Revisiting a landmark study-system: no evidence for a punctuated mode of evolution in Metrarabdotos

Is speciation generally a ‘special time’ in morphological evolution or are lineage splitting events just ‘more of the same’ where the end product happens to be two separate lineages? Data on evolutionary dynamics during anagenetic and cladogenetic events among closely related lineages within a clade are rare, but the fossil record of the bryozoan genus Metrarabdotos is considered a textbook example of a clade where speciation causes rapid evolutionary change against a backdrop of morphological stasis within lineages. Here, we point to some measurement theoretical and methodological issues in the original work on Metrarabdotos. We then reanalyze a subset of the original data that can be meaningfully investigated using similar quantitative statistical approaches as in the original studies. We consistently fail in finding variation in the evolutionary process during within-lineage evolution compared to cladogenetic events: Neither the rates of evolution, the strength of selection or the di...