We do not prove in science. Evolution explains these fossils, and no other scientific theory does so.
It is Inference based on all the available physical data. Not "assumption."
Criticism is the basis of scientific evaluation of ideas. If you claim that an accepted theory is wrong, you better be able to back it up. If you cannot handle criticism, stay out of the kitchen.
Science is not a democracy. Not all ideas are given equal value. You have to back up your conclusions in science, or you will feel it.
You know, I have heard this argument about what "science" does and doesn't do so often here. The definition of "science" and what it proves or the fact that it "proves" nothing, is presented here over and over.
Who really knows what the definition of "science" is and what does it matter?
The fact is...... fossils are a static piece of data that show what a particular creature had for bones. It is anyone's guess as to what that creature had for parents and all you know for sure is that it had some.
You cannot say what it's great great great grandfather was or it's great great great grand kid was. You cannot even tell if it had kids, brothers or sisters.
The information from a fossil is limited, in fact, greatly limited.
So, what definition of "science" that you want to present has no bearing on the amount of information that you can learn from a bone, pile of bones or what ever. Taking it beyond the absolute facts is extrapolation, speculation, interpretation, assumptions and in most cases a pipe dream at best. You have taken it out of the realm of any form of science and put it into guessing.
The fact that some dude has a bunch of letters after his name does not mean that in some miraculous way, he can see into the past to see what this creature had for ancestors. Nor can he extrapolate what happened to the creatures offspring. It's a guess, period.
If you gather 1,000,000 million of these dudes together and they agree, it still doesn't magically create a fact out of a guess. Truth is not proven by a democracy.
As far as someone presenting a criticism of these guesses, it happens from time to time. The critic is promptly discredited for being a creationist and therefore, biased. Meanwhile, everyone of the egg heads promoting the assumption are also biased.
There is an unspoken, unmerited, unprofessional, unscientific, and unmentionable opression on those who speak out against the theory of evolution.
Truth is being squashed in order to keep the theory of evolution on life support.