Ancient Cholesterol Confirms Dickinsonia as One of Earth’s First Animals

The first complex organisms emerged during the Ediacaran period (635-541 million years ago). Ediacaran fossils are as ‘strange as life on another planet’ and have evaded taxonomic classification, with interpretations ranging from marine animals or giant single-celled protists to lichens. Fossils of one of these creatures — a flat, oval-shaped organism called Dickinsonia — have been particularly difficult to classify. Now, researchers from the Australian National University and elsewhere have analyzed biomarkers from organically preserved Dickinsonia fossils and found that the fossils contained cholesterol, a marker found only in animals.

Dickinsonia, which lived more than 550 million years ago, were flat, soft-bodied creatures that moved along the sea bed to eat microbes and algae. Image credit: University of California, Riverside.

Dickinsonia, which lived more than 550 million years ago, were flat, soft-bodied creatures that moved along the sea bed to eat microbes and algae. Image credit: University of California, Riverside.

Dickinsonia is a large genus of extinct fossil organisms that includes around 200 species.

These creatures grew up to 4.6 feet (1.4 m) in length and were oval shaped with rib-like segments running along the body.

They belong to the Ediacaran biota, a group of soft-bodied organisms that lived on Earth 20 million years prior to the ‘Cambrian explosion’ of modern animal life.

“The Cambrian explosion was when complex animals and other macroscopic organisms began to dominate the fossil record,” said Dr. Jochen Brocks, from the Research School of Earth Sciences at the Australian National University.

Dr. Brocks, Australian National University PhD scholar Ilya Bobrovskiy and their colleagues discovered a Dickinsonia fossil so well preserved in a remote area near the White Sea that the tissue still contained molecules of cholesterol, a type of fat that is the hallmark of animal life.

Organically preserved Dickinsonia from the Lyamtsa locality of the Ediacara biota in the White Sea region. Image credit: Bobrovskiy et al, doi: 10.1126/science.aat7228.

Organically preserved Dickinsonia from the Lyamtsa locality of the Ediacara biota in the White Sea region. Image credit: Bobrovskiy et al, doi: 10.1126/science.aat7228.

“Paleontologists normally study the structure of fossils, but we extracted and analyzed molecules from inside the Dickinsonia fossil found in ancient rocks to make the breakthrough discovery,” Bobrovskiy said.

“I took a helicopter to reach this very remote part of the world — home to bears and mosquitoes — where I could find Dickinsonia fossils with organic matter still intact,” he added.

“These fossils were located in the middle of cliffs of the White Sea that are 200 to 330 feet (60-100 m) high. I had to hang over the edge of a cliff on ropes and dig out huge blocks of sandstone, throw them down, wash the sandstone and repeat this process until I found the fossils I was after.”

“The fossil fat molecules that we’ve found prove that animals were large and abundant 558 million years ago, millions of years earlier than previously thought,” Dr. Brocks said.

“Scientists have been fighting for more than 75 years over what Dickinsonia and other bizarre fossils of the Edicaran biota were: giant single-celled amoeba, lichen, failed experiments of evolution or the earliest animals on Earth.”

“The fossil fat now confirms Dickinsonia as the oldest known animal fossil, solving a decades-old mystery that has been the Holy Grail of paleontology.”

The results appear in the journal Science.

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Ilya Bobrovskiy et al. 2018. Ancient steroids establish the Ediacaran fossil Dickinsonia as one of the earliest animals. Science 361 (6408): 1246-1249; doi: 10.1126/science.aat7228

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