Approximately 230 million years ago, giant dolphin-like reptiles called ichthyosaurs came together to reproduce in protected waters, much as many contemporary whales do today.
Researchers in Nevada’s Berlin-Ichthyosaur State Park came to this conclusion after doing research on a mystery ichthyosaur cemetery there. The fossil assemblage of Shonisaurus popularis, one of the biggest ichthyosaurs ever found, may be found at this park, which is home to the world’s finest fossil collection of the species.
Randall Irmis, a palaeontologist at the National History Museum of Utah in Salt Lake City, adds that “this is something we see in current marine animals – grey whales make voyage to Baja California every year” to reproduce. The museum is located in Salt Lake City. The whales may feel secure in the warm, protected water they are swimming in.
According to Irmis, the new discovery, which was published on December 19 in the journal Current Biology, demonstrates that this behaviour “dates back at least 230 million years.” “In a significant manner, it bridges the gap between the past and the present.”
Erin Maxwell, a palaeontologist at the State Museum of Natural History in Stuttgart, Germany, who was not involved in the new research, says that the concept of birthing areas for ichthyosaurs has been proposed in the past and is even well-known enough to often be incorporated into artists’ renderings of the creatures. This is according to Maxwell, who was not involved in the new research.
Paleontologists have been scratching their heads for decades over the ichthyosaur fossil treasure in Nevada. The presence of a large number of ichthyosaur fossils in an area that is today a park but was once a tropical sea around 230 million years ago is an interesting aspect of this location. A further peculiarity is that the location gives the impression that it is nearly totally occupied by enormous S. popularis adults that are at least 14 metres in length. And then there’s the intriguing mystery of what led them to die in the first place.
In the past, researchers have hypothesised that the reptiles, which could grow to reach around the length of a school bus when fully grown, had gathered together for some unexplained purpose just before something caused their deaths in vast numbers.
There are a number of concentrations, or quarries, of specimens dispersed around the park. At one location, park authorities had left previously found bones half-encased in the granite for public viewing. Irmis and his colleagues were able to identify at least 112 individuals of the ichthyosaur in these quarries, including at the location where they were placed.
Neil Kelley, a palaeontologist at Vanderbilt University in Nashville, explains that because of the picture of the moment of death, scientists were able to investigate how the fossils were placed in relation to one another, which may provide insight into the behaviour of the reptiles.
After collecting hundreds of measurements of the bone bed along with the half-buried reptiles using digital cameras and a laser scanner, Kelley, Irmis, and their colleagues used the data to create a three-dimensional representation of the location. In addition to this, the team examined the proportions and forms of bones found all across the park, including those that are now housed in museum collections. In addition to this, the researchers investigated earlier images and field notes, as well as evaluated the chemical composition of the rocks in the area.
The researchers were able to begin to comprehend what they were looking at with the assistance of these stray pieces of evidence, which led them to possibly answer at least one long-standing mystery: what brought together these many organisms.
The researchers discovered that despite the fact that virtually all of the Shonisaurus bones in the park are of fully grown adults, the location does include the remains of a few extremely young ichthyosaurs. The researchers found out that some of the tiniest bones were those of embryonic and newborn Shonisaurus by using a technology called micro-computed tomography, which is a kind of three-dimensional imaging that employs X-rays to view within the fossils.
The discovery led the scientists to the conclusion that the location was a breeding area for the species. The fact that there were so many of the same species in the same spot alongside infants might be explained in this way, the researchers suggest.
Additionally, it seems that Shonisaurus used this location as a breeding habitat for a considerable amount of time. According to the findings of the experts, rather than all of the quarries dating back to around the same period, various ones are separated by a minimum of hundreds of thousands of years.
Irmis claims that they do not have any information on the cause of death of the reptiles.
Harmful algal blooms and widespread volcanic activity were two of the explanations that were put up to explain a mass death event. However, the new data on the chemistry of rocks ruled out those events as possible causes.
It is possible that a significant number of animals in each quarry succumbed to their injuries. Because of the concentration of the animals in a single location for the purpose of reproduction, the reptiles may have been more susceptible to a sudden catastrophic occurrence that buried them in silt, such as an underwater landslide.
Irmis believes that the fossils might indicate “simply regular mortality over time,” given the fact that the species seem to have returned to the location on several occasions, although this explanation is not the only one.