EDS AND CT ANALYSIS OF A TRIASSIC SILICIFIED PTERONISCULUS SP. NODULE FOUND IN NORTHERN MADAGASCAR

Triassic-aged nodules containing fish, crustaceans, and ammonites are well known from the Diana Region, near the city of Ambilobe, northern Madagascar. Traditionally, the fossils from this fauna have been studied as crack-out remains when the nodule is opened. CT-scanning technology allows us the opportunity to see within the nodule and visualize the 3D relationship of the skeletal elements. A nodule containing the fish Pteronisculus sp. was analyzed morphologically and taphonomically for this study. The silicified nodule preserved the fossil as a void within the center with minor compaction, suggesting early cementation driven by the early stages of decay. The fossil itself is an external mold with no remains of the boney or soft parts of the fish. The mold is distinguished from the rest of the nodule by its high abundance of iron oxides, which are not present in such high abundances elsewhere in the nodule.