In 2011 a paper published in the journal Nature Communications on two harvestmen fossils uses expressions like “surprisingly modern”, “remarkable similarities”, “extensive morphological stasis” and "fully modern body plans", suggesting that the long-legged creatures have hardly changed at all in “305 million years.”
The authors begin with some background information:
“Harvestmen, the third most-diverse arachnid order, are an ancient group found on all continental landmasses, except Antarctica. However, a terrestrial mode of life and leathery, poorly mineralized exoskeleton makes preservation unlikely, and their fossil record is limited. The few Palaeozoic species discovered to date appear surprisingly modern, but are too poorly preserved to allow unequivocal taxonomic placement.”
Then they highlight the importance of their discovery:
“Here, we use high-resolution X-ray micro-tomography to describe two new harvestmen from the Carboniferous (~305 Myr) of France. The resulting computer models allow the first phylogenetic analysis of any Palaeozoic Opiliones, explicitly resolving both specimens as members of different extant lineages, and providing corroboration for molecular estimates of an early Palaeozoic radiation within the order. Furthermore, remarkable similarities between these fossils and extant harvestmen implies extensive morphological stasis in the order. Compared with other arachnids—and terrestrial arthropods generally—harvestmen are amongst the first groups to evolve fully modern body plans.”
Charles Darwin could hardly have anticipated how rapidly the list of living fossils would evolve 150 years after The Origin of Species.
Garwood, Russell J., Jason A. Dunlop, Gonzalo Giribet and Mark D Sutton. 2011. Anatomically modern Carboniferous harvestmen demonstrate early cladogenesis and stasis in Opiliones. Nature Communications 2: 444.