Wednesday, 9 May 2012

New Fossil Evidence Reveals The Origins Of The Hadrosaurines

The bones of Wulagasaurus dongi
The hadrosaurines are some of the most diverse, well known and bizarre dinosaurs to have walked the planet. Evolving during the mid Cretaceous some 100 million years ago, their basic shape was similar to that of the predatory dinosaurs.

They walked on two legs with the tail balancing out the body, but unlike their carnivorous cousins, their front limbs were long enough to allow quadrupedal motion. They also led a herbivorous lifestyle.

Over time, some truly incredible fossils have been found, including complete skeletons and even skin. We know a vast amount about the hadrosaurines, from their lifestyle to physiology, but as with many other animal groups, little about their origins.

New fossil evidence, however, reveals exactly where these giant, duck-billed dinosaurs came from. Recently, an international team of researchers excavated several hundred disarticulated bones from a lambeosaurine (a sister group to the hadrosaurines, which together make up the group hadrosauridae) called Sahaliyania elunchunorum.

A small portion came from the hadrosaurine Wulagasaurus dongi. The remainder were recovered from Cretaceous Yuliangzi formation from the Wulaga outcrop in Heilongjiang Province near the Sino-Russian boundary.

When the researchers looked at the geographical placement of China and North America during the Cretaceous, they saw that the two landmasses were once joined together. 'Phylogenetic analysis indicates that Wulagasaurus, Brachylophosaurus and Maiasaura form a monophyletic basal clade of hadrosaurines. It is likely that this basal hadrosaurine clade originated in Asia and subsequently dispersed to North America via the Bering land bridge, following a biogeographical pattern also seen in some other hadrosaurine groups' said lead author Xing Hai, a palaeontologist graduate student of the IVPP (Institute of Vertebrate Palaeontology and Palaeoanthropology).

Analysis of the bones, along with antique specimens has shown that both creatures were very closely related to a North American hadrosaurines called Brachylophosaurus and Maiasaura. All four creatures comprise some of the most primitive hadrosaurids on Earth.