Taphonomy - Lecture 14 Flashcards
What is Forensic Taphonomy?
any damage caused by an external environment
What can be classified as/are some postmortem changes? (in a natural context)
- loss of bone or parts of bone
- cracks, pits, grooves, and other marks on bone
- modifications to bone shape (ie fractures)
What can be determined by the types of postmortem changes?
- type of environment the body was in or exposed to
- can determine the postmortem interval (PMI)
What is the postmortem interval (PMI)
time since death
By the time someone has become skeletonize, how much time has passed?
months to years, depending on the environment and other factors
What are some variables to consider when calculating the PMI
- temperature
- humidity
- exposure (buried or exposed)
- soil type and hydration
- types of scavengers (birds, carnivores, rodents, sea creatures)
What kind of soil will speed up decomposition and degradation of the bone?
acidic
What are the 3 major effects carnivore scavenging has on bone?
- scatter and disarticulate remains
- gnawed epiphyses
- break bones by trampling or chewing
What type of remains are most likely to be targeted by scavengers?
exposed
What is the specific sequence a carnivore will follow to dismember a body?
- soft tissues of head and neck
- ventral thorax opened and contents of stomach & chest eaten followed by sternum and rib ends
- upper limbs, including scapulae and clavicles separated from thorax
- lower limbs removed from pelvis (sometimes with os coxa attached)
- thorax removed from area where body deposited (parts of spine may remain articulated)
- long bones separated from each other and ends chewed
- all bones disarticulated, scattered, and chewed
What are the types of carnivore marks on bone? Describe them.
Puncture:
- a hole through the bone
- from animal canines
Pit:
- an incomplete hole
- from animal canines
Depressed fractures:
- less complete pit
- cortical surface being forced into trabecular layer
Scoring:
- light scratches on the bone
- from animals chewing on the bone for a long time
Furrows:
- deeper scratches from animals chewing
Gnawing on epiphyses:
- kind of v shaped
- cortical bone flaking off
- caused by animal canines
Fracturing and splintering:
- long bones being broken apart into spiral fractures
How can you use the completeness of a recovered skeleton to estimate PMI?
- if more than 80% of a body is recovered it has been less than 6 months since death
- if less than 20% of a body is recovered it has been more than 6 months
Why are the PMI intervals based on 6 month intervals?
because of the seasons
What do gnaw marks on dried bone indicate? What is the estimated PMI if these are present?
- they are indicative of rodents
- 2.5 years +/- 1 year
What are the patterns of rodent gnaw marks on bone? Where on the bone are they? What can measuring the groves between the gnaw marks indicate?
- parallel striations close together
- clustered around the edges of the bone
- size of the rodent
What is weathering?
the effect of uv radiation, heat, humidity, and precipitation on the bone
How long does it take for visible changes caused by weathering to the bone to happen?
years
What is cortical exfoliation (aka delamination)? What is it caused by?
- caused by weathering when the periosteum dries up the cortical bone is exposed to uv radiation
- caused by a differential drying out of the bone that results in delamination
- delamination is when the layers of lamellar bone start to pull away from one another due to them drying out at different stages
What are the 6 stages of weathering?
Stage 0:
- less than a year on the surface
- bone hasn’t been impacted by uv radiation and hasn’t begun to bleach or discolour
- layers of cortical bone still intact
Stage 1:
- 1-3 years on the surface
- longitudinal cracking (length of the bone)
- fine longitudinal cracking
beginning of bone delamination
Stage 2:
- between 3-5 years of exposrue
- beginning of lamellar bone flaking in thin layers
Stage 3:
- 5-10 years of exposure
- bone underneath is exposed from delamination
- fibrous bone exposed
Stage 4:
- 10-15 years of exposure
- really deep cracking and the longitudinal cracks get deeper
Stage 5:
- 15-30 years of exposure
- disintegration
- very fragile and easily fragmented
Why is the rate of PMI extended when a body is buried?
- because a body is protected from animal and insect activity and protected from weathering
- it is also kept cooler which slows down decomposition rates
What is one week of damage to a body on the surface equivalent to if the body was buried?
8 weeks
What are the effects of root erosion on a buried body?
- the mild acid secreted from roots will erode the cortical bone and leave an imprint of their pattern
- can disarticulate bones and joints and grow in the skull
How will the colour of a bone change when buried?
the bone will change into the colour of the soil its buried in
What are the stages of water transport damage?
- air escapes the lungs and body sinks and travels away from original point
- damage caused by body scraping across ocean or riverbed - body bloats and floats to surface and travels further
- skull, mandible, hands, then feet, lower limbs, and arms separate
- amount of transport depends on body part - independent movement of individual body parts
- round segments can travel far
- flat points tend to stay closer to body’s entry point into the water
- can travel up to 80 km or further depending on the part
