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Re: Hell Creek seaway
Finally, occurrences of marine-related fish in the Hell Creek of
> eastern Montana are of special interest (see Bryant, 1989,
> U.Cal.Geol.Sci., v. 134). These include sawfish (Ischyrhiza), rays
> (Myledaphus), hybodont sharks (Lissodus), orectolobid sharks
> (Squatirhina), and marine teleosts (Belonostomus, pachyrhizodontids).
> A few taxa of rays and sawfish live in brackish to fresh water in the
> modern world (in the lower few hundred kms of some tropical river
> systems), but the overall aspect of the Hell Creek assemblage
> certainly suggests marine influence -- Bryant "consider[s] these fish
> indicative of nearby marine conditions." These marine-related Hell
> Creek fish occur throughout the Hell Creek sequence, including the
> uppermost part. They are known to occur in the Bug Creek and Harbicht
> Hill channels, which encompass faunas straddling within a few meters
> of the K-T boundary (latest Cretaceous-earliest Paleocene). As
> suggested by Bryant (p. 8), "the presence of sharks and rays in the
> uppermost Hell Creek formation is indirect evidence that the seaway
> remained nearby until virtually the terminal Maastrichtian."
Bryant's view on elasmobranchs as the freshwater elasmobranch fauna of
the Lance first appears in the latest Albian and is recorded in all
freshwater microsites (representing stage and in some cases substage of
the cretaceous). In some cases sites are well recorded as 100s of miles
from ocean. Some taxa like Myledaphus and earlier undescribed genera in
the lineage have never or very rarely been found in marine strata.
Lisodus is known in freshwater back to the Triassic.
Bryant's bonyfish are marine taxa however.