Quote:
Originally Posted by NotReady
I don't know how Godidit. Maybe through some natural process. But this kind of evidence makes it difficult to see how a fishapod becomes a tetrapod if tetras were here first, and how it could be gradual if they are so close together in time.
Okay, let's try and untangle this a bit.
The way things work in changes in species isn't like a line where one becomes the next thing that becomes the next thing. It isn't a straight line and the "previous type" doesn't necessarily die off. Also, we are speaking of something happening all over the world, and making a timeline from what we have found.
So, the timelines are always pretty elastic. You can say: "Tetrapods appeared at this time..." But scientists know when they read that, that it is shorthand for, "The oldest example of this type of animal we have found to date is..." Paleontology doesn't give "dates of birth" to classifications of animals. Not very specific ones, anyway.
There were "salamander-like" creatures with feet and toes, who literally walked on the bottom of the seabed, that is, not air-breathers, before we find examples of primitive lunged animals. So, the feet came first for some species. But, we have now African fish who crawl out onto the mud and are able to breathe air, and they use their fins, so in mud-hoppers, the lungs are coming first.
It's not a line, it's a jumble. Australopithecines evolved from gibbon-like primates. But we still have gibbons and siamangs. However, we no longer have Australopithecines. Biological evolution is the most complex branch of science there is, IMO, and it is taught in very simplistic ways. This leads pretty much everyone into not understanding much of how it works.
Not that we understand that much, anyway.