H. geei was initially described as Clupea geei from multiple specimens, one relatively complete, in an Eocene estuarine fossil fish assemblage discovered near Malgin in Kohat District, Pakistan.[2]H. intertrappea was described in the new genus Horaclupea from several articulated specimens from freshwater sediments in the Intertrappean Beds of India.[1] These formations were initially dated to the Late Paleocene or early Eocene, but have been more recently dated to the latest Cretaceous or earliest Paleocene.[3]
The abundance of H. geei in estuarine sediments, in addition to the occurrence of H. intertrappea in freshwater sediments, suggests that Horaclupea may have been an anadromous taxon that migrated up rivers to breed and schooled in large shoals. It was initially suggested that H. geei may represent the young stage of a hilsa-like clupeid, but the lack of any adult specimens in the Kohat assemblage, as well as the presence of similar individuals in the Intertrappean Beds, indicates that it may just represent a small-sized clupeid species.[1][2]
It was described as being potentially related to Diplomystus[1], but that taxon has since been classified into a different order (Ellimmichthyiformes). However, recent taxonomic reviews have retained Horaclupea as an indeterminate clupeid.[4][5]