ARSTANOSAURUS

Arstanosaurus was named in 1982 and described as a hadrosaurid by Shilin and Suslov. But by 1995, Nessov was convinced it was a ceratopsid due mainly to similarly "double-rooted teeth", as reported in the original description. Later still, Norman and Kurzanov announced that it was incorrectly described in the first place as x-rays showed the teeth had a single root. On top of that, the angle of the published photos distorted the fossils, which threw a curveball at future reviewers who hadn't seen them in person. Because it appeared to lack specifically diagnostic characters, they proclaimed it a nomen dubium. But at the same time, they tentatively assigned it to the hadrosaurid subfamily Lambeosaurinae because of features of its upper jaw, lamented a lack of features in common with any then-known Kazakh hadrosaurid due mainly to a lack of comparable parts, and paradoxically noted broad anatomical similarities to a Chinese hadrosauroid called Bactrosaurus.

A juvenile skeleton (PIN, no. 3458/5) found by Sergei Kurzanov in the Bayinshire Formation at Bayshin Tsav in Mongolia's Gobi Desert during the Joint Soviet-Mongolian Paleontological Expedition of 1971, previously and unofficially tagged "Gadolosaurus" by Tsunemasa Saito in a guide book documenting its tour of Japan as part of a Soviet expedition, was labelled as Arstanosaurus sp. in a display at the Moscow Paleontological Museum once it returned to Russia. Several palaeontologists followed that lead in assigning it to Arstanosaurus and ditto for several other specimens from Mongolia. But that was mainly in personal communication among themselves, with nothing in the way of justification ever being published.

Officially, Arstanosaurus is mostly mugged off as dubious due to its diagnosis-dodging remains. But it isn't beyond the realms of possibility that it's the same critter as Batyrosaurus, which was found at the same locality in the same formation and described by Godefroit et al. in 2012, despite the only comparable parts being teeth, which are apparently different. The juvenile specimen, however, appears to be something else entirely. But no one has been brave enough to either afford it its own name or assign it to one of the numerous hadrosaurids already known from Asia and Kazakhstan, despite poking it with a stick every now and again over the last four decades.