Prehistoric fish ‘missing link’ in human brain and nervous system evolution

By Mark Waghorn via SWNS

A prehistoric fish that travels through water, mud and across land is a "missing link" in the evolution of the human brain and nervous system, according to new research.

Lungfish are nicknamed "living fossils" as they have survived practically unchanged for more than 400 million years.

They led to the emergence of tetrapods - four-limbed vertebrates that include amphibians, reptiles, birds and mammals.

Lead author Dr. Alice Clement, of Flinders University said: "Studying our 'fishy cousins' continues to help us understand how they first left the water some 350 million years ago and started to become land animals - and later humans.

"Perhaps some of their nervous system traits remain in us still."

The international team compared detailed 3D digital brain reconstructions, known as endocasts, of six ancient lungfish fossils and their surviving sister group of land vertebrates.

They found the olfactory region of the lobe-finned fish appears to be more highly plastic than the hindbrain - and undergoes significant elongation.

Clement said: "Our discovery shows the brains of lungfish have been evolving constantly throughout their 400 million-year history.

"But it suggests they have likely always relied on their sense of smell rather than vision to navigate their environments.

"This is quite unlike other fish which use sight much more powerfully.

"Understanding how lungfish brains have changed throughout their evolutionary history helps to understand of what the brains of the first tetrapods - our land-based ancestors - might have looked like too.

"This can give us an idea of which senses were more important than others - such as vision versus olfaction."

The study in the journal eLife used powerful imaging methods to create the virtual models.

Senior author Dr. Tom Challands, of the University of Edinburgh, said they have important evolutionary and paleontological implications.

He explained: "This paper effectively doubles the number of lungfish endocasts known.

"Their preservation quality is often damaged by a fossil being crushed or broken.

"The brain itself has very poor preservation potential and is not currently known in any fossil lungfish.

"Lungfish have persisted for more than 4OO million years from the Devonian Period to present day.

"They provide unique insights into the condition of the earliest tetrapods as well as their own evolutionary history."

The lungfish specimens from Australia, the US, Russia and Germany were studied non-destructively using a scanning technique called X-ray tomography.

They are known as Iowadipterus halli, Gogodipterus paddyensis, Pillararhynchus longi, Griphognathus whitei, Orlovichthys limnatis and Rhinodipterus ulrichi.

Like all fish, lungfish have organs known as gills to extract oxygen from water. The biological adaptation of the lung allows lungfish to also extract oxygen from the air.