A team of paleontologists announces the discovery of a new species of hadrosaur – or duck-billed dinosaur – whose remains were excavated on one of the islands in southern Japan. Details of this work are published in the journal Scientific reports.
Hadrosaurs, known for their broad, flattened snouts, were the most common dinosaurs during the late Cretaceous Period. Fossil records have in fact been discovered mainly in deposits in Europe, East Asia and Africa. Derived forms have also been found in Upper Cretaceous rocks on all continents except Australia and the Indian subcontinent.
These animals were characterized, among other things, by their dentition. They did not develop an articulated jaw like mammals, but a hinge between the skull and the upper jaw. This structure allowed these dinosaurs to make tooth movements in all directions: from bottom to top, front to back, left and right. This way, they could shred food like no one else before swallowing it.
These teeth thus slid against each other. As they wore out and fell out, they were replaced with new teeth developed below the previous ones. The efficient ability of hadrosaurs to chew vegetation is one of the factors that has led to their diversity and abundance, the researchers say.
A new dinosaur in Japan
That being said, a team of paleontologists led by Anthony R. Fiorillo of Southern Methodist University and Yoshitsugu Kobayashi of the Hokkaido University Museum recently identified a new representative of this large family of dinosaurs.
The remains of this animal – the lower jaw, teeth, neck vertebrae, shoulder bones and a tail vertebra – were discovered in 2004 in a layer of sediment about 71 to 72 million years ago on the Japanese island of Awaji.
This dinosaur, which has just been named Yamatosaurus izanagii, was distinguished by its dentition, precisely. The structure of its teeth suggests that it evolved to devour different types of vegetation than other hadrosaurs, according to Anthony R. Fiorillo.
Yamatosaurus is also distinguished by the development of its shoulder and forelimbs. According to paleontologists, this specimen represents an evolutionary stage in the change of gait of these animals, from a bipedal walk to a quadrupedal walk.
Finally, the fossilized find provides new information on the migration of hadrosaurs. It suggests that these herbivores migrated from Asia to North America via the Bering land bridge, and not the other way around. At the time when this species evolved in present-day Japan, this now insular territory was attached to the eastern coast of Asia. Tectonic activity only separated these lands about fifteen million years ago, long after the extinction of the dinosaurs.