The new species of stegosaurus is the oldest discovered in Asia, and possibly in the world
Newswise – A relatively small but fearsome-looking stegosaurus measured about 2.8 meters (9 feet) from nose to tail, but scientists can’t say whether the remains are those of an adult or a juvenile.
A new species of one of the most recognizable types of dinosaur is the oldest stegosaurus ever found in Asia, and one of the oldest discovered in the world, according to a study published today in the peer-reviewed magazine. Journal of Vertebrate Paleontology.
Stegosaurus remains, which included back, shoulder, thigh, foot and rib bones, as well as several armor plates, date to the Bajocian stage of the Middle Jurassic period – long before most known stegosaurs. .
A team from China’s Chongqing Geological and Mineral Resources Exploration and Development Bureau and London’s Natural History Museum named him Bashanosaurus primitivus – “Bashan” in reference to the ancient name of the region of Chongqing in China where the dinosaur was found, and the Latin for “first” – primitivus.
The new dinosaur, which roamed the planet 168 million years ago, plays a role in the discovery of the evolution of stegosaurs – of which, to date, little is known.
It has a smaller, less developed blade, narrower, thicker bases for its armor plates, and other features that are unlike any other Middle Jurassic stegosaurs discovered so far. However, it bears similarities to some of the earliest armored dinosaurs, which are over 20 million years older.
“All of these features are clues to the place of stegosaurs in the dinosaur family tree,” says Dr. Dai Hui of the Chongqing Geological and Mineral Resources Exploration and Development Bureau, who led the research. “Bashanosaurus can be distinguished from other Middle Jurassic stegosaurs, and clearly represents a new species.
“Furthermore, our family tree analysis indicates that it is one of the earliest divergent stegosaurs along with the Chongqing lizard (Chungkingosaurus) and Huayangosaurus. These have all been excavated from the Middle to Late Jurassic Shaximiao Formation in China, suggesting that stegosaurs may have originated in Asia,” adds Hui.
Instantly recognizable by their huge back plates, long tail spikes, and small heads, stegosaurs were four-legged, herbivorous dinosaurs that lived in the Jurassic and early Cretaceous. Stegosaurus fossils have been found on every continent except Antarctica and Australia, and 14 species of stegosaurus have been identified so far.
Well-known members of Stegosauria include Huayangosaurus (one of the most primitive stegosaurs), giantspinosaurusremarkable for its enormous dorsal spines, and Miragaia for its extremely long neck. However, fragmentary fossil material has hampered attempts to understand how stegosaurs evolved and how they relate to each other.
With the discovery of this new species, the mystery begins to unravel. Bashanosaurus primitivus has several primitive features that are similar to early stegosaurs like Huayangosaurus and giantspinosaurus and early branching thyreophores (armored dinosaurs). These include longer tail vertebrae, a narrower, flared scapula, and features of the dorsal vertebrae that are similar to those of the first armored dinosaur. Scelidosaurus, who lived in the Lower Jurassic.
The fossilized remains of Bashanosaurus also reveal a host of features that make it unique from other known stegosaurs. For example, the bony tip at the end of the scapula is small and less well developed than in other stegosaurs; a bony projection of the femur (fourth trochanter) is positioned under the middle of the diaphysis; and the bases of the armor plates curve outward and are thicker than the plates on the backs of its later relatives.
“The discovery of this Middle Jurassic stegosaurus from China adds to a growing body of evidence that the group evolved during the Early Middle Jurassic, or possibly even the Early Jurassic, and as such represents some of the earliest dinosaurs to rumps of known birds,” says Dr Susannah Maidment, co-author and paleontologist at the Natural History Museum in London.
“China appears to have been a hotspot for stegosaur diversity, with many species now known from the Middle Jurassic through the Late Lower Cretaceous.”