Post Mortem Interval Of Skeletonised Remains Biology Essay

Published:

This essay has been submitted by a student. This is not an example of the work written by our professional essay writers.

I have designed an experiment to assess the post-mortem interval of skeletonised remains with regards to bone weathering in a United Kingdom environment. Bone weathering was first published by Behrensmeyer in 1978, which the study was observed on Cow and Elephant bones in Kenya. It is actually quite possible to impose a post-mortem timeframe with regards to Bone Weathering; however external factors such as temperature, location, etc have such an effect on the speed of weathering. This is very important in forensic cases because the external variables can have such an effect and only studies have generally been implemented on either warm temperature i.e. Kenya or periglacial environments (Todisco and Monchot, 2008).

Bone weathering can be simply defined as the process by which the original microscopic organic and inorganic components of bone are separated from there situ and possibly destroyed mostly by physical and chemical agents. Behrensmeyer proposed six key stages of bone weathering in Kenya from the first three stages of 0-6 years and the last three stages composing of the years of 4-15+ years, which can be clearly seen as not the most precise time scales.

Behrensmeyer noted six key stages which she observed to be a continuous spectrum. Identification purposes are quite clear the first stage usually exhibits no cracking or flaking, the bone is usually still fresh and typically greasy. Stage two upon observation usually has flaking and slight longitudinal cracking. Stage three exhibits large patches of rough homogenous bone, the cracked edges are now more rounded. Stage four bone tissue is now coarsely fibrous, it is also starting to splinter from its situ and the effects of weathering has penetrated deep into bone cavities. Typical signs of stage five are the bone is now deteriorating from its situ, which includes large splintering and the bone shape may be difficult to interpret. The bone overall is very fragile at this late stage as the cancellous bone is usually exposed.

There are major problems which must be noted that small and compact bones (such as phalanges) weather more slowly than larger bones (Haglund, 1997). Another main problem is that other bones of different taxa weather at different rates, Behrensmeyer, 1982). Another major effect of bone weathering is that the less equable the immediate environment (such as temperature) the faster the bone should weather (Haglund, 1997), generally due to the nature of disarticulation, which smaller assemblages are lost more rapidly. Larger bones should generally be implemented for the estimation of which weathering stage, such as the femur or tibia. Behrensmeyer (1972) proposed that a one-centimetre cubed area must exhibit the specific bone stage characteristics for a more accurate estimation; regarding the smaller bone types such as fibulas, carpals, etc, this would be highly problematic with the smaller bones. Along with other procedures such as only utilising shafts of large limb bones, flat surfaces of bones such as scapulas, mandibles etc. Bone edges or where there is clear evidence of physical damage should not be recorded. With regards to this experiment Behrensmeyer also stated animals over 5kg’s most only be used, this is because smaller mammals posses more fragile skeletal systems and will weather more rapidly. Generally within taphonomy bone weathering has been estimated in different climates to a United Kingdom or European Climate and thus is the reason for this experiment, there has been such an experiment in Wales, but this was at a high altitude (Andrews, 1995).

Method

I have chosen pig femurs and tibias for my main assessments of bone weathering, the reason in which I have chosen this is because pigs are the closest representation to homo-sapiens (REFERENCE) and thus should provide the most similar results. The pig bones will need to be defleshed, these will need to be done effectively to not leave marks on the bones. The reason the bones will need to be defleshed is because bone weathering cannot begin when soft tissue is still present (Lyman, 1994). With selection of pig types size and age must be consistent for a more accurate and unbiased result, because juvenile bones will weather more rapidly and with older bones will as well (Behrensmeyer, 1978). The pigs must also not exhibit any pathology which can affect the bone weathering, for example no bone breakage or fractures or other pathologies which will cause rapid weathering.

To gain accurate knowledge on the bone weathering in an England environment the bones must be protected from outside factors such as scavengers, arthropods, etc. To prevent such animals affecting the bone surface the bones will be protected in a wire mesh (see figure 1). This may have an affect on the bone weathering, but will prevent rodents, larger animals such as badgers, gnawing or chewing on the bone. The experiment will also be conducted within a closed environment, which means where it is not subject to disturbance from humans or animals alike. Arthropods will not affect the bone to much (REFERENCE), however this little affect cannot be effectively eradicated without keeping the bone in a complete fully enclosed environment, which will affect the weathering. The wire meshing will be made of steel, so it doesn’t erode over time. A major factor that will need to be overcome is the bones need to be held somewhat to prevent wind and storm damage. The bones will be tied with rope to prevent storm damage, but these erode after time and thus should be observed intimately and when required replaced.

Figure 1. Illustrating the mesh wire and rope holdings protecting the bones from scavengers and from storm damage.

Unlike Andrews, (1995), the elevation will be at sea-level, with consistent natural ultra-violet light levels, as the bones will be subjected to continuous sunlight throughout the day. Considering the bones will be left outside for long periods of time the humidity will be changing throughout, this will not be consistent and cannot be illustrated as the experiment will take up to fifteen years to complete, so there will be a lot of variation in humidity. Along with humidity the temperature will be highly varied for example during winter periods the temperature will be very low and during summer periods it will peak higher. Again temperature and humidity do play factors with bone weathering, but for a generalised natural weathering experiment I will record temperatures and humidity for only large abnormalities but I cannot control any of these variations. Soil pH must be considered, however when it rains or similar weather the pH will change depending on the rain type (such as acid rain).

The main issue with this set experiment is time, because I am setting this experiment up from the beginning, it could potentially take around 15 years to publish the complete findings, Behrensmeyer (1978) stated stage five is the last stage and is around 15 years or more). I will consistently record the information and stages which the bone exhibits throughout the course of the experiment. Shading is a major issue with bone weathering, it is somewhat believed that if a bone is in shaded conditions then weathering will be more laggard. Considering that this is the major effector of weathering, this will be controlled in a way that exhibits shaded and non-shaded differences for comparison.

For abnormalitie measuring I will measure the soil pH, while measuring the temperature will be done by thermometer, this will measure daily temperatures and any major abnormalities can be explained. Generally these are just recorded for any major changes to the samples.

I will use a sample size of twenty pigs of average size and age. This will provide forty femurs and forty tibias, bringing a total of eighty bone samples size. I will use these two large bones so accurate estimation of bone weathering can be achieved. Janjua and Rogers (2008) found that using larger bones such as femurs can show more accurate weathering information then smaller bones such as metatarsals. I will than split fifty percent of each bone type to illustrate the effects of shading and non-shading, so twenty femurs and twenty tibias will be in shaded conditions. Where as twenty tibias will be in non-shading locations and twenty femurs will also not be in shaded locations.

I will recover all of the bones periodically after one year, two years, 3 years, 5 years, 7 years, 9 years, 11 years, 13 years and 15 years. These may seem inappropriate but due to the time spans with bone weathering they will be appropriate. I will measure that one centre metre cubed area exhibits the specific bone weathering pattern, which Behrensmeyer proposed in 1974. After the data is collected I will place the bones back into the mesh wire to prevent scavenging.

Whilst measuring I will try and prevent touching the bones in anyway, as the later stages occur the bone progressively becomes more fragile and can be damaged easier. Whilst generally bone weathering exhibits cracking and damage occurred while handling the bone will have to be recorded and disposed as the pathologies will increase the speed of weathering.

I will record the data in the following tables:

Shaded Tibia = 20 sample size.

Years Since Death

Weatheri

1

Ng Stage

2

3

4

5

Total Number of Observations

<1

1-2

2-3

3-5

5-7

7-9

9-11

11-13

13-15

Shaded Femur = 20 sample size.

Years Since Death

Weatheri

1

Ng Stage

2

3

4

5

Total Number of Observations

<1

1-2

2-3

3-5

5-7

7-9

9-11

11-13

13-15

Unshaded Femurs = 20 sample size.

Years Since Death

Weatheri

1

Ng Stage

2

3

4

5

Total Number of Observations

<1

1-2

2-3

3-5

5-7

7-9

9-11

11-13

13-15

Unshaded Tibia = 20 sample size.

Years Since Death

Weatheri

1

Ng Stage

2

3

4

5

Total Number of Observations

<1

1-2

2-3

3-5

5-7

7-9

9-11

11-13

13-15

Bar Chart

(Percentages)

Percentage|

|

---------- Weathering stage

From these results, I can establish how accurate the stages are in a UK environment and propose how long stages take to surface. A T-test could be used to analyse the results to see if there was a significant difference the two types of weathering on the two bones. Significance will be accepted of P<0.05 If there was a significant difference then when estimating pmi of skeletal remains only a certain bone can be used for specific times .

I predict that the bone weathering process will be of slower years then Behrensmeyer’s experiment in 1978, because of the humidity and general lower temperature of the UK weather in comparison to warmer climates such as Kenya or Tropical rainforests. The shading condition bone experiments should also be singificantly slower and I will expect they will not reach the final stage once the experiment is terminated.

Discussion

If this experiment illustrates usefull and practical data about bone weathering within an UK environment then this can be implemented with estimating post-mortem intervals of skeletonized remains. This is a very useful experiment in a forensic standpoint because of the estimation of post-mortem intervals.

This experiment could influence other researchers to gather data in similar scenarios for a number of different countries. Future research could be implemented:

Upon different bone types

With external factors (i.e. open to rodent gnawing, etc)

Bones partialy buried or in water deposits

Different humidity and temperature experiments (in different countries)

Writing Services

Essay Writing
Service

Find out how the very best essay writing service can help you accomplish more and achieve higher marks today.

Assignment Writing Service

From complicated assignments to tricky tasks, our experts can tackle virtually any question thrown at them.

Dissertation Writing Service

A dissertation (also known as a thesis or research project) is probably the most important piece of work for any student! From full dissertations to individual chapters, we’re on hand to support you.

Coursework Writing Service

Our expert qualified writers can help you get your coursework right first time, every time.

Dissertation Proposal Service

The first step to completing a dissertation is to create a proposal that talks about what you wish to do. Our experts can design suitable methodologies - perfect to help you get started with a dissertation.

Report Writing
Service

Reports for any audience. Perfectly structured, professionally written, and tailored to suit your exact requirements.

Essay Skeleton Answer Service

If you’re just looking for some help to get started on an essay, our outline service provides you with a perfect essay plan.

Marking & Proofreading Service

Not sure if your work is hitting the mark? Struggling to get feedback from your lecturer? Our premium marking service was created just for you - get the feedback you deserve now.

Exam Revision
Service

Exams can be one of the most stressful experiences you’ll ever have! Revision is key, and we’re here to help. With custom created revision notes and exam answers, you’ll never feel underprepared again.