Half-billion-year-old microfossils can provide new insights into the origins of animals

When and how did the first animals appear? Science has long sought an answer to this question. Researchers and colleagues from the University of Uppsala in Denmark have now jointly discovered embryo-like microfossils in Greenland up to 570 million years ago, revealing that such organisms were scattered around the world. The study is published in Communications biology.

“We believe this discovery improves our ability to understand the period in Earth’s history when animals first appeared, and is likely to spark a lot of interesting discussions,” says Sebastian Willman, first author of the study and paleontologist at the University of Uppsala.

The existence of animals on Earth around 540 million years ago (mya) is well documented. It was then that the evolving event known as the “Cambrian Explosion” took place. There are fossils of a huge number of creatures from the Cambrian period, many of which are shelled. The first animals must have evolved even earlier; but there are divergent views in the research community as to whether existing fossils dating from the Precambrian era are truly classifiable as animals.

New findings from the Portfjeld formation in northern Greenland may help improve understanding of the origin of animals. In rocks that are 570-560 mya, scientists from the University of Uppsala, the University of Copenhagen and the Geological Survey of Denmark and Greenland have found microfossils of what may be animal eggs and embryos. These are so well preserved that single cells and even intracellular structures can be studied. The organisms concerned lived in the shallow coastal seas around Greenland during the Ediacaran period, 635–541 million years ago. The immense variability of microfossils convinced the researchers that the complexity of life at that time must have been greater than previously known.

Similar finds have been discovered in the Doushantuo Formation of southern China, which is nearly 600 million years old, more than three decades ago. Since then, researchers have debated what kind of life form microfossils represent, and some think they are eggs and embryos of primeval animals. Fossils from Greenland are a little younger, but largely identical to those from China.

The new discovery means that researchers can also say that these organisms have been spread around the world. When they were alive, most continents were south of the Equator. Greenland was where the expanse of the Southern Ocean is now (which surrounds Antarctica) and China was at roughly the same latitude as present-day Florida.

“The vast, largely unexplored bedrock of northern Greenland offers opportunities to understand the evolution of the first multicellular organisms, which in turn developed into the first animals which, in turn, led to us,” says Sebastian Willman.