Alligators and caimans

(Alligatoridae)

Class Reptilia

Order Crocodylia

Suborder Eusuchia

Family Alligatoridae

Thumbnail description
Powerful animals with a long and muscular tail, four short limbs straddling a scaly body, and strong jaws lined with obvious teeth

Size
4–20 ft (1.2–6 m) in total length

Number of genera, species
4 genera; 8 species

Habitat
Calm or slow-moving freshwater areas

Conservation status
Critically Endangered: 1 species; Lower Risk/Conservation Dependent: 1 species

Distribution
Central to northern South America, parts of southern and western Central America and Mexico, the southeastern United States, and a small area of eastern China

Evolution and systematics

Although the order Crocodylia dates back at least 200 million years to the Age of Reptiles, its living members, including those of the family Alligatoridae, can hardly be described as primitive. Instead, they survived the mass extinction 65 million years ago that ended the dinosaurs' reign and evolved over the centuries into animals well suited to their current place in the natural world. Like other members of the order, the family Alligatoridae are the descendants of the Archosauria, or "ruling lizards," which included the dinosaurs. A defining characteristic of these animals is a diapsid skull, which has two temporal openings. Turtles, by comparison, have anapsid skulls with no temporal openings.

Within the crocodilians, the family Alligatoridae can be followed as far back as the Paleocene (57–65 million years ago), when caiman ancestors are thought to have roamed the earth. Ancestors of other species, including the American alligator (Alligator mississippiensis) and Chinese alligator (Alligator sinensis), date back to the Miocene and Pleistocene, respectively. The alligatorids are separated into two major groups: the alligators (subfamily Alligatorinae) and the caimans (subfamily Caimaninae). The former group has two living representatives in the Alligator genus. The other six species of alligatorids fall under three genera within the caimans. (Some systematists list only five caimans, with the Yacaré as a subspecies of the common caiman.) In all, the eight species are as follows:

• American alligator, Alligator mississippiensis
• Chinese alligator, A. sinensis
• common caiman, Caiman crocodilus
• broad-snouted caiman, C. latirostris
• Yacaré, C. yacare
• black caiman, Melanosuchus niger
• Cuvier's dwarf caiman, Paleosuchus palpebrosus
• smooth-fronted caiman, P. trigonatus

Physical characteristics

In general appearance, alligators are similar to crocodiles, with stout bodies and powerful tails that are at least as long as their bodies. They have long snouts and noticeably toothed upper and lower jaws. Alligatorids are distinguished most notably from the crocodiles by their mandibular teeth, all of which slide inside the upper jaw and out of view when the mouth is closed. In contrast, the fourth mandibular teeth in crocodiles are visible outside the closed jaw.

Alligatorids are grayish, sometimes tending toward green, brown, yellow, or black, depending on the species. The young are often banded. Adult size ranges from about 4 ft (1.2 m) in Cuvier's dwarf caiman (P. palpebrosus) to 13 ft (4 m) in the American alligator (A. mississippiensis).

Like the crocodile's body, the alligatorid body is armored with tough osteoderms and, frequently, large scales that do not overlap. The osteoderms in some species do not extend onto the belly, making this smooth part of the skin highly

desirable as leather for human uses. Alligatorids have short legs tipped with claws. The forelimbs are smaller than the hind limbs and have five, rather than four, partially webbed toes. Their body form allows them to glide in a sinuous pattern through the water, normally with just the side-to-side motion of the tail providing the locomotive force. On land the strength of their legs makes them quick and formidable predators.

Distribution

Primarily a New World group, all but the two Alligator species occur in southern Mexico, parts of Central America, or northern to central South America. Alligator mississippiensis is the only member of this family to be found in the United States, where it exists in southeastern states, from the Carolinas to Texas. A. sinensis makes its home in eastern China, far distant from its New World relatives.

Habitat

Alligatorids are restricted to freshwater areas and frequently are found in lakes, slow-moving streams and rivers,

swamps, marshes, and other wetland habitats. Some species even make use of roadside ditches. They prefer sites with slow-moving or still waters. They often inhabit vegetated areas, sometimes with muddy or murky water.

Behavior

Alligatorids are ectotherms ("cold-blooded" animals) and most often are seen basking on the shoreline to raise their body temperature. Sometimes they are seen sliding along the shoreline on their bellies, using their feet to push them through the mud and muck to the water. They also do the "high walk," which is somewhat similar to a lizard's walk; alligatorids, however, hold their legs more upright than straddled. Although they may look sedate much of the time, their short legs can give them quick acceleration for grasping a passing mammal.

Careful observers also see them floating at the surface of the water, where only their most dorsal surface and occasionally

just the nose and the tip of the head are exposed. Often, the animal actually is maintaining its internal temperature through this activity, either lying in the sun-heated upper layers of the water column to warm up or moving to shady, chillier waters to cool off. Their presence is made known when they begin to sweep their tails slowly and propel themselves gracefully forward. While they usually are motionless or swim slowly, they can make quick movements in the water. One noticeable trait is their ability to jettison almost vertically out of the water. This maneuver typically is accompanied by a quick chomp of the jaws around a startled bird or other prey item.

Alligatorids, including those in more temperate climates, do not hibernate. While temperatures in the southeastern United States and China can approach freezing in the winter, American and Chinese alligators remain active all year, though they are more subdued as temperatures dip and may even become dormant. To beat the cold, they move to shallow water and lie motionless, with just the nose poking into the cold air. Young alligators, on the other hand, may retreat to the mother's den to survive cold snaps. Juveniles and adults make use of burrows during winter months.

Alligatorids often live in groups and form dominance hierarchies, at least during the breeding season and sometimes all year. The highest-ranking individuals exert their dominance through various ritualized behaviors, which may include slaps of the head against the surface of the water, loud vocalizations, and open-mouthed charges.

Feeding ecology and diet

A typical juvenile diet includes snails and other invertebrates, whereas adults of various species commonly eat fish, small mammals, other reptiles (including smaller alligatorids), or birds. Opportunistic feeders, alligatorids continue to eat clams, snails, and invertebrates into adulthood. The larger species, including the black caiman, are known to take large prey, such as small deer and cattle.

Predation of alligatorids occurs primarily among eggs and hatchlings. Raccoons, coati, skunks, foxes, and other mammals, as well as snakes and various raptors, are known to raid nests or snatch up young alligatorids. Once an alligatorid reaches about 3 ft (1 m) in length, the risk of predation decreases. Nonetheless, anacondas in South America occasionally kill adult caimans, and alligatorids have been reported to have cannibalistic tendencies. Cannibalism is rare, however, and alligatorids frequently live peacefully in large groups.

Reproductive biology

Alligatorids begin the reproductive season in the spring. Following courtship, which may include loud bellows, tactile types of behavior, and underwater vibrations of the male's trunk, alligatorids use vegetation to construct nest mounds, where they lay from one dozen to five dozen eggs, depending

on the species. Egg laying generally takes place once a year, in midsummer, with hatching one to two months later. Female alligatorids typically respond to sounds emanating from the neonate, dig up the nest, and assist in their hatching. Temperature-dependent sex determination has been associated with several species, including the American alligator and common caimans. Low nest temperatures (below 88°F, or 31°C) produce female hatchlings, and high temperatures (above 90°F, or 32°C) produce males.

Conservation status

The Chinese alligator is listed by the IUCN Red Book as Critically Endangered. This status stems primarily from loss of habitat due to human encroachment. According to the IUCN Crocodile Specialist Group, "The Chinese alligator is the most critically endangered crocodilian in the world. Thousands are bred in captivity, but fewer than 150 remain in the wild." The group is working with the Chinese government to protect the species and has launched the Chinese Alligator Fund to assist in these efforts. In addition, many conservation efforts over the past three decades have been implemented to prevent overharvesting of other alligatorids. The only other species listed by the IUCN is the black caiman, which is listed as Lower Risk/Conservation Dependent.

Significance to humans

Although the benefit is difficult to quantify, some species of alligatorids play an important role in the tourism industry. American alligators in the southeastern United States, for example, have become tourist attractions, drawing visitors to the Everglades of southern Florida and the bayous of Louisiana. Several members of this family are hunted, especially for their skin, which is used as leather for shoes, bags, and various accessories. Humans also hunt these animals for meat and, recently, for their gonads, which are used to make perfume.

Species accounts

List of Species

American alligator

Alligator mississippiensis

subfamily

Alligatorinae

taxonomy

Alligator mississippiensis Daudin, 1801, "les bords du Mississipi," United States. No subspecies are recognized.

other common names

English: Gator, pike-headed alligator, Florida alligator, Mississippi alligator, Louisiana alligator; French: Alligator de Amérika; German: Hechtalligator, Mississippi-Alligator; Spanish: Aligator de Mississippi.

physical characteristics

With a broad snout and heavy, armorlike, dorsal scales, American alligators are dark grayish green to black, with pale whitish bellies. The young commonly have conspicuous yellow markings on the back and tail. In their geographic range, the only other crocodilian is the American crocodile (Crocodylus acutus), which has a noticeably narrower and tapering snout. Adults generally reach lengths of about 8–13 ft (2.4–4 m), though some individuals may top 19 ft (5.8 m).

distribution

The American alligator is found throughout the coastal plains of the southeastern United States from the Carolinas south to Florida and west to Texas.

habitat

This species inhabits freshwater, especially marshes, swamps, lakes, and slow-moving rivers.

behavior

Alligators often form extended families of sorts, with several generations living in the same vicinity for many years. When the breeding season arrives, the courtship ritual includes a series

of tactile behaviors, including gentle bumping and rubbing between the male and female. Both males and females bellow, with the male's roars a bit louder than the female's and more plentiful during mating season. Females often utter low grunts when calling the young. Males and females of all ages hiss when threatened. This species may become dormant during the winter, but it does not hibernate.

feeding ecology and diet

The largest reptiles in North America, adult American alligators are at the top of the food chain in their habitat. They are carnivorous and eat almost anything that is in or near the water, including turtles; fish; small mammals, such as otters; and even young alligators. If possible, the alligator swallows its prey whole. If the prey item is large, however, it first drowns the victim, then tears off bite-sized chunks. Younger alligators eat primarily fish and small invertebrates.

reproductive biology

Males and females mature at 10 years or older. Mating occurs each spring. Each nest contains about three dozen to four dozen eggs, of which two-thirds or more typically survive to hatching. Egg gestation is about two months. Females provide parental care by guarding the nest and young, by opening the buried nest to assist in hatching, and by transporting hatchlings to water. Young remain near their mother in a "pod" for at least two to three months and often as long as two to three years. Their life span can run 50 or more years.

conservation status

Not listed by the IUCN.

significance to humans

The species is a source of meat and hides for such uses as shoes, belts, and purses. In some places, they also have become a boon to the tourist industry.

Chinese alligator

Alligator sinensis

subfamily

Alligatorinae

taxonomy

Alligator sinensis Fauvel, 1879, "Chinkiang" (= Zhenjiang/Chinkjang/Chenchiang), Kiangsu Province, People's Republic of China. No subspecies are recognized.

other common names

English: Yangtze alligator, Tou lung, Yow lung, T'o, China alligator; French: Alligator de Chine; German: China-Alligator; Spanish: Alligator de China.

physical characteristics

A yellowish gray alligator with osteoderms on the belly as well as on the back and a heavy snout that tapers toward its vaguely upturned end. This is a small alligator that has an average total length of about 5 ft (1.5 m) in males and 4.5 ft (1.4 m) in females. Maximum lengths have been recorded at

about 6.6 ft (2 m) in the male and 5.7 ft (1.7 m) in the female. Young are similar to adults in appearance but have noticeable yellow banding.

distribution

This species occupies a small area in the Yangtze River basin along China's central Atlantic coastline.

habitat

The Chinese alligator inhabits the subtropical temperate ecotone in marshy areas, ponds, lakes, and languid rivers.

behavior

This species is dormant during the late fall, winter, and early spring and relatively inactive during much of the rest of the year owing to the cool temperatures in its geographic area. Each year in April, the alligators emerge from their winter burrows, which line still waters, and find sunny spots in which to bask. As summer begins, they switch to more nocturnal habits and begin their annual mating rituals. During courtship, bellowing from the males and females becomes pronounced, though they bellow at other times of the year as well.

feeding ecology and diet

The young prefer insects and other small invertebrates, whereas larger individuals also take fish, clams, and the occasional small mammal or waterfowl. They have blunt teeth adapted well to crushing shelled animals.

reproductive biology

Females mature at about five to seven years. Mating occurs in early summer, with the females building nests about two to three weeks later and laying up to four dozen eggs; fewer than two dozen is common. Hatchlings generally emerge in September. Females provide parental care, including assisting in the hatching process and carrying the newly hatched young from the nests, which are located on land, to the water. The life span of these alligators in captivity nears 70 years, and they can reproduce into their 50s.

conservation status

The species is listed as Critically Endangered by the IUCN. Their decline is associated primarily with habitat destruction.

significance to humans

None known.

Common caiman

Caiman crocodilus

subfamily

Caimaninae

taxonomy

Caiman crocodilus Linnaeus, 1758, type locality not specified. Four subspecies are recognized.

other common names

English: Spectacled caiman, brown caiman; French: Caiman è lunettes; German: Brillenkaiman, Krokodilkaiman; Spanish: Caimán común.

physical characteristics

Dark cross-banding, tough dorsal armor, and a bony facial ridge are the most distinguishing features of this greenish gray to brownish gray crocodilian. Adults can reach 4–6 ft (1.2–1.8 m), with rare individuals growing up to 10 ft (3 m).

distribution

The species is found primarily in the Amazon and Orinoco River basins, but it extends from southern Mexico to northern Argentina and to the islands of Trinidad and Tobago north of eastern Venezuela. It also inhabits southern Florida and has been introduced in Cuba and Puerto Rico.

habitat

The common caiman inhabits freshwater areas, particularly swamps but also lakes, rivers, and even water-filled roadside ditches.

behavior

During the breeding season, the males bellow to help establish their territories. More than one female may mate with a single

male and build a nest in his territory. During the remainder of the year, which usually is much drier than the wet breeding season, caimans congregate in whatever freshwater pools are available.

feeding ecology and diet

The caiman diet varies from land invertebrates among the youngest individuals to snails among juveniles and mainly fish among adults.

reproductive biology

Caimans begin breeding during the annual wet season. Females lay about one dozen to three dozen eggs in a terrestrial nest made of vegetation. The mother provides parental care by helping in the hatching process and by carrying the neonates, which are typically about 8 in (20 cm) long, to nearby water. The male guards the nest. After hatching, the young generally remain near the parents until they are almost a year old. Common caimans have been known to live into their 60s, though this is rare.

conservation status

Not listed by the IUCN. One of the four subspecies (C. c. apaporiensis) of the common caiman, however, is under threat by range overlap and cross-breeding with another subspecies, C. c. crocodilus.

significance to humans

The common caiman is harvested, sometimes illegally, as food or for its skin. It also has been seen in the pet trade.

Smooth-fronted caiman

Paleosuchus trigonatus

subfamily

Caimaninae

taxonomy

Paleosuchus trigonatus Schneider, 1801, type locality not specified. No subspecies are recognized.

other common names

English: Schneider's smooth-fronted caiman; French: Caiman è front lisse de Schneider; German: Keilkopfkaiman; Spanish: Jacaré coroa cachirre.

physical characteristics

These caimans are called smooth-fronted because they lack the bony ridge typically seen between the eyes of other caimans. They are dark gray to black, with highly ridged dorsal scales and a tail that is barely as long as the body. Males reach 4.9–5.5 ft (1.5–1.7 m), and females attain a length of 3.9–4.6 ft (1.2–1.4 m).

distribution

The species is distributed throughout northern and north-central South America.

habitat

The smooth-fronted caiman usually is found in very shallow streams of heavily vegetated rainforests.

behavior

Unusual for alligatorids, this species spends much of its time in hiding spots on land (such as under logs), rather than basking along the shoreline. It does, however, follow the typical alligator pattern of building nest mounds of vegetation, where it lays its eggs.

feeding ecology and diet

Hatchlings have an insectivorous diet, but juveniles and adults share a diet of reptiles and birds. Adults also commonly take mammals, including porcupines.

reproductive biology

The timing of this species' breeding period coincides with the annual fluctuation of dry and wet seasons. Courtship, nest building, and egg laying take place toward the end of the dry season, and hatching ensues shortly after the rains begin to fall. A typical nest contains about a dozen eggs.

conservation status

Not listed by the IUCN.

significance to humans

None known.

Resources

Books

Alderton, D. Crocodiles and Alligators of the World. New York: Facts on File, 1991.

Ashton, Ray E., and Patricia Sawyer Ashton. Handbook of Reptiles and Amphibians of Florida. Part 2: Lizards, Turtles and Crocodilians. 2nd edition. Miami: Windward Publishing Co., 1991.

Behler, J. L., and D. A. Behler. Alligators and Crocodiles. Stillwater, MN: Voyager Press, 1998.

Campbell, G., and A. L. Winterbotham. Jaws Too: The Natural History of Crocodilians with Emphasis on Sanibel Island's Alligators. Ft. Myers, FL: Sutherland Publishing, 1985.

Guggisberg, C. A. W. Crocodiles: Their Natural History, Folklore, and Conservation. Harrisburg, PA: Stackpole Books, 1972.

Hirschhorn, Howard H. Crocodilians of Florida and the Tropical Americas. Miami: Phoenix Publishing Co., 1986.

King, F. Wayne, and Russell L. Burke, eds. Crocodilian, Tuatara and Turtle Species of the World: A Taxonomic and Geographic Reference. Washington, DC: Association of Systematics Collections, 1989.

McIlhenny, E. A. The Alligator's Life History. Boston: Christopher Publishing, 1935.

Minton, S. A., Jr., and M. R. Minton. Giant Reptiles. New York: Scribner, 1973.

Neill, W. T. The Last of the Ruling Reptiles. New York: Columbia University Press, 1971.

Ross, Charles A., ed. Crocodiles and Alligators. New York: Facts of File, Inc., 1989.

Zug, George R, Laurie J. Vitt, and Janalee P. Caldwell. Herpetology: An Introductory Biology of Amphibians and Reptiles. 2nd edition. San Diego: Academic Press, Inc., 2001.

Periodicals

Brazaitis, P., M. Watanabe, and G. Amato. "The Caiman Trade." Scientific American 278 (March 1998): 70–76.

Stewart, D. "Visiting the Heart of Alligator Country." National Wildlife 38, no. 4 (June/July 2000): 20–27.

Thorbjarnarson, J. "The Hunt for Black Caiman." International Wildlife 29 no. 4 (July/August 1999): 12–19.

Thorbjarnarson, J., X. Wang, and L. He. "Reproductive Ecology of the Chinese Alligator (Alligator sinensis) and Implications for Conservation." Journal of Herpetology 35, no. 4 (December 2001): 553–558.

Zimmer, C. "Prepared for the Past." Natural History 110, no. 3 (April 2001): 28–29.

Organizations

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>

Other

Animal Diversity Web. [cited December 2002]. <http://animaldiversity.ummz.umich.edu>

"Crocodilian Species List." 2002 [cited December 2002]. <http://www.flmnh.ufl.edu/cnhc/csl.html>

"Alligatoridae." The Reptipage. August 2002 [cited December 2002]. <http://reptilis.net/crocodylia/gators/alligatoridae.html>

"Alligatoridae: Alligators, Caimans, and Their Prehistoric Relatives." December 1999 [cited December 2002]. <http://www.kheper.auz.com/gaia/biosphere/vertebrates/crocodylia/Alligatoridae.html>

"Crocodilian Biology Database." August 2002 [cited December 2002]. <http://www.flmnh.ufl.edu/cnhc/cbd.html>

Leslie Ann Mertz, PhD