Resolution-enhanced stable isotope profiles within the complete tooth rows of Late Pleistocene bisons (Middle Urals, Russia) as a record of their individual development and environmental changes

Well-preserved left hemi-mandibles with complete tooth row from two late-Pleistocene individuals of bison Bison priscus were discovered in the Bobylek cave deposits in the Middle Urals, Russia. One of the mandibles belonged to a young bison, approximate age of two, and another belonged to a mature bison, approximate age of eight. We investigated the oxygen (δ18Ocarb) and carbon (δ13C) isotope variations in structural carbonate of hydroxyapatite and carbonate content in sequential enamel samples from all teeth from both individuals to address inter- and intra-individual variability in the timing of tooth formation of studied fossil bison as well as their environments. The isotopic and chemical data presented the intra-tooth profiles which were compiled into individual intra-row profiles for both specimens. A comparison between the chemical and isotopic (δ18Ocarb and δ13C) intra-row profiles inferred no interdependent relationship, indicating that the fossil enamel did not undergo significant diagenetic modifications and primary isotopic signals were preserved. Carbonate content decreased as enamel maturated. The δ18Ocarb intra-row profile demonstrated sinusoidal shape variations (with an amplitude of 3.6‰ for one bison and 3.0‰ for another bison) related to seasonal isotopic variability in precipitation during the course of enamel formation of all permanent teeth with except mandibular first molar (M1). The δ18Ocarb values in M1 enamel could be controlled by intrauterine metabolic processes as M1 started its formation at early embryonic life. The timing of formation of second and third molars of fossil specimens was estimated to be several months later compared to modern bison (B. bison). The δ18Ocarb variations within tooth row of both specimens reflected environmental conditions in which bison lived that were estimated to be significantly colder than today. Basing on the average δ18Ocarb value of the sinusoidal signals of intra-row profiles (∼18.2‰ for both bison), the annual mean δ18O value in precipitation was estimated to be approximately 16.9‰. It was lower by 2.7‰ than today in the Middle Urals. Using the local relationship between δ18O values in modern precipitations and air temperatures we estimated the mean annual air temperature to be approximately 6.6 °C, ∼9 C° lower than today. The carbon isotope data from serially sampled bison teeth revealed that isotope diet of both bison was seasonally independent and determined by C3-type plants.