An Ancient Case of Paget’s Disease

A new study has identified a potential case of Paget’s disease in the bones of a 298 million year old lizard-like animal. The results come from a study of two fused tail vertebrae recovered from a fossilised cave system in Richards Spur, Oklahoma, USA. Today Paget’s disease is a relatively rare condition, which mainly effects older people, with the official website of the Paget’s Association stating that 1% of people over the age of 55 in the UK suffer from the disease.

Paget’s disease is a disease of the bones. Today sufferers may experience aching, stiffness and shooting pains that can travel across the body, which are usually treated with anti-inflammatories and pain killers. Unfortunately there is no current cure. The condition is caused by a fault in the way the patient’s body recycles and regenerates bone tissue. Osteoclasts are cells that are responsible for reabsorbing old bone. This is a perfectly normal and healthy process which allows new bone tissue to replace old. However, in Paget’s disease these osteoclasts malfunction, and instead absorb old bone tissue at a much faster rate than normal. This then forces the body’s osteoblasts (cellular cousins of the osteoclasts that make new bone) to start overproducing new bone tissue to replace it. Over time this can leave bones fragile and deformed. This makes it a good target for palaeopathologists, because evidence of the disease will more easily show up in the fossil record.

1280px-Mycterosaurus
An artist’s reconstruction of Mycterosaurus, a Varanopidae possibly similar to that recovered in Richard’s Spur. Image Credit: Wikimedia Commons

The fossils this study examined came from an animal that wasn’t exactly a lizard. Instead it belonged to an extinct group of animals called the Varanopidae, which first evolved around 300 million years ago. The Varanopidae would have seemed superficially very lizard-like to our modern eyes, with most species resembling slender monitor lizards, but their exact location in the tree of life is still something of a debate. Traditionally they were considered more closely related to the ancient ancestors of mammals, but a recent analysis has instead classified them with basal reptiles. Regardless they were a pretty wide-spread group, ranging all across the single, enormous landmass of Pangea which existed at the time. They mostly reached 1-2m in length, including their tails, with proportionally long jaws and very sharp little teeth.

These particular vertebra are tiny, together the fused segment is only 23mm long, and they came from the tail of the animal. The fact the two individual vertebrae are fused was actually the first sign to the researchers that they dealing with a pathology of some kind. The researchers at the Museum für Naturkunde Berlin scanned the vertebrae using a micro-CT scanner which allowed them to not only examine the exterior features of the fossils, but also their interiors. By examining the scans researchers identified areas where the bones were unusually thin from being reabsorbed, and other areas where there was an excessive overgrowth of bone, which is what ultimately led to the vertebrae fusing. Taken together all these different deformities are highly suggestive of a disease like Paget’s.

This isn’t actually the first time that Paget’s disease has been detected in the fossil record. In 2011 a paper was published describing the condition in a late Jurassic dinosaur specimen. However, this new discovery would be the oldest known example of the disease. The exact causes of Paget’s are still up for debate, although genetics seems to play a role in predisposing people to the condition, and there is an apparent link to viral infection as well. This means that if this little Varanopidae was indeed suffering from Paget’s then this could also be the oldest known example of a virus in the fossil record. It also suggests that this disease has been with us for a very, very long time. This could help shed some light on the causes of what is still considered a pretty enigmatic condition even in modern humans.

Reference:

Yara Haridy, Florian Witzmann, Patrick Asbach, Robert R. Reisz. Permian metabolic bone disease revealed by microCT: Paget’s disease-like pathology in vertebrae of an early amniotePLOS ONE, 2019; 14 (8): e0219662 DOI: 10.1371/journal.pone.0219662

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