Ichthyosaurs, a type of marine reptile that resembled whales and dolphins, are thought to have collected to give birth in an area of the ocean where there were no nearby predators.

It's possible that the abundant collection of ichthyosaur fossils discovered in Nevada is made up of the remains of a breeding habitat that existed more than 200 million years ago. The enormous animals appear to have congregated in a tranquil area of the ocean where few predators would endanger their offspring.

The discovery suggests that the reptilian ancestors of modern marine mammals like whales engaged in the same types of mating behaviors.

Between approximately 250 million years ago in the Triassic Period and around 90 million years ago in the Cretaceous, ichthyosaurs, which superficially resembled modern whales and dolphins, lived in the oceans while dinosaurs roamed the land.

Palaeontologists under the direction of Charles Lewis Camp excavated the Berlin-Ichthyosaur State Park site where the Nevada ichthyosaurs were discovered between the 1950s and 1970s. The specimens were mostly neglected for several decades after his description of the animals was published posthumously in 1980, five years after his tragic death from pancreatic cancer.

These ichthyosaurs are members of the Shonisaurus popularis species. They existed some 215 million years ago, at the conclusion of the Triassic Period, and measured between 11 and 15 meters in length.

In his account, Camp hinted that there may have been a major stranding incident, similar to those that occasionally affect whales and dolphins in modern times. According to Neil Kelley at Vanderbilt University in Nashville, Tennessee, "He imagined that they were hunting around in the shallows and the tide had gone out, and they had accidentally been left behind."

Because they could have escaped even in shallow water, this explained why there were no smaller animals like fish among the fossils. Geological evidence, however, indicated that the fossils were formed in deep water, thus it didn't match.

The evidence has now undergone further review by Kelley and his coworkers. They searched for evidence of environmental disturbances that may have killed the ichthyosaurs, such as volcanic eruptions or low oxygen levels. "We could not find any direct evidence of any of that," he claims.

They did discover young ichthyosaurs, though. Paige dePolo, a team member at the University of Edinburgh in the UK, has spent years organizing the fossils, which were first scattered. DePolo had to look over every piece of rock that had been excavated because Camp's 1980 work just mentioned embryos; it did not depict or illustrate them. She claims that "the literal last block" is where she discovered the small ichthyosaurs.

There were numerous huge adult ichthyosaurs, at least three youngsters, or embryos, and hardly any other animals, according to the reanalysis. The research team hypothesizes that the ichthyosaurs chose an underdeveloped oceanic zone where there is little food since there would be fewer predators to endanger their offspring. According to dePolo, "The palaeontological evidence we have does not support that there are other vertebrates that might eat the young in this region."

According to Benjamin Kear of Uppsala University in Sweden, the fossil record is constantly subject to interpretation, therefore we can't be completely certain. Despite that, I believe it to be quite conceivable.

He claims that several lines of evidence support this. For instance, ichthyosaurs only had a small number of young at a time, suggesting parental care. Like other whales and dolphins, they might have lived in pods.

There are indications that other marine reptiles utilized these nesting sites. Long-necked plesiosaur fossils that were discovered by Kear and his colleagues in 2006 were from an inland seaway close to the South Pole. Numerous tiny, young animals may be found in the bones, all of which were dwelling in "a huge embayment" that would have acted as "a sheltered calving ground."