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

与当时世界上其他地方一样，加拿大北极群岛的志留纪(约4.45亿至4.15亿年)被许多不寻常的生物占据，其中包括一种非常丰富的海洋浮游动物的优势类群--笔石。笔石演化非常迅速，在志留纪，现有物种消失了，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片的极佳化石，这一过程被称为生物地层学。北极群岛的笔石虽然像其他地方一样在整个志留纪岩层中连续存在，但在它们的保存模式上几乎是世界上独一无二的：它们最初的3D骨骼材料被包裹在石灰岩结核中，通过将岩石溶解在稀酸中很容易提取，产生了保存完好的标本。因此，北极笔石序列被认为是世界上最好的序列之一。出于这个原因，我多年来一直在研究这些保存完好的笔石，并将继续研究。对新发现的物质的程序继续如下：首先检查其形态，以获得有关其形态和物种识别的新信息，其次是不断发展和完善其生物地层学，以便能够与世界其他地方的岩石细碎时间片进行比较和对比，最后从这一背景提高对其进化史的认识。志留纪期间，笔石见证了许多物种的大规模灭绝。在北极的一次事件中，50个灭绝前的物种突然减少到只有两个灭绝后物种，恰逢海平面大幅下降，碳13大幅增加。未来的研究将更详细地研究这一点，并扩展对志留纪早期和晚期物种灭绝事件的研究，目的是更好地了解浮游生物灭绝的性质，以及总体上的灭绝。最后，在继续学习更多关于笔石及其栖息地的同时，我的首要目标是扩展这些知识，以帮助了解加拿大北极地区在志留纪期间的地质和生物历史，包括气候。

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.