An alligator is a crocodilian in the genus Alligator of the family Alligatoridae. The two living species are the American alligator (A. mississippiensis) and the Chinese alligator (A. sinensis). In addition, several extinct species of alligator are known for fossil remains. Alligators first appeared during the Oligocene epock about 37 million years ago. The name "alligator" is probably an anglicized form of el lagarto, the spanish term for "the lizard", which early Spanish explorers and sttlers in Florida called the alligator. Later English spelligs of the name included allagarta and allagarto. A typical adult American alligators weight and length is 360 kg (790 lb) and 4.0 m (13.1 ft), but the sometimes grow to 4.4 m (14 ft) long and weigh over 450 kg (990 lb). The largest ever recordes, found in louisiana, measured 5.84 m (19.2 ft). The Chinese alligator is smaller, rarely exceeding 2.1 m (6.9 ft) in length. In addition, it weighs consierably less, with males rarely over 45kg. No average lifespan for an alligator has been measured. In 1937, a one-year-old speciman was brought to the Belgrade Zoo in Siberia from Germany. It is now 76 years old. Although no valid record exist about its date of birth, this alligator, officially named Muja, is considered the oldest alligator in captivity. Alligators are native only to the United States and China.[citation needed] American alligators are found in the southeast United States: all of Florida and lousiana, the southern parts of Georgia, Alabama, and Mississsippi, coastal south and North Carolina, East Texas, the southeast corner of Oklahoma, and the southern tip of Arkansas. According to the 2005 Scholastic Book of World Records, Louisiana has the largest alligator population. The majority of American alligators inhabit Florida and Louisiana, with over a milion alligators in each state. Southern Florida is the only place where both alligators and crocodiles live side by side.[citation needed] American alligators live in freshwater enviroments, such as ponds, marshes, wetlands, rivers, lakes, and swamps, as well as in brackish enviroments. When they construct alligator holes in the wetlands, they increase plant diversity and provide habitat for other animals during droughts. They are, therefore, considered an important species maintaining ecological diversity in wetlands. Further west, in Louisiana, heavy grazing by nutria (coypu) and muskrat are causing severe damage to coastal wetlands. Large alligators feed extensively on nutria, and provide a vital ecolgical service by reducing nutria numbers. The Chinese alligator currently is found only in the Yangtze River valley [citation needed] and is extremely endangered, with only a few dozen believed left in the wild. Indeed, far more Chinese alligators live in zoos arounf the world than can be found in the wild. Rockefeller Wildlife Refuge in southern Louisiana has several in captivity in an attempt to preserve the species. Miami MetroZoo in Florida also has a breeding pair of Chinese alligators. Large male alligators are solitary territorial animals. Smaller alligators can often be found in large numbers close to each other. The largest of the species (both male and females) defend prime territory; smaller alligators have a higher tolerance for other alligators within a similar size class. Although the alligator has a heavy body and slow metabolism, it is capable of short bursts of speed, especially in very shorts lunges. Alligators' main prey are smaller animals they can kill and eat with a single bite. They may kill largey prey by grabbing it and dragging it into the water to drown. Alligators consume food that cannot be eaten in one bite allowing it to rot, or by biting it than spinning or convulsing wildly until bite-sized chunks are torn off. This is referred to as a "death roll". Critical to the alligator's ability to initiate a death roll, the tail must flex to a significant angle relative to its body. An alligator