Preservation bias obscures gradual Ordovician reef evolution

Area of Science:

• Paleontology
• Stratigraphy
• Evolutionary Biology

Background:

• The Great Ordovician Biodiversification Event (GOBE) is traditionally viewed as an abrupt diversification of reef-building metazoans.
• This apparent burst challenges gradual evolutionary models.
• The GOBE's timing, around 460 million years ago, suggests a rapid evolutionary event.

Purpose of the Study:

• To investigate the role of preservation biases in the perceived suddenness of the GOBE.
• To re-evaluate the evolutionary trajectory of early reef-builders.
• To understand the impact of stratigraphic incompleteness on interpreting major evolutionary events.

Main Methods:

• Integration of stratigraphic data with fossil occurrence records.
• Analysis of unconformities and sea-level fluctuations during the Middle Ordovician.
• Correlation between carbonate deposition, preservation, and reef-builder occurrences.

Main Results:

• The apparent GOBE burst is largely an artifact of a global sea-level fall (~475 to 460 Ma).
• Widespread unconformities and erosion during this period erased the fossil record of early reef-builders.
• Minimal carbonate deposition and fossil occurrences during the Dapingian Stage (471–469 Ma) highlight preservation biases.

Conclusions:

• The GOBE was not a discrete evolutionary event but a continuous trajectory influenced by sea-level fluctuations.
• Stratigraphic incompleteness, termed the "Sppil-Rongis effect," distorted the understanding of GOBE in reef ecosystems.
• Early reef-builders likely diversified earlier than previously thought, with their record obscured by geological processes.