Come back in a million years or so.

June 29, 2020 7:32 AM

An overview of evolution and atmospheric changes. Why birds have great lungs and mammals don't.
posted by Nancy Lebovitz (14 comments total)

I love this genre of whimsical children's stories backed up by hard science. Also in this genre, Grandmother Fish (previously)
posted by otherchaz at 8:03 AM on June 29, 2020 [2 favorites]

Reading this story leads me to a question that had never occurred to me before: If all these shifts in oxygen levels are linked to carbon storage, does that mean there should be enough fossil carbon to reduce oxygen levels in the atmosphere back to very low levels if we find and burn it all? I.e. does this suggest that there's a lot more carbon than we've found so far?
posted by clawsoon at 9:00 AM on June 29, 2020 [1 favorite]

Yes, though it needn’t all be in high-energy-density fuel form.
posted by clew at 9:13 AM on June 29, 2020 [3 favorites]

e.g. calcium carbonate, chalk.
posted by justsomebodythatyouusedtoknow at 9:19 AM on June 29, 2020 [3 favorites]

Yes, it’s called a literary conceit.
posted by Big Al 8000 at 12:54 PM on June 29, 2020 [3 favorites]

Birds have better eyes, too. Much better acuity, and better color vision. Four cones, instead of three. Mammals that survived the KT event were small and burrowing, so their eyes weren't that great, which is why we can't see infrared or ultraviolet.

And octopi don't have blind spots.
posted by leotrotsky at 1:16 PM on June 29, 2020 [2 favorites]

Bird senses are mindblowing. Pigeons were once trained to search for overboard boaters by the USCG, although advanced cameras have replaced them.

Lots of animals can see into UV but I don't think any can see into near IR.
posted by head full of air at 1:55 PM on June 29, 2020

Birds also have amazingly compact brains.
posted by Nancy Lebovitz at 1:58 PM on June 29, 2020 [2 favorites]

How do the air sacs in birds' bones connect past the points of articulation?
posted by Joe in Australia at 2:41 PM on June 29, 2020

Lots of animals can see into UV but I don't think any can see into near IR.

Maybe ferrets?
posted by jedicus at 3:38 PM on June 29, 2020

head full of air

Animals that can see in the IR

Pit vipers (they can sense IR, but is that seeing?), some frogs, blood-sucking insects, and some fish.
posted by Nancy Lebovitz at 4:36 PM on June 29, 2020

I stand corrected! I had no idea fish and frogs can see into the near IR! So cool. They have an enzyme that uses vitamin A2 to shift their cones 30-60nm towards red (so they can see up to ~730-780nm).

It can be hard to figure out what some pop-science articles mean by "IR" vision since it is every wavelength from 700nm-1mm, a range much broader than visible light (~400-700nm)

At the near end is light just beyond red, which apparently some animals can see with their eyeballs. Heat infrared or long wave infrared is what pit vipers can see (8,000-12,000nm) using the heat-sensitive pits on their face, but not their eyes. Although vision pits are a primitive form of eye.

Do ferrets have wet noses? That might explain why they could identify IR LEDs, even if they couldn't see them, since LEDs do emit some heat. It was recently discovered that dogs can detect thermal infrared with their wet noses.

The trail cam market is definitely upselling 870nm and 920nm LEDs as "invisible IR" for animal photography. Most security cams have 740nm LEDs and if I look at them at exactly the right angle I can usually see some dim red, and I assume other mammals can too.
posted by head full of air at 10:17 PM on June 29, 2020

The author is the same Walter Murch who did sound design for a wide range of prestigious films. When Kipling told his various animal origin stories to his daughter Josephine it was his meticulous editing and storytelling prowess - that led her to demand that he re-tell them in exactly the same manner, without change - and hence "Just So". Murch seems to have the same sort of creative outlook. What I like is that he slips in so many scientific concepts that most adults (me included) would be ignorant about - into a story that is nominally intended for a child.

He frames natural selection as being the result of decisions and long term goals. That's incorrect even in a children's story.

True - but then the Just So Stories would be very much excluded on the same grounds, and the world would be a poorer place for that. As one of the commenters on the article put it - the head of R&D would surely be Gaia, however.
posted by rongorongo at 3:17 AM on June 30, 2020 [1 favorite]

So did the proto-dinosaurs really evolve the entire lung system after oxygen had declined, or was there some sort of preadaptation that accidentally set them up for the shift? It's almost always the latter when something complex like that appears relatively quickly...

--Ah, here's a great recent review: Respiratory evolution in archosaurs. Apparently crocodilians have unidirectional airflow though they lack many of the other avian/dinosaur adaptations, and that's likely what the proto-dinosaurs had:

Airflow in the secondary bronchi and parabronchi of crocodilians is unidirectional [19,26], a feature once thought to be unique to birds. Unidirectional airflow through the lungs is maintained by aerodynamic valving and is a result of airway geometry in crocodilians [19,26].

Though the article generally supports the hypoxia scenario, it also says:

However, this hypoxia scenario is not well supported by the fossil record. Many faunas were still synapsid dominated in the immediate aftermath of the P-Tr extinction [92], and some Triassic synapsids grew to large sizes similar to their archosaurian contemporaries [93]. Archosaurs did not become the main faunal components in terrestrial ecosystems until the Late Triassic [94], 30 Ma after the P-Tr extinction.

A fun read, and Figure 1 in particular gives a nice evolutionary tree.
posted by chortly at 10:07 PM on June 30, 2020