[4] The proposed lower boundary is the first appearance of the trilobite Lotagnostus americanus around 491 million years ago, but other fossils are also being discussed (see below).
The upper boundary is defined as the appearance of the conodont Iapetognathus fluctivagus which marks the beginning of the Tremadocian and is radiometrically dated as 486.85 million years ago.
[9] The ICS is still discussing which geological section and biostratigraphic marker will be used to define the base of the 10th Cambrian stage.
[13] The first appearance of Eoconodontus notchpeakensis is favored by many authors because it is globally widespread and is independent of facies (known from continental rise to peritidal environments).
[6] The Eoconodontus notchpeakensis proposal would also incorporate a non-biostratigraphic marker to correlate the beginning of stage 10 globally.