Earliest multicellular animals uncovered.

• Position: Embryonic Fossils

Fossilized embryos predating the Cambrian Explosion by 10,000,000 years provide evidence that early animals already had begun to adopt some of the structures and processes seen in today's embryos, say researchers from Amherst (Mass.) College and nine other institutions.

Scientists from the U.S., United Kingdom, China, Sweden, Switzerland, and Australia have reported the first direct evidence that primitive animals 550,000,000 years ago were capable of asynchronous cell division--which allows the formation of unique shapes--during embryonic development.

"We're learning about how the very earliest muticellular animals formed embryos and how the embryos developed," indicates Amherst's James Hagadorn, lead author of the report. "This gives us an enormous and entirely surprising look at half-billion-year-old embryos in the act of cleaving. What a window on the past. We've had no prior idea what they might have done."

The researchers also believe they have identified specialized structures inside the cells, such as bubble-like vesicles that the cells might have used to transport, store, or metabolize molecules. Slight abberations during the fossilization of dead em bryonic cells even reveal what appear to be dividing nuclei. It was assumed such structures existed in early animals, but no known fossils of the structures were accessible.

The scientists procured 162 "relatively pristine" animal embryo fossils from the Neoproterozoic...