Abstract

Osmeriformes represent an important component of freshwater ecosystems in Australia and New Zealand yet are poorly represented in the fossil record in these countries. Here we describe Ferruaspis brocksi gen. et sp. nov. from the Miocene of New South Wales, Australia. Phylogenetic analyses place the species as a basal member of the southern radiation of Osmeriformes. The fossils are embedded and mineralized in the iron oxide-hydroxide mineral goethite, resulting in an extraordinary unusual degree of structural preservation. Preserved stomach contents indicate an opportunistic benthopelagic diet, evidenced by the remains of numerous phantom midge larvae (Chaoborus), two insect wings, and a bivalve. Another bivalve (Unionidae) was found attached to the tail of one of the specimens. The distribution of melanophores preservation of melanosomes indicates that the species was counter-shaded with two lateral stripes. Discovering this species west of the Great Dividing Range, with a population that includes a range of body sizes, suggests that at least this population if not the species spent its entire life in freshwater, unlike most extant Osmeriformes. The description of F. brocksi highlights the ability of exceptionally well-preserved specimens thatwith preserved soft tissues to reveal aspects of the paleobiology of extinct species.