Received Sep 13; Accepted Feb This article has been cited by other articles in PMC. 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.
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. 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 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. Introduction Analyses of both extant and extinct fauna are essential for understanding the evolutionary ecology of discrete regions through time.
The two most important pieces of information required are: 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.
The tropics, which are most noted for high biodiversity, conversely have the poorest survival record for faunal remains due to the high temperature and humidity that adversely affects protein i. Specimens that may appear [morphologically] to be relatively well preserved, often lack sufficient collagen yields for successful radiocarbon dating [ 2 ], resulting in either failed dating or the acquisition of an expensive date that is questionable due to potential external contaminant biomolecules [ 3 ].
Advanced methods of proteomic characterisation may therefore provide a better approach to investigate collagen preservation for successful and reliable dating, with the additional benefit of taxonomic identification.
Current 14C screening techniques The construction of a temporal framework of biodiversity patterns in faunal assemblages allows insight into the effects of ecological changes on habitats, including human-induced impacts. However, one of the most appropriate means to achieve such a framework—radiocarbon dating—is significantly costly, both in terms of equipment and time [ 4 ]. Radiocarbon dating is also destructive, especially when the specimens to be dated are small, and there are a number of commonly accepted issues that surround the success of this technique, including sample survival and contamination with external organics [ 5 ].
Other than visual clues into diagenetic maturity, or external information relating to deposition environment both of which can be highly uninformative , there are few simple and reliable sample selection procedures in the literature to screen bone appropriate for dating.
However, this technique is both time consuming and involves destruction of samples to obtain thin sections for light microscopy. Though simple, cheap and fairly reliable, this method is invasive and also requires samples to be destructively sectioned. However, screening in older i. Similarly, either the whole bone carbon: N or the C: N ratio of purified collagen collagen C: N can be used to indicate the state of collagen preservation.
N ratio of between 2. N threshold of Routine collagen extraction procedures at radiocarbon laboratories often include ultrafiltration steps that work to improve 14C dates whilst removing some, but not all, exogenous contaminants including organic acids [ 12 ]. These contaminants from the depositional environment, particularly when coupled with low collagen content, have previously led to an acquisition of inaccurate, unreliable and expensive dates [ 12 , 13 ].
Independent techniques that test collagen presence and quality prior to 14C dating can therefore provide supporting evidence to ensure dates have been acquired from endogenous collagen rather than external contaminants, thereby producing reliable and publishable dates. Extracted collagen, analysed via soft ionisation mass spectrometry, relies upon a tryptic digestion to generate a peptide mass fingerprint PMF.
Exogenous contaminants that can skew dating should not affect a PMF to the same extent as dating. Additionally, collagen fingerprints are unique down to genus level in many organisms [ 19 , 20 ], and in some cases to species level e. Analysis of this sturdy triple-helical structural protein for species identification in this manner also allows circumvention of contamination issues that commonly occur through other techniques, such as polymerase chain reaction PCR required during aDNA amplification [ 14 , 19 , 22 ].
Radiocarbon dating on the Cayman Islands The best conditions for molecular preservation of Late Quaternary vertebrate remains in the tropics lies almost exclusively within cave systems [ 23 ]. Within such microenvironments, remains can become isolated from temperature changes, humidity variation, soil organisms and humic acids [ 24 ]. Bones deposited in caves may also become encased in calcareous matrices, such as is common on the Cayman Islands Fig 1 , increasing the likelihood of exceptional protein preservation.
Samples such as these are ideal to perform ZooMS upon, given their potential for increased collagen survival.