A diverse Upper Darriwilian radiolarian assemblage from the Shundy Formation of Kazakhstan: insights into late Middle Ordovician radiolarian biodiversity

Abstract. A diverse and well-preserved radiolarian assemblage was extracted from a carbonate sample of latest Darriwilian age from the Shundy Formation of the Aksuran Mountain (North Balkhash Region, Kazakhstan). The fauna is represented by 32 species or morphotypes which belong to nine genera, four families and two orders (Spumellaria and Entactinaria), including four new species described herein (Syntagentactinia? angulata n. sp. Pouille & Danelian, Polyentactinia spinulenta n. sp. Pouille & Danelian, Haplotaeniatum circulus n. sp. Pouille & Danelian and H.? giganteum n. sp. Pouille & Danelian). Representatives of the family Inaniguttidae are particularly abundant, representing c. 70% of the studied assemblage, especially genera Triplococcus and Inanihella that dominate the assemblage. Although the studied fauna contains both of the characteristic species and most of the genera of the previously defined Haplentactinia juncta–Inanigutta unica assemblage, differences in the assemblage structure are striking. The studied fauna also establishes that the two characteristic species of the Inanihella bakanasensis–Triplococcus akzhala assemblage are not restricted to the early–mid-Darriwilian, but their age range also extends to the latest Darriwilian.