Mammals from the Upper Cretaceous Aitym Formation, Kyzylkum Desert, Uzbekistan

Abstract

The Upper Cretaceous (?Santonian) Aitym Formation in the central Kyzylkum Desert, Uzbekistan, produced remains of a cimolodontan multituberculate ( Uzbekbaatar wardi), a spalacotheriid symmetrodont (cf. Shalbaatar sp.), a deltatheroidan (cf. Deltatherus sp.), possibly the asioryctithere aff. Daulestes sp., possibly two zalambdalestids ( Kulbeckia sp. cf. K. kulbecke and aff. Kulbeckia sp.), two supposed lipotyphlans ( Paranyctoides sp. cf. P. aralensis and Paranyctoides sp.), and zhelestid ungulatomorphs (cf. Aspanlestes sp., Parazhelestes sp. aff. P. minor, Parazhelestes sp. cf. P. robustus, and Eoungulatum sp. cf. E. kudukensis). The Aitym mammal fauna is most similar to the more diverse mammal fauna of the underlying Bissekty Formation (upper Turonian–Coniacian). Uzbekbaatar and Shalbaatar were most probably derived from North American immigrants. Paranyctoides and ‘Zhelestidae' are of Middle Asian (a commonly and long used Soviet geographic region approximately extending from the Caspian Sea on the west to the Chinese border on the east, and from the Iranian and Afghan borders on the south to southern Kazakhstan on the north) origin and migrated to North America during the late Santonian–early Campanian. A dispersal route was present in Beringia during the entire Late Cretaceous, which may have worked as a cold filter, allowing intercontinental dispersals between Asia and western North America in both directions, especially during shorter, warm climatic phases.