Berlin, Nevada, is A treasure chest for paleontologists. Just down the road from the now abandoned gold and silver mines, a collection of bones in the rock hints at an even richer past. The Berlin-Ichthyosaur State Park is filled with fossils of ancient marine reptiles. That bed of bones is so rich and strange that researchers have been scratching their heads for decades.
“There are sites with denser ichthyosaur bones, including places in Chile and Germany,” said Nick Pyenson, curator of marine mammal fossils at the Smithsonian National Museum of Natural History. . “But this place, the Berlin-Ichthyosaur in eastern Nevada, has really gone unresolved for a long time.” In a particular quarry, at least seven individuals from the genus Shonisaurus—a bus-sized dolphin with four flippers that resemble four limbs—basically lying on top of each other.
Previous theories have mainly focused on physical or environmental reasons for the fossil cluster. One idea is that these animals ran aground in shallow water and died in herds about 230 million years ago. Or maybe a volcanic eruption brought them in. Pyenson has another hunch, one that his team tested using 3D images of the site, as well as fossils and other clues in the geological record.
Write diary Current biology, Pyenson’s team today give the proof that shonisaurs went there reproduction. The team concluded that these animals migrated long distances to give birth, like some whale species today. This finding not only represents an example of ‘convergent evolution’, in which similar traits evolve independently in different species, but also longest life span example of group migration to a designated spawning ground.
“They’re making a pretty convincing case,” said Lene Liebe Delsett, a vertebrate paleontologist at the University of Oslo, Norway, who was not involved in the study. “Ichthyosaurs were the first large tetrapods in the sea. And throughout the Triassic, they vary quite a bit so there is great diversity. It was just a very exciting time to know more about it.”
Origin story of shonisaurs begins with death — many of them.
About 251 million years ago, between the Permian and Triassic, Earth biggest extinction event destroy about 95 percent of all marine species. This so-called “Great Death” has devastated the diverse landscape of creatures in the ocean. Some animals that regrow in their places turn out to be more exotic and bigger more than ever.
The next Trias began an evolutionary arms race. Prey has evolved harder shells and better mobility, predators burrow through ammonite shells and hunt fish better than ever before, etc. Ichthyosaur, which evolved from a terrestrial reptile into a new species with various sizes, somewhat repelled this pressure and quickly dominated the ocean. The Shonisaurus genus, in particular, have become some of the largest marine predators around. “They’ve gotten to whale size before anything else,” Pyenson said.
Pyenson is usually more of a whale guy; He specializes in mammals, which diverged from reptiles about 325 million years ago. But ancient marine reptiles such as those of the order Ichthyosaur share many similarities with existing marine mammals. Their ancestors came from the land, they were born at a young age, they have the same flippers and they are tetrapods, that is, with four limbs. And Pyenson is well versed in this kind of mystery. About a decade ago in Atacama, Chile, he and his South American collaborators used 3D mapping and chemical analysis to show that a tight cluster of at least 40 fossil whales must have died from a toxic algae outbreak 7 to 9 million years ago.
