Precursors of the Nummulites gizehensis and N. partschi group from Egypt

Abstract

Studies on the precursors of Nummulites gizehensis group and Nummulites partschi group from the Eocene of Egypt has permitted the identification of seven species. Two of these, namely Nummulites rushdisaidi n.sp. and Nummulites qenaensis n.sp. are new. This study suggests that the group might have evolved polyphyletically since the early Ypresian with more marked diversification during the Middle Eocene and attained maximum test size during Bartonian (Nummulites lyelli Archiac and Haime, 1853). This group has been studied in stratigraphic sequence, taking into consideration their geographic distribution. Some known Ypresian precursors such as Nummulites delaharpei Said, 1951 and Nummulites mariettei Said, 1951 (topotypes) and Nummulites rollandi Ficheur, 1890 are also described and illustrated for the first time. During the evolution, retrogenesis was noticed with species evolving from lax to tightly coiled whorls in microspheric forms, whilst the megalospheric forms become progressively lax internally and tighter externally, or vice versa. In addition, duplication of the spiral was noticed in N. qenaensis n.sp. Also, reflexive coiling expressing change in the course of the septa in the outer whorls has been noticed