When is a dinosaur bone not a dinosaur bone?

Mount Holyoke professor Mark McMenamin seeks clues to the valley’s Jurassic past hidden away in fossilized bones.

Science is an iterative process. Hypotheses are formed and tested. No matter how exciting a finding may be, it must change as new evidence emerges. 

Professor of Geology Mark McMenamin recently experienced an object lesson in the provisional nature of scientific knowledge. The object? A dinosaur bone fossil belonging to a previously unknown predatory dinosaur reaching up to 30 feet in length — at least, that was McMenamin’s initial conclusion.

The story begins in August 2021, when McMenamin, with his wife, was collecting some decorative rocks for his garden from the University of Massachusetts Amherst campus. After they returned with their haul, he noticed that one of the rocks had an unusual texture and porosity, as well as a smoother patch about two inches long of what appeared to McMenamin’s trained eye to be intact outer bone. 

Paleontologists have long known that dinosaurs once roamed the area now known as the Pioneer Valley. In 1802, fossilized dinosaur tracks were discovered in South Hadley. Despite ample evidence that they once roamed the area, there’s always been a paucity of dinosaur bone fossil findings in the area, largely because “glaciers scooped up and scattered them willy-nilly over the landscape,” McMenamin said. For this reason, each possible fossil find is a tantalizing addition to our understanding of the creatures that once lived in the area.

McMenamin, who is a paleontologist as well as a geologist, used the scanning electron microscope at Mount Holyoke to perform a geochemical test on his find. The test revealed a high level of phosphorus, a crucial component of bone, on the sample’s exterior. That, along with the specimen’s texture, hinted of dinosaur bones to McMenamin.

“It was starting to look pretty good,” he said. “Its shape seemed quite comparable to a dinosaur elbow bone.” Experts he showed the specimen to agreed. 

He wrote up preliminary findings in an article in Academia, describing a new dinosaur that lived nearly 200 million years ago, “a large neotheropod from the Lower Jurassic of Massachusetts.” A handful of news stories followed early this year.

But McMenamin’s Pioneer Valley fossil hunt was just getting started. “My general policy is to try to squeeze the fossil record until it cries for mercy,” he said, laughing. During spring break, he conducted fieldwork in an area about eight miles north of Amherst and found another bone-like rock with a texture and porosity similar to the first find. Further geochemical tests, however, confirmed the presence of phosphorus in the interior of the first find but not the second.

“The phosphorus is a real anomaly if [the first specimen] is not fossil bone,” he said. But as of early April, there was still no clear conclusion. “This is typical in paleontology,” said McMenamin. “You have to be really careful when you’re interpreting fossils.”

A College tradition

Mount Holyoke College has played a key role in moving the science of paleontology in the valley forward. Professor Mignon Talbot became the first woman to discover and describe a nonbird dinosaur when she discovered a set of fossils not far from campus. Talbot, who taught at the College for more than 30 years in the early 20th century and chaired both the geology and the geography department, named the creature Podokesaurus holyokensis. The fossils were lost when Williston Hall burned down on campus in 1917 — but Podokesaurus holyokensis gained a new lease on life when it became Massachusetts’ official state dinosaur late last year.

For McMenamin, the rarity of fossils in the area and the challenges of identifying his recent finds underscore the inherent difficulties of paleontology. “It is one of the hardest sciences,” he said. “It has all the complexity of biology, plus the temporal aspect, plus the fact that you’re dealing with an extremely limited and shoddy data set.” The multidisciplinary science requires careful interpretation of data, and positive outcomes are never assured. “It’s a fun game, but it’s a hard game,” McMenamin said.

But even if both his recent finds prove to be rocks, there’s still value in that negative result, McMenamin stressed. It helps to slightly narrow the fossil search. “We’ll know what not to look for,” he said. 

He is confident that evidence of the large neotheropod he hypothesized is nearby, waiting to be found. “We have tracks that match that size of the animal,” McMenamin said. “So fossils are somewhere in this area.”

Eventually, McMenamin speculated, scientists will move beyond tiny snippets of information to develop a much fuller picture of what was going on in the Pioneer Valley during the Jurassic period. But it will take a mix of luck and keen observation from scientists both professional and amateur. 

If they know what they’re looking for, amateur paleontologists can potentially find a fossil in plain sight, he said. “As Louis Pasteur once said, ‘Chance favors the prepared mind.’”

Ed. note: Just before publication, results came in from radiology that proved the specimen was a rock, not a fossil. However, McMenamin is not daunted. “Another specimen has turned up in the Hartford basin,' he said. 'The search continues.”

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