Ancient brain of our closest fish cousins

An ancient, big-brained Australian fish is the subject of new research that effectively drags its brain millions of years through time.

A group of researchers from Sweden and Australia used 3-D modelling and X-ray technology to reveal links between the brain of the Australian lungfish and its 365-million-year-old relatives, fossils of which were uncovered in Western Australia.

The lungfish is the world’s most enduring vertebrates, remaining relatively unchanged since the Cretaceous period when it lived alongside the dinosaurs. The oldest lungfish lived over 410 million years ago. 

Among fish species, is also the closest living relative to humans. Their relatively big brain fills about 80% of their cranial cavity, a trait which makes them more human-like than most fish.

These fishy cousins of ours offer “great insight into our ancient ancestors who first crawled out of water and onto land some 370 million years ago”,  says Flinders University evolutionary biologist and lead author of the paper, Alice Clement.

The new “brain-warp” method is important because when it comes to ancient anatomy, brains are extremely difficult to study.

“Animals’ soft tissue usually breaks down, so discovery of a fossilised brain is very rare,” explains John Long, a palaeontologist at Flinders University and co-author of the paper.

“We believe our new brain-warp technique can be adopted across many other fossil groups and will revolutionise the way scientists restore fossil brains and how they study them.”

Through a CT scan of one of three living species of Australian lungfish (Neoceratodus), Clement and her colleagues used the relationship between brain and cranium as a template to reconstruct the shape of the brain of the ancient lungfish (Rhinodipterus) from its fossilised skull.

“We can use the ‘brain warp’ computer technique to virtually morph the ‘modern’ brain of the lungfish into the early cranial cavity, or fossil endocast, from the fossil Rhinodipterus found in a renowned Devonian site in Western Australia,” Clement explains.

Researchers say understanding brain development in different species will provide a crucial piece of the evolutionary puzzle.

“This is an exciting way to more accurately reconstruct and understand changes in the brain and behaviour over the centuries,” Clement says.

“In fish, it can help us understand in which groups and when certain senses such as smell or vision became more important than others, and how the development of higher cognitive centres may have helped some groups flourish while others flounder.”

The technique was published in the journal Royal Society Open Science.