MOUTH-SIZE ESTIMATION OF THE SHARK, PETALODUS OHIOENSIS, FROM THE HUGHES CREEK SHALE (CARBONIFEROUS) OF SOUTHEASTERN NEBRASKA

The Chondrichthyan shark, Petalodus ohioensis, is the only carnivorous species commonly recovered in the Hughes Creek Shale Member of the Foraker Formation (Carboniferous) of the US midcontinent. Teeth are the only body parts known for the species, and their morphology suggest that their diet consisted of the shelly invertebrates of the diverse benthic fauna. Despite numerous reconstructions actual body size and mouth size remain unknown. Tomita (2011) developed a regression method for estimating mouth size (and subsequently body size) from isolated tooth elements. Using an extension of the Tomita method on teeth collected from two different exposures of the Hughes Creek Shale in Richardson County, Nebraska, supplemented by measurements taken from the literature, allow for preliminary estimates to be made for the first time on a Paleozoic shark species (upper jaw lengths up to 10cm). Such jaw sizes could easily accommodate any potential prey species from the documented fauna of the Member, although no actual Petalodus-bite marks have ever been recorded. Tomita (2011) created the method for extant and younger fossil species of the Lamniformes, and our uniformitarian extension of the method to extinct Petalodontiformes remains tentative