I was very excited to be asked by Scientific American to reconstruct the fossil apes for David Beguns article because it was my foray into the Miocene epoch. I really wanted to go there because in order to understand the evolution of the human family, you need to know something about the evolution of the apes.
One of the things that emerges when you take even a casual look at the tree of fossil apehood is that there is an incredible diversity of apes. There are only a few left today--five species if you count humans--but those are just the last relics of a once very lush bush. And that bush includes a great physical diversity. For this article I picked the five fossil apes that are the most completely known. Thus you have Dryopithecus and Ouranopithecus, which are probably closely related to the African great apes, including humans. And in fact, in the final reconstructions, these two look like African apes. Then there is Sivapithecus, which is closely related to orangutans on almost everyones evolutionary tree. Sivapithecus is really outrageous, because it takes some of the things that make orangutan faces stand out from other living apes to an unbelievable extreme. Orangs have long, tall faces; Sivapithecus had an incredibly tall face, with a great vertical distance between the nose below and the eye sockets above. And the eyes are very very close together. If someone had done the reconstruction from pieces of a Sivapithecus skull and it looked like that, people would be very skeptical indeed. But the fairly complete face thats known for Sivapithecus is not ambiguous in the form that it indicates.
Oreopithecus is another bizarre ape, and the fourth that I rendered. It has a number of great ape-like characteristics, but some of the features in its cranium and teeth are not great ape-like at all, leaving researchers conflicted as to how to classify it. Complicating the matter is the fact that the best specimen of Oreopithecus is a smashed skeleton--a flattened roadkill of a fossil. But its a weird looking skull any way you reconstruct it.
The fifth ape I reconstructed is Proconsul, the best-known of the earliest apes (it is represented by, among other things, a fairly complete skull). Its monkeylike in a lot of ways. It has a small cranium and brain size, a smooth forehead and very inderstated browridges--unlike living great apes. Its also got a fairly projecting muzzle.
To flesh an animal out, I start with casts of as many fossils of that species as I can get ahold of, because each one may preserve a bit that the next one is missing. Then I reconstruct the skull--that was necessary in all cases for this project. For Proconsul it meant undeforming the skull. To do that I had to make a mold of a reconstruction of the Proconsul skull made by Alan Walker of Pennsylvania State University and then deform that so that it was bilaterally symmetrical. For the other apes I had to build in missing pieces of the cranium. The only one I didnt reconstruct three-dimensionally was Oreopithecus. Because the specimen is squashed, I felt that there wasnt a strong enough basis for building a three-dimensional model of the skull, so I did the reconstruction graphically, basing it on an existing skull restoration by anthropologists Harrison and Rook.
The next step was to put tissue on the skulls. I have a lot of data from dissections of great apes that Ive done over the last 20 years. These dissections have revealed certain relationships between bone and flesh that allow me to predict the soft tissue morphology based on clues from the bone. For Proconsul, an archaic ape, I used relationships that hold true across the board in all of the living apes to estimate its soft-tissue anatomy. For Ouranopithecus and Dryopithecus, which are most closely related to African apes and humans, I used the relationships that you find in the African apes (chimps, bonobos and gorillas). For Sivapithecus I turned to the relationships found in orangs. Having said that, a lot of the relationships are quite close in all of those groups. The ratio of the diameter of the eyeball to the width of the eyesocket, for example, is comparable in chimps, gorillas and orangs.