Pregnant ichthyosaur. Photo: Nobumichi Tamura

The fossil was found when scientists cut open a limestone boulder from North Yorkshire. After it was polished and scrutinized, paleontologists found not just one, but nine, separate fossils.

The ichthyosaur, a shark-like reptile that dominated the oceans in the Jurassic Era, died while pregnant with eight embryos inside about 180 million years ago, as scientists report in the latest Proceedings of the Yorkshire Geological Society.

The fossil is also the centerpiece of a new exhibit at the Yorkshire Museum, which opened on March 24.

“This is an incredible find,” said Sarah King, a curator at the Museum. “It is the first example of fossilized ichthyosaur embryos to be found in Yorkshire. Its display in Yorkshire’s Jurassic World incorporates the latest digital technology to reveal the embryos and to explain the significance of the discovery.”

Ichthyosaurs were carnivores that fed on other reptiles, as well as fish and marine invertebrates like belemnites, an early mollusk.

In the fossil from the limestone, the large adult ribs are visible, as are strings of much smaller vertebrae, and an assortment of other tiny bones.

Pregnancy may not be the only explanation for the assortment of ancient remains. The other possibility for the fossil find is cannibalism: that the bigger ichthyosaur had eaten smaller members of its own species.

But they did not find any damage from stomach acids on the tiny bones – and there were no other typical food items found in the context of the smaller fossils.

“Due to the very incomplete nature of the adult specimen, it is impossible to argue their embryonic status merely from their positions within the body of the adult,” the researchers write. “However, we consider it inherently unlikely that an adult ichthyosaur would consume, at about the same time, at least six similar-sized neonates (or, more likely aborted embryos, based on their size and preservation) of its own or a distinct species – or of both.”

Indeed, other ichthyosaurs in England and Germany have reported similar presence of embryos captured forever in the rock, within the mother.