Since Wodehouseia spinata and Aquillapollenites subtilis are known in the Americas only from the Late Maastrichtian, the presence of these palynomorphs in the Udurchukan caused Godefroit to consider the unit and its
lambeosaur dominated fauna to be coeval with the
Lance Formation and
Hell Creek Formation. However, research in the
Songliao Basin indicates Wodehouseia spinata is also known from the early (albeit not basal) and middle Maastrichtian of Asia.
The latest view, appearing in the paper on comparative
osteology of Edmontosaurus and Shantungosaurus, is that one Udurchukan Formation locality,
Kundur, is late−early Maastrichtian; and the other,
Blagoveschensk, is early−late Maastrichtian. The Udurchukan Formation now appears somewhat older than the Lance and Hell Creek, albeit not by much.
^Alifanov, Vladimir & Bolotsky, Yu. (2010). Arkharavia heterocoelica gen. et sp. nov., a new sauropod dinosaur from the Upper Cretaceous of the Far East of Russia. Paleontological Journal. 44. 84-91. 10.1134/S0031030110010119.
Y. A. Popov. 1971. Historical development of the infraorder Nepomorpha (Heteroptera). Akademiya Nauk SSSR, Trudy Paleontologicheskogo Instituta 129:1-228