Body size evolution in Mesozoic birds: little evidence for Cope's rule

Area of Science:

• Evolutionary Biology
• Paleontology
• Macroevolutionary Studies

Background:

• Cope's rule, a macroevolutionary generalization, posits a tendency for evolutionary increases in body size.
• Its applicability and identification are debated, particularly in the context of evolutionary directionality.
• A previous study claimed evidence for Cope's rule in Mesozoic birds, attributing it to among-lineage species sorting.

Purpose of the Study:

• To reassess the evidence for Cope's rule in Mesozoic birds.
• To investigate both among- and within-lineage patterns of body size evolution.
• To evaluate the robustness of previous findings using phylogenetic methods.

Main Methods:

• Reanalysis of a prior study on Mesozoic bird body size evolution.
• Application of nonphylogenetic and phylogenetic comparative methods.
• Ancestor-descendant analyses incorporating current phylogenetic hypotheses.

Main Results:

• Nonphylogenetic methods used previously are insufficient to distinguish between among- and within-lineage processes.
• Statistical support for the prior study's conclusions regarding Cope's rule was found to be weak.
• Within-lineage analyses incorporating phylogenetic data revealed little compelling evidence for Cope's rule in Mesozoic birds.

Conclusions:

• Cope's rule is not supported by available data for Mesozoic birds.
• Body size evolution in this group does not currently offer insights into survival during the Cretaceous-Paleogene mass extinction.
• Methodological limitations in prior studies may have led to erroneous conclusions about macroevolutionary trends.