The Centre for Isotope Research (CIO) at the University of Groningen has operated a radiocarbon (14C) dating laboratory for almost 70 years. In 2017, the CIO received a major upgrade, which involved the relocation of the laboratory to new purpose-built premises, and the installation of a MICADAS accelerator mass spectrometer. This period of transition provides an opportunity to update the laboratory’s routine procedures. This article addresses all of the processes and quality checks the CIO has in place for registering, tracking and pretreating samples for radiocarbon dating. Complementary updates relating to radioisotope measurement and uncertainty propagation will be provided in other forthcoming publications. Here, the intention is to relay all the practical information regarding the chemical preparation of samples, and to provide a concise explanation as to why each step is deemed necessary.

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Understanding extinction events requires an unbiased record of the chronology and ecology of victims and survivors. The rhinoceros Elasmotherium sibiricum, known as the 'Siberian unicorn', was believed to have gone extinct around 200 ka, well before the Late Quaternary megafaunal extinction event. However, no absolute dating, genetic analysis, or quantitative ecological assessment of this species has been undertaken. Here we show, by AMS radiocarbon dating of 23 individuals, including cross-validation by compound specific analysis, that E. sibiricum survived in Eastern Europe and Central Asia until at least 39 ka BP, corroborating a wave of megafaunal turnover prior to the Last Glacial Maximum in Eurasia, in addition to the better-known Late-glacial event. Stable isotope data indicate a dry steppe niche for E. sibiricum and, together with morphology, a highly specialised diet that likely contributed to its extinction. We further demonstrate, with DNA sequence data, a very deep phylogenetic split between the subfamilies Elasmotheriinae and Rhinocerotinae that includes all the living rhinos, settling a debate based on fossil evidence and confirming that the two lineages had diverged by the Eocene. As the last surviving member of the Elasmotheriinae, the demise of the 'Siberian unicorn' marked the extinction of this subfamily. The rhinoceros family (Rhinocerotidae) was formerly much more diverse than it is today, with some 250 named species 1 of which only five survive. During the Miocene (ca. 23-5 Ma), rhinos were a dominant part of the large mammal fauna in Africa, Eurasia, and North America. Phylogenetic analysis of fossil species has resolved two main lineages: the Rhinocerotinae, which includes all living species and the recently-extinct woolly rhinoceros (Coelodonta antiquitatis), and the extinct Elasmotheriinae 2. Based on morphological diagnoses of early remains, the two subfamilies are thought to have diverged very early in rhinoceros evolution, by at latest 35 Ma 2,3. The Elasmotheriinae subsequently gave rise to some 20 genera, of which only Elasmotherium survived the Miocene, with E. sibiricum its last surviving member, although some authors have separated Elasmotherium from other members of the group and place it within Rhinocerotinae 4,5. A spectacular megafaunal species of Eurasia, at ca. 3.5 tonnes, E. sibiricum was the largest Quaternary rhinoceros. E. sibiricum was also remarkable in its anatomy: relatively slender limbs indicating adaptation for running, despite its mass 6 ; absence of incisors and canines; and-uniquely among rhinos-continuously-growing cheek-teeth with distinctive, highly convoluted enamel plates. The presence of a massive single horn in Elasmotherium has been inferred from the bony protuberance on the frontal bone of the skull which implies a horn base much larger than in any other rhino, living or extinct; hence the informal name 'Siberian unicorn' (Fig. 1). The known geographical ranges of both E. sibiricum and related (in some cases possibly synonymous) Elasmotherium species ...

The radiocarbon (14C) calibration curve so far contains annually resolved data only for a short period of time. With accelerator mass spectrometry (AMS) matching the precision of decay counting, it is now possible to efficiently produce large datasets of annual resolution for calibration purposes using small amounts of wood. The radiocarbon intercomparison on single-year tree-ring samples presented here is the first to investigate specifically possible offsets between AMS laboratories at high precision. The results show that AMS laboratories are capable of measuring samples of Holocene age with an accuracy and precision that is comparable or even goes beyond what is possible with decay counting, even though they require a thousand times less wood. It also shows that not all AMS laboratories always produce results that are consistent with their stated uncertainties. The long-term benefits of studies of this kind are more accurate radiocarbon measurements with, in the future, better quantified uncertainties.