| Carolowilhelmina geognostica|
Arthrodira, Rhachiosteus, Rolfosteus, Hadrosteus, Oxyosteus
Carolowilhelmina geognostica is an extinct arthrodire placoderm fish that lived in the Late Eifelian epoch (of Middle Devonian) of Spain. In life, C. geognostica was a long-snouted pelagic fish, superficially similar to the Australian Rolfosteus, from Gogo Formation and the European Oxyosteus of the Kellwasser facies of Bad Wildungen, Germany. As with Rolfosteus, Carolowilhelmina possessed a long tubular rostral plate, with small postnasal plates and low inferognathal plates. According to Mark-Kurik & Carls (2002), this placoderm may have lived in an pelagic environment with lush, floating algae and epiplankton. It is currently known only from an incomplete cranium that is about 40 cm (16 in) long. The fossil material is housed in the Palaeontological Museum of the University of Zaragoza, Spain (Museo Paleontológico de la Universidad de Zaragoza).