The Mexican free-tailed bat or Brazilian free-tailed bat (Tadarida brasiliensis) is a medium-sized bat native to the Americas, so named because its tail can be almost half its total length and is not attached to its uropatagium. It has been claimed to have the fastest horizontal speed of any animal, reaching top ground speeds over . It also flies the highest among bats, at altitudes around . It is regarded as one of the most abundant mammals in North America. Its proclivity towards roosting in huge numbers at relatively few locations makes it vulnerable to habitat destruction in spite of its abundance. For instance, up to 1.5 million bats reside under just one bridge in Austin. The Texas Legislature designated the Mexican free-tailed bat the state mammal (flying) in 1995. The bat is considered a species of special concern in California as a result of declining populations. Taxonomy The Mexican free-tailed bat was described as a new species in 1824 by French zoologist Isidore Geoffroy Saint-Hilaire. Geoffroy placed it in the now-defunct genus Nyctinomus with a binomial name of Nyctinomus brasiliensis. The holotype had been collected in Brazil. Molecular sequence data indicate T. brasiliensis'''s closest relatives are the sister species Sauromys petrophilus of South Africa and Tadarida aegyptiaca of Africa and South Asia. These three species form a clade believed to be about 18 million years old. Physical description Mexican free-tailed bats are typically in length and weigh around with females tending to be slightly heavier than males by 1-2 grams for increased fat storage to use during gestation and nursing. Their tails are almost half their total length and stretch beyond the uropatagium, giving them the name "free-tailed" bats. Their ears are wide, rounded, and large compared to their heads, nearly meeting at the front of the face, but distinctly not joined at the midline and projecting anterodorsally from just before the muzzle to the back of the head. They use their large ears to help them find prey using echolocation. T. brasiliensis is distinguished among North American Tadarida bats in possessing deep wrinkles on the upper lip and in having a Z-shaped upper third molar, which is used for grinding insects. These individuals possess canines which are larger in males than in females. The wings are elongated and narrow with pointed tips, making them well-equipped for quick, straight flight patterns. Their fur color ranges from dark brown to