Unearthed in the Swiss Alps between 1976 and 1990, the fossils include the largest ichthyosaur tooth ever found.
The habitat and animals that were found together with the giant ichthyosaurs in the Kössen Formation, Switzerland. Image credit: Heinz Furrer.
Ichthyosaurs swam the world’s oceans for millions of years during the Triassic, Jurassic and Cretaceous periods.
They had an elongated body and a relatively small head. But shortly before most of them became extinct some 200 million years ago — only the familiar dolphin-like species survived until 90 million years ago — they evolved into gigantic forms.
“With an estimated weight of 80 tons and a length of more than 20 m, these prehistoric giants would have rivaled a sperm whale,” said Professor Martin Sander, a researcher in the Institute of Geosciences at the University of Bonn.
“However, they left scarcely any fossil remains; why that is remains a great mystery to this day.”
In the new study, Professor Sander and his colleagues examined the remains of three giant ichthyosaurs from the Kössen Formation in the eastern Swiss Alps.
The finds are between 210 and 200 million years old and include a very large tooth lacking most of the crown, a postcranial bone association of one very large vertebra and ten rib fragments, and an association of seven very large vertebral centra.
The paleontologists compared this material with the two largest ichthyosaurs known from partial skeletons, Shonisaurus popularis (15 m long) and Shastasaurus sikkanniensis (21 m) from Nevada and British Columbia, respectively.
According to the team, the incomplete tooth from the Kössen Formation confirms that at least some giant ichthyosaurs had teeth.
Based on their proportional differences, the two sets of skeletal remains may represent two different species of Shastasaurus-like ichthyosaurs.
The larger and geologically younger specimen may have been nearly the size of Shastasauru sikkanniensis, and the smaller that of Shonisaurus popularis.
“Bigger is always better,” Professor Sander said.
“There are distinct selective advantages to large body size. Life will go there if it can.”
“There were only three animal groups that had masses greater than 10-20 tons: long-necked dinosaurs (sauropods); whales; and the giant ichthyosaurs of the Triassic.”
“These monstrous reptiles patrolled Panthalassa, the world’s ocean surrounding the supercontinent Pangea during the Late Triassic, about 205 million years ago.”
“They also made forays into the shallow seas of the Tethys on the eastern side of Pangea.”
A paper on the findings was published in the Journal of Vertebrate Paleontology.
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P. Martin Sander et al. Giant Late Triassic ichthyosaurs from the Kössen Formation of the Swiss Alps and their paleobiological implications. Journal of Vertebrate Paleontology, published online April 27, 2022; doi: 10.1080/02724634.2021.2046017
Source link: https://www.sci.news/paleontology/koessen-formation-ichthyosaurs-10754.html
