This photograph of a shot Bili ape appeared in Vol. 1 of Adolf Friedrich Herzog von Mecklenburg’s tome Vom Kongo zum Niger und Nil: Berichte der Deutschen Zentralafrika-Expedition 1910/1911, which was published in 1912 – more than a century before this highly distinctive ape form’s reality was formally recognised by science
Here's the latest in my occasional series of ShukerNature cryptozoology articles re anomalous and controversial chimpanzee forms (click here for my account of the pygmy chimpanzee or bonobo, here for the koolookamba, here for Ufiti, and here for 'apeman' Oliver).
Until quite recently, even amid the many remote regions of darkest Africa, the possibility of an unknown form of anthropoid existing there yet still eluding scientific recognition seemed ludicrous - but then came the Bili (aka Bondo) ape.
The saga of this remarkable, highly controversial primate began more than a century ago, when in 1898 a Belgian army officer returned home from what is now the Democratic Republic of Congo with some gorilla skulls obtained by him in a forested region near the village of Bili, on the Uele River in northern Congo's Bondo area - even though no other gorillas had been found within hundreds of miles of Bili before (or since). He donated them to Belgium's Congo Museum in Tervueren, where in due course they were examined by its curator, Henri Schouteden. He was sufficiently struck by their anatomical differences from other gorilla skulls as well as by their unique provenance (roughly halfway between the extreme edges of the western and eastern distribution of any gorilla populations) to classify them as a new subspecies of gorilla, which he dubbed Gorilla gorilla uellensis.
Less convinced of their separate taxonomic status, conversely, was mammalogist Prof. Colin Groves, whose examination of these skulls in 1970 led him to announce that they were indistinguishable from western lowland gorillas. Thereafter, the Bili ape sank back into obscurity - until 1996, when Kenyan-based conservationist and wildlife photographer Karl Ammann, intrigued by its strange history and apparent disappearance, set out on the first of several Congolese quests to rediscover this mysterious primate.
And rediscover it he did, bringing back such compelling evidence for its presence that several other notable investigators launched their own searches, and returned with equally fascinating clues concerning the Bili ape's nature. Such researchers included primatologist Dr Shelly Williams from Maryland's Jane Goodall Institute, Dr Richard Wrangham from the Leakey Foundation, Dr Christophe Boesch from Leipzig's Max Planck Institute for Evolutionary Anthropology, Dr Esteban Sarmiento from New York's American Museum of Natural History, and Dr George Schaller from New York's Wildlife Conservation Society.
What made their various finds so especially interesting was the ambivalent identity that they collectively yielded for the Bili ape - because, uniquely, it deftly yet bemusingly combines characteristics of gorillas with those of chimpanzees, creating a shadowy anthropoid that is at once both yet neither. For instance: if the Bili ape is a chimpanzee, it is a veritable giant, because videos of living specimens and photographs of dead ones suggest a height of 5-6 ft - a mighty stature supported by the discovery of enormous footprints, some measuring almost 14 in long, and therefore nearly 2 in longer even than those of the mountain gorilla!
A dead Bili ape, revealing its noticeably large size (http://www.factzoo.com/mammals)
Also, very large ground nests constructed by Bili apes have been found that compare with those created by gorillas; normal chimps build smaller, tree-borne nests. Further evidence of the Bili ape's great size comes from local Bondo hunters, who distinguish two distinct apes - 'tree-beaters' (normal chimps) and 'lion-killers' (the Bili apes). The latter earn their name from their combined size and ferocity, a mix potent enough to ensure their terrestrial safety even in a jungle profusely populated by lions and leopards.
Indeed, so unafraid of these great cats are the Bili apes that according to media claims they hoot loudly when the moon rises and sets - an activity unknown among normal, smaller chimps, who avoid doing so in case they attract predators. However, these latter claims have been denied by Amsterdam University field researcher Cleve Hicks, who spent a year with colleagues tracking Bili apes during from mid-2005 to June 2006, followed by a second study spanning July 2006-February 2007.
Particularly noticeable is the presence of a pronounced sagittal crest running along the top of one of the original skulls collected by the Belgian army officer, and also on a Bili ape skull found by Ammann in 1996 - because this crest, normally an indication of powerful jaws as the jaw muscles are attached to it, is characteristic of gorillas, not of chimps. Conversely, the facial anatomy of the Bili skulls is decidedly chimp-like, not gorilla-like. In addition, hair samples taken from Bili ape ground nests have been shown to contain mitochondrial DNA similar to that of chimps, and the fruit-rich content of examined faecal droppings is again consistent with a chimp identity - although, perplexingly, the droppings themselves outwardly resemble those of gorillas.
So what is the Bili ape - a gorilla-sized chimp (freak population?/new subspecies?/new species?), an aberrant form of gorilla (freak population?/new subspecies?/new species?) that has evolved certain chimp-like anatomical and behavioural characteristics, or even possibly a genuine chimpanzee-gorilla hybrid? No confirmed crossbreeding between chimp and gorilla has ever been recorded, but the two species are sufficiently similar genetically to engender viable offspring. Mitochondrial DNA is passed down exclusively from the maternal parent, so if such interspecific matings are indeed occurring they must involve female chimps and male gorillas, to explain why the mitochondrial DNA from the Bili ape samples is chimp-like.
Happily, however, the Bili ape's identity was eventually unmasked. Comprehensive DNA analyses, including nuclear DNA (thus shedding light on both the maternal and the paternal lineages of the Bili ape), had been underway since autumn 2003 at Omaha's Henry Doorly Zoo, under the auspices of conservation geneticist Dr Ed Louis, and involving DNA comparisons with gorillas, chimps, and also bonobos (pygmy chimps).
So too had analyses of mitochondrial DNA taken from faecal samples conducted by Dr Cleve Hicks and other Amsterdam University colleagues, who had also examined these primates' behaviour in the field. And in 2006, this latter team announced that their findings all confirmed that the Bili ape belongs to a known subspecies of chimp – the eastern chimpanzee Pan troglodytes schweinfurthii. Presumably, therefore, the Bili ape's very distinctive morphological features have evolved through its population's isolation from others of this subspecies but involve relatively little change at the genetic level. After years of mystery and intrigue, the riddle of the Bili ape had at last been solved.
This ShukerNature post is excerpted from my book The Encyclopaedia of New and Rediscovered Animals (Coachwhip: Landisville, 2012).