Crenulosepta perlisensis

Fossil of Crenulosepta perlisensis（圖片來源：Fassihi S et al. (2024)，採用 CC BY 4.0 授權）

Age

Permian（Artinskian）

290.1-283.5 Ma

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Taxonomy

Phylum: Retaria

Subphylum: Foraminifera

Order: Fusulinida

Family: Schwagerinidae

Genus: Crenulosepta

Species: Crenulosepta perlisensis

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Morphological description

The test of Crenulosepta perlisensis is planispirally coiled, with mature individuals typically completing five to six whorls. From early growth to the adult stage, the shell maintains a slight asymmetry. The axial length of the test ranges from approximately 9.5 to 12.4 mm, while the width across the median region measures about 1.6–2.2 mm.

The septa are numerous and thin, forming folds that originate from both sides of the polar regions. In the lower part of the septa, narrow and evenly spaced wrinkles are present; these structures produce chamberlets at the base of the chambers. In contrast, the upper portions of the septa are smoother, displaying gently undulating or nearly straight profiles.

The spirotheca is of moderate thickness, measuring about 0.03–0.1 mm in the outermost whorl. It consists of a thin tectum and a compact alveolar keriotheca. The proloculus is spherical, with an external diameter of approximately 0.08–0.16 mm, and weak chomata can be observed above it.

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Etymology

The genus name Crenulosepta combines crenulo- meaning "finely serrated" or "with small tooth-like notches," and -septa, referring to the septa of the shell.

The species name perlisensis refers to the type locality, Perlis, located in the northwestern part of Peninsular Malaysia. The name commemorates the Early Permian depositional environment and fossil locality preserved in this region, where the fossils of Crenulosepta perlisensis were collected.

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Biological description

Fossils of Crenulosepta perlisensis were discovered in the uppermost sandy limestone layers of the Kubang Pasu Formation in northwestern Peninsular Malaysia. The geological age of this formation corresponds to the Artinskian stage of the Early Permian.

This species shares several characteristics with other members of the genus known from North America, including an elongated test, regular low septal folding, planispiral coiling, and the presence of narrow passages that may occur only in the outer whorls. However, Crenulosepta perlisensis differs from previously known species in several morphological features, such as slightly blunt poles, the presence of a small but recognizable chomata, and an overall coiling pattern that differs from most other species within the genus.

Previously, the genus was known only from eastern North America, particularly from the Santa Rosa Flat and Conglomerate Mesa areas in east-central California, where these fossils are considered relatively rare fusulinid foraminifera. The discovery of Crenulosepta perlisensis in Malaysia therefore indicates that the geographic distribution of the genus was broader than previously recognized, and it may also reflect biological dispersal associated with marine transgressions and warming events during the Early Permian.

（Author: Shui-Ye You）

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Reference

Fassihi S et al. (2024). A new fusulinid species from the early Permian of northwestern Peninsular Malaysia: Evidence of the Artinskian warming event in the eastern Peri-Gondwanan Sibumasu Block. Marine Micropaleontology.

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