Cambrian Stage 3 is the third, unnamed stage of the Cambrian period. It follows Cambrian Stage 2 and is followed by Cambrian Stage 4. However, the exact start and end points of Cambrian Stage 3 have not been officially set. Scientists plan to use the first appearance of trilobites, about 521 million years ago, as a reference for its lower boundary. However, because trilobites appeared at different times in different parts of the world, a different, globally consistent marker is needed to define the base. The upper boundary of Cambrian Stage 3 and the start of Cambrian Stage 4 are informally marked by the first appearance of the trilobite genera Olenellus or Redlichia around 514.5 million years ago.

Although Cambrian Stage 3 has no official name, it is significant because it includes important fossil collections, such as the Chengjiang biota and the Sirius Passet biota.

Naming

The International Commission on Stratigraphy has not given an official name to the third stage of the Cambrian. This stage is similar to the "Atdabanian," which is used by scientists who work in Siberia.

Biostratigraphy

The oldest known trilobite is Lemdadella, which first appears in the Fallotaspis zone. This marks the end of the Cambrian radiation of animal groups, following the development and appearance of arthropods, molluscs, lophophorates, chordates (including vertebrates), and others.