Occurrence, morphology, and taxonomy of the late Cambrian Laurentian dikelocephalid trilobite Osceolia Walcott, 1914

Abrupt appearance of the dikelocephalid trilobite genus Osceolia in later Cambrian strata of the upper Mississippi Valley immediately above a flooding surface is succeeded by widespread regional occurrence among approximately eight parasequences in the early part of a falling stage systems tract. All of Osceolia ’s sclerite types are illustrated for the first time. The taxonomy is revised to recognize two species, of which O. tumerispina is new and known only from a dolomitic horizon at a single locality. All five of Ulrich and Resser’s (1930) Osceolia species are synonymized within O. osceola (Hall, 1863), a species widespread in regional dolomitic mudstones and feldspathic sandstones. Osceolia osceola shows notable polymorphism in the presence of an axial ledge in the anterior cranidial border. Holaspid ontogenetic variation evident within bedding-plane collections of O. osceola scales with that occurring among collections and across facies. Collection-related morphological differences among the samples beyond those related to size are subtle. The occurrence of larger individuals in more distal settings may reflect ontogenetically related habitat preference. Osceolinae Ulrich and Resser, 1930 is rejected. The closest relatives of the two Osceolia species may occur outside of the upper Mississippi Valley. Material of a local, stratigraphically older, and possibly related Ulrich and Resser 1930 nomen nudum is figured and described for the first time. Osceolia ’s cranidial morphotype was converged upon several times during the evolution of Cambrian trilobites among relatives both phylogenetically close and distant. UUID: http://zoobank.org/bdd2cf1b-331f-4204-8957-eadce195610d