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Clades reach highest morphological disparity early in their evolution
Martin Hughes1, Sylvain Gerber, Matthew Albion Wills
1Department of Biology and Biochemistry, University of Bath, Bath BA2 7AY, United Kingdom.
Summary
Most animal groups show maximum morphological variety early in their evolutionary history, a pattern called early high disparity. This trend persists across the Phanerozoic, independent of mass extinctions.
Area of Science:
- Evolutionary Biology
- Paleontology
- Macroevolutionary Studies
Background:
- Macroevolutionary trends are often difficult to verify.
- The concept of 'early high disparity' suggests clades reach peak morphological variety early in their history.
Purpose of the Study:
- To test the hypothesis of early high disparity in metazoan clades.
- To analyze disparity profiles across the Phanerozoic and their relationship with mass extinctions.
Main Methods:
- Meta-analysis of 98 metazoan clades.
- Quantification of disparity profiles using center of gravity (CG).
- Resampling tests to assess statistical significance of CG values.
Main Results:
- A significantly bottom-heavy mean CG (early high disparity) was observed in clades not ending at mass extinctions.
- Clades terminating at mass extinctions showed truncated, top-heavy CG profiles.
- Early high disparity is the predominant pattern throughout the Phanerozoic, with no clear temporal trend in profile shapes.
Conclusions:
- The study confirms early high disparity as a predominant macroevolutionary pattern.
- The findings suggest that the evolution of key early-stage traits (apomorphies) may drive this pattern, rather than ecological factors like ecospace clearing after extinctions.
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