Jurassic ichthyosaurs dominated upper trophic levels of marine ecosystems. Many species coexisted alongside each another, and it is uncertain whether they competed for the same array of food or divided dietary resources, each specializing in different kinds of prey. In new research, paleontologists tested whether feeding differences existed between species of ichthyosaurs that lived during the Early Jurassic epoch, about 183 million years ago. Their findings suggest that physical differences in their snouts show they evolved to have different diets and were not competing for the same resource.
Life restoration of Ichthyosaurus anningae. Image credit: James McKay.
Ichthyosaurs were dolphin-shaped marine predators that fed on fish and squid-like swimming shellfish.
These creatures originated and diversified from 249 million years ago, around 3 million years after the end-Permian mass extinction event, and their fossil record spans about 160 million years.
They played an important role as apex predators in Mesozoic oceanic ecosystems.
Partitioning of food resources, hunting modes and swimming styles, and oceanic sub-habitats allowed for the diversification of these apex predators into a variety of dietary and life mode preferences.
“Modern predators like sharks and killer whales tend to eat anything they can, so it is exciting to be able to show that in the Jurassic there were definite specializations,” said University of Bristol’s Professor Michael Benton, senior author of the study.
“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 of the Jurassic oceans.”
Professor Benton and colleagues examined two juvenile ichthyosaur specimens, Hauffiopteryx typicus and Stenopterygius triscissus, from the Strawberry Bank Lagerstätte, a shallow marine environment from the Early Jurassic of southern England.
“Functional studies need excellent 3D specimens and the Lower Jurassic ichthyosaur fossils from Strawberry Bank in Ilminster are just that. Mary Anning’s fossils are amazing, but they are mostly squashed flat,” said co-author Matt Williams, a researcher at Bath Royal Literary and Scientific Institution.
“Our idea was to CT scan the specimens,” added co-author Dr. Ben Moon, a researcher at the University of Bristol.
“The scans allow us to make a detailed, 3D model of the skull in the computer, and it can then be tested for the likely forces experienced during biting.”
“After we had the models, we could stress test them,” said Dr. Andre Rowe, a researcher at the University of Bristol.
“We tested and confirmed the hypothesis that the slender-snouted ichthyosaur had a quick but weak bite, and the broad-snouted ichthyosaur had a slow but powerful bite.”
“Confirming the supposition was important,” Professor Benton said.
“It’s important we apply rigorous scientific approaches such as these engineering analyses.”
“The two species of ichthyosaur presumably chased fast-moving prey (the fast biter) and slower, tough-shelled prey (the slow, powerful biter).”
The results appear in the Journal of Anatomy.
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Sarah Jamison-Todd et al. Dietary niche partitioning in Early Jurassic ichthyosaurs from Strawberry Bank. Journal of Anatomy, published online September 29, 2022; doi: 10.1111/joa.13744
Source link: https://www.sci.news/paleontology/jurassic-ichthyosaur-diet-11256.html
