Jiangshanian

The Jiangshanian is an important time period in Earth's history, part of the middle section of the Furongian series. It came after the Paibian Stage and was followed by an unnamed stage called Stage 10 during the Cambrian period. Scientists define the beginning of the Jiangshanian by the first appearance of a special kind of trilobite called Agnostotes orientalis. This happened about 494.2 million years ago, and the Jiangshanian lasted until around 491 million years ago.

This stage gets its name from the city of Jiangshan in Zhejiang province, China. It was here that scientists chose the global reference point, called a GSSP, to mark the start of this important time in the fossil record. The Jiangshanian helps scientists understand how life on Earth was changing during this part of the Cambrian explosion, when many new types of animals were appearing in the oceans.

Stratigraphy

The Jiangshanian is a middle stage of the Furongian series in the Cambrian period. Its beginning is marked by the first appearance of a trilobite called Agnostotes orientalis, which happened about 494.2 million years ago.

Scientists have chosen a place called the Duibian B Section, west of the village of Duibian and north of Jiangshan, as the main location to define this stage. Another possible location near the Kyrshabakty River in southern Kazakhstan was suggested but is still under discussion.

Major events

At the start of the Jiangshanian time, there was a big increase in the number of different species, similar to what happened in the middle of the Guzhangian. After this, a period known as the Jiangshanian extinction happened, lasting from about 493.9 to 491.3 million years ago. This event decreased the number of species by about 55.2%. Following this, there were smaller changes in the number of species until the start of the Ordovician period.

Paleontology

Scientists have discovered nearly 50 different groups of ancient animals and plants from the Jiangshanian time period. These fossils come from places like the Sandu Formation in Guangxi, South China, and the Wiśniówka Sandstone Formation in Poland. The fossils include simple plants called algae, small sea animals called graptolites, and many types of arthropods, which are animals with exoskeletons and jointed legs, like aglaspidid and mollisoniid forms.

Fossils of trilobites, which are extinct sea creatures with hard shells, have also been found in places such as western Tasmania and the Wichita Mountains in Oklahoma, USA. Some of the trilobite groups found include Parabolina, Hedinaspis, Eugonocare, and Cermatops. These discoveries help scientists understand what the world was like millions of years ago.