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[dinosaur] Pterosauria body size evolution: Bergmann’s rule and Cope’s rule

Ben Creisler

A recent paper:

Fabricio Villalobo, Miguel Á. Olalla-Tárraga, Cleiber Marques Vieira, Nicholas Diniz Mazzei and Luis Mauricio Bini (2017)
Spatial dimension of body size evolution in Pterosauria: Bergmann’s rule does not drive Cope’s rule.
Evolutionary Ecology Research 18: 169-186 


Background: Little is known about the existence or validity of ecogeographical rules – spatial patterns in biological traits – over geological time scales and in extinct clades. Some have claimed that pterosaurs, a Mesozoic clade of flying reptiles, follow Cope’s rule – the trend of increasing body size through time – yet no conclusive explanations for this rule have been provided and some explanations even converge with those about Bergmann’s rule: the tendency of species to be larger in colder environments.

Goals: Determine whether Bergmann’s rule exists in pterosaur reptiles over their evolutionary history, and discuss its potential association with Cope’s rule.

Data: Previously published morphological, phylogenetic, and geographic occurrence data of Pterosauria.

Search methods: We applied cross-species and assemblage-based approaches along with phylogenetic comparative methods as well as sister-pair comparisons to evaluate the validity of Bergmann’s rule in Pterosauria.

Conclusions: Pterosaurian body size did not follow Bergmann’s rule during the Triassic-Jurassic. But a converse Bergmann’s rule may have been present during the Cretaceous. There is no strong evidence to support an influence of Bergmann’s rule in the evolution of pterosaurian body size. Therefore, Cope’s rule in Pterosauria seems to be a mechanistically independent macroevolutionary pattern.