I literally cited the first hit from the most obvious google search. You sound curious and dissatisfied with the science reporting. Why don't you look up the paper, possibly use sci-hub if it isn't freely available, and actually read what the scientists say?
I was hoping someone would save me the searching and link me directly to relevant papers. I think the article should have done it itself, as the assumption is rather fundamental to the whole theory.
Similarly I didn't see any mention of intermediate evolutionary stages being found for either a case 1 or 2? If someone sees a paper that does that, it'd be cool
The dissatisfaction is warranted as the article is ONLY noteworthy IFF one assumes there was a complete extinction event on the atol.
Without the assumption of this extinction event, the story is simply this: "There are rails on this island. And, there are fossils of rails on this island."