Cambrian Stage 3

Cambrian Stage 3 is the third part of the Cambrian period, but it does not have an official name yet. It comes after Cambrian Stage 2 and before Cambrian Stage 4. Scientists plan to mark the start of this stage by the first appearance of trilobites, tiny sea creatures with hard shells, which appeared about 521 million years ago. The end of Cambrian Stage 3 is informally marked by the first appearance of certain trilobite groups, such as Olenellus or Redlichia, around 514.5 million years ago.

Even though this stage does not have a name, it is very important in Earth's history. This time includes famous fossil sites like the Chengjiang biota and the Sirius Passet biota, which show us many different kinds of ancient life that lived in the oceans long ago. These fossils 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. This stage is often called the "Atdabanian" by geologists who study rocks in Siberia.

Biostratigraphy

The oldest known trilobite is called Lemdadella, and 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, where many animal groups like arthropods, molluscs, lophophorates, and chordates (which include vertebrates) began to appear and diversify.