OVUMMURIDAE

Hussain, Rowshi, Rogers, Steven L. & Blackburn, Joel A., 2022, Ovummuridae (calcareous microfossils) from the Much Wenlock Limestone Formation, Shropshire, UK, Palaeontologia Electronica (a 27) 25 (2), pp. 1-24 : 5

Family OVUMMURIDAE

Munnecke, Servais and Vachard, 2000

Derivation of name. After Ovummurus , first genus described.

Genera included. Ovummurus Minoura and Chitoku, 1979 ; Minourella Munnecke, Servais, and Vachard, 2000 ; Arouxina Munnecke, Servais, and Vachard, 2000 ; Samtlebenella Munnecke, Servais, and Vachard, 2000 ; Natantesprifmata gen. nov; Hartonella gen. nov. and Munneckella gen. nov.

Original diagnosis (Summarised from Munnecke et al. 2000). Calcareous microfossils with an unknown biological affinity characterised by their small size and consisting of two or more chambers, an aperture at the apex of the chamber and a calcareous wall comprising of small slab or tablet like calcite crystals regularly arranged in concentric or pseudo-concentric layers.

Original description (Summarised from Munnecke et al. 2000). Spherical to ovoid or dolioform in shape with a maximum diameter of <100 µm. The walls are composed of 1 µm thick calcite tablets in roughly lamellar series and appear similar to those described in bryozoans and tentaculitoids ( Larsson, 1979; Minoura and Chitoku, 1979; Munnecke and Samtleben, 1996). The wall thickness varies within different parts of the test. The partitioning of the internal cavity by a subequatorial or equatorial pseudo-septum is a common characteristic of the family. The apertures are variable, and, where present, determine the axial plane of the test.

Remarks. The Ovummuridae observed within the Much Wenlock Limestone Formation showed similar size ranges to those observed within the Silurian of Gotland with the majority of specimens under 100 µm. A few specimens observed did, however, exceed the original dimensions of 120 µm maximum diameter for Ovummurus as originally described by Minoura and Chitoku (1979), and some exceeded the 100 µm described by Munnecke et al. (2000). Here, we observe diameters ranging from 20 µm–298 µm.

The characteristics of the Ovummuridae are described as more or less spherical by Munnecke et al. (2000) and Minoura and Chitoku (1979), however, we note morphotypes of prismatic and elongated nature and some with triple chambers as first observed by Munnecke et al. (2000) followed by MacNeil and Jones (2006). Hence, we propose the addition of three new genera to the family. The composition of ovummurid walls in many specimens observed comprise pyrite crystals as well as the calcite tablets noted in the original diagnosis by Munnecke et al. (2000). Their walls are almost identical to the walls of bryozoans. Several specimens contained clastic grains within their chambers similarly described by Minoura and Chitoku (1979), Munnecke et al. (2000) and MacNeil and Jones (2006). MacNeil and Jones (2006) were unconvinced of reports of Samtlebenella circumcamerata sp. within the Upper Carboniferous samples of Munnecke et al. (2001) and believed they were mistaken for bryozoans. Here, we observe a small number of Samtlebenella circumcamerata with one or two chambers within their walls.

Stratigraphical range. Lower Silurian to Upper Permian ( Munnecke et al., 2001).