The tracks and burrows, dating back half a billion years to the Ediacaran Period, were made by some of the earliest bilaterian animals, and reveal that more complex lifeforms arose earlier than previously thought.
This places them perhaps even 10 million years before the "Cambrian Explosion" (roughly 541 million years ago), the moment in time which sparked the incredible evolution of life that led to the wonderful diversity of species that we see today.
"These trace fossils represent the earliest known trackways". Thus one can say that the sudden surge in bio-diversity around five hundred and ten to five hundred and forty million years ago.
The footprints themselves look like two rows of holes punched in the ancient sediment and apparently lead away from the remains of a burrow. "Also, they are organised in repeated groups, as expected if the animal had multiple paired appendages".
Until now, there had been no evidence of limbed creatures prior to the Cambrian Explosion, say the researchers from Virginia Tech in the US. They are often assumed to have appeared and radiated suddenly during the "Cambrian Explosion" about 541-510 million years ago, although it has always been suspected that their evolutionary ancestry was rooted in the Ediacaran Period.
While bilaterian animals - including arthropods and annelids - were suspected to have first stretched their innovative legs prior to the Cambrian explosion, in what's called the Ediacaran Period, before now there was no evidence for it in the fossil record. Take that, rest of the pre-Cambrian life forms! "It is important to know when the first appendages appeared, and in what animals, because this can tell us when and how animals began to change to the Earth in a particular way".
"At least 3 living groups of animals have paired appendages (represented by arthropods such as bumble bees, annelids such as bristle worms, and tetrapods such as humans)".
The animal appears to have paused from time to time, since the trackways seem to be connected to burrows that may have been dug into the sediment, perhaps to obtain food.