Fish find could cast light on ‘watershed moment’ by identifying the birth of breathing

Original story at ABC News

The emergence of life from water on to land is a pivotal moment in evolutionary history, and scientists say a new discovery may shed light on how it was able to happen.

Palaeontologists have verified a 200-year-old hunch about an African fish and, in the process, showed how the first land animals developed the ability to breathe.

The scientists found the polypterus, a bony fish species, receives most of its oxygen not through gills but primitive nostrils on the top of its head.

Scientists had previously noticed similar holes, known as spiracles, in fossils of much more ancient species which are today regarded as the ancestors of modern land animals.

His new research, in conjunction with a team based at the Scripps Research Institute in the US, has now been published in the journal Nature Communications.

He says the spiracles in ancient species were a key step in evolution, allowing marine life to survive on land for the first time.

 

“For many years, us palaeontologists have found fossils of ancient fish that have these peculiarly large holes on the top of their heads,” he said.

“We never knew what they were for so the evidence from our study shows these ancient fossil fishes were using these holes to breathe air.”

The scientists examined polypterus specimens for 360 hours, measuring the amount of oxygen inhaled by the fish.

“We can actually see what it does with the spiracles. It rises up to the surface of the water so the head’s still under water, but just the top of the head hits the surface,” Professor Long said.

“These little valves in the top of the head open and it sucks in.

“These sort of fish take in a lot of their oxygen through their gills but they top it up with lungs so they use both, so it’s a sort of evolutionary half-way if you like between true fishes breathing with gills and land animals that breathe entirely through their lungs.”

History of human hearing linked to origin of breathing

Professor Long says the spiracles were eventually replaced in most species as they switched to breathing through their noses and mouths.

But their legacy remains in our bodies and without them, we may not have adapted such an acute sense of hearing.

“Our new research has really nailed the origin of breathing in our deep, distant ancestors and as a by-product it’s also give us the story about how human hearing has its deep ancestry way back in the evolution breathing,” Professor Long said.

“When [the fish] left the water and invaded land and began to breathe air through the regular way, you know, through your nose and nostrils and mouth, this hole had another purpose.

“It then switched to becoming a hearing tube and eventually evolved into the tube leading to the inner ear.”

Professor Long says the research has an interesting lineage in its own right.

The groundwork was laid by French naturalists who noticed the strange spiracles on the polypterus when they were in Egypt as part of the Napoleonic invasion

“Napoleon lost his battles and so they had to rush back to France,” Professor Long said.

“They thought these fish were breathing in through the holes in the top of their head but nobody believed them and then a detailed a study done in 1968 by scientists in a laboratory said that these fish definitely do not breathe through their heads.”

But scientists became suspicious when they examined the set-up of those experiments.

“They were in a laboratory that was not reflecting [the fish’s] natural conditions,” Professor Long said.

“The new group thought that work was wrong because the fish were stressed.”

Proof perhaps of Isaac Asimov’s quip that “the most exciting phrase to hear in science … is not ‘Eureka’ but ‘that’s funny’.”