A new paraclupeid fish (Clupeomorpha: Ellimmichthyiformes) from the Lower Cretaceous Sidi Aich Formation of southern Tunisia: phylogenetic and paleobiogeographic implications.

A new paraclupeid fish, Tunisiaclupea speratus, gen. et sp. nov., is described from the Upper Barremian (Early Cretaceous) of the Chotts Basin, southern Tunisia. With a series of predorsal scutes of different size and shape, it is distinguished from other paraclupeids by the following combination of characters: anterior neural spines unfused; first uroneural bearing a dorsal laminar expansion and extending anteriorly nearly to third preural centrum; and hypural diastema present. The results of a phylogenetic analysis reconfirmed the monophyly of Ellimmichthyiformes and resolved Sorbinichthyoidei (Gasteroclupeidae + Sorbinichthyidae) as the most basal clade, with the Diplomystus clade the next, Armigatidae more derived than Diplomystus clade but with few diagnostic features, and Paraclupeidae with well-supported monophyly. Tunisiaclupea was resolved as a basal paraclupeid and an intermediate lineage between Ellimma branneri from the Lower Cretaceous of Brazil and Tycheroichthys dunveganensis from the Upper Cretaceous of North America. Tunisiaclupea is among the oldest ellimmichthyiforms known so far and extends the distribution of Paraclupeidae to the southern Mediterranean Tethys in the Early Cretaceous. Ellimmichthyiform diversity reached its peak in the Mediterranean region during the early Late Cretaceous, which might have resulted from allopatric speciation promoted by the sea-level highstand and the consequential land-sea distribution with increased food input, dispersal routes, and habitat fragmentation for these fishes. [ABSTRACT FROM AUTHOR]