Tiny fossils shaped like spheres found in rocks of southern China could be the embryos of an animal previously unknown to science that lived 500 million years ago, scientists say.
Researchers from U.S. universities were looking for soft-tissue fossil remains of Cambrian creatures like trilobytes when they made the unexpected discovery of the tiny spheres, some carrying polygonal marking on their surface.
The tiny fossils are likely fossilized embryos of some previously unknown species of animal, the researchers reported in the Journal of Paleontology.
"We found over 140 spherically shaped fossils, some of which include features that are reminiscent of division-stage embryos, essentially frozen in time," University of Missouri researcher James Schiffbauer said in a statement.
Schiffbauer, along with Jesse Broce of Virginia Tech and other colleagues, hand-chiseled the rocks found in China's Hubei province to expose the fossils after an attempt to dissolve them from the surrounding limestone with acid caused serious damage to the spherical objects.
Taking the rock samples from the Shuijingtuo rock formation to a lab, researchers examined the fossils with several techniques including X-rays and scanning electron microscopes.
Although the polygon patterns resemble those seen on fossilized examples of embryos of another Cambrian creature, a worm-like organism known as Markuelia, the researcher say they have no idea what the new embryos might have developed into.
Because they were significantly smaller than other fossil embryos known from the same time period, it is likely they represent a yet undescribed organism, the researchers said.
Determining how these particular fossils were preserved is important, because their chemical makeup can offer clues about the nature of the organisms' original tissues.
Because soft tissue fossils contain chemical patterns that differ from harder, skeletal remains, researchers can often identify the processes that contributed to their preservation.
"My work focuses on those harder-to-find, soft-tissue organisms that weren't preserved quite as easily and aren't quite as plentiful," Schiffbauer says.
"Something obviously went wrong in these fossils," he added. "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."
The find is not the first time embryos have been found in the fossil record; fossils of dinosaur embryos still inside their eggs have been found, as has a fish fossil with a fossilized embryo still inside it.
