Identifying human versus non-human skeletal remains in the field

Amy E. KellyForensic Investigator

Coconino County Medical Examiner’s Office

Human vs. Non-human

In modern forensic cases, 25-30% of the presented cases are non-human in origin.

Access to and using a comprehensive comparative collection is necessary.

Using a variety of literature in the field is helpful and an easy and efficient means to improve animal vs. human identification (Cruz-Uribe and Klein 1994, Gilbert 1990, Ubelaker 1989).

If in any doubt, GPS, photograph and describe the specimen and “scene” before moving or collecting the remains and bringing it to the CCME office for analysis. If appropriate, call me or the CCME investigator on-call.

Human vs. Non-human

The first question that should be asked is “Is it bone?” and not wood, shell or plastic or rock.

If yes, is it cranial or post-cranial? (cranial bones are usually thin, flat or even irregular in structure; look for sinuses, sutures or sockets)

Post-cranial bones are typically long, skinny and can be flat. Exceptions are the bones of the hands and feet, vertebrae and the pelves.

Then, look to see if the bone is whole or fragmented.

Also, are the bones adult in age or juvenile? (Fused or unfused epiphyses)

And lastly but most importantly, could this be human?

Human vs. Non-human

Most mammalian bones share similar morphological features between species. The exceptions are marine mammals and some unusual critters like tree sloths.

The primary difference is size. However some animals, such as deer, have bones that are very close in size to an adult human.

Other mammals that cause confusion are bear and raccoon for their paws (Klepinger 2006). Bear paws look similar to adult hands and raccoon paws are easily confused for children’s hands.

Human vs. Non-human

Which hand is human versus bear?

Human vs. Non-human

Human versus raccoon

Human vs. Non-human

Easy identifications

Human vs. Non-human

But what if you come across bones like these?

Human vs. Non-human Humans: bipedal

Pelvis is broad and shallow (bowl-shaped) The femur is the longest bone in the body with a single linea

aspera The tibia and fibula are separate bones and the tibia is

triangular in cross-section with a small tibial tuberosity Long and narrow foot with multiple bones for bipediality

Other mammals: Quadrupedal (mostly) Pelvis is long and narrow The femur is short relative to the body size. If the femur’s

length is comparable to an adult human femur, the diameter may be twice as thick as a human femur (i.e., cow) with a double or plateau linea aspera

The tibia and fibula are often fused and the tibia is more rounded in cross-section with a large tibial tuberosity or longitudinal ridge.

Legs of larger mammals are modified toes and fingers for speed and agility

Human vs. Non-human

Humans: Large, broad and flat vertebral body Short spinous process (2-3 inches at the most) Sacrum is triangular in shape and composed of 5 fused

vertebrae, which are broad compared to length and flattened anteriorly-posteriorly

Other mammals: Small vertebral body, often convex on one side and

concave on the other Long spinous process (>6 inches in some larger

mammals) Sacrum is long and narrow with fewer fused vertebrae

(3-4)

Vertebrae

Human vs. Non-human

Humans: Designed for rotation (i.e., throwing, swinging) Long axis of scapula is perpendicular to scapular spine, which is why

it’s triangular shaped Clavicle present Humerus, radius and ulna are not weight bearing so they are not

robust. Ulna and radius not fused Large thumb

Other mammals: Designed for front-back stride Long axis of scapula is parallel to scapular spine, which is why it’s

rectangular shaped Clavicle absent in most non-human mammals Humerus, radius and ulna are weight bearing and robust. Ulna and

radius are often fused to support these weight bearing limbs Small thumb, even on mammals with similar hands (bear and

raccoon)

Forelimbs

Human vs. Non-human

Juvenile Remains The most common human bones to be mistaken for

animal bones are bones from infants. The ends of the long bones, bones of the hands and

feet and clavicle are not fused These unfused bones have indistinct edges Multiple ossification centers and unfused epiphyses

increase the number of bones in infants and children Epiphyses (the ends of long bones) when separated

from the rest of the skeleton do not look human to the untrained eye

Long bones are thinner in cross-section Cranial bones can separate and lack the diploe

structure, are uniform in thickness and can be confused with tortoise carapace. Petrous portion is separate in infants and due to it’s dense nature, often survives burial better

Can be confused with smaller mammals such as raccoon, rabbit or even bird

Human vs. Non-human

Human vs. Non-human

Mandibles from infants Petrous bones circled

Human vs. Non-human

Human infant and fetal bones, recovered from a burial

Human vs. Non-human

Fragmented and burned remains are more challenging to correctly identify than intact remains for distinguishing between human and non-human remains Ids can be done macroscopically by morphology** Ids can be done microscopically (histological

examination)

**For our purpose, we only need to discuss macroscopic analysis

Human vs. Non-human

Skull Fragments?

Human vs. Non-human

Fragmentary and burnt bison bones.

Human vs. Non-human

Traumatized and burned pig bones

Human vs. Non-human

Macroscopic characteristics: cortical bone much thicker in animal long bones than in human; humeral and femoral cortical thickness in humans is about ¼ of total diameter

Bone macroscopic characteristics: cranial bone diploe relative to cranial cortical (tabular) bone is thinner in animals compared to humans

Human vs. Non-human

Review: Ask first, “Is it bone?” Ask second, “Could it be human

and why?” (i.e., context, size/shape of bones, do the bones fit bipedal locomotion?)

Have some reference material to aide in more accurate assessment of human versus animal (I can provide photocopies)

If in doubt, no matter how much, GPS, photograph and document the remains, then collect or call me or the on-call investigator

Human vs. Non-human

Call me directly if you ever come upon this…