The first complete skeleton of an early sauropod has been found in China, providing a glimpse of the ancestor of all those colossal, four-legged dinosaurs that came later.
The sauropod, tentatively named Yizhousaurus sunae, lived 200 million years ago on the plains of what is today the Yunnan Province of southern China. Yizhousaurus was 30 feet long and already had the signature sauropod long neck, heavy-duty skeleton and four-legged stance.
But what really makes the case for its pivotal role in the evolution of sauropods is its intact skull, which is an extremely rare find, explained paleontologist Sankar Chatterjee of Texas Tech University.
"The skull has very, very crucial information about its affinities," Chatterjee said. In the case of Yizhousaurus, the skull is wide, domed, short-snouted and has eye sockets on the sides to make it easier to watch for predators. It also has a broad, U-shaped jaw that looks a lot like those seen in later sauropods.
The teeth tell a lot about the beast as well. Yizhousaurus had a lot of serrated and spoon-shaped teeth on upper and lower jaws. These could slice past each other like scissor blades, allowing Yizhousaurus to shear off the vegetation on which it dined as well as chew. It also appears that the animal could raise its head and snip leaves and branches from trees.
The reason few early sauropod skulls are found is that they are very delicately built compared to the rest of a sauropod, Chatterjee said. They are also very small despite the huge bodies they once commanded.
What also helps make the case for Yizhousaurus as a missing sauropod link are the other fossils near which it was found. Decades ago fine specimens of what are called prosauropods were found in the same rocks. As the name implies, prosauropods are generally thought to be the precursors of the sauropods.
Despite the findings, the transition between them has been fuzzy. Yizhousaurus helps to sharpen the image a bit.
"I would say this is a very important fossil that will shed light on the early evolution of sauropodomorph dinosaurs," said Spencer Lucas, curator of geology and paleontology at the New Mexico Museum of Natural History and Science. "It once again demonstrates the richness and importance of the Chinese vertebrate fossil record."
Chatterjee will be presenting Yizhousaurus discovery on Oct. 31 at the annual meeting of the Geological Society of America in Denver.