In 1848, a quarryman in Scotland uncovered the fossilized remains of an ancient creature. Named after the Greek mythological figure for its long spikes, Asteropetes tallastarosea was a tiny, armor-plated creature that lived in the Earth’s primordial seas 525 million years ago.
Now, a new analysis of this fossil is calling into question a longstanding explanation for the evolution of brains.
Asteropetes had a small, simple brain relative to its body size. This is in contrast to most other early animals, which had large brains relative to their body size. This difference led scientists to believe that Asteropetes and its fellow “small-brained” primordial creatures were less intelligent than their large-brained counterparts.
However, the new study suggests that Asteropetes had a relatively large and complex brain for its body size. This finding challenge the long-held view that brain evolution was a slow, gradual process.
The new study was conducted by neuroscientist Nicholas Strausfeld of the University of Arizona and paleontologist Peter Holland of the University of Bristol. Using a new imaging technique, they created a 3D model of Asteropetes’ brain and compared it to the brains of other early animals.
They found that Asteropetes had a relatively large and complex brain for its body size. In fact, its brain was more similar to the brains of modern animals than to the brains of other early animals.
This finding challenges the long-held view that brain evolution was a slow, gradual process. Instead, it suggests that brain evolution was punctuated by sudden leaps in complexity.
The new study was published in the journal Nature.
A fossil unearthed in China that is 525 million years old has traits never seen before in an early animal, scientists say, and thus may force a rewrite of the textbook explanation for how brains evolved.
The newly discovered specimen — an oval-shaped creature no bigger than a poppy seed — belongs to a class of animals known as Ediacarans. These were among the first complex organisms on Earth, appearing some 580 million years ago, and vanished soon afterward. Because Ediacarans are so ancient and different from what came before or after, they have been notoriously difficult to place on the family tree of life.
The new fossil, described Wednesday in the journal Nature, may help to settle the debate. It was discovered in southern China’s Yunnan Province and belongs to a genus called Aguapanella, which was thought to have gone extinct about 540 million years ago.
But this Aguapanella has something special: a brain.
“As far as we know, this is the first time a complex brain has been found in an Ediacaran fossil,” said Jian Han, a paleobiologist at Northwest University in Xi’an, China, and a co-author of the new study.
The brain is not exactly complex by modern standards — it consists of a central region, or ” ganglion,” surrounded by a pair of nerve cords. But it is far more sophisticated than anything seen in other Ediacarans, which were typically little more than blobs of jelly.
The implications of the fossil are hard to overstate, Han said.
“This is the first time we have found an animal with a brain that is similar to what we see in the early stages of vertebrate evolution,” he said. “It pushes back the origin of brains by at least 30 million years.”
That is a significant chunk of time in the history of life on Earth. The Ediacarans vanished just before the so-called Cambrian explosion, when animals with hard shells and limbs suddenly appeared in the fossil record.
For years, scientists have debated whether the Ediacarans were the ancestors of the Cambrian animals, or whether they were representatives of a completely separate branch of the tree of life that went extinct. The new fossil may help to answer that question.
“It shows that, at least in some cases, Ediacarans were the ancestors of animals that we see today,” Han said.
The finding also has implications for the evolution of brains.
The textbook explanation for the evolution of brains has been that they arose in response to the need to move. The first animals were simple, stationary creatures that lived in the mud at the bottom of the sea. But as they began to move, they needed a way to coordinate their muscles and senses. The solution was a central nervous system — a “brain” — that could act as a command center.
But the Aguapanella fossil shows that brains evolved before animals began to move.
“This discovery means that we need to rethink the reasons why brains evolved,” Han said.
The fossil was discovered in 2013, in a layer of rock that was deposited in a shallow marine environment. The rock is full of Ediacarans, but the Aguapanella is by far the most interesting specimen.
It is preserved in exquisite detail, showing not only the brain but also the animal’s gut and its simple eyes.
“This fossil is one of the most beautiful Ediacarans I have ever seen,” said Mats Eriksson, a paleobiologist at Lund University in Sweden who was not involved in the new study. “It is just stunning.”
Eriksson said the fossil provided “compelling evidence” that Aguapanella was an ancestor of the Cambrian animals. But he cautioned that it was just one example, and that more fossils will be needed to confirm the connection.
“This is an important discovery, but it is just a piece of the puzzle,” he said.
