Data from: Isotaphonomy in concept and practice: an exploration of vertebrate microfossil bonebeds in the Upper Cretaceous (Campanian) Judith River Formation, north-central Montana

Vertebrate microfossil bonebeds (VMBs)—localized concentrations of small resilient vertebrate hard parts—are commonly studied to recover otherwise rarely found small-bodied taxa, and to document relative taxonomic abundance and species richness in ancient vertebrate communities. Analyses of taphonomic comparability among VMBs have often found significant differences in size and shape distributions, and thus considered them to be non-isotaphonomic. Such outcomes of “strict” statistical tests of isotaphonomy suggest discouraging limits on the potential for broad, comparative paleoecological reconstruction using VMBs. Yet it is not surprising that sensitive statistical tests highlight variations among VMB sites, especially given the general lack of clarity with regard to the definition of “strict” isotaphonomic comparability. We rigorously sampled and compared six VMB localities representing two distinct paleoenvironments (channel and pond/lake) of the Upper Cretaceous Judith River Formation to evaluate biases related to sampling strategies and depositional context. Few defining distinctions in bioclast size and shape are evident in surface collections, and most site-to-site comparisons of sieved collections are indistinguishable (p≤0.003). These results provide a strong case for taphonomic equivalence among the majority of Judith River VMBs, and bode well for future studies of paleoecology, particularly in relation to investigations of faunal membership and community structure in Late Cretaceous wetland ecosystems. The taphonomic comparability of pond/lake and channel-hosted VMBs in the Judith River Formation is also consistent with a formative model that contends that channel-hosted VMBs were reworked from pre-existing pond/lake assemblages, and thus share taphonomic history.

脊椎动物微化石骨层（Vertebrate microfossil bonebeds，VMBs）是指小型耐久脊椎动物硬体的局域富集体，学界常通过其研究获取罕被发现的小型类群，并记录古脊椎动物群落中的相对分类单元丰度与物种丰富度。针对VMBs间埋藏学可比性的分析常发现其尺寸与形状分布存在显著差异，因此认为这些骨层不满足同埋藏学条件。这类“严格”同埋藏学统计检验的结果，似乎限制了利用VMBs开展大范围对比古生态重建的潜力，不免令人沮丧。然而，敏感统计检验能凸显不同VMB位点间的差异，这并不出人意料——尤其是考虑到学界对“严格”同埋藏学可比性的定义普遍缺乏明确性。本研究对代表上白垩统朱迪河组两种不同古环境（河道与池塘/湖泊）的6处VMB位点开展了严格采样与对比，以评估采样策略与沉积背景相关的偏差。地表采集物中鲜见明确的生物碎屑尺寸与形状差异，而多数筛洗采集物的位点间比较结果并无显著区别（p≤0.003）。这些结果有力证明了朱迪河组多数VMBs具备埋藏学等效性，为后续古生态研究——尤其是针对晚白垩世湿地生态系统的动物群组成与群落结构研究——提供了良好基础。本研究中池塘/湖泊与河道赋存VMBs的埋藏学可比性，也与“河道VMBs是从预先存在的池塘/湖泊组合再沉积改造而来，因此共享埋藏学历史”的形成模式相一致。