Artist reconstruction of the extinct Miocene long-snouted eurhinodelphinid dolphin.
Illustration by Tim Scheirer, courtesy of the Calvert Marine Museum
The geological features at George Washington Birthplace National Monument hold irreplaceable pieces of paleontological resources that are part of our national heritage.
What is Paleontology?
Paleontology is the study of ancient life. The scientists who research and study the fossils of ancient life are called paleontologists. These fossils are evidence of past life that has been preserved.
Paleontology is not the same as archeology, although they are often confused. Archeology is concerned with human activities and cultures.
Fossils are the primary tools used by paleontologists to assemble the puzzle of past ecosystems and the animals that lived within them. They are the meeting place between geology and biology.
Fossils Run Deep
Exposed along the water's edge at George Washington Birthplace is the geological Calvert Formation. The Calvert Formation was deposited between about 22 and 14 million years ago, during what geologists describe as the early and middle Miocene Epoch. At the Monument, some of the upper part of the formation is exposed, from about 15 million years ago. Although many geologic formations have hardened into durable rocks, the Calvert Formation is relatively young and has not completely hardened from silty sand into hard sandstone. This formation is well-known in eastern Virginia and the western Chesapeake Bay region of Maryland for its abundant fossils of shallow marine life. Within the Monument, it is found at low elevations along the Potomac River and Popes Creek.
Fossils of many different kinds of plants, animals, and microscopic organisms have been found in the Calvert Formation throughout Virginia, Maryland, and Delaware. Some of these fossils have been found at the Monument itself or within a few miles. The most abundant fossils are actually uncountable numbers of microfossil, from single-celled algae and amoeba-like organisms that secreted "shells". Although they are no larger than sand grains, and often much smaller, these fossils are very important for helping to determine how old their host rock or deposit is, and for the information they preserve about past environments. These organisms are often very sensitive to temperature, salinity, and other factors, so by knowing what kinds of microfossils are present, we can get an idea of these conditions.
Plants are known from fossils of pollen and spores, and from pieces of larger hard parts, from seeds and tiny chips of wood all the way up to logs, washed in from the coastal forests that surrounded the Calvert sea. They show that this area would have had plants similar to those found today in Florida and the southern Atlantic Coastal Plain.
Many species of shellfish have been found, although it is not uncommon for the original shell material to have been chemically dissolved, leaving behind only a natural impression or cast. Other invertebrates, such as worms, did not have hard parts suitable for fossilization, but they are known to us from their burrows, which can be so abundant that they make an exposure look "ropy" or "wormy".
Vertebrate fossils are the most famous fossils of the Calvert Formation. Most of them belong to marine animals, such as sharks, rays, bony fish, and marine turtles and mammals, but there are also some fossils of land animals that washed out to sea. Shark teeth make good fossils because they are already made of hard material, and a shark frequently replaces it many teeth throughout its lifetime. Depending on the shark, it might produce tens of thousands of potential fossils. Bones of marine mammals, especially skull bones and back bones of various species of large and small whales, are also relatively common.
Challenges to Preservation
Fossils are non-renewable resources. Once gone, their scientific value can never be replaced.
The paleontological resources in the park are impacted by natural and human-caused factors. Naturally fossils are subject to tides and strong storms. Human factors consist of the theft and vandalism of the resources.
You may see fossils at the Monument. If so, feel free to take photos, but remember to leave the fossils in place. Tell a Ranger about your discovery to see if further actions are needed. Fossils in the National Parks belong to all of us, and we're counting on you to do the right thing.
