Oolon Colluphid

Moved from my Entomological thread, cos nobody’s responded...

I’ve been debating with myself as to whether there’s something ludicrous about echidnas (apart from the reduced poison spur).

Apparently, echidnas can curl up when laying their eggs (which are very small), and so in effect lay the egg straight into the pouch. Fine. But why not lay it there from an inside opening, as I suggested for marsupials? And then, why does it need a shell? Shells are for holding things together while outside the body.

But I’ve not convinced myself it’s a really stupid design.

Conversely, one might think that if a pouch is a Good Idea™ for an egg-laying thing, that it would save birds having to fanny around with nests. Ah, you’ll say, but birds have to fly, and having a nestfull of infants in a pouch would make flight difficult. Sure... but not for flightless birds! If a kangaroo pouch is so great a design, why don’t ostriches have it?!

But like I say, I’ve not convinced myself. Can anyone else suggest why these things are good design really? Or more flaws with these designs?

Cheers, Oolon

Doubting Didymus

Right-o.

Given that the echidna is already a yoga expert and CAN curl itself half inside out and place its egg in its own pouch, what would the actual benifit be to the spiky little bastard if it could lay the egg straight into the pouch? Are there complications associated with laying the egg the normal way that the new setup would avoid? (Obviously its a different question with marsupials that habitually make their live young climb the proverbial everest to get to the pouch)

As for having shells at all, I reckon they're a good idea for the situation the monotremes find themselves in, which is why they actually persisted all these years where every other mammal discarded them. I'm sure you could redesign the monotremes so that they don't need eggs anymore, but the eggshells probably don't use up that much in the way of rescources anyway.

I do thing you're on to something with the flightless birds. Pouches would be a terrific benifit for most of them, and one in particular. I'm thinking of the penguin, and I'm sure you were too. Penguins, like every other bird, need to keep their eggs warm. Living in the silly places they do, however, means they can't have a nest (made of what? shaved ice?). Instead, the poor little buggers have to sit the egg on their feet and cover it with a flap of groin skin. When they do this, they can hardly move, and they have to swap it over to other penguins if they want to go and grab a bite to eat, which often involves rolling it along the ice. Its a dangerous way of warming a goog, and imagine how much easier it would be for them to have that flap of skin surrounded with contractile muscles, like a marsupial pouch between its legs. If it was really good at sealing, (some sort of glands producing water resistant mucous?), then the bird could even take the egg with it swimming for food. There is no questioning that a better developed pouch would be useful to penguins, given that they try as hard as they can to have one anyway.

Nic Tamzek

There *is* a marsupial in australia that has a sealable pouch and goes swimming with baby inside...

With penguins, they don't really have any predators on land, so the 'sit still for three months' plan works.

Doubting Didymus

Which one?

Kuu

I can't think of an Australian marsupial that has a sealable pouch though I do know that the Yapok (Water Opossum) from South America does.

Nic Tamzek

Sorry, I meant 'South America' when I said 'Australia'. Got my neurons crossed or something.

Hey, it's all Gondwanaland to me...

Oolon Colluphid

[/creationist]But . . . but . . . the eggs might get broken! [/creationist]

So, uh, how about having live young? Some snakes manage it!

Thanks, all, for your suggestions. DD, you put the point so well, do you mind if I more or less use it please?

Cheers, Oolon

Oolon Colluphid

Creationists might also argue that the eggs would be too heavy to carry around. Well pregnant mammals have to manage -- seals, for instance. I’ll bet that a nearly-full-term set of seal pups weighs at least as much proportionally as penguin eggs do.

Similarly, other flightless birds would not be leaving their eggs and chicks so vulnerable if they carried them with them. That can’t be any worse than those placentals that carry their infants around. Hey, why don’t monkeys have pouches? Why cling to fur when you could be in a marsupial-type pocket?

I love this sort of speculation. Once you really buy into the Intelligent Designer idea, there’s no end to the things that might be better done in other ways!

Cheers, Oolon

Oolon Colluphid

And what's the betting that viviparous snakes start to make shells before laying, then reabsorb the shell...? Doov will know...

Oolon

Doubting Didymus

Narr worries. Add a dash of yapok while you're at it, just to prove that a watertight pouch is well and truly feasable.