NEW YORK (AP) —
Scientists have uncovered new clues about a curious Nevada fossil site, a graveyard for dozens of giant marine reptiles. Rather than the site of a mass die-off as suspected, it could be an old 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 as big as a school bus. The creatures – the name means fish lizard – were underwater predators with large paddle-shaped fins and long jaws full of teeth.
Since the Nevada ichthyosaur bones were unearthed in the 1950s, many paleontologists have investigated how all of these creatures may have died together. Now, researchers have proposed another theory in a study published Monday in the journal Current Biology.
“Several lines of evidence point to one argument here: that this was a place where giant ichthyosaurs came to give birth,” said study co-author Nicholas Pyenson, curator of marine mammal fossils 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, with vertebrae the size of dinner plates and bones of their fins as thick as boulders, researchers used 3D scanning to create a detailed digital model, Irmis said.
They identified fossils of at least 37 ichthyosaurs scattered across the area, dating back about 230 million years. The bones were preserved in different layers of rock, suggesting the creatures could have died hundreds of thousands of years apart rather than all at once, Pyenson said.
A big breakthrough came when the researchers saw some tiny 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 during childbirth, like today’s sea giants. The fossils are believed to be from the mothers and offspring who died there over the years.
“Finding a place to give birth separate from a place where you could eat is very 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 massive shifts 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 stranding, Irmis said.
The new study offers a plausible explanation for a site that has baffled paleontologists for decades, said Dean Lomax, an ichthyosaur specialist at England’s University of Manchester who was not involved in the study.
The case may not be completely closed yet, but the study “really helps unlock a little more about this fascinating site,” Lomax said.
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