Two years ago fossil collector Paul de la Salle of the Museum of Jurassic Marine Life found a piece of bone on Lilstock beach, Somerset, in the UK. Subsequent searches found more pieces of the same animal. Now an extrapolation based on the size of these bits has estimated the animal they belonged to as being 26 meters (79 feet) long, far exceeding any of its known relatives. Although blue whales were larger, the Triassic reptile the bones came from could still rank very high in the list of largest ever species.
"Initially, the bone just looked like a piece of rock but, after recognizing a groove and bone structure, I thought it might be part of a jaw from an ichthyosaur,” de la Salle said in a statement. Before removing the bone, de la Salle had a geologist examine it in situ, estimating its age at 205 million years.
Once extracted, the jaw bone was found to be larger than the same bone in Shonisaurus sikanniensis, the largest previously known ichthyosaur. Other than size, however, this bone is similar enough to S. sikanniensis for Dean Lomax of the University of Manchester and Dr Judy Massare of SUNY College New York to conclude it was a closely related species, living around the same time.
“Using a simple scaling factor and comparing the same bone in S. sikanniensis, the Lilstock specimen is about 25 percent larger. Other comparisons suggest the Lilstock ichthyosaur was at least 20-25 meters," Lomax said. "Of course, such estimates are not entirely realistic because of differences between species. Nonetheless, simple scaling is commonly used to estimate size, especially when comparative material is scarce."
Lomax, Massare and de la Salle have published their study of the jaw in PLOS One.
Wonderful as it is to discover such giants, the authors argue the work should force a rethink of the Aust Cliff bones. These were found in 1846 and the years soon after, just a day's walk along the English coast from Lilstock in rocks dated a few million years earlier. Some were lost in the 1940 bombing of Bristol. At the time they were identified as being from giant dinosaurs. The authors argue the latest discovery, and its similarities to the previously puzzling microstructure of the Aust Cliff bones, makes it much more likely they were actually from marine reptiles.
Although ichthyosaurs were first found in England, the previous largest British specimen was a mere 15 meters (50 feet) long.
"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," Lomax said. However, "To verify these findings, we need a complete giant Triassic ichthyosaur from the UK – a lot easier said than done!"