heavily clawed for digging. The eggs emerge covered with a lubricating mucous, which cushions the brittle shells from cracking as they fall into the nest hole. These species are dry-season nesters whose young hatch with the coming of the rains when many small prey items also emerge.
Nine species of crocodiles are mound nesters. The female gathers together a heap of vegetation, soil, and compost using her legs and jaws. She compacts the mound by crawling over it and then excavates a hole on the top in which to lay her eggs. Mound nesters lay their eggs at the start of the wet season, and the young hatch when the water is highest, a time when there is plenty of small prey.
Female crocodiles (and sometimes males) generally stay near their nest during incubation, repeatedly visiting the site, especially when hatching time approaches. When ready to hatch, the young call with quacking grunts and the parent releases the young from the nest and carries them to the water. Crèche formation is essential for hatchling survival and sometimes both parents guard the young for several weeks or more until they disperse. Adult crocodiles are conditioned to respond to distress calls of the young. Despite parental care, mortality in hatchling crocodiles is generally over 90% due to predators like fishes, crabs, snakes, monitor lizards, raptors, large wading birds, mongooses, foxes, and jackals.
Most of the 14 species of crocodiles have been greatly reduced in numbers due to overhunting and habitat loss. The fact that some of the larger species such as the saltwater crocodile and Nile crocodile sometimes kill domestic animals and humans has contributed to the unpopularity of these predators in many parts of the world. The hunting of crocodiles for skins was a major reason for the decline of most species. Now, however, sustainable-use programs are responsible for the recovery and continued survival of several species, notably the Nile crocodile, saltwater crocodile, and New Guinea crocodile (C. novaeguineae). In the 1980s the world trade in crocodile skins was close to 500,000 per year, most from the wild. In 1999 the annual trade was about 398,000, the majority from managed wild populations and farms such as the Samut Prakan Crocodile Farm in Thailand and Mainland Holdings in Papua New Guinea, which together have over 80,000 crocodiles. In general, countries that harvest crocodiles from the wild and on farms on a sustainable basis are successfully protecting their species.
The 2002 IUCN Red List includes 10 species of crocodiles: 3 are Critically Endangered, 2 are Endangered, 3 are Vulnerable, 1 is Lower Risk/Conservation Dependent, and 1 is Data Deficient.
Significance to humans
Crocodiles have long figured in religious beliefs, myths, and folktales around the world. It is not surprising that such huge, ancient looking, and dangerous reptiles should inspire fear, respect, and awe from the human race. Nile crocodiles were mummified and buried with the pharaohs of Egypt. The Hindu river goddess, Ma Ganga, sometimes sits astride a mugger crocodile, and more than one New Guinean indigenous creation myth features the saltwater crocodile. At the same time, indigenous people all over the world have considered crocodiles a wonderful source of tasty eggs and meat. The real challenge to the survival of this ancient reptile's lineage started in the later nineteenth century when the slaughter for skin began. Crocodile leather demand reached its peak
in the mid-twentieth century, when over a million skins were being traded per year.
Conservation efforts with sustainable use at the forefront started in the early 1970s and quickly reversed the fate of several endangered crocodiles. Today, up to half a million crocodile skins are traded internationally each year, more than half from farms and ranches.
List of SpeciesAmerican crocodile
Crocodylus acutus Cuvier, 1807 Antilles.
other common names
English: American saltwater crocodile; French: Crocodile amèricain; German: Mittelamerikanisches Krokodil; Spanish: Cocodrilo americano.
The American crocodile has a somewhat narrow snout and slender build. Adults average 10–11 ft (3–3.5 m) in length, but males can grow to 20 ft (6 m). Females average 8–10 ft (2.5–3 m). A distinctive hump on the skull of adults just in front of the eyes is diagnostic of the species. Yellowish to gray with dark cross-marks when young; older American crocodiles often lose the bands and are a uniform sandy color or dark brown. The underside is white.
Coasts along mangroves, estuaries, large rivers, and sometimes inland lakes.
This is a social animal, coexisting in large groups. The American crocodile has a high tolerance to salt water and excretes excess salt from lingual glands on the tongue.
feeding ecology and diet
This species eats large fish, frogs, turtles, birds, and small mammals. In some places they take livestock, and there are occasional reports of very large individuals attacking humans. Hatchlings feed on crabs, insects, small frogs, tadpoles, and fish.
Although usually a hole nester, the female American crocodile may make a mound nest of sand, vegetation, and compost. The breeding season is late April to early May in Florida. In South America the breeding season is March to May. They lay 30–60 eggs, which hatch in 80–90 days, depending on incubation temperature. The female crocodile guards her nest, assists the hatchlings, and thereafter protects them from predators. Juveniles appear to disperse from the vicinity of the nest site within a few days.
This species is fairly widespread, but only small populations of the American crocodile are left throughout its range. The species is protected in most countries where it occurs, but enforcement is often inadequate. Threats are habitat fragmentation and direct human disturbance. Estimated wild population is 10,000 to 20,000. It is listed as Vulnerable on the IUCN Red List, and appears under Appendix I of CITES.
significance to humans
Eggs are used as a food source by indigenous people in parts of the range.
Crocodylus johnsoni Krefft, 1873, Herbert River, Queensland.
other common names
English: Freshie, Australian freshwater crocodile; French: Crocodile de Johnstone; German: Australien Krokodi; Spanish: Cocodrilo de Johnstone.
Johnstone's crocodile has a very narrow snout. Adults average 6.5 ft (2 m) in length. Males grow to over 10 ft (3 m); females grow to 6.5 ft (2 m) and average 5 ft (1.5 m). Dark or light brown in color with black bands or spots on the body and tail. The underside is white. The dorsal scales are quite smooth, arranged in six neat rows.
Tropical regions of northern Australia.
This species inhabits freshwater rivers, streams, and pools, but occasionally estuarine habitats.
Social animals, Johnstone's crocodiles may form dense aggregations during the annual dry season. Large males and females assert territoriality and dominance by chasing and biting the tails
of smaller ones. These crocodiles migrate considerable distances overland in the dry season. Where there is no water they seek refuge under embankments and in piles of leaves and dense vegetation. Johnstone's crocodiles are quite vocal and growl in response to loud noise or a human presence in "their" pond.
feeding ecology and diet
Crustaceans, insects, spiders, fish, frogs, lizards, snakes, birds, and mammals. Insects are the most common food item, followed by fish, which are caught by using a "sit-and-wait" strategy. Johnstone's crocodiles are also known to stalk larger prey; large crocodiles catch and eat wallabies and water birds.
These crocodiles court and mate at the beginning of the dry season (around May). Females dig nest holes in sand banks, sometimes communally, and lay an average of 13 eggs. Average incubation time is 74 days. Females rarely guard the nest and only become attentive when the young signal they are ready to hatch and emerge. The female opens the nest and carries the young to the water, sometimes inflicting puncture wounds on the hatchlings with her sharp teeth. The female stays with her crèche of hatchlings for a month or more. Juveniles that survive to maturity are known to return to the same breeding and nesting areas from which they were hatched.
Seriously depleted by the skin trade but recuperating. Threats to the species are habitat destruction and the introduction of the poisonous cane toad (Bufo marinus), which has led to mortality in otherwise healthy populations. Estimated wild population is at least 100,000. This species no longer appears on the IUCN Red List, but it is on Appendix II of CITES.
significance to humans
Johnstone's crocodiles and their eggs remain a traditional source of food for several indigenous groups and as part of their folklore.
Crocodylus palustris Lesson, 1834, Ganges River, India.
other common names
English: Marsh crocodile; French: Crocodile à front large; German: Sumpfkrokodil; Spanish: Cocodrilo marismeño.
Relatively stocky reptiles, adult males average 10 ft (3 m). Adult females average 7.4 ft (2.25 m), and may reach 10 ft (3 m). The maximum size on record is 18 ft (5.5 m). Gray, olive, or brownish above with dark markings that become less distinct as the animal gets older. The underside is white or yellowish. The dorsal scutes are prominent and often quite irregular in arrangement, giving the reptile an untidy appearance. Presence of large postoccipital scutes differentiate this species from the sympatric (in India and Sri Lanka) saltwater crocodile.
Mainly India and Sri Lanka. Small populations still occur in southeastern Iran, and in parts of Pakistan, Nepal, Bhutan, and Bangladesh.
A very adaptable crocodile, muggers are found in clear hill streams up to 1,975 ft (600 m) above sea level, as well as in sewage-treatment ponds, large rivers, lakes, swamps, and even saline habitats.
These are social animals. Unless under hunting pressure, muggers are conspicuous, basking in the open to thermoregulate. Younger muggers are more solitary and cryptic. Muggers can migrate overland for 6 mi (10 km) or more to find water during the dry season. They also dig horizontal tunnels 33 ft (10 m) or deeper in lake and river banks to allow them to survive dry periods and even severe drought.
feeding ecology and diet
Muggers are opportunistic feeders. The diet of the young consists of insects, crabs, frogs, fish, carrion, as well as occasional small reptiles, birds, and mammals. Mature muggers over 6.5 ft (2 m) long catch larger prey such as mammals (from monkeys to deer), water birds, and large catfishes. Near human habitation, muggers will sometimes take farm animals and birds. Muggers have rarely been known to prey on humans.
The annual mating season is December/January on mainland south Asia, variable in Sri Lanka. After about 40 days of gestation, the female mugger digs a hole nest and lays 20–40 eggs between March and May, the number increasing with her size. The female typically remains close to the nest for the 60–70 days of incubation to release and care for the young.
This species has vanished from most of its range. In 2002 there were over 8,000 crocodiles at various rearing stations, including India's largest breeding center, the Madras Crocodile Bank, with no protected areas to release them. The mugger crocodile is strictly protected in the seven countries in which it occurs. The species is listed as Vulnerable on the IUCN Red List and is on CITES Appendix I. Estimated wild population is 5,000–10,000.
significance to humans
When muggers were still plentiful, their eggs and meat were important food resources for many of south Asia's indigenous people. Attacks on humans are rare, but muggers are treated with caution, respect, and sometimes animosity by local people. A well-planned and managed industry based on muggers as a sustainable resource would benefit both humans and crocodiles in south Asia.
Crocodylus niloticus Laurenti, 1768, India and Egypt.
other common names
French: Croco afrique; German: Nordöstliches Nilkrokodil; Spanish: Cocodrilo del Nilo; Swahili: Mamba.
This is a heavyset species with prominent dorsal scales or scutes arranged in even rows. Average adult lengths are 11.5 ft (3.5 m) for males and 8 ft (2.5 m) for females. Males grow to a maximum length of 18 ft (5.5 m); females to 11.5 ft (3.5 m). Young Nile crocodiles are brown or olive with strong darker markings. In adults the markings are vague and older animals are uniformly dark brown or gray. The belly is yellowish, white, or gray.
South of the Sahara desert throughout much of tropical and southern Africa and Madagascar.
This species inhabits wetlands, rivers, and lakes, inclusive of coastal areas.
Although a social animal, adult males square off for territory and mates during the breeding season. It is common for large groups of adults of both sexes to bask and feed in one area.
feeding ecology and diet
Young Nile crocodiles feed largely on insects and spiders with frogs, fish, snakes, and other small vertebrates. Subadults and adult crocodiles mainly eat fish, although very large adults kill and eat antelopes, warthogs, domestic animals, and occasionally humans. These crocodiles use various techniques to catch their prey, including the "hide and wait" method at water holes and river crossings, waiting underwater for fish, and following scent trails to carrion, even when far from water.
The nesting season across Africa occurs from August to January. The female digs a nest hole above the high water line to lay 50–80 eggs. The female stays close to the nest for the 80–90 days of incubation. When the young hatch, she digs them out of the underground nest and carries them to the water. Nests are raided by a variety of predators, namely monitor lizards, hyenas, and humans. The crèche of young stay together for a month or more under the watchful eye of the parent.
The Nile crocodile forms the basis of a successful sustainableuse program for skins and meat in several African countries. In other parts of its range, notably Central and West Africa, the crocodile is in decline and there is very little status information. It is afforded some level of local protection throughout its range, and is no longer included on the IUCN Red List. As of 2002, the Nile crocodile was on Appendix I of CITES, except for ranched animals in Botswana, Ethiopia, Kenya, Malawi, Mozambique, South Africa, Tanzania, Zambia, and Zimbabwe. Nile crocodiles are on Appendix II in Madagascar and Uganda, where there is an annual hunting quota. The estimated population in the wild is 250,000–500,000.
significance to humans
There is a long history of reverence for the Nile crocodile, dating back to the time of the pharaohs when hundreds of crocodiles were mummified along with dead kings. Today there is less reverence and more fear and intolerance toward these crocodiles, which sometimes prey on livestock and humans.
Crocodylus porosus Schneider, 1801, Ceylon and western India.
other common names
English: Estuarine crocodile, Indo-Pacific crocodile; French: Crocodile marin; German: Leistenkrokodil; Spanish: Cocodrilo poroso Bahasa.
This is the world's largest crocodilian, growing to over 20 ft (6.1 m) in length and weighing up to 2,200 lb (1 metric ton). Adult males average 13–16.5 ft (4–5 m) in length, and females 10–11.5 ft (3–3.5 m). The saltwater crocodile may be black, dark brown, or yellowish dorsally, with lighter flanks spotted with black. The underside is white or yellowish. Unlike all other crocodilians, the enlarged postoccipital scales are usually absent. Instead, the postoccipital region on the back of the neck is covered with small beadlike scales. The hind feet are strongly webbed.
Scattered populations from the east coast of India to Australia. This is the most widely distributed crocodilian in the world.
Although most at home in brackish tidal mangrove waterways, saltwater crocodiles can be found in freshwater habitats hundreds of miles (or kilometers) inland.
Large, adult males are territorial and solitary. Females typically have small home ranges of a few square miles (or kilometers) while adult males have been known to patrol territories of 100 mi2 (260 km2).
feeding ecology and diet
Young saltwater crocodiles feed mainly on small crabs and fish. Adult saltwater crocodiles may lie in wait for large mammals, both wild and domestic, at water holes. Humans are sometimes taken.
The breeding season occurs from April to May in India, and January to February in Australia. The female lays 40–70 eggs in a mound of vegetation. A nesting female will typically make herself a wallow near the nest from where she will guard it for the 70–80 days incubation. She releases the hatchlings and then guards them, but predation on hatchlings is still high.
Although widely distributed, saltwater crocodiles have been killed out of fear and for their valuable skins throughout their range. Only in Australia and Papua New Guinea are there effective management programs in place, which allow sustainable use of saltwater crocodiles for skin and meat. Other Asian countries in the range of the saltwater crocodile need to enforce existing protective legislation while educating people on how to live with crocodiles. The saltwater crocodile is afforded protection on paper throughout its range. It is no longer listed on the IUCN Red List, but it appears on CITES Appendix I. Estimated wild population is 200,000–300,000.
significance to humans
Large saltwater crocodiles consider humans and their livestock as prey items. This has led to animosity toward this species; yet the saltwater crocodile forms the basis for a skin industry for a large number of indigenous people in the Asia/Pacific region.
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Crocodile Specialist Group, Florida Museum of Natural History. Box 117800, Gainesville, FL 32611-7800 USA. Phone: (352) 392-1721. Fax: (352) 392-9367. E-mail: [email protected] Web site: <http://www.flmnh.ufl.edu/natsci/herpetology/crocs.htm>
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Romulus Earl Whitaker III, BSc