Bashanosaurus

Bashanosaurus (meaning "Bashan lizard", after an ancient name for Chongqing) is a genus of stegosaur dinosaur recovered from the Bajocian (Middle Jurassic)-aged Shaximiao Formation of Yunyang, Chongqing, China. The type species is Bashanosaurus primitivus. It is one of the basalmost stegosaurs and is also the oldest known stegosaur, supplanting the previous oldest known stegosaur, Adratiklit, which is roughly one million years younger.

Discovery and naming[]

Two specimens of Bashanosaurus — A, photograph (top) and interpretative sketch (bottom) of Bashanosaurus primitivus (CLGPR V00006-1) on the west side of the Dinosaur Fossil Wall. B, photograph (top) and interpretative sketch (bottom) of Bashanosaurus primitivus (CLGPR V00006-2) in the middle of the Dinosaur Fossil Wall.

Bashanosaurus is known from two partial skeletons, along with a vertebra that comes from a third individual; these remains were preserved on the Dinosaur Fossil Wall, preserved within the Zigong Dinosaur Museum, along the with another specimen, a partial cranium, a dorsal vertebra, and a piece of dermal armour (CLGPR V00006), which belongs to an unnamed indeterminate stegosaur. The material was recovered from a quarry in Chongqing discovered in 2016, hailing from the Shaximiao Formation. The specimens were given the name Bashanosaurus primitivus in a 2022 paper, in reference to the old name of Chongqing and its basal position.

The holotype, CLGPR V00006-1, includes limb bones, back and tail vertebrae, plates and a spike. The second specimen CLGPR V00006-2, consists of five vertebrae, a right lower leg and a plate. The third specimen is CLGPR V00006-3, a back vertebra. A fourth specimen, CLGPR V00006-4, a partial skeleton with skull, was not referred as it does not share unique traits with the holotype.

Description[]

Bashanosaurus primitivus is the earliest record of Stegosauria in Asia and represents one of the earliest records of this dinosaur group from anywhere in the world. The recently discovered stegosaur species roamed the Earth during the Middle Jurassic period, around 168 million years ago. Scientifically named Bashanosaurus primitivus, the ancient creature was about 2.8 m (9 feet) long. It had a smaller and less developed should blade, narrower and thicker bases to its armor plates and other features that are different from all other Middle Jurassic stegosaurs discovered so far. However, it had similarities with some of the first armored dinosaurs, which are over 20 million years older.

The stegosaurs were an iconic group of armored dinosaurs with hypertrophied dermal armor plates and/or spines extending from the neck to the end of the tail. Stegosaurs fossils have been found on all continents except for Antarctica and Australia. The first stegosaurs are known from the Middle Jurassic of Europe, China, Argentina, and Morocco. Stegosaurian diversity appears to have decreased after the Jurassic period, and they seem to have gone extinct by the Middle Cretaceous. About 14 stegosaur genera are currently recognized.

“All these features are clues to the stegosaurs’ place on the dinosaur family tree,” said Dr. Dai Hui, a paleontologist with the Chongqing Bureau of Geological and Mineral Resource Exploration and Development.

“Bashanosaurus primitivus can be distinguished from other Middle Jurassic stegosaurs, and clearly represents a new species.” The fossilized remains of Bashanosaurus primitivus — bones from the back, shoulder, thigh, feet, and ribs — were found in the Shaximiao Formation near Laojun village, Chongqing municipality, China.

“Our analysis of the family tree indicates that Bashanosaurus primitivus is one of the earliest-diverging stegosaurs along with Chungkingosaurus and Huayangosaurus,” Dr. Hui said. “These were all unearthed from the Middle to Late Jurassic Shaximiao Formation, suggesting that stegosaurs might have originated in Asia.”

“The discovery of this stegosaur from the Middle Jurassic of China adds to an increasing body of evidence that the group evolved in the early Middle Jurassic, or perhaps even in the Early Jurassic, and as such represent some of the earliest known bird-hipped dinosaurs,” said Dr. Susannah Maidment, a paleontologist at the Natural History Museum, London.

“China seems to have been a hotspot for stegosaur diversity, with numerous species now known from the Middle Jurassic right the way through until the end of the Early Cretaceous period.” The team’s paper was published in the Journal of Vertebrate Paleontology.

Bashanosaurus

Discovery and naming[]

Description[]

References[]

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