Science & Technology

Why Dino Fossils Throw Their Necks Back in a 'Death Pose'

Dinosaur fossils often preserve the creatures in an odd pose: neck bent backward at a seemingly impossible angle, like a yoga class gone terribly wrong. It's so common that it had scientists wondering: Is this how the animals died or did the bending happen after death? By studying dinosaurs' modern cousin — the chicken — some researchers were finally able to solve this ancient mystery.

Got a Crick in Your Neck?

You might recognize the dinosaur death pose from the Arc'teryx logo. The outerwear clothing brand is named after the first known bird, Archaeopteryx lithographica, which is immortalized in a well-preserved fossil known as the Berlin specimen. Archaeopteryx is estimated to be around 150 million years old, but dinosaurs from all throughout the Mesozoic Era have been found in similar positions.

A study published in Paleobiology in 2007 includes sketches of several contorted dinosaur skeletons: There's the turkey-sized Compognathus (which is 140–145 million years old) and the Cretaceous giant Gorgosaurus (73–80 million years old). The death pose seems to affect dinosaurs of all shapes and sizes, from bird-like beasts to monstrous lizards.

There are a couple of different theories about why the dinosaur death pose happens. The authors of the 2007 study proposed that the odd posture results from damage to the central nervous system, specifically to the cerebellum. The cerebellum is responsible for fine movement, and when it's damaged, the muscles it usually controls will yank at full force. The pulling would cause an animal's head and tail to arch back in a posture medically known as opisthotonus.

The implication of this theory is that dinosaurs may have died from suffocation due to the ash associated with a volcanic eruption, or perhaps from disease or another kind of brain trauma. As they died, the trauma would yank their muscles into that odd pose. What's more, other research has suggested that the ancient reptiles may have actually been warm-blooded. An animal with a relatively low metabolic rate, like a lizard or crocodile, would not have been so traumatically affected by a loss of oxygen to the brain. If dinosaurs died of hypoxia, as suggested by their death pose, it would mean they have more in common with living mammals.

Just Add Water

Critics of the so-called "death throe hypothesis" have pointed out that it is unlikely that a dinosaur carcass would fossilize in the exact position of its death. The beasts more realistically fell into bodies of water before settling in the sediment down below. In this scenario, dinosaurs would assume the death pose post-mortem.

One such critic, Achim Reisdorf, decided to perform a study to test how immersion in water might affect dinosaurs after death. Of course, he couldn't find a preserved Tyrannosaurus rex corpse for experimentation, so he got the next best thing: chickens. (Might we remind you that birds are technically dinosaurs?) The scientist purchased chicken necks from a local butcher and watched how they reacted in water. When they went underwater, the necks bent backward almost immediately. After sitting in the water for three months, they each reached a 140-degree angle.

Reisdorf's results were confirmed by another research team at Brigham Young University. Both groups concluded that the bending came from contractions of the ligaments in the birds' necks. Usually, the weight of a creature's body pulls on those ligaments, providing a counterbalance to hold the neck upright. But the buoyancy of water (and its erosive properties over time) tip the balance in favor of the neck ligaments' backward pull.

But not all dino fossils formed in water or mud, so this would only explain some fossils. For dinosaurs who died on land, the death-throe hypothesis might hold up. Or another theory could explain the whole thing — another, less cited study from a few years later simulated the death pose with chickens and found that it's actually natural for dinosaurs' flexible necks to arch backward after death, regardless of the immediate cause. But the next time you see a fossil's neck bent at an awkward angle, there's no need to worry — it's likely that the animal wasn't alive to feel it happen.

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Can't get enough fossils? Check out "The Story of Life in 25 Fossils: Tales of Intrepid Fossil Hunters and the Wonders of Evolution" by Donald Prothero for more. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Written by Andrea Michelson November 26, 2019

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