The ontogeny of, and relationships between, Middle Miocene and Quaternary Orbulina (Foraminifera)
Abstract. The early, coiled stages of Orbulina suturalis and O.universa are described from both Middle Miocene (zones N9–N12) and Quaternary samples. The coiling mode of Orbulina is unique to that genus, and has remained unchanged (as have the spines characteristic of the coiled growth stage) since that genus and its species first evolved. Orbulina universa is monophyletic and its evolutionary history appears to provide an example of “punctuated equilibria” in the development of Cainozoic Globigerinacean development. “O. suturalis “, on the other hand, appears to be a name which has been applied both to the Middle Miocene species and to phylogenetically different forms of Quaternary age.