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

Abstract

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.

The preburning condition of Chalcolithic cremated human remains from the Perdigões enclosures (Portugal)

“…The former displayed warping in 67% of the cases and the latter in 18%. Yet the study of Gonçalves, Cunha, and Thompson () quantifies heat‐induced curved fractures per individual; the study of Vassalo et al () quantifies warping per bone, and the results of this study for Pit 40 inevitably quantify both per bone fragment (due to extreme fragmentation and commingling of a minimum of 147 individuals). Thus, although our results of heat‐induced curved fractures and warping appear more consistent with burning of dry skeletons, differences in quantification methodology prevent a direct comparison of results and so our results are inconclusive due to lack of appropriate comparative reference studies.…”

“…In their study, comparing the frequency of heat‐induced curved factures between cremated cadavers and dry bones, Gonçalves, Cunha, and Thompson () report curved fractures in 96% of the cadavers and 22% of dry skeletons. Vassalo et al () compared the frequency of heat‐induced warping between bones cremated after buried for less than 20 years and bones cremated after being buried for at least 80 years. The former displayed warping in 67% of the cases and the latter in 18%.…”

“…When exposed to heat, bones may warp. Although this morphological change has, for quite some time, been said to occur only in wet or fleshed bones (Baby, ; Binford, ; Etxeberria ), it has also been identified in dry cremated bones (Gonçalves, Cunha, & Thompson, ; Gonçalves et al, ; Vassalo, Cunha, de Carvalho, & Gonçalves, ; Vassalo, Mamede, Ferreira, Cunha, & Gonçalves, ). Thus, presence/absence of warping is an inconclusive indicator of the preburning condition of bones (Gonçalves et al, ).…”

“…Thus, presence/absence of warping is an inconclusive indicator of the preburning condition of bones (Gonçalves et al, ). Yet warping is more frequent in bones that were burned after being buried for shorter periods than in bones burned after being buried for longer periods (Vassalo et al, ), and so high frequencies of warping may reflect absence or short periods of burial before cremation. Here, we quantify the presence of warping (scored as present or absent) and use its frequency to infer if bones were likely buried for long periods prior to cremation.…”

Burned Fleshed or Dry? The Potential of Bioerosion to Determine the Pre-Burning Condition of Human Remains

“…they can occur in remains that were burnt fresh (either fleshed or recently defleshed) or dry (Buikstra and Swegle 1989;Spennemann and Colley 1989;Whyte 2001;Gonçalves et al 2011Gonçalves et al , 2015. Other factors, such as collagen content, temperature increment and even the force of gravity, appear to be influencing variables in the occurrence of such features (Vassalo et al 2016(Vassalo et al , 2019. We are therefore in need of other, more reliable indicators for pre-burning funerary deposition and bodily state.…”