I've noticed that a lot of clades that first appear in the early Paleozoic seem to immediately be present across the globe, even though the continents at the time were mostly disconnected and separated by oceans. For example, (calcified) trilobites suddenly appear in Cambrian Stage 3, but are already present in Laurentia, Siberia and parts of Gondwana, despite the vast distance and oceanic separation of the landmasses. Similarly, Rugose corals appear in the late Middle Ordovician, but already seem to present across the equatorial regions of the globe.
How did these benthic/sessile clades(so I'm not referring to pelagic trilobites) manage to spread geographically wide so fast? Is there any way we could know what landmass was the actual "birthplace" of some of them?