Wuliuan

The Wuliuan is an important time period in Earth's history. It was the fifth stage of the Cambrian period and the first stage of the Miaolingian Series. Scientists officially defined it in 2018. The start of the Wuliuan is marked by the first appearance of a special trilobite called Oryctocephalus indicus, and it ends when another trilobite, Ptychagnostus atavus, first appears, about 504.5 million years ago.

The exact spot that marks the beginning of the Wuliuan is in a place called the Wuliu-Zengjiayan section of the Kaili formation, near Balang Village in the Miaoling Mountains of Guizhou, China. This spot is known as the 'golden spike' and helps scientists around the world identify this important time in Earth's past.

GSSP

Three places were considered to mark the start of the Wuliuan stage: near Balang in Guizhou province (China), Split Mountain in Nevada (USA), and along the Molodo river in Russia. Scientists chose the Wuliu-Zengjiayan section in China as the official location in 2018. They decided that the first appearance of a trilobite called Oryctocephalus indicus would be the marker to define the beginning of this stage.

Major events

The start of the Wuliuan stage marks an important moment for tiny sea creatures called trilobites. At this time, a group of trilobites known as the Olenellids disappeared in an event called the Olenellid Biomere boundary. This change in the ancient sea life happened along with a shift in the chemistry of carbonate rocks.

Paleontology

During the Wuliuan time, many different kinds of ancient sea creatures lived and left fossils behind. One group, called graptolites, became very diverse and one type, Sphenoecium, was found all around the world. We also know of many other sea animals from this time, such as trilobites, agnostoids, hurdiids, and bradoriids, all of which lived in the oceans long ago.