Techniques and Tools of the Trade
Forensic analysis of a skeleton depends upon careful observation. With bones you have to look closely!
As specialists in reading human remains, forensic anthropologists must know and understand the human skeleton inside out. Taking standardized measurements, photography, and radiography are all essential components of a comprehensive examination. During the examination process, even the handling of the remains can provide clues. The weight of a bone, for example, might reveal something about a person’s health or age. Subtle details can also be important and must not be overlooked. Here are a few of the tools used in forensic examinations:
Calipers are handheld tools for taking precise measurements on the skull, teeth, and skeleton. Different forms are available depending on the measurements being taken. Common types include sliding and spreading calipers.
A 3-D Digitizer is a computerized measuring instrument with a mechanical arm used to record three-dimensional measurements of bones, most often the cranium. Computer software uses x, y, and z coordinates to create three-dimensional virtual models. Cranial measurements, taken by either of these methods, can be used to determine sex or ancestry by comparison to data for documented samples. For example, are the measurements of this unidentified cranium more similar to that of males or females?
The osteometric board is a common tool for measuring lengths of long bones such as the humerus or femur. These measurements can be used to estimate the age of a child or, in the case of adults, to determine stature (height).
Tools for a Closer Look
A stereozoom microscope is a handy instrument for magnifying small features on the surface of a bone. Magnification enables evaluation of tiny structures that are not as easily studied with the eyes alone. Postmortem tooth marks made by scavenging animals or perimortem cuts made by edged weapons are more easily documented with magnification (see Discovering Jane for an example). On some occasions, we use the higher magnifications available through scanning electron microscopy (SEM). Tooth wear can be observed visually, but studying microscopic striations on tooth enamel provides even more information about diet and various techniques for preparing foods.
Traditional ways of recording size and shape of bones and most other natural history objects in the Smithsonian’s collections are based on measuring external surfaces. Sometimes, however, you need to see inside. The Natural History Museum has equipment for taking traditional radiographs (x-rays) as well as computed tomography (CT). Radiographic images of bones show internal structures and irregularities that may not be fully apparent externally. These images are especially important when trying to identify and determine cause of a pathological condition. Suspected gun shot wounds in bone are generally x-rayed to determine whether tiny metallic fragments from the bullet are present. A CT scanner is a powerful instrument often used with living patients undergoing medical evaluation and treatment. Scientists at our museum use a Siemens scanner to generate 3-D images of artifacts and bones and to see inside without causing damage to the object. In forensic case work, positive identification of unknown remains can be established by comparing antemortem radiographs or CT scans with postmortem images produced using the same technique.
Video: Meet the Smithsonian's Bone Detectives
These are some of the tools forensic anthropologists at the National Museum of Natural History use to analyze human bones. What do the bones reveal about the individuals they belonged to? Video courtesy of the History Channel.