The identity of Earth's first multicellular creatures, called Ediacarans, has long mystified scientists. The only evidence of the little floppy sea creatures, which lived about 600 million years ago, are impressions in sandstone. As nothing is known of their guts, researchers have classified Ediacarans as everything from jellyfish and giant protozoa to insects or even lichens.
Now two paleontologists, Kenneth Schopf of Harvard and Tomasz Baumiller of the University of Michigan, Ann Arbor, have done a novel experiment that they believe might persuade at least some of their colleagues to rethink their view of Ediacarans. As reported in the summer issue of Lethaia, Schopf and Baumiller replicated the 13-cm-long, flat, oval-shaped Dickinsonia in various densities of Jell-O-like Polygel and placed the models in water flowing at different speeds. The results show that Dickinsonia with densities similar to that of a soft-bodied worm are unstable at currents fast enough to deposit coarse sands of the type found at the main Ediacaran sites in Australia. To be stable, the scientists say, Dickinsonia would have needed to be as dense as, say, a flounder--or it would have to have lived buried within the seabed. Either hypothesis would shake up ideas about Dickinsonia and a number of other Ediacarans, says the duo.
Experts are skeptical of the interpretation. Soren Jensen of Cambridge University says he still favors a scenario in which traditional-looking Ediacarans live in placid environments and have no trouble sticking to the seabed. However, he says, modeling Ediacarans in gel is an approach that has "great potential."