Thus, the musculature has to arise roughly simultaneously, and be tailored to the particular skeletal structure it is to move. But not only that! Muscles don't move without something like a nervous system. Thus, it has to grow at roughly the same time, and be tailored to the particular construction of the skeleton and musculature. But not only that: there must be some sort of circulatory system, and aeration system, and digestive system......
And oh, look. 600 million years ago these things began happening (well, much earlier, but we have fossils this far back), and 500 million years ago we had the basics. So it took only 100,000,000 generations or so to get there... a basic circulatory system and a rudimentary notochord, protected by a primitive bony membrane, breathing with oxygen filters (gills), wrapped in basic muscular tissue... a sea cucumber, or advanced worm, more or less. |
