5:15 PM - 7:15 PM
[BPT03-P02] Analysis of Amino Acids Preserved in Miocene Fossil Shark tooth from Wajima, Japan, for Estimation of Trophic Levels
Keywords:shark, Elasmobranchii, enameled, trophic level, Diagenesis, amino acid
The food web in a marine ecosystem can be viewed as an ecological pyramid. The trophic position of an organism in the ecological pyramid is called the trophic level (TL) (Chikaraishi et al. 2010), and is expressed by using the increase in nitrogen isotope composition (δ15N) inherited predatory-prey interactions. In particular, Compound-Specific Isotopic Analysis of Amino Acids (CSIA-AA) is a method that uses the δ15N of each amino acid. This method enables us to discuss the evolution of organisms in an ecosystem by simplifying complex food webs. CSIA-AA has been used relatively recent fossil samples, and demonstrated its usefulness and validity (Naito et al., 2010a; Naito et al., 2016b; Hagehashi 2016MS; Yugami 2018MS). In addition, poorly preserved samples are likely to provide incorrect estimates of the trophic level and the application of CSIA-AA to fossil samples requires thorough examination of fossil preservation conditions (Yugami 2018MS). Thus, CSIA-AA has been applied to Miocene fossil samples, but the number of samples is still small, and the preservation of fossils and the amount of remaining organic matter are important issues. In this study, we conducted basic research to reconstruct the Cenozoic paleoecosystem using shark tooth enameloid, highly mineralized bioapatite, which is likely to have preserved organic matter unaffected by diagenesis (Enax et al., 2012; Kast et al., 2022). We worked on the following: (1) created a database that serves an index for evaluating the diagenesis of fossil samples, and (2) applied the method of inter-crystalline protein removal to enameloid, which has been applied to mollusk shells. In addition, (3) evaluated diagenesis of Carcharodon sp. from the Miocene and detected amino acids. The results showed that it is possible to estimate the trophic level by CSIA-AA in terms of sample volume and diagenesis. Our results indicate that amino acids are preserved in enameloid even in 14Ma fossils, and that it is possible to reconstruct paleoecosystem on a 10Ma scale.