A rare fossil find offers a window into Cambrian life.
Though it happened over the course of some 30 million years, the “Cambrian Explosion” by all accounts saw an incredible eruption of marine life, an evolutionary outburst that heralded the arrival of almost every creature living on the planet today.
Scientists study life in the Cambrian period by using fossils found in places such as the much-celebrated Burgess Shale, a 500-million-year-old Canadian formation noted for its amazingly preserved specimens. Another fruitful fossil deposit is the Cambrian Shuijingtuo Formation, a mostly limestone fossil bed in China’s Hubei Province.
It was from samples found here that MU researcher Jesse Broce, a Huggins Scholar and doctoral candidate in geological sciences, along with his advisor James Schiffbauer, assistant professor of geological sciences, made a rare discovery — a cache of very old embryos. These “soft-tissue” fossils, the researchers say, could yield important clues about both the origins and the developmental biology of early animals. “Before the Ediacaran and Cambrian Periods, organisms were unicellular and simple,” says Schiffbauer. “The Cambrian Period, which occurred between 540 million and 485 million years ago, ushered in the advent of shells. Over time, shells and exoskeletons can be fossilized, giving scientists clues into how organisms existed millions of years ago. This adaptation provided protection and structural integrity for organisms.”
Soft-tissue fossils, on the other hand, have different chemical patterns than these harder, skeletal remains. Such patterns help researchers identify the processes that contributed to their preservation, says Schiffbauer.
Understanding how the fossils were preserved is important, he adds, because their chemistry offers clues about the nature of the organisms’ original tissues.
“Something obviously went wrong in these fossils,” Schiffbauer says. “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.”
Schiffbauer and Broce believe the embryos may represent previously undescribed organisms because their size is significantly smaller than that of similar fossils from the same time period. What organism they came from, and where they fit into the evolutionary scheme of things, is yet to be determined, they say.
Kriti Sen Sharma and Shuhai Xiao, from Virginia Tech, and Ge Wang of the Rensselaer Polytechnic Institute, also contributed to the project.
The research was supported by the National Science Foundation and was published in the March 2014 special edition of the Journal of Paleontology on the Ediacaran–Cambrian transition, which Schiffbauer co-edited.