Wednesday, February 14, 2007

Further rounds of the God game

Sometimes you kick a rock and all you get is a sore toe. Sometimes you kick a rock and it hits some other rocks and pretty soon half the mountain is coming down.

It's probably too early to tell on this one. I blogged on Brain Candy Topic #117 the other day--or, as some would have it, threw down a gauntlet. Darren Naish picked it up. We'll see where it goes. I've already gotten some good suggestions, and I'm sure Darren will get a lot more.

I've got more ideas. Ideas for speculative zoology, and ideas about speculative zoology. I'm putting the former in this post and the latter in the next.

This evening I grabbed some awesomely cheesy, greasy pizza with my freakishly productive labmate, Randy Irmis, and we took turns coming up with evolutionary experiments.

I would like to see how Actinopterygii (ray-finned fishes) would fare if all the sarcopterygians (lungfish, coelocanths, all vertebrates with legs) suddenly went extinct. I assume they'd invade the land, but how? Their limb musculature is all inside their bodies. Would they be forced to truck around on fins modified into stilts? Maybe they would evolve jointed limbs actuated remotely by freaky long tendons. In gestalt appearance, they might be closer to arthropods than tetrapods.

I would also like to clear out all tetrapods other than bats. I've always been intrigued by the utter absence of flightless bats, and the flightless bats from After Man were wicked cool. What would a world repopulated by flightless bats look like? Would some bats find new uses for their fingers and wing membranes if they were no longer constrained to be airworthy? Would we get penguin bats? Whale bats? Fossorial bats? What if some bats lived in caves and only came out at night? Oh, wait.

I think games like this are a good heuristic for finding out what animals you are possibly more interested in than you realize. I would like to see a world where edentates took over. No, monotremes. No, lissamphibians.

As for Randy, he'd go back to the Triassic and rub out the cynodonts (basal synapsids get to live). Would mammals still evolve, or would reptiles get the whole pie? (My guess: the latter. Mammalian success in the Triassic looks like a fluke to me.) He'd to go the K/T and let the mosasaurs slip through. Do whales, sirenians, and pinnipeds even have a chance to evolve? (My guess: yes. Marine mammals evolved in the presence of sharks, and later in the presence of other marine mammals. You don't have to get there first if you can get there better.)

He would go back to the Cambrian and whack the early chordates. Excellent choice. It is hard to imagine most non-chordates stepping into those shoes. But then they've never had the chance, have they? That's the whole point.

After a while, "kill X" or "kill everything but X" gets a little old. So we started tinkering with the world in more subtle ways.

What if the Earth had no axial tilt? No seasons. That could have some radical implications for ecology. In a classic paper, Hairston, Smith & Slobodkin (1967; free PDF here) posed the question, "Why is the world green?" Why aren't herbivores able to eat up all of the available plant biomass? "Because they'd starve to death" is not a convincing answer. If starvation was all that was holding the herbivores back, we ought to see constant cycles of overgrazing, mass starvation, and recovery. But we don't. Something is keeping the herbivore populations in check. Maybe it's predators, maybe it's plant defenses. I suspect a big part of the answer is seasonality. We may look at the green world and think, "This place could support a lot more herbivores," but the real question is, how many herbivores can a region support when it is dry or brown or covered in snow?

But what if there were no seasons? No dry season, no winter. Without seasonal harshness to hold them down, could herbivores catch up with plants? Maybe the world would become a wasteland, populated by fast-growing plants that could flower within a single day, and prowled by lean, fast-moving herbivores that would range over wide areas eating plants as soon as they appeared and aestivating between rains. Even if herbivores couldn't catch up, something would have to change. Possibly evolutionary arms races would be accelerated. Plants would need more horrendous defenses, and burgeoning populations of herbivores would need some way to fight off the carnivores. Would a world without seasons be a hyperkinetic pressure cooker of biotic destruction? (As a proponent of Predator Theater, I'm not opposed to that.)

What if the collision that created the moon had never happened? (Image courtesy of Nova Celestia.) The Earth would be a little smaller, a little lighter. It would spin faster. Days would be shorter. And with no moon to slow things down, days would stay short for a long time. What would tectonics be like on this smaller, lighter, faster-spinning planet?

Speaking of, what if we could turn the tectonic fires up, down, or off? Say plate tectonics stopped right now. How long would it take for erosion to grind everything down? Presumably the whole world would eventually be under water. How long would it take? What would the topography of this static world be like, as the mountain ranges wore down and the ocean basis filled up? Perhaps the flattening land and the filling, rising seas would meet in huge mud flats, hundreds or thousands of miles across. How would plants and animals adjust to Mudworld? Maybe there would not be empty mud flats, but mangrove forests spanning entire continents.

All of this brain play is not in vain. In the next post, I'm going to take a stab at a big question: why engage in speculative zoology?


If you like wacky chimaeric critters, check out the photoshopped animal contests at Worth1000, where I stole a couple of the images above.

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Anonymous Sordes said...

I had also some time ago my thoughts about the possibility of fish which reconquered terrestrial terrain. One thing I discovered was that terrestrial fish would not cogently have to have legs. Eels (which are already today well-suited for a distinct terrestrial lifestyle) could become terrestrial and evolve into various snake-or probably caecilian-like animals with a wide variety of different ways of life. If you look how many fish have already today a more or less amphibious behavior, it seems strange that amphibians evolved only once. There were also many debates why animals like Acanthostega developed legs and fingers, although they lived still in the water. The fact that there are even today fish with "legs" and "fingers" around, could make things much easier. The amazing anglerfish-family has some members which uses their flipper in the same way as amphibians underwater, and in fact it´s nearly insultung to call their jointed limbs still flippers. They have even some sort of claws at the end of the fingers and use them to climb on coralls, rocks or algea, or actually walk on the bottom. Such fish would good candidates for a re-conquering of the land, but as they live only in the sea and only very few species come close to shores, other species would be probably faster.
The evolution of terrestrial bat is also very fascinating, and I still wonder why there was not much more radiation of the New-Zealand bats.

5:26 AM  
Blogger Mike Taylor said...

I think games like this are a good heuristic for finding out what animals you are possibly more interested in than you realize. I would like to see a world where edentates took over. No, monotremes. No, lissamphibians.

Sauropods! Sauropods!

(Yeah, I know it's predictable, but wouldn't you have disappointed if I hadn't?)

Dwarf arboreal frugivorous sauropods. Vicious killer carnivorous sauropods. Giant herbivirous sauropods. Wait -- already got those, you say? Not this big you haven't!

Excuse me. I have to go and lie down.

7:44 AM  
Anonymous wolfwalker said...

Here's an interesting speculation I came up with a while ago: Go back to the Devonian (or further if necessary) and develop tetrapods in which the vital inputs (food, respiratory, sensory) are not all concentrated close together in the head. Every living tetrapod herbivore is handicapped by the fact that while it's actually eating, its eyes and nose are basically useless. How much difference would it make if herbivores could keep watch for danger while they're eating?

8:16 AM  
Blogger Poseidon said...

This is one concept for which I've been doing some illustrations:

All biota on land (other than bacteria) are utterly wiped out at some point in the Holocene. The oceans, however, are largely unaffected by the catastrophe, except in the intertidal zones, etc. The recolonization of land has to re-start, beginning with algae, then arthropods (I used amphipods for the role), then mudskippers and related fish with strong pectoral fins. These would compete with fish who acquired snake-like motion on land (I looked at sordes' post and saw he came up with a similar idea!).

Could we please, please start a message board for this? We could have illustrators, scientists, and writers all working together!

11:04 AM  
Anonymous Sordes said...

Here´s a very cool video of a bizzare frogfish which walks on the sea-floor like a cross between a toad and a hedgehog:

8:45 AM  
Blogger Dr. Vector said...

Wolfwalker, I like your functional segregation thing. I think some of Nemo Ramjet's critters are split like that. Barlowe's Expedition might be another source to check. Of course, they were both working with overtly alien animals. It would be cool to think about how something like that would play out here on Earth.

Sordes, you're right about the frogfish etc. I wish I knew more about the functional morphology of those guys, and especially of mudskippers. Both look like good potential candidates to colonize the land.

Poseidon, I've got too much going on to set up a website for this stuff, but you might be able to find others who want to play. Tim Morris has taken the torch from Darren and set up "Squamate World" on a new blog, Squamozoic.

If you could find some like-minded people, a shared blog would seem to be the way to go. If you put anything together, let me know.

2:42 AM  

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