ALBERT

Description: Globotruncanita insignis (Gandolfi, 1955) is a planktonic species commonly recognized in Late Cretaceous foraminiferal assemblages, but uncertainty about its morphologic variability and phyletic relationships have led to different interpretations of it. The taxon was considered to be morphologically and evolutionary related to Globotruncana rosetta (Carsey, 1926), phyletically linked to Globotruncanita elevata (Brotzen, 1934), or a junior synonym of the latter species. In addition, the neotype that replaced the lost holotype caused a taxonomic debate and compromised the identification of G. insignis, which has been assigned to both Globotruncanita and Globotruncana. This study resolves the taxonomic problems and reconstructs the phyletic lineage of this species on the basis of a continuous sequence of exceptionally well preserved and highly diversified planktonic foraminiferal assemblages in the Contusotruncana plummerae and Radotruncana calcarata zones, recently recovered from southeastern Tanzania drillholes. In addition to common G. insignis that characteristically have a strongly convex umbilical side, we recognized succession of morphotypes intermediate between Globotruncanita stuartiformis and G. insignis that demonstrates an ancestor-descendant relationship between the two taxa and further validates the assignment of G. insignis to Globotruncanita. Moreover, our results confirm that the neotype falls in the same phyletic lineage, but it represents a primitive form of G. insignis.

Description: The evolution of planktic foraminifera in the Paleocene-Eocene time interval is characterized by a high rate of diversification after the major extinction event observed at the Cretaceous/Paleogene boundary. An accelerated speciation rate resulted in the appearance of several new genera. Phylogenetic relationships among many of genera are still poorly understood. This study investigates the origin and phylogeny of the genus Igorina, which is characterized by a thick, nonspinose and incrusted wall. Igorina appears in Subzone P3a (early late Paleocene) and disappears in Zone P11 (middle Eocene). To date, nine species have been assigned to the genus Igorina (I. pusilla, I. trichotrocha, I. tadjikistanensis, I. convexa, I. albeari, I. laevigata, I. lodoensis, I. broedermanni, and I. anapetes) based on both wall texture and morphologic similarities. However, the taxonomic identification at species level is affected by several problems, mainly those resulting from poor descriptions and illustrations of the primary type specimens of several species. This study reconstructs the phylogeny and evolution of the igorinids through cladistic analysis by applying the method of parsimony. Phylogenetic relationships of the species assigned to Igorina are determined through stratocladistic analysis by using a data matrix of 23 taxa (including key species of Acarinina), 31 morphological characters (unordered), and a stratigraphic character (ordered) mapping the first occurrence of the taxa under investigation. The matrix (Appendix 1) was processed with PAUP* 4.0b10 software by using the heuristic search option to discover the most parsimonious trees. Results suggest that I. pusilla is the first representative of the Igorina lineage, and it is followed by I. laevigata, I. convexa, and I. albeari. Morphotypes of uncertain taxonomic identification have been coded and analyzed separately as morphotypes A-F to determine their ancestor-descendant relationships and to evaluate their validity as discrete species. As the result of our analysis, two new species are formally described as I. praecarinata (= morphotype A) and I. paraspiralis (= morphotypes C, E, and F). Finally, our analysis provides evidence that I. lodoensis, I. broedermanni, and I. anapetes are more closely related to Acarinina than to Igorina and clearly belong to a different lineage.