Eggshell and the archaeological record: new insights into turkey husbandry in the American Southwest

Eggshell in the archaeological record has interpretive potential beyond simple species identification. Structural features of eggshell itself indicate the degree of development of the embryo. Using a scanning electron microscope, a reference collection of modern eggshell characteristics has been produced that can be used for species determination and for the assessment of embryo development of prehistoric eggshell. We apply this technique to a sample of prehistoric eggshell from northwestern New Mexico and conclude that purposeful breeding of captive turkey populations is present during the 12th century AD. These preliminary results suggest a behavioral shift in turkey husbandry, concomitant with the well documented phenomenon of intensified turkey utilization after about AD 1100 in the American Southwest.     

ZooMS: making eggshell visible in the archaeological record

Avian eggshell is a common component of many archaeological deposits, but its archaeological potential remains largely unexplored. The most obvious reasons are two-fold. Firstly, despite its abundance on many sites, eggshell is often overlooked during excavation. Even when it is recovered, small fragmented remains are difficult to identify taxonomically. Here we introduce a minimally destructive qualitative analytical technique for taxonomic identification of eggshell fragments based on highly sensitive mass spectrometry and peptide mass fingerprinting (ZooMS), and illustrate its application to eggshell recovered from the Viking Age urban site at Hungate, York. We adopt a more extreme version of the method of bleach treating used to prepare ancient eggshell for DNA analysis, followed by conventional peptide mass fingerprinting using MALDI-ToF mass spectrometry. The development of this technique will allow future research to make better use of eggshell fragments recovered from archaeological sites.     

The geochronological potential of isoleucine epimerisation in cassowary and megapode eggshells from archaeological sites

Our research demonstrates that the extent of isoleucine epimerisation (A/I) in fragments of avian eggshells provides geochronological information in archaeological contexts. In the archaeological sequence of Hay Cave, northern Queensland, Australia, there is an excellent correspondence between the A/I values of Australian brush-turkey (Alectura lathami) eggshells (n = 99) and independent geochronological control (n = 16 radiocarbon ages including 4 on eggshell calcite). The A/I values identify three phases of deposition during the Holocene at Hay Cave. In contrast to the Alectura eggshell A/I values, a poor correspondence was observed between the A/I values of cassowary (Casuarius) eggshells from Toé (n = 35) and Kria caves (n = 23) (Ayamaru Plateau, Papua) and the depths from which the specimens were recovered in these stratified sequences. Given coherent archaeofauna trends and radiocarbon chronologies (n = 8 and 2 eggshell calcite radiocarbon ages at Toé and Kria, respectively) with respect to depth, the variable A/I values are not explicable in terms of mixing. Rather, the variability is most likely due to exposure of the eggshells to the high temperatures of campfires. Despite the variability, eggshells with relatively low A/I values amongst specimens recovered from similar depths (and therefore presumably least influenced by high temperatures) exhibit a gradual increase in A/I with respect to depth, as expected in a stratified deposit. From this observation it is suggested that the identification of heated eggshells will increase confidence in geochronological information provided by A/I. These studies illustrate the complications that arise from campfire-induced acceleration of amino acid racemisation and emphasise that although this phenomenon is common, it is not universally encountered in archaeological contexts.