It may be a secret breeding ground for ichthyosaurs

Some 230 million years ago, large dolphin-like reptiles, called ichthyosaurs, were collected in order to safely breed in the waters – as many modern whales do.

This is the conclusion that researchers came to after investigating a mysterious ichthyosaur cemetery in the Berlin City-Ichthyosaur Park in Nevada. The park is home to the world’s largest collection of fossils Shonissaurus popularone of the largest ichthyosaurs ever discovered (SN: 8/19/02).

“This is what we see in modern marine vertebrates – they do it with the gray whale.” [the] trek to Baja California every year,” says Randall Irmis, a paleontologist at the Utah National Museum of History in Salt Lake City. The safe, warm water provides whale survival (SN: 1/19/80).

A new discovery, described on December 19 Current Biologyshows that this procedure “returns at least 230 million”, says Irmis. “It really connects the past to the present in a big way.”

The idea of ​​ichthyosaur birthing sites has been proposed before and is well-known enough that they are often incorporated into the creature’s artistic changes, says Erin Maxwell, a paleontologist at the State Museum of Natural History in Stuttgart, Germany. not involved in the new investigation. But this study, he says, “is the first to confirm these theories with data.”

The Nevada ichthyosaur fossil discovery has been a puzzle to paleontologists for decades. One curiosity is the many ichthyosaur fossils gathered in what is now a park, but about 230 million years ago it was part of a tropical sea. Another oddity is that the site seems almost entirely occupied by a giant, 14-meter-long adult St. popular. And then there is the question of what caused so much death.

Doctors had previously suggested that the reptiles, which could have been school-aged adults, had gathered together for some unknown reason before any of their mortality occurred.

A number of chests or quarries of specimens are scattered throughout the park. All told, Irmis and colleagues identified at least 112 individual ichthyosaurs in these fossils, including one site where park officials had left bones previously found in rock in public view.

The death snapshot meant scientists could explore how the fossils were arranged relative to each other, possibly providing insight into reptile behavior, says Neil Kelley, a paleontologist at Vanderbilt University in Nashville.

Kelley, Irmis and colleagues used a digital camera and laser scanner to collect hundreds of measurements of bone beds with semi-buried reptiles, placing the data in 3-D space. The team also studied the sizes and shapes of bones from across the park, some of which are now in museum collections. And the researchers analyzed the chemical composition of the surrounding rocks and developed them through ancient photographic and field data.

These spurts of evidence have helped researchers begin to understand what they’re looking at — and potentially solve at least one age-old mystery: what brought these creatures together.

Although almost all park’s Shonissaurus The skeletons of fully grown adults, the site has a few very small remains of ichthyosaurs, scientists have found. With micro-computed tomography, a 3-D imaging technique that uses X-rays to see inside fossils, the researchers found that some of the bones were small embryos and newborns. Shonissaurus.

The discovery led the team to conclude that the site was the land of the birth. That could explain why so many of the same creatures were born in the same place in the same country, the researchers say.

The site also seems to have been the place of childbirth Shonissaurus for a long time Rather than all the quarries being dated at about the same time, the researchers found the various ones separated by at least hundreds of thousands of years.

We do not know what killed the snakes, said Irmis.

Among the hypotheses for the cause of mortality are harmful mass algal blooms or large-scale molar activity. But new rock chemistry data exonerated those things as culprits.

Some of the animals still died in each prey. When the creatures were gathered together in one place, they may have left the reptiles vulnerable to a sudden, catastrophic event that buried them in the sediment, such as an underground collapse.

But the fossil finds could also indicate “just mortality over time,” Irmis says, given how the creatures seem to have come to the same place over and over again.