This species was previously mentioned in-
Leshchinskiy, Voronkevich, Fayngertz, Maschenko, Lopatin and Averianov, 2001. Early Cretaceous vertebrate locality Shestakovo, Western Siberia, Russia: A refugium for Jurassic relicts? JVP 21(3) 73A.
It is apparently known from at least two skeletons and is "the largest and one of the most derived species of the genus".
Now, there is another published reference-
Averianov, Voronkevich, Maschenko, Leshchinskiy, and Fayngertz, 2002. A sauropod foot from the Early Cretaceous of Western Siberia, Russia. Acta Palaeontologica Polonica 47(1) 117?124.
"Another sauropod occurrence in Siberia is the Early Cretaceous Shestakovo complex of localities in Kemerovo Region, Western Siberia (Fig.1), which previously yielded partial skeletons of Psittacosaurus (Rozhdestvensky 1960). More recently, this locality has yielded a diverse and important vertebrate assemblage including ... the ceratopsian Psittacosaurus sibiricus Voronkevich and Averianov, 2000, .... ."
Unfortunately, Voronkevich and Averianov 2000 is not listed in the references, although the following is mentioned-
Voronkevich, 1998. A large representative of the genus Psittacosaurus from the locality Shestakovo-3 [in Russian]. In- Vylcan (ed.), Aktual?nye voprosy geologii i geografii Sibiri. Materialy naučnoij konferencii 1, 190?193. Tomskij Gosudarstvennyj Universitet, Tomsk.
Does anyone know the actual citation for Voronkevich and Averianov 2000?