A Paleocene (Danian) marine osteoglossid (Teleostei, Osteoglossomorpha) from the Nuussuaq Basin of Greenland, with a brief review of Palaeogene marine bonytongue fishes

The early Palaeogene represents a key interval in the evolution of modern
marine fish faunas. Together with the first appearances of many familiar
fish lineages characteristic of contemporary marine environments, early
Palaeogene marine deposits worldwide feature the occurrence of
osteoglossid bonytongues. Their presence in marine rocks is surprising, as
these fishes are strictly associated with freshwater environments in
modern settings and other parts of the fossil record. Despite its possible
relevance to faunal recovery after the K–Pg extinction, this marine
osteoglossid radiation is relatively understudied. Here we describe an
osteoglossid specimen from marine Danian deposits of western Greenland
(Eqalulik Formation, northern Nuussuaq Peninsula). It consists of
disarticulated cranial, pectoral and vertebral material belonging to a
relatively large-bodied predator, similar to the widespread †Brychaetus
but with some distinctive features. This specimen expands the geographic
range of extinct osteoglossids to the Arctic and represents one of the
earliest records of this group in marine deposits. We review other fossil
occurrences of marine osteoglossids, highlighting temporal and
biogeographic patterns that characterize their rise, diversification and
sudden disappearance in the middle Eocene. It is likely that the
transition from freshwater to marine environments occurred around the K–Pg
boundary, possibly related to ecological replacement of predatory fish
lineages that went extinct at the end of the Cretaceous. Further study of
the Eqalulik Formation fauna could yield additional insight into the
consequences of the end-Cretaceous extinction on marine fish evolution and
on the assembly of modern marine faunas.