Nevada’s ichthyosaur grave was actually a 230-million-year-old maternity ward

Researchers have finally solved the mystery of a site where dozens of large marine reptiles died 230 million years ago. A team led by Nicholas Pyenson, a paleontologist and marine biologist at the Smithsonian National Museum of Natural History, reported the finding.

Scientists re-examined the ichthyosaur mass grave in central Nevada. In the 20th century, paleontologists recovered the remains of the largest Triassic ichthyosaurs—Shonisaurus species that could reach up to 15 meters long—at the site. The cemetery sits inside Berlin-Ichthyosaur State Park, near the old mining town of Berlin. These now-desert areas were once covered by ocean water, Smithsonian Magazine reported.

Pyenson’s team reconstructed why groups of large ichthyosaurs went to the site and died there. They conclude pregnant ichthyosaurs came into these waters to give birth.

Shonisaurus breeding ground

The Berlin-Ichthyosaur State Park is named for the prehistoric animals found there. Over time, researchers have uncovered numerous bones in the local rock formations. The large aquatic predators known as ichthyosaurs are often called “fish lizards.”

A new study published in Current Biology proposes that large ichthyosaurs gathered in this area to breed.

The team found fossils of adults alongside newborns and embryos in the quarry. Earlier reports from the site didn’t mention embryonic remains.

Paleontologists used methods they had tested on prehistoric marine mammals in the Atacama Desert — laser scanning, photogrammetry, and computer vision.

The researchers concluded these large marine reptiles used the area as a nursery. They think Shonisaurus gathered near the shoreline of a relatively deep ocean basin. That’s similar to how whales travel to Monterey Bay to give birth, Pyenson said.

If the team’s hypothesis is correct, ichthyosaurs returned to the same spot to give birth for more than 100,000 years.

Previous studies offered other explanations for the mass deaths: algal poisoning, stranding on a sandbar, or a volcanic eruption. None of those theories has been definitively proven.