Ostracods are small organisms with hinged, two-part shells that are common in the fossil record. Ostracod remains can form huge deposits and are the main component of some shelly limestones (coquinas) that are used for building. They first appeared in the Cambrian more than 500 million years ago and are still abundant today. The evidence an ostracod leaves behind is its shell. Because they are widespread and well-preserved, ostracod shells serve as ecological indicators of past conditions. The location of fossil ostracods and chemistry of their shells provides paleobiologists information about water depth, temperature, salinity, and nutrients. Several indices of paleoclimates have been developed based on ostracod distributions. For example, the MOTR (Marine Ostracod Temperature Range) extrapolates from temperatures tolerances of modern ostracods to infer paleoclimates where fossil ostracods are found. The oil industry even uses fossil ostracods to find sites for exploration because ostracods are associated with particular types of rock.

The most common type of microscope, a light microscope, illuminates small objects with beams of light and magnifies their image with a series of lenses. When an object is too small to be seen using a light microscope or greater detail is needed, electron microscopes are used. There are two varieties of electron microscopes: Scanning electron microscopes (SEM) and transmission electron microscopes (TEM). Both types shoot beams of electrons at objects to get their images, though the methods differ.

SEM imagery creates a highly detailed picture of the surface of a specimen. To perform scanning electron microscopy, the specimen is first firmly mounted to a holder. Often the specimen will be coated in a conductive metal like gold or chromium. Then, specimens are placed into the microscope and scanned using a beam of electrons. The electron beam hits the specimen and these electrons, or new electrons emitted by material in the specimen, travel away from the specimen. A special detector registers the electrons coming from the sample and uses the information to construct an image of the specimen’s surface.

Not all fossils are giant dinosaur bones, and SEM imagery can be used to get a closer look at the very small ones, like microscopic grains of pollen or tiny ostracode shells.

Most animals, like humans, have bilateral symmetry – they can be divided with a line into left and right sides. These two sides usually look like mirrored images of each other, but there can still be differences. For example, male fiddler crabs have a claw on one side that is much larger than the other. This larger claw, which can be on either the left or right side, is used by males in a behavioral display as they court females.

Knowing the difference between the left and right sides of animals is very useful when studying fossils, as often paleontologists will find only a single bone or shell and need to determine what part of the animal it came from. Small crustaceans called ostracodes are common fossils and have mirrored left and right sides, but with subtle changes between the two. Their bodies are protected by a two-sided, hinged shell. One side of the shell is always a little larger, so they can pull in their limbs and close the shell tightly when they are threatened. The part of the shell with the hinge also often has small differences between the left and right sides.