WEEK 4-taphonomic studies of human remains Flashcards
Taphonomic
study of how organisms decay and become fossilized
Biosphere to lithosphere
Taphonic processes- the biological and physical changes that occur
- post mortem= before burial
- post burial= before excavation
- Post excavation= before study
What does taphonomy help the investigator determine?
The depositional history of a given set of skeletal remains
identify agents of modification and destruction
cultural activates as opposed to natural changes- human intervention?
biases of human composition
Agents, processes and factors?
- Agents- source which causes the modification eg. human, animal
- process- action performed by the agent that causes the modification eg. scavenging butchery
- factor- chemical, physical, biological, cultural
Why was it originally developed?
for palaeontology to explain how and why extent animals become fossilised and preserved in the geological record
taphonomy impetus from research advances in forensic anthropholgy
Understanding the post mortem history of human skeletal remains, trauma analysis, violence vs excavation damage
How can you tell whether remains are human or animal?
Surface of animal bones are more polished and bones are more denser
How can you tell if bones are modern or archaeological?
Modern bones has organic collagen component present, it is heavier and denser and has a more greasy feel
archaeological= more rougher
Assessing the condition of the bones
- Completeness- % of skeleton present
- fragmentation-post mortem breakage
- preservation- condition of the cortical surfaces (erosion, burning, weathering)
Scavenging affect on bones
canviores disarticulate animal carcasses in a regular sequence
early - femur from hip, mandible from cranium, atlas from cranium, humerus from scapula, caudal vertebrae, distal phalanges
middle- femur to hip bone, tibia from femur, tarsals, metatarsals, ribs, humerus from radius, carpals, metacarpals etc
late- sacrum from hip, cervical thoracic and lumbar vertebrae
Fragmentation- incidental
- Disturbance in burial
- breakage during excavation- depending on condition of soil, breaking bones,
- trampling
- peri-mortem fracturing
Intentional fragmentation
- Peri mortem fracturing- can result from interpersonal violence
- butchery- animal
- amputation/ disemberment
Bone surface modification- like amputation with saw
sharp edges would suggest patient did not survive
could also be intentional disposal of human body parts
Intrinsic preservation factors of bone degradation
size- larger bones more likely to survive
porosity
amount of compact or cancellous bone- high amounts of cancellous vs compact
extrinsic Factors for preserving bone degradation
Soil PH- more acidic causes pitting of bone together and thinning of cortical bone margins
Presence of H20 and O2
temp
microbial organisms- action of bacteria is driving decay
duration of burial
Recording surface preservation (brickley et al 2004)
0) absence of modification of surface
3) most surface affected with some details obscured
5) heavy erosion of surface and modifying profile
* increase degradation down scale
Fluvial transport and dispersal
Action of water on bone, influence of water currents on preservation
fluvial dispersal on bones depends on bone shape and density
Fluvial dispersal bone groups
1- light bones that tend to float and are easily moved: ribs, vertebrae, sacrum, sternum
2- intermediate bones that sink and are intermittently lomved- long bones, scapula, pelvis, metapodials, phalanges
3- dense bones that sink and are relatively immobile, forming a lag deposit : mandible, animal skull, deer antler
How can you tell if there is carnivore and rodent gnawing?
Puncture marks and removal of epiphyses (human bone)- tend to be around the long bones
Chiselling pattern
*rodents gnaw to wear down their teeth
Criteria for identifying cutmarks by structural features
- linearity of groove
- steep sided, v shaped cross section
- parallel scratch marks along walls-shouldering of displaced bone
- regularity in deep groove
Criteria for identifying cutmarks by location
- purposive anatomical location
- clustering of grooves, repeated in location and direction
- directionality
What marks are made by trampling?
rough and random marks , not linear cuts
Marks on bones by root marks?
root grow around skeleton and leave impressions on it
more sinuous impressions
randomly occurring
chemical etching may leave residue of discolouration
Marks from teeth
going around bone rather then in it
Curation damage
V shaped, random, projecting regions
light colour clean groove
*anything happening to remains after excavation
What do cutmarks on animals indicate?
Butchary at the joints
humans= body disposal, cannibalism, burial, ritual
Speed of bone decay can depend on intrinsic influences
- age- children faster decay
- sex
- health problem- someone suffering from acute or chronic disease- sepsis
Extrinsic factors for speed of bone decay
climate and temp depth of burial soil type PH, O2 ,H20 insects and scavengers bacteria
What happens if human remains are left above ground
weather, insects and carnivores
normal conditions- loss of soft tissue, leave only bone and teeth
How does mummification affect bone decay?
if bacteria cant survive in certain conditions, you wont see the same decay
preservation of soft tissue
Rate of decay underground
4x more slowly
depends on depth and type of burial
What is fossilation
process where remains are embedded into sediment
soft tissue decay, minerals infill bone and form crystals, causing hardening
Rate of decay underwater
Slower than bodies exposed to air- less O2 and lower temp
different type of scavengers
currents of water influence dispersal
some bodies float some stay submerged
Bog bodies
natural mummification
highly acidic water, anoxic conditions
preservations of internal organs and skin
Bones are generally not that well preserved bc of high acidity
What is a cremation
funeral rite
cremated skeletal remains can survive across acidic soil
burned- not efficient, difficult, requires high temperatures over prolonged period of time
What is the weight of cremated remains?
0.2-2kg
Increasing the heat affect on colour change
200 degrees- natural colour
500- darkens to blue/ black
800- white
Physical changes in bone during cremation when heat is increased
200- dehydration
300- conversion of organics
500- loss of organics, shrinkage and some discolouration
800- conversion of hydroxyapatite to tricalcium phosphate, shrinkage, more discolouration, cracking
structure of bone and composition
myriad of circular structures (osteons) with an outer layer of straight lamellar bone
each osteon has a central canal (haversian canal) where nutrient vessels pass through
layers contain both inorganic and organic structures- mostly collagen
What do the miscroscopic view of human bones show
Plain light- inorganic component of bone
Polarised light- osteons ‘light up’- birefringence and a cross structure can be seen dissecting each osteon (bc collagen fibres transve in different directions and so break the light differently)
Measures of microbial decay
useful to see how much microbial infiltration is going on
Histology
microbial damaged bone shows localised mineral alteration and loss of birefringence
Porosimetry
increase in porosity at 0.6-1.2 micrometres
Crystallinity
increase in minimum dimension of apatite crystals above ~5nm
example measurement of microscopic degradation
good external cortical preservation
dark areas are bacterial tunnelling below the periosteal and endosteal surfaces
microscopic longitudinal section through the cortex shows pattern of bacterial tunnelling
Poorly preserved bone shown in polarised light
Due to microbal sction
very limited reflection of collagen fibres
big patches showing loss of quality and distinctive maltese crosses
Cremation- loss of optical birefringence due to heat damage to collagen
Mechanism 1 of bone degradation pathway
Hydrolysis of bone collagen— infilling of interstitial pore spaces— fossilisation
Mechanism 2 of bone degradation pathway
dissolution of bone mineral— chemical or microbial collagen degradation– complete loss
Mechanism 3 of bone degradation pathway
microbial attack of organic component— focal destruction and re-crystallisation — partial loss
