Carangaria (jacks, flatfishes, billfishes, and kin) are a
morphologically diverse clade of primarily marine spiny-rayed
fishes characterized by a wide array of peculiar behavioral and
anatomical novelties. The oldest undisputable body-fossil
records of carangarians are from around the Paleocene-Eocene
boundary, with many examples from faunas apparently
coincident with the Paleocene-Eocene Thermal Maximum
(~56 Ma). Molecular clocks point to the origins of the group
late in the Cretaceous or early in the Cenozoic. Here, we
report on a new species of the carangarian Mene from the
Eastern Desert of Egypt. The fish-bearing horizon
characterizes the anomalous marl beds of the Latest Danian Event, a hyperthermal, and is securely dated to 62.2 Ma.
Assignment of the new specimens to Mene is supported by
numerous synapomorphies (e.g., compressed disc-like body,
anteroposteriorly elongated dorsal and anal fins with relatively
short rays, narrow pelvic fins with a compressed and greatly
elongated second ray. However, these new specimens exhibit
a unique combination of features compared to other species of
Mene: separate first and second neural spines, no lateral
laminar expansions of the dorsal pterygiophores, rounded
dorsal and ventral profiles of the maxilla, a distinctive patterns
of ridges on the frontal-supraoccipital crest, straight posterior
border of the angular, and a rectangular shaped ceratohyal
with no dorsal expansion. These suggest that the Danian Mene
from Egypt represents a new species, with the retention of
primitive features indicating it might represent the sister
lineage of all other members of the genus. The discovery of
definitive material of Mene in the early Paleocene extends the
record of that genus by over six million years. More
significantly, the highly specialized anatomy of Mene makes
the new Egyptian fossils an robust new marker for establishing
the timeline of diversification within Carangaria, and indicates
that some of the most specialized anatomies within the group
were already present a few million years after the CretaceousPaleogene extinction. The remarkable similarity of Mene
species over 60 million years of evolutionary history
represents a striking example of anatomical stasis. |
