An early Cambrian shallow-marine ichnofauna from the Puncoviscana Formation of northwest Argentina: the interplay between sophisticated feeding behaviors, matgrounds and sea-level changes

Abstract

An early Cambrian ichnofauna consisting of Helminthoidichnites tenuis, Helminthopsis tenuis, Multina isp., Oldhamia alata, and Pilichnus cf. dichotomus is documented from shallow-marine deposits ranging from the upper offshore to the offshore transition in the Puncoviscana Formation of northwest Argentina. Although the ichnogenus Oldhamia is more common in Cambrian deep-marine environments, this occurrence provides further evidence that it is also present in shallow-marine environments. The burrow network Multina (senior synonym of Olenichnus) is preserved at the base of tempestites, representing the activity of post-storm colonizers. A drowning surface separating offshore-transition deposits below from upper-offshore deposits above contains widespread evidence of trace fossils in direct association with matgrounds. The undermat miners Oldhamia alata and Pilichnus cf. P. dichotomus occur on this surface, revealing exploitation of organic matter in the biomat. Low sediment rate during drowning and paucity of bioturbation by sediment bulldozers may have promoted the establishment of the matground. In comparison with the simpler animal-matground interactions characteristic of the Ediacaran, the combination of Cambrian evolutionary innovations and the presence of microbial mats promoted more sophisticated interactions. Complex feeding trace fossils revealing that systematic undermat mining, as displayed by Oldamia alata and Pilichnus cf. dichotomus, is a product of the Cambrian explosion.

Ediacaran matground ecology persisted into the earliest Cambrian

“…However, the evolutionary innovations of the Cambrian explosion allowed for more complex interactions to develop, making the Fortunian a pivotal point in the history of the biosphere 25,26 . This combination of a microbial matground-based ecology and the appearance of new body plans and associated locomotory mechanism, actually resulted in a peak in diversity of animal-matground interactions during the Fortunian (Fig.…”

“…In the Fortunian, this strategy is recorded by the appearance of systematically branching burrow systems exploiting the organic matter concentrated within microbial mats from below. In Fortunian rocks in Newfoundland and elsewhere, sophisticated strategies involving strophotaxis (proclivity to make U-turns so that the animal turns around 180°at intervals), phobotaxis (which prevents the organism from crossing its own and other trails) or thigmotaxis (which makes the animal to keep close contact with a former trail) have been documented in microbial matgrounds by the presence of ichnospecies of Oldhamia, which reveal complex morphological patterns 26,29,33 . Direct external digestion of the mat, which has been suggested for the Ediacaran Dickinsonia 34 and represented by the ichnogenus Epibaion 31 , is a type of animal-matground interaction unrecorded in the Cambrian.…”

Trace fossils associated with Burgess Shale non-biomineralized carapaces: bringing taphonomic and ecological controls into focus

“…Both ichnogenera are considered grazing trails (Pascichnia). Marine examples of Helminthopsis are typically regarded as produced by vermiform animals [42]. In marine settings, Cochlichnus is commonly considered as produced by free living nematodes, which represent the dominant meiofaunal group in muds, and are strongly linked to the detritus/bacteria food chain [13].…”

Unravelling Phanerozoic evolution of radial to rosette trace fossils

“…Volkichnium has been tentatively synonymized with Dactyloidites (Stachacz ) and here is provisionally retained as a separate ichnogenus. Volkichnium is present in shallow‐marine deposits of the lower Cambrian Puncoviscana Formation of northwest Argentina (Buatois & Mángano , ) and Lower Ordovician Phycodes beds, Thuringia, Germany (Pfeiffer ), to deep‐marine deposits of the Lower Ordovician Skiddaw Group, Lake District, England (Orr ). The youngest occurrence of Volkichnium in deep‐marine deposits of the Lower Carboniferous Bordenschiefer, Thuringia, Germany (Benton ), is taken into account, but must be confirmed.…”