Stable isotope analysis and differences in diet and social status in northern Medieval Christian Spain (9th–13th centuries CE) by Pérez-Ramallo, P, Lorenzo-Lizalde, JI, Staniewska, A, Lopez, B, Alexander, M, Marzo, S, Lucas, M, Ilgner, J, Chivall, D, Grandal-d́Anglade, A, Roberts, P