The complex effects of mass extinctions on morphological disparity

Area of Science:

• Paleontology
• Evolutionary Biology
• Biodiversity Science

Background:

• Biodiversity studies over deep time reveal at least five mass extinctions in the last 500 million years.
• Species richness (diversity) changes during mass extinctions are well-documented.
• The impact of mass extinctions on morphological diversity (disparity) remains unclear, with diversity and disparity often decoupled.

Purpose of the Study:

• To model and understand changes in morphological disparity across mass extinctions.
• To investigate whether mass extinctions cause general patterns in morphological disparity.
• To differentiate between random and trait-selective mass extinctions' effects on disparity.

Main Methods:

• Developed simulations using continuous traits and birth-death trees to model disparity changes.
• Analyzed changes in trait range, variance, and morphospace occupation density.
• Assessed the impact of random versus trait-selective mass extinctions.

Main Results:

• The range of trait values consistently decreases after mass extinctions, regardless of selectivity.
• Variance and morphospace occupation density decline specifically after trait-selective mass extinctions.
• Identifying trait selectivity in mass extinctions remains methodologically challenging.

Conclusions:

• Mass extinctions impact morphological disparity in discernible ways, though patterns differ based on extinction selectivity.
• Trait selectivity in mass extinctions influences long-term evolutionary dynamics, favoring models beyond simple Brownian motion.
• Comprehensive analysis of morphospace occupation is essential for studying morphological evolution during mass extinctions.