Biostratigraphic Synthesis: Late Oligocene and Neogene of the Western Tropical Pacific

Biochronology and evolution of Pulleniatina (planktonic foraminifera)

“…4d). Our interpretation, based on our observations at IODP Site U1488, is that once established, P. primalis underwent rapid evolutionary change and that so-called "transitional" specimens between N. acostaensis and P. primalis that have occasionally been reported are more likely to be the earliest representatives of the P. primalis lineage, which Brönnimann and Resig (1971) referred to as P. praepulleniatina. Evidence for this is that such forms in the lowermost sample at Site U1488 containing P. primalis are predominantly sinistral but occur beside predominantly dextral N. acostaensis in the same samples, which appear morphologically unchanged in comparison to lower samples.…”

“…Its position in the core of the Western Pacific Warm Pool is in the centre of the geographic range of the genus, which occurs continuously in the sediment at high abundance. The site is just ∼ 28 km northwest of Deep Sea Drilling Project (DSDP) Site 62 (Shipboard Scientific Party, 1971) where pioneering work on the taxonomy and biostratigraphy of Pulleniatina was previously conducted (Brönnimann and Resig, 1971;Brönnimann et al, 1971). For these reasons we have re-studied the site to improve on the shipboard biostratigraphy.…”

“…In their study of DSDP Site 62 on Eauripik Rise in the western equatorial Pacific, Brönnimann and Resig (1971) proposed a formal name for morphotypes intermediate between acostaensis and primalis of "Pulleniatina praepulleniatina". Given that the holotype of P. primalis is a relatively "advanced" form, there is indeed scope to apply this taxonomic split, but we have not elected to do that because almost all subsequent workers have included such forms within a broad concept of P. primalis.…”

“…Given that the holotype of P. primalis is a relatively "advanced" form, there is indeed scope to apply this taxonomic split, but we have not elected to do that because almost all subsequent workers have included such forms within a broad concept of P. primalis. Brönnimann and Resig's (1971) study is very well documented, but unfortunately the timing of the evolutionary transition is difficult to constrain because of uncertainty in dating the lower part of the record at Site 62. Belyea and Thunell (1984) performed the only morphometric study so far published of the N. acostaensis -P. primalis transition, an outline shape analysis of populations from below and above the Bottom of P. primalis at DSDP Site 214 on the Ninety East Ridge in the Indian Ocean.…”

“…The main lineage (comprising the morphospecies P. primalis -P. praecursor -P. obliquiloculata -P. finalis) is characterized by a tendency for relatively abrupt switches in the dominant coiling direction (e.g. Brönnimann and Resig, 1971;Saito, 1976;Resig et al, 2001;Pearson and Penny, 2021), a phenomenon that can be traced back to its ancestor Neogloboquadrina acostaensis and beyond that to N. continuosa in the middle Miocene (e.g. King et al, 2023).…”