Biologists describe animals with such teeth as having heterodont dentition. By contrast, the teeth of homodont animals, such as iguanas, are all the same shape. As with some carnivores that have teeth to aid in prey capture, some omnivores have teeth that help them to obtain, rather than process, their food. Rodents are famous for their long, continuously growing incisors, which they use to chew through husks, shells and wood.
Area 51 is located in the southern portion of Nevada in the western United States, 83 miles (134 km) north-northwest of Las Vegas. Situated at its center, on the southern shore of Groom Lake, is a large military airfield.
Area 51, while not part of this grid, borders Area 15. Many say the site got the name Area 51 by transposing the 1 and 5 of its neighbor. Another popular theory is that the number 51 was chosen because it was not likely to be used as part of the NTS system in the future (in case the NTS expanded later on).