Cambrian Stage 3

Cambrian Stage 3 is the third part of the Cambrian period. It does not have an official name yet. It comes after Cambrian Stage 2 and before Cambrian Stage 4.

Scientists mark the start of this stage by the first appearance of trilobites. Trilobites were tiny sea creatures with hard shells. They appeared about 521 million years ago. The end of Cambrian Stage 3 is marked by the first appearance of certain trilobite groups, such as Olenellus or Redlichia, around 514.5 million years ago.

This stage is very important in Earth's history. It includes famous fossil sites like the Chengjiang biota and the Sirius Passet biota. These fossils show many different kinds of ancient life that lived in the oceans long ago. They help scientists understand how life on our planet developed and changed over millions of years.

Naming

The International Commission on Stratigraphy has not given an official name to the third stage of the Cambrian period. Many geologists call this stage the "Atdabanian" when they study rocks in Siberia.

Biostratigraphy

The oldest known trilobite is called Lemdadella. It appears at the start of the Fallotaspis zone. This stage marks the end of a big change in life on Earth, called the Cambrian radiation. Many animal groups like arthropods, molluscs, lophophorates, and chordates (which include vertebrates) began to appear and diversify.