so now fish are not tetrapods
Both fish and tetrapods are vertrebrates. And Eukaryotes.
This is why you need to be carefull in your choice of words. "
Totally different" is what you said. But both are vertebrates and eukaryotes. So there goes the "totally".
Also, you might want to keep in mind that the "fish" ambhibians evolved from are not the same fish you can see swimming around
today. Nore are the ancestral amphibians the frogs etc that you can see
today.
Extant fish are the result of hundreds of millions of years of evolution. And the same goes for extant amphibians.
Evolution is a gradual process that works through accumulation of micro changes over generations.
At no point did a "fish" give birth to a "frog".
Now in each case there are also some similarities...
Exactly. So not "totally" different.
And it's the similarities that are important here. If you map out all the similarities between any and all species... you'll start noticing a pattern after some time. A hierarchical pattern. A
nested hierarchical pattern.
If you draw that pattern out, you get a nested tree of similarities. We call this a "phylogenetic tree".
Here's the kicker: you can draw this tree based on multiple
independend lines of investigation.
You can do it by comparing anatomy. By tracing the similarities of a SINGLE bone or physiological feature. By mapping the similarities of a single gene, gene sequence, genetic marker, entire chromosomes,... Even by mapping out the geographic distribution of species.
Each and every one of these
independend lines of mapping, gives us the same basic structure for that tree.
Why is that?
ps: if evolution is true, such a tree is predicted. If this nested hierarchy wasn't present in life, evolution would be falsified.
As for a series of tetrapodal oviparous vertebrates I see them also but do not see reason to assume lineage
How about
conclude?
I do not believe reptiles BECAME either avians OR mammals. Yes we all share anatomical and even genetic similarities but that does not necessitate lineage (just what works).
Actually, it does... at least, if you understand inheritance of DNA works and what it means.
To say otherwise would effectively result in having to deny that things like paternity tests based on DNA, works.