[D] Amurosaurus riabinini [sG] [Su] [T]
Bolotsky & Kurzanov, 1991
Cretaceous Late Maastrichtian
Ornithischia Ornithopoda Hadrosauridae Lambeosaurinae
Udurchukan Formation, Tsagayan Group [Tsagayanskaya Svita], Amur river basin, far eastern Russia, near the Chinese border.
Genus - Typespecies - Skull
Two apparently intact skeletons had been found. Discovered on the outskirts of the town of Blagoveshchensk. Despite the Late Maastrichtian age proposed for the Blagoveschensk locality A. riabinini looks verry primitive: its skull and dention present several plesiomorphic characters not observed in North American lambeosaurines. Its skull was probably capped with a crest similar to that observed in the North American genera Corythosaurus or Hypacrosaurus
Holotype: AEHM 1/12, associated left maxilla and dentary.
Type locality: Upper part of Nagornaia Street, west of Blagoveschensk City, Amur Region, Russia.
Type horizon: Udurchukan Formation [The oldest geologic formation in the Tsagayanskaya Svita] (Wodehouseia spinata– Aquila− pollenites subtilis palynozone), “middle”–late Maastrichtian, Late Cretaceous.
Godefroit, P., Bolotsky, Y.L., and Van Itterbeeck, J. 2004. The lambeosaurine dinosaur Amurosaurus riabinini, from the Maastrichtian of Far Eastern Russia. Acta Palaeontologica Polonica 49 (4): 585–618.
Amurosaurus riabinini Bolotsky and Kurzanov, 1991 (Dinosauria, Hadrosauridae) is described on the basis of numerous disarticulated bones from the Maastrichtian Udurchukan Formation of Blagoveschensk, Far Eastern Russia. Comparisons with North American palynozones and their well calibrated ages suggest that this formation is late Maastrichtian in age. It is shown that A. riabinini is a valid species, characterised by cranial and postcranial autapomorphies. A phylogenetic analysis, based on 40 cranial, dental, and postcranial characters, indicates that this taxon occupies a relatively basal position within the lambeosaurine subfamily as the sistertaxon of a monophyletic group formed by the parasauroloph and corythosaur clades. This cladogram also demonstrates that lambeosaurines have an Asian origin. In eastern Asia, lambeosaurine dinosaurs dominate late Maastrichtian dinosaur localities, whereas this group is apparently no longer represented in synchronous localities from western North America.
The Blagoveschensk dinosaur locality is situated within the city limits of Blagoveschensk (Amur Region, Far Eastern Russia). The outcrops of the dinosaur site are limited to a talus a few metres high. The dinosaur−bearing sediments are green−coloured claystones with a considerable amount of dispersed granules. A basal pebble lag with amaximum clast size of 20 cm occurs at the base of these sediments, The total thickness of the Cretaceous sediments in outcrop is estimated as 2–3 m. Indurated metamorphic rocks, which are weathered at the top, form the basal part of the outcrop. In outer appearance and the apparent lack of sorting by size of the bones, fluvial transportation over a long distance seems unlikely. The abundance of theropod shed teeth and the frequency of toothmarks on the bones is indicative for an intensive activity of predators or scavengers.
Emended specific diagnosis: Lambeosaurine dinosaur characterised by the following autapomorphies: prominent median process between basipterygoid processes; sagittal crest particularly elevated on the caudal part of the parietal and forming a high, triangular and deeply excavated triangular process on the occipital aspect of the skull; squamosals separated from each other by this crest along their entire height; caudal process of postorbital particularly elongated, narrow, and regularly convex upwardly; prefrontal forming at least half of the width of the floor for the supracranial crest; ulna and radius sigmoidal both in lateral and in cranial views.