The distinction between human and non-human bone is a foundational step in forensic science. Identification is often complicated by the similar size and general structure shared between human remains and those of common large mammals like deer, pigs, or bears. An initial visual inspection by an untrained person can easily lead to misidentification, especially when remains are fragmented or weathered. Specialized knowledge is required to systematically evaluate skeletal differences across three major categories: overall architecture, microscopic composition, and developmental features. Determining the species of origin is necessary before any further forensic or archaeological investigation can proceed.
Assessing Gross Morphology
The initial assessment relies on the bone’s overall shape, size, and architectural features, which reflect the species’ primary mode of locomotion. The human pelvis is broad and shallow, shaped like a bowl to support the weight of the upper body during upright posture. Quadrupedal mammals possess a long, narrow pelvis optimized for four-legged movement.
Differences are also clear in the limbs. Human long bones, such as the femur and tibia, are relatively straight to facilitate bipedal walking. Non-human long bones often exhibit more pronounced curvatures or robust ridges that serve as attachment points for powerful musculature required for carrying weight on four limbs. Furthermore, the radius and ulna are separate bones in humans, allowing for a wide range of motion, while these bones are often fused in many weight-bearing animals to increase stability.
The skull offers distinct indicators due to the human need for a larger braincase. The human cranium is large and globular, dominating the facial structure, which is relatively small and flat. Many animals, including deer and bears, have a smaller, more angular cranium relative to a much larger, often elongated muzzle. The absence of a sagittal crest, a bony ridge on the top of the skull for large jaw muscle attachment often seen in carnivores, is another typical feature of the human skull.
Internal Structural Differences
The microscopic structure of bone tissue provides definitive, non-visual evidence for species identification, starting with cortical thickness. Human long bones typically have a thinner cortical layer relative to the overall diameter of the shaft, often measuring about one-quarter of the total diameter. In comparison, the limb bones of large, weight-bearing animals often have a thicker cortex, sometimes approaching half of the total diameter, to manage greater mechanical stress.
Microscopic analysis focuses on the organization of osteons, the cylindrical units containing blood vessels known as Haversian systems. In mature human bone, these systems are generally scattered and evenly spaced throughout the cortical tissue. This pattern differs from that found in many non-human species, particularly fast-growing animals like pigs, cattle, and deer.
These animals often exhibit plexiform bone, a highly organized, brick-like arrangement of tissue that allows for rapid growth. While plexiform tissue is largely absent in mature human bone, its presence or the alignment of osteons into distinct rows (osteon banding) is a strong indicator of non-human origin. Histological measurements of the Haversian system and canal diameters are also used, with human bones typically having larger central canals than those of many other mammals.
Developmental and Fusion Indicators
Skeletal features related to growth, development, and the demands of bipedalism offer definitive distinctions between human and non-human remains. The position of the foramen magnum, the opening at the base of the skull where the spinal cord connects, is a marker of posture. In humans, this opening is centrally located underneath the cranium to balance the head directly over the vertical spine, reflecting bipedalism. Quadrupedal animals, whose spines are horizontally oriented, have the foramen magnum situated more toward the posterior of the skull.
The human femur also displays a specific adaptation for upright walking known as the bicondylar angle. This angle causes the femur to slope inward from the hip, positioning the knees and feet directly beneath the body’s center of gravity. This configuration is absent in most quadrupeds, whose femurs descend straight down.
Developmental stage is another differentiator, particularly when examining juvenile remains. The timing and pattern of epiphyseal fusion, where the growth plate merges with the main shaft of the bone, are species-specific. For example, a small, fused pelvis indicates an adult animal, as a human juvenile pelvis of comparable size would still be in multiple, unfused pieces.
Dental morphology is also highly specialized and durable, providing reliable species identification. Human teeth reflect a generalized diet, featuring molars with low, rounded cusps (bunodont) and a parabolic-shaped dental arcade. Herbivores like deer possess specialized selenodont (crescent-shaped) cusps, while many carnivores have sharp, shearing carnassial teeth, all distinct from the human pattern.
Reporting and Preservation Protocols
The discovery of suspected human remains requires immediate and specific protocols to ensure the integrity of any potential investigation. If a bone is found and is believed to be human, the first step is to leave the remains completely undisturbed. Moving or collecting the bone destroys the context and spatial relationship of the remains and any associated evidence, which is invaluable to law enforcement and forensic experts.
Once the area is secured, the finder must immediately notify local law enforcement or the medical examiner/coroner’s office. These agencies are legally mandated to handle such discoveries and will dispatch trained personnel to assess the scene and recover the remains. The finder should note the precise location, often using GPS coordinates, and may take photographs of the remains in situ before authorities arrive.
The recovery and subsequent analysis of human remains, regardless of their age, are governed by state and federal laws. Recent remains fall under criminal statutes, while older remains may involve laws like the Native American Graves Protection and Repatriation Act (NAGPRA). Leaving the remains in place and reporting the finding immediately ensures compliance with the law and aids the professional process of scene documentation and evidence retrieval.