Casting Dinosaur Footprints: Bringing Home a Piece of the Jurassic

Featured Science

New England isn’t known for its vast paleontological finds, but there have been some significant dinosaur-related discoveries over the years. The very first dinosaur footprints discovered by European immigrants were in South Hadley, Massachusetts, in the sandstone of the Connecticut River Valley. These footprints can be seen in the Beneski Natural History Museum, along with the rest of the ichnological collection of Edward Hitchcock, who taught geology at Amherst College in the nineteenth century. All along the Connecticut River Valley, people have found dinosaur footprints over the years, as well as a few fossilized skeletons. Possibly the biggest site of footprints is in Rocky Hill, Connecticut, where Dinosaur State Park is located.

On August 23, 1966, construction worker Edward McCarthy was bulldozing a plot of land outside of Hartford, Connecticut intended for a new State Highway Department building. When he looked at the sandstone bedrock beneath the soil he had moved, he saw hundreds of large three-toed footprints. Before the week was out, it was decided that the site would become a museum. An indoor exhibit space was built around some of the footprints, and curators added large murals and dioramas of Triassic and Jurassic vistas, many examples of fossils, and displays about the history of both the museum site and paleontology in the Connecticut River Valley. The rest of the footprints have been buried following a special procedure to preserve them. Dinosaur State Park stands as a tribute to Connecticut’s historical heritage of discovery and science.

The print I chose to make a cast of. Image: Melanie R. Meadors

I visited Dinosaur State Park recently to make a cast of one of these dinosaur footprints, so I could take a piece of early Jurassic history that was formed 200 million years ago home with me and use it in my educational programs. The entire procedure took about an hour and is basically the same that scientists would do out in the field to record new footprints. First, I had to bring and gather materials: about ten pounds of plaster of Paris, about a quarter cup of vegetable oil, a big bucket, rags, a metal ring large enough to encompass the footprint, and water—about 3/4 gallon to mix with the plaster as well as enough to clean up with.

Dinosaur print prepped for plaster. Image: Melanie R. Meadors
After the plaster pour. Image: Melanie R. Meadors

First, I oiled the track to make it easier for the cast to release after it dried. I rubbed the vegetable oil all over the track as well as on the inside of the metal ring. Then, I put the rags all around the outside of the ring so that the plaster wouldn’t leak from the gaps under it. The ground is just rock, after all, so it’s not exactly level. A helper held the ring steady while I poured the plaster mixture into the ring over the track. After about ten minutes, the plaster was hard enough for me to write my name on it, much like putting your initials in wet cement. Then I had to let it sit for about forty-five minutes to harden completely. This gave me the opportunity to hike some of the grounds of the park and see an outcrop of basaltic rock that resulted from volcanic activity back when the continents of Laurentia and Gondwana came together with ocean floor sediment between them to form the area we now know as Connecticut. Much of the rock in the New England area is metamorphic, formed from older rocks that have been under extreme heat and pressure—mostly schist and gneiss. Visitors to the park are lucky in that they are able to see two types of rock that have not been metamorphosed, basalt and sandstone.

Sandstone with dinosaur footprints. Image: Melanie R. Meadors
Basalt outcropping. Image: Melanie R. Meadors

Once the plaster was hardened, I removed the rags and carefully removed the ring. Then I was able to bring it home! Now, I have to keep it in a cool dry place for a couple of months before it is completely cured. It’s still quite wet, so I will be keeping it on a rack rather than on a flat hard surface.

Final product. Image: Melanie R. Meadors

You can use this same cast method to make impressions of footprints you find in the forest or your yard as well. Always get permission before you make a cast of prints that aren’t on your property, especially if it is of something like a dinosaur footprint. There are, after all, only a limited number of these, and we can’t exactly make more!

Coyote and bobcat track casts. Image: Melanie R. Meadors

NOTE: Fossilized footprints have two sides, the impression and the relief, because of the way they form. (The creature makes the print, the print dries, and then is buried under mud, where it is compressed for millions of years.) I chose to make my cast of the relief side of the dinosaur print so that my cast looks like a footprint. The casts above the bobcat and coyote are in relief—as in, sticking up rather than looking like a footprint that has been pressed into mud—because they only have one side to make an impression of, the actual track that was made by the animal. These tracks are not fossilized and therefore have not been buried, so the only relief that exists is the one I made with plaster!

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