The passage discusses the bidirectional movement of animals across a bridge, indicating that it wasn't a simple one-way migration. While notable species such as the mastodon, saber-tooth cat, and rhinoceros made their way from Asia to the Americas, other creatures, including the camel, actually emerged in America and migrated to Asia, showcasing a complex interchange of species between the continents.

This exchange highlights the dynamic nature of animal migration and evolution, revealing how flora and fauna traversed borders, contributing to the biodiversity of both regions. The author, James A. Michener, emphasizes the significance of these movements in shaping the ecosystems of the new world and Asia alike.