Researchers at the University of Missouri have discovered rare, fossilized embryos that may provide valuable insight into a time of rapid expansion and diversification among the world's first organisms, according to a release from the school.

Known as the "Cambrian explosion," most of the world's marine invertebrates first appeared in the fossil record during this period. While much of the record is comprised of skeletal structures - which may or may not give researchers an accurate picture of prehistoric organisms - the University of Missouri find includes previously undiscovered soft-tissue fossils, which could help with future interpretations of evolutionary history.

"Before the Ediacaran and Cambrian Periods, organisms were unicellular and simple," said James Schiffbauer, assistant professor of geological sciences at the University of Missouri. "The Cambrian Period, which occurred between 540 million and 485 million years ago, ushered in the advent of shells."

He said the shells and exoskeletons become fossilized over time, giving scientists clues into how organisms existed millions of years ago. He added that the development of shells provided "protection and structural integrity for organisms."

Schiffbauer's work focuses on harder-to-find, soft-tissue organisms that were not preserved as well and, thus, are less plentiful.

His team, which includes Missouri University doctoral student Jesse Broce, now is studying fossilized embryos in rocks that provide rare opportunities to study the origins and developmental biology of early animals during the Cambrian explosion.

Broce collected fossils from the lower Cambrian Shuijingtuo Formation in the Hubei Province in southern China and analyzed samples to determine the chemical makeup of the rocks. Soft tissue fossils have different chemical patterns than harder, skeletal remains, allowing researchers to identify the processes that contributed to their preservation.

"Something obviously went wrong in these fossils," Schiffbauer said. "Our Earth has a pretty good way of cleaning up after things die. Here, the cells' self-destructive mechanisms didn't happen, and these soft tissues could be preserved. While studying the fossils we collected, we found over 140 spherically shaped fossils, some of which include features that are reminiscent of division stage embryos, essentially frozen in time."

The next steps will be to identify the parents of the discovered embryos and their place on the evolutionary timeline.

Schiffbauer and his colleagues published their research in the Journal of Paleontology