Generation game: earliest evidence of reproduction in complex species found

A close up of a single Fractofusus specimen. The many branches that make up the organism can be clearly seen. This type of branching is known as and is currently unknown in any other living or fossil organism. Photograph: EG Mitchell

They looked like plants but were almost certainly animals; they drifted back and forth in in the deep ocean currents 565 million years ago; and by 540 million years ago, they were gone.

And yet, in one of palaeontology’s triumphs, researchers at Cambridge now know how these mysterious organisms spread themselves around the pre-Cambrian world. And the answer is one that every gardener would recognise: they sent out runners, and established new growths. Just like strawberries.

Life has existed on Earth for about 3.5 billion years, but the first complex creatures – plants or animals that were not just single-celled microbes – appeared in a period called the Ediacaran. Among these were animals called rangeomorphs: organisms that varied in size from 10 centimetres to two metres in length. Rangeomorphs were rooted to the seabed, and, like sponges or corals, filtered nutrients from the sea water. They grew like ferns, with a fractal pattern, but flourished at depths that light could not reach, so could not have been plants. They also could not move, which probably made them easy pickings when the first predators appeared. Despite their immobility rangeomorphs could spread, and now scientists know how.

An artist’s reconstruction of three generations of a Fractofusus community. The large individuals are the primary colonisers, with their offspring clustered around them, who are themselves surrounded by their own offspring. Illustration: CG Kenchington

Emily Mitchell, an earth scientist at Cambridge University, and colleagues report in Nature today that a match of preserved fossils from Newfoundland rocks and sophisticated statistical techniques have helped them reconstruct how one rangeomorph species called Fractofusus played the generation game – and the regeneration game.

They identified three different layers of settlement in the fossil patterns of ancient rocks: a “grandparent” or founder colony that had probably drifted to a new location as the Ediacaran equivalent of a seed or a spore, and then a pattern of “parent” colonies and then “children”. It suggested a form of asexual reproduction now common in plants.

“Rangeomorphs don’t look like anything else in the fossil record, which is why they’re such a mystery,” Dr Mitchell said “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.”