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The rotaliporids, a polyphyletic group of Albian-Cenomanian planktonic foraminifera: Emendation of genera Gonzalez-Donoso, J.M.; Linares, D.; Robaszynski, F. (2007). The rotaliporids, a polyphyletic group of Albian-Cenomanian planktonic foraminifera: Emendation of genera. J. Foramin. Res. 37(2): 175-186. https://dx.doi.org/10.2113/gsjfr.37.2.175
In: Journal of Foraminiferal Research. Cushman Foundation for Foraminiferal Research: Washington. ISSN 0096-1191; e-ISSN 1943-264X, meer
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Trefwoorden |
Geological time > Phanerozoic > Geological time > Mesozoic > Cretaceous > Cretaceous, Upper > Cenomanian Foraminifera [WoRMS] Marien/Kust |
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Abstract |
(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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