Clupeiformes

Clupeiformes is the order of ray-finned fish that includes the herring family, Clupeidae, and the anchovy family, Engraulidae and sardines. The group includes many of the most important forage and food fish. Clupeiformes are physostomes, which means that their gas bladder has a pneumatic duct connecting it to the gut. They typically lack a lateral line, but still have the eyes, fins and scales that are common to most fish, though not all fish have these attributes. They are generally silvery fish with streamlined, spindle-shaped bodies, and they often school. Most species eat plankton which they filter from the water with their gill rakers. The former order of Isospondyli was subsumed mostly by Clupeiformes, but some isospondylous fishes (isospondyls) were assigned to Osteoglossiformes, Salmoniformes, Cetomimiformes, etc. Their sister group were the extinct Ellimmichthyiformes, which were dominant throughout much of the Cretaceous and into the Paleogene, and often coexisted with clupeiforms at many known localities. Both groups closely resembled each other morphologically, although the ellimmichthyiformes evolved some highly divergent body plans later in the Cretaceous. Several fossil clupeiforms are known from the Early Cretaceous of South America that appear to be more closely allied with Clupeioidei over the Denticipitidae. This suggests a very deep divergence within the crown group Clupeiformes that must have occurred during the Early Cretaceous or before.