What does the broad success of the Xenacanthidae family imply about ancient connectivity?

Gene flow was possible between continents via viable waterways

The successful adaptation of the broader shark group, Xenacanthidae, resulting in a wide, potentially cosmopolitan distribution across global freshwater environments when continents were configured differently, suggests a high degree of connectivity. This implies that living populations were able to maintain gene flow between areas that would eventually become separated continents, such as North America and Europe. This connectivity was dependent on the intervening or connecting waterways remaining viable across extended durations, allowing the lineage to colonize a broad spectrum of ecological niches unavailable to their contemporaneous marine relatives before continental drift and later climate shifts eventually restricted their final ranges.