Search

New ichnological data from the Lower Triassic (Induan) Dongchuan Formation (Longmendong, South China) record the recovery interval of marginal-marine communities following the end-Permian mass extinction. Here, we document six ichnogenera from the upper part of the Dongchuan Formation of Dienerian (Early Triassic) age in the Longmendong area, Sichuan Province, South China. These are Cylindrichnus , Diplocraterion , Palaeophycus , Planolites , Siphonichnus , and Teichichnus , illustrating a depauperate Cruziana Ichnofacies. Facies analysis suggests that the depauperate Cruziana Ichnofacies is present in deposits recording the transition from fluvial to tide-dominated estuarine settings. Compilation of worldwide brackish-water ichnofaunas from Permian (average alpha ichnodiversity = 6.2) to Triassic (average alpha ichnodiversity = 5.5) suggests that no significant ichnodiversity decrease took place in these settings as a result of the mass extinction and further implies that the impact of the mass extinction may have been less severe in marginal-marine settings. Ichnofaunas in pre- and post-extinction marginal-marine environments are remarkably similar and tend to be dominated by facies-crossing ichnotaxa (e.g., Diplocraterion , Palaeophycus , Planolites ) produced by opportunistic faunas. [ABSTRACT FROM AUTHOR]

Dictyodora has been generally considered an ichnogenus with a restricted temporal range from the Cambrian to the Mississippian. Until now, there have been no reports of Dictyodora after the Mississippian. Here we report on well-preserved and abundant Dictyodora from deep-sea sediments of the Lopingian Maomaolong Formation in West Qinling, central China, which is hitherto the youngest occurrence of Dictyodora and extends the stratigraphic range of Dictyodora to the Late Permian. Two ichnospecies of Dictyodora are distinguished: D. zimmermanni and D. cf. scotica. Unlike the small-sized Dictyodora in the pre-Pennsylvanian, the three-dimensional morphology of Dictyodora studied here shows larger amplitudes and longer limbs with clearly inclined walls and basal burrows, which are interpreted to have been made by a soft-bodied worm-like organism with a snorkel-like organ as similarly documented in previous studies. Detailed systematic ichnological features and SEM and EDS results indicate that Dictyodora here is not simply a respiration structure made during the locomotion of the trace maker, but resulted from active filling by the trace maker. Dictyodora is probably not a good indicator of the deep-marine environment in the Paleozoic. From our dataset, Dictyodora originated from the shallow-marine environment in the early Cambrian, then migrated into the deep sea in the Ordovician and the marginal-marine setting in the Wenlock, and was finally restricted to the deep-marine environment in the Carboniferous and Permian. Both Psammichnites and Dictyodora are structures made by organisms with snorkel-like organs, and both were eliminated during the end-Permian mass extinction. • The youngest known Dictyodora was reported in the Late Permian. • The three radiation trends of Dictyodora were proposed in the Paleozoic. • Both Dictyodora and Psammichnites were extinct in the EPME. [ABSTRACT FROM AUTHOR]