Alligator Species • Caiman Species • Anatomical Features • Nesting • Habitat and Behaviors • Bibliography • Additional Readings

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Alligator

Article by: Cash, W. Ben Department of Biology, Maryville College, Maryville, Tennessee. Campbell, Howard W. National Fisheries and Wildlife Laboratory, Gainesville, Florida. Publication year: 2014 DOI: http://dx.doi.org/10.1036/1097-8542.024200 (http://dx.doi.org/10.1036/1097-8542.024200)

Content

• Alligator species • Caiman species • Anatomical features • Nesting • Habitat and behaviors • Bibliography • Additional Readings

A large aquatic reptile of the family Alligatoridae. Common usage generally restricts the name to the two species of the genus Alligator. The family also includes three genera (five species) of caiman. With the crocodiles and gharial (also spelled gavial), these are survivors of archosaurian stock and are considered close to the evolutionary line which gave rise to birds.

Alligator species

The two living species have a disjunct subtropical and temperate zone distribution. The American alligator (A. mississippiensis) ranges throughout the southeastern United States from coastal North Carolina (historically from southeastern Virginia) to the Rio Grande in Texas, and north into southeastern Oklahoma and southern Arkansas (see illustration).

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Half-submerged American alligator (Alligator mississippiensis). (Photo courtesy of W. Ben Cash)

Poaching and unregulated hunting for the valuable hide decimated the alligator populations until the animal was placed on the U.S. Endangered Species List in 1967. The species has responded well to protection and has become abundant in many areas in its range, particularly in Florida and parts of Georgia, Louisiana, and Texas, where it is now a common sight in the freshwater habitats, including swamps, marshes, lakes, rivers, and even roadside ditches.

The second species is the Chinese alligator (A. sinensis), restricted to the region of the Yangtze River valley, where it inhabits burrows in the floodplains and riverbanks. This species is considered “critically endangered” by international conservation organizations. It is believed that less than 200 individuals remain in the wild.

The American alligator is by far the larger of the two species, exceeding 15 ft (4.5 m). The average length of A. sinensis is 4–5 ft (1.2–1.5 m).

Caiman species

There are five species of caimans, once often sold as “baby alligators.” Caimans differ from alligators in technical details of their internal anatomy and scale characteristics.

The black caiman (Melanosuchus niger) of the Amazon Basin of South America strongly resembles the American alligator in superficial appearance and may reach a length approaching 16 ft (5 m). The spectacled caiman (Caiman crocodilus), with its several subspecies, is sold in the pet trade. It is the most widely distributed of the caimans, ranging from southwestern Mexico to Paraguay and Bolivia. Spectacled caimans reach a length of 8 ft (2.5 m) and can be distinguished from alligators by the presence of a ridge across the snout between their eyes, the nose bridge of the “spectacles.”

The broad-nosed caiman (C. latirostris) occurs from southern Brazil to Paraguay and northern Argentina and reaches a length of 9 ft (3 m). The two species of smooth-fronted caiman, Paleosuchus trigonatus and P. palpebrosus, are the smallest of the family, reaching a maximum length of 7 ft (2 m). They occur over most of northern South America, south to Peru, Bolivia, and southeastern Brazil.

Anatomical features

Alligators, including caimans, are generally distinguished from crocodiles by their broader, rounded, and more massive snout, the arrangement of their teeth, and other technical anatomical details. As in all crocodilians, the teeth are conical and sharp, equivalent in shape (homodont), and replaced throughout life. Moreover, as in all crocodilians, alligators possess a functionally four-chambered heart, a secondary palate, a septum or “diaphragm” that separates the lung and peritoneal regions, a compressed tail, webbed feet, and other adaptations for an aquatic existence.

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Nesting

All alligators build a conical nest of available materials near the water's edge, where they deposit 15–60 leathery-shelled eggs. Incubation takes 30–60 days; females of at least some species may guard the nest, assist in the hatching process, and remain with the young for as long as 3 years. In some cases, females carry young in their mouth to nearby water.

Habitat and behaviors

Alligators are generalized carnivores, feeding on any invertebrates, fishes, reptiles and amphibians, birds, or mammals that can be caught and overpowered. They play a dominant role in the energy and nutrient cycling in their habitats, and through their construction of “gator holes,” which often retain water in times of drought, are considered important to the survival of many others species.

Alligators have also been found to have a complex social system that relies heavily on communication. Visual, tactile, auditory, and even subauditory communications have been described in alligator populations. Males roar during the breeding season to attract females, and females bellow and growl to communicate receptiveness to males. Using trunk muscles and low-frequency sound, alligators create rapid vibrations on the water surface to communicate. The vibrations coupled with the low-frequency sound can be heard at great distances (perhaps up to a kilometer). Males use a diversity of sounds as a threat warning, including a “cough” and hiss. Juveniles employ distress calls when they feel threatened. These calls attract the attention of the nearby female. See also: Archosauria (/content/archosauria/048900); Cardiovascular system (/content/cardiovascular-system/109900); Crocodile (/content/crocodile/168600); Crocodylia (/content/crocodylia/168610); Dentition (/content/dentition/186400); Reptilia (/content/reptilia/581800)

W. Ben Cash Howard W. Campbell

Bibliography

S. Grenard and W. Loutsenhizer, Handbook of Alligators and Crocodiles, Krieger, Melbourne, FL, 1995

S. B. Hedges and L. L. Poling, A molecular phylogeny of reptiles, Science, 283:998–1001, 1999 DOI: 10.1126/science.283.5404.998 (http://dx.doi.org/10.1126/science.283.5404.998)

D. W. Linzey, Vertebrate Biology, McGraw-Hill, New York, 2001

F. H. Pough et al., Herpetology, 3d ed., Prentice Hall, Upper Saddle River, NJ, 2004

K. A. Vliet, Social dynamics of the American alligator (Alligator mississippiensis), Amer. Zool., 29:1019 –1031, 1989

G. R. Zug, L. J. Vitt, and J. P. Caldwell, Herpetology, Academic Press, San Diego, 2001

Additional Readings

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K. H. Redford et al., What does it mean to successfully conserve a (vertebrate) species?, Bioscience, 61 (1):39–48, 2011 DOI: 10.1525/bio.2011.61.1.9 (http://dx.doi.org/10.1525/bio.2011.61.1.9)

R. K. Sanders and C. G. Farmer, The pulmonary anatomy of Alligator mississippiensis and its similarity to the avian respiratory system, Anat. Rec., 295(4):699–714, 2012 DOI: 10.1002/ar.22427 (http://dx.doi.org/10.1002/ar.22427)

P. A. Siroski et al., Comparison of plasma dipeptidyl peptidase IV activity in two caiman species: Caiman latirostris and Caiman yacare (Crocodylia, Alligatoridae), Anim. Biol., 61(2):199–210, 2011 DOI: 10.1163/157075511X566524 (http://dx.doi.org/10.1163/157075511X566524)

J. B Thorbjarnarson and X. Wang, The Chinese alligator: Ecology, Behavior, Conservation and Culture, Johns Hopkins University Press, Baltimore, MD, 2010

C. A. Ugarte et al., The influence of regional hydrology on nesting behavior and nest fate of the American alligator, J. Wildlife Manage., 77(1):192–199, 2013 DOI: 10.1002/jwmg.463 (http://dx.doi.org/10.1002/jwmg.463)

U. Zapata et al., Material properties of mandibular cortical bone in the American alligator, Alligator mississippiensis, Bone, 46(3):860–867, 2010 DOI: 10.1016/j.bone.2009.11.010 (http://dx.doi.org/10.1016/j.bone.2009.11.010)

Bibliography of Crocodilian Biology (http://utweb.ut.edu/hosted/faculty/mmeers/bcb)

Crocodilians: Florida Museum of Natural History, University of Florida (http://www.flmnh.ufl.edu/cnhc/cnhc.html)

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