Cook's Grison

Often when new animals and plants are given a scientific name, part of that name is based on the name of a person. The reasons for using a person's name are as varied as the personalities doing the descriptions. Often the reason is straightforward; it is an acknowledgment of a scientist's contributions to the study of a group of organisms, or to recognize the person who first discovered the specimen. Such a practice has always been associated with the description of new animals from Hagerman starting in 1933 when C.L. Gazin described a new species of fossil shrew, naming it Blarina gidleyi after James Gidley. Gidley was Gazin's predecessor at the Smithsonian and the first paleontologist to work at Hagerman.

The following year Gazin published the first paper on the carnivores of Hagerman Fossil Beds and described the mustelids (the carnivore group to which weasels, skunks, badgers and wolverines belong). Among the animals described was an animal closely related to the living South American grison (known as the huron in Spanish and furao in Portuguese) which he named Lutravus cooki. Although later studies of this animal and its relatives resulted in a change in the first name, we now refer to this animal by the scientific name Trigonictis cooki.Anyone who has spent any time reading about the history of paleontology at Hagerman Fossil Beds can probably guess the individual after whom the species was named, Elmer Cook. Elmer, born in 1887 in Glenwood, Utah came to Hagerman as a boy about 1901 and was a long time resident. In many of the early scientific papers written about the fossils of Hagerman, Elmer is credited as being instrumental in bringing the fossils in the Hagerman area to the attention of the scientific community. He worked for the Smithsonian during their excavations at the Hagerman Horse Quarry and ending in 1934, but continued to collect specimens for the Smithsonian. In recognition of his many contributions, Gazin named this newly discovered animal after him.

While most people may not know too many details about the anatomy of the family Mustelidae, most people are familiar with at least one of the group's obvious attributes - their well developed scent gland! While the development of a scent gland is carried to the extreme in skunks, a well developed scent gland is present in all members of the group including weasels, badgers and wolverines. Like all soft tissues, such as muscle or nerves, the scent glands are not preserved as fossils (for which paleontologists are grateful). Given the absence of this important feature, the question might be raised, "How do we know the fossil forms like those found at Hagerman are related to the living species in South America?" As is the case for many mammals, the patterns and shapes of the teeth are distinctive. Gazin based his original description of Trigonictis cooki on a lower jaw with two premolars and a molar preserved. The number of teeth in the jaw, their relative size to each other, and the shape of the cusps of the different teeth all provided clues as to the type of animal from which the jaw came. However, there were enough differences to also demonstrate that this was a new member of the group and that it deserved a new and distinctive name, thus providing an opportunity for Gazin to recognize Elmer Cook's contributions.

Members of the Mustelidae family are found around the world, including South America, where relatives of our fossil animal Trigonictis cooki live today. One species does get as far north as southern Mexico, but is also found as far south as central Peru and southeastern Brazil.

Along with the grison there are other members of the Mustelidae that are found in South America, but like the grison, all are derived from North American ancestors, and many have ancestors known from fossil localities all over North America. It may be that the species of Trigonictis found at Hagerman and elsewhere, is the direct ancestor of the living genus Galictis which includes the two species that are known as grisons.

The living grison is about the size of a mink and has a similar elongated body seen in weasels and minks. Since Gazin's original description, additional specimens of Trigonictis cooki have been found, including partial skeletons which provide a better idea of the size and proportions of the animal. In addition to Trigonictis cooki, there is a second larger species of Trigonictis known from Hagerman. This second species was also described by Gazin as Trigonictis idahoensis but it has since been determined that this is the same as an earlier described species now known as Trigonictis macrodon (meaning large tooth). At one time it was thought that the smaller species cooki might be the female form of the larger species macrodon. At first this seems possible since we know in modern weasels and their relatives, the males are noticeably larger than the females. However, many features of Trigonictis cooki distinguish it from the larger species. While we might not expect to have two closely related species of carnivore living in one place, a close relative of the living grison, called the tayra is also found from southern Mexico into South America. The tayra is larger than the grison, and while the grison lives on the ground in more open country, the tayra is a forest animal and lives in trees.

Perhaps the two species of Trigonictis found at Hagerman were similar with the smaller cooki being the open country form and the larger macrodon preferring forests. Based on our current knowledge of the geology and paleoecology at Hagerman, we know that both types of habitats were present in the area 3.5 million years ago. As more specimens of Cook's grison and the "large tooth" grison are found, we will have more information with which to work.

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Bjork, P.R. 1970. The Carnivora of the Hagerman Local Fauna (Late Pliocene) of Southwestern Idaho. Transactions of the American Philosophical Society, new series, 60(7):54 pp.

Gazin, C.L. 1934. Upper Pliocene Mustelids from the Snake River Basin of Idaho. Journal of Mammalogy 15(2): 137-149.

Ray, C.E., E. Anderson, and S.D Webb 1981 The Blancan Carnviore Trigonictis (Mammalia Mustelidae) in the Eastern United States. Brimleyana No. 5:1-36.

This article originally appeared in The Fossil Record, Fall 1998

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