I have always been confused by the Moa's Ark theory which is part of a debate as to whether the Ratite families (Ostriches, Emus, Kiwis, Moa, Cassowarie, Rhea) got split up from each other when Pangea split, since they're all flightless and can't swim far. Or whether their ancestors did fly and migrated to the separate continents and then they all lost flight later down the line but then how does that work?
Also just generally interested in a wider understanding of bird speciation following continental splits. For example with passerines colonising Africa by travelling first through Europe and Asia but then also apparently some jumping straight across the ocean from Australia?