A very ancient and fish-like smell

Heard a number of fish stories this week, at least three of which are worth repeating.

The Gogo formation, an ocean reef that ended up in the middle of the Australian desert, has thrown up another fi.. err .. funny fossil. Except that this fossil apparently sat around in a museum for about 30 years before being reinterpreted (did I hear something about going slow & looking closely ?) Placoderms were armored fish, distantly related to today's sharks and bony fishes, that swam around during the Devonian, and died out in the same great extinction that took out the trilobites. This placoderm was an early arthrodire, a variety with even more armor than usual, and some neat features like a movable neck and armor plates instead of teeth. A bit like how a medieval knight out for a swim might look (sans horse and lance perhaps). What makes this particular find fascinating is the presence of fossil embryos inside some of the fish, and what might have been some kind of claspers for use in mating. Read all about the convergent evolution of claspers, or how to keep that fish from getting away.

Throw in sex, and one thing usually leads to another. In this case, I was led to a story from last year that illustrates the next chapter in the tale: live birth. Head-down baby whales last week, pregnant placoderms this time (and I thought water birthing was a fad). Gogo read about Attenborough's mother fish.

So it looks like the ichthyosaurs were just reinventing yet another old strategy. Time for this week's question: how many times did live birth get invented as animals went in and out of water ? Write in with your lists, readers and contributors !

Legged like a man and his fins like
arms! Warm o' my troth! I do now let loose
my opinion; hold it no longer: this is no fish
- The Tempest, Act II, Scene 2

This next fish only sat on a shelf for about 17 years, but is a catch worth bragging about. It walks on the sea floor, swims about with jet propulsion, but balls up and bounces along the seabed every once in a while. And in spite of a face to launch a thousand squids, this anglerfish holes up in tiny crevices and ambushes curious wanderers. Histiophryne psychedelica, or how I learnt to stop tripping and love the snorkel. Now in technicolor.

Legged like men, though, was whoever left these footprints. And left-legged too. Escape from bad onomatopoeia, and run away to read about this leap of evolution.

You can never run away too far however, especially if you're a crocodile. Hoping to confound the bearings of these persistent navigators, humans are now resorting to magnets, because the theory out there is that crocodiles somehow use magnetic fields to find their way back home from hundreds of miles away. As far as I've been able to find out though, there doesn't seem to be any serious study reporting the use of magnetic compasses in crocodiles ... if you know of any sources write in and make a crocodile-fan happy. As for whether the magnets will actually work to confuse them, my money's on the archosaurs. As one Thai proverb goes, don't teach a crocodile to swim.¹

This of course says the same thing as that old Roman saw - piscem natare doces - you're teaching a fish to swim. Evidently it isn't just old jokes and fish fins that get recycled.

--
1) สอนจระเข้ว่ายน้ำ (son jarakeh wai-naam)

If Nature had intended us to fly, she would have given us fingers

You cannot learn to fly by flying. First you must learn to walk, then to run, then to climb, then dance.
- Friedrich Nietzsche

Nietzsche should perhaps have added swimming to that list - but then again, there are more things on earth than are dreamt of by philosophers, so on to this week's list.

Here is a lecture on the evolution of flight by John Maynard Smith. Maynard Smith started off as an aeronautical engineer designing planes during World War II, but is much more famous for his work in using game theory to understand animal behaviour. This lecture is especially fun because Maynard Smith applies basic aerodynamics to make a pretty deep observation about the evolution of flight in animals. Flying, as far as we know, independently evolved four times: among insects, pterosaurs, birds and bats. Maynard Smith shows how a tail is necessary for flight stability, and how as the ability to fly develops, all four groups seem to have moved to shorter tails and more complicated flight controls for better maneouvrability. I was delighted to look at the fossil of the bat Icaronycteris this week, and see how bats had long tails too when they evolved during the Eocene !

In comparison, animals seem to have independently evolved aquatic lifestyles many more times. My list so far has ichthyosaurs, plesiosaurs, mosasaurs, whales & dolphins, seals (?), elephants ... and I'm surely missing some (Can you think of any more ? Write in and let me know !) I wonder if aerodynamics also constrains the evolution of swimming animals. Anyway, what we do know from this past week are more details of the path that whales took, about all the walking and running and giving-birth-head-first that they did before taking to the water like a .. err ... like a fish: here's the tale of the good mother whale. Or an awful limerick - take your pick.

Whale was once a land-lubber
Who would wallow in pools and slumber.
Slowly, his hands became fins
So his legs he traded in
For some flukes and a coat of blubber.

Bears don't fly, but they surely know how to walk, and run, and swim very well. I was brought up to believe that the Jungle Book song couldn't be true, but bears can dance too ! And get themselves some bare necessities while they're at it: a sort of fish slapping dance.

If all this makes you feel bad for the poor salmon though, you might just be looking out for family -- so cheer up and have a whale of a week.

A Jawful of Ears

Been 'earing a lot of things this week. First off, an article for biologically-challenged physicists about echolocating bats & dolphins that I found from Sep 2007. Evidently, dolphins reverted to the older listen-through-your-jawbone formula - do jawbones work better as acoustic antennas in water ? Those clicks and whistles do a lot more than just find food though. Take a look at this beautiful set of videos from lifeonterra.com: Ocean Acrobats gets both thumbs and both toes up.

Elephants, which of course can never make up their minds about anything ⁽¹⁾, pick up low-frequency sounds through their feet and then pass them on to their ears. Now some primates want to use these signals to lure marauding pachyderms to safety: Elephantine Valentine messages ?

Now I've heard of cats climbing trees, but catfish climbing up trees sounds a little ... fishy. Not content with inventing radio communication, some catfish apparently decided to go out on a limb. They're launching satellites next, as you read this.

And, here's Bucky !










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^{1) KT, who has often said.}