Silurian graptolite biofacies on Arctic Canada: taxonomy, biostratigraphy, biogeography, paleoenvironments and evolution

加拿大北极群岛的志留纪（约4.45亿至4.15亿年），与当时世界的其他地方一样，被许多不寻常的生物占据，包括一个非常丰富的海洋浮游动物的优势群体，笔石。笔石演化非常迅速，在志留纪期间，现有物种消失，新物种频繁出现，使它们成为将志留纪地质柱细分为许多精细时间切片的绝佳化石，这一过程被称为生物地层学。北极群岛的笔石虽然贯穿整个志留纪岩石序列，但与其他地方一样，它们的保存方式在世界上几乎是独一无二的：它们最初的3D骨骼材料被包裹在石灰石结核中，并且很容易通过将岩石溶解在稀酸中提取，产生保存完好的标本。因此，北极笔石序列被认为是世界上最好的笔石序列之一。出于这个原因，我多年来一直在研究，并继续研究这些保存完好的笔石。新发现的材料的程序如下：首先检查它们的形态，以获得关于它们形态和物种识别的新信息，其次是不断发展和完善它们的生物地层学，以便与世界其他地方岩石的精细时间切片进行比较和相关，最后从这个背景中推进它们进化历史的知识。笔石在志留纪期间见证了一系列的大规模灭绝。一个在北极很明显的事件，见证了50个灭绝前物种突然减少到只有两个灭绝后物种，并且与海平面的强烈下降相吻合，也与碳13的强烈增加。未来的研究将更详细地研究这一点，并将研究扩展到志留纪早期和晚期的灭绝事件，目的是更好地了解浮游生物灭绝的性质，以及一般的灭绝。最后，我的首要目标，同时继续了解更多关于笔石及其栖息地，是扩大知识，以帮助了解地质和生物历史，包括气候，在志留纪时期的加拿大北极。

The Silurian (~445 to 415 million years) of the Canadian Arctic Islands, as elsewhere in the then-existing world, were occupied by many unusual organisms, including one dominant group of very abundant marine plankton animals, the graptolites. Graptolites evolved very rapidly and through the Silurian existing species disappeared and new species appeared very frequently, making them excellent fossils to subdivide the Silurian geologic column into many fine time slices, a procedure known as biostratigraphy. The graptolites of the Arctic Islands while continuous through the entire Silurian rock sequence, as is normal elsewhere, are virtually unique in the world in their mode of preservation: their original 3D skeletal material is encased within limestone concretions, and are easily extracted by dissolving the rock in dilute acid, yielding beautifully preserved specimens. As such, the Arctic graptolite sequence is considered to be one of the best in the world. For that reason, I have for years studied, and continue to study, these beautifully preserved graptolites. The procedure for newly recovered material continues as follows: firstly examination of their morphology for new information on their morphology and for species recognition, secondly the continual process of the development and refinement of their biostratigraphy to enable comparison and correlation with the fine time slices of rock elsewhere in the world, and finally from this background to advance the knowledge of their evolutionary history. Graptolites witnessed a number of mass extinctions during the Silurian. One event, well marked in the Arctic, witnessed the abrupt reduction of 50 pre-extinction species to only two post-extinction species, and coincided with a strong drop in sea level, and also with a strong increase Carbon 13. Future studies will examine this in more detail, and extend studies into earlier and later Silurian extinction events, with the goal of better understanding the nature of plankton extinction, and of extinctions in general. Finally, my overriding goal while continuing to learn more about graptolites and their habitats, is to extend that knowledge to help understand the geological and biological history, including climate, of the Arctic Canada during the Silurian Period.