A case of Mesozoic misidentification
Did you know that some times scientists make mistakes? Yep, I know it might be shocking, but they’re not always right, despite liking to think so some times. But this is one of the beautiful things about science. It is an inherently human endeavour, and therefore subject to human error and uncertainty. Scientists make deductions and conclusions based on the best possible evidence available to them at any given time. It’s what sets science apart from, let’s say, politics.
But what happens when the evidence changes? Well, so do our scientific conclusions, then. And palaeontology is no exception to this.
Often, for example, what might be identified as one animal or species in the fossil record turns out to be something completely different after new information comes to light. Known as the study of taxonomy, such reidentifications are actually fairly common as our knowledge improves with every new discovery. Each new fossil specimen we discover tells us a little more about the evolution of life on this planet.
Solving a 150 year identification crisis
Enter fossil collector Paul de la Salle. On the beaches of Lilstock in Somerset, UK, Paul recently discovered the ancient fossilised lower jawbone of an ichthyosaur. He contacted several ichthyosaur specialists about the discovery to see what they made of it.
Dean Lomax (University of Manchester, UK) and Prof. Judy Massare (SUNY College at Brockport, NY, USA) carefully studied the new specimen, and realised that it was part of the lower jaw of an ichthyosaur, a bone called the surangular. The strange thing about this specimen though was that it was relatively huge compared to virtually anything the researchers had seen before.
The researchers also realised something very odd, related to a puzzling historical conundrum. Bones from Aust Cliff, Gloucestershire, UK, that were discovered in 1850 have been identified as limb bones of an early and huge dinosaur (or close relative), such as a stegosaur or sauropod. However, Lomax and Massare noticed that they actually looked almost identical to the newly discovered Lilstock specimen. Rather than being bits of dinosaur, it seems they too are jaw fragments of a long extinct and previously unknown species of giant ichthyosaur.
Dean said: “One of the Aust bones might also be an ichthyosaur surangular. If it is, by comparison with the Lilstock specimen, it might represent a much larger animal. To verify these findings, we need a complete giant Triassic ichthyosaur from the UK – a lot easier said than done!”
This case of mistaken identity reveals that there were ichthyosaurs that were even bigger than dinosaurs swimming around the UK at the same time as them.
A Triassic leviathan
The Lilstock specimen comes from a period known as the Triassic, around 205 million years ago. This was a period when the ancient seas were ruled not by mammals like today, but a weird variety of marine reptiles, including numerous ichthyosaurs.
Some ichthyosaurs, such as Shonisaurus, grew up to be around 21 metres in length. That’s pretty huge for an ancient fish lizard! However, estimates of the newly analysed specimens put it at around 26 metres in length, making it the biggest ichthyosaur currently known.
To test to see just how big this animal was, Lomax and Massare set off to Canada, to the Royal Tyrell Museum in Alberta. Here, they compared the metre-long jawbone to those of the largest ichthyosaurs otherwise known. What they realised is that the new specimen represents the largest individual currently known, with a hint of uncertainty as only a single bone from the animal exists.
They also recognised a lot of similarities with Shonisaurus, suggesting that the specimen from Lilstock represents a species from a group known as shastasaurids – the group with the largest ichthyosaur species. Whatever its affinities, this means that huge ichthyosaurs were alive and kicking in the Late Triassic period, even close to the time of the end-Triassic mass extinction.
So, how long now until the Hollywood monster movie..?
Lomax DR, De la Salle P, Massare JA, Gallois R (2018) A giant Late Triassic ichthyosaur from the UK and a reinterpretation of the Aust Cliff ‘dinosaurian’ bones. PLoS ONE 13(4): e0194742. https://doi.org/10.1371/journal.pone.0194742
Featured image: Shonisaurus skeletal reconstruction (Scott Hartman)
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