Abstract
Collagen is the dominant organic component of bone and is intimately locked within the hydroxyapatite structure of this ubiquitous biomaterial that dominates archaeological and palaeontological assemblages. Radiocarbon analysis of extracted collagen is one of the most common approaches to dating bone from late Pleistocene or Holocene deposits, but dating is relatively expensive compared to other biochemical techniques. Numerous analytical methods have previously been investigated for the purpose of screening out samples that are unlikely to yield reliable dates including histological analysis, UV-stimulated fluorescence and, most commonly, the measurement of percentage nitrogen (%N) and ratio of carbon to nitrogen (C:N). Here we propose the use of collagen fingerprinting (also known as Zooarchaeology by Mass Spectrometry, or ZooMS, when applied to species identification) as an alternative screening method for radiocarbon dating, due to its ability to provide information on collagen presence and quality, alongside species identification. The method was tested on a series of sub-fossil bone specimens from cave systems on Cayman Brac (Cayman Islands), chosen due to the observable range in diagenetic alteration, and in particular, the extent of mineralisation. Six 14C dates, of 18 initial attempts, were obtained from remains of extinct hutia, Capromys sp. (Rodentia; Capromyidae), recovered from five distinct caves on Cayman Brac, and ranging from 393 ± 25 to 1588 ± 26 radiocarbon years before present (yr BP). All of the bone samples that yielded radiocarbon dates generated excellent collagen fingerprints, and conversely those that gave poor fingerprints also failed dating. Additionally, two successfully fingerprinted bone samples were screened out from a set of 81. Both subsequently generated 14C dates, demonstrating successful utilisation of ZooMS as an alternative screening mechanism to identify bone samples that are suitable for 14C analysis.
Highlights
Analyses of both extant and extinct fauna are essential for understanding the evolutionary ecology of discrete regions through time
Radiocarbon dates were successfully obtained from ancient bone material, revealing ages ranging from 393 ± years before present (yr BP) to 1588 ± yr BP, identified as extinct hutia, Capromys sp., as revealed by Zooarchaeology by Mass Spectrometry (ZooMS) analysis (Table 1, Figs 2 and 3)
ZooMS analyses of sub-fossil specimens from Cayman Brac indicate the presence of preserved collagen in bone material of >1,500 years old (Table 1, Figs 2 and 3)
Summary
Analyses of both extant and extinct fauna are essential for understanding the evolutionary ecology of discrete regions through time. For archaeological and palaeontological material the former of these is typically obtained through morphological analyses of the bones, whereas the latter can be achieved through various dating methods, but most accurately through the use of radiocarbon dating (when samples are sub ~50 k BP). Both of these sources of information are affected by environmental conditions, including climate (temperature and humidity changes), and other taphonomic considerations such as deposition environment, and matrix and pore water geochemistry. Advanced methods of proteomic characterisation may provide a better approach to investigate collagen preservation for successful and reliable dating, with the additional benefit of taxonomic identification
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