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Ancient Archosaur Arthritis

When we envision prehistoric life, we often picture long-extinct animals in the most healthy state possible. Each restored individual is the acme of its particular species—be it Allosaurus or a woolly mammoth—but we know that things in the natural world are never so clean and neat. Not only do indi...

The fused vertebrae of an archosaur with a diagram of where they fit on the living animal. From Cisneros et al., 2010.


When we envision prehistoric life, we often picture long-extinct animals in the most healthy state possible. Each restored individual is the acme of its particular species—be it Allosaurus or a woolly mammoth—but we know that things in the natural world are never so clean and neat. Not only do individual animals of any species vary from one another thanks to heredity, but injury and disease is ubiquitous. Just as animals break bones and contract ailments today, so did creatures during the past. (To their credit, some paleoartists such as Michael Skrepnick have deliberately illustrated individual animals with interesting pathologies.) A 245-million-year-old fossil from South Africa illustrates the long fossil record of a pathology that is still with us today.

There was not much left of the animal described by Juan Carlos Cisneros and colleagues; just a set of three vertebrae from the tail of an archosaur (the group containing crocodiles, pterosaurs, dinosaurs and their close relatives). The bones appear to have belonged to a crocodile-like creature that lived just a few million years after the mass extinction which marked the end of the Permian, and they had become fused together. This was not their normal condition—something must have happened to this animal to cause these three vertebrae to become fused.

When the scientists performed a neutron tomography scan—a type of 3-D scan similar to an X-ray—they found no evidence of fractures, traumas, or tumors which could account for the pathology on the bones. Neither did they find evidence consistent with the hypothesis that the animal had been born with this condition. After examining the list of potential causes, a particular kind of inflamed bone growth called spondarthritis appeared to be most consistent with the pathology seen on the vertebrae. If this identification is correct, it would be the oldest record of spondarthritis in the fossil record, with the next oldest cast being seen in an individual of the circa 147-million-year-old sauropod dinosaur Camarasaurus.

Just how the archosaur became afflicted with spondarthritis is unknown. As the authors point out in their description, even when doctors can examine people who suffer from this same condition, it can be difficult to uncover the cause. What can be determined, however, is that the pathology was probably painful for the archosaur and constrained the movement of its lower back and tail. Whether this pathology contributed to the death of this animal is unknown, but it certainly didn't provide it with any benefits!

References:

Cisneros, J., Gomes Cabral, U., de Beer, F., Damiani, R., & Costa Fortier, D. (2010). Spondarthritis in the Triassic PLoS ONE, 5 (10) DOI: 10.1371/journal.pone.0013425
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About Brian Switek
Brian Switek

Brian Switek is a freelance science writer specializing in evolution, paleontology, and natural history. He writes regularly for National Geographic's Phenomena blog as Laelaps.

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