Today’s post is by museum Curator of Micropaleontology, Christina Belanger.
The image you saw on Wednesday was only about 100 microns (0.003 inches) across because the total fossil is only ~500 microns in its widest dimension; a scanning-electron microscope was needed to take its picture. This tiny creature is a benthic foraminifer called Pseudononion costiferum. Foraminifera are single-celled protists that create a shell, or test – this particular species has a test made out of calcium carbonate (CaCO3) and lived on the sea floor on the coast of what is now Oregon ~20 million years ago.
Foraminifera can tell us a lot about the past oceans despite being about the size of a grain of sand. As the foraminifera grew, it recorded information about the ocean in the chemistry of its test. For example, the ratio of different isotopes of oxygen (the “O” in CaCO3) in foraminifer tests give can us information about how much ice was at the poles or the temperature of the water. The ratio of different isotopes of carbon (the “C” in CaCO3) in foraminifer tests can tell us about how much productivity was occurring in the ocean if the test formed in the surface ocean. If the species is one that lives inside the seafloor sediment between grains of sand, the carbon isotope ratio can give us clues to how much organic carbon (“food” to organisms on the sea floor) rained down to the bottom of the ocean.
Hundreds of individuals of P. costiferum were analyzed from samples collected in the sea cliffs of Oregon and from this data we reconstructed a time series of environmental data. We learned that from 20 to 18 million years ago, the waters near Oregon warmed, the ocean became more productive, and more organic matter made it to the bottom of the seafloor.
This had consequences. Much like modern warming, which has intensified upwelling on the modern Oregon Coast, this warming event created low-oxygen conditions on the sea floor. In the modern, these “dead zones” are uninhabitable by active animals like crabs and fish. On the ancient Oregon coast, we also saw that animals, like clams, which were preserved as fossils in the same sediments as the foraminifera, were affected by the environmental change – some species disappeared from the area and others stayed, but grew slower as if they were “stressed” by the environment.
Paleontologists use past climate changes like this Miocene event as “natural experiments” to study how ecosystems are affected by environmental changes. Fossils like P. costiferum have played an important role in understanding Earth’s environmental history.