Berlin, Nevada, is a treasure chest for paleontologists. Just down the street from now-abandoned gold and silver mines, a rockbound assortment of bones hints at an excellent richer previous. The Berlin-Ichthyosaur State Park is teeming with dozens of fossils of historic marine reptiles. That bone mattress is so ample and peculiar that researchers have been scratching their heads over it for many years.

“There are sites with way more dense occurrences of ichthyosaur skeletons, including places in Chile and Germany,” says Nick Pyenson, curator of fossil marine mammals on the Smithsonian National Museum of Natural History. “But this place, Berlin-Ichthyosaur in eastern Nevada, has really escaped explanation for a long time.” In one specific quarry, no less than seven people from the genus Shonisaurus—a bloated, bus-sized dolphin with 4 limb-like flippers—lay primarily stacked atop each other.

Previous hypotheses largely targeted on bodily or environmental causes for the cluster of fossils. One recommended that the animals had gotten stranded in shallow water and died as a gaggle some 230 million years in the past. Or perhaps a volcanic eruption did them in. Pyenson had one other hunch, one which his workforce examined utilizing 3D visualizations of the location, in addition to fossils and different clues within the geological report.

Writing within the journal Current Biology, right this moment Pyenson’s workforce presents evidence that the shonisaurs got here there to breed. The workforce concludes that the animals migrated lengthy distances to provide start, like some whales do right this moment. The discovery not solely represents an instance of “convergent evolution,” during which the identical traits independently evolve in several species, but additionally the oldest instance of migration in teams to a delegated calving floor.

“They’re making quite a convincing case,” says Lene Liebe Delsett, a vertebrate paleontologist on the University of Oslo, Norway, who was not concerned within the examine. “Ichthyosaurs were the first large marine tetrapods. And throughout the Triassic, they varied quite a lot, so there was a large diversity. It’s just a very interesting period of time to know more about.”

The origin story of the shonisaurs begins with dying—quite a lot of it.

Some 251 million years in the past, between the Permian and Triassic intervals, Earth’s biggest extinction event annihilated about 95 percent of all marine species. This so-called “Great Dying” mowed down the varied panorama of creatures within the ocean.Some of the animals that grew again of their place turned out to be weirder and bigger than ever earlier than.

The ensuing Triassic began an evolutionary arms race. Prey developed tougher shells and higher mobility, predators crunched by way of ammonite shells and hunted fish higher than ever, and so forth. Ichthyosaurs, which developed from terrestrial reptiles into new species of varied sizes, partly drove this stress and shortly dominated the ocean. The Shonisaurus genus, specifically, grew to be among the largest marine predators round. “They achieved whale sizes before anything else,” says Pyenson.

Pyenson is often extra of a whale man; he makes a speciality of mammals, which break up from reptiles about 325 million years in the past. But historic marine reptiles like these below the order Ichthyosaur bear many similarities to current marine mammals. Their ancestors got here from land, they birthed reside younger, that they had related flippers, and they’re tetrapods, that means four-limbed. And Pyenson is nicely versed in one of these thriller. About a decade in the past in Atacama, Chile, he and his South American collaborators used 3D mapping and chemical analyses to point out {that a} tight cluster of at least 40 fossilized whales will need to have died from a poisonous algal bloom 7 to 9 million years in the past.