Data from: Fish and tetrapod communities across a marine to brackish salinity gradient in the Pennsylvanian (early Moscovian) Minto Formation of New Brunswick, Canada, and their palaeoecological and palaeogeographical implications

Euryhaline adaptations in Pennsylvanian vertebrates allowed them to
inhabit the marine to freshwater spectrum. This is illustrated by new
assemblages of fish and tetrapods from the early Moscovian Minto Formation
of New Brunswick, Canada. Fish include chondrichthyans (xenacanthids and
the enigmatic Ageleodus), acanthodians (gyracanthids and acanthodiforms),
sarcopterygians (rhizodontids, megalichthyids and dipnoans), and
actinopterygians (eurynotiforms). Tetrapods include small- to
medium-sized, and largely aquatic, stem tetrapods (colosteids) and
anthracosaurs (embolomeres). A key finding is that the parautochthonous
fossil assemblages are preserved across a salinity gradient, with
diversity (measured by the Simpson Index) declining from open marine
environments, through brackish embayments, and reaching a nadir in tidal
estuaries. Chondrichthyans dominate the entire salinity spectrum (65% of
fossils), a distribution that demonstrates a euryhaline mode of life, and
one large predatory chondrichthyan, Orthacanthus, may have practised
filial cannibalism in coastal nurseries because its heteropolar coprolites
contain juvenile xenacanthid teeth. In contrast, other fish communities
were more common in open marine settings while tetrapods were more common
in coastal brackish waters. While all these faunas were also likely to
have been euryhaline, their osmoregulation was, perhaps, less versatile.
The demonstration of widespread euryhalinity among fish and aquatic
tetrapods explains why Pennsylvanian faunas generally show a cosmopolitan
biogeography because taxa were able to disperse via seaways. It also
resolves the paradox of enriched strontium isotopic signatures observed in
these faunas because organisms would have been, at times, exposed to
continental water bodies as well. Therefore, our new findings contribute
to the long-running debate about the ecology of Pennsylvanian fishes and
tetrapods.