Chemosteometric regression models of heat exposed human bones to determine their pre-burnt metric dimensions.

OBJECTIVES: Heat exposure can lead to apparently random osteometric changes that hinder the application of metric methods used for biological profiling. The impracticality of using objective and burn-specific osteometric methods reduces the chances of establishing the biological profiles of unknown individuals based on their skeletal remains. We investigated the potential of chemometry analysis based on infrared spectroscopy to predict the amount of heat-induced osteometric changes and how this reflected into sex estimation. MATERIAL AND METHODS: Bones from 41 identified adult skeletons (24 females and 17 males with ages between 62 and 90 years old) were experimentally burnt to maximum temperatures ranging from 450°C to 1,100°C (attained after 65 to 240 min). Measurements were taken both before and after each experiment and powder samples were analyzed through FTIR-ATR. Correlations among heat-induced metric changes and chemometric indices (crystallinity index; B-type carbonates; carbonate [A + B] to carbonate B ratio; hydroxyl to phosphate ratio; 630 cm-1 , 1450 cm-1 , 3572 cm-1 , and 3642 cm-1 ) were tested. Significant variables were used to build regression models to predict heat-induced metric change which were then tested on an independent set of samples. Agreement in sex estimation between the pre- and post-burnt samples was also evaluated. RESULTS: All indices were significantly correlated to heat-induced metric changes (α = .01) and the highest correlations were obtained for the 630 cm-1 , 3572 cm-1 , and crystallinity index. We confirmed that regression models based on chemometrics obtained from infrared spectra through FTIR-ATR are better at estimating heat-induced metric changes affecting bone and at sexing remains than other osteometric methods such as those based on correction factors or on metric references specific to calcined bones. DISCUSSION: Regression models avoid the subjectivity associated with the application of other methods. While the latter can be applied only to calcined bones, which is difficult to assess sometimes, regression models can be applied to all bones regardless of their condition. Also, regression models have the advantage of allowing to infer about heat-induced metric change on a case-by-case basis.

Preliminary results of an investigation on postmortem variations in human skeletal mass of buried bones.

Extreme fragmentation can complicate the inventory of human skeletal remains. In such cases, skeletal mass can provide information regarding skeleton completeness and the minimum number of individuals. For that purpose, several references for skeletal mass can be used to establish comparisons and draw inferences regarding those parameters. However, little is known about the feasibility of establishing comparisons between inherently different materials, as is the case of curated reference skeletal collections and human remains recovered from forensic and archaeological settings. The objective of this paper was to investigate the effect of inhumation, weather and heat exposure on the skeletal mass of two different bone types. This was investigated on a sample of 30 human bone fragments (14 trabecular bones and 16 compact bones) that was experimentally buried for two years after being submitted to one of four different heat treatments (left unburned; 500 °C; 900 °C; 1000 °C). Bones were exhumed periodically to assess time-related mass variation. Skeletal mass varied substantially, decreasing and increasing in accordance to the interchanging dry and wet seasons. However, trends were not the same for the two bone types and the four temperature thresholds. The reason for this appears to be related to water absorption and to the differential heat-induced changes in bone microporosity, volume, and composition. Our results suggest that mass comparisons against published references should be performed only after the skeletal remains have been preemptively dried from exogenous water.

Potential of Bioapatite Hydroxyls for Research on Archeological Burned Bone.

The estimation of the maximum temperature affecting skeletal remains was previously attempted via infrared techniques. However, fossilization may cause changes in the composition of bones that replicate those from burned bones. We presently investigated the potential of three OH/P indices (intensity ratios of characteristic infrared bands for OH and phosphate groups, respectively) to identify bones burned at high temperatures (>800 °C) and to discriminate between fossil and burned archeological bones, using vibrational spectroscopy: combined inelastic neutron scattering (INS) and FTIR-ATR. The INS analyses were performed on two unburned samples and 14 burned samples of human femur and humerus. FTIR-ATR focused on three different samples: (i) modern bones comprising 638 unburned and 623 experimentally burned (400-1000 °C) samples; (ii) archeological cremated human skeletal remains from the Bronze and Iron Ages comprising 25 samples; and (iii) fossil remains of the Reptilia class from the Middle Triassic to the Eocene. The OH/P indices investigated were 630 cm-1/603 cm-1, 3572 cm-1/603 cm-1, and 3572 cm-1/1035 cm-1. The OH signals became visible in the spectra of recent and archeological bones burned between 600 and 700 °C. Although they have episodically been reported in previous works, no such peaks were observed in our fossil samples thus suggesting that this may be a somewhat rare event. While high crystallinity index values should always correspond to clearly visible hydroxyl signals in burned bone samples, this is not always the case in fossils which may be used as a criterion to exclude burning as the agent responsible for high crystallinity ratios.

Rather yield than break: assessing the influence of human bone collagen content on heat-induced warping through vibrational spectroscopy.

Warping has been used to determine the pre-burning condition of human skeletal remains. In the literature, this modification has been associated more often with the burning of fleshed and green bones, but it also arises during the burning of dry bones. The objective of this paper was to assess if bone collagen content has a significant effect on the occurrence of warping in a sample of experimentally burned human bones. The presence of collagen was analyzed in two different samples through a vibrational spectroscopy technology-FTIR. One of them was composed of 40 archeological bones from the seventeenth to twentieth centuries AD. The other one was composed of bones from 14 skeletons belonging to the 21st century identified skeletal collection. The results confirmed that the amide I band assigned to the collagen was much more intense in bones presenting heat-induced warping. Nonetheless, although significant (p = 0.040), the collagen content was not as useful as other variables to the regression model we proposed for explaining warping. Factors such as the maximum temperature (p < 0.001) and burning time (p = 0.001) contributed more significantly. Results demonstrated that the mere preservation of collagen is not enough to explain warping. Burning dynamics seem to have an important role as well although we failed to clearly document its specificities. Other factors such as the asymmetric distribution of collagen and other components within bone, the gravity force, the shape of the bone, and the position in which it is burned may also play an important role on heat-induced changes and require further analysis.

One for all and all for one: Linear regression from the mass of individual bones to assess human skeletal mass completeness.

OBJECTIVES: Complete and accurate human skeletal inventory is seldom possible in archaeological and forensic cases involving severe fragmentation. In such cases, skeletal mass comparisons with published references may be used as an alternative to assess skeletal completeness but they are too general for a case-by-case routine analysis. The objective is to solve this issue by creating linear regression equations to estimate the total mass of a skeleton based on the mass of individual bones. MATERIALS AND METHODS: Total adult skeletal mass and individual mass of the clavicle, humerus, femur, patella, carpal, metacarpal, tarsal, and metatarsal bones were recorded in a sample of 60 skeletons from the 21st century identified skeletal collection (University of Coimbra). The sample included 32 females and 28 males with ages ranging from 31 to 96 years (mean = 76.4; sd = 14.8). Skeletal mass linear regression equations were calculated based on this sample. RESULTS: The mass of individual bones was successfully used to predict the approximate total mass of the adult skeleton. The femur, humerus, and second metacarpal were the best predictors of total skeletal mass with root mean squared errors ranging from 292.9 to 346.1 g. DISCUSSION: Linear regression was relatively successful at estimating adult skeletal mass. The non-normal distribution of the sample in terms of mass may have reduced the predictive power of the equations. These results have clear impact for bioanthropology, especially forensic anthropology, since this method may provide better estimates of the completeness of the skeleton or the minimum number of individuals. Am J Phys Anthropol 160:427-432, 2016. © 2016 Wiley Periodicals, Inc.

Reaching new heights: Testing the performance of metric approaches to estimate stature from burned skeletal remains.

Bone heat-induced changes complicate osteometric stature estimation of human remains from forensic settings. The validity of current methods has not been tested to a great extent. Our aim was to determine how precise are stature estimations obtained from three different approaches, namely by using (i) Rösing's method (Rösing 1977), (ii) a 10% shrinkage correction factor (Strzalko et al. 1972) and (iii) chemosteometry (Gonçalves et al. 2020). For this purpose, pre- and post-burned head measurements from the humerus, radius and femur were used. The sample comprised 46 human skeletons of known sex and age-at-death. These were experimentally burnt to maximum temperatures ranging from 700 to 1100°C (attained after 90-188 min) for other research purposes. Stature estimations were performed through measurements in both pre-burned and burned bones using the three approaches and based on the method of Olivier and Tissier (1975). Mean absolute differences and the relative technical errors of measurements (TEM%) between the pre-burned and the estimations were calculated. Absolute mean differences indicated that the chemosteometric approach allowed for potentially more precise stature estimations than the other two procedures. However, the TEM% was very low for all approaches (smaller or close to 1%), and stature estimations were thus well within the error margin reported by Olivier and Tissier (1975). Results suggest that the chemosteometric approach enables more accurate predictions of the actual heat-induced shrinkage of each bone thus rendering more precise stature estimations. Nonetheless, the other procedures also provided quite reliable estimations although they require confirmation that the bone is calcined.

Burned and buried: A vibrational spectroscopy analysis of burial-related diagenetic changes of heat-altered human bones.

OBJECTIVES: The analysis of burned human remains can be very challenging due to heat-induced alterations. Occasionally, human bones present these coupled with diagenetic changes, offering even more of a challenge, since there is a lack of studies regarding interactions between both taphonomic phenomena. With this study, we aimed to assess and document the effects of inhumation on the chemical composition of both unburned and burned human skeletal remains. MATERIALS AND METHODS: We buried, for 5 years, four groups of human bone samples comprising unburned bones and bones experimentally burned at 500, 900, and 1050 °C. Periodic exhumations were carried out to collect bone samples to be analyzed through Fourier transform infrared spectroscopy in attenuated total reflectance mode, in order to calculate four chemical indexes: (1) crystallinity index (CI); (2) type B carbonates to phosphate index (BPI); (3) total carbonates (A + B) to carbonate B ratio (C/C); and (4) OH to phosphate ratio (OH/P). RESULTS: After inhumation, CI and C/C of unburned bones and bones burned at 500 °C, and BPI of bones burned at 1050 °C did not vary significantly. However, the remaining indexes showed both relevant increments and reductions throughout observations, depending on burning temperature and index. DISCUSSION: Our results suggest that diagenesis can have an effect in bone's molecular composition. However, these effects do not seem to significantly affect the conclusions that can be taken from the analysis of infrared bone spectra, at least in the case of inhumations with a duration of 5 years or less.

The effects of burning on isotope ratio values in modern bone: Importance of experimental design for forensic applications.

This study examined preservation of isotope ratio values by comparing isotope composition of bones before and after burning. We analyzed common geoprofiling isotope systems (δ13C, δ15N, δ18O, and 87Sr/86Sr) and lesser studied systems (δ34S and δ88/86Sr) to evaluate if inferences about diet and residence history were altered by the burning process. We used two burn methods: one to simulate previous academic studies using a muffle furnace and one to more closely resemble a house fire or body disposal attempt using open flame. To mimic previous burn studies, ribs and femora from four dry modern human skeletons were heated in a muffle furnace. To resemble a forensic burn situation, fleshed pig ribs from a single geographic location were burned on an open fire both with and without use of a diesel accelerant. Isotope ratios from bone collagen, carbonate, phosphate, and strontium were analyzed. Fleshed pig samples burned in an open fire maintained unaltered isotope ratio values. Dry human samples burned in a muffle furnace maintained unaltered isotope ratio values in most isotope systems, except for δ18O values in carbonate and phosphate, which showed a depletion of 18O at higher temperatures. This research suggests that the isotope composition of fleshed burned bone retains the geoprofiling inferences of unburned bone, at least within the parameters of the open fire burn used in this study. However, oxygen isotopes of carbonate and phosphate from dry bone burned in a muffle furnace do not retain the geoprofiling inferences. This research demonstrates the need for research using an experimental design relevant to a specific burn situation.