Early bursts of disparity and the reorganization of character integration

‘Early bursts' of morphological disparity (i.e. diversity of anatomical types) are common in the fossil record. We typically model such bursts as elevated early rates of independent character change. Developmental theory predicts that modules of linked characters can change together, which would mimic the effects of elevated independent rates on disparity. However, correlated change introducing suboptimal states should encourage breakup (parcellation) of character suites allowing new (or primitive) states to evolve until new suites arise (relinkage). Thus, correlated change–breakup–relinkage presents mechanisms for early bursts followed by constrained evolution. Here, I analyse disparity in 257 published character matrices of fossil taxa. For each clade, I use inverse-modelling to infer most probably rates of independent change given both time-homogeneous and separate ‘early versus late' rates. These rates are used to estimate expected disparity given both independent change models. The correlated change–breakup–relinkage model also predicts elevated frequencies of compatible character state-pairs appearing out of order in the fossil record (e.g. 01 appearing after 00 and 11; = low stratigraphic compatibility), as one solution to suboptimal states induced by correlated change is a return to states held before that change. As predicted by the correlated change–breakup–relinkage model, early disparity in the majority of clades bot...

Source: Proceedings of the Royal Society B: Biological Sciences - November 14, 2018 Category: Biology Authors: Wagner, P. J. Tags: palaeontology, developmental biology, evolution Palaeobiology Source Type: research