Cambrian Stage 10

Stage 10 of the Cambrian is the last and still-unnamed part of the Furongian series. It comes after the Jiangshanian and right before the Ordovician Tremadocian Stage. Scientists suggest that the beginning of Stage 10 is marked by the first appearance of a special trilobite called Lotagnostus americanus, which lived about 491 million years ago. However, they are also looking at other fossils to help define this boundary.

The end of Stage 10 is marked by the appearance of a conodont named Iapetognathus fluctivagus. This tiny fossil helps scientists know when the Tremadocian Stage of the Ordovician began, which happened around 486.85 million years ago. Studying these ancient fossils helps us understand how life on Earth changed and evolved long ago.

Naming

The 10th stage of the Cambrian has not yet received an official name from the ICS, though several local names are used. Some scientists suggest calling it the "Lawsonian," named after Lawson Cove in the Wah Wah Mountains of Utah. Another name that fits this time period is the North American Skullrockian Stage. In 2011, a third name, "Nelegerian," was proposed, after the Neleger River in Yakutia.

Stratotype

The ICS is still deciding which rock layer and fossil marker will define the start of the 10th Cambrian stage.

One suggestion was a site near Duibian in Zhejiang, China. But many scientists now prefer a site called Steamboat Pass in the House Range of Utah. If they use a special type of ancient tooth called a conodont, many more places could work, like sites in Australia, Kazakhstan, and Canada. Scientists are looking at different fossils, such as the first appearance of a type of trilobite called Lotagnostus americanus, or another ancient tooth called Cordylodus andresi. Many like the idea of using Eoconodontus notchpeakensis because it can be found all over the world, no matter where the rocks were formed. This choice would also use a special change in carbon to help match the start of this stage everywhere.

Subdivisions

Cambrian Stage 10 can be divided into smaller parts using different groups of ancient life. Scientists look at special types of tiny teeth from ancient sea creatures called conodonts to help sort these parts. They also study trilobites, which were like bugs with hard shells, to further understand how this stage can be split into smaller sections.