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.

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1) สอนจระเข้ว่ายน้ำ (son jarakeh wai-naam)