AN UPDATED ICHNOTAXONOMIC TREATMENT OF THE DAKOTA GROUP, FRONT RANGE, COLORADO, USA

An ichnotaxonomic treatment of the Dakota Group (DG) from outcrops along the Colorado Front Range is necessary to provide an up-to-date assessment of trace fossil morphologies and revisions to their ichnotaxonomy. The DG was deposited during the Albian–Cenomanian and occurs in Colorado, Kansas, Iowa, Nebraska, New Mexico, and Utah. Strata within the DG contain oil and gas reservoirs whose geometries and distributions are characterized by combined sedimentologic and ichnologic analysis, which particularly strengthens the reconstruction of paleoenvironments and paleoecology of these dinosaur-bearing sedimentary successions. The DG in Colorado is subdivided into the Lytle, Plainview, Glencairn (Cañon City), Skull Creek Shale (Morrison, Fort Collins), and Muddy formations. The Lytle Formation (Fm) represents fluvial environments and contains a few trace fossils, such as Naktodemasis and Planolites, along with poorly preserved dinosaur tracks. The Plainview Fm was deposited in a nearshore environment and contains Archaeonassa, Asthenopodichnium, Aulichnites, Chondrites, Cochlichnus, Conichnus, Cylindrichnus, Lockeia, Margaritichnus, Palaeophycus, Planolites, Protovirgularia, Rhizocorallium, Rosselia, Scolicia, Skolithos, Taenidium, Teichichnus, and Thalassinoides, along with Teredolites borings in wood fragments. Tracks of ankylosaurid and theropod dinosaurs are also present. The Glencairn Fm was deposited in deltaic or estuary environments and contains Cruziana, Gyrolithes, Lockeia, Ophiomorpha, Planolites, Rusophycus, Skolithos, Teichichnus, Thalassinoides, and Zoophycos. The Skull Creek Shale was deposited in a deltaic environment and contains Arenicolites, Asterosoma, Diplocraterion, Palaeophycus, Rhizocorallium, Rosselia, Schaubcylindrichnus, Skolithos, Teichichnus, Thalassinoides, and Zoophycos. The Muddy Fm was deposited in a shoreface and deltaic environment and contains Arenicolites, Archaeonassa, Asthenopodichnium, Aulichnites, Chondrites, Cylindrichnus, Diplocraterion, Macaronichnus, Ophiomorpha, Palaeophycus, Planolites, Protovirgularia, Rhizocorallium, Rosselia, Scolicia, Skolithos, Taenidium, Teichichnus, Thalassinoides, and Treptichnus. Also present are crocodylian, ornithopod, and theropod tracks.