Dino of the Week: Chungkingosaurus

Type Species: Chungkingosaurus jiangbeiensis

Classification: Dinosauria – Ornithischia – Thyreophora – Stegosauria – Huayangosauridae 

Time Period: Late Jurassic

Location: China

Diet: Herbivore 

The stegosaur Chungkingosaurus was discovered in the Shaximiao Formation of China. This bone-bed dates back to the Oxfordian stage of the Late Jurassic, and this stegosaur is one of three stegosaurs found in the environment (the other two are Chialingosaurus and Tuojiangosaurus; some believe Chialingosaurus and Chungkingosaurus are the same animal). Contemporaries of Chungkingosaurus included sauropods such as Mamenchisaurus and Shunosaurus, theropods such as Yangchuanosaurus and Gasosaurus, and ornithischians such as the early ornithopod Agilisaurus and a heterodontosaur holdout from the earlier Jurassic known as Tianyulong. 

Two Chungkingosaurus specimens have been found; both were adults, with one thirteen feet long and the other sixteen and a half feet long. This could be a matter of sexual dimorphism, though stegosaurs have traditionally been interpreted as loners (though some stegosaurs may have traveled in small family groups). Chungkingosaurus resembled in many ways its larger contemporary Tuojiangosaurus, which lived in the same environment. Subtle differences between the two include the fact that Chungkingosaurus was smaller, had a deeper snout and front lower jaws (resulting in a high, narrow skull), and non-overlapping teeth with less pronounced denticles. Chungkingosaurus’ hips and humerus are more primitive than more derived stegosaurs. The deep skull may be a relict of a primitive trait or an adaptation for supporting stronger muscles for eating tougher vegetation. This stegosaur had two rows of plates and spikes on its back; they were arranged in pairs, but the total number is unknown (though most scientists believe it had fourteen rows of plates). Its plates were thickened in the middle, as if they were modified spikes, and they resemble those of Tuojiangosaurus. The thagomizer – the tail spikes used as a defensive weapon – are known only from one specimen. Its thagomizer consisted of two pairs of obliquely vertical stout spikes. It may have had a third pair towards the front of the back two pairs that was present when the specimen was discovered but lost during the excavation. A unique feature of its thagomizer was an additional pair of spikes at the very end of the tail; these were long, thin spikes oriented horizontally, giving the full thagomizer a ‘pin-cushion’ spike array.