Carboniferous Onychophora from Montceau-les-Mines, France, and onychophoran terrestrialization.

The geological age of the onychophoran crown-group, and when the group came onto land, have been sources of debate. Although stem-group Onychophora have been identified from as early as the Cambrian, the sparse record of terrestrial taxa from before the Cretaceous is subject to contradictory interpretations. A Late Carboniferous species from the Mazon Creek biota of the USA, Helenodora inopinata, originally interpreted as a crown-group onychophoran, has recently been allied to early Cambrian stem-group taxa. Here we describe a fossil species from the Late Carboniferous Montceau-les-Mines Lagerstätte, France, informally referred to as an onychophoran for more than 30 years. The onychophoran affinities of Antennipatus montceauensis gen. nov., sp. nov. are indicated by the form of the trunk plicae and the shape and spacing of their papillae, details of antennal annuli, and the presence of putative slime papillae. The poor preservation of several key systematic characters for extant Onychophora, however, prohibits the precise placement of the Carboniferous fossil in the stem or crown of the two extant families, or the onychophoran stem-group as a whole. Nevertheless, A. montceauensis is the most compelling candidate to date for a terrestrial Paleozoic onychophoran.