Thursday, January 19, 2017

Amurosaurus by atrox1 on DeviantArt

Amurosaurus (“Amur lizard”) is a genus of lambeosaurine hadrosaurid dinosaur found in the latest Cretaceous period (66 million years ago) of eastern Asia. Like most lambeosaurs, it would have been a primarily bipedal herbivore with a “duckbill” shaped snout and a hollow crest on top of its head, although such a crest has not been found. Fossil bones of adults are rare, but an adult would most likely have been at least 6 metres (20 ft) long. According to Gregory S. Paul, it was about 8 metres (26 ft) long and weighed about 3,000 kilograms (6,600 lb)

Skeletal reconstruction of Amurosaurus riabinini Bolotsky and Kurzanov, 1991. Black elements are not preserved in the available material. By Pascal Godefroit, Yuri L. Bolotsky, and Jimmy Van Itterbeeck

Russian paleontologists Yuri Bolotsky and Sergei Kurzanov first described and named this dinosaur in 1991. The generic name is derived from the Amur River and the Greek word sauros (“lizard”). The Amur (called Heilongjiang or “Black Dragon River” in Chinese) forms the border of Russia and China, and is near where this dinosaur’s remains were found. There is one known species (A. riabinini), named in honor of the late Russian paleontologist Anatoly Riabinin, who conducted the first Russian expeditions to recover dinosaur remains in the Amur region in 1916 and 1917.

In cahoots with Godefroit and Itterbeeck, Bolotsky revisited the Blagoveschensk bone pile in 2004 and realised that many of the bones belonged to Amurosuarus, albeit seperate individuals, and it instantly became the most abundantly known dinosaur ever discovered on Russian territory. On top of that the age of the Udurchukan Formation bodes well for the “Asian origin for lambeosaurines” hypothesis, and experts surmise that these duck-billed critters and other Asian vertebrate groups travelled across the Beringian isthmus into western North America via a land route that may have opened during the Aptian–Albian and persisted during the Late Cretaceous.

Amurosaurus is characterized by many autapomorphies, or unique features, of the skull, as well as the sigmoidal shape of the ulna (a lower arm bone) when viewed from the front or side. Most other known lambeosaurines have hollow crests on the top of their skulls, and although the bones that would make up such a crest are unknown in this dinosaur, the bones of the roof of the skull are modified to support one, so it can be assumed that Amurosaurus was crested as well.

Olorotitan and Amurosaurus belong to the same group as the iguanodons. These two hadrosaurs were excavated by a team made up of our paleontologists and their Russian counterparts, in 2001 and 2003. Photo: Royal Belgian Institute of Natural Sciences

As most of its features were described recently, as of early 2006, Amurosaurus has only been subjected to one cladistic analysis, which placed it as a basal member of the lambeosaurine subfamily of hadrosaurs, but more derived than either Tsintaosaurus or Jaxartosaurus.

All known basal lambeosaurines come from Asia, which has led to the hypothesis that lambeosaurines originated there and then later dispersed across the Bering Strait to North America. Two derived groups, the parasaurolophins (ParasaurolophusCharonosaurus) and lambeosaurins (CorythosaurusNipponosaurusLambeosaurus, etc.) evolved later. As members of both groups are found in North America and Asia (And one from Europe, which one is not solidly known.), there must have been further dispersal after their evolution, although in which direction that dispersal occurred is still unclear.