[2][3] Neither the upper nor lower boundary has yet been defined by the International Commission on Stratigraphy.
[4][5] The preferred definitions for the lower boundary are the first appearance of the molluscs Watsonella crosbyi or Aldanella attleborensis around 529 million years ago.
[6][7] The correlation between the lowest occurrences of A. attleborensis and W. crosbyi with the Zhujiaqing positive carbon isotope excursion (ZHUCE) has led to the conclusion that the combination of these two markers are a reliable indicator of the boundary between the Fortunian and Stage 2.
[8] The proposed upper boundary might be the first appearance of trilobites around 521 million years ago.
[4] The name "Laolinian" after the Laolin village in Yunnan, China, was proposed for the Stage 2 in 2012.