Is Macaronichnus an exclusively small, horizontal and unbranched structure? Macaronichnus segregatis degiberti isubsp. nov.

Abstract

The new ichnosubspecies Macaronichnus segregatis digiberti from Miocene deposits of Cádiz, SW Spain, is described. This ichnotaxa shows the characteristic presence of a mineralogical segregation within the tube, with a core made up of low density material, surrounded by a rim of glauconite. However significant differences in size, orientation and branching with respect to the type species of Macaronichnus are observed. Macaronichnus segregatis digiberti is characterized by a diameter between 4 mm and 12 mm, with common obliquely an even vertically oriented galleries, and the presence of frequent branching. Different types of branching can be observed, including false, primary/secondary successive, and true, simultaneous branching. Specimens occur in a wide range of palaeoenvironmental contexts, from inner to outer siliciclastic shelf. This includes deeper and more distal habitats than those usually interpreted for Macaronichnus. Macaronichnus segregatis digiberti could be produced by a new tracemaker showing a composite behaviour, pascichnia being the main strategy an dominichnia/cubichnia or repichnia, a secondary, sporadic one