It’s hard to get a bearing on the kind of organisms that existed before life absolutely exploded onto the scene during the Cambrian Period. Fossils from the Ediacaran Period before that are relatively scant, since lifeforms hadn’t yet evolved the kinds of shells and body types that fossilize easily, but they did leave other traces of themselves behind. Now, paleontologists have discovered a set of tiny fossilized burrows, created by some of the earliest complex organisms more than half a billion years ago.

http://newatlas.com/fossil-worms-oldest-complex-life/51295/?utm_source=Gizmag+Subscribers&utm_campaign=0019c1b0bf-UA-2235360-4&utm_medium=email&utm_term=0_65b67362bd-0019c1b0bf-92533145

https://www.nature.com/articles/s41559-017-0301-9

Ichnological evidence for meiofaunal bilaterians from the terminal Ediacaran and earliest Cambrian of Brazil

Luke A. Parry, Paulo C. Boggiani, Daniel J. Condon, Russell J. Garwood, Juliana de M. Leme, Duncan McIlroy, Martin D. Brasier, Ricardo Trindade, Ginaldo A. C. Campanha, Mírian L. A. F. Pacheco, Cleber Q. C. Diniz & Alexander G. Liu

Nature Ecology & Evolution (2017)

doi:10.1038/s41559-017-0301-9

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Abstract

The evolutionary events during the Ediacaran–Cambrian transition (~541 Myr ago) are unparalleled in Earth history. The fossil record suggests that most extant animal phyla appeared in a geologically brief interval, with the oldest unequivocal bilaterian body fossils found in the Early Cambrian. Molecular clocks and biomarkers provide independent estimates for the timing of animal origins, and both suggest a cryptic Neoproterozoic history for Metazoa that extends considerably beyond the Cambrian fossil record.

We report an assemblage of ichnofossils from Ediacaran–Cambrian siltstones in Brazil, alongside U–Pb radioisotopic dates that constrain the age of the oldest specimens to 555–542 Myr. X-ray microtomography reveals three-dimensionally preserved traces ranging from 50 to 600 μm in diameter, indicative of small-bodied, meiofaunal tracemakers.

Burrow morphologies suggest they were created by a nematoid-like organism that used undulating locomotion to move through the sediment. This assemblage demonstrates animal–sediment interactions in the latest Ediacaran period, and provides the oldest known fossil evidence for meiofaunal bilaterians. Our discovery highlights meiofaunal ichnofossils as a hitherto unexplored window for tracking animal evolution in deep time, and reveals that both meiofaunal and macrofaunal bilaterians began to explore infaunal niches during the late Ediacaran.

Yes. Worm burrows have long been hypothesised to be an indication of the transitional form between Ediacaran and Cambrian lifestyles.