ON XIPHENAX JURASSICUS COCKERELL (COLEOPTERA) AND ITS LOOK-ALIKES FROM THE NORTH AMERICAN JURASSIC

The North American Jurassic is almost completely devoid of entomological reports, with the notable exception of two lithographic limestone deposits: the Sundance Formation, located in northern Wyoming and southern Montana, and the Todilto Formation, located in northern New Mexico, both Callovian, upper Middle Jurassic. While the Sundance is rich in an aquatic paleoentomofauna, particularly coleopterans and heteropterans, the Todilto is apparently depauperate. The first insect formally described from the Todilto was Xiphenax jurassicus Cockerell, an aquatic insect known from only one specimen. After seeking illumination at the British Museum, and with much hesitation, the noted entomologist of the late 19th and early 20th century T. D. A. Cockerell declared X. jurassicus to be a coleopteran larva. Nevertheless, this enigmatic organism of uncertain family placement bears some resemblances to extinct members of the Adephaga, such as the Coptoclavidae, as well as to the modern Amphizoidae. Additionally, among the over 3,000 fossils from the Sundance housed in the Department of Paleobiology at the National Museum of Natural History (Washington, DC) currently being studied by us, we have found several dozen of currently undescribed Xiphenax-like fossils. The largest specimens range from 22 to 25 mm long and 7 to 9 mm maximum width. We present additional data on these beetle larvae, including X. jurassicus, and emphasize the role of technology, including several types of microscopical approaches, in highlighting characters that typically are difficult to image, allowing more detailed paleobiological studies.