Mysterious ichthyosaur graveyard may have been a breeding ground

Some 230 million years in the past, large dolphinlike reptiles referred to as ichthyosaurs gathered to breed in secure waters — identical to many trendy whales do.  

That’s the conclusion that researchers arrived at after learning a mysterious ichthyosaur graveyard in Berlin-Ichthyosaur State Park in Nevada. The park is house to the world’s richest assemblage of fossils of Shonisaurus popularis, one of many largest ichthyosaurs ever found (SN: 8/19/02).  

“That is one thing we see in trendy marine vertebrates — grey whales make [the] trek to Baja California yearly” to breed, says Randall Irmis, a paleontologist on the Nationwide Historical past Museum of Utah in Salt Lake Metropolis. The sheltered, heat water provides safety for the whales (SN: 1/19/80).

The new finding, described December 19 in Present Biology, reveals that this habits “goes again no less than 230 million years,” Irmis says. “It actually connects the previous to the current in a giant method.”

The thought of birthing areas for ichthyosaurs has been proposed beforehand, and is even well-known sufficient to usually be included into artists’ renderings of the creatures, says Erin Maxwell, a paleontologist on the State Museum of Pure Historical past in Stuttgart, Germany, who wasn’t concerned within the new analysis. However, she says, this research “is the primary to help these speculations with knowledge.”

Nevada’s ichthyosaur fossil trove has been a puzzle to paleontologists for many years. One curiosity is the numerous ichthyosaur fossils clustered in what’s now the park, however about 230 million years in the past, was a part of a tropical sea. One other oddity is that the positioning appears as if it had been nearly fully populated by large, 14-meter-long grownup S. popularis. After which there’s the tantalizing query of what brought about the deaths.

Scientists have beforehand urged that the reptiles, which may very well be roughly the size of a college bus when grown, had congregated collectively for some unknown cause earlier than one thing brought about their mortality en masse.

A number of pockets, or quarries, of specimens are scattered throughout the park. All informed, Irmis and colleagues recognized no less than 112 ichthyosaur people in these quarries, together with at one website the place park officers had left beforehand found bones half-encased within the rock for public viewing.

That dying snapshot meant that scientists might study how the fossils had been organized relative to 1 one other, maybe providing perception into the reptiles’ habits, says Neil Kelley, a paleontologist at Vanderbilt College in Nashville.

Kelley, Irmis and colleagues used digital cameras and a laser scanner to gather a whole lot of measurements of the bone mattress with the half-buried reptiles, combining the information right into a 3-D mannequin of the positioning. The staff additionally studied the configurations and dimensions of bones from throughout the park, together with some now in museum collections. And the researchers analyzed the chemical make-up of the encompassing rocks and pored over older images and subject notes.

These scraps of proof helped the researchers start to grasp what they had been — and probably clear up no less than one long-standing thriller: what introduced these creatures collectively.

Although nearly all the park’s Shonisaurus skeletons are fully-grown adults, the positioning does have a couple of very tiny ichthyosaur stays, the scientists discovered. Utilizing micro-computed tomography, a 3-D imaging method that makes use of X-rays to see contained in the fossils, the researchers found that some tiny bones had been these of embryonic and new child Shonisaurus.

The discovering led the staff to conclude that the positioning was a birthing floor. That might clarify why there have been so most of the identical creatures in the identical place alongside newborns, the researchers say.

The location additionally appears to have been a birthing floor for Shonisaurus for a very long time. Somewhat than all of the quarries courting to roughly the identical time, completely different ones are separated by no less than a whole lot of 1000’s of years, the researchers discovered.

As for what killed the reptiles, “we don’t know,” Irmis says.

Among the many hypotheses for a mass mortality occasion had been dangerous algal blooms or large-scale volcanic exercise. However the brand new rock chemistry knowledge eradicated these occasions as culprits.

A number of the animals in every quarry might have nonetheless died en masse. Having the creatures grouped in a single place to breed could have left the reptiles susceptible to a sudden catastrophic occasion that buried them in sediment, akin to an undersea landslide.

However the fossil finds may additionally symbolize “simply regular mortality over time,” Irmis says, given how the creatures appear to have come to the positioning repeatedly.