What killed the dinosaurs? Or more specifically, what killed these dinosaurs?
Rearing up with their heads thrown back, mouth open and teeth bared, their final poses seem to bring them to life. But could this body position, called opisthotonic posture (or death pose), give us clues about how and why they died? That’s right, it’s time to play Dino-Detective!
Opisthotonic death pose is very common in fossils, and so characteristic that you can generally spot it with ease in even the smallest of fossil exhibits. The head and tail are arched over the animal’s back, and the legs are often drawn into rigid-looking positions. But despite being known about and discussed for 150 years, people are still unsure why exactly dinosaurs so frequently adopt this petrified posture.
Many different reasons for the posture have been suggested, ranging from the very plausible to the downright bizarre. For example, it’s been suggested that the pose it is actually a sleeping posture (does that look relaxed to you?!), or that the animal dived headfirst into mud and got stuck (it probably happened rarely, but is very unlikely in the case of large theropods or Camarasaurus, unless they were particularly stupid).
Such suggestions are pretty easy to rule out, and aren’t talked about seriously. Rather, the big bone of contention revolves around whether the opisthotonic pose occurred before or after the dinosaur bit the dust.
Many people think that the pose is a post-mortem change, meaning that it happens after death. Different causes have been suggested, from water currents manipulating the body, to rigor mortis, to the ‘pull’ of drying tendons. However, Faux and Padian, writing in 2007 had a different idea. A background in veterinary medicine gave the authors a different perspective – rather than a change after death, perhaps the pose was a clinical sign of underlying pathology. Faux and Padian thought that these dinosaurs were still alive when they assumed the position, and the posture was a symptom of impaired brain function. It’s a symptom that medical professionals and many others will recognise…
Muscles are pretty trigger happy, and need inhibitory messages from the central nervous system to stop them contracting all the time. A problem in the brain or spinal cord can interfere with this inhibition. When that happens, the muscles all contract at once. Some are stronger than others (usually the extensor muscles) and pull the body into opisthotonic posture by force.
If Faux and Padian are right, it gives us clues about what might have killed these dinosaurs – severe head injuries, infections (e.g. tetanus and meningitis), poisoning, heat stroke, and lack of oxygen (e.g. drowning) can all cause opisthotonus and eventually death.