2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 327-6
Presentation Time: 2:45 PM


MCMENAMIN, Mark A.S. and HUSSEY, Meghan C., Geology and Geography, Mount Holyoke College, South Hadley, MA 01075, husse22m@mtholyoke.edu

Ever since Mary Anning and William Buckland recognized bezoar stones as coprolites, these fossils have provided important paleoecological data. The Late Triassic (Carnian-Norian) Luning Formation of Nevada is best known for its giant ichthyosaurs (Shonisaurus). Interpretations of the Luning Formation depositional setting and paleoecology are controversial, thus any new information regarding the paleoecology and diet of the ichthyosaurs is potentially significant. We report here a large (9.2 cm x 5.8 cm) coprolite (cf. Heteropolacopros; reconstructed dimensions 16 cm x 9.5 cm) from the Luning Formation. EDS analysis of the coprolite shows a significant phosphorus peak, consistent with interpretation of the ichnofossil as being derived from a predatory animal. CT scan analysis shows internal clot mottling comparable to that of Late Triassic (Revueltian) coprolites from the Bluewater Creek Formation, New Mexico. CT scanning also reveals polygonal shrinkage fractures comparable to those of Rhynchocopros soutoi (Middle Triassic, Santa Maria Formation, Brazil). The size and morphology of the large coprolite suggests that it may have been produced by a shonisaur. An elasmobranch origin seems unlikely as the coprolite lacks a spiral fabric; furthermore, shark teeth or ray jaw plates have not been reported from the Luning Formation. Bony fish remains (?palatine fragment) are visible on a broken surface near the center of the large coprolite. A second, smaller Luning Formation coprolite (also cf. Heteropolacopros; ?juvenile; greatest dimension 2.3 cm x 1.5 cm, reconstructed dimensions 3 cm x 1.7 cm) shows clot-mottling fabric at roughly the same interior position as seen in the larger specimen. Both coprolites may have been produced by shonisaurs, and if so, they are among the earliest known ichthyosaur coprolites as well as the first to be reported from the Luning Formation. The partially‑digested fish bone in the larger specimen provides direct evidence for the Shonisaurus diet.