Biggest Ichthyosaurus Fossil Was Pregnant When She Died

It turns out that the animal was pregnant when she died some 200 million years ago. University of Manchester 

Swimming the seas while the dinosaurs were walking the land, ichthyosaurs were a highly diverse group of marine animals. Now, a fossil unearthed in the mid-1990s has been found to be the largest Ichthyosaurus ever discovered, and only the third ever identified as being pregnant at the time of death.

Discovered over 20 years ago in Somerset on the southern coast of England, the fossil was on display in a museum in Hannover, Germany, before it was spotted by a palaeontologist there on a visit. It turns out that the skeleton was far more important than the museum had realized. The work is to be published in the journal Acta Palaeontologica Polonica.

The fossil belongs to the group of ichthyosaurs known rather conveniently as Ichthyosaurus. The creature measures in at between 3 and 3.5 meters (10 and 11.5 feet) long, making it the largest member of this group ever discovered.

“It amazes me that specimens such as this [the biggest] can still be 'rediscovered' in museum collections,” says the University of Manchester’s Dean Lomax, who co-authored the study that will describe the specimen, in a statement. “You don't necessarily have to go out in the field to make a new discovery.”

But the size of the marine creature was not the only thing that was so special about this fossil. After studying the remains in detail, the researchers were also able to ascertain that the animal was pregnant when she died over 200 million years ago.

The fossil shows the remains of a tiny embryo nestled in the abdomen. Only a small portion of backbone measuring just seven centimeters (2.7 inches) long, a forelimb, and a few ribs remain, suggesting that the embryo was not yet ossified and thus still developing in the womb at the time of death.

Interestingly, the researchers were also able to reveal that the fossil was something of a chimera. They found that the tail of the animal did not actually belong to the body, but had been added to make the fossil appear more complete and visually appealing.

“It is often important to examine fossils with a very critical eye. Sometimes, as in this instance, specimens aren't exactly what they appear to be,” says Sven Sachs, who was the first person to actually spot the fossil in Hannover. “However, it was not 'put together' to represent a fake, but simply for a better display specimen.”

As one of the most common fossils found in the United Kingdom, ichthyosaurs can tell us quite a lot about the health and ecology of the oceans during the Triassic.

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