WULAGASAURUS

Wulagasaurus was discovered in a Yuliangze Formation quarry that was dominated by fossils of a lambeosaurine known as Sahaliyania, but stood out like a sore thumb because of its strange upper arms with distinctive joints and ridges for muscle attachment, and a long slender lower jaw. Since then, a plethora of remains from the same site have been assigned to it with varying degrees of certainty, but most of them — including braincases, upper jaw bones and shoulder blades — actually belong to a lambeosaurine. And it may not be Sahaliyania.

Wulagasaurus is a member of Saurolophinae (previously known as Hadrosaurinae) — the sister group to Lambeosaurinae — and although Asian and currently the oldest representative known from anywhere it sports a couple of weird features found only in Brachylophosaurus and Maiasaura who are both from the U.S of A. Given their respective age, it seems likely that saurolophines (and thus all hadrosaurids) evolved in Asia during the Late Santonian of the Early Cretaceous, then dispersed to North America during the Middle Campanian via the Bering land bridge. This stretch of land has joined Asia to America at various points and times when sea levels were low, and is still inhabited by "Beringian" folks in Alaska and the Russian Far East, though the rest of it is now under the Bering and Chukchi seas.

The Late Maastrichtian (latest Late Cretaceous) of eastern Asia is a hotspot for hadrosaurids, having yielded the likes of Charonosaurus, Amurosaurus, Kerberosaurus, Olorotitan, Sahaliyania and Wulagasaurus from the Amur region alone. In contrast, ceratopsian fossils are as rare as pigeon teeth, which suggests hadrosaurids were the dominant herbivores in that area at the end of the age of dinosaurs, but in North America during the same period, it's the ceratopsians that by far outnumber the hadrosaurids.