Dinosaur fossil shakeup
If your family tree is muddled up you could end up drawing some pretty incorrect conclusions about where you came from. Now, the entire dinosaur family tree has been called into question, which could mean we’ve been making mistakes when looking at how they evolved, and where they came from. Scientists have always classified dinosaurs very neatly into two simple groups: those with bird-like hips, and those with lizard-like hips. It's been the conventional wisdom for almost 130 years, but this week, a paper published in Nature suggests that we may need a shake down and reclassification of the entire dino family tree. Georgia Mills went to look at some fossils with lead author and PhD student at Cambridge University, Matthew Baron…
Matthew - We’re currently standing in the main gallery of the Sedgwick Museum in Cambridge which is the university’s earth science and palaeontology museum.
Georgia - We’ve got quite a few dinosaurs around us, which is very exciting. So could you tell me a bit about how dinosaurs are classified at the moment?
Matthew - The traditional model that’s been around since the late 1800s was proposed by a Cambridge scientist called Sealey, and his idea was all dinosaurs were either in this one category or they were in this other category. So, on the one hand, we had what were called Ornithischians - this is the bird-hipped dinosaurs, not the birds but the bird-hipped dinosaurs and examples include triceratops, stegosaurus, and this iguanodon that we’re stood in front of.
Georgia - Let's go look at iguanodon cause this thing is towering about us. It’s standing on two legs; it’s got a massive tail; it’s got a ribcage I could comfortably get in, and then there’s a giant head.
Matthew - These guys were sort of the very large cows of the Jurassic and Cretaceous. A large family of herbivores. So they are the ornithischians. Then, on the other hand, all the other dinosaurs were lumped into another group called Saurischia, which means lizard-hipped. Their hips look more like primitive reptiles than birds. Saurischia is made up of, in the old model, theropods, which are the meat eaters.
Georgia - Like T-Rex.
Matthew - Just like T-Rex and many earlier forms, and eventually birds. The other group are the sauropodomorphs, which some people shorten to sauropods, and they are the long-necked tree browsers like diplodocus (dippy at the Natural History Museum), brontosaurus, brachiosaurus.
Georgia - So those groups, in some ways they make quite a lot of sense. There’s the bird-hipped dinosaurs and the lizard-hipped dinosaurs. But then again, you have one group which is the veggies like triceratops, stegosaurus but then you have this other group which contains all the two-legged carnivores, but then these massive four-legged diplodocus-like creatures. So you’ve looked at these groups and you thought - no! So can you tell me what you’ve done and what you’ve found?
Matthew - We started looking at as many early dinosaurs as we could and we built a long list of specimens we thought were relevant and interesting in early dinosaur evolution. We cross-examined them for a very large list of anatomical features and we built the largest ever dataset of early dinosaurs and our computer software worked out for us various ways in which they could be related, which would be the most likely given certain circumstances. And what we found was that the old groupings that have always been thought to exist were just not recovered in our analysis, so were not supported by the anatomy, by the data. Our data suggest that the meat-eating theropods are more closely related to ornithischians like triceratops than either of those groups are to the long-necked tree browsers.
Georgia - So you looking at dinosaurs, you don’t have the luxury of just popping them all in a DNA analysis. So you have to look at all of their physical traits and then pump all that into a computer which can look at the similarities and the differences and work out the most likely scenario for the family tree?
Matthew - Yeah. Essentially, we are limited by the skeleton. All we have to work on is the skeleton and features of the skeleton, so we had to look at a lot of skeletons to see what features might be useful. We tried to be as objective as possible and then we built this very large dataset where each specimen was given a score for each feature that we thought was relevant. It was about 35,000 individual data points that we had to enter by hand - I had to enter by hand and, eventually, we were able to put together this huge dataset after three years and it produced drastically different results.
Georgia - So this is challenging over 100 years of the accepted theory. I remember learning about this in my text books and in museums and things like that. So this is quite a bold reshuffle you’re proposing?
Matthew - It is, yeah. And we’re expecting some degree of backlash but that’s just how science works. We have a hypothesis; we get new data; we look at old data in new ways and we present new hypotheses; we test them and test them again. But yes, the old scheme was the fundamental fact on dinosaurs in kids books, in museums and maybe they’re all going to need a rewrite.
Georgia - Do you suspect there’s going to be quite a big debate following this paper?
Matthew - I certainly hope so, yeah. I’m looking forward to the next big conference where I have to face all of the people that may disagree with me, but such is science. We’ve put that idea out there now and this flies in the face of 130 years of thinking. Completely disagrees with some very prominent people’s PhD theses and is drastically different to anything we’ve ever thought. So yes, there’s going to be some flack.