So you have "a number of scientists who disagree with" what, exactly? That the Cambrian period was 50 million years in duration? Or that there are precursor fossils? Which is it? Or perhaps it's both. I can provide links to evidence of pre-Cambrian fossils. Can you provide links to credible sources claiming that these fossils are bogus?
For one thing, there are scientists who state that evolution during the Cambrian period occurred from the top down. That is, major new lifeforms appeared suddenly, with small changes occuring after that. They also indicate there are no precursor fossils to show that these major new lifeforms 'evolved slowly over time.'
"Can you provide links to credible sources claiming that these fossils are bogus?"
I gave you the name of a book to read earlier. If you are interested in seeing another point of view, read it. If you'd prefer to protect your worldview, then don't.