Understanding animal terrestrialization, the process through which animals
colonized the land, is crucial to clarify extant biodiversity and biological
adaptation. Arthropoda (insects, spiders, centipedes and their allies) represent
the largestmajority of terrestrial biodiversity.Herewe implemented amolecular
palaeobiological approach, merging molecular and fossil evidence, to elucidate
the deepest history of the terrestrial arthropods. We focused on the three independent,
Palaeozoic arthropod terrestrialization events (those of Myriapoda,
Hexapoda and Arachnida) and showed that a marine route to the colonization
of land is the most likely scenario.Molecular clock analyses confirmed an origin
for the three terrestrial lineages bracketed between the Cambrian and the Silurian. While molecular divergence times for Arachnida are consistent with the fossil record,Myriapoda are inferred to have colonized land earlier, substantially predating trace or body fossil evidence. An estimated origin of myriapods by the Early Cambrian precedes the appearance of embryophytes and perhaps even terrestrial fungi, raising the possibility that terrestrialization had independent
origins in crown-group myriapod lineages, consistent with morphological arguments for convergence in tracheal systems. This article is part of the themed issue ‘Dating species divergences using rocks and clocks’.