Locked within Rusinga Island are secrets from the past. Secrets of life long gone trapped in the ash of an ancient volcano. It is sat in the north east of Africa’s largest lake known by locals as Nam Lolwe, Nnalubaale, and Nyanza, and was called Lake Victoria by the British in 1858. Fossils on Rusinga Island have been known by locals for many centuries, including the remains of extinct crocodiles, antelopes, and ancient primates.
A gold prospector discovered the first primate fossil, a small jaw bone, on the island in 1909. But it wasn’t until expeditions in the 1930s and 1940s by Louis and Mary Leakey and their team that put this and other fossils on the world stage. Louis and colleagues found several teeth and bones from primates in the 1930s, which they named Proconsul. In 1948, Mary found the first fossil skull of this ancient ape. Originally seen as an ancient link between humans and apes, the media around the world flocked to see this beautiful specimen, which set up the Leakeys for lots of generous funding opportunities for the future.
Today there are four known species of Proconsul, which lived between 23 and 14 million years ago. It was not an ape-human ancestor, or the ancestor of chimpanzees, as was once thought. Lacking a tail, Proconsul may be one of the earliest ancestors of apes, or it may just be an evolutionary dead end, leaving no descendants.
It wasn’t just the ecosystem of 23 million years ago that Rusinga Island has revealed. Life in the Pleistocene, the time of the Twilight Beasts, was also preserved in younger rocks. Fossils of turtles, extinct antelopes (Damaliscus hypsodont), extinct pigs (Kolochoerus) and many other extinct species of bovids have been found. Including one very odd species, Rusingoryx atopocranion, the bellowing antelope.
Rusingoryx is a relative newcomer to the mélange of Pleistocene beasts. Found on a site, appropriately named Bovid Hill, the first fossils were named in 1984. It was almost 20 more years until more excavations found many more specimens, some of which showed signs of being butchered by humans. Closely related to the wildebeest, this animal was a much smaller antelope, with some peculiar features. (A quick side note on antelopes and bovids. Antelopes may be more familiar as those fast, springy, deer like animals seen on nature programmes. They are however a kind of catch-all name for animals in the Family Bovidae that are not cows, sheep, or goats. So wildebeests are called antelopes despite looking more like cows or bison, because of their anatomy. And our strange beast, Rusingoryx, is also an antelope.)
Although Rusingoryx has been found at other sites in Kenya, the abundance of fossils at Bovid Hill have given us a lot of information about this unusual bellowing beast. The skull, well the skull was weird. With a pointy nose, it has a feature not seen in any other mammal: a large empty nasal passage. The rest of the skeleton shows that this antelope was fast and well adapted to running in open landscapes to flee from predators.
So many individuals have been found at Bovid Hill, that they may have been from a single herd, which were all buried very quickly in a shallow river channel around 65,000 years ago. But this herd may not have died naturally. There are stone tools in the same deposits, and cut marks on the bones, showing that this may have been a kill site for Homo sapiens. How did humans kill such a large group of fast herbivores isn’t known, but it does show that they did hunt them and trap them, perhaps in water to slow them down.
In the past, Rusinga Island was not an island, but joined to the mainland of Kenya until the lake subsided over time, flooding more of the land until Rusinga was seperated. All these herds of different species were roaming and moving across the plains of Kenya. The adaptations of Rusingoryx and other species show that the plains of Kenya were open grasslands, different from the drier grasslands in Kenya today. This may be the reason for their extinction. These unique creatures were well adapted to the open plains, but their teeth were not adapted to drier grasses. Although they were hunted by humans, it may have been the changing environment that caused Rusingoryx to vanish.
And that weird nasal passage full of air? Well, it was quite bizarre and unlike anything seen for 80 million years. It was hollow, and some researchers suggest that it may have been used to make deep bellows, similar to hadrosaur dinosaurs. This is an example of convergent evolution, where two completely different species evolved similar traits independently. Just like hadrosaurs, Rusingoryx may have used their nasal dome for vocalisation to communicate in the herd, or to attract a mate. It would have been amazing to hear the low bellow of this beast on the plains of Kenya, and our species did. Sadly, they became extinct sometime around 10,000 years ago, so like the trumpeting dinosaurs, we can only imagine the sounds they made.
Written by Jan Freedman (@JanFreedman)
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