The spiny water flea (Bythotrephes cederströmii), a freshwater crustacean considered to be the world’s best-studied invasive zooplankter, was first recorded in North America in the Laurentian Great Lakes during the 1980s. Its arrival is widely considered to be the result of ocean-going cargo ships that translocated contaminated ballast water from Eurasia to the Great Lakes during the 1970–1980s. The subsequent first discovery of the species in inland lakes is consistent with the hypothesis that propagules dispersed initially from established Great Lakes populations. Here we present evidence of exoskeletal remains, including mandibles, tail spines, and resting eggs, in ²¹⁰Pb-dated lake sediment cores, which suggests that B. cederströmii was already resident in four inland North American lakes (two in Minnesota, USA; two in Ontario, Canada) by at least the early 1900s. Densities of exoskeletal remains were low and relatively steady from first appearance until about 1990, after which time they increased in all cores. The earliest evidence that we found was a mandible at 33-cm depth (pre-1650) in the sediments of Three Mile Lake, Ontario, Canada. These unexpected findings challenge the current paradigm of B. cederströmii invasion, renew uncertainty about the timing and sequence of its colonization of North American lakes, and potentially question our ability to detect invasive species with traditional sampling methods. We attempted to eliminate errors in the dated stratigraphies of the exoskeletal remains that might have been introduced either methodologically (e.g., core-wall smearing) or naturally (e.g., bioturbation). Nonetheless, given the very low numbers of subfossils encountered, questions remain about the possible artifactual nature of our observations and therefore we regard our results as ‘preliminary findings’ at this time.

刺水蚤 ( Bythotrephes cederströmii ) 是一种淡水甲壳类动物，被认为是世界上研究最充分的入侵性浮游动物，于 20 世纪 80 年代首次在北美劳伦森五大湖中被记录。它的到来被广泛认为是 1970-1980 年代远洋货船将受污染的压载水从欧亚大陆转移到五大湖的结果。随后在内陆湖中首次发现该物种，这与繁殖体最初是从五大湖现有种群中分散的假设相一致。在这里，我们提供了^{210 个}铅测年湖泊沉积岩芯中外骨骼遗骸的证据，包括下颌骨、尾刺和休眠卵，这表明B. cederströmii已经生活在四个北美内陆湖泊中（两个在美国明尼苏达州；两个在美国明尼苏达州；两个在美国明尼苏达州）。至少在 1900 年代初就出现在加拿大安大略省。从首次出现到 1990 年左右，外骨骼遗骸的密度较低且相对稳定，此后所有核心的外骨骼遗骸密度均有所增加。我们发现的最早证据是加拿大安大略省三英里湖沉积物中 33 厘米深（1650 年之前）的下颌骨。这些意想不到的发现挑战了当前的B. cederströmii入侵模式，重新确定了其在北美湖泊定殖的时间和顺序，并可能质疑我们用传统采样方法检测入侵物种的能力。我们试图消除外骨骼遗骸的过时地层中的错误，这些错误可能是通过方法（例如，核心壁涂抹）或自然（例如，生物扰动）引入的。 尽管如此，鉴于遇到的亚化石数量非常少，我们的观察结果是否可能是人为的仍然存在疑问，因此我们目前将我们的结果视为“初步发现”。