370-million-year-old tracks unearthed on West Campus spark a Duke paleontologist's quest to uncover the fossil's story
In late March, Curt Farmer got a request to remove walkway stone near Bostock Library.
As the Project Coordinator for Buildings and Grounds, Farmer manages the repair or removal of damaged paver stones in the walkways lacing West Campus, so this wasn't unusual. The reason, however, was something new.
Paleontologist Alexander Glass, a Senior Lecturer in Earth and Climate Sciences at Duke's Nicholas School of the Environment , spotted small imprints on the particular slab of Pennsylvania Bluestone and believes it holds fossilized footprints that might offer insights into how animals first began moving on land.
"Something walked here - with legs - and left an impression in the sandstone that's been preserved for around 380 million years," Glass said.
In geology classes he's taught at Duke since 2007, Glass shows how rocks tell stories about the vast stretches of our planet's early history. As a researcher - he's an expert on the evolution of brittle stars, a delicate cousin of starfish - Glass searches for stories in clues left by tiny ancient organisms.
Glass first noticed the trace fossils while walking between Perkins and Bostock Libraries on a winter morning not long after arriving at Duke in 2007. As the sun peeked over the rooftops of West Campus, the light hit the walkway stone pavers at a low enough angle to bring their rugged surfaces into sharp relief.
Amid the ridges and shadows on one slab, Glass spotted an orderly line of small indentations that processed from one end of the slab to the other. Such a sight would go unnoticed by the vast majority of passersby, but Glass immediately recognized it as footprints left by an ancient animal.
But that, in itself, didn't make his discovery remarkable.
Pennsylvania Bluestone is known for yielding fossils. A popular variety of sandstone, it's quarried from an area of northeastern Pennsylvania and southern New York that, several hundred million years ago, was where ancient rivers flowed into tidal flats.
Over time, as layers of sediment were compacted and cemented together, fragments of plants and marine life, as well as indentations left in dried sand, were locked into the rocks.
And when that rock was split into pieces many millennia later for use in modern buildings and walkways, the fractures followed those ancient layers, revealing the fossils hidden inside.
Fossils are so common in Pennsylvania Bluestone that Glass often points out prehistoric plant fragments and ancient tide ripples in West Campus walkway slabs during his geology classes.
For many years, Glass figured the mystery of the footprints in the slab by Bostock Library - which he estimated were left around 360-to-390 million years ago - was something solved by someone else.
Scholars have been studying Pennsylvania Bluestone fossils for over a century. Finding a piece with prehistoric tracks isn't necessarily a breakthrough.
Earlier this year, to placate his own curiosity and learn the story behind the tracks in the slab, Glass shared a photo of them with other paleontologists.
"I always figured there was probably a description of this somewhere and it's a known species people have seen before," Glass said. "But people said 'What is this? This is unknown from this site.'"
One expert suggested that the track might have been left by some kind of early tetrapod, or four-legged vertebrate animal, or by some kind of crawling arthropod, which is an organism similar to a horseshoe crab.
That's when Glass decided it was time to get the slab out of the walkway and into a lab. For that, he needed Farmer's help.
"This is one of the neatest jobs I've been a part of," said Farmer, the Project Coordinator for Buildings and Grounds for Duke Facilities Management . "When he explained that these tracks were made by an animal over 300 million years ago, I was just like 'Wow!'"
On a recent Wednesday morning, with Farmer watching close by, a crew of contractors carefully cut loose the stone and lifted it onto a blanket-covered cart that Glass slowly wheeled back to his Grainger Hall workspace.
Later this summer, the slab will be placed in a display case in Grainger Hall, joining photos of other walkway fossils. Meanwhile, Glass hopes to uncover how the stone paver ended up at Duke and explore ways to scan its surface. A clearer view of the tracks could offer clues about what made them and when.
"There are lots of fossils of plant and animal fragments in the stone slabs here, but it's clear that this one is different," Glass said. "It might be something interesting and new."
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