Zoophycos

Abstract: Modern crabs are common inhabitants of shallow subtidal, intertidal, and supratidal environments, and many crabs are capable of producing traces that can be preserved in the rock record. The first crabs, Early Jurassic in age, probably were not fossorial. By Cretaceous time, however, diverse endobenthic lineages were established. Some of these undoubtedly produced domiciles that are preserved in shallow marine to quasimarine sediments and that should be useful in characterizing the depositional environment of the sediments. Nonetheless, most such dwelling structures have been studied little and remain essentially unnamed. The ichnogenus Psilonichnus Fuersich is amenable to the taxonomic concept of several forms of crab burrows; presently recognized ichnospecies include P. tubiformis Fuersich and P. upsilon (n. ichnosp.). The occurrence of Psilonichnus upsilon and related burrow forms should prove to be a useful criterion for the identification of marine-margin facies in the rock record. Certain crabs also produce domiciles referable to Thalassinoides, Gyrolithes, and Skolithos, and possibly Macanopsis and Spongeliomorpha. Except for Skolithos, such structures traditionally have been attributed to shrimp, lobsters, or stomatopods. Ethologic and taxonomic re-evaluation of these burrow forms is needed.--Modified journal abstract.

Abstract: Tracks, trails and burrows made by organisms are commonly preserved in Phanerozoic sedimentary rocks. These biogenic sedimentary structures, or trace fossils, have been most intensively studied from rocks deposited in marine environments, and have proven to be extremely useful in palaeoenvironmental reconstruc-tions. Our systematic analysis of occurrences in the stratigraphic record of two of the most common trace fossils, Zoophycos and Ophiomorpha, indicates that occurrences for each show an environmentally linked directional pattern through time. Zoophycos is commonly reported from Palaeozoic strata deposited from nearshore to deep-sea environments, whereas in post-Palaeozoic stratait is generally reported only from rocks deposited in deeper-water environments. Ophiomorpha first appeared in Permian shallowwater environments and was common in deep-sea fan environments by the Cretaceous, and has been distributed from nearshore to deep-sea environments since then. These onshore-offshore trends, which are similar to those previously reported for Phanerozoic benthic macroinvertebrate assemblages and individual higher taxa, require integration into future palaeoenvironmental reconstructions that use trace fossils.

Abstract: The ichnofacies paradigm has evolved over a six-decade period since its original inception by Dolf Seilacher. It is a multidimensional framework underpinned by recurring, facies-controlled groupings of biogenic structures that reflect animal responses to paleoenvironmental conditions. These constitute spatially and temporally extensive associations commonly regarded as “Seilacherian Ichnofacies.” The marine realm hosts five recurring softground ichnofacies (Psilonichnus, Skolithos, Cruziana, Zoophycos, and Nereites), generally distributed in a proximal–distal trend reflecting a passive response to increasing water depth (i.e., controlled by depositional factors that progressively change with bathymetry). There are three substrate-controlled ichnofacies (Trypanites, Teredolites, and Glossifungites), recording organism occupation of palimpsest substrates. Finally, there are six continental ichnofacies (Scoyenia, Mermia, Coprinisphaera, Termitichnus, Celliforma, and Octopodichnus–Entradichnus), mainly recording organism responses to temperature and the availability of moisture (i.e., climate-driven associations) in terrestrial settings or oxygenation, depositional energy, and substrate consistency in subaqueous settings. The Seilacherian ichnofacies operate as facies models, built through the distillation of ichnological characteristics derived from numerous modern and ancient case studies. Like lithofacies models, they serve as a norm for comparison, a framework for observations, a predictor in new situations, an integrated basis for interpretation, and a basis for teaching and communication.