Modularity is a hallmark of molecular evolution. Whether considering gene 
regulation, the components of metabolic pathways or signaling cascades, the 
ability to reuse autonomous modules in different molecular contexts can expedite 
evolutionary innovation. Similarly, protein domains are the modules of proteins, 
and modular domain rearrangements can create diversity with seemingly few 
operations in turn allowing for swift changes to an organism's functional 
repertoire. Here, we assess the patterns and functional effects of modular 
rearrangements at high resolution. Using a well resolved and diverse group of 
pancrustaceans, we illustrate arrangement diversity within closely related 
organisms, estimate arrangement turnover frequency and establish, for the first 
time, branch-specific rate estimates for fusion, fission, domain addition and 
terminal loss. Our results show that roughly 16 new arrangements arise per 
million years and that between 64% and 81% of these can be explained by simple, 
single-step modular rearrangement events. We find evidence that the frequencies 
of fission and terminal deletion events increase over time, and that modular 
rearrangements impact all levels of the cellular signaling apparatus and thus 
may have strong adaptive potential. Novel arrangements that cannot be explained 
by simple modular rearrangements contain a significant amount of repeat domains 
that occur in complex patterns which we term "supra-repeats". Furthermore, these 
arrangements are significantly longer than those with a single-step 
rearrangement solution, suggesting that such arrangements may result from 
multi-step events. In summary, our analysis provides an integrated view and 
initial quantification of the patterns and functional impact of modular protein 
evolution in a well resolved phylogenetic tree. This article is part of a 
Special Issue entitled: The emerging dynamic view of proteins: Protein 
plasticity in allostery, evolution and self-assembly.