In 1981, reports of a lake-dwelling monster caught the attention of Herman Regusters, an aerospace engineer then at California Institute of Technology's Jet Propulsion Laboratory.
The creature was called Mokele-mbembe and was a prehistoric monster of some kind. It was said to be much like a sauropod; a long-necked dinosaur. But Regusters had a hunch it was still out there.
He decided he wanted to go to a poorly-mapped part of Africa, which now lies within the Republic of Congo, and find the beast himself. After trying unsuccessfully to get his employer and the US Department of Defense to pay for the trip, by arguing that useful maps could be made of the region, Regusters planned to fund the venture himself with the help of some private donors.
Regusters' wife Kia accompanied him and, along with a team of locals, he ventured to the remote freshwater Lake Tele. But, like many others before and since, the American explorer came back with little more than some entertaining stories, which he recounted in talks and written reports.
He claimed several sightings, but there were no photos or videos. In fact, one instance was apparently witnessed by the whole team "except the photographer", Regusters later wrote.
The trip had not been easy. The explorers were beset by sweat bees, had trudged through miles of swamp, endured hot days and uncomfortably cool, wet nights, and survived on locally-caught game such as monkey meat. Still, they were determined to find the monster.
Western references to Mokele-mbembe mostly date to the early 20th Century. German and French visitors to the region told tales inherited from local people about a great monster that lived out in the forest. The details in each report were quite variable.
In some it was truly gigantic – an elephant-eater – while in others it was not much bigger than a hippo. Some mentioned a snakelike head; others said it had a hump.
One instance was apparently witnessed by the whole team "except the photographer"
Any documentary evidence gathered seemed prone to disaster. Photographic film was destroyed, sketches were burned, and audio was riddled with noise.
But that is perhaps the enduring appeal of Mokele-mbembe. It is said to live in such a remote and inhospitable part of the world that some people still cling to the possibility that it is out there. Are they right?
The answer, according to Paul Barrett, a palaeontologist at London's Natural History Museum, is a resounding "no". There is no way that a sauropod-like creature could still exist without humans being aware of it, he says.
"We have no evidence in the fossil record for the last 66 million years for anything that looks like a sauropod anywhere in the world," he says.
Even setting aside dinosaurs, a really big land or lake animal, of whatever sort, is unlikely to be hiding in the African jungle. Humans have not discovered a creature that weighs more than a tonne for at least half a century, notes Barrett.
"Big animals need big populations to keep going," he says. "They also need large geographic ranges to fulfil their feeding needs."
That just wipes out this idea that you could expect ancient relics in Africa
The idea that one or two giants are hiding out in Lake Tele just does not make sense.
Darren Naish, a science writer and palaeontologist, agrees. Some cryptozoologists who believe in Mokele-mbembe say that prehistoric creatures could have persisted in Africa because it is so "unchanged". But, as Naish points out, this is a mistaken view. Flora and fauna on the continent have gone through a wide catalogue of changes, up to and after the dinosaurs.
"Even the rainforests, they waxed and waned substantially over the years," he says. "They're geologically young things, so that just wipes out this idea that you could expect [ancient] relics in Africa."
But could some of the stories told to local explorers relate to some other large creature that once lived in the area?
Perhaps, says Naish. Some now think an extinct species of rhino used to inhabit land near to Lake Tele. Stories of it could have been passed down and changed over time.
Local discoveries of fossils or footprints could have inspired myths about their origin
Some of these animals could also have been mistaken for Mokele-mbembe or something like it, Naish adds. Hippos, crocodiles, large turtles, swimming elephants – even odd-shaped logs floating around could be misinterpreted.
Perhaps the most intriguing thing is that this is not an unusual story. Aside from Mokele-mbembe and Scotland's long-rumoured Loch Ness Monster, there are other such tales. There is reportedly a "Bessie" in Lake Erie in North America and "Tessie" in Lake Tahoe, a "Bownessie" in England and "Kussie" in Japan. It seems that many lakes have monsters to go with them.
Barrett suggests one possible reason. Some age-old stories could be the relics of warnings from parents trying to keep their children from drowning. If children stay clear of a lake "monster" they will, in theory, be safer.
In the early 1900s, there was something of a "dinosaur craze"
Local discoveries of fossils or footprints could have inspired myths about their origin, says Martin Sander at the University of Bonn in Germany, who has written several papers on sauropods. He gives a good example: the "snakestones" of England.
These are ammonite fossils with a snake's head carved into them by humans, which give the impression of a coiled reptile. They were said to be the remnants of snakes turned to stone by St Hilda in the 7th Century. In reality, they are simply fossils that have been tampered with.
As for the Mokele-mbembe stories, the era in which they were reported by Western explorers may have been a key factor, says Naish. In the early 1900s, there was something of a "dinosaur craze", he says. "It was bigger than [Jurassic Park]."
What's more, Sander notes that several references come from a well-known animal dealer called Carl Hagenbeck in 1909, as an apparent publicity stunt. Hagenbeck reported stories about Mokele-mbembe that he had heard from others. "He would have known about these German palaeontological excavations [in the region]. He was a hunter but he also ran the Hamburg Zoo," says Sander.
Any expedition to uncover the unknown has the potential to yield interesting and unexpected findings
What's more, a long-running assumption about the monster is that it is a lake and swamp-dweller. This is the sort of life that people thought sauropods enjoyed one hundred years ago, but we now believe that they generally stuck to dry land. The fact that old speculations have got caught up with the Mokele-mbembe myth is another reason to doubt that these stories were ever grounded in fact.
Despite that, there is still value in such myths, says Barrett. Any expedition to uncover the unknown has the potential to yield interesting and unexpected findings. As long as trained field biologists are present to capture a true record of anything out of the ordinary, should it rear its head from murky waters.
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