Paleoecologic and paleoenvironmental implications of a new trace fossil recording infaunal molting in Devonian marginal-marine settings

摘要: Abstract Luancaia igen. nov. and its two new ichnospecies, L. candasensis elongata, from the Middle Devonian Naranco Formation of Asturias, northern Spain, record infaunal molting. The ichnogenus has an elongate to oblong outline, displays a distinctly trilobate appearance that includes axial longitudinal lobe characterized by distinctive ridge flanked lateral lobes at each side. Well-defined transverse ridges convey metameric-like consisting up nine distinct segments. anterior-most part is more variable, but consistently features pair oval strongly convex, or subtriangular fan-like in well-preserved specimens. similar Rusophycus general segmented appearance, suggesting euarthropod producer, differs presence absence scratch imprints. closely resembles dorsal side enigmatic Carboniferous oniscid-like Camptophyllia. We propose records supine (i.e. upside-down) molting with exoskeletal morphology Camptophyllia, which exuviation was facilitated anchoring on firm muddy substrate. sedimentation shallow- marginal-marine setting times affected fluvial discharge most likely during storm floods. In particular, preserved storm-flood beds accumulated relative proximity river mouth. These latter deposits consist sparsely bioturbated sandstone mudstone reflect deposition under stressful conditions, such as salinity stress, erosion pass high rate, turbidity. By burrowing into sediment, producer avoided stressed physical conditions sediment surface. Marginal-marine settings, where competition predation pressures were significantly lower than adjacent fully marine environments, may have served safe sites mid-Paleozoic radiation.