De Loys's Ape (Ameranthropoides loysi), Tarra River, Venezuela

François de Loys was a Swiss oil geologist and Doctor of Sciences. Between 1917 and 1920 he led a petroleum survey near the border of Colombia and Venezuela, in the forests south-west of Lake Maracaibo. By one account, 20 people set out and only 4 survived. The rest were lost to disease and to attacks by the Motilone people.

The party was camped on the bank of a tributary of the Tarra River, near the village of Casigua. George Montandon's 1929 paper puts the date in 1917, while most retellings say 1920. Two large creatures, a male and a female, came towards the camp. De Loys first took them for bears, then saw they were ape-like. In Karl Shuker's words, they were "tall, hairy, tailless apes walking on their hind legs."

They "advanced howling and gesturing, as well as breaking and holding some branches." They screamed and ripped foliage from the vegetation. By the account, they even threw their own excrement at the explorers. The party fired, killing the female and wounding the male, which escaped.

The men sat the body upright on a packing crate and propped its chin with a long stick. They measured it at 1.57 m. It had no tail and 32 teeth, where New World monkeys have 36. The fur was greyish-brown. A pale triangular patch marked the forehead.

Then the evidence slipped away. The skull was reportedly used as a salt container and fell apart. The skin decayed. Most of the photographs were said to be lost when a boat capsized. One survived.

In 1929 Montandon found that photograph in de Loys's files. On 11 March he presented it to the Académie des sciences and named it Ameranthropoides loysi, Loys's American ape. The Illustrated London News ran it on 15 June 1929, and the pushback was quick. In August, Sir Arthur Keith called it "nothing more than an ordinary spider monkey." Primatologist Philip Hershkovitz also judged the account unreliable.

A. James Durlacher had interviewed former members of the expedition in 1927. He later told Earnest Hooton the animal was "a spider monkey, known in that region as the marimonda." On 19 July 1962, Venezuelan physician Enrique Tejera, who had known de Loys in Venezuela and called him a "bromista", or prankster, wrote to El Universal. In Tejera's telling, the animal was a monkey whose infected tail had been amputated, and it died at Mene Grande. De Loys posed it and photographed it as a joke.

The picture itself holds a clue. Banana plants stand across the river. Bananas are cultivated, which places the scene near people, not in unexplored jungle. In 2008 Urbani and Viloria concluded that Montandon and de Loys arranged the fraud together. Others tie Montandon's enthusiasm to his racist theory of "hologenesis", in which human races descended from different apes.

Not everyone closed the file, and in 1991 Michael Shoemaker argued that the chest, hands and face did not match a spider monkey. Heuvelmans allowed it was "possibly not an unknown ape, but certainly a gigantic spider monkey." Most now identify it as the white-fronted marimonda, Ateles belzebuth. Still, the image anchors the South American Mono Grande tradition and has run through books from Heuvelmans to Jerome Clark's Unexplained!. One photograph, one crate, one stick beneath the chin.