Animals evolved later than some hints suggested

Chemically modified fossil algae molecules resemble steroid molecules of sponge-like animals

Max Planck Researchers and colleagues have resolved a longstanding controversy surrounding the origins of complex life on Earth. In two joint studies they found that ancient steroid molecules extracted from 635-million-year-old rocks aren’t the earliest evidence of animals, but instead derive from common algae.

“We were able to demonstrate that molecules from common algae can be altered by geological processes – leading to steroid molecules which are indistinguishable from those produced by sponge-like animals”, said Lennart van Maldegem, co-lead author of one study. Such fossil steroid molecules were assumed to represent the earliest traces of animal life. The study results are part of van Maldegem’s PhD project conducted in the Max Planck Research Group Organic Paleobiogeochemistry at the Max Planck Institute for Biogeochemistry, Jena, and at Marum - Center for Marine Environmental Sciences at the University of Bremen.

“One of the great enigmas in early animal evolution was the lack of a recognisable fossil record even though chemical remains, presumably originating from sponge-like animals, seemed to be abundant,” said Benjamin Nettersheim, the second co-lead author of the study from the same research group.

“We’ve now been able to solve this mystery. While it holds true that sponges are the only living organism which can produce these steroids, chemical processes can mimic biology and transform common and abundant algae sterols (a steroid sub-group) into “animal” sterols,” said Ilya Bobrovskiy, lead author of the second study from The Australian National University (ANU) and California Institute of Technology (Caltech). Both research teams were able to reproduce in pyrolysis experiments the “fossil animal” sterols, from either sterols extracted from algae or pure chemicals, thus simulating geological processes.

The researchers involved in the studies, including scientists from University of Strasbourg (CNRS, France) and CSIRO, Australia, underline the importance of their new findings for our understanding of evolution. “Understanding the rise of animals is so incredibly important because it stands at the root of our very own existence” said senior author of the first study Christian Hallmann. “Before we can search for the drivers for the evolution of organismic complexity, we first need to figure out the temporal framework, which has been intensely debated during the past decades”.

“Our results bring the oldest evidence for animals nearly 100 million years closer to the present day”, concludes Benjamin Nettersheim, “which is around 560 million years before present”.