A close-up photograph of a Fractofusus from the ‘E’ surface Mistaken Point, Newfoundland. (EG Mitchell)

Rangeomorphs, which lived about 565 million years ago, were pretty strange. They're often considered to be some of the first animals to evolve on Earth, but they share little in common with modern critters — they look more like plants. But according to a new study, their reproductive techniques were astonishingly complex — and familiar, too.

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The research, published Monday in Nature Communications, used statistical analysis to determine what kind of reproductive strategy was used by the genus Fractofusus, a type of rangeomorph. Based on the population distributions found in fossils, the researchers report, these creatures used a two-pronged reproductive approach. They may even have been the first group to develop such a nuanced plan for populating the world.

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"Rangeomorphs don't look like anything else in the fossil record, which is why they're such a mystery," lead study author Emily Mitchell, a postdoctoral researcher in Cambridge's Department of Earth Sciences, said in a statement. "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."

Because these creatures — which had beautiful fractal branches like intricate little ferns — were immobile, well-preserved fossils can show entire ecosystems of them as they lived and died. That means that scientists can analyze the way they're clustered to determine how their populations grew.

An artist's illustration of the reproduction of rangemorphs. The large individuals represent the primary colonizers of the site. Their offspring cluster around them, and are themselves surrounded by their own offspring -- the third generation on the bed. The stolon-like protrusions are faintly visible and weave in and out of the microbial mat which covers the seafloor. (CG Kenchington)

According to that analysis, Fractofusus would send out "grandparents" — little bits of itself ejected out into the water, kind of like seeds or spores — to colonize new areas. Once settled in a new spot, those "grandparents" would produce "parents" and "children" using stolons, or runners — cloned organisms connected to each other, much like strawberries grow today. It's a rapid technique for asexual reproduction, especially compared to the "grandparent" technique. But those waterborne bits, while inefficient, could be used to propagate new areas, perhaps even sexually.

Combined, these two techniques make it easy to see how rangeomorphs ruled the sea. At least until the Cambrian period, when newly evolved, mobile creatures turned them into sitting ducks.

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