Life, sex and death for dinosaurs

Stegosaurus is arguably one of most iconic dinosaurs we know, with a back bristling with armoured plates and a wickedly spiked tail. Recently, the Natural History Museum in London acquired an exquisite specimen of Stegosaurus from North America, nicknamed Sophie. Sophie has been on display in the museum for several months now, and will be the focal dinosaur attraction as Dippy the Diplodocus heads for greener pastures.

Stegosaurus is part of a group called Stegosauridae, all characterised by armour plating across their backs, and known from the Middle Jurassic to Early Cretaceous. They’re known from almost all over the world through this time, except for Antarctica and Australia.

Sophie was found in Red Canyon Ranch Quarry in Wyoming, and presents an unparalleled opportunity to perform a detailed study on this important, but actually relatively under-studied dinosaur. She was discovered in 2003 by Bob Simon, actually completely by accident! Apparently Simon was moving a bulldozer during a windstorm one evening, and accidentally grazed the side off a hill. The next morning, lo and behold, the remains of a dinosaur were waiting there!

Now, Susie Maidment from Imperial College London and Colleagues from the Natural History Museum in London have performed one of the most detailed descriptions of any dinosaur to date, and published in PLOS ONE. At a whopping 107 pages, the paper is packed with new information about the anatomy of Sophie, and has more than 70 figures to illustrate her in beautiful detail.

Importantly, this detailed analysis allows us to gain insight into the growth, sex, and death of Sophie. By looking at different features of the preserved bones, Maidment and colleagues were able to tell that Sophie hadn’t finished growing before she died. They were able to show this, as parts of the vertebral column remained unfused to each other, which indicates that the skeleton was not fully mature.

Additionally, by chopping open Sophie’s bones, and looking at them in cross-section using a microscope, they were able to tell that she was a young adult. This was based on features called lines of arrested growth that, much like the rings of a tree, can be used to tell how old an animal is.

Perhaps most bizarrely, the researchers were unable to show whether or not Sophie was a male or a female dinosaur! Perhaps a little misleading based on her name. But it can be very difficult to determine the sex of a dinosaur based purely on features of their skeletons.

Mysteriously, the cause of death for Sophie remains unknown too. Often, dinosaurs are preserved with marks or traces that we can use to infer how they met their end. Fractured bones or tooth marks, for example, are pretty reliable. But for Sophie, there is no evidence of predator or scavenging interaction, and no other pathologies to provide clues. The researchers conclude that the probable cause of death then could be starvation, or perhaps even a disease that doesn’t leave traces by only affecting parts of the body that aren’t preserved.

It’s thanks to the completeness of this specimen, and the great work of excavators, preparators, and researchers, that we’re able to get such insight into an animal that has been dead for around 150 million years. Let’s hope Sophie will continue to delight visitors to the Natural History Museum for years to come!