Where the coastal hypothesis connects to the USR1 story is through the model of how the Ancient Beringian and proto-First American lineages diverged.

If the proto-First Americans moved south along the coast while the Ancient Beringians remained in the interior of the Beringian region, the geographic separation of the two groups would have facilitated the genetic divergence that produced the distinct lineages.

The Ancient Beringians would have been the interior Beringian branch; the proto-First Americans would have been the coastal branch, moving south along a route that eventually connected Beringia to the rest of the Americas.

This geographic model is speculative — it goes beyond what the USR1 genome alone can establish — but it is consistent with the genetic evidence and with the geographic distribution of the two lineages as far as it can be characterized.