AT THE Montana Raptor Conservation Center in Bozeman, dedicated staff and volunteers work hard to save the lives of injured birds of prey. The raptors arrive in various states of distress from all over the area, including Yellowstone National Park. Most have been hit by cars, electrocuted, poisoned or shot.
The centre does what it can, but sometimes the birds have to be put down. That’s a bitter-sweet moment for Cynthia Marshall Faux, a volunteer veterinarian at the centre who also moonlights as a palaeontologist at the Museum of the Rockies on the other side of town. Marshall Faux has a special interest in recently deceased raptors: she needs them for her research on the death of dinosaurs.
Not their extinction, mind, but individual dinosaur deaths. Marshall Faux wants to know why dinosaur skeletons are so often found in a characteristic posture: head thrown back, hind limbs bent, tail extended. This seemingly simple question has troubled palaeontologists for more than a century and many ideas have been put forward, including “diving into mud and getting stuck”. But nobody knew for sure.
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Until now. Thanks to a steady trickle of dead birds from the raptor centre, not to mention some fresh beef tendons and a few rancid quails, Marshall Faux and her colleague Kevin Padian of the University of California, Berkeley, think they have .
Birds, of course, are living dinosaurs and they make a good proxy for their long-departed ancestors. The best-known example of the “dead dinosaur posture”, technically known as opisthotonos, is actually seen in a dead bird – a 150-million-year-old . It is also found in many well-preserved dinosaur and pterosaur skeletons. Too many, in fact, to be a coincidence. This curious fact was first pointed out in 1927 by the great German geologist Johannes Weigelt in his classic book on , or the science of how organisms fossilise.
Weigelt himself thought the posture was caused by the contraction of tendons as the dead animal dried out, but his was by no means the only idea on the table. Other researchers have proposed a range of different causes: rigor mortis, dehydration in salt water, dying while asleep, being dragged into position by moving water and, of course, diving into mud and becoming stuck.
To Marshall Faux, none of these rang true. “I’d read in the literature about rigor mortis, tendons drying out and all, but it didn’t mesh with what I know from my experience as a vet. Dead bodies moving? That didn’t make sense.”
Marshall Faux also knew that diseased and dying animals often adopt the posture when they are barely alive, especially if they have been poisoned or hit by a car. To her that suggested opisthotonos was not caused by events after death, but was the hallmark of a dinosaur’s final agonised throes as it slipped towards dino heaven.
Don’t try this at home
She shared her thoughts with Jack Horner, curator of palaeontology at the museum. “He said ‘fine – show me’,” she recalls. “That’s where the experiments came from. I thought, well, if it’s caused by drying, let’s dry something. If it’s caused by drying tendons, let’s dry some tendons.” And if it’s caused by rigor mortis, why not take a look at rigor mortis. So she did.
Being a volunteer at the raptor centre came in handy – it’s an excellent place to observe freshly dead birds going into rigor mortis and out of it again. Marshall Faux tried several different species, including horned owls, red-tailed hawks, kestrels and merlins. She would lay the still-warm birds on a table and make a note of their positions. A couple of hours later she would check them. “They’d be as solid as a rock, but they never moved.” Several hours later, once the rigor mortis had passed, she’d check them again. “Never once did they move from the position I put them in.”
Next, she tried desiccation. She allowed the carcasses of two red-tailed hawks to dry out to see if their withering muscles, tendons and ligaments contorted the limbs. After three months, both carcasses were “dry, solid and stiff”, but neither had moved a millimetre.
And so onto the beef tendons. To test whether drying tendons could cause a dead animal to change its posture, she bought two fresh beef tendons from a supermarket. These she pinned to styrofoam sheets, one of them tautly, before burying them in silica gel to dry them out quickly. After nine days both tendons had lost more than half of their weight but neither had shrunk in length, and the pins remained stubbornly unmoved. If a drying tendon cannot even dislodge a small pin from a styrofoam sheet it’s hard to picture it moving a dead dinosaur’s head, she says. It was a similar story when she tried soaking tendons in ultra-salty water.
Still Marshall Faux wasn’t satisfied. To rule out salt water altogether she needed to test it on whole carcasses, so she bought three frozen quails, put them in buckets of salt water and left them in her garage. Nothing much happened. The quails steadfastly refused to sink, did not change their posture, and were still “fully flexible” by the time the buckets had accumulated what Marshall Faux describes as “excessive bacterial overgrowth” and had to be thrown out.
All in all, her experiments were a glorious failure. “None of the stuff worked,” she says. It was a good return for some serious personal inconvenience. “The tendons I had in the fridge. I used my garage for some of the smellier experiments. The dry stuff was just kind of hanging round the house.”
Just three contenders remained to be ruled out: dying while asleep, diving into mud and becoming stuck, and being dragged into position by moving water. These were not so easy to test, so Marshall Faux and Padian used their powers of deduction. They dismissed the first because no known animal sleeps in that posture. They dismissed the second on the grounds of implausibility. The third they decided was more credible, but pointed out that the death pose often involves the neck and limbs pointing in opposite directions, which is unlikely in fast-moving currents.
To Marshall Faux, this leaves only one possible explanation: death throes. Among veterinarians it’s well known that animals sometimes go into the opisthotonic posture shortly before they die as a result of a severe malfunction of the central nervous system. While Marshall Faux was at the raptor centre, birds that had died in the night were often found in this position in the morning, she says. Humans go into it too, when suffering from strychnine poisoning or meningitis, for example. Few recover. “The posture itself isn’t terminal, but it’s not a good sign,” she says.
It’s easy to see why palaeontologists barely considered death throes as an option: by definition they don’t spend much time around dying animals. Now Marshall Faux has pointed out their error, they may have some rethinking to do. Palaeoecology, the study of past environments, often draws inferences based on death positions, for example that the animals lived in a desert, or died in running water. If the death pose isn’t caused by something that happens after death, perhaps much of this needs to be re-evaluated.
Marshall Faux says her ideas have been well received by dinosaur specialists, but she’s aware that her work isn’t the last word on the matter (). “Some day somebody may dry a horse,” she says. “I didn’t take it that far. Dead horses are not easy to come by. But I’m very curious. I bet it wouldn’t move, but it would be fun to try.” Make a note not to go past her garage once that experiment gets under way.
Dinosaurs – Learn more in our comprehensive special report.
