Article: A new polyseptate thecideacean brachiopod from the Middle Jurassic of the Cotswolds, England

Study of material from a new locality reveals the presence of an Aalenian thecideacean which, in its morphology and shell microstructure, is similar to certain upper Jurassic and lower Cretaceous species. The new Aalenian specimens are assigned to Mimikonstantia sculpta gen. et sp. nov. because of the doubtful validity of the upper Jurassic genus Konstantia Pajaud 1970. Although impunctate, the shell microstructure, with its suppressed secondary fibrous mosaic, closely resembles that of the lower Cretaceous Thecidiopsis tetragona (Roemer) and T. lata Smirnova. It is therefore considered that Mimikonstantia, Konstantia, and Thecidiopsis are phylogenetically linked. The evidence obtained from the study of M. sculpta enables the onset of the neotenous suppression of the secondary fibrous shell layer to be placed much earlier in the history of the Thecideidina than has previously been suspected.