A review of the brachylepadomorph cirripede genus Pycnolepas, including the first record of an Early Cretaceous species from the Russian Far East*

Abstract

To date, twelve species have been assigned to the brachylepadomorph cirripede genus Pycnolepas Withers, 1914, some of them on the basis of very limited material. The current status of all these taxa is briefly reviewed. Added are notes on a small collection of isolated capitular valves from middle Albian (Lower Cretaceous) strata in the lower reaches of the Amur River (Vassinskaja protoka, Khabarovsk region); this constitutes the first record of Pycnolepas from the Russian Far East (North Pacific Province). It is noted that species of Pycnolepas are almost exclusively European in distribution; notable exceptions are P. articulata (?lower Aptian; Alexander Island, Antarctica), P. orientalis (unspecified Upper Cretaceous, Kuzna-chaj, Azerbaijan; here considered to be a nomen dubium), P. nov. sp. (upper Paleocene; Turgay Strait, northwestern Kazakhstan), and the present lot which appears to be closely related to P. rigida from the lower Albianmiddle (?upper) Cenomanian of Europe (England, France). In the absence of other valves (terga, rostra and imbricating plates), for now we refer to this lot as P. aff. rigida, and consider it a vicariant species, awaiting the discovery of additional material. In the literature, it has been pointed out that amongst associated faunal elements (in particular, ammonoids and buchiid/inoceramid bivalves) at Vassinskaja protoka and nearby sections along the Amur River, there are species which are closely related to European taxa, and their occurrence appears best explained by vicariance biogeography. The absence of Pycnolepas in younger strata in the Russian Far East suggests that no subsequent radiation took place, but collection failure cannot be ruled out either in view of the vastness of the area and the generally small size of cirripede valves.