Convergent evolution of giant size in eurypterids

Eurypterids, Paleozoic marine and freshwater arthropods commonly known as
sea scorpions, repeatedly evolved to remarkable sizes (over 0.5 m in
length) and repeatedly colonized continental aquatic habitats. We compiled
data on the majority of eurypterid species and explored several previously
proposed explanations for the evolution of giant size in the group
including the potential role of habitat, sea surface temperature and
dissolved sea surface oxygen levels using a phylogenetic comparative
approach with a new tip-dated tree. Overall, there is no compelling
evidence that the evolution of giant size was driven by temperature or
oxygen levels, nor that it was coupled with the invasion of continental
aquatic environments, latitude, or local faunal diversity. Eurypterid body
size evolution is best characterized by rapid bursts of change that
occurred independently of habitat or environmental conditions. Intrinsic
factors likely played a larger role than previously recognized in
determining the convergent origin of gigantism in eurypterids.