On the origin of the fusulinids

Abstract

The earliest Fusulinida are used to assess the widely accepted hypothesis that Pseudoendothyra arose from Eostaffella, that Eostaffella arose from Eoparastaffella, and that Eoparastaffella was derived from Eoparastaffellina. The possible relationship between these taxa are examined using material from northern England. Transitional forms between Eoparastaffella and Pseudoendothyra are observed, with similar shape, profile, and wall structure, but with discernible differences in the coiling of the inner whorls, as well as a clear age overlap between these genera, which suggests a direct evolution between them. The origin of Eostaffella is not sufficiently well established and could be derived either from Eoparastaffella (as many authors have proposed) or from the dainellid Paralysella. Thus, it cannot be ruled out that the order Fusulinida might be polyphyletic. The genus Eoparastaffellina is considered a valid genus and independent from Eoparastaffella with their inclusion in the different orders of Endothyrida and Fusulinida, respectively.