Data from: Cope’s Rule in a modular organism: directional evolution without an overarching macroevolutionary trend

Cope’s Rule describes increasing body size in evolutionary lineages
through geological time. This pattern has been documented in unitary
organisms but does it also apply to module size in colonial organisms? We
address this using 1169 cheilostome bryozoans ranging through the entire
150 million years of their evolutionary history. The temporal pattern
evident in cheilostomes as a whole shows no overall change in zooid
(module) size. However, individual subclades show size increases: within a
genus, younger species often have larger zooids than older species.
Analyses of (paleo)latitudinal shifts show that this pattern cannot be
explained by latitudinal effects (Bergmann’s Rule) coupled with younger
species occupying higher latitudes than older species (an ‘out of the
tropics’ hypothesis). While it is plausible that size increase was linked
to the advantages of large zooids in feeding, competition for trophic
resources and living space, other proposed mechanisms for Cope’s Rule in
unitary organisms are either inapplicable to cheilostome zooid size or
cannot be easily evaluated. Patterns and mechanisms in colonial organisms
cannot and should not be extrapolated from the better-studied unitary
organisms. And even if macroevolution simply comprises repeated rounds of
microevolution, evolutionary processes occurring with lineages are not
always detectable from macroevolutionary patterns.