Ichnology of the Ediacaran-Cambrian Puncoviscana Formation of northwestern Argentina: recent progress in understanding its potential in paleoecology and macroevolution

The Ediacaran-Cambrian Puncoviscana Formation of northwestern Argentina is a classic unit that provides valuable information on a critical time in the history of the marine biosphere. Research during the last decade has signifi cantly changed our view of this ichnofauna. The Puncoviscana ichnofauna displays a wide variety of ethological categories, including feeding structures (Circulichnis montanus, Multina isp., Pilichnus cf. dichotomus, Oldhamia alata, O. antiqua, O. curvata, O. flabellata, O. geniculata, O. radiata, Treptichnus pollardi, Saerichnites isp., Volkichnium isp.), grazing traces (Archaeonassa fossulata, Cochlichnus anguineus, Helminthoidichnites tenuis, Helminthopsis abeli, H. tenuis, Psammichnites saltensis), locomotion traces (Asaphoidichnus trifidus, Didymaulichnus lyelli, Dimorphichnus isp., Diplichnites isp., Tasmanadia cachii) and dwelling traces (Palaeophycus tubularis). This ichnofauna displays strong similarities with other trace-fossil assemblages worldwide in rocks now considered of Fortunian age, a view more consistent with recent geochronologic and chronostratigraphic data from northwest Argentina. While the relatively diverse Psammichnites association (illustrating the Cruziana Ichnofacies) characterizes the wave-influenced shallow-marine deposits of the eastern belt, the less diverse Oldhamia association typifies the deep-marine turbidite systems represented by the western belt. In contrast to previous views, the Nereites Ichnofacies is not present in the Puncoviscana Formation. The Puncoviscana ichnofauna illustrates the importance of feeding strategies related to the development of microbial matgrounds and the appearance of new body plans (as revealed by arthropod-produced trace fossils) and sophisticated feeding strategies (Psamichnites saltensis, Oldhamia ispp.).