In mid-July of 2013, the Deep Time exhibits team went to North Dakota to collect fossils. Our goal was to find 66-million-year-old fossils from the Late Cretaceous for our new exhibitions, and to learn more about paleontology. This is the first post in a series about our experiences in the field.
The Hell Creek Formation is a microfossil treasure trove— if you know what to look for. Photo of Abby Telfer collecting microfossils. Photo by Kay Behrensmeyer, Smithsonian Institution
Before our trip, many exhibits team members had no field experience. Luckily, we could turn to our curators for advice and encouragement. They helped us learn what to look for and where, and how to identify fossils.
How do professional paleontologists know something is a fossil? Years of practice! But even with a little experience around fossils, you’ll have an easier time picking one out from a pile of rock by looking for three traits:
The black and grey fossil bone fragment on the left is a different color than the surrounding reddish rocks. It is also denser than the weathered modern bone on the right. Photo by Juliana Olsson, Smithsonian Institution
Fossils tend to have a different color from the surrounding rock. They may be lighter than the rocky substrate, or they might be darker – it all comes down to the weathering process, and the fossil materials. Plant fossils are almost always darker than the rock in which they’re found. If you’re searching for microfossils on the ground, they’ll probably be a lighter, almost creamy color since they have been exposed to the elements—though teeth, claws, and scales are dark and glossy.
This piece of turtle shell embedded in the rock has a distinct, dimpled texture, which makes it noticeable even though it’s only about 4 cm wide. Photo by Kay Behrensmeyer, Smithsonian Institution
Bones are more porous than rock, and this texture difference makes them easier to spot. Because of its “spongy” texture, if you touch a fossil to your tongue it will typically stick, whereas rock and soil won’t. If you’re not in the mood to do the tongue test, you can also look for pores through a hand lens.
Some bone patterns can tell you who the original owner might have been. Turtle shells have little pits and grooves on one side. Crocodile scutes have even more pronounced pits, and sometimes a little ridge in the middle. Young and old members of the same species differ in the growth patterns on their bones, a fact which can help scientists determine the biological age of a fossil. Sometimes bones even have little marks on them where muscles used to be attached.
If you’re lucky, the item’s shape will be an even bigger clue. While many bone fragments are unidentifiable, there are many bones that are highly diagnostic for an entire group of animals, if not for a species. These diagnostic bones tend to be things with complex shapes, like vertebrae, skull bones, and even teeth and claws. For plants, the diagnostic features tend to be the leaf edges and bases, as well as the pattern of veins.
The fossils we found came in a wide variety of shapes, from blade-like gar scales (box at bottom right), to oval fish vertebrae (above the gar scales), to pointy conical teeth! Photo by Kay Behrensmeyer, Smithsonian Institution
Distinctive bones aren’t the only fossils with easily identifiable shapes. Coprolites (fossil poop) look the way you’d expect them to, and tend to be a little bit lighter than the rocks around them. Casts, molds, and steinkerns (internal molds) look like the original organism; mollusks and other animals with shells are often preserved this way.
If you spend even a short time looking for fossils, you’ll learn how to tell that the thing in your hand is a vertebra or a root. But to know what genus it belongs to, you’ll have to spend some time handling fossils and doing research. Generations of scientists have taken the time to describe in detail the anatomy of animals past and present, and you can compare your fossils to these descriptions. You can visit university websites like UCMP for more information on identifying fossils, volunteer at your local prep lab, or come see our fossil exhibits in person. You can also follow Deep Time at the Smithsonian (or the NMNH Facebook and Twitter feeds) for more on fossils and updates about the exhibit.
by Juliana Olsson, NMNH Office of Exhibits Writer with the support of Angela Roberts and Siobhan Starrs