The Rodríguez onza: a legendary cat shot in the Sinaloa sierra

In the mountains of Sinaloa and Sonora, people have long spoken of the onza. A cat like a puma, but slimmer, with long legs and large ears. The Jesuit Ignaz Pfefferkorn described it in 1757 as "a little thinner and lighter in color than the puma, but much fiercer". In 1938, Dale and Clell Lee, with Indiana banker Joseph Shirk, shot an onza near La Silla mountain. Months before the events of 1986, J. Richard Greenwell, secretary of the International Society of Cryptozoology, had visited the area with Robert Marshall, asking about unusual cats. The local men remembered him.

1 January 1986. About 10:30 at night. Andrés Rodríguez Murillo was out in the Sierra Madre Occidental with his companion Ricardo Zamora. Eyes glowed in the dark. The men took them for a deer. Then the animal showed itself. A large cat. It seemed ready to charge. Rodríguez thought a jaguar was about to attack him, and he shot it.

When he looked at the body, it did not seem to be a jaguar. Nor did it look like an ordinary puma. Manuel Vega, a nearby rancher and experienced hunter, knew the shape. It matched the onza his father had shot in the 1970s, whose skull Vega had kept and given to Greenwell. This, Vega said, was an onza.

Ricardo Urquijo Jr. had the specimen placed in fisheries cold storage in Mazatlán. Greenwell was called in. On 20 February 1986, a team led by University of New Mexico mammalogist Troy Best examined and dissected it at the Regional Diagnostic Laboratory of Animal Pathology of the Mexican Ministry of Agriculture. Greenwell and graduate student Ned Gentz worked beside him.

Greenwell's notes recorded an adult female, at least 4 years old. "Upon inspection, the cat, a female, appeared to be as described by the native people." She weighed about 27 kg after freezing. Total length, 186 cm. Tail, 73 cm. The ears measured about 100 mm, very long for a puma. Small horizontal stripes marked the inner surfaces of her forelimbs. She had the coloration of a puma, but she was lean, with long legs and a cheetah-like outline. Karl Shuker noted she had adequate body fat. The slenderness was natural. Her stomach held deer.

Tissues, blood and skeletal material went to institutions in the United States. Texas Tech University reported "great similarity and no significant differences" from an ordinary puma. Greenwell argued this was not conclusive. In 1986 the society's journal, in a footnote to Bernard Heuvelmans's checklist of unknown animals, reported that the cat was not closely related to the fossil cheetah Acinonyx trumani.

The decisive work came from the laboratory of Stephen J. O'Brien at the US National Cancer Institute. P. A. Dratch and colleagues ran protein tests and mitochondrial DNA analysis. They weighed a new species, a puma subspecies, a puma and jaguar hybrid, and a relict cheetah. Their verdict was plain: "we must conclude that the 1986 Onza specimen was a puma."

Shuker had already suspected that Vega was mistaken, and that the cat might be a malformed or infirm puma. After the results he wrote: "it seems that my suspicions may indeed have been justified." He also cautioned that this "does not necessarily mean that all onzas are pumas." Greenwell continued to argue that the species question was open. Writing in Mastozoología Neotropical in 2008, Reyes pointed out that "onza" has been applied to almost every Latin American wild cat.

The Rodríguez onza remains the only onza body that scientists have examined in the flesh. A legend became a specimen on a laboratory table. For some, the DNA closed the case. For others, it closed only one chapter, and the long-legged cat of the sierra still walks in the stories of Sinaloa.