150-million-year-old Jurassic-era stomach stone fossil found in the UK

The examination confirmed that the fossil was of "biological origin" rather than geological origin.

Hard to ascertain the species 

Larkin and colleagues compared the stone fossil to other collections at the Royal College of Surgeons of England and UCL Pathology. 

This helped them determine that this is, in fact, a stone fossil. It was identified to be a stone, or "calculus," which may form naturally in a variety of organs such as the stomach, bladder, or kidney. 

Microscopic examinations indicated that the calculus developed in the ancient creature's gastrointestinal tract (stomach). However, due to the lack of skeleton remains, the team was unable to identify this Jurassic-era species.

“Unless stomach stones are actually found preserved within a skeleton it is almost impossible to tell what sort of animal it might have formed inside,” noted Larkin. 

Larkin further added: “The size of this stomach stone, and considering it was found in clay from the Upper Jurassic era, indicates it most likely formed inside a large marine reptile such as an ichthyosaur, plesiosaur, pliosaur or crocodilian. The stomach stone did not come from a dinosaur - as dinosaurs lived on land - but this is still a very exciting and rare discovery.”

Rare to find such stone fossils

The finding extends the stone fossil record by roughly 59 million years, thereby, making it the oldest known fossilized specimen to date.

The fossil record also confirms that even ancient marine creatures suffered from mineral stones, and not just the terrestrial ones.

Prior to this discovery, experts had detected similar stones in Egyptian mummies, but only a few fossilized examples have been discovered to date. Thus, making it a rare find. Moreover, it is also the only example known to have been discovered in the United Kingdom.

Mineral stones can occur in any animal, including humans, as a result of particular dietary or environmental circumstances. 

The findings have been reported in the journal Proceedings of the Geologists’ Association.

Study abstract:

A calculus is a solid mineral concretion such as a kidney stone, bladder stone, gall stone or stomach stone that forms naturally in a body under certain dietary or environmental conditions. Calculi that form in the gastrointestinal tract are enteroliths and these are often near-spherical objects, sometimes with a hollow centre, with a concentrically layered structure composed of radiating crystals oriented perpendicular to the surface. They are known in the archaeological record but are almost entirely absent from the fossil record, most likely due to them simply not being recognised for what they are. We describe a fossil calculus from the Upper Kimmeridge Clay (Upper Jurassic, c., 150 million years old) marine deposit at Kimmeridge in Dorset, UK. This is the oldest calculus known from the fossil record with previous confirmed records from the terrestrial Oligocene of Colorado and the marine Upper Cretaceous Chalk of Germany: it extends the temporal range of known calculi in the fossil record by at least 59 million years. Although there are a wide range of potential hosts, the Kimmeridge calculus may have been produced by a large marine reptile.