The Greater grison is a slender animal with short legs, a long neck, and a short, bushy tail. It can be found only in the Americas. The back, flanks, top of the head, and the tail of this mustelid are grizzled grey in color, while the rest of the body is much darker, and usually solid black. A narrow whitish stripe separates the darker and lighter fur on the head and shoulder, but not further back, where the two colors may, in some individuals, blur into one another. The tail is covered with bushy hair similar in color to that on the animal's back. The head is flattened and broad, with short, rounded ears, and dark brown to black eyes. The legs are muscular, with five webbed toes, each ending in a sharp, curved claw.
Greater grisons are native to Central and South America, ranging from southern Mexico in the north, to central Brazil, Peru, and Bolivia in the south. They inhabit a wide range of forest and cerrado habitats and are usually seen near rivers and streams. In some regions, grisons may also be found in cultivated areas, such as plantations and rice paddies.
Greater grisons are primarily terrestrial, although they can climb trees and swim well. They are mostly diurnal, and only occasionally active at night. They live alone or in pairs within home ranges that take at least 4.2 square kilometers (1.6 sq mi). They spend the night sleeping in cavities in hollow logs or beneath tree roots, or in the abandoned burrows of other animals. Greater grisons have an interesting way of hunting their prey. These animals move in a zigzag pattern, making short bounds and occasionally stopping to look around with their heads raised and sniff the air. When moving more cautiously, they press their bodies close to the ground in a movement that has been described as 'snake-like'. When feeling threatened Greater grisons make a series of grunts that rise in intensity and frequency until they become rapid barks, and finally, a single loud scream with their teeth bared. Like many other mustelids, Greater grisons have anal scent glands that secrete a yellowish or greenish musk; this can be sprayed at attackers and can be used to mark the grison's home territory.
Greater grisons have a carnivorous diet. They mainly feed on small vertebrates, such as fish, amphibians, lizards, birds, and other mammals. They will also sometimes eat fruits.
The breeding season of Greater grisons usually takes place in October. After the gestation period of around 40 days, the female gives birth to 2-4 young. Newborn baby grisons weigh less than 50 grams (1.8 oz), and are initially blind, although with a short coat of hair already bearing the adult pattern. Their eyes open after 2 weeks, and they begin to eat solid food at 3 weeks. The adult size is usually reached at the age of 4 months.
Although not considered threatened Greater grisons suffer from hunting and trapping for their body parts. They are also popular in the pet trade.
The IUCN Red List and other sources don’t provide the number of the Greater grison total population size. Currently, this species is classified as Least Concern (LC) on the IUCN Red List and its numbers today are stable.