Abstract

The Order Lagenida is a monophyletic group of calcareous foraminifers that originated in Middle Pennsylvanian time via acquisition of hyaline-radial wall structure and loss of microgranular wall structure, the latter being characteristic of the close sister group and likely ancestor, the Fusulinida. Early lagenides are delineated into subgroups on the basis of presence or absence of partitioning within their tests, and among partitioned forms, on continuous versus discontinuous growth styles. Partitioned, discontinuously growing forms may be further delineated on the basis of test symmetry and on modifications to chamber shape and apertural complexity. Early lagenides underwent rapid taxonomic differentiation during late Moscovian and early Kasimovian time. Taxonomic differentiation was accompanied by rapid dispersal from the presumed center of origin in the midcontinent-Andean area to tropical and subtropical shelves worldwide. By Early Permian time certain lagenides were adapted to cool water paleoenvironments, as evidenced by their occurrences in high paleolatitudes and even in glaciomarine basins. Early Permian lagenides do not exhibit marked provincialism, but there is evidence for paleolatitudinal control on assemblages. The midcontinent-Andean and present Arctic areas contain similar, diverse faunas from low- to mid paleolatitudes along the western margin of Pangaea. These faunas share many elements in common with faunas from the tropical and subtropical eastern margin of Pangaea (Paleotethys). In contrast, the Europe-Urals, Siberian and Australian areas are characterized by a slightly different faunal association from mid- to high paleolatitudes in both hemispheres. Panthalssan faunas are less well known, but seemingly contain only cosmopolitan taxa.

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