Amber preserves an exceptional record of tiny, soft-bodied organisms and chemical environmental signatures, elucidating the evolution of arthropod lineages and the diversity, ecology, and biogeochemistry of ancient ecosystems. However, globally, fossiliferous amber deposits are rare in the latest Cretaceous and surrounding the Cretaceous-Paleogene (K-Pg) mass extinction. This faunal gap limits our understanding of arthropod diversity and survival across the extinction boundary. Contrasting hypotheses propose that arthropods were either relatively unaffected by the K-Pg extinction or experienced a steady decline in diversity before the extinction event followed by rapid diversification in the Cenozoic. These hypotheses are primarily based on arthropod feeding traces on fossil leaves and time-calibrated molecular phylogenies, not direct observation of the fossil record. Here, we report a diverse amber assemblage from the Late Cretaceous (67.04 ± 0.16 Ma) of the Big Muddy Badlands, Canada. The new deposit fills a critical 16-million-year gap in the arthropod fossil record spanning the K-Pg mass extinction. Seven arthropod orders and at least 11 insect families have been recovered, making the Big Muddy amber deposit the most diverse arthropod assemblage near the K-Pg extinction. Amber chemistry and stable isotopes suggest the amber was produced by coniferous (Cupressaceae) trees in a subtropical swamp near remnants of the Western Interior Seaway. The unexpected abundance of ants from extant families and the virtual absence of arthropods from common, exclusively Cretaceous families suggests that Big Muddy amber may represent a yet unsampled Late Cretaceous environment and provides evidence of a faunal transition before the end of the Cretaceous.

中文翻译：

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加拿大新的琥珀矿床填补了白垩纪末期大灭绝化石记录的空白

琥珀保存了微小软体生物和化学环境特征的特殊记录，阐明了节肢动物谱系的进化以及古代生态系统的多样性、生态和生物地球化学。然而，在全球范围内，白垩纪晚期和白垩纪-古近纪（K-Pg）大灭绝周围的含化石琥珀矿床很少见。这种动物区系的差距限制了我们对节肢动物多样性和跨越灭绝边界的生存的理解。对比假设提出，节肢动物要么相对不受 K-Pg 灭绝的影响，要么在灭绝事件之前经历了多样性的稳步下降，随后在新生代迅速多样化。这些假设主要基于化石叶子上的节肢动物进食痕迹和时间校准的分子系统发育，而不是对化石记录的直接观察。在这里，我们报告了加拿大大泥泞荒地晚白垩世（67.04 ± 0.16 Ma）的多样化琥珀组合。这个新矿床填补了跨越 K-Pg 大规模灭绝的节肢动物化石记录中长达 1600 万年的关键空白。已发现 7 个节肢动物目和至少 11 个昆虫科，使大泥泞琥珀矿床成为 K-Pg 灭绝附近最多样化的节肢动物组合。琥珀化学和稳定同位素表明，琥珀是由西部内陆航道遗迹附近亚热带沼泽中的针叶树（柏科）产生的。现存蚂蚁科出乎意料地大量存在，而白垩纪常见科中几乎没有节肢动物，这表明大泥琥珀可能代表了一个尚未采样的白垩纪晚期环境，并提供了白垩纪末之前动物群转变的证据。