A FIELD EMISSION SCANNING ELECTRON MICROSCOPIC EXAMINATION OF EOPLIS EKDALEI ICHNOFOSSIL LATE JURASSIC MORRISON FORMATION, ADDITIONAL EVIDENCE FOR A TERMITE GENESIS

The Late Jurassic Eoplis ekdalei (Smith et al, 2020) ichnofossil from the Morrison Formation in Utah is a proposed as a social insect trace that is supported by the gross morphology and associated small-scale structures. The proposed trace maker was narrowed to probable termite origin. Cosrinsky et al. (2005) proposed a series of micromorphological criteria that permit the identification of a termite origin. Cosrinsky et al. (2005) criteria include: microaggregate pellets, coarse mineral components, and fine materials which includes clay microaggregation, plant remains, and termite cuticle fragments all distributed along the cut rock surface.

Employing these criteria, Eoplis ekdelei was examined in Field Emission Scanning Electron Microscope (FESEM) and Electron Dispersive Spectrometer (EDS) and lends additional support for a termite origin of this ichnofossil. The Morrison Formation ichnofossil microaggregate pellets are <100 µ and oblong shaped defined by very porous encasing clays and silts. Coarse mineral components are present and range from fine sand to granule size. Fine materials including clay microaggregates are present in various sizes and orientations, some layer appears to lay vertical, horizontal, and even radial infilling near voids where plant and insect remains exist. Silt-size plant remains are present. Cuticle fragments occur and >100 µ. External molds of apparent arthropod fragments are present. In addition to these criteria, FESEM microimaging displays complex textures consisting of variations in porosity on the 100 µ range. EDS analysis of the substrate and voids consists of semi-rounded quartz, spherical opal, late-stage radial and pore-filling barite, and clays. Clusters of 40 by 140 µ ellipsoids of unknown origin may be evidence to termite activity possibly representing fecal pellets. Fibers are present and fungal activity is observed in the same material. These ichnofossil features are congruent with termite traces and important for understanding termite nest evolution.