The most basic assumption of macroevolution, that of common descent, cannot be questioned ... sacrosanct.
Yes they can be questioned, just do the research, write a paper citing your falsifiable evidence, and submit it for peer-review.
“While biologists do draw a distinction between micro-evolution and macro-evolution it really is a distinction without much difference. Or to put it another way, the distinction is a rather artificial one imposed by biologists. The simple answer is that the process at work in macro-evolution is precisely the same one at work in micro-evolution. So to say I believe micro-evolution, but not macro-evolution may sound erudite to the uneducated, but to those who are familiar with the topic you sound like a boob. It is like saying I believe in molecules, but not in atoms, electrons, protons and neutrons.” ~ Steve Verdon
“Microevolution is a term - when used by creationists - that is the evolutionary equivalent of the belief that the mechanism you use to walk from your bedroom to the kitchen is insufficient to get you from New York to Los Angeles.” ~ Unknown
There are different kinds of assumptions. The word can refer to taking something to be true without any evidence: "I assume that if we ask them nicely, Al-Qaeda will be our friends." It can also mean taking something to be true because so much evidence supports it: "I assume that if I throw this ball in the air, it will come down."
At this point, common descent is much closer to the second kind. Lots of new evidence could have weakened it as a hypothesis; instead, new evidence from fossils, molecular biology, lab experiments, and more have tended to support it. So now it's an assumption the way a gardener assumes he has to water his crops. It's not something to reconsider every time he plants a new garden--and common descent isn't something scientists reconsider every time they find a new fossil.
Which isn't to say it can't be questioned. But scientists aren't going to pay attention to someone questioning it just on the basis of its being an assumption and saying they have to demonstrate its validity all over again, any more than a gardener is going to listen to someone saying, "Are you sure you need to water those?" The questioner needs to bring an awful lot of counterevidence to get those kinds of assumptions reconsidered. And that's as it should be.