This is VERY interesting. I'm going to have to print
this out to digest it.

https://onlinelibrary.wiley.com/doi/epdf/10.1002/ajpa.24923
Founder effects identify languages of
the earliest Americans

Abstract
The known languages of the Americas comprise
nearly half of the world's language families
and a wide range of structural types, a level
of diversity that required considerable time
to develop. This paper proposes a model of
settlement and expansion designed to integrate
current linguistic analysis with other
prehistoric research on the earliest episodes
in the peopling of the Americas. Diagnostic
structural features from phonology and
morphology are compared across 60 North
American languages chosen for coverage of
geography and language families and adequacy
of description. Frequency comparison and
graphic cluster analysis are applied to
assess the fit of linguistic types and
families with late Pleistocene time windows
when entry from Siberia to North America
was possible. The linguistic evidence is
consistent with two population strata defined
by early coastal entries 24,000 and 15,000
years ago, then an inland entry stream
beginning 14,000 ff. and mixed
coastal/inland 12,000 ff. The dominant
structural properties among the founder
languages are still reflected in the modern
linguistic populations. The modern
linguistic geography is still shaped by the
extent of glaciation during the entry windows.
Structural profiles imply that two
linguistically distinct and internally diverse
ancient Siberian linguistic populations
provided the founding American populations.

Results:
There is enough evidence (linguistic,
archeological, genetic, and geological) to
indicate four glacial-age openings allowing
entries to North America: coastal c.24,000
and 15,000 years ago; inland c. 14,000 years
ago and continuing; and coastal c. 12,000
years ago and continuing. Geographical
distribution of modern languages reflects
the geography and chronology of the openings
and the two human and linguistic population
strata they formed, and plausibly also the
structural types of the founding languages.