FIELD EMISSON SCANNING ELECTRON MICROSCOPE AND ENERGY DISPERSIVE SPECTROMETER MICROTAPHONOMIC INVESTIGATION OF A TRIASSIC SEMIONOTID, NEWARK BASIN, NEW JERSEY

Macroscopic systematic examination and collection well-preserved fossil fish from the Newark basin provided information concerning diverse fish groups, including semionotids, coelacanths, redfieldiids, and holosteans. Important insights gleaned from these studies include recognition of species flocks, timing of rapid speciation events, species endemism, atavism, and rapid fluctuations in species diversity linked to specific components of lacustrine Milankovitch cycles. Taphonomy of isolated skeletal element deposits have been described previously but this study documents the micro-scale taphonomic processes preserving the complete skeletons.

The semionotid is contained in very fine siltstone to shale. In cross section multiple layers of fish skeletal material is present. The complete specimen was cut into multiple pieces to analyze with Field Emisson Scanning Electron Microscope (FESEM) and Energy Dispersive Spectrometer (EDS). Under FESEM, ovoid isolated to clustered pits are present on numerous bone surfaces including scales and skull bones. These pits transition from isolated to clustered to completely corrugated surface. Pit walls are either smooth-lined or coated with 200 nm spheres. In numerous places, the pitted surface is overlain by sheets of amorphous material with sub-micron embedded spheres and capsules overlain by porous sheets of 1-2 mm voids formed by a 3d a matrix of connected nodules of approximately 300 nm in diameter. EDS analysis indicates nm nodules are predominately carbon enclosed in CaCO₃. Within the sheets of amorphous material, euhedral rhomboids are found lying atop matrix. EDS analysis of the rhombs indicates the presence of an iron-sulfide mineral- possibly pyrite. Voids record the former presence of bacteria that corroded bone and are now preserved as external molds by carbon. Rare 1-1.5 mm long by 100 nm wide twisted sheaths with inflated ends or multiple strands up to maximum ~100 mm length and branching off shoots recording the rare presence of possible fungus.