Billion-year-old fossil sheds light on animal origin, scientists say

SHEFFIELD, England — In the Scottish Highlands, scientists have unearthed an extraordinary fossil at least a billion years old. This rare find is thought to be the “missing link” in mammalian development.

Researchers from the University of Sheffield and Boston College say the billion-year-old microfossil comprises two unique cell types and may be the oldest multicellular animal ever discovered. The fossil sheds new light on how single-celled creatures evolved into sophisticated multicellular animals. The most primitive living organisms are unicellular holozoa. This newly discovered fossil indicates an organism halfway between singular and multicellular animals.

This enhanced image of Bicellum brasieri shows an outer wall of sausage-shaped cells enclosing an inner cell mass. The fossil reveals a multicellular structure in an early animal form 400 million years earlier than previously established. (Credit: Paul K. Strother)

In a recent study published in Current biologythe fossil was given the name Bicellum brasieri. “The origins of complex multicellularity and the origin of animals are considered two of the most important events in the history of life on Earth, our discovery sheds new light on these two elements”, states the co-author. Charles Wellmanprofessor in the Department of Animal and Plant Sciences at Sheffield, in a statement.

The fossil, unearthed by scientists in Loch Torridon in the Scottish Highlands, is remarkably preserved. Thanks to this, the researchers were able to analyze the individual cells of the organism and even the subcellular components.

“We have found a primitive spherical organism composed of an arrangement of two distinct cell types, the first step towards a complex multicellular structure, something that has never before been described in the fossil record,” says Professor Wellman. “The discovery of this new fossil suggests to us that the evolution of multicellular animals occurred at least a billion years ago and that the earliest events predating animal evolution may have occurred in lakes. freshwater rather than in the ocean.”

The team is now searching for other intriguing fossils in the Torridonian strata that may provide more clues to the origin of the multicellular creatures.

“Our study of life in billion-year-old lakes is challenged by our ability to determine what kinds of organisms are represented in these deposits,” adds Boston College paleobotanist Paul K. Strother, in a press release. “Previously, we assumed that most of what we see in these deposits are various types of extinct algae, but the morphological characteristics of Bicellum more closely resemble those of modern single-celled relatives of animals. This leads us to broaden our approach to reconstruct the diversity and ecology of life on Earth a billion years ago.