The more carefully we peer back in time, the more surprises we find. Only recently, scientists discovered that life on Earth began far earlier than we previously thought, right at the end of the fiery first chapter of our planet 4.1 billion years ago. Now, new research has revealed that the first complex skeletons evolved at least as early as 550 million years ago – 9 million years before the Cambrian Explosion, the period of ancient time complex life appeared to suddenly and rapidly evolve in. The new research was published in Proceedings of the Royal Society B.
Namacalathus hermanastes, a long-extinct, sessile marine creature, was unearthed in Namibia, found as a well-preserved fossil. It was sporting a rigid, intricate skeleton made of calcium carbonate, a common hard material that the shells of many marine animals are constructed from. It was found in a geological deposit that dates back to the Ediacaran Period, which spans 635-542 million years ago.
Around 575 million years ago, in an event known as the Avalon Explosion, a wide range of enigmatic life forms (biota) appeared for scientists to later discover as fossils. Paleontologists still aren’t sure what kind of life they are, but they were likely plant forms, algae, microbial mats, fungi or very primitive life forms called protists. Either way, they were largely passive marine life forms, notable for being the world’s first multicellular life forms.
Mysteriously, by 542 million years ago, the Ediacaran biota disappeared from the fossil record. It is perhaps no coincidence that this evaporation of life occurred simultaneously with the Cambrian Explosion, another sudden appearance of life, and one which we can trace most life around today back to. The new drove the old into extinction.
Image credit: Reconstruction of the living Namacalathus. Various features have been labelled by the researchers, but the skeletal features are – 8, inner skeletal layer; 9, internal (middle) skeletal later; 10, external outer skeletal layer. (credit: J. Sibbick).
Skeletal fossils have been found before dating back to this period of time, but none had been shown to have a complex skeleton like N. hermanastes. Dating back to around 550-541 million years ago, its skeleton was truly advanced for the time. It shielded the tiny organism's soft tissue from predatory attack using an external, folded skeletal structure – the ultrastructure – the formation of which requires a complicated array of organic grids that can produce material that can be mineralized into a shell. The ultrastructure appears to be similar to that of the molluscs and brachiopods, shelled creatures that were thought to have evolved later in the evolutionary record.
Professor Rachel Wood, of the University of Edinburgh's School of GeoSciences, who led the study, said in a statement: “We have suspected that these complex animals were present in the Ediacaran, but this study provides the first proof.”
Once again, the treasure chest of fossils at the beginning of our planet’s time has revealed a new secret: life was indeed far more complex millions of years earlier than we previously thought.