Sylvain Rigaud

A new genus of Norian involutinid foraminifers: Its morphological, biostratigraphic, and evolutionary significance

The Late Triassic was a time of pronounced radiation in several groups of foraminifers. The rapid evolutionary processes in the Suborder Involutinina caused particularly high diversification of these aragonitic foraminifers, which became a key group for Upper Triassic biostratigraphy. Among them, Triasina hantkeni and Triasina oberhauseri are regarded as the most precise guide fossils. However, while these species are widely used, a poor documentation of the detailed test structure of T. oberhauseri has resulted in misidentifications. The exceptional preservation and abundance of Triasina oberhauseri in the Upper Triassic deposits of the Black Marble Quarry (Wallowa terrane, Oregon, USA) has allowed us to make the first detailed observations of its coiling, innermost structure and lamellae arrangement and to recognize morphological features that were either wrongly interpreted or not described in the original systematic definition of the species. In this paper, we demonstrate that the species possesses characteristics that hamper its assignment to Triasina and we propose a new genus, Aulosina, to accommodate this taxon. Placing emphasis on the accuracy of the morphological description, the diagnosis and the systematic definition of the species are here improved. The identification of innovative features in Aulosina oberhauseri (strengthenings, shortened lamellae) highlights new evolutionary trends for the lineage of Involutinina that have proved useful for the establishment of phylogenetic links between involutinid genera and for understanding the evolutive steps leading to the formation of inner-pillars in tubular foraminifers. The increasing complexity of Involutinina representatives at the end of the Triassic, notably marked by the appearance of internal structures in Triasininae, leads us to regard them as probable symbiont-bearing foraminifers.

Taxonomy, phylogeny, and functional morphology of the foraminiferal genus Involutina

Early Jurassic aragonitic foraminifers are outstandingly well-preserved in the Marmorea crust, a multiphased ferromanganese layer limiting the Schnöll and Adnet formations (Adnet, Northern Calcareous Alps, Austria). This remarkable preservation, related to the pervasive impregnation of aragonitic tests prior to their recrystallization, allowed observing unknown diagnostic features of the genus Involutina, which typifies the Suborder Involutinina. Thanks to a detailed examination of the Adnet specimens, this paper clarifies the taxonomy, systematic position, and phylogeny of Involutina. A new diagnosis, structural model, and lineage are introduced for the group. Involutina is the direct descendant of Aulotortus and the two taxa probably showed a parallel evolution. As Aulotortus, Involutina presents a high intraspecific variability and its diversity must be revised downward. Current phylogenetic and taxonomic frames of the Suborder Involutinina are firmly questioned as, contrary to previous schemes, the type-genus possesses more than one lamellar deposit per whorl. In Involutina, the height and distribution of papillae on the test surface is not random and probably related to a biological function. We here propose that the papillose lamellae and tube infoldings that characterize representatives of the genus were rudimentary features for light catching and symbiont positioning, respectively.

Insights from exceptionally preserved Cenomanian trocholinids (benthic foraminifera) of northern Cantabria, Spain

Rich and diverse trocholinid assemblages have been recorded from the lower to middle Cenomanian Altamira and Bielba formations of the Bascocantabrian Basin, northern Spain. They occur in bioclastic for-algal grainstones and near-reefal rudstones referred to platform margin environments. This material, partially impregnated by iron-rich solutions, is unusually well-preserved and offers the unique opportunity to carry out a detailed study of the last diversified assemblages of the aragonitic foraminiferal order Involutinida. It notably allows (1) describing one new subfamily (Coscinoconinae n. subfam.), two new genera (Hensonipapillus n. gen. and Paracoscinoconus n. gen.), and five new species (Coscinoconusdiscoideus n. sp., Frentzenella pygmaea n. sp., Hensonipapillus cantabricus n. sp., H. altamirensis n. gen., n. sp., and Paracoscinoconus semiinvolutus n. sp.); (2) clarifying the relationship between the umbilical canal system and the laminar deposits in Late Jurassic–Cretaceous coscinoconins; (3) emending and providing new combinations for “Trocholina”lenticularis Henson, 1947“T.” minima Henson, 1947 and “T.”burlini Gorbatchik, 1959 which have been repeatedly misidentified in the literature; (4) discussing the epibenthic mode of life of trocholinids; and (5) proposing an explanation for their extinction at the Cenomanian–Turonian boundary.

New lineage of Triassic aragonitic Foraminifera and reassessment of the class Nodosariata

The new, atypical aragonitic foraminifer Tubulastella comans gen. et sp. nov. is described from the Late Triassic of Panthalassa (Wallowa terrane, north-east Oregon, USA). This rectilinear, undivided tubular form is closely related to ‘Coptocampylodon? rhaeticus’, a Rhaetian incertae sedis commonly found in the western Tethys. Morphologically and structurally distinct from other aragonitic foraminifers, Tubulastella comans gen. et sp. nov. and T. rhaetica gen. et comb. nov. are part of an independent aragonitic lineage, here embodied by the family Tubulastellidae fam. nov. To understand the origination and taxonomic affinity of this unique taxon, a comparative study between Tubulastella and the calcitic syzraniid foraminifer Rectostipulina is carried out. Although these forms differ in wall composition, they present identical constructional patterns, providing evidence of their close phylogenetic relationship. The existence of an aragonitic branch in Nodosariata evolution deeply challenges current foraminiferal classifications and evolutionary hypotheses. We here propose to limit the class Nodosariata to a monophyletic group of bi- to plurilocular foraminifers originating from a Silurian earlandiid ancestor, and the order Nodosariida to a monophyletic lineage of primarily single-layered built foraminifers, which takes root in the Middle Pennsylvanian. This new classification reflects an evolutionary transition from calcitic to aragonitic walls, as documented in other shelled organisms, and definitively excludes calcitic unilocular foraminifers (i.e. Ellipsolagenidae and Lagenidae) from the class Nodosariata. http://zoobank.org/urn:lsid:zoobank.org:pub:D8281D59-38FD-4D88-BEC6-14D5C7B8FD2B

New robertinid foraminifers from the Early Jurassic of Adnet, Austria and their evolutionary importance

New benthic multichambered foraminifers have been discovered in the Hettangian—Sinemurian of the Northern Calcareous Alps (Adnet, Salzburg, Austria). Originally aragonitic, these forms are completely recrystallized but the early impregnation of their tests by Fe-Mn solutions has, to some extent, allowed an indirect preservation of their primary structure. The most remarkably preserved specimens are found in close vicinity to the marmorea crust, a heavily mineralized multiphased hardground. We describe two new genera, Velleditsiella gen. nov., a microgastropod look-alike foraminifer, which includes the species V. felicitaszae gen. et sp. nov. and V. spinaferra gen. et sp. nov., and Rossanella gen. nov., the first known representative of the superfamily Conorboidoidea, which includes the species R. martinii gen. et sp. nov. Considering their structural and morphological characteristics, Velleditsiella and Rossanella phylogenetically derive from two distinct Triassic lineages, respectively the families Trochosiphoniidae and Variostomatidae. The discovery of diverse aragonitic assemblages in earliest Jurassic strata dismisses the long believed hypothesis that all Jurassic aragonitic multichambered foraminifers originated from a single Oberhauserellidae ancestor. It also supports a lower impact of the Triassic/Jurassic biotic crisis on the evolution of aragonitic foraminifers. Hypotheses for the short term and long term evolution of aragonitic multichambered foraminifers are discussed and new phyletic trees are proposed.