Stature estimation, perimortem trauma, and forensic taphonomy

stature estimation

final adult height is the stature

sources of stature variation

• taller in the morning, shorter in the evening → can lose 1-3cm

• overestimation in self-reported stature → driver’s license

• Imprecision on measurement → free standing, feet together, without shoes

• loss of height with age → especially in vertebrae

• Cadaveric height doesn’t equal living stature

cadaveric height

is 2.5cm greater; loss of muscle tension upondeath; embalming process can fill joint spaces with fluid.

most common method for stature estimation

mathematical models or regression equations

we need to use one or more bone lengths to estimate stature

allometry

Refers to the growth of a part of an organism in relation to the growth of the entire organism.

• The ability to estimate stature from long bone length depends upon the patterned and proportional relationship between the size of body parts

• sex specific; same population variation

allometry disadvantages

Different regression formulae are required for different populations and for each sex.

• Fortunately, there are many standards → trotter and gleser

• applicable to only adults

regression equation

The length of a single bone is measured and entered into a regression equation.

• available for all long bones, singularly and combined, as well as for some sections of incomplete long bones.

postmortem

after death; soon after death, the bone is still fresh, covered by characteristics of perimortem trauma

perimortem trauma

around the time of death

perimortem trauma characteristics

• sharp edges (no evidence of healing) → not antemortem

• hinging → a section of the bone bends away from the blow’s direction

• multiple/patterned fracture lines

• fracture angle acute or obtuse

• staining from hematoma

bone modelling/remodelling

bony bridges between fragments

• absent in perimortem and postmortem

• present in antemortem

signs of plastic response

Permanent bone deformation after exceeding the elastic response limit

• absent in postmortem

• usually present in antemortem and perimortem

bone flakes

small bone fragments attached to the impact site.

• present in perimortem

• absent in postmortem

edge morphology

the relative sharpness of the fracture margin

• smooth from healing in antemortem

• sharp, angled, bent edges in perimortem

• sharp, squared edges, no bending in postmortem

fracture colour

only relevant if the bones are buried or submerged;

• n/a for antemortem and perimortem

• The newly fractured surface is lighter in postmortem

fracture angle

angle between the cortical table and the direction of the fracture

• acute or obtuse in antemortem and perimortem

• right on postmortem

fracture texture or tactile roughness

morphology of the broken bone surface

• smooth on both antemortem and perimortem

• rough in postmortem

cortical delamination or beveling

Cleavage between the diploe and the inner/outer table.

• present in perimortem

• absent in postmortem

forensic taphonomy

The study of the body’s history since death helps us estimate the time since death and the circumstances of death

involves studying the factors affecting decomposition, dispersal, erosion, and burial, and re-exposure of organisms at and after death

involves plant damage, root etching, and fungal growth

taphonomy research

requires methods for recognition, search, recovery, documentation, and analysis of human remains.

• Excavation/exhumation is an irreversible process

damaged and weakened bone

more susceptible to further taphonomic damage

External factors

abiotic and biotic factors

abiotic factors

involves physical, mechanical, and chemical factors

physical abiotic factors

temperature, moisture, oxygen, depth, coffin/shroud

abiotic mechanical factors

compaction, movement, freeze-thaw cycle

biotic factors

involves plants and animals

• animals → microorganisms, insects, fish, amphibians and reptiles, mammals including humans.

Causes for forensic taphonomy

temperature and moisture, soil

temperature and moisture

A humid environment is the worst, as it often causes high fragmentation

A dry (arid; can be hot) environment can be good if the bones aren’t exposed to the sun, which can cause leaching and distortion

Soils

Acidic soils are poor for preservation → found in rainforests/tropics.

• alkaline soils generate less damaging

Weathering

Process by which the original microscopic organic and inorganic components of a bone are separated from each other and destroyed by physical and chemical agents operating on the bone in situ, either on the surface or within the soil zone

weathering stages for the Amboseli recent bone assemblage

1. cow mandible with initial cracking parallel to the bone fiber structure

2. The opposite side of the same cow mandible shows flaking of the outer bone layers

3. The bovid scapula with fibrous, rough texture and surface bone remnants is near the lower R border

4. A part of the scapula shows deep cracking, coarse, layered structure

5. The scapula blade shows the final stages of deep cracking and splitting

postmortem animal activity

very common in outdoor settings

• 15%-46% of forensic remains cases had evidence of postmortem animal activity.

• can cause a high degree of fragmentation and scattering of bones

• Leaves marks that are often easy to identify → long bones ends are the first to get marrow, leaving ragged edges → claw marks and tooth marks

terrestrial animals

scavenging; the primary subsistence category

includes herbivores, omnivores, and carnivores

herbivores

mostly rodents (squirrels, chipmunks, porcupines), ungulates, and deer

omnivores

some rodents (mice, rats, opossums), raccoons, bears, badgers, and pigs.

carnivores

dogs, wolves, foxes, coyotes, hyenas, felids, weasels, wolverines

carnivore marks

punctures, pits, scoring, and furrows

punctures

holes penetrating through cortical bone

pits

like punctures, but they don’t penetrate through the cortical bone

scoring

roughly parallel group of scratch lines across the cortical surface; usually along the shaft of the bone

furrows

similar to scoring but deeper, usually at the ends of the bone.

rodents

includes voles, mice, rats, squirrels, marmots, and beavers

Why do rodents gnaw on bones?

To keep their incisor teeth worn down and to obtain calcium.

gnaw marks

striaight grooves with flat floors that come in pairs

How do rodent gnaw marks differ from carnivore marks?

Rodent marks have flat floors, while carnivore marks tend to have V-shaped grooves.

Which bones are most commonly affected by rodent gnawing?

Small tubular bones

How can rodent activity help estimate PMI (postmortem interval)?

Rodents typically arrive late, around 30 months postmortem or later; their late arrival indicates a more advanced stage of decomposition.

How can burrowing animals affect skeletal remains?

They can displace bones over long distances.

What types of birds are involved in scavenging remains?

Vultures, ravens, crows, buzzards, eagles, hawks, owls, and gulls.

What marks do birds leave on bones?

Beak or talon scores

What feeding pattern do birds create on joints?

A fluffy, stringy pattern from picking connective tissue.

What happens when animals swallow small or fragmented bones?

It causes pitting and dissolution, often exposing spongy bone.

Which animals may ingest bones?

Birds (e.g., owl pellets), mammals, and rodents.

Which insects are involved in late-stage decomposition?

Beetles, termites, ants, moths, flies, and cockroaches.

What is the pugilistic pose?

A “boxer’s pose” caused by heat-induced shrinkage of soft tissue.

Fires

Can be natural or human-made; causes heat-induced changes, like the shrinkage of soft tissue, causing a pugilistic pose.

Bones don’t burn uniformly

What factors affect how bones are altered by fire?

Proximity to heat, fat and water content in bone, and body fat acting as fuel.

Which parts of the skeleton are most vs. least affected by fire?

Axial skeleton is more affected; hands and feet are least affected.

What happens to the skeleton in low-temperature or short-duration fires?

Much of the skeleton survives

What happens in high-temperature or long-duration fires?

The skeleton can be reduced to fragments.

What is a cremulator used for?

To process burned remains into ash (though teeth may survive).

prolonged firing of fresh cranium

The idea that prolonged firing of the brain led to expansion, such that the cranium would ‘explode’ from the ‘inside-out’

not a well supported idea

How does bone color change with increasing heat exposure?

yellowish-brown colour → dark brown → black → grey → light grey with blue → pure white (calcined bone)

How does heat affect bone size?

Shrinkage increases with increasing temperatures

How much can bone shrink at temperatures over 800°C?

About 10–15%

fleshed/fresh (‘green’) bone

It burns differently from dry bone because of differences in moisture and fat content

fleshed/flesh bone

deep transverse fracture lines or crescents (U-shaped fractures), substantial warping

dry bone

fewer fracture lines (grid-like fracture pattern), little warping, lots of superficial cracking

Dehydration

the removal of water; 100-500 C

Decomposition

The organic (protein) component is lost; 200-600 C

Inversion

Involves changes to the inorganic (mineral) component; 500-1100 C

Fusion

The mineral crystals melt and coalesce; 700-1200 C