Unraveling the Tethyan Eocene: A Review of Middle–Upper Eocene Gaziryina and Allied Species in Phylogeny, Regional Biostratigraphy and Paleobiogeography

Abstract

Larger benthic foraminifera during the Eocene within the Tethyan realm played a crucial role in regional biostratigraphy. In the Middle East, particularly in Libya, Tunisia, and Egypt, nummulitids are key constituents of nummulitic limestone reservoirs, making the taxonomic identification of this structurally complex group vital for biostratigraphic and petroleum applications. This review focuses on the genus Gaziryina of the nummulitids, clarifying its taxonomic status, biostratigraphic utility, and paleobiogeographic significance using biometric data from published literature. Previously misidentified as Nummulites pulchellus, Gaziryina species have been systematically reassessed based on biometric data from published literature. The findings confirm Gaziryina as a distinct genus comprising two species: Gaziryina basatinensis (late Lutetian–Bartonian, SBZ15-18a) and Gaziryina pulchellus (late Bartonian–Priabonian, SBZ18a/b-20). Morphological characters (test shape, size progression, chamber configuration, protoconch enlargement) and ontogenetic trends (tight to lax) indicate a phylogenetic transition where Gaziryina basatinensis evolved into Gaziryina pulchellus, consistent with Cope's rule. Paleobiogeographic reconstruction indicates a probable origin in the southern Neo-Tethys, likely the Western Desert of Egypt, with subsequent dispersal across the northern and southeastern Tethys. These findings confirm Gaziryina as a key biostratigraphic marker, necessitating further research on its evolution and biostratigraphic framework.

Keywords

Gaziryina pulchellus / larger benthic foraminifera / regional biostratigraphy / paleobiogeography / Middle–Upper Eocene / Tethys

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2025 Geological Society of China