Researchers found small round fossils that could be ancient embryos of an undetermined animal.
The fossils are believed to be between 540 million to 485 million year old, which is known as the Cambrian, LiveScience reported.
Animals with hard exoskeletons preserve well, but those with softer tissue are harder to find. Researchers excavated an area of the Hubei province of southern China in hopes of finding evidence of ancient worms or other relatively boneless creatures; instead they found something even more unexpected. The fossils were found embedded in local limestone.
The team stumbled upon "small spheres" covered in polygonal patterns; these strange objects could have once been embryo.
"We found over 140 spherically shaped fossils, some of which include features that are reminiscent of division-stage embryos, essentially frozen in time," James Schiffbauer of the University of Missouri said, LiveScience reported.
The researchers examined these possible embryos by taking thin slices out of them and examining them using a microscope. They also used "X-ray and scanning electron microscopy and X-ray techniques" to make their fidnings, LiveScience reported.
The clear polygonal patterns present on the fossils were similar to those seen before on the fossil Markuelia, which is a worm from the Cambrian period. These newly-discovered fossils are believed to be something called "blastulas," which are organisms at a "multicellular stage of embryonic development," the news release.
The team found the fossils were made up of a "phosphate-rich envelope surrounding a ball of calcite," LiveScience reported. Calcite is a past organic compound that has mineralized over the millions of years.
The researchers are unsure of what animal the cells would have grown up to be. Fossilized embryos have rarely been found in the past, but it has happened on rare occasions. A 380-million-year old fish embryo was once discovered inside the stomach of its mother, and dinosaur embryos have been found inside ancient eggs.
