Goniocamax christenseni n. sp. (Belemnitellidae, Belemnitida) – a new species from the Upper Cretaceous of Russia

Abstract

A new species of Goniocamax Naidin: Goniocamax christenseni n. sp. is described from the Upper Turonian and the lowermost Coniacian strata of the Volga river region in Russia. The new species occur together with ‘primitive’ species of Goniocamax i.e. Goniocamax intermedius (Arkhangelsky) and G. surensis (Naidin), which suggests that two parallel evolutionary lineages in Goniocamax sensu Naidin, 1964 were present and both of unknown origin. The origin of G. lundgreni (Stolley) can be explained by gradual calcification of the anterior part of the guard in the intermedius/surensis group. G. christenseni n. sp. has a well calcified pseudoalveolus and an acute angle at the bottom of the ventral fissure of the wall of the pseudoalveolus. Thus, G. christenseni n. sp. resembles the first representatives of Belemnitella D’Orbigny and is considered the likely ancestor of the Belemnitella group. Phylogeny and palaeobiogeography of the Late Turonian belemnitellids (genera Praeactinocamax Naidin and Goniocamax Naidin) are discussed.