Forensic Taphonomy Flashcards
What is forensic taphonomy?
The study of processes that affect:
1) Decomposition
2) Dispersal
3) Burial
4) Re-exposure
Of bones
What does forensic taphonomy help to determine?
- Decompositional history of skeletal remains
(how the bones got there)
- Identify agents of modification and destruction
(how LONG the bones have been there, what type of environment they are buried in)
- Cultural activities vs natural changes
- Identify biases in composition of skeletal samples
What is the first stage of analysis of bones?
Burial environment and skeletal preservation
What is the difference between the archaeology of bones and bones in a forensic context?
Archaeological:
- 100+ years
- Research into social and environmental influences on life and death in the past (history)
Forensic:
- <75 years
- Aiming to assign ID and circumstances of death
- Evidence provided in the court of law
What does archeology and forensics help to build up?
An osteological profile of the individual
What is taphonomy?
The branch of palaeontolgoy that deals with the process of fossilisation
The transition of organic remains from the biosphere to the lithosphere
What are the physical and biological changes that can occur during the taphonomic process?
- Post-mortem (after death/before burial)
- Post-burial (after burial/before excavation)
- Post-excavation (during/after excavation)
Eg. bones may be damaged/broken/worn down
What 3 things may lead to the modification of bones?
1) Agent (source that causes the modification)
2) Process (Action by the agent that causes the modification)
3) Factor (Agents and processes)
Examples of agents that may lead to the modification of bones?
Source, Eg:
- Human
- Animal
- Machinery (eg. ploughing)
Examples of processes that may lead to the modification of bones?
Action, Eg:
- Scavenging
- Butchery (cutting)
- Trampling
- Weathering
Examples of factors that may lead to the modification of bones?
Agents and processes, Eg:
- Chemical (soil pH)
- Physical (water, temperature)
- Biological (animal, plant)
- Cultural (human, hunting, butchery)
What do we want to understand, using forensics, about the skeletal remains?
Want to understand the post-mortem history:
- Time between death and recovery (post mortem interval)
- Circumstances of death
- Trauma analysis
- Post death treatment (eg. burning)
What determines the post-mortem interval?
Time between death and recovery, determined by:
DECOMPOSITION
What is decomposition?
A series of biological changes that occur after death
What are the 2 stages of which the body degrades?
1) Soft tissue (decomposition)
2) Bone and teeth (diagenesis) - Takes longer
What are the 4 stages of decomposition?
Describe them
Normal biological functions stop (cessation of blood flow and cooling of the body):
1) Hypostasis
2) Algor mortis
3) Rigor mortis
Spread of the bacteria out of the gut and around the body:
4) Putrefication
What happens in rigor mortis?
8-36 hours: body stiff and cold
36+ hours: body softens again
What happens in putrefication?
Destruction of the body tissue
Swelling/bloating
Discolouration of skin
What influences decomposition?
External factors (eg. heat, ground etc)
What influences bone degradation/speed of decay?
Depending on many different factors/minerals, Eg:
Above ground:
- Oxygen
- Temperature and weather
- Insects and carnivores
Underground:
- Restricted/no oxygen
- Soil pH
- Temperature
- Insects
- Depth
Underwater:
- No oxygen
- Temperature
- Water type
- Scavengers
- Currents
What does skeletonisation result from?
Above ground or underground contexts
What does mummification result from?
Above ground contexts
What does fossilisation result from?
Underground contexts
What do bog bodies result from?
Underwater contexts
What are the first questions that must be asked when find bones?
1) HUMAN or ANIMAL?
2) MODERN or ARCHAEOLOGICAL?
After identifying if the bones are of interest to forensics (human and modern) what must be done next?
Identification of:
1) Completeness (disarticulation of the parts of the skeleton)
2) Fragmentation (whole bones becoming parts of bones)
3) Surface preservation
Of the bones
What do you look at when looking at the completeness of the skeleton?
The proportion of the skeleton (or skeletal element) that is present
What do you look at when looking at the fragmentation of the skeleton?
The extent of post-mortem breakage of the skeletal element
What do you look at when looking at the preservation of the skeleton?
What can this tell us?
The condition of the CORTICAL bone surface
Eg. erosion, burning, weathering, gnawing etc
Can tell us the environment the bones were in
How to tell the difference between human and animal bones?
Size, shape, morphological features
Animal:
- Heavier
- More compact (denser)
- More polished surface
- Greasier
How to tell between modern and archaeological bones?
Overall appearance and surface texture
Modern:
- Heavier (due to the organic material not yet decayed)
- Greasy feel/more polished surface (due to the retention of fat components)
Archeological:
- Lighter
- More porous
- Less polished, less greasy feel
What features can not be used to determine if a modern or archaeological bone? Why?
Colour of the bones/extent of decay?
Why:
- As the some archaeological bones may have been better preserved than modern boned
- Due the exposure to different factors
How can we tell if incompleteness of a skeleton is down to scavenging by carnivores?
Carnivores disarticulate animal carcasses in a regular sequence
What are the early bones to be disarticulated from a carcass by carnivores?
Abdomen, chest and throat:
- Forelimb
- Mandible
- Humerus (from scapula)
- Distal phalanges
What are the middle bones to be disarticulated from a carcass by carnivores?
Legs and disarticulating the bones taken:
- Femur
- Tibia
- Tarsals and metatarsals
- Ribs
- Humerus (from radius and ulna)
- Proximal and middle phlanges
What are the late bones to be disarticulated from a carcass by carnivores?
Vertebral column:
- Sacrum
- Cervical, thoracic and lumbar vertebrae
- Radius from ulna
What are the 2 types of fragmentation that can occur?
1) Incidental
2) Intentional
What are examples of incidental fragmentation? (on purpose)
1) Disturbance of the burial environment (eg. ploughing/intercutting
2) Breakages during excavation
3) Trampling (from animals)
What is the difference between a perimortem (before death) breakage of the bone and a postmortem (after death) breakage of the bone?
Why?
Perimortem:
- SAME colour as the rest of the bone
- Smooth
Postmortem:
- Lighter in colour than the rest of the bone
- Rough
Due to the perimortem break degrading at the same time as the bone
What are examples of intentional fragmentation?
1) Peri-mortem fracturing (before death)
2) Butchery (animals)
3) Amputation/dismemberment (humans)
What are the 2 situations where amputation can occur?
- Medical intervention
- During disposal of the body
How can you tell if a breakage in the bone was done PRIOR to death (eg. medical intervention etc.)
Healing at the site of the break
What does amputation of a bone look like?
Truncation of the normal bone
What do gnaw marks on a bone look like?
Divots/chiselling along the bone (from the incisor teeth)
Irregular, light marks (kind of generally flat marks?) - no striations
U shaped/symmetrical cross section
On the ENDS and PROJECTIONS of bones
What do drill marks on a bone look like?
Holes
What do cut marks on a bone look like?
- Linear grooves (from a sharp tool)
- Regular in depth
- Steep sided, V-shaped cross section
Tend to have purposeful ANATOMICAL location:
- Eg. across the humerus
- Eg. around joint surfaces
- CLUSTERING of the grooves (repeated location and direction) - parallel striations
- Directionality - same direction = purposeful
What do excavation marks on a bone look like?
V or U shaped
Usually random
On projecting regions
LIGHT in colour
What do saw marks on a bone look like?
On the diaphysis of the bone (typically long bones)
On the end - regular, shallow lines
What do trephination marks on a bone look like?
Hole drilled into the skull - used to treat bleeding on the brain
What do root marks on a bone look like?
U-shaped cross section
Sinuous direction (many curves and turns)
Random locations
Chemical etching - forms a pattern
What do canine puncture marks on a bone look like?
Little holes in the bone
Can also see the removal of the epiphyses (end part of a long bone)
What do burning marks on a bone look like?
Change of colour and quality of the bone depending on the heat
Patching of colours on the bone as they go through the burning process
What happens to the bone when burnt at 200 degrees?
Natural colour
Dehydration
What happens to the bone when burnt at 300 degrees?
Darkness to red, grey or yellow
What happens to the bone when burnt at 500 degrees?
Darkness to black or blue
Bones start to shrink and distort
What happens to the bone when burnt at 600 degrees?
Lightens to grey
What happens to the bone when burnt at 700 degrees?
Lightens to white
What happens to the bone when burnt at 800 degrees?
White
Further shrinkage, distortion and pottery like bones
Cracking of the bone
What can affect the surface preservation of bones?
- External environment (wind, rain, climate, scavengers)
- Inside burial environment (pH, root intrusions, insects)
- Type of bone (amount of compact (dense) or cancellous (porous) bone, larger bones survive better)
- Duration of the burial
Why is the preservation of bone of interest?
- Time factor (see how ‘fresh’ the bones are)
- Indications of the type of environment they have been exposed to
- Destruction of cortical bone - indication as to how likely evidence of pathology will have survived/potential for bimolecular analysis
- Taphanonmic history (eg. discolouration)
How is surface preservation recorded?
Using a scoring system from 0 (well preserved) to 5 (heavy erosion) to score how much of the external environment has been affected by the process
Brickley et al (2004)
What does a score of 0 for surface preservation show?
Absence of modification of the surface:
- Clearly visible surface morphology
- No modifications
What does a score of 1 for surface preservation show?
Slight, INTERMITTENT surface erosion:
- Slight and PATCHY surface erosion (no penetration)
What does a score of 2 for surface preservation show?
More extensive surface erosion, slight penetration:
- DEEPER penetration
What does a score of 3 for surface preservation show?
MOST of the surface affected with some DETAILS obscured:
- Most of the bone surface affected by some degree of erosion
- General morphology maintained but the detail of parts of the surface is masked by erosive action
What does a score of 4 for surface preservation show?
ENTIRE surface eroded but general profile maintained:
- Depth of modification is NOT UNIFORM across the whole surface
What does a score of 5 for surface preservation show?
HEAVY bone erosion, MASKING the surface and MODIFYING the profile:
- Unable to identify the bone
What does the surface degradation of bones in a marine environment look like?
Smooth - abrasion and rounding
How does fluvial transport and dispersal of bones in a marine environment occur?
Depends upon the bone shape and density
Lighter bones that float are easily moved (ribs, skull, sacrum, vertebrae)
Intermediate bones that sink are intermittently moved (long bones, scapula, pelvis)
Dense bones that sink are immobile (mandible)
How to determine the MNI?
What must be wary of when trying to determine this?
Minimum number of individuals present
Look for duplications of bones/different sizes of bones
Need to be careful because different colours doesn’t mean different people - bones of the same person may have been exposed to different conditions
How can juvenile bones be identified?
1) By the texture and density of the metaphyseal surface (bobbly appearance - bones haven’t fused yet)
2) The size and proportions of the bones
What is the composition of bone?
70% inorganic material
30% organic matrix (osteoid)
What is an osteoid made of?
Mostly type I collagen, water and non-collagen proteins
What is the structure of bone?
Myriad of circular structures (osteons)
Each osteon has a Haversian canal where nutrients and vessels pass through
Outer layer of straight lamella bone
What happens to the internal structure of the bone after death?
When does this occur?
What contributes to this process?
Enzymes produced that break down the ORGANIC part of the bone
Occurs after death in the burial environment
Contributed to by:
- Water percolation
- Soil composition
What can been seen in the bone as collagen is broken down?
What light is needed to see this?
Can see the reduction of the collagen using POLARISED LIGHT
See birefringence (cross): - BRIGHT/DEFINED cross = good preservation of collagen
- ABSENT/REDUCED cross = poor preservation of collagen/collagen destruction
What can also be seen in both plain and polarised light?
Bacterial tunneling (dark bands)
How can you tell the difference between plain and polarised light?
Polarised light:
- Contrasting colours
- Collagen appears ‘shiny’ (osteons ‘light up’)
Plain light:
- Looks ‘boring’
- No contrast
