The third largest cat in the world (after tigers and lions), and the largest western hemisphere cat. Males can reach up to 300 pounds in the Pantanal region of Brazil, but are more commonly 250 pounds, with females about 200 pounds. Jaguars in northern Mexico are only about 150 pounds for males, 100 for females. Jaguars used to be found in the southern United States but are considered extinct here now; a male occasionally crosses over from Mexico, but there is no breeding population. The last wild one recorded in California was shot in the late 1800's. Sub speciation in jaguars is under debate; all captive jaguars are currently managed as one meta-population. They look like a larger, stronger cousin of the leopard. Their rosettes are larger and set farther apart, with enclosed spots more common than in the leopard. They are much more muscular, in particular in the neck region. They are one of only a few cats that enjoy water. In many areas they are declining or near extinction, however they are listed as Near Threatened because of the large numbers surviving in the Amazon basin rainforests. Overall they are close to Vulnerable status, with three potential subspecies being in worse shape. They face extirpation at the hands of local cattle ranchers, fragmentation of forest habitats, deforestation rates of up to 15%, and competition with humans for prey.

To some, jaguars look very much like leopards, but they are sturdier and heavier. The easiest way to distinguish a jaguar from a leopard, beside the jaguar’s much more powerful build, is by the rosettes. The rosettes on a jaguar’s coat are larger, fewer in number, and usually darker with thicker lines that enclose smaller spots. The head of the jaguar is more round and it has shorter, stockier limbs. Because of this the jaguar is sometimes referred to as the “bulldog” of the cat world. The Jaguar, in a recent National Geographic special titled “In Search of the Jaguar,” was named pound for pound the strongest animal in the world.

Jaguars vary from 5.3 to 6 feet in length, excluding a 30 in tail, stand around 27 to 30 inches tall at the shoulder, and weigh between 124 and 211 lb with larger individuals, recorded by scientists, weighing between 288 to 333 lb. Females are typically twenty percent smaller than males. Jaguars in southern Mexico and Central America are typically smaller, 123 lb and 90 lb for males and females respectively.

Jaguars are powerful animals for their size. "They are powerful enough to drag an 800-pound bull 25 feet in its jaws and pulverize the heaviest bones." Throughout the evolution history of mammals, the size and power of predators are proportional to those of their preys. A predator needs to be strong and fast enough to catch its prey. Jaguars hunt wild animals in the range of 300 kg and below in dense jungle, and therefore, their short and sturdy physique is an adaptation to hunt those preys in that environment.

Known for their strong swimming abilities, the jaguar is one of the few cats besides tigers that enjoy water. They often prefer to live by rivers, swamps, and in dense forest with thick cover for stalking prey. They are the largest carnivore in the Western Hemisphere. Jaguars, on rare occasions, are seen as far north as the southwestern United States, particularly in Arizona, New Mexico and Texas. In the early 1900s, the jaguars' range actually extended as far north as Southern California and western Texas. As recently as 2004, wildlife officials in Arizona have photographed and documented jaguars in the southern parts of the state. Presently it is unclear whether recent sightings indicate whether there is a permanent population developing in the Southwest or that these cats are simply transients straying over the border from Sonora, Mexico. However, jaguars are a protected species in the United States under the Endangered Species Act and are considered nongame, therefore making it illegal to shoot a jaguar for its pelt. Fossils of jaguars from as far north as Missouri confirm these cats inhabited much of the Southern U.S. during prehistoric times. These prehistoric jaguars were significantly larger than the jaguars of today.

The jaguar's habitat ranges from the rain forests of South and Central America to marshy and even desert terrain in Mexico, but they are rarely seen in mountainous regions. The jaguar's wide range means that it should not be in danger of extinction in the foreseeable future. The species has declined numbers in some areas due to habitat loss, especially in rain forests and grassland turned into cropland and hunting for their pelts. Jaguars are hunters that do not work with one another outside the breeding season. They hunt around 85 different species including: deer, tapirs, peccaries, and even caiman, up to a certain size. They are opportunists and will take anything from frogs, mice, birds, fish, to domestic livestock. A jaguar's bite can pierce the shell of a turtle (Emmons, 1987). Jaguars are considered a stalk and ambush predator and are not meant to run over long distances but prefer to surprise unsuspecting prey.

The jaguar uses a different killing method from most cats to kill its prey. Instead of biting the neck, to suffocate or sever the spinal cord, the jaguar delivers a fatal bite directly to the skull, piercing the brain. It is because of this killing technique that jaguars often break teeth as they progress in age. Jaguar eat up to 10-70 pounds of food daily.

People in Central and South America see the jaguar as a symbol of power and strength. During Mayan civilization, the jaguar was believed to communicate between the living and the dead, as well as protect the royal household. The Maya saw these powerful felines as their companions in the spiritual world. The Aztec civilization also had the same image of the jaguar as the representative of the ruler and as a warrior. The Aztecs formed an elite warrior class known as the jaguar knights.