“As far as we know, this is the oldest brain fossil we know of to date,” said Nicholas Straussfeld, Regent’s professor in the Department of Neuroscience at the University of Arizona.
Published Date – Sat 26 Nov 22 03:45pm
Photo: Nicholas Strausfeld/University of Arizona
New York: The fossil of a tiny sea creature that died more than 5 billion years ago could force a science textbook to rewrite how the brain evolved.
A study published in the journal Science reveals the fossils of a tiny sea creature with a 525-million-year-old preserved nervous system, settling a century-old debate about how the brains of arthropods, the largest animals on Earth, evolved. The most species-rich group of the animal kingdom.
“As far as we know, this is the oldest brain fossil we know of to date,” said Nicholas Straussfeld, Regent’s professor in the Department of Neuroscience at the University of Arizona.
Strausfeld and Frank Hirth, Reader in Evolutionary Neuroscience at King’s College London, are the first to describe in detail Cardiodictyon catenulum, a worm-like animal preserved in rocks in southern China’s Yunnan province.
Measuring just half an inch (less than 1.5 centimeters) long, the fossil was first discovered in 1984, and until now harbored an important secret: a well-preserved nervous system, including the brain.
Cardiodictyon belonged to an extinct group of animals known as armored phyllopods that abounded during the early Cambrian period, when almost all major animal lineages arose in the extremely short period of time between 540 and 500 million years ago.
Lobopodians likely moved across the ocean floor using multiple pairs of soft, stubby legs that lacked the joints of their descendants, euarthropods—Greek for “truly articulated feet.”
The closest relatives of phyllopods today are the velvet worms that live mainly in Australia, New Zealand and South America.
“This anatomy was completely unexpected, since the heads and brains of modern arthropods, as well as some of their fossil ancestors, have been thought to be segmented for over a hundred years,” Strausfeld said.
“Since the 1880s, biologists have noticed the distinctly segmented appearance of the torso typical of arthropods and essentially extrapolated it to the head,” Hirth said. “Assuming the head is an anterior extension of the segmented torso, that’s what the field has concluded.”
“But the Cardiodictyon shows that the early head was not segmented, and neither was its brain, suggesting that the brain and trunk nervous systems may have evolved separately,” Strausfeld points out.
The findings also provide information on continuity as Earth undergoes dramatic changes under the effects of climate change.
“At a time when major geological and climatic events are reshaping the planet, simple marine animals such as the Cardiodictyon give rise to the world’s most diverse biota—the euarthropods,” eventually spreading to every emerging habitat on Earth, But now threatened by our own ephemeral species,” the researchers said.
