Ellimmichthyiformes

Ellimmichthyiformes Temporal range: Early Cretaceous–Late Oligocene PreꞒ Ꞓ O S D C P T J K Pg N
Diplomystus dentatus from Wyoming
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Superorder:	Clupeomorpha
Order:	†Ellimmichthyiformes Grande, 1982
Type genus
†Ellimmichthys Jordan and Gilbert, 1919
Families
†Armigatidae †Gasteroclupeidae †Paraclupeidae †Sorbinichthyidae

The Ellimmichthyiformes, also known as double-armored herrings, are an extinct order of ray-finned fish known from the Early Cretaceous to the Oligocene. They were the sister group to the extant true herrings, shad and anchovies in the order Clupeiformes, with both orders belonging to the suborder Clupeomorpha.^[1]

A highly successful group throughout the Cretaceous, they were found worldwide and are known to have inhabited both marine and freshwater habitats. They appear to have been a largely marine group for most of their history, with the first freshwater lineages appearing during the Late Cretaceous.^[2]

Shortly after the origin of the Ellimmichthyiformes in the Early Cretaceous, the Mediterranean portion of the Tethys Ocean appears to have been a major center of diversification for them, as the majority of fossils of this group are known from there. Following this, they saw an explosion in diversity during the Cenomanian, possibly due to the high sea levels of the Tethys at the time and the resulting impact on geography and food distribution, with the group evolving numerous different body plans.^[2][3] However, they were devastated by the Cretaceous–Paleogene extinction event and saw a drastic reduction in range. Only a few freshwater species in the genera Diplomystus and Guiclupea survived primarily in North America and China (although the unusual Gasteroclupea of South America appears to have briefly survived into the Paleocene), including Diplomystus dentatus of the famous Green River Formation. A few marine lineages survived in the Tethys Ocean near modern Italy, such as "Diplomystus" trebicianensis in the Paleocene and Eoellimichthys, the last marine ellimmichthyiform, during the Eocene. The last surviving ellimmichthyiform, Guiclupea, was a freshwater species that occurred in southern China during the Oligocene, representing the youngest member of the group.^[3][4]