Fine-scale temporal processes, such as the synchronous deposition of organic materials, can be challenging to identify using 14C datasets. While some events, such as volcanic eruptions, leave clear evidence for synchronous deposition, synchroneity is more difficult to establish for other types of events. This has been a source of controversy regarding 14C dates associated with a hypothesized extraterrestrial impact at the Younger Dryas Boundary (YDB). To address this controversy, we first aggregate 14C measurements from Northern Hemisphere YDB sites. We also aggregate 14C measurements associated with a known synchronous event, the Laacher See volcanic eruption. We then use a Monte Carlo simulation to evaluate the magnitude of variability expected in a 14C dataset associated with a synchronous event. The simulation accounts for measurement error, calibration uncertainty, “old wood” effects, and laboratory measurement biases. The Laacher See 14C dataset is consistent with expectations of synchroneity generated by the simulation. However, the YDB 14C dataset is inconsistent with the simulated expectations for synchroneity. These results suggest that a central requirement of the Younger Dryas Impact Hypothesis, synchronous global deposition of a YDB layer, is extremely unlikely, calling into question the Younger Dryas Impact Hypothesis more generally.

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Researchers have established a Holocene pattern of Bison spp. diminution on the Great Plains of North America. This pattern, however, is less clear west of the Rocky Mountains. This lack of clarity stems from a relative paucity of paleontological and archaeological bison assemblages sufficiently large enough to understand local bison diminution. To begin filling this important gap in knowledge, we analyze a large bison assemblage from Baker Cave, a Late-Holocene archaeological site located on Idaho's Snake River Plain. Measurements of humeri, radii, tibiae, metatarsals, and calcanei demonstrate that these animals were significantly smaller than Early-Holocene bison from both the Great Plains and Snake River Plain. Middle-Holocene bison from the Great Plains are generally larger than those from Baker Cave, but this size difference varies by skeletal element. The Baker Cave bison do fall within the range of Late-Holocene morphological variation present in both Snake River Plain and Great Plains bison populations. These results provide a necessary first step for understanding bison morphology in the region, but establishing a pattern of diminution west of the Rocky Mountains will require follow-up studies with other faunas.

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