Discoaster brouweri Tan Sin Hok, 1927
Eu-discoaster Tan Sin Hok, 1927
Helio-discoaster Tan Sin Hok, 1927
Hemi-discoaster, Tan Sin Hok, 1927
Asterolithes Sujowski, 1931
Gyrodiscoaster Stradner, 1961
Agalmatoaster (Gemminiodicoaster) Prins, 1971
Radiodiscoaster (Curvidiscoaster) Prins, 1971
Truncodiscoaster Prins, 1971
Turbodiscoaster Prins, 1971
- Stellate, rosette shape or discoidal nannolith, often concave-convex.
- The segments are non-birefringent in plan view.
- The inner end of the segments may form distal and proximal processes.
- The segments entirely or partly join each other.
- The termination of segments can be simple, bifurcated or twisted.
- The ridges, depressions, or other ornamentations may be present on the segments.
- The two major groups can be identified [each group can be further subdivided]:
- Rosette-shaped discoasters have segments joined to each other almost entirely along their length.
- Stellate discoasters, having segments only partly joined to each other, leaving a distinct free length of segments.
Herendeen (2016) confirmed that the International Code of Nomenclature (ICN) had approved the proposal by Dowel (2014) to conserve the name Discoaster. This decision ensures the continued use and recognition of the name Discoaster in scientific literature and research, maintaining consistency and clarity in the classification and study of these essential nannofossils.
The optical properties of Discoaster, including constant extinction (dim) in the plan view and interference colours due to birefringence in the side view under XPL, align with those observed in the family Discoasteraceae.
The species of Discoaster are identified based on the following main criteria:
Morphological Classification of Discoaster Assemblages
To streamline biostratigraphic analysis and trace macroevolutionary trends within the genus Discoaster, the recovered asteroliths are categorized here into three informal, visually distinct morphogroups based on segment (=arm=ray) architecture and geological occurrence: rosettes, stellates, and neostellates. The rosettes encompass Paleogene forms characterized by numerous segments that remain tightly joined along most or all of their length, yielding a closed, flower-like profile. In contrast, the stellates comprise Paleogene star-shaped lineages whose segments have distinctly free lengths and typically exhibit high segment counts (ranging from 8 to 30). Finally, the term neostellates is introduced here as an informal grouping restricted to Neogene assemblages. These forms are morphologically segregated from their Paleogene predecessors by a highly reduced segment count—strictly stabilized at 3 to 7 arms with free lengths. While neostellates are predominantly characterized by straight, bilaterally symmetrical segments, notable exceptions exist within this Neogene group. These are represented by forms displaying distinctly asymmetrical arm arrangements, occurring across both the Miocene and Pliocene intervals, as exemplified by Discoaster asymmetroivrachiones and Discoaster asymmetricus, respectively. This three-part classification simplifies down-hole microscopic identification while directly reflecting the primary evolutionary shift from complex, crowded Paleogene structures to the streamlined geometries of the Miocene and Pliocene.
Prins, B. 1971. Speculations on relations, evolution and stratigraphic distribution of discoasters. In: Farinacci, A. (Ed.) - Proceedings of the Second Planktonic Conference Roma 1970. Edizioni Tecnoscienza, Rome 2: 1017-1037.
Stradner, H. 1961. Vorkommen von Nannofossilien im Mesozoikum und Alttertiär. Erdoel-Zeitschrift 77(3): 77-88.
Sujkowski, Z. 1931. Étude pétrographique de Crétacé de Pologne. Sprawozdania Polskiego instytutu geologicznego. 6: 485-628.
Tan Sin Hok. 1927a. Discoasteridae incertae sedis. Proceedings of the Koninklijke Nederlandse Akademie van Wetenschappen. Sect Sci, 30: 411-419.