The relationships of Gasteroclupea branisai Signeux, 1964, a freshwater double-armored herring (Clupeomorpha,Ellimmichthyiformes) from the Late Cretaceous-Paleocene of South America

The clupeomorph fish Gasteroclupea branisai Signeux, 1964 from the Late Cretaceous-Paleocene of El Molino Formation, Cayara locality, Bolivia is redescribed in detail. This South American double-armored herring is the sole member of the family Gasteroclupeidae and exhibits a unique combination of features (skull roof ornamented with fine tubercles, beryciform foramen, endopterygoid teeth, about 16–18 supraneurals, a series of 35–38 predorsal and 40 ventral scutes, median fins small and containing 12–14 rays) that clearly supports its assignment to the extinct clupeomorph order Ellimmichthyiformes. G. branisai shares a number of synapomorphies with Sorbinichthys elusivo and S. africanus (five hypurals, second hypural autogenous, distal end of the second uroneural not reaching the distal end of the first uroneural) with which it forms a monophyletic assemblage recognized herein for the first time as the new suborder Sorbinichthyoidei. The peculiar morphology of Gasteroclupea that is characterized by having an extremely deep abdominal profile, hypertrophied coracoid, and elongated pectoral fins, resembles in many aspects the body plan of extant freshwater hatchetfishes of the characiform family Gasteropelecidae, suggesting that the morphological adaptations of G. branisai can be related, at least in part, to a similar lifestyle.