Paleontologists May Have Solved the Mystery Behind a Prehistoric Reptile Graveyard

There was no one who could explain why so many huge lizards were grouped together. In the middle of the Nevada desert, in rocks dating back more than 200 million years, paleontologists found the remains of at least seven enormous marine reptiles called Ichthyosaurs. A new analysis published Monday in Current Biology offers a compelling theory of why they were together in the first place. The great saurians were in the water when the pileup occurred.

The Berlin-Ichthyosaur State Park in Nevada has been home to many bones and skeletons of the Shonisaurus over the course of more than a century. Paleontologists have not been able to explain why the marine reptiles have been found in such large numbers. Nicholas Pyenson and colleagues from the National Museum of Natural History combed over the quarry and fossils around it to come up with a new interpretation of the site. As part of their life cycle, the Shonisaurus traveled to this place hundreds of million of years ago.

The fossils of the Shonisaurus are the key to unraveling the mystery. The majority of the specimen are adults. It was almost done. The area contains fossils of the embryo of the Shonisaurus, as well as those that had just begun to swim on their own. In a 1980 monograph, embryology was mentioned from the locality, but no details were given in the publication.

The new paper concludes that the fossils are evidence that the Shonisaurus were here to give birth. There was a dominance of adult-sized Shonisaurus and then a small amount of embryology. The team didn't find any fossils of juvenile Shonisaurus, which experts would expect if the deposit was from a disaster like volcanic activity or toxic plankton.

The new research is related to what Pyenson and other researchers have done in the past. Paleontologists have found skeletons of whales and other marine mammals washed up on a tidal flat. They wanted to see if the same thing had happened at Berlin- Ichthyosaur. Laser scanning, photogrammetry and computer vision were all applied in the same way. A multiyear effort created a digital data set of the site that allowed for a broader analysis than just looking at museum specimen.

Dean Lomax, a University of Manchester paleontologist, was not involved in the new study.

Studies have suggested that Shonisaurus lacked teeth and was a gentle giant. This interpretation did not take into account some of Camp's finds from the 1950s. According to Pyenson and colleagues, this Ichthyosaur was a member of the cut guild and was an immense killer whale.

Most of the fossils have been found in a certain area. The problem is that there isn't any prey large enough for such a predator in the same rocks. The lack of non-Shonisaurus is a surprise to me. The paleontologists don't have evidence of cannibalism, but they do have evidence that Shonisaurus deposited their babies in the warm waters of Berlin-Ichthyosaur. Even though it was fairly deep water, we think Shonisaurus congregated close to the coastline. The pattern is similar to that of whales that travel to give birth in a different place in the ocean.

If the hypothesis is correct, Shonisaurus would return to the same area time and again to give birth to her offspring.

It's not clear why so many Shonisaurus died and were buried in this area. It would be fair to say that Berlin-Ichthyosaur is a mystery. The first question is addressed in the new study, but the second is still open. It is not known why several marine reptiles died at the same time, but we have a better idea of why they gathered in the first place.