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

Abstract

The new ichnosubspecies Macaronichnus segregatis degiberti from Miocene deposits of Cadiz, 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 degiberti is characterized by a diameter between 4 mm and 12 mm, with common obliquely and even vertically oriented galeries, and the presence of frequent branching. Different types of branching can be observed, including false, primary/secondary successive, and true, simultaneous branchings. Specimens occur in a wide range of palaeoenvironmental contexts, from inner to outer sliciclastic shelf. This includes deeper and more distal habitats than those usually interpreted for Macaronichnus. Macaronichnus segregatis degiberti could be produced by a new tracemaker showing a composite behavior, pascichnia being the main strategy and dominichnia/cubichnia or repichnia, a secondary, sporadic one.