Chemometric study of the preservation modes of Athabaskia anax (Trilobita, Cambrian Precordillera, Mendoza, Argentina). Implications for taxonomy. (August 2021)

• Record Type: Journal Article
• Authors: D'Angelo, José A.; Bordonaro, Osvaldo L.; Raviolo, Mariana M.; Bruno, Natalia; Camí, Gerardo
• Is Part Of: Journal of South American earth sciences. Volume 109(2021)
• Publication Date: 2021-08
• Subjects: Corynexochida -- Pygidium -- Diagenesis -- Taphonomy -- Taxonomy -- Chemometrics; Geology -- Latin America -- Periodicals; Earth sciences -- Latin America -- Periodicals; Geology -- Antarctica -- Periodicals; Earth sciences -- Antarctica -- Periodicals; Geology -- Caribbean Area -- Periodicals; Earth sciences -- Caribbean Area -- Periodicals; Géologie -- Amérique latine -- Périodiques; Sciences de la terre -- Amérique latine -- Périodiques; Géologie -- Antarctique -- Périodiques; Sciences de la terre -- Antarctique -- Périodiques; Géologie -- Caraïbes (Région) -- Périodiques; Sciences de la terre -- Caraïbes (Région) -- Périodiques; Earth sciences; Geology; Antarctica; Caribbean Area; Latin America; Periodicals; 550.5
• DOI: 10.1016/j.jsames.2021.103232
• Languages: English
• ISSNs: 0895-9811

Abstract

Abstract: Selected pygidia of the middle Cambrian corynexochid trilobite Athabaskia anax (Walcott 1916) from the Miaolingian Series of San Isidro (Precordillera, Mendoza, Argentina) are analyzed for the first time using scanning electron microscopy in combination with energy-dispersive X-ray spectrometry (SEM-EDX). Pygidia occur in a single stratigraphic level composed of fine-grained calcareous sandstones and show four types of morphological preservations. The purpose this case study is threefold: (1) to analyze in detail the sample types by means of SEM-EDX in order to explore the chemical changes of the exoskeleton induced by diagenesis; (2) to use principal component analysis (PCA) to focus on groupings as a function of the chemical composition; and (3) to analyze the possible systematic implications of the chemical data. Results show that PCA supports the distinction among the four types of morphological preservations, based mainly on differences in the contents of Ca, Al, and K, as well as Si and Mg. This suggests that diagenesis followed distinct taphonomic pathways in the single stratigraphic level and resulted in contrasting chemical compositions of the four types of morphological preservations. It is interpreted that some morphological characteristics of the pygidia are the result of chemical and structural changes taking place during fossilization and do not represent real morphological differences in the living organisms. Our results dictate caution when using some morphological characteristics of the exoskeletons to erect new taxa, which, in turn, could be used to draw erroneous conclusions on their biostratigraphy, biogeography, and palaeoecology. Graphical abstract: Image 1 Highlights: Athabaskia anax (Walcott) from Mendoza (Argentina; Miaolingian) is studied. First SEM-EDX study of pygidia with different chemical preservation states. Chemical changes of the exoskeletons are induced by diagenesis. Pygidia morphological characteristics and chemical variations are correlated. Caution is advised when using morphological features in taxa delimitations.