OSTEOLOGY OF MIOCENE FOSSIL FISHES FROM THE NEVADA TEST SITE

Fossilized remains of an unknown species of cyprinidontiformes (top minnows/pupfish) fish were recovered on the grounds of the Nevada Test Site. The specimens were found in Miocene volcaniclastic lake sediments and range in size up to 10 cm. The original bone material of most specimens was missing, leaving high-fidelity natural molds in hard silicified silt. Silicone rubber molding compound was used to reproduce the original appearance of the bones. Images of these rubber casts were made with a high-resolution, flat-bed scanner and with a scanning electron microscope. From these images it is possible to compare the skeletal structure of these fish to modern fish, and to other Miocene fish fossils. Individual anatomical structures were recognized by utilizing a disassembled carp skull. Notable structures are key to the reconstruction of lost species. Although the species has not yet been determined, it appears that only one species is represented, suggesting a stressed environment in these volcanic lakes. The high-resolution casts also show growth lines on the scales and ostracods in the gut, giving a clue to the trophic structure of the paleoecological community. This study gives us a window into the late Cenozoic era, and the environment of the fish. Like their ancient counterparts, modern topminnows live in extreme habitats. Finding how these fish met their end could give us insight into how we might protect similar, threatened, species today.