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Author Topic:   Evolving the Musculoskeletal System
Member (Idle past 1132 days)
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008

Message 171 of 527 (578639)
09-02-2010 7:08 AM
Reply to: Message 165 by Bolder-dash
09-02-2010 5:25 AM

The origins of skeletons
Bolder-dash, please do not reply to this message in this thread. Please take these issues to your New name for evolution, "The Bacteria Diet" thread. --Admin
So talk us through this Melindoor, what do YOU personally think the first mutations to those primitive fish without any skeletons at all would have looked like?
Here was this soft fleshy kind of fish thing, that had no spine, and no bones of any kind. And then what do you think that very first mutation that started the whole process out looked like? Was it a piece of bone near where the spine already was? Or was it a piece of bone that started off somewhere near his belly, and then over time and many generation slowly migrated over towards his back? Do you think those early first fish with the bones near their stomach looked silly, compared to the others? Do you think the other fish laughed at him, or do you think the female fish decided he was special, and so he got a good selection advantage, and that is why more fish ended up with the bony stomach?
As Meldinoor pointed out, we can't be certain of the exact route the evolution of the skeleton took. What we can do, though, is to look at fossils, and at still existing animals with primitive skeletons, to work out which bits probably came first.
The oldest skeletons were cartilage, which was only (partially) replaced by bone later. Looking at the near relatives of the vetebrates, we find the lancelets. These little creatures don't have any skeleton, nor do they have a proper brain, a heart, or any paired fins. They do, however, have little bits of cartilage. These aren't randomly strewn around the body, they're in places like the tail, where stiffness helps them get the propulsion they need to burrow into the sand, and supporting the gill arches.
The big step to the development of a skeleton came with the evolution of a skull. We can be confident the skull came first, as there are living and fossil animals, like hagfish, which have skulls but no other skeleton. The advantage of a skull is, I hope, obvious. It protects the newly evolved brain from damage. Sexual selection is unlikely to have played much of a role in any of this - the skeleton just had clear survival advantages.
Edited by Admin, : Add moderation comment.

This message is a reply to:
 Message 165 by Bolder-dash, posted 09-02-2010 5:25 AM Bolder-dash has not replied

Member (Idle past 1132 days)
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008

Message 184 of 527 (578935)
09-03-2010 4:42 AM
Reply to: Message 182 by crashfrog
09-02-2010 3:45 PM

The varieties of coelacanth
And, of course, the modern Coelacanth is about a fifth of the size of any of its evolutionary precursors.
I think you go a bit confused here - fossil coelacanths range in size from tiny to massive. Modern coelacanths have a total length of between about 4' and 6'. Coelacanthus, the type genus, were no longer than 3'. Polyosteorhynchus doesn't seem to have gotten any bigger than 7" or so, while giant Cretaceous coelacanths like Megalocoelacanthus have been discovered with lengths up to 11'.
Clearly though, coelacanths haven't remained the same as time has gone by.

This message is a reply to:
 Message 182 by crashfrog, posted 09-02-2010 3:45 PM crashfrog has not replied

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