An anatomy and vertebrate paleontology student from Oklahoma State University Center for Health Sciences was a lead author on a study examining how sauropod dinosaurs dispersed in North America during the Late Jurassic.

Colin Boisvert and a team of international researchers published their research in Palaeontologia Electronica, the longest-running, peer-reviewed electronic journal of paleontology, in October.

The study focused on diplodocids, a group of long-necked sauropod dinosaurs that existed between roughly 135 and 170 million years ago. Using a mathematical model, Boisvert and the research team examined how these dinosaurs existed within the Morrison Formation.

The Morrison Formation is a well-known fossil-bearing rock formation that extends through the western United States. Paleontologists have studied it for more than 150 years, so the team went into this study with a good idea of the ecosystems and organisms within it.

“The Morrison Formation contains a vast array of dinosaurs from many different clades, or families, many of them with relatives in other locations around the globe. It tells us more about how these animals dispersed and diversified during the Late Jurassic,” he said.

Using a computer program called BioGeoBEARS, the team tested different biogeographic models for diplodocids using current fossil and evolutionary data.

The program generated a range of scenarios showing how these dinosaurs may have evolved and dispersed across different regions, allowing researchers to compare the models and identify the most likely explanation that best fit the data.

One of Boisvert’s colleagues would run the program and help him interpret the results and write the portions of the manuscript related to the results and methodology, which he said was the most challenging part of the research, but a valuable learning experience.

The results revealed that diplodocids were widely spread across the Morrison Formation.

“These animals potentially occupied a large territory in life, along with a wide dispersal as they adapted to changing environments in the Late Jurassic. It also shows that they were successful in terms of the expansion and diversity seen with this clade in North America,” said Boisvert.

Possible mechanisms to explain how diplodocids dispersed across the Morrison Formation include regionalized extinction and a process called allopatric speciation, when populations become geographically separated by a physical barrier and evolve into different species over time.

Their analysis also revealed diplodocids possibly originated in South America or the northern region of the Morrison Formation, a discovery that surprised Boisvert.

“We found the potential origin could either be in the northern region of the Morrison Formation or South America. It was surprising because we find many diplodocids in the Northern Hemisphere, but fewer in the Southern Hemisphere,” he said.

Some sites within the Morrison Formation contain fossils of up to six distinct sauropods, many of them several times larger than an elephant. Boisvert said the dispersal of diplodocids within the formation raises a larger, ecological question: How did so many large-bodied, long-necked dinosaurs coexist in the same environment at the same time?

The study’s findings also contribute to a broader evolutionary question.

“In terms of evolution, it provides another piece of the puzzle we still have yet to solve regarding how dispersal between Europe and North America occurred at this time,” said Boisvert. “We know several other clades dispersed between these landmasses, but the direction, timing and frequency of these movements are still unknown.”

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