Modem 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. Many representatives of these lineages 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. None- theless, most such dwelling structures have been studied little and remain essentially unnamed. The ichnogenus Psilonichnus Fiirsich is amenable to the taxonomic concept of several forms of crab burrows; presently recognized ichnospecies include P. tubiformis Fiirsich and P. upsilon (n. ichnosp.). Future work may reveal the need for further ichnospecific differentiation. 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.

Tracemaking activities of crabs and their environmental significance

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.

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Tracemaking Activities of Crabs and Their Environmental Significance: The Ichnogenus Psilonichnus

/pdf/fossil-calibrations-for-the-arthropod-tree-of-life-4ite4o70cy.pdf

Fossil calibrations for the arthropod Tree of Life

Categories of architectural designs in trace fossils: A measure of ichnodisparity

Upper Carboniferous tidal rhythmites of the Tonganoxie Sandstone Member (Stranger Formation) at Buildex Quarry, eastern Kansas, USA, host a relatively diverse arthropod-dominated ichnofauna. Bilaterally symmetrical traces displaying unique anterior and posterior sets of morphological features are well represented within the assemblage. A new ichnogenus, Tonganoxichnus, is proposed for these traces. T. buildexensis, the type ichnospecies, has an anterior region characterized by the presence of a frontal pair of maxillary palp impressions, followed by a head impression and three pairs of conspicuous thoracic appendage imprints symmetrically opposite along a median axis. The posterior region commonly exhibits numerous delicate chevron-like markings, recording the abdominal appendages, and a thin, straight, terminal extension. T. buildexensis is interpreted as a resting trace. A second ichnospecies, T. ottawensis, is characterized by a fan-like arrangement of mostly bifid scratch marks at the anterior area that records the head- and thoracic-appendage backstrokes against the substrate. The posterior area shows chevron-like markings or small subcircular impressions that record the abdominal appendages of the animal, also ending in a thin, straight, terminal extension. Specimens display lateral repetition, and are commonly grouped into twos or threes with a fix point at the posteriormost tail-like structure. T. ottawensis is interpreted as a jumping structure, probably in connection with feeding purposes. The two ichnospecies occur in close association, and share sufficient morphologic features to support the same type of arthropod producer. T. buildexensis closely mimics the ventral anatomy of the tracemaker, whereas T. ottawensis records the jumping abilities of the animal providing significant ethologic and paleoecologic information. The presence of well-differentiated cephalic, thoracic, and abdominal features, particularly in T. buildexensis, resembles the diagnostic tagmosis and segmentation of insects. Detailed analysis of trace morphology and comparison with described Paleozoic insect fossils and extant related forms suggest a monuran as the most likely tracemaker.

R. G. Osgood

Papers

Chagrinichnites brooksi, a new trace fossil of arthropod origin