Scientists have uncovered new clues about a curious fossil site in Nevada, a graveyard for dozens of giant marine reptiles. Rather than the site of a mass death as suspected, it may have been an ancient maternity ward where the creatures came to give birth.
The site is famous for its fossils of giant ichthyosaurs – reptiles that dominated the ancient seas and could grow to the size of a school bus. The creatures – the name means fish lizard – were underwater predators with large paddle-shaped flippers and long jaws full of teeth.
Since the Nevada ichthyosaur bones were unearthed in the 1950s, many paleontologists have investigated how all these creatures could have died together. Now, researchers have proposed a different theory in a study published Monday in the journal Current Biology.
“Multiple lines of evidence all point toward one argument here: that this was a place where giant ichthyosaurs came to breed,” said co-author Nicholas Pyenson, curator of fossil marine mammals at the Smithsonian National Museum of Natural History.
Once a tropical sea, the site — part of Nevada’s Berlin-Ichthyosaur State Park — is now in a dry, dusty landscape near an abandoned mining town, said lead author Randy Irmis, a paleontologist at the University of Utah.
To get a better look at the massive skeletons, which have vertebrae the size of dinner plates and bones from their flippers as thick as boulders, researchers used 3D scanning to create a detailed digital model, Irmis said.
They identified fossils from at least 37 ichthyosaurs scattered in the area, dating back about 230 million years. The bones were preserved in different rock layers, suggesting the creatures could have died hundreds of thousands of years apart rather than all at once, Pyenson said.
A big break came when the researchers discovered some small bones among the massive adult fossils and realized they belonged to embryos and newborns, Pyenson said. The researchers concluded that the creatures traveled to the site in groups for protection when they gave birth, like today’s marine giants. The fossils are believed to be from the mothers and offspring that died there over the years.
“Finding a place to give birth separate from a place where you can eat is really common in the modern world — among whales, among sharks,” Pyenson said.
Other clues helped rule out some previous explanations.
Testing the chemicals in the dirt showed no signs of volcanic eruptions or major changes to the local environment. And the geology showed that the reptiles were preserved on the ocean floor quite far from shore — meaning they probably didn’t die in a mass beaching event, Irmis said.
The new study provides a plausible explanation for a site that has puzzled paleontologists for decades, said Dean Lomax, an ichthyosaur specialist at England’s University of Manchester who was not involved in the research.
The case may not be completely closed yet, but the study “really helps unlock a little bit more about this fascinating site,” Lomax said.
Neil P. Kelley et al., Grouping behavior in a Triassic marine apex predator, Current Biology (2022). DOI: 10.1016/j.cub.2022.11.005
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