Today we know that some of the large marine mammals, such as rorquals and whales, and even some sharks, annually make long and massive voyages across the oceans to breed and give birth in calm, food-rich waters safe from the Predators.
Now, a new investigation suggests that 200 million years before the largest beings on our planet evolved, another type of animal, giant reptiles that could reach the size of a bus and are called ichthyosaurs They already used this strategy to give birth to their young under the protection of a large group of congeners and under the protection of a safe area.
The work, collected in an article that under the title Grouping behavior in a Triassic marine apex predator was published in the magazine Current Biologyexamines a rich underwater fossil bed in the so-called Berlin Ichthyosaur State Park -BISP- in Nevada’s Humboldt-Toiyabe National Forest, where lie the remains of a large group of petrified ichthyosaur fossils over 15 years old. meters in length of the species The popular Shonisaurus.
Elephant Island, a home for Fin Whales
The study, co-led by the associate professor at the University of Utah and curator of the Museum of Natural History in the same city, Randall Irmisoffers a plausible explanation for how at least 37 of these huge prehistoric marine reptiles met a common fate in this very locality, a question that has puzzled paleontologists for more than half a century.
Ichthyosaurs, the first migratory marine giants
“These ichthyosaurs died here in large numbers because they were migrating to this area to give birth over many generations and over hundreds of thousands of years,” explains study co-author and curator at the Smithsonian National Museum of Natural History, Nicholas Pyenson. “That means that this kind of behavior that we see today in whales has been around for more than 200 million years.”
Already for decades, some paleontologists had proposed that BISP’s ichthyosaurs—predators that resemble large plump dolphins—died in a mass-stranding event like those that sometimes affect whales. Another theory in this regard postulates that the creatures could have been poisoned by toxins from a nearby harmful algae bloom. The problem, however, is that these hypotheses lacked solid scientific evidence to back them up.
“This type of behavior that we see today in whales has been around for more than 200 million years.”
In most paleontological sites, fossils are excavated and removed so that scientists at research institutions can study them more closely. In the case of BISP, however, the main attraction is an area where ichthyosaurs have been left embedded in rocks for the public to visit.
Thus, in one of the locations at the site lie the partial skeletons of approximately seven individual ichthyosaurs that appear to have all died at the same time, so the scientists turned to high-resolution 3D modeling to study the remains of the fossil bed, and they then examined the chemical composition of the rocks surrounding the remains to determine if environmental conditions were responsible for the large concentration of these creatures at the site. “Once we determined that the reasons why so many ichthyosaurs congregated here were not due to environmental conditions, we were able to focus on possible biological reasons,” Irmis explains.
Utah Museum of Natural History / Mark Johnston
The team then performed a series of geochemical tests to look for signs of environmental disturbance. Thus, they measured the presence of mercury and ruled out that the massive death of these animals was the product of large-scale volcanic activity. They similarly ruled out the possibility of some sudden event that would have resulted in a decrease in available oxygen in the water (although ichthyosaurs, like whales, came to the surface to breathe).
What was most revealing for the team of Neil Kelley, professor at Vanderbilt University and lead author of the paper, was to realize that the limestone and shale in the area were littered with large adult specimens of Shonisaurusand yet the remains of other marine vertebrates were relatively sparse. “There are dozens of adult skeletons of Shonisaurus in this place, but pretty much nothing else,” Pyenson declares. “There are no remains of things like fish or other marine reptiles that these ichthyosaurs feed on, nor are there any juvenile skeletons of Shonisaurus”.
Cymbospondylus youngorum: the first giant on Earth was an ichthyosaur
The intrigue and mystery surrounding the concentration of these ichthyosaurs at BISP continued to plague researchers for some time until the key piece of the puzzle emerged among the smaller BISP ichthyosaur fossil remains stored in older collections. Careful comparison of these bones and teeth from X-rays and microcomputed tomography revealed that these small bones did, in fact, belong to Shonisaurus in embed staterionary and newborns.“Once it became clear that there was nothing for them to eat here, and that there were large Shonisaurus adults along with embryos and newborns, but not juveniles, we began to seriously consider whether this could have been a birthplace”, explica Kelley.
Further, more detailed analysis of the various strata in which the different groups of ichthyosaur bones were found also revealed that the ages of the many BISP fossil beds were separated by hundreds of thousands of years, and even millions of years.
The last meal of a newborn ichthyosaur
“Finding these different locations with the same species spread over geologic time and with the same demographic pattern tells us that this was a preferred habitat for these large oceanic predators that they returned to for generations,” Pyenson explains. “This is a clear ecological signal, so we argued that this was a place where Shonisaurus it used to give birth very similar to how whales do today. We now have evidence that this type of behavior is at least 230 million years old.”