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Mammaphibians?; Where reptiles never existed.
Topic Started: Feb 24 2010, 03:16 AM (580 Views)
Pando
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First of, I would like to say hi to everyone!

Second, I was wondering, what if in an alternate world mammals came straight from amphibians 300 million years (around 20 million years after reptiles evolved) and the bats are extinct (bats have evolved in this world), having evolved into the more successful birds 50 million years ago. How would life be in this strange world? With synapsids and reptiles never existing (the P-Tr extinction and KT extinction must be kept in mind).
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Dean
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Well, if we think about it, the basal amniote body, from which synapsids and diapsids evolved was more similar to the pelycosaur, than the diapsid body, because synapsids branched off earlier from the amniote line, and the stuff that makes diapsids different (scaly, glandless skin, uric acid production) evolved later.

Technically the only thing that distinguishes basal amniotes from reptiliomorph tetrapods is the ability to lay eggs on land, and the only thing that makes pelycosaurs different from basal amniotes is their synapsid skull.

Mammals are actually more similar to reptiliomorph amphibians than to reptiles!

So a pelycosaur-like group that evolves from reptiliomorph amphibians can be imagined, but their amphibian mode of reproduction (laying eggs in water, tadpoles) would restrict their size and they would be more dependent on water, so maybe the group couldn't continue on a road towards more the mammal-like therapsidian forms.

If they don't evolve a temporal fenestra analogue, they couldn't evolve better jaw muscles that would eventually lead to chewing.
Edited by Dean, Feb 24 2010, 06:28 AM.
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Pando
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I said that they were mammals, so they would have all the characteristics that define mammals. They are mammary glands, sweat glands, fur, and 3 middle ear bones. Because they have mammary glands they do raise their young.

Also, you forgot about the birds. I don't know how bats could of retained egg laying (so that the birds have all the characteristics of today), maybe the bats could of had a pouch in which they stored their eggs, or maybe in the caves that they sleep?

And the ones that I'm wondering the most would be what would fill snakes and crocodiles? I think that amphibians could hold the crocodile niche, but I can't think of a snake niche filled by mammals.

BTW, the eggs of the mammals are amniotic, so they can colonize land. Also the fact that the young are raised means that they won't occupy several niches in their life, which gives even more mammals. Would a placenta evolve at all? And would the birds out compete the bats, or would the amount be around 50/50, since bats seem to do pretty well even with birds around today.
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Pando
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And for the bats, they have evolved feathers from the beginning, but besides that everything the same, like poorly developed feet, no airsacs, etc.. But the birds are exactly like ours, except for maybe the toothless part.
Edited by Pando, Feb 24 2010, 02:20 PM.
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