Early Jurassic juvenile ichthyosaurs show predatory specializations, University of Bristol scientists have revealed.
Their findings, published today in the Journal of Anatomy, suggest that the physical differences in their snouts show that they evolved to have different diets and were not competing for the same resource.
Ichthyosaurs, the classic ‘sea dragons’, were dolphin-like marine predators that fed on squid-like swimming fish and shellfish. The ichthyosaurs of the Lower Jurassic, about 185 million years ago, are known because the first specimens were found more than 200 years ago in Lyme Regis, southern England, by the famous fossil collector and paleontologist Mary Anning . Some of their specimens have long and slender snouts and others have short and wide snouts.
“Functional studies need excellent three-dimensional specimens,” said Matt Williams of the Bath Royal Literary and Scientific Institution, “and the Lower Jurassic ichthyosaur fossils from Strawberry Bank in Ilminster are just that. The Mary Anning fossils are amazing, but most of them are crushed.”
“Our idea was to CT scan the specimens,” said Dr Ben Moon, from Bristol’s School of Earth Sciences and supervisor of the study. “The scans allow us to make a detailed 3D model of the skull on the computer, and then the likely forces experienced during the bite can be tested.”
“After we had the models, we could test them,” Supervisor Andre Rowe said. “We tested and confirmed the hypothesis that the thin-snouted ichthyosaur had a fast but weak bite, and the broad-snouted ichthyosaur had a slow but powerful bite.”
“Confirming the assumption was important,” added lead author Professor Michael Benton. “It is important that we apply rigorous scientific approaches like these engineering analyses. The two ichthyosaur species presumably pursued fast-moving prey (the one that bites fast) and slower, hard-shelled prey (the one that bites slowly and powerfully ).
Sarah Jamison-Todd, who completed the work as part of her Masters in Palaeobiology, said: “I learned about CT scanning, model building and biomechanical testing using standard engineering software that is used to test how buildings and large structures bend.”
Professor Benton concluded: “Modern predators such as sharks and killer whales tend to eat anything they can, so it’s exciting to be able to show that there were definite specializations in the Jurassic. The work can be extended to explore other marine reptiles such as plesiosaurs and crocodiles, so we get a detailed picture of these amazing and alien worlds in the Jurassic oceans.”
Role:
‘Dietary niche partitioning in Early Jurassic Ichthyosaurs from Strawberry Bank’ by Sarah K. Jamison-Todd, Benjamin C. Moon, Andre J. Rowe, Matt Williams and Michael J. Benton in Journal of Anatomy.