ROOM 10 · INTERPRETIVE THREAD

Bridges Allowed Migration

After the Dinosaurs

DEEP TIME INTERPRETATION

Source Institution: Smithsonian National Museum of Natural History

Source Exhibit: David H. Koch Hall of Fossils - Deep Time

Source Url: https://naturalhistory.si.edu/visit/virtual-tour/current-exhibits/deep-time-virtual-tour-fossil-list

Source Kind: interpretive_topic_or_panel

Use: research inspiration only; SAGE will write original interpretation

Dossier Status: scientifically_enriched_concept_room_10

Plain Language Explanation: Changing geography can turn oceans into barriers and then open routes between continents. During Pleistocene glacial periods, lower sea level exposed Beringia between Asia and North America. Mammoths, bison and many other lineages used this broad landscape during episodes of dispersal. Land connections were not permanent highways, and climate and habitat could make a connection usable for one species but unsuitable for another.

Evidence: Pleistocene sea-level fall repeatedly exposed the Bering Land Bridge.; Fossil distributions document mammoth and bison dispersal between Eurasia and North America.; Genetic evidence shows that migration was episodic rather than constant unrestricted movement.

Examples From Collection: Mammuthus primigenius; Bison priscus

Migration Guard: Presence of a land bridge does not prove every species crossed it or that populations moved continuously in both directions.

Common Misconception: The Bering Land Bridge was not a narrow temporary footpath. At times it was a vast exposed region with its own ecosystems.

What Scientists Still Debate: Researchers continue refining the timing and direction of individual dispersal events using fossils, dating and ancient DNA.

Sources: https://www.nps.gov/articles/beringiamegafauna.htm; https://www.nps.gov/subjects/beringia/about.htm; https://home.nps.gov/articles/000/quaternary-period.htm

Enrichment Method: SAGE original interpretive concept; natural Earth-system change separated from human-driven change; migration, body size, ecosystem reconstruction and human impacts tied to explicit evidence and uncertainty