Fossils and our earliest ancestors

We had the chance to visit a fossil site today in what they call the Cradle of Humankind.  The area around Johannesburg has a number of major fossil sites with evidence of early hominids going back more than 3 million years.  The site we visited, Drimolen, has produced fossils from 5 different kinds of early hominid species.  We drove out to the site, about an hour out of Johannesburg, through golden savannahs with gentle hills and small rocky rises.  The land where the site was is also an animal preserve, so as we got closer, we starting seeing wild animals, almost like a drive-through safari park.  We saw all kinds of bok, zebras, giraffes, rhinos, buffalo, and a jackal.  We also saw several warthog families complete with babies (and yes, they were adorable!).  The road to the site narrowed and got rougher and rougher until we reached a point where our bus couldn’t continue.  We thought we might walk the rest of the way (just a mile or two), but the idea of those animals out there made us call for help from the wildlife preserve rangers.  They showed up with a giant open-sided safari vehicle, and bumped us along the road until we got there.

When we arrived, we sat out under a grove of graceful trees and had some tea and coffee while we listened to one of the experts who excavates at the site.  Dr. Morris Sutton told us about the geography that makes this are particularly fossil-rich, with ancient caves filled with millions of years of sediment that has compacted into a kind of concrete-like rock called breccia.  Fossilized bones get compounded into the breccia and are accessible via digging and drilling.  The Drimolen site we visited has hominid fossils, including homo erectus, dating from 3.2 million years ago.  Dr. Sutton also told us how they identify different species and gather information from the fossils about how these hominids lived.  We had the chance to see and handle a number of plaster casts of hominid skulls so we could see their similarities and differences, and see how small differences in jawlines, teeth, and spinal stems allow scientists to understand species differentiation.  One of the most interesting fossils from the site is a piece of the back of a skull of an adolescent male.  It has two round puncture marks, which perfectly match the teeth of a now-extinct animal called a false saber toothed tiger.  We also got to see a piece of breccia, which was heavy and in which smaller stones and fossils were easily visible. 

After the open-air lecture, Dr. Sutton took us down into the excavation site.  They are currently working in a small cave where the roof has collapsed, so it looks more like a deep pit or grotto.  Down the walls of the cave, we could see layers of breccia and actual fossils in the stone—including an elephant tusk!  This cave is part of a large system of caves in the area, although they are mostly filled in with hardened sediment that deposited there over millions of years.  This sedimentation is what washed bones and other debris into the caves, which then fossilized over time.  We had the chance to explore the site, and then Dr. Sutton took us higher up on the hill, where there was another cave, with its mouth hidden in a small grove of trees.  This cave is connected to the first underground, although its all filled in and not passable.  They have not begun serious excavation in the second cave yet, although initial investigation suggests that they will have to go deep before they hit fossil layers.  Apparently, the small grove of trees at the mouth are a particular kind of tree that thrives on some of the minerals that are exposed by these caves, and one way to find cave mouths is to look for groves of these trees.  We looked around us on the rolling hills and spotted several small stands of these trees—so this particular cave system is huge!  Dr. Sutton suggested that for this area, the old-fashioned tree grove method of finding caves is more reliable even than the modern usage of Google Earth (which apparently is being used more and more by archeologists these days).

We walked back down to the lecture site and had a really lovely picnic lunch, and had the chance to examine all the skulls.  We also had the chance to take photos of some of the animals around us:  sheep on the farm near us, and a friendly family of warthogs that happened by while we were there.  The sound of birds was all around us, the sun was out, and there was a gently breeze that ruffled the small leaves on our charming grove of trees. With the rolling hills and the golden grass covered slopes, it was an absolutely gorgeous time.  It was easy to get the sense of why our earliest ancestors would have lived—and thrived—in this area.