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THE ROTALIPORIDS, A POLYPHYLETIC GROUP OF ALBIAN-CENOMANIAN PLANKTONIC FORAMINIFERA: EMENDATION OF GENERA

¹ Departamento de Ecología y Geología de la Universidad de Málaga, 27071 Málaga, Spain.
² Faculté Polytechnique, 9 rue de Houdain, 7000 Mons, Belgium.

³ Correspondence author. E-mail: jmgd{at}uma.es

The rotaliporids are a group of mid-Cretaceous planktonic foraminifera that have gained increasing stratigraphic importance in the last few decades. Six genera are presently described: Rotalipora, Thalmanninella, Anaticinella, Pseudoticinella, Pseudothalmanninella and Pseudorotalipora. All are identified on the basis of their morphological characters. Recent systematic studies of planktonic foraminifera have, however, highlighted the importance of an approach based on lineage affinities rather than simple morphological differences. Using this philosophy, we propose a revision of the rotaliporids according to their polyphyletic origin. In particular, we emend and redescribe the three genera Thalmanninella, Pseudothalmanninella and Rotalipora, including species previously attributed to Anaticinella, Pseudoticinella and Pseudorotalipora. We include Anaticinella (senior synonym of Pseudoticinella) in the genus Thalmanninella and Pseudorotalipora in Rotalipora. The retained genera are as follows.

1. Pseudothalmanninella, which became extinct during the earliest Cenomanian, shows (a) a progressive development of a peripheral single keel and raised spiral sutures and (b) the development of periumbilical ridges and raised umbilical sutures.
   
2. Thalmanninella, which became extinct in the latest Cenomanian, is characterized by progressive evolution (in several stages) that may be summarized as follows: (a) a progressive development of a peripheral single keel and spiral sutural ridges; (b) the appearance of periumbilical ridges and raised umbilical sutures on the umbilical side; and (c) the disappearance of these previously acquired characters in almost the reverse order during the final evolutionary stage. This includes the loss of umbilical sutural ridges followed by weakening and loss of the peripheral keel and spiral sutural ridges. This genus also shows a continuous variability in other features that are normally used for morphological definition of species: e.g., relative convexity of both sides, number of chambers, whorl expansion rate, shape of the equatorial periphery and other characters. This variability is the reason why, in the past, many species have been described and attributed to Thalmanninella.
   
3. Rotalipora, which became extinct in the latest Cenomanian, shows (a) a progressive development of a peripheral single keel; (b) a development of raised spiral sutures; and (c) a development of a triradial ridge in the middle part of chambers on both the umbilical and dorsal sides.
   

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