Mário Pereira de Souza's mapinguari encounter on the Jamanxim River

The mapinguari belongs to the folklore of the Amazon. Local accounts describe something nearly 6 feet tall, with huge claws, thick hair, a large monkey-like head and a foul smell. It walks on two legs. Witnesses speak of an extraordinarily loud, human-like scream. Its tracks are said to be "round as a pestle" and "like people's, but backwards."

David C. Oren, an American-born ornithologist at the Museu Paraense Emílio Goeldi in Belém, first heard these tales while doing doctoral bird research in Brazil. Over time he came to think the creature was real.

1975. Mário Pereira de Souza was working as a hunter for a mining camp along the Jamanxim River. The river flows into the Tapajós just south of Itaituba. He was alone. No companions are mentioned.

A long-haired creature screamed. It came staggering toward him on its hind legs, swaying and unsteady. Then the smell. "The horrible smell entered into me and made me dizzy," Souza said.

The encounter stayed with him. "I was not right for two months," he said. He has never set foot in the rainforest again. He later lived in Itaituba, doing odd jobs for the highway department.

Oren visited Souza at least three times. On the third visit, stopping in Itaituba on his way to Barra do São Manuel, he heard the story once more. Souza was clearly reluctant to tell it again. Marguerite Holloway recorded the account in "Beasts in the Mist," published in Discover in September 1999. It remains the only source that names him.

Oren's 1993 paper argued that mapinguari descriptions were "surprisingly consistent with the characters expected of a relatively small (approximately 1.8 m), forest-dwelling mylodontid ground sloth." By 1999 he had more than 50 firsthand witnesses and six expeditions behind him. The evidence disappointed. A hair clump came from an agouti, and faeces yielded no DNA except, in one case, a giant anteater. Oren himself warned that footprint casts carry no scientific weight "because they can be easily faked."

No one has accused Souza of a hoax. The wider search drew doubt. Brazilian scientists were largely sceptical, and one unnamed ornithologist called Oren "a kook." Paul S. Martin argued that ground sloths could not have survived, since no Holocene remains were known. Later work suggested Glossotherium robustum survived into the early Holocene, with a range reaching Amazonia. Others proposed a spectacled bear, an unknown primate, as Bernard Heuvelmans suggested, or a composite folk figure linked to the Curupira.

In 2007 Oren told the New York Times: "It is quite clear to me that the legend of the mapinguari is based on human contact with the last of the ground sloths." Some later accounts say he came to regard it as a myth. No specimen was ever found. The legend lives on in Brian Dunning's Skeptoid and in PBS's Monstrum.

Souza's account remains as he told it. A scream. A swaying figure on two legs. A smell that made him dizzy.