Take Auyán-tepui, one of the largest of the group, with the distinction of featuring the world's tallest waterfall, Angel Falls. In 1977 amateur entomologist, Dr Silvano Lorenzoni mentioned leading three expeditions to its summit, and finished his article with the following paragraph:
Moreover, there is one witness who asserts that he has seen three "plesiosaur-like things," about 50 cm. [20 inches] long (with 25 cm. necks) swimming in a river atop the Auyan-tepuy. While this witness can scarcely be called a scientist (he is an adventurer that roams the area digging for diamonds) his statement remains to be one more fascinating piece of information in a jigsaw puzzle that is already taking on a recognizable shape.Reference: Dr Silvano Lorenzoni (1977). 'Extant dinosaurs: a distinct possibility', Pursuit 10(2): pp 60-61. (This was the official publication of the now defunct Society for the Investigation of the Unexplained.)
Would you believe? This very same witness again turned up - this time in the august pages of the National Geographic.
In 1986, the German explorer-writer, Uwe George joined a helicopter expedition to the top of Auyán-tepui. But first they called on 75-year-old Alexander Laime, whom they found living alone in a termite-eaten shack on an island in the middle of a major river, surrounded by his subsistence gardens. Here was man who obviously had carved out his own little niche, and let the rest of the world go by. "Publicity hound" is not a description which springs readily to mind. But let Herr George tell his story:
Alexander is a keen student of wildlife on the tepuis, and he insists that on his 1955 expedition to Auyan he encountered three dinosaur-like lizards. Over tea in a corner of his garden he told us he had come upon them while searching for diamonds in one of the rivers on top of Auyan-tepui.Drawn to scale, they were revealed to be slightly less than three feet long. So what were they? A species of large, long-necked otter was one suggestion. But then one of the scientists in the group pointed out that the rivers up there contain no fish, making it rather difficult for even one otter to survive - let alone three. Also, to the best of my knowledge, otters have furry legs, not scaly fins.
"They were sunbathing on a rocky ledge above the river," he said. "At first I thought they were seals, but when I sneaked closer, I saw they were creatures with enormously long necks and ageless reptilian faces. Each had four scale-covered fins instead of legs."
For proof Alexander rummaged through a pile of papers and came up with some drawings that he had made at the time. To me they resembled plesiosaurs, marine reptiles that became extinct 65 million years ago. [pp 546, 548]
But, you might ask, whatever they were, why haven't they been seen since? After all, there have been many expeditions up Auyán-tepui, and it is even the site of tourist treks. In that case, you have no idea of the sheer ruggedness of the terrain, and the fact that the summit covers 270 square miles. It was not until Herr George's second expedition that they encountered a mountain lion, or puma. What was it doing there? And it had two cubs, so it wasn't just a transient which had scaled the terrible, steep inclines; there was a breeding population. Yet its chief prey, the lowland tapir would never be able to get up there. And yet ...a third expedition discovered tapir tracks in the same general location on the summit.
Reference: Uwe George (1989) 'Venezuela's Islands in Time' , National Geographic May 1989, pp 526 -561