Preliminary chemometric study of early Triassic cynodonts from Mendoza, Argentina

PREVITERA ELENA; DANGELO JOSE; MANCUSO ADRIANA

La Rioja

Jornada; Jornadas Argentinas de Paleontología de Vertebrados; 2013

CRILAR CONICET/ APA

The non-mammalian therapsids dominated the terrestrial ecosystems during the Late Paleozoic-Early Mesozoic. The cynodonts have been studied from a taxonomic, osteologic, and functional morphology perspective. However, their bone diagenesis using chemometrics has been poorly researched. This report includes a rib cynodont (MHNSR-Pv 1160) from the Puesto Viejo Group (Mendoza, Argentina). The fossil is studied for the first time using SEM-EDX. Semi-quantitative data derived from SEM-EDX spectra are evaluated by principal component analysis to gain new insights regarding the differing diagenetic pathways changing the bone microstructure. Thin section of the rib was studied using a petrographic polarizing microscope to analize bone features (mineral composition, fracturing, and diagenetic deformation). The multivariate model supports the distinction of different specimen areas (bone, transition zone and rock matrix), in terms of chemical parameters. Differentiation is based mainly on varying contents of Ca, P, F, Si, Al, K, O, and Fe content. These results along with thin section petrographical analysis confirm some substitution of hydroxyapatite by fluorapatite into the bone microstructure. Fossil-diagenetic processes include three permineralization events during the burial history: (1) hematite cementation (early diagenesis), (2) calcite precipitation (mesodiagenesis), occurring in both vascular canals and fractures, and (3) cementation of iron carbonate minerals in the bone wall (late diagenesis). The presence of calcite and iron enrichment indicates local reducing conditions under the water table during precipitation. This chemometric approach to the study of Triassic cynodont remains proved useful to value the chemical pathways changing the bone microstructure.