It was a hot, windy February in 2009. Bushfires tore through the Australian state of Victoria destroying everything in their path. Numerous people, livestock, pets, and wild animals were killed — their remains left fragmented and unrecognizable. It was under these challenging circumstances that the forensic team attempted to identify the victims of the fires. One of the initial steps in the identification process was determining whether remains were human or animal in origin. In cases such as this, forensic anthropologists draw on their knowledge of skeletal anatomy to make the correct species determination. Here are three things to consider when establishing whether a bone is animal or human.
One of these things does not belong: distinct skeletal features.
Many animals have adapted to living environments that are very different to the environments we live in; therefore, they often possess distinct skeletal elements that humans do not have. The bones of birds are well suited to flying because they are very light. Additionally, birds have unique bones that are not found in the human skeleton, including the furculum (wishbone) and the synsacrum (an extended sacrum). The presence of these bones in a skeletal assemblage is a tip off that the bones are not human.
Some bony elements, though distinctive can be confused with human bones when fragmented. Pieces of sun-bleached turtle shell can mimic bits of the human skull. The key to distinguishing turtle shell from human remains is to examine the cross sections of the pieces. Human skull bones have an interior composed of spongy looking cancellous bone, but turtle shells do not.
A primer on shapes: the role of morphology.
Although animals and humans share many of the same skeletal elements, these elements often look very different from one another. For example, humans and chimpanzees both have pelvises, but because the human pelvis is designed for walking upright it has a distinctively different shape from that of a chimpanzee. The human pelvis is bowl shaped, whereas the chimpanzee has a long thin pelvis allowing it to walk easily on all fours.
There are a select few animal bones that closely resemble human bones. It may seem surprising, but the bones of a bear’s paw are similar to the bones of the human hand. Careful examination of each bone shows that the bear paw bones are more robust than the human hand bones. Fragments of a pig tibia (the large bone in the shin) can look like a human tibia. Through thorough analysis and comparison to known pig and human skeletons the correct species can be determined.
Larger and older: a closer look at maturity.
Some small animals have bones that look like tiny adult human bones. An untrained person might think these small bones belong to a human child, but they would be wrong. A forensic anthropologist familiar with the development of the human skeleton knows that the bones of children do not look like small replicas of adult bones.
Until humans reach adulthood, their bones are still growing in size and changing in shape. Many of the bones of a human child do not look identical to adult bones because they are split into pieces that fuse as the child grows. For example, the femur (the large bone in the thigh) of an adult and a child are very different. The adult femur is one large bone, but the femur of a child is split into five parts. The largest part is the shaft and although it bears a resemblance to an adult femur, it is missing many of the features of the mature bone. It is only when all the parts fuse that the femur is fully developed and this does not occur until a human is at least 18 years old. Therefore, if someone finds a tiny mature-looking femur they will know that it does not belong to a human child, but likely originated from a small animal.
Your Turn: Ever take a walk in the woods and come across a suspicious-looking bone? We’d love to hear your story. Have a question about femurs or (bone) fusion? Let us know in the comments.