This one’s awesome, evo/devo nerds: in the uppermost Ediacaran Dengying Formation (in the Three Gorges region of China, with the formation apparently centered in or largely in Guizhou province), Phys.org is reporting that researchers from Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences and Virginia Tech have found footprints arranged in two irregular but separate rows that are almost certainly the result of an ancient bilaterian traveling over the sea floor.
The Dengying Formation is contiguous with and immediately overlying the more famous Doushantuo Formation, a known Lagerstätte that has provided invaluable (though frequently disputed) insights into the middle-Ediacaran Chinese biota. While the Dengying is by definition pre-cambrian, the layer is dated to the last 10 million years of the Ediacaran, so while the new ichnites almost certainly are the oldest known bilaterian footprints, they don’t beat out the early Cambrian fossils by more than several million years – a long time for sure in absolute terms, but the difference is not large either as a percentage of the total ages or even in evolutionary terms when discussing the time needed to assemble a new body plan.
Overall, this new research supports the view that bilaterians existed as separate populations from other animals long before the dawn of the Cambrian and that even the relatively sudden increase in bilaterian diversity during the first tens of millions of years of the Cambrian (from its start to the time of the Burgess Shale Lagerstätte) is likely to be partly explained by an increase in biomineralization among some animals with largely pre-Cambrian body plans. It is my uninformed, inexpert opinion that this is a non-controversial view. Though not being a biologist, I could easily be wrong.
Despite the fact that we should expect that some leggy bilaterians existed in the Ediacaran, finding the hard evidence is very exciting, and I do think it says something about the evolution of novel body plans that these ichnites are being found several million years before the start of the Cambrian and not twenty-five million years prior (as in the Mistaken Point Avalonian assemblage) or earlier. Though the Doushantuo fossils have often inspired fierce debate over proper interpretation, the clear photos (available in Phys.org’s story) look pretty unlikely to my amateur eye to have been made through abiologic processes and I have no reason to think that the interpretation of these rock markings as bilaterian ichnites will cause the same uproar as did identifying microscopic Doushantuo fossils as 570mya bilaterian larvae.
In short: Hordes of Freuding Freudians, Batman: fossil footprints of bilaterians in the pre-Cambrian! Thank goodness the trackways don’t show hopping behavior or we’d really be in the sediment without a burrowing-capable body plan!
If you’re more informed than I, you can and should read the original paper from Science Advances.