With the exception of one famous mythical creature we all know and love (we're looking at you, Nessie), Scotland is hardly a place that conjures up images of 'monstrous' marine reptiles. But rewind 170 million years or so and Scotland was a very different place ... for one, it was partially underwater. Its shallow seas were dominated by a range of now extinct reptilian groups, from the long-necked plesiosaurs to the remarkably dolphin-like ichthyosaurs.

Ichthyosaur specimens from the Isle of Skye, which lies off the Scottish west coast, have been known for over half a century, but they've never really been studied very closely. Recently, however, a team of University of Edinburgh researchers led by Dr Steve Brusatte tracked down some rare ichthyosaur fossils hidden deep in the University of Glasgow's Hunterian Museum – and they discovered the remains of something completely new to science.

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The research team behind the ichthyosaur discovery. Image: Bill Crighton

Among the fossils at the museum were fragments belonging to a previously unknown species of ichthyosaur – now named Dearcmhara shawcrossi. The scientific name is based on the Gaelic word for 'marine lizard' (pronounced ‘jark vara’) and a nod to the amateur collector and fossil enthusiast, Brian Shawcross, who generously donated the specimen to a public museum in 1959.

Along with other fragmentary specimens from the Isle of Skye, these new finds reveal that ichthyosaurs cruised the ancient Scottish seas for at least 33 million years, from around 199-166 million years ago. Despite their large size – Dearcmhara shawcrossi was up to 14 feet (four metres) from tail to snout – they probably weren’t the apex predators of the time, falling prey to other marine reptiles like plesiosaurs. There is even evidence of predation (and/or scavenging) on the preserved humerus (arm bone) the researchers examined, with several tooth marks on the surface of the bone (whether or not this relates to this particular individual's cause of death will always be a mystery).

What is more important is what Dearcmhara can tell us about the evolution of ichthyosaurs. Our knowledge of marine reptiles during the Early Jurassic (201.3-174.1 million years ago) is actually quite poor compared to other time periods – the fossils simply don’t exist. There are, however, tantalising hints that this time period represents an important phase in the evolution of reptiles as a whole, when an evolutionary shake-up in the seas saw primitive marine life replaced by more advanced forms. 

“Smaller and more primitive ichthyosaurs were replaced by the generally larger and more advanced ... ichthyosaurs, which would go on to spread around the world and remain dominant until all ichthyosaurs went extinct 80 million years later,” explains Brusatte.

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The discovery of Dearcmhara shawcrossi could help scientists shed light on a time of evolutionary upheaval during the Early Jurassic period. Image: Todd Marshall

The discovery of Dearcmhara provides us with insight into what was happening at this significant time. “[Dearcmhara] is a smaller, more primitive ichthyosaur, so is hinting that this [shake-up] was not complete by 170 million years ago, and probably was fairly gradual, and took place at different times across the globe instead of synchronously,” Brusatte continues. “That, in turn, probably hints that [these changes] weren't rapid events caused by a sudden change in climate or ocean circulation, or a big volcanic eruption or asteroid impact or something of that nature.”

The causes of this evolutionary changeover remain a mystery for now. What is clear is that more advanced ichthyosaurs must have had an advantage of some sort over their more primitive kin. This could have been a visual advantage, allowing them to see better in increasingly murky waters. Different swimming capabilities and the ability for different ichthyosaur species to travel and disperse into new seas could also have been an advantage. Either way, Dearcmhara will no doubt be a critical animal in unravelling this Jurassic mystery.

For Brusatte, the find is crucial for other reasons too. “The new discovery is important for Scotland because it's the first uniquely Scottish ichthyosaur that has ever been found, and we hope that it will continue to encourage amateur collectors and academic scientists to work together.” (That's a positive outlook based on a lot of recent discussion on the role amateur fossil collectors play in the palaeontology realm).

Top header image: Todd Marshall