Morphological complexity promotes origination and extinction rates in ammonoids

Area of Science:

• Paleontology
• Evolutionary Biology
• Macroevolution

Background:

• Heterogeneity in evolutionary rates is a central question in macroevolution.
• Morphological traits, including complexity, are known to influence evolutionary rates, but the precise relationship remains unclear.
• Ammonoids, a well-studied fossil group with complex conch structures, exhibit significant variation in turnover rates, making them ideal for studying morphology-evolutionary rate links.

Purpose of the Study:

• To establish a quantitative method for assessing ornamental complexity in ammonoids.
• To investigate the relationship between morphological complexity and evolutionary turnover rates (origination and extinction) in ammonoids.
• To understand how morphological complexity affects ammonoid diversification dynamics.

Main Methods:

• Development of a quantitative measure: the two-dimensional ornamentation index (2D-OI).
• Application of the 2D-OI to describe the ornamental complexity of ammonoid taxa.
• Analysis of the correlation between 2D-OI values and ammonoid origination/extinction rates across different spatiotemporal scales and clades.

Main Results:

• Morphologically complex ammonoid genera and species exhibited higher origination and extinction rates compared to simpler taxa.
• Diversity fluctuations in ammonoids with complex ornamentation significantly influenced overall net diversification rates.
• A positive correlation was found between morphological complexity and turnover rates in ammonoids.

Conclusions:

• Morphological complexity in ammonoids acts as a 'double-edged sword,' promoting rapid evolution while increasing extinction risk.
• The study provides a novel quantitative method (2D-OI) for assessing morphological complexity in fossils.
• Understanding the interplay between morphological complexity and diversification is crucial for comprehending species survival over geological timescales.