Is it common to find a variety of dinosaur bones?

Chris put this question from James on Facebook to palaeontologist Jason Head, from the University of Cambridge, and Lee Berger from the University of Witwatersrand. "Are they served up beautifully on a plate, one specimen, all in one place, easy to sort out or is it a bit of a mess that you have to try and unpick?"

Jason - It’s a bit of both and it all has to do with physically where the animal dies, and what are the various way in which it enters into the rock record and so you have different kinds of what we call “depositional environments.” These are areas where the sediments that form the rocks the dinosaurs are in are actually physically accumulate. For some of these environments you can have an animal effectively follow and be completely buried and then you have a very well-preserved articulated skeleton.

In terrestrial environment, more often than not, what you have is an animal die and then you’ll have some kind of water action that takes the remains and transports them into basically a river system or a lake system. In that case, yeah, you generally do find a jumble of bones from different dinosaurs or different animals, so you get a lot of disarticulation. You have different kinds of preservation as well where certain bones will be exposed in weather on the surface before they then get transported and buried.

So yes, it is very common. It’s more common than not to find multiple types of dinosaur bones mixed in together.

Chris - Is that your experience Lee?

Lee - Yeah. Ours is a field where, particularly when we’re looking for human ancestors, we find them one by one. Up until recently, the story of paleoanthropology was probably in excess of 90% of the entire record was made of isolated teeth or isolated small bone fragment. That’s exactly the situation of an animal dying on the surface and going about the usual process in Africa or elsewhere where it’s eaten or dragged apart and disintegrates.

More recently though, we’ve been very fortunate both on terrestrial deposits, but also in these underground cave environments, finding more and more complete specimens. We have complete skeletons like Little Foot skeleton in South Africa, an australopithecus, but we’re starting finally to find deposits in more extreme, more protected environments where we have more and more complete specimens and we’re able to put individuals together. We can do like these hands I’ve got here; that hand was found curled up just like that, just in a death grip.

Chris - This is a replica of Homo naledi isn't it, your most recent specimen that you've uncovered at the Rising Star system near Johannesburg? And the amazing thing about the work that you’re now doing is, unlike historically, where you’d find a specimen like this and then you’d study it and it would be your sole preserve, now you’re scanning these things and 3D printing them to produce a sub-millimetre precision thing a bit like that, which you can then share round the world and a scientist anywhere could then begin to work on your specimen?

Lee - Not only can we - we do. If you go onto morphosource.org you can download any of our fossils and 3D print them yourself in your local 3D printer in your library...

Chris - A DIY Homo naledi?

Lee - … or home, and they are accurate to just a few microns of the originals and it doesn’t have to be a scientist. In fact, the tens of thousands of downloads we’re getting from school children are people who just want to have a hand.

Chris - And give you a hand, as well!