Gilianelles: Late Cretaceous microproblematica from Europe and Central America

Abstract

During the last two decades, a range of microfossils have been collected from strata of Late Cretaceous (Coniacian-Maastrichtian) age. The name gilianelles has been coined to accommodate these microproblematica. On the basis of many thousands of specimens, typical features of this group have now been assessed. Distinctive traits are calcareous unilocular, basically axially symmetrical test, in the size range 80-200 lm, with a single-layered wall of radially arranged crystals, 15 lm thick, the outer surface with a crochet-like nanostructure, a small-sized aperture (one tenth of test diameter), situated on the upper surface in vivo. Secondary criteria include modification of axial test symmetry into radial or bilateral symmetry, development of expansions, either spiny or laminar and presence of longitudinal and latitudinal ornament. To date, 60 taxa have been described from northern Spain to northern Germany and from Central America. Evolutionary patterns of gilianelles are diverse, with both short-and long-ranging forms, some of which comprise lineages that were affected by a marked crisis dated at about 73 Ma. This event is here illustrated by the tribe Coraliellini, of which a key taxon, Coraliella cognatio, is described as new. Previous interpretations of Gilianelles as dinoflagellate cysts are discussed and rejected.

Revision and evaluation of the systematic affinity of the calcitarch genusPithonellabased on exquisitely preserved Turonian material from Tanzania

“…Further complication in the taxonomy of this group arose from an isolated observation of densely packed specimens that may be interpreted as colony formation in the pithonellid genus Bonetocardiella (Villain, 1975)-a life strategy not known among modern dinoflagellates. Also the pithonellid genus Tetratropis appears to be related to the so-called gilianelles that are not regarded to be dinoflagellates (Odin, 2011). These ambiguities result in a dilemma where, on the one hand, the pithonellid calcitarchs would be stratigraphically and paleogeographically widespread enough (Dias-FIGURE 2-Map of research area and location of Tanzania Drilling Project drill Sites discussed in this study.…”

“…Tetratropis is associated with microfossils not considered to be dinocysts, or tabulation is thought to represent ornamentation Odin (2011); Versteegh et al (2009) Sub-angular apical suture…”