This discovery provides more insight into how animals evolved from single-celled organisms and shows that there's more to be discovered at this world-famous fossil bed.

Across the vast expanse of Earth's 4.6-billion-year-long history, life has taken many forms. With the first microbes likely appearing a good billion years following the planet's initial formation, the history of life is filled with long periods of seemingly unchanging stability punctuated by moments of immense destruction or practically exponential growth. One of the best known examples of that latter phenomenon is the Cambrian Explosion -- the geologic period some 530 million years ago when Earth saw an immense uptick in the complexity of life in its oceans.

However, complex life was well underway even before this "explosion," and nowhere can this be seen more clearly than at the 150,000-acre Nilpena Ediacara National Park in South Australia. Located on the western fringe of the Flinders Range -- the largest mountain range in the Australian state -- this national park (as its name suggests) contains the richest collection of fossil specimens from the Ediacaran period (a 96 million-year-long geologic span that follows the Cryogenian period and is known to some as "Snowball Earth") and the aforementioned Cambrian period. Since this fossil bed's discovery in 1946, paleontologists have uncovered 40 species embedded in the rock of what was once an ancient seafloor.

Now, an international team of scientists lead by Scott Evans -- assistant professor of geology at Florida State University -- has uncovered what could be one of the earliest (and strangest) forms of animal life to date at the site. Called Quaestio simpsonorum (pronounced kways-tee-oh), this ancient marine animal likely lived around 555 million years ago, and looked like a flattened pancake with a question mark shape in the middle of its body.

While that's puzzling in itself, the more shocking piece of this discovery is evidence that Q. simpsonorum could move on its own -- it would have shifted around sort of like a robotic vacuum cleaner, slowly hoovering up all kinds of microscopic algae and bacteria. The results of this study were published in the journal Evolution & Development.

"There aren't other fossils from this time that have shown this type of organization so definitively," Evans, the lead author of the study, said in a press statement. "This is especially interesting as this is also one of the first animals that was capable of moving on its own."

According to the researchers, as Q. simpsonorum puttered around this ancient seafloor gobbling up microbes, it left behind an organic mat of nutrients, which they describe as a kind of slime. These left-behind trails became trace fossils, which the team also uncovered in its discovery of Q. simpsonorum.

"One of the most exciting moments when excavating the bed where we found many Quaestio was when we flipped over a rock, brushed it off, and spotted what was obviously a trace fossil behind a Quaestio specimen -- a clear sign that the organism was motile; it could move," Harvard University's Ian Hughes, a co-author of the study, said in a press statement.

The importance of this discovery extends far beyond just one species that's been extinct for half a billion years. It gives researchers a glimpse at the gene expressions necessary to create these first forms of complex life, all while adding context to how complex life can form -- whether on Earth or some other planet.

Of course, it also gives hope to experts who continue excavating the area that something else might be waiting to be discovered. "We're still finding new things every time we dig," Hughes said in a press statement. "Even though these were some of the first animal ecosystems in the world, they were already very diverse. We see an explosion of life really early on in the history of animal evolution."