Gasteroclupea is a genus of prehistoric clupeiform fish related to modern anchovies and herrings.
Clupeiformes are physostomes, which means that the gas bladder has a pneumatic duct connecting it to the gut. This handy little evolutionary feature lets them fill or empty the gas bladder via their mouth. They typically lack lateral lines but have nicely defined eyes, fins and scales. They are generally silvery fish with streamlined, spindle-shaped, bodies, and often found in schools. Most species eat plankton which they filter from the water with their gills.
Gasteroclupea date back to the Maastrichtian of the Late Cretaceous. We find fossils of the genus in the Yacoraite Formation of Argentina and in the El Molino Formation of Bolivia, as you see here. Photo credit: Gilberto Juárez Huarachi.
