By identifying specific biomarkers preserved alongside fossils of oval-shaped life forms from the Ediacaran Period, fossils from which are typically considered one of the greatest mysteries in paleontology, researchers say the ovular organism is not a fungus or protist, as some have thought, but an early animal. This makes it one of the oldest animals yet identified in the fossil record. The new study further suggests that the first complex organisms on Earth emerged during the Ediacaran period more than 542 million years ago as a prelude to the Cambrian explosion of life. Ediacaran biota, which lived 575-541 million years ago, represent the earliest complex organisms on Earth yet discovered in the fossil record. However, according to the authors, Ediacaran fossils are as "strange as life on another planet." As such, their place on the family tree of life has been contentious and difficult to discern, and interpretations on taxonomic affiliation are often varied. This is particularly true for dickinsoniids, an iconic oval-shaped Ediacaran life-form, which is argued to be a fungus, a giant single-celled protist and a marine animal. Here, Ilya Bobrovskiy and colleagues use a method to identify diagnostic hydrocarbon biomarkers preserved in association with individual fossils. Most multicellular life leaves behind stable sterane hydrocarbons, which can be preserved in sediments for hundreds of millions of years. The molecular structures and abundances of these compounds can be specific to certain source organisms. Bobrovskiy et al. found a striking abundance of cholesteroids (up to 93%) in Dickinsonia fossils when compared to that in surrounding microbial mat-based sediment (approximately 11%). Furthermore, the fossils they studied lacked the levels of ergosteriods characteristic of fungi. According to the authors, the results firmly place Dickinsonia within the animal kingdom. In a related Perspective, Roger Summons and Douglas Erwin write: "Further refining of the phylogenic signals from biomarkers may also help to resolve the early history of animals during the Cryogenian and early Ediacaran."
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Journal
Science