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Fossils reveal strange reproduction of Earth’s oldest animal

It goes without saying that Earth was a very different place 565 million years ago. There was little or no life on land, few complex organisms in the seas and you have to figure cell phone reception would have been pretty lousy. That’s what makes a discovery by researchers at the University of Cambridge all the more remarkable: They’ve identified the reproduction method used by rangemorphs, believed by some to be the earliest animals.

“Rangeomorphs don’t look like anything else in the fossil record, which is why they’re such a mystery,” said Dr Emily Mitchell, a postdoctoral researcher in Cambridge’s Department of Earth Sciences, and the paper’s lead author. “But we’ve developed a whole new way of looking at them, which has helped us understand them a lot better – most interestingly, how they reproduced.”

Using high-resolution GPS, spatial statistics and modelling, Mitchell and her team examined fossils left by Fractofusus, a type of rangemorph found in modern-day Newfoundland, Canada. They discovered that the organism actually reproduced by two methods. Clustering of the fossils suggested that “grandparent” generations were randomly deposited by waterborne propagules, which could have been either sexual or asexual in nature. Subsequent generations, however, developed nearby via rapid, asexual reproduction through the use of stolons or runners – a system used by many modern plants.

Some scientists regard rangemorphs as the first animals, but it’s difficult to say for sure. They were immobile, which makes them ideal for study. They also lacked things like mouths or legs or orifices. The difficulty in knowing more about them lies in the fact that like many other Ediacaran organisms, they abruptly disappeared at the start of the Cambrian period about 540 million years ago. That makes it more or less impossible to link them to any living organisms. Animal or not, however, what the rangemorph was able to accomplish so long ago was pretty remarkable.

“Reproduction in this way made rangeomorphs highly successful, since they could both colonise new areas and rapidly spread once they got there,” said Mitchell. “The capacity of these organisms to switch between two distinct modes of reproduction shows just how sophisticated their underlying biology was, which is remarkable at a point in time when most other forms of life were incredibly simple.”