Evolutionary History
Fossils from the early Cambrian bear a striking resemblance to the velvet worms. These fossils, known collectively as the lobopods, were marine and probably represent a stem group to the onychophorans. They are found in the Cambrian, Ordovician, Silurian and Pennsylvanian periods.
Historically, all fossil Onychophora and lobopods were lumped into the taxon Xenusia, further subdivided by some authors to the Paleozoic Udeonychophora and the Mesozoic/Tertiary Ontonychophora; living Onychophora were termed Euonychophora.
It is not clear when the transition to a terrestrial existence was made, but it is considered plausible that it took place between the Ordovician and late Silurian—approximately 490 to 430 million years ago—via the intertidal zone.
The low preservation potential of the non-mineralised Onychophora means that they have a sparse fossil record, and crown group representatives are known only from amber—there is a single, partial specimen from the Cretaceous, and a more comprehensive record in Eocene deposits from 40 million years ago.
Read more about this topic: Onychophora
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