Diversity of the genus Ancyrochitina in the Middle Devonian of Bolivia

CAMINA, SONIA CLARA; RUBINSTEIN, CLAUDIA VIVIANA

Londres

Congreso; The Palynological Society 53° Annual Meeting; 2021

The Palynological Society

Ancyrochitina, one of the best represented and most diversified chitinozoan genus in the Middle Devonian basins of Western Gondwana, has been recorded in large numbers in the Los Monos Formation of the Tacobo X-1001 borehole, located in the southern foothills of Bolivia. The sedimentary succession is characterized by shallow marine deposits, recently dated as late Eifelian? to middle Givetian, based on spores and organic-walled phytoplankton. A moderately well-preserved chitinozoan assemblage was analyzed under SEM. The chitinozoans are completely flattened; nevertheless, systematic was carried out without applying a correction factor for flattening in the measurements and morphology relations were calculated. All the specimens show the general vesicle outline of Ancyrochitina, with a conical body chamber, a conspicuous neck, and a crown of basal processes. The morphology (simple or branched), the complexity (order of branching), and the number and size of the basal processes of well-preserved specimens allowed the positive identification of 12 species. Moderately damaged specimens were assigned as cf. to three species, and poorly preserved individuals were left in open nomenclature at the species level. The genus Ancyrochitina in the Tacobo X-1001, is represented by more species than in other Middle Devonian assemblages from all over the world. Additionally, it shares more Ancyrochitina species with Western Gondwana basins than with other coeval basins, in particular with the Brazilian Paraná basin. This demonstrates a well-known connection between Bolivian and Brazilian basins at the Middle Devonian, with some species restricted to Western Gondwana, such as Ancyrochitina arirambaensis and Ancyrochitina biconstricta, and Ancyrochitina monosi only known from Bolivia. Species such as Ancyrochitina aculeata and Ancyrochitina tomentosa were recorded for the first time in Western Gondwana, in this study.