Davidbukrya perchnielseniae Varol, 2023
In honour of renowned nannofossil specialist Professor Emeritus Dr David Bukry, USA.
A moderately large circular rosette-shaped asterolith comprising a non-birefringent disc and a birefringent tube cycle without a proximal shield.
The disc appears lenticular but less convex at the proximal side and comprises radially arranged segments joined along most of their length. The relatively narrow tube cycle is often parallel-sided but rarely widens towards the proximal/more concave side. A shallow depression may be present at both ends of the narrow canal. The proximal shield is underdeveloped.
Optical properties: In cross-polarised light, the disc appears nonbirefringent, whereas the tube cycle is strongly birefringent in plan view. The entire specimen is birefringent in the side view. The extinction pattern is difficult to distinguish in some cases. The inclined extinction lines are dextrogyre on the distal side but laevogyre on the proximal side of the disc. In contrast, the inclined extinction lines are laevogyre on the distal side but dextrogyre on the proximal side of the tube cycle. With a gypsum plate, the blue interference patterns occupy the horizontal axis on the distal side; in contrast, the blue interference patterns occupy the vertical axis on the proximal side.
Davidbukrya may have evolved into Discoaster, but it differs from it by having a birefringent tube cycle. Davidbukrya is distinguished from Carlamuelleria by lacking any proximal shield. Discoasteroides kuepperi, the type species of Discoasteroides, is also a rosette-shaped asterolith with a large flaring birefringent proximal process that is formed by the inner end of the segments. Discoasteroides kuepperi lacks a birefringent tube cycle, as does Davidbukrya.
In plan view, differentiation of Davidbukrya from Markalius is challenging. However, the mobile mount technique and the optical properties associated with proximal and distal sides assist in identification.
In plan view, the most striking optical difference between Davidbukrya and Markalius is the alignment of the interference colour in the tube cycle and disc. In Markalius, the interference colour of the tube cycle and the shields occupy opposite positions, whereas the interference patterns of the tube cycle and the shields are aligned in Davidbukrya. Additional evidence, when identifying Markalius, may be obtained in bright-field and phase-contrast illumination by detecting the proximal shield (Plate 1, Figs. 4, 8,16, 20 in Varol, 2023). Markalius and Davidbukrya can be consistently and correctly distinguished in the mobile mount in their side view (e.g., Davidbukrya has no proximal shield, and Markalius has a spaced proximal shield with an acute inclination angle).
Varol, O. 2023. New paleocene calcareous nannofossils: Carlamuelleria, Davidbukrya, Mauriceblackia, Noelia and Senelia. Marine Micropaleontology. 180: 1-41.