Evidence that land animals evolved the ability to breathe air as ancient fish

January 24, 2014, Flinders University

Evolution’s first breath
Professor John Long.
(Phys.org) —In a major evolutionary discovery, Flinders University palaeontologist Professor John Long (pictured) has found evidence to show that four-legged animals first developed the ability to breathe air as ancient fish in water.

Published yesterday (Thursday, January 23) in the international journal Nature Communications, the research shows the Polypterus, the most primitive living bony fish, breathes air through large canals on top of its head called spiracles.

The discovery marks the first step in the evolutionary transition of similar ancient fishes to the land as tetrapods, or four-legged animals.

Professor Long, the Strategic Professor in Palaeontology at Flinders, said the research points to the likely conclusion that the ancient Gogonasus – which belonged to a group of fish widely regarded by scientists as the ancestors from whom the first land animals evolved – originally developed its breathing abilities using its spiracles.

He said the groundbreaking discovery signals the origins of breathing for the four-legged descendants of these ancient fish.

"Polypterus had holes on top of its head but we never knew what they were actually for until we observed the fish over a long period of time and found they were breathing through their spiracles," Professor Long said.

"Until now we've only had theories about the origins of breathing in the evolution of fish to land animals – some early 19th Century scientists had these wacky ideas that fish just jumped onto the land and started gasping for breath and developing limbs," he said.

"But our research shows that the transformation actually started happening within the fish themselves while they were still in water."

As part of the study, a team based at The Scripps Research Institute in the US observed species of Polypterus for 360 hours and measured the amount of oxygen it was taking in.

He said the findings on Polypterus is the "smoking gun" that points to fossils such as Gogonasus as being capable of breathing in air through their spiracles.

"Other lobed-finned fish fossils of that age show large spiracles on top of their heads and the earliest known tetrapod fossils also have large open spiracles on their heads.

"All this points to the ability of these fishes to take in air from their spiracles as the first type of breathing, which ultimately helped them leave the water and invade the land."

Professor Long said once the four-legged descendants of the lobed-finned fish abandoned the water, the ability to breathe through their spiracles declined as they switched to breathing using their mouths and nostrils, as humans do today.

"The spiracles eventually became the hearing canal in which tetrapods transmitted sound to the brain via tiny inner ear bones, and this has remained throughout the evolution of fish right through to humans," he said.

"If not for the bold evolutionary experiments of these prehistoric in air through the top of their heads, we might not have evolved such a keen sense of hearing."

Explore further: Lungfish provides insight to life on land

More information: "Spiracular air breathing in polypterid fishes and its implications for aerial respiration in stem tetrapods." Jeffrey B. Graham, Nicholas C. Wegner, Lauren A. Miller, Corey J. Jew, N Chin Lai, Rachel M. Berquist, Lawrence R. Frank, John A. Long. Nature Communications 5, Article number: 3022 DOI: 10.1038/ncomms4022
Received 01 May 2013 Accepted 27 November 2013 Published 23 January 2014

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1.8 / 5 (5) Jan 24, 2014
The learned prof is too quick to jump to conclusions. Insects and some more derived spiders have spiracles on their exoskeletons to allow air to enter the trachea. Does that mean humans, insects and spiders have common a piscine ancestor?
5 / 5 (4) Jan 24, 2014
"Until now we've only had theories about the origins of breathing in the evolution of fish to land animals – some early 19th Century scientists had these wacky ideas that fish just jumped onto the land and started gasping for breath and developing limbs," he said.

Are those the only theories they had?? What are some of the credible alternatives to fish breathing air before developing limbs and moving to land? This "discovery" sound like a no-brainer.
5 / 5 (6) Jan 24, 2014
@gcbailey: They are not homologous spiracles, because (as can be seen from the article) spiracles on the head is not the ancient state of fishes. We can see that in modern fishes I think.

@jahbless: They likely didn't know of the tetrapods at the time. So they envisioned a different pathway (land first, limbs later). Even today, among established competition from us tetrapods, many non-tetrapod fishes do fine traversing land (but a closer examination shows many of those indeed use the fins).
5 / 5 (4) Jan 24, 2014
Actually, already the abstract responds to questions put here. An excerpt:

"The polypterids (bichirs and ropefish) are extant basal actinopterygian (ray-finned) fishes that breathe air and share similarities with extant lobe-finned sarcopterygians (lungfishes and tetrapods) in lung structure. They are also similar to some fossil sarcopterygians, including stem tetrapods, in having large paired openings (spiracles) on top of their head. The role of spiracles in polypterid respiration has been unclear, with early reports suggesting that polypterids could inhale air through the spiracles, while later reports have largely dismissed such observations. Here we resolve the 100-year-old mystery by presenting structural, behavioural, video, kinematic and pressure data that show spiracle-mediated aspiration accounts for up to 93% of all air breaths in four species of Polypterus."
2.7 / 5 (7) Jan 25, 2014
That fossil has been misidentified, obviously not an ancient fish but an ancient shoe, you know giants walked the earth back then.
Whydening Gyre
1 / 5 (1) Jan 25, 2014
That fossil has been misidentified, obviously not an ancient fish but an ancient shoe, you know giants walked the earth back then.

Actually, pretty much the same size. The EARTH was smaller, but it's center was expanding... which might explain the why for tectonic plate activity...:-)
not rated yet Jan 25, 2014
@Torbjorn_Larsson_OM. Not homologous - true, but that's sidestepping the issue. The simple truth is that all the evidence shows design of whole species, not darwinian evolution (hence the phyletic vs. PE theories).

1 / 5 (1) Jan 25, 2014
I like it. In the last sentence/figure-of-speech, he disowns the whole evolutionist's dogma of the "blind forces of nature". Just a habit of mind and language? Are you sure?
Whydening Gyre
5 / 5 (1) Jan 25, 2014
Weren't "spiracles" olfactory sensors originally?
Seems to me that, fortuitious circumstance presented a group of fishes an opportunity to develop the habit of "sniffing" the air above the water. Energy of critters above that water is higher density, leading to the habit of eating said critters.
Additionally. Oxygen is more readily available in air than water. If I'm not mistaken, olfactory systems signal the presence of this vast reservoir of oxygen to the brain. Brain says, hmm, how can we capitalize on that? DNA says - here, hold my beer, I wanna try somethin'...
Voila! Another habit is born!
Also fairly convincing evidence that an organism's reproductive organs (that, coincidentally, manage to pass on those habits) are direct-wired to the brain's habit forming mechanism...
Another connection! Sex addiction ain't so hard to believe!
Whydening Gyre
not rated yet Jan 25, 2014
5 / 5 (1) Jan 26, 2014
Some ideas seem "obvious" and some are logical inferences.


but my post was not as cool as WG
Whydening Gyre
not rated yet Jan 26, 2014
Apologies for the seeming triteness of post - at 2 in the morning, my brain just does that kinda stuff, y'know?
BTW. Good links, ACW.
Got my mind churning on adaptive connection to breathing out of water.
Whydening Gyre
not rated yet Jan 26, 2014
Or maybe you were referring to the empty one...?

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