How Undersea Enigmas Reproduced Before the Dawn of Sex

Birds do it. Bees do it. And over 541 million years ago, weird organisms that looked like armored carpets did it. Exactly how they did so, though, was a bit different from the ways we’re familiar with.

University of Cambridge paleontologist Emily Mitchell and colleagues were the ones to reconstruct how these puzzling species reproduced. They focused on a species from the Ediacaran period called Fractofusus. The fossil is a strange, branching frond preserved as flat impressions in the ancient sediment, but it’s so unlike anything alive today that scientists are still unsure whether it was an animal, a plant, or what. Nevertheless, by studying the geographic pattern of how these fossils are preserved across the rocks of Newfoundland, Canada, Mitchell and coauthors have been able to reconstruct how Fractofusus made more Fractofusus.

It wasn’t as simple as catching Fractofusus in The Act. This was still tens of millions before the earliest days of internal fertilization, after all. Rather, Mitchell and colleagues write, the clusters of Fractofusus are patterned in such a way that suggests they’re organized by reproductive factors rather than by currents or other environmental details.

The diagram of Fractofusus spatial arrangements. From Mitchell et al., 2015.
The diagram of Fractofusus spatial arrangements. From Mitchell et al., 2015.

The largest, and therefore oldest, Fractofusus seem to be arranged randomly in respect to each other. This may indicate that these were the first to colonize the habitat, initially carried as tiny “waterborne propagules” that then settled and grew. But from there, Mitchell and coauthors wrote, Fractofusus started doing something different.

The smallest Fractofusus, the researchers found, grouped around the medium-sized ones, which in turn clustered around the largest individuals. With no evidence of little buds or fragments coming off any of the fossils, Mitchell and colleagues suggest that this pattern belies reproduction and connection by a way of a stolon – a wispy “runner” that connects individuals into a kind of communal group. Marine invertebrates, such as some bryozoans, do this today, and, in the prehistoric case, the large Fractofusus would have sent out runners to produce a garden of little Ediacaran clones.

Reference:

Mitchell, E., Kenchington, C., Liu, A., Matthews, J., Butterfield, N. 2015. Reconstructing the reproductive mode of an Ediacaran macro-organism. Nature. doi: 10.1038/nature14646

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