Abstract
Two Biradiolites species described from the Yigeziya Formation of the southwestern Tarim Basin are revised. The Maastrichtian Biradiolites boldjuanensis is small and pipe-like species that is usually preserved as clusters or bouquets. Although it was considered to be endemic to Central Asia, similar specimens are abundant in Maastrichtian of other Tethyan regions. Biradiolites minor specimens have no relationship with the genus Biradiolites because their ventral and posterior bands are protruding ridges and interband is depressed broad groove. This species is comparable with the Campanian-Maastrichtian eastern Arabian species Glabrobournonia arabica, by the character of smooth outer shell layer in right valve, and simple radial bands and ridges on margin of each shell flank, but it differs from the latter species in size and the shape of left valve. This study will be a supportive tool for the establishment and reconstruction of the palaeogeographic connection between Central Asia and other Tethyan regions.
Highlights
Biradiolites d’Orbigny 1850 is radiolitid which is characterized by the protruding interband and relatively depressed ventral and posterior bands, as well as the absence of the ligament infolding and central tooth in right valve
It was considered to be endemic to Central Asia, similar specimens are abundant in Maastrichtian of other Tethyan regions
This species is comparable with the Campanian-Maastrichtian eastern Arabian species Glabrobournonia arabica, by the character of smooth outer shell layer in right valve, and simple radial bands and ridges on margin of each shell flank, but it differs from the latter species in size and the shape of left valve
Summary
Biradiolites d’Orbigny 1850 is radiolitid which is characterized by the protruding interband and relatively depressed ventral and posterior bands, as well as the absence of the ligament infolding and central tooth in right valve. It has a cosmopolitan distribution with the age ranging from Turonian to Maastrichtian. Two Biradiolites species, Biradiolites boldjuanensis Bobkova 1960 and Biradiolites minor Pojarkova 1955, had been described by Lan and Wei (1995) from the Yigeziya Formation of the southwestern Tarim Basin X. Rao considered as endemic species that are restricted to the southeast Central Asia including Tajik, Fergana and Tarim Basin. As similar specimens have been recorded from other Tethyan regions like eastern Arabia [1], the taxonomic position and distribution of these two species need to be revised
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