The age-old puzzle of "which came first, the chicken or the egg?" has been solved by scientists. A fossilized prehistoric creature discovered in 2017 has led experts to conclude that eggs appeared long before the first animals evolved, implying that they predate chickens.

Chromosphaera perkinsii, a single-celled organism found in Hawaii, was first identified at least a billion years ago and underwent cell division to produce what appeared to be the precursor to eggs.

Scientists from the University of Geneva discovered that the creature formed multicellular structures that bore striking similarities to animal embryos.

The findings, published in the journal Nature, suggest that eggs existed long before the first animals emerged. "Although Chromosphaera perkinsii is unicellular, this behavior suggests that multicellular differentiation and coordination were already occurring in this species long before the first animals appeared on Earth," said study lead author Omaya Dudin.

Single-celled life forms such as yeast or some bacteria also appeared on this planet long before multicellular organisms such as animals developed from a single egg cell into complex organisms.

This embryonic development follows very specific stages that are known to be very similar across animal species.

Researchers now suspect that this process occurred much earlier, dating back to the time before animals emerged. But exactly how the transition from single-celled to multicellular organisms occurred remains poorly understood.

In the new study, scientists assessed the ancestral life form C perkinsii, which diverged from the animal evolutionary lineage more than a billion years ago, and found important insights into the mechanisms behind the transition to multicellular life.

They found that when C perkinsii reached its maximum size, it divided without growing any further, forming multicellular colonies that resembled the early stages of an animal embryo. The colonies, which contained at least two distinct cell types, persisted for about a third of their lifespan, a phenomenon the researchers called “surprising” for this type of organism.

They say the way these populations divide into distinct three-dimensional structures is “strikingly reminiscent” of the earliest steps involved in embryonic development in animals.

Based on this discovery, the researchers say the genetic tools needed to “make eggs” existed long before nature “invented chickens” more than a billion years ago.

However, it is possible that the mechanisms behind multicellular development may have evolved separately in C perkinsii, and the researchers said they hope that further studies of the organism will reveal which case is more likely.

“It is fascinating that a recently discovered species allows us to go back more than a billion years in time,” said Marine Olivetta, another author of the study.