Comparative Skeletal Anatomy of Human and Non-Human

Introduction

Only a forensic anthropologist or someone with training in osteology should be able to tell the difference between human and non-human bone. The purpose of studying this has two-fold importance:

First, it is included to demonstrate that non-human bones can easily be mistaken for human bones and to reinforce why an experienced osteologist should be making the final determination; and,

Second, this also introduces them to different examples of non-human bones that can be easily confused with human bones.

Human Skeleton

In the field, an experienced forensic anthropologist or forensic archaeologist should be able to answer several question: Determine whether the suspected material is bone?, and if so, whether it is human or non-human?

For example, rocks may take on the appearance of human bones. Rocks are frequently heavier than bone, according to one rule of thumb. The patella, carpals (wrist bones), and tarsals (ankle bones), which could be mistaken for rocks, have a larger concentration of trabecular or cancellous bone, making them significantly lighter than rocks. A skilled forensic anthropologist will be able to tell the difference between nonosseous and osseous material with simplicity.

More commonly, the forensic anthropologist will be asked to determine whether the skeletal material is human or non-human? In many cases, being able to differentiate human from faunal bones enables the investigator to eliminate what may have been at first considered to be a forensic case (although, some non-human remains may be forensically relevant).

William Bass (1995), a noted forensic anthropologist, has stated that as many as 25 to 30% of all the cases submitted to forensic anthropologists for identification are non-human in nature and many of those end up being butchered domestic animals. As a result, knowing the basics of human and non-human skeletons can help save time when determining the forensic importance of entire or fragmented skeletal remains. Of course, as a rule of thumb, all bones recovered from a scene should be examined by a forensic anthropologist, since such an expert will have the expertise to determine whether the bones are human or non-human.

Take digital images and transmit them to a forensic anthropologist if you don’t have a forensic anthropologist on the scene or readily available. Many forensic anthropologists have reviewed photos via email to determine human versus non-human bones. This can help to save a lot of time and money.

Cremations or Thermal Damage to Skeletal Remains

Cremation is a method of rapidly reducing a body to ashes and small bone pieces using high heat. Bodies are typically burned before burial or within the grave and maybe charred, or partially, incompletely, or completely burned depending on the intensity of the fire to which the body was exposed. The remains may be mixed in with other elements of the burial (for example, clothing or wood), left as a surface deposit, or held in some type of container.

During a forensic investigation, forensic anthropologists examine cremated remains that have been left behind as a result of criminal behavior as well as regular cultural rituals when a loved one dies. Because it takes extremely high temperatures (over 1600¬į C/2912¬įF) to destroy bone, remains cremated as a result of the perpetrator‚Äôs purposeful attempt to dispose of the remains will most likely range from charred to incompletely burned. It is almost impossible to destroy all evidence of a body through burning. As a result of this, cremations in crematoriums are typically reduced to very minute particles, depending on the type of processor used to reduce the remains.

Distinguishing Humans from other Mammals

Large mammal bones such as bear, deer, dogs, and pigs are most often confused with adult human bones, and small animals may be confused with juvenile or fetal bones. When bones are heavily weathered, eroded, and fragmented, identification may be impossible without the assistance of a qualified osteologist.

Humans and other non-human mammals’ skeletal components can be highly similar anatomically, and because humans are mammals, they share many of the same skeletal traits. For example, Mammals have similar numbers and types of bones. Furthermore, important characteristics such as bone structure are comparable, with most mammals having long bone shafts made of thick cortical bone and long bone ends made of trabecular bone. If just a small bone fragment is recovered without any morphological indicators, the only way to identify whether it is human or non-human would be through histological (microscopic) examination or DNA analysis. On a gross level, there are two key properties of bones that can assist in distinguishing between human and non-human bones: maturity and morphology.

Comparison of different stages of growth of a Human femur

Maturity aids in distinguishing small non-human animals with bones that are comparable in size to juvenile humans even after reaching adulthood. Juvenile human long bones may have unfused separate epiphyses, depending on their phase of development. Conversely, those of a small adult non-human animal will display fused epiphyses. As a result, the amount of bone development can clearly distinguish non-human bones from adolescent human bones. Where the epiphyses will eventually fuse to the metaphysis, the proximal and distal ends of the juvenile long bones are roughened in appearance.

Other morphological indicators that can help distinguish tiny animals from human juvenile long bones include non-human skeletal traits including the fusion of the fibula and tibia, as well as the curvature of the long bone shaft (diaphysis). Small mammals’ long bone shafts, for example, maybe significantly bent where they are straight in healthy juveniles. An example of the differences between young human long bones and those of small adult animals. One structure of small mammals could be confused with human or fetal bones in the pelvis. If a small pelvis is fused into one unit, it will be a non-human pelvis because a human juvenile pelvis of comparable size is still in multiple pieces. Unless there is a pathological condition, the two mature human pelvic bones do not fuse.

Pictorial comparison of the anterior view of (a) a right new born femur, with those of small adult mammals such as a (b) rabbit; (c) an armadillo; and (d) a raccoon.

Difference in diaphyseal curvature (shown in lateral view) between (a) a human new born femur and (b) a raccoon

The second characteristic of bone that helps distinguish human from non-human mammalian bone is morphology or the shape of the bone. Humans and other mammals have the same types of bones (for example, two femora, two humeri, and two scapulae) and the same basic structure required by our soft tissue systems, as previously stated. Humans differ from all quadrupeds that are evolved for four-legged movement because they are bipedal and have different physical traits associated with walking upright.

When comparing humans and other mammals, the dissimilarity in the shape of long bones and other bones of the body such as the scapula can be very distinct and can quickly lead to an identification of human or non-human remains. For example, in several small animals, including mammals, the fibula is reduced in size and is fused to the shaft of the tibia. The fibula does not normally fuse to the tibia in humans unless there is a disease such as ossification of ligaments that maintain the two bones articulated together. A bent and fused radius and ulna are also found in some bigger mammal species (e.g., pigs, sheep, and deer). Recognition of these two bones immediately excludes humans as both the radius and ulna. They have straight diaphysis and remain unfused throughout life.

Comparison of an anterior right human fetal/infant ulna to ulnae from small mature non-human animals. Posterior/lateral view of left radii from (a) a squirrel; (b) opossum; (c) armadillo; and (d) a fox.

Comparison of mammalian scapulae: (a) pig; (b) sheep; (c) adult human; and (d) dog

The presence of metapodial distinguishes mammals belonging to the order artiodactyl (hoofed mammals with an even number of digits on each foot ‚ÄĒ two or four) from humans. In these animals (for example, deer, sheep, goat, moose, caribou), the third and fourth metacarpals and metatarsals are fused into one structure early in development, and the generic name for both is metapodial.

Comparison between (a) a human new born tibia and (b) the fused tibia and fibula of the rabbit

Metapodials can be misinterpreted for long bones in some species because they are long bones. Metapodials are easily recognized by several morphological indicators the shafts are long, thin, and straight, and they still retain a clear groove down the shaft where they have fused. The proximal articulation is flat, while the distal articulation has two rounded articulations. Furthermore, metacarpals and metatarsals can be distinguished from one another by the cross-sectional shape of their shaft ‚ÄĒ metatarsals are square-shaped and metacarpals are D-shaped in cross-section. Humans have a big, spherical braincase and a flat, or orthognathic, face in profile, which sets them apart from other mammals. Because human crania differ so much from those of other mammals.

Non-Human Animal Bones Commonly Confused with Human Bones

Several non-human animals have bone structures or features that appear similar to human skeletal material. Some bones, on the other hand, are frequently misidentified. The bones of a bear paw, pig teeth, a pig’s knee, and a turtle shell are all animal bones that can be confused. Disarticulated bear paws are commonly confused with human hands. The claws of a hunted bear are frequently removed as trophies, and the paws are sometimes discarded after they have been skinned. After the soft tissue has begun to decompose, a bear paw and a human hand have a striking resemblance. Examining the various bones makes it easy to distinguish the bear paw from a human hand, and it can also be distinguished from a human hand without removing the soft tissue from the bone. A radiograph can be used to differentiate the bear paw from the human hand because the morphology of human hand bones is different.

Pig molar teeth are also strikingly similar to human molars because pigs, like humans, are omnivore and their teeth are developed for a broad diet. However, pig molars are larger than human molars and have pointier cusps.

In addition, the proximal part of the pig tibia, called the tibial plateau, can be easily misidentified as a human tibial plateau by an inexperienced osteologist as they share a similar morphology. The tibial plateau of a butchered pig knee or an un-fused proximal tibial epiphysis may be easily identified when a portion of the proximal pig fibula is also available for examination. However, if only the top of the tibial plateau and not the shaft of the tibia are present, it can be difficult to distinguish from a human tibia.

The tibial plateau of the deer, on the other hand, is easily distinguished from the human knee due to its markedly distinct form. The underlying shell of a turtle may resemble the top of a human head when the upper layer of the shell, made up of fragments called scutes, breaks off. This is especially true if only a portion of the shell’s top is visible through the soil and has been bleached by exposure to the sun. Also, fragments of turtle shells from archaeological contexts can be easily mistaken for fragments of human cranial bone because the flat shape and thickness are similar to human cranial vault fragments. If there are no diagnostic characteristics on the outside of the turtle shell fragment, then the cross-sectional morphology of the shell can be used to differentiate it. This is the unique cross-section of human cranial bones, which are composed of diploe, or cancellous bone.

Reference

Bass WM. 2005. Human Osteology: A Laboratory and Field Manual. 5th ed. Springfield, MO: Missouri Archaeological Society.

Broughton JM, Miller SD. 2016. Zooarchaeology & Field Ecology: A Photographic Atlas. Salt Lake City: University of Utah Press.

Christensen AM, Passalacqua N V., Bartelink EJ. 2014. Forensic Anthropology: Current Methods and Practice. Elsevier. Available from: https://linkinghub.elsevier.com/retrieve/pii/C20130097605

James T. Watson, Ph.D., John McClelland, Ph.D., Distinguishing Human from Non-Human Animal Bone (https://statemuseum.arizona.edu/sites/default/files)

Haley N. O’Brien, University of Montana,2019, Missoula, Human Vs. Non-Human Bone: A Nondestructive Histological Method.

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