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.[2]
Their sister group were the extinct Ellimmichthyiformes, which were dominant throughout much of the Cretaceous and into the Paleogene,[5] 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 CretaceousofSouth 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.[6][7]
^lfonso L. Rojo (2017). Dictionary of Evolutionary Fish Osteology. CRC. p. 170. ISBN978-1-351-36604-5. Under the name Isospondyli, Regan (1909) grouped the fishes having the verterbrae immediately after the skull similar in shape to the remaining ones, in contrast to the ostariophysans, in which the anterior vertebrae are greatly modified. Modern classifications have rejected this artificially constructed group, and the fishes previously assigned to it have been distributed among different orders (Clupeiformes, Osteoglossiformes, Salmoniformes, Cetomimiformes, etc.)
^Sébastien Lavoué, Peter Konstantinidis & Wei-Jen Chen: Progress in Clupeiform Systematics. in Konstantinos Ganias (Hrsg.): Biology and Ecology of Sardines and Anchovies. CRC Press, 2014, ISBN978-1482228540
^Froese, Rainer, and Daniel Pauly, eds. (2023). "Clupeiformes"inFishBase. July 2023 version.
