African mammals started out weird. When the dinosaurs bowed out sixty-five million years ago after a rough season with a few Indian volcanoes and a rough weekend with an asteroid near Cancun, Africa was already a continent adrift. Much like the modern island continent of Australia, home to unique mammalian lineages like kangaroos, Tasmanian devils, and platypuses, Africa would have been a very strange place to visit in its early mammalian days.
Elephants wallowed in the mud like hippos while hyraxes – squat rabbit-like animals today – wandered the forests and plains as deer-like and rhino-like herbivores. Mixed into the herbivorous fauna was the elephantine Arsinotherium the earliest relatives of monkeys and apes, and the all-important extinct carnivorous mammals, the creodonts. But the exclusive African club couldn’t last forever. When Africa docked with Asia, the floodgates were opened and pulses of immigrants from the northern continents made their way into the bizarre world of giant hyraxes and buck-toothed elephants. For the next twenty million years, the mammals of Africa became more modern with the giant-headed creodonts fading out as dogs, cats, and hyaenas moved in and the hyraxes disappearing while giraffes, cows, and antelope found the continent a perfect place to set up shop. This was the Lion King-ification of the African ecosystem.
The transition from the ancient to the modern in Africa is a Miocene story, a time period Dr. Mikael Fortelius and Dr. Meave Leakey have spent decades exploring. Our first field excursion for paleontology was to a newly discovered site near the Napudet Hills that may reveal these faunas in flux. The excursion was actually Dr. Leakey’s first visit to the locality since a lot of new material was discovered. Her field crew had carefully marked and documented several fossils, but despite years of work in the Turkana Basin, some fossils seemed unfamiliar, evidence that the site may be older than any other rock explored by the crew accustomed to the Plio-Pleistocene.
We piled off the truck and set out over the basalt cobbles that litter the place, evidence of the recent eruptions that built the nearby hills. Rob pointed out the artifacts that dotted the outcrop, though below the stone tools were much more ancient remains. Our first stop was to a large anthracothere tooth, an extinct relative of pigs and hippos that has been implicated in the origins of whales. Anthracotheres were part of the ancient African fauna, and were extinct by the end of the Miocene when hippos really got rolling.
Dr. Fortelius explained how to recognize this ancient beast and we began a survey of the dried creek bed around the tooth. Everything was blanketed in basalt and the field crew’s honed fossil hunting skills were on full exhibition. Those of us less familiar with the conditions managed to find only a few scraps let alone the tiny cusp of a buried tooth.
Our next stop was along a low slope where the teeth of a gomphothere, a relative of the mastodon and distant relative of modern elephants, had exploded from the outcrop. Spalls of teeth formed a thin crust around postcranial bones such as the ankle bone and long bones of the strange elephant. Immediately flags were distributed and the students began flagging all fossil material in the vicinity. By the time the hunt was over, more of the gomphothere had been discovered on the surface, including the other ankle bone. The entire squat elephant was hunkered into the hill along with the remains of a few giant hyraxes and some of the immigrant bovids that had begun their incursion into East Africa.
As we hiked back, Dr. Leakey and Dr. Fortelius kept an eye out for layers of ash that could be used to get a date for the site. A possible candidate was found with an ancient termite mound rising from the tuff.
It was time to say goodbye to Napudet, but not the mysterious Miocene. Later in the week we blasted forward in time to the very end of the Miocene in the rocks preserved at Lothagam.
You may remember Lothagam as a geological mecca we visited during the geology module with Dr. Craig Feibel. Then we were primarily interested in learning about the uplift of the ancient outcrop and the evidence of flowing water and changing climates preserved in the rock. This time we would be spending more time with the myriad fossils that carpet Lothagam that record the slow demise of ancient Africa and set the ecological stage for the diversification of our own bipedal lineage.
The fossiliferous (fossil bearing) section at Lothagam begins with the animals that lived and died in the area 7.4 million years ago. Today, Lothagam is capped by the monolithic horst overlooking the intense oranges and reds of the Lothagam badlands. 7.4 million years ago, the badlands were a meandering river system. As we spread out from the lorry, the ancient denizens of the river system made themselves known: crocodiles of all shapes and sizes were mushed in with the abundant hippopotamus material. In a site so rich, it’s easy for a fossil hunter to only see the large bone fragments and miss the small teeth of primates and carnivores that may not be as obvious as an elephant femur.
In order to more fully sample the site, Meave and Mikael introduced the field school to detailed transect techniques. The students spread out at arms length and tried to move in a straight line while collecting everything along the path. Easier said than done.
Fossils were bleeding from the ground and it was easy to be distracted by all the bone and lose track of the line’s destination leading a few line wanderers to reset themselves every few minutes and a few discussions of where we were heading.. The blazing sun doesn’t make it any easier to keep on the straight and narrow either.
Along the route, fragments of a hippo’s humerus came together along with the wrist bones and toes of an elephant who hadn’t fully reached adulthood (an observation made after an end cap, or epiphysis, was found near the animal’s toe bones).
A second transect took place further up in the appropriately named Upper Nawata Member. At this point, East Africa had taken on a very modern character. If we could visit, there would still be a lot of unfamiliar animals, but the climate and the creatures – big cats, massive elephants, and large baboons – would have looked more familiar than they did in the lower section.
After a survey that turned up a hippo pelvis, turtle shrapnel, and a giraffe limb, we once again stooped at arms length and tried to find those elusive primate teeth. No such luck on our steeply dipping transect surface.
Back at camp we poured out the collection bags and everyone worked on identifying the finds. The elephant navicular was successfully identified by Sam and Aaron weighed in with some smaller carpels from the same animal. Ana found a long, thin toe bone of a terrestrial hippo. Yes, Lothagam had prancing hippos. Evolution is an amazing thing.
Once everyone had emptied their bags and identified the fragments that could be given names, we sat down to review the data. Our single day of sampling turned in an impressive collection of material that was carefully accessioned for further research in the dynamic world of the Miocene.
Now that we had collected material, it was time to prepare and analyze the fossils to figure out what they tell us about the environment our earliest ancestors called home…