Rusinga: primate paradise in the African Miocene… and more!
Among the new illustrations that I prepared for the 3d edition of “Our Origins” there is a scene showing several primate species that lived in what is now Rusing Island, Kenya, during the early Miocene.
Rusinga is a small island at the Northeastern corner of Lake Victoria in Kenya, but some 17 million years ago the area corresponded to an alluvial floodplain. The vegetation was rather open in the plains, but there were dense gallery woods along the water margins. That combination of environments provided excellent habitat for many species of primates, including 2 species of the genus Proconsul, as well as Dendropithecus and Limnopithecus.
Here is the Rusinga scene with the various early Miocene primates, including Proconsul nyanzae (foreground), Proconsul africanus (top left), Dendropithecus (top right), and Limnopithecus (center right).
While the primate fossils, and especially those of Proconsul, have made Rusinga a familiar word among paleontologists, the site has yielded fossils of many more mammal species, from tiny flying squirrels to ponderous anthracotheres, looking somewhat like a cross between a pig and a hippo…
A scene in the early Miocene of Rusinga, with flying squirrels (Paranomalurus), a chalicothere (Chalicotherium) and two anthracotheres (Masritherium)
Were there sabertooths in Rusinga to trouble the lives of our early relatives? There were indeed, although they were not as impressive as one might expect. Afrosmilus was an early member of the family Barbourofelidae, but with the approximate size of a lynx, it was much smaller than its later relatives from the late Miocene of Eurasia and North america, such as Barbourofelis. Also, its canines were only slightly enlarged, but often it is in such modest animals that the potential for future specialization is to be found.
So, this sabertooth was hardly the dominat predator in the Rusinga environment. That privilege did not even correspond to a member of the order Carnivora, but rather to a creodont, a survivor of an ancient lineage of predatory mammals which flourished in the early part of the Tertiary, and by the Miocene were extinct in most of their former range. But in Africa they not only survived, but they reached truly enormous size. Hyainailouros, the giant creodont from Rusinga, would have weighted as much as a modern lion, but like other members of the family Hyaenodontidae (the “dog-like creodonts”) it had a disproportionately large skull for its body size. This means that the jaws of this beast, armed with teeth suited for tearing meat and crushing bone, could easily turn a limb apart from a human like you or me with a single devastating bite.
Meet Hyainailouros, the giant creodont from Rusinga.
So, we can only imagine how nightmarish the apparition of Hyainailouros would be for our early relatives from Rusinga. Small wonder that all these primates displayed excellent climbing abilities, because the treetops were the one place were Hyainailouros could not follow them. Like all hyaenodontinds, these predators had limbs specialized for locomotion on the ground, almost like those of an ungulate. But the more modest, cat-like Afrosmilus probably did not have that limitation. So it is possible that, after all, the Rusinga primates had more to fear from the unprepossessing early sabertooth than from the monstrous creodont…