Cluster of prehistoric giant marine reptile fossils in Central Nevada believed to be birthing grounds

RENO, Nev. — As many as 37 fossilized, school bus-sized marine reptiles from 225 million years ago are clustered in a remote, mountainous desert region of central Nevada in the Berlin-Ichthyosaur State Park. A team of scientists have offered new evidence for solving the decades-old puzzle of why the extinct ichthyosaurs are there.

The research, published in the science journal Current Biology, suggests that the 50-foot-long marine reptiles called ichthyosaurs (Shonisaurus popularis) migrated to this location, which was an ocean at the time, to breed and give birth together in relative safety, similar to how modern-day whales migrate.

The research involved collaborations between nine institutions, including the Smithsonian Institution and the University of Nevada, Reno’s Mackay School of Earth Sciences and Engineering. Paula Noble, professor of geological sciences and engineering, and one of her former undergraduate students Paige dePolo, have been working since 2014 with lead author of the research article Neil Kelley. Kelley is a Vanderbilt University scientist and former Smithsonian’s National Museum of Natural History Peter Buck postdoctoral fellow.

Using newer paleontological techniques such as high-resolution 3D scanning and geochemistry, researchers have unearthed evidence that the 50-ton creatures, predators resembling oversized chunky dolphins that have been adopted as Nevada’s state fossil – were migrating and congregating year after year along the same stretch of coastline, and over a period of hundreds of thousands years, if not millions. The main attraction for visitors to the Nevada State Park is a barn-like building that houses an array of ichthyosaurs that have been left embedded in the rock for the public to see and appreciate. To closely study the fossils, the team measured individual bones as well as created a full-color, high resolution 3D model of the site.

The research, conducted over eight years, methodically eliminated many previous theories about the extinction site. The team ruled out a cataclysmic event such as a large-scale volcanic event that would have deprived the reptiles of air or disturbed the ecosystem in which they died, such as a deadly algal bloom or a mass stranding event such as a beaching or stranding, as the fossils were found at what was the bottom of the ocean.

DePolo, now pursuing her doctorate in vertebrate paleontology at the University of Edinburgh, Scotland, is a coauthor on the paper for the research she began as an undergraduate in Noble’s lab. For dePolo, the research adds new dimension to these very ancient animals.

“This latest inference about Nevada's ichthyosaurs gives us insight into these organisms as animals fully alive and dynamically inhabiting their environment,” dePolo said. “It's so neat how carefully integrating the geology and fossil record of a site can yield a rich sense of how ancient animals lived. We're getting a window to behavior more than 200 million years in the past.”

Of interest to the researchers was the fact that, though the area’s limestone was chockfull of large adult Shonisaurus specimens, other marine vertebrates were scarce. The research team found a key piece of the puzzle when they discovered tiny ichthyosaur remains among new fossils collected at Berlin-Ichthyosaur State Park in Nevada’s Humboldt-Toiyabe National Forest, and hiding within older museum collections.

DePolo spent six months at the Nevada State Museum in Las Vegas organizing and cataloging the ichthyosaur material, at which time she found a rib block with embryo remains as well as an isolated vertebra that was incorrectly labeled as an ammonite.

“When I realized that I'd found parts of the embryo that the team had been trying to find for years at that point, it was such an exciting day,” dePolo said. “I didn't get a lot of cataloging work done that day because I was running around the museum trying to find the curators and exhibits staff and excitedly show them the smear of bones on the block.”

Careful comparison of the bones and teeth using micro-CT X-ray scans at Vanderbilt University revealed that these small bones were in fact embryonic and newborn Shonisaurus.

“Once it became clear that there was nothing for them to eat here, and there were large adult Shonisaurus along with embryos and newborns but no juveniles, we started to seriously consider whether this might have been a birthing ground,” lead author Kelley said.

Further analysis of the various strata in which the different clusters of ichthyosaur bones were found also revealed that the ages of the many fossil beds of the State Park were separated by at least hundreds of thousands of years, if not millions. This further confirmed the new theory and, for dePolo, inspired a new perspective of the species and its relationship to the probable birthing ground.

“When I was younger and through my undergraduate studies at UNR, I thought of Shonisaurus popularis as Nevada's ichthyosaur,” dePolo said. “My mind cruxed the specialness of these animals around them being found in the state I called home. Knowing that Shonisaurus was potentially migratory and that Berlin-Ichthyosaur State Park potentially was a place where the animals could gather in large numbers to give birth, flips the framing for me. It makes the ocean shelf that would eventually become part of Nevada just as special a place for these marine reptiles as it is for me.”

The University has become a recent hub of Ichthyosaur research, led by Noble and her students.Noble also contributed to this scientific article.

Noble formed the initial connection with the Smithsonian team in 2014, sorted out logistics of permitting, supplied university equipment and vehicles and provided support in the form of graduate and undergraduate researchers. The relationship between the University and the Smithsonian has been mutually beneficial.

“The Smithsonian National Institution is very much in agreement with our mission to educate the populous about our iconic state fossil,” Noble said. “You can talk to people in our state who don’t have any background in STEM. They may not know about stratigraphy and timelines, but they know what the ichthyosaur is. Maybe they’ve visited the State Park, but the ichthyosaur has always been a really fun way to engage with people in our state around something we’re all excited about.”

The 3D scans of the site are now available for other researchers to study and for the public to explore via the open-source Smithsonian’s Voyager platform, which is developed and maintained by Blundell’s team members at the Digitization Program Office. An interactive digital experience about the research team’s study, including a 3D model of ichthyosaur sites analyzed, is also available on the Digitization Program Office’s website.

The research team, led by Kelley, and co-authored by the museum’s curator of fossil marine mammals Nicholas Pyenson, colleagues from the Natural History Museum of Utah, the University of Utah, University of Texas at Austin, Vrije Universiteit Brussels and University of Oxford.

This research was conducted under research permits issued by the U.S. Forest Service and Nevada State Parks, and it was supported by funding from the Smithsonian, University of Nevada, Reno, Vanderbilt University and University of Utah.

In the Photo: Paige dePolo (front) works to measure ichthyosaur fossils in the Berlin-Ichthyosaur State Park’s public quarry as an undergraduate at the University of Nevada, Reno. She is accompanied by the Smithsonian 3D Programs team manager Holly Little, University of Nevada, Reno Professor Paula Noble and lead author Neil Kelley. Photo courtesy of Paula Noble.