What is Nummulites lyelli? Evolution in large foraminifera during the Middle Eocene, Egypt

Abstract

Nummulites lyelli D'Archiac and Haime 1853, is described for the first time from photographs of both generations, using material from the species type locality at El-Mishgigah, in the El-Gharaq Formation exposed in the Fayum Depression. Nummulites praelyelli n.sp., described from the Mokattam Formation below the Citadel of Salah El Din, in the eastern part of Cairo, is interpreted to be the ancestor of Nummulites lyelli Archiac and Haime. The main ontogenetic trend in this newly identified lineage is a gradual change from tight to lax coiling during growth, whereas the opposite onotgenetic trend is found in the lineage of Nummulites gizehensis (Forskål) In this work, the group of Nummulites gizehensis and allied species is separated from the group of Nummulites lyelli, partly on this basis but definitively on the basis of granulation and septal morphology. We suggest that at the beginning of the Bartonian, Nummulites lyelli ecologically displaced the Late Lutetian Nummulites gizehensis in both space and time, rather than evolving from it.

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

“…Its ontogenetic development of coiling conforms to that of N. lyelli and opposes to that of N. gizehensis sensu stricto (see Hussein-Kamel, 1993 andKamal, 2003 Fig. 3).…”

“…In the Paleogene of Egypt; some species closely related to Nummulites gizehensis (Forskal) (sensu lato) represent an important group in Nummulites, which attracted the attention of many authors (de la Harpe, 1881;1883b;Cuvillier, 1930;Said, 1951;Kenawy, 1979;Schaub, 1981;Schaub et al, 1995;Omara and Kenawy, 1984;Abdel Ghany, 1990;Boukhary and Hussein-Kamel, 1993;Boukhary and Kamal, 2003;Hussein, 2004;Hussein et al, 2004). However, different species closely related to N. gizehensis (s.l.)…”

“…Recently, Boukhary and Kamal (2003) described the new species Nummulites praelyelli as the ancestor of N. lyelli. Furthermore, they dissociated N. lyelli from the N. gizehensis group after concluding that N. gizehensis became extinct at the beginning of the Bartonian, and was ecologically replaced by N. lyelli rather than evolving from it.…”

A stratigraphic review of the Eocene to Miocene rock units in the al Jabal al Akhdar, NE Libya

“…6). Large-sized nummulitids, such as N. gizehensis and N. lyelli, are well known from the Middle Eocene assemblages of the southern Mediterranean regions (see for example Schaub, 1981;Boukhary and Hussein-Kamel, 1993;Boukhary and Kamal, 2003). The top of the Middle Eocene in all studied sections is defined by the last occurrence of N.lyelli, Orbitolites complanatus and associated taxa (Figs.…”

Lineage ofArxina schwageri(Silvestri, 1928) new genus (Nummulitacea) from Middle Eocene of Egypt and Sultanate of Oman

“…In spite of the fact that the larger foraminifera of the Eocene sections of Egypt and Sultanate of Oman has attracted the attention of many authors (Cuvillier 1930;Shama 1981;Boukhary and Hussein-Kamel 1993;Racey 1995;Boukhary and Kamal 2003), the foraminiferal operculiniforms have had lesser attention. This note aims at discussing the phylogeny of a group of species which is traditionally described under genus Operculina, the fact that its type species is still living (recent).…”