Test structure and evolution in the Foraminifera

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Abstract
For about a decade shell structures have formed the basis of the main taxonomic subdivision of the Foraminifera. Recent investigations have shown that within the monolamellar nodosariaceans no evolution with respect to wall structure has taken place since the Permian. The bilamellar aragonitic forms have remained stable at least since the Jurassic (Triassic?). The bilamellar calcitic forms have remained stable since the Jurassic (Triassic?). The wall structure of the non-lamellar porcellaneous forms has shown no change since the Carboniferous. The non-lamellar monocrystalline forms first occurred in the Upper Carboniferous and appear to have remained stable ever since. The microgranular Foraminifera, first appearing in the Cambrian, disappeared in the Triassic. Their primary structure is not known. The agglutinated forms seem to have started in the Cambrian, if not before. Evolutionary development leading to a higher degree of complexity of shell structure seems to be present (agglutinated—porcellaneous—monocrystalline—monolamellar and bilamellar), and may culminate in a more phylogeny-oriented systematic subdivision than the one we have today.