The Jaguar (Panthera onca) is one of the four big cat species of the world - coming in third to the tiger and lion, and reigning supreme as the largest cat of the Western hemisphere. Although its range was once much wider, currently the Jaguar can be found in Mexico/Central America down to Paraguay and northern Argentina. They can sometimes be spotted in the southwest United States, but apart from a small breeding population in Arizona they're extremely rare.
The Jaguar resembles the Leopard in appearance and the Tiger in behavior. They're built more solidly than the Leopard, weighing up to 211 lbs. - one large male Jaguar weighed in at 350 lbs.! And they measure about six feet from nose to base of the tail, with a short 30-inch tail.
Jaguars are what's known as a keystone species, which means that they are integral to the stability of the ecosystems in which they live. Like the Tiger, they are solitary, opportunistic ambush hunters with an extremely powerful bite - even relative to the other big cats. This bite strength allows them to pierce the shells of large turtles, and deliver killing bites to the skulls of the deer, caimans, capybaras, tapirs, foxes and anacondas (!!!) it catches. Basically, it eats whatever the hell it wants to.
Jaguars have a bit of color morphism in their populations. The melanistic Jaguar (pictured) is the most common variation, and are known as black panthers even though they are NOT a separate species. Much more rare is the white panthers - albino individuals that are not as common because the gene for albinism is recessive rather than dominant, like the melanistic gene.
Jaguars are crepuscular, meaning that they are most active during the twilight and dawn hours. It is listed as Near Threatened because of its population decline due to loss of habitat and hunting - even though the trade of Jaguars or their body parts is illegal.