PRELIMINARY STUDY ON THE FEASIBILITY OF BONE HYDROXYLAPATITE STABLE CARBON ISOTOPIC COMPOSITION INDICATING EARLY CRETACEOUS BIRDS' DIET

Reconstructing the diet of Early Cretaceous birds is crucial for comprehensively understanding the evolution of early birds and the Mesozoic terrestrial ecosystem. Nowadays the stable carbon isotopic composition of bone hydroxylapatite (delta C-13(B-HA)) provides an effective way to analyze the paleodiet, however, no research applied to early birds has been reported yet. In this study, bones from four Early Cretaceous birds including Confuciusornis and Sapeornis were collected for Fourier Transform Infrared (FTIR) analysis, to preliminarily determine whether the delta C-13(B-HA)-based paleodietary analysis was feasible for early birds. FTIR spectra of CoqfUciusornis STM 14-112, Sapeornis STM 15-27, and Sapeornis STM 15-7 present characteristic absorption peaks of H2O, PO43- and CO32- which are comparable to those of modern hydroxylapatite. Their FTIR indexes including PCI (3.18-3.41), Ca1P (0.27-0.30) and CO32- contents (7.71-8.25%) fall within the corresponding ranges of modern vertebrates (<4.3, 0.15-0.7, 2-13.4%, respectively), further indicating those early bird's bones are less affected by diagenesis during burial. Therefore, the delta C-13(B-HA) values of Confuciusornis STM 14-112, Sapeornis STM 15-27, and Sapeornis STM 15-7 could effectively reflect their diets. While the FTIR spectrum of Sapeornis STM 15-33 shows peak (at 710 cm(-1)) that indicating calcite, and its CO32- content (13.7%) is greater than the modern hydroxylapatite's, suggesting the bone of Sapeornis STM 15-33 is contaminated and the diet infotniation that initially contained in its delta C-13(B-HA) value is altered. In general, both FTIR spectra and FTIR indexes of the Early Cretaceous birds show that the delta C-13(B-HA) method is feasible in reconstructing the early birds' diet, and the contamination test before delta C-13(B-HA) analysis is necessary.