335 Review of the Bullia group: evolution and biogeography

Review of the Bullia group (Gastropoda: Nassariidae), with comments on its evolution, biogeography, and phylogeny - BAP #335

The "Bullia group", comprising those gastropods of the family Nassariidae not assignable to the subfamilies Nassariinae or Cylleninae, is a relatively small group presently confined to temperate and subtropical shallow water habitats in the South Atlantic and Indian Oceans. The group has a significant and complex fossil record, however, that indicates greater morphological diversity and wider geographic distribution in the Tertiary than today. This fossil record suggests that Nassariidae arose and diversified initially in the New World in the Late Cretaceous and Early Tertiary, spreading to Europe, Africa and beyond by Miocene times.

The genus Bullia s. s. is today an important and diverse component of the South African sandy shore molluscan fauna. The current status of Bullia s. s., however, is probably a relatively recent development. Bullia apparently did not reach Africa until the late Miocene or early Pliocene, and its approximately 40 living species are of Pliocene age or younger. Consideration of the phylogenetic and biogeographic history of the entire group suggests that the ancestors of modem Bullia s. s. may have reached Africa from South America via chance dispersal across open ocean, a mode usually not seriously considered for marine prosobranchs lacking a planktonic larval stage.

Methods of phylogenetic inference, particularly as applicable to fossil gastropods, are discussed. An informal method (the "faunal survey" method) for considering the effects of the completeness of the available fossil record on phylogenetic reconstruction is suggested. The fossil record is considered to be of unique and special importance in interpreting the evolutionary history of this group. A phylogenetic analysis of the family Nassariidae, based primarily but not exclusively on conchological characters, is presented, but the taxonomic position of several fossil and Recent groups remains unresolved. A classification for the group to the subgenus level, and a new subfamily, the Bulliinae, are proposed. 

This paper points out a number of gastropod groups in need of detailed taxonomic study, and highlights the currently meager knowledge of the basic patterns of Cenozoic marine molluscan biogeography.

W.D. Allmon