Paleontologists are using chemical traces in ancient rocks and the genetics of living animals to get a glimpse of life more than a billion years ago. Research published December 1 in Nature Communications combines geology and genetics to show how changes on the early Earth prompted shifts in the way animals eat.

Paleontologists led by David Gold are revealing the evolution of early life through chemical traces in ancient rocks and genetic studies. They found that changes in sterol lipids in rocks coincided with major changes in animal diets and the rise of algae, shedding light on life more than a billion years ago.

David Gold, associate professor in the Department of Earth and Planetary Sciences at the University of California, Davis, is engaged in research in the new field of molecular paleontology, using tools from geology and biology to study the evolution of life. With new technology, it may be possible to recover chemical traces of life from ancient rocks where animal fossils are sparse.

Lipids can remain in rocks for hundreds of millions of years. In rocks dating back 1.6 billion years, biologists have found traces of sterol lipids from cell membranes. Currently, most animals use cholesterol, a sterol containing 27 carbon atoms (C27), in their cell membranes. In contrast, fungi typically use C28 sterols, while plants and green algae produce C29 sterols. C28 and C29 sterols are also called plant sterols.

Archaeologists have found C27 sterol in rocks dating back 850 million years, while traces of C28 and C29 appeared about 200 million years later. This is thought to reflect the increased diversity of life at this time and the evolution of the first fungi and green algae.

In the absence of actual fossils, it's difficult to say which animal or plant these sterols came from. However, a genetic analysis by Gold and colleagues revealed some problems.

Most animals cannot make their own plant sterols, but they can obtain them by eating plants or fungi. Recently, researchers discovered that annelids (arthropods, including common earthworms) have a gene called smt that is required to make long-chain sterols. By studying SMT genes from different animals, Gold and colleagues created an SMT family tree first in Cyclotes and then throughout animal life.

They found that the gene originated during the earliest animal evolution and then underwent rapid changes during the same period when plant sterols appeared in the rock record. Subsequently, most animal germ lines lost the smt gene.

"Our interpretation is that these fossilized phytosterol molecules record the rise of algae in ancient oceans, and that animals gave up phytosterol production when they became readily available from this increasingly abundant food source," Gold said. "If we are right, then the history of the smt gene records changes in feeding strategies early in animal evolution."

References T.Brunoir, C.Mulligan, A.Sistiaga, K.M.Vuu, P.M.Shih, S.S.O'Reilly, R.E.Summons, and D.A.Gold published a paper in "Nature-Communications" on November 31, 2023: "A common origin of sterol biosynthesis points to a shift in feeding strategies in Neogene animals."

DOI:10.1038/s41467-023-43545-z

Compiled source: ScitechDaily