Metazoan phylogenies: falling into place or falling to pieces? A palaeontological perspective

Metazoan phylogeny is in a state of ferment, stirred by the addition of new molecular trees as well as controversial interpretations of molecular ‘clocks’. Concerning the latter topic, the clocks recurrently point to divergence times substantially older than the known fossil record. Some attempt reconciliation by appealing to a conveniently cryptic interval prior to the first fossils. This effectively reduces the fossil record to an erratic search-light giving only glimpses into the true evolutionary history. Other options, however, remain open. Molecular clocks may themselves run erratically and what happens in molecular history may not coincide with the emergence of body plans.