They are similar in appearance to smelts (family Osmeridae) but have much smaller mouths.

They form large schools close to the sea floor, and feed on plankton, especially krill, amphipods, small cephalopods, chaetognaths, and ctenophores.

The earliest fossil argentinid remains are indeterminate otoliths from the Barremian Kimigahama Formation of Japan.

The presence of these fossils in what is thought to have been a shallow-water environment contrasts with the present occurrence of argentinids in deepwater habitats, suggesting that they must have adapted to deep-sea environments later in the Cretaceous.

[1] Otoliths assignable to Argentina are known from the Late Cretaceous (Maastrichtian) of the United States and Germany.