Pregnant ichthyosaur largest of its species

A fossil Ichthyosaurus originally found in the English county of Somerset and later sent to a museum in Germany has been re-examined and found to contain the only known embryo of the species.

In a paper published in the journal Acta Palaeontologica Polonica, Dean Lomax of the University of Manchester in the UK and Sven Sachs of Germany’s Bielefeld Natural History Museum report finding among the adult Ichthyosaurus’s remains a seven-centimetre string of vertebrae, a tiny forefin and some ribs.

The bones were still partly cartilaginous, indicating they belonged to a partially formed animal still in the womb.

Artist impression of pregnant ichthyosaurus.
Artist’s impression of pregnant Ichthyosaurus.
Credit: Joschua Knüppe

Only a few months earlier, Lomax and another colleague, Judy Massare, identified the 3.5-metre adult fossil as a new species of Ichthyosaurus, which they named Ichthyosaurus somersetensis. It was the second new Ichthyosaurus the pair formally claimed this year, bring the total number of species in the genus to seven.

The embryo is not the first to be found, but is the first conclusively identified to species level.

The main fossil had originally been excavated from Doniford Bay in England – something of a happy hunting ground for fossickers – in the 1990s. Some time later it was acquired by the German museum.

When Lomax and Sachs decided to take a detailed look at it, the embryo wasn’t the only surprising discovery they made. They also realised that the tail of the beast had, in fact, been added from another, smaller specimen.

“It is often important to examine fossils with a very critical eye,” says Sachs.

“Sometimes, as in this instance, specimens aren’t exactly what they appear to be. However, it was not put together to represent a fake, but simply for a better display specimen.

“But, if ‘fake’ portions remain undetected then scientists can fall foul of this, which results in false information presented in the published record.”

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