Richards, M., & Hedges, R. (2003). Variations in bone collagen δ13C and δ15N values of fauna from Northwest Europe over the last 40 000 years. Palaeogeography, Palaeoclimatology, Palaeoecology, 193(2), 261-267. https://doi.org/10.1016/s0031-0182%2803%2900229-3