Origin and phylogeny of the Cretaceous thoracican cirripede family Stramentidae

A cladistic analysis of basal scalpellomorph cirripedes was undertaken in order to identify the phylogenetic position of the Stramentidae. This yielded a well-supported tree, in which the family is positioned crownwards of Archaeolepas, but basal to the families Scalpellidae and Zeugmatolepadidae. A new genus, Loriolepas, is described to accommodate some species previously referred to Archaeolepas. Basal scalpellomorphs display a remarkable change in shell mineralogy from calcium phosphate to calcium carbonate (Eolepas to Archaeolepas); the latter group is identified as a monophyletic clade, the Thoracicalcarea nov. A revised taxonomy of the predominantly Late Cretaceous cirripede family Stramentidae is presented. Stramentidae are subdivided into two subfamilies, Loriculinae subfam. nov., and Stramentinae, based on characters of tergum, carinolatus and peduncular plates. The former subfamily includes Loriculina Dames, 1885, Metaloriculina gen. nov. and, doubtfully, Blastolepas Drushchits & Zevina, 1969, and three new species are described, Loriculina ifrimae sp. nov., Metaloriculina stramentioides sp. nov and Metaloriculina norvicensis sp. nov. The Stramentinae include Leweslepas gen. nov., Stramentum Logan, 1897 and Parastramentum gen. nov. New species are Leweslepas hattini sp. nov, L. hauschkei sp. nov, L. wrightorum sp. nov, Parastramentum albertaensis sp. nov, P. brydonei sp. nov, P. peakei sp. nov, Stramentum alekseevi sp. nov and S. praecursor sp. nov. Cladistic analysis of the Stramentidae, based on 25 characters, supports the monophyly of the family, but relationships between subfamilies and genera are poorly resolved. However, in north-west Europe there is an evolutionary morphocline, stratigraphically calibrated, from the early Cenomanian Leweslepas hauschkei gen. et sp. nov. through the middle Cenomanian Stramentum praecursor sp. nov. to the late Cenomanian–Turonian S. pulchellum. A split from this lineage is found in the Western Interior Basin of North America, and the early Turonian S. canadensis gave rise to the middle Turonian S. elegans, which lived epibenthically. Stramentum elegans gave rise to Parastramentum gen. nov.