Mike and Jen here –
I couldn’t believe what I was seeing. I was on a tour of campus for my paleontology course, and Dr. Sandy took us to a low retaining wall in front of the Science Center. There it was: a large Pentamerus brachiopod (Fig 1). I’d walked by this wall for years and never noticed it before! During the rest of the tour, I saw fossils all over campus, and I had never even thought to look for them in the building materials.
Ever since then, I’ve taken closer looks at the stones used in buildings to see if there are fossils. You should, too! But ignore the igneous rocks and marble, just go for the limestone, dolostone, and sandstone pieces. The fossils I’ve seen include trace fossils and body fossils. Trace fossils are fossilized behavior of an organism, whereas body fossils are the actual skeletal or imprint of remains.
Primarily, I’ve encountered trace fossils. The Dayton Limestone, a formation found near Dayton, Ohio, is Silurian-aged (443.8-419.2 million years ago) limestone that was used for building foundations all over the state. It is full of burrows that are highlighted by a lining of hematite (Fig 2). The hematite likely came into the burrows after the organisms were done occupying them. This mineral helps the burrows stand out in the rock. The foundation on the left is a building on the campus of the University of Dayton. The founding on the right is a building in downtown Springfield.
Further exploration for urban fossils led me to find trails on the base of a lamppost outside of one of the courthouses in Springfield (Fig 3). I forgot a scale for this picture, but these trails were about 10 cm in length. I found this next burrow (Fig 4) in one of the retaining walls outside of the library at UD. See what I mean about fossils in places you wouldn’t expect them?
Marine animal body fossils are quite easy to find in building materials. I found these Silurian fossils in a retaining wall near some of the older buildings on UD’s campus. Large brachiopods and gastropods may be found in these stones (Fig 5), as well as colonial corals and horn corals (Fig 6). Sometimes it is difficult to recognize the fossils because the animal is within the rock and you are only getting a two-dimensional view of what it looks like.
Sometimes, the fossils can be very small and hard to pick out from the rock they are in. I walked by this wall for nearly 15 years and never noticed all of the gastropods, bryozoans, and crinoids until just a few weeks ago (Fig 7)! Another example of small fossils was found by Jen when she went to the Biltmore Estate in Asheville, North Carolina. She was chatting with her family when she looked down and recognized the rock, it was filled with small gastropods and bryozoans that she knew to be Mississippian (360-325 million years ago) in age (Fig 8).
Be sure to be on the lookout inside of buildings, too! Many building stones are made of fossiliferous rocks and they are quite visually appealing so they end up as table tops, counters, and even bathroom stalls! Jen saw this table, made of polished fossiliferous limestone, inside of the Biltmore house (Fig 9). I found these ammonites in the flooring at the Ohio Statehouse (Fig 10). Each side of the tile was about 2 ft in diameter.
Where Jen lived in Eastern Tennessee, the common limestone is called the Holston Limestone. This is the ‘marble’ that gave Knoxville the name of Marble City. Marble is a metamorphic rock whereas limestone is a sedimentary rock. Sometimes limestone can have really small grains that makes it look like marble. As a local rock it is used all over the city in a variety of places. It decorates the exterior of buildings downtown (Fig 11) and is even sculpted into monuments of past events (Fig 12).
Maggie and Jen went on a recent research trip to Oklahoma and noticed something interesting about their window sill in the kitchen (Fig 13). It was a nice pink color with lots of white specks. It happened to be the Holston Limestone from where they both were living in Eastern Tennessee! This rock has very specific features that allow you to identify it wherever you may be. Jen even discovered this rock in an old hotel (now a university) in St. Augustine, Florida.
These just a few examples of the fossils that we have seen used in construction and design. As you walk around city buildings, be on the lookout for limestone blocks, especially on older buildings. There may be a few fossils hiding in plain sight!