Attacking an enigma with engineering.

One of the biggest headaches in paleontology is the so-called Ediacaran fauna--a group of squishy, bathmat-shape beings that filled the oceans half a billion years ago. Some of these sheetlike creatures are recognized as the first known animals. Others have resisted categorization, leading some researchers to suggest that these organisms weren't animals at all but belonged to some extinct kingdom. Two paleontologists have delved into this debate with a simple engineering test designed to explore what these life-forms were made of.

Kenneth M. Schopf of Harvard University and Tomasz K. Baumiller of the University of Michigan in Ann Arbor studied a fossil of the organism called Dickinsonia, which had a rippled oval body. Some paleontologists have classified Dickinsonia as the earliest known worm, while others have envisioned it a member of a separate kingdom--giant unicells filled with multiple nuclei and protoplasm.

Schopf and Baumiller fashioned two types of Dickinsonia models, one using latex molds and the other employing plastic bags filled with solutions of Karo syrup. They varied the densities of the models from a value equal to that of water to a much meatier substance. Then they observed how each model fared when placed in a tank with a moving current of water.

Models with densities resembling those of worms and of protoplasm were so light that they got pushed by the current, the scientists report in the summer issue of Lethaia. The results suggest either that Dickinsonia, which lived on the seafloor, was denser than paleontologists previously suspected or that the organism was held down by the mats of microbes that covered the ocean bottom at the time.