Stegosaurus body characteristics and living habits

Similar to the situation with sauropods, stegosaurs likely appeared in the early Jurassic. However, scientists' understanding of early stegosaurs actually began with Huayangosaurus unearthed from Dashanpu, Zigong, Sichuan, my country.

Huayang Dragon

1. Huayanglong—the earliest stegosaurus from China

Huayanglong is nearly 4 meters long and weighs 1 to 4 tons. Compared with Shulong, Chieflong and Emeilong that lived in the same era and in the same area, Huayanglong was too short and too small. Therefore, while those big guys raised their necks to chew leaves on tall trees, Huayanglong could only eat low plants near the ground.

The shorter body of Huayangosaurus also seems to make it easier for them to become prey targets of carnivorous dinosaurs such as Aerosaurus. However, as the earliest stegosaurus, Huayangosaurus has developed a unique set of defensive weapons, which are the long spines on its shoulders, waist and the tip of its tail. When a hungry air dragon attacks the Huayang dragon, the Huayang dragon will turn its body to a suitable position so that its long spines point toward the attacker; at the same time, it will violently whip the enemy with its long spines. Although these weapons and such defense methods are not powerful enough to kill large predators, they are usually enough to have a deterrent effect, causing those predators to stop chasing Huayangosaurus in order to avoid injury and instead look for more powerful predators. Easy prey.

During the Middle Jurassic, riversides were usually covered with dense green carpets of dwarf ferns, and there were generally no tall trees in such places. When Huayangosaurus used their small teeth suitable for gnawing and grinding to eat on such open "grasslands", their young often became the targets of predators such as air dragons. However, as long as the little Huayang dragons stay close to their parents, the predators still dare not attack easily. Obviously, the parent-child behavior of parents protecting their young is essential for Huayang dragons.

On the back of Huayang Dragon, there are two symmetrical rows of heart-shaped sword plates arranged from the neck to the middle of the tail. Many later stegosaurs had two rows of sword plates on each side of the back. In addition, the front and rear legs of Huayangosaurus were almost the same length, while the front legs of later stegosaurs were significantly shorter than the hind legs. These characteristics indicate that Huayangosaurus is indeed a primitive stegosaurus.

2. Geosaurus—the possible ancestor of Stegosaurus represented only by a broken lower jaw

We introduce Huayangosaurus as the earliest Stegosaurus because its fossil materials are relatively complete and can be accurately identified as Stegosaurus. In fact, in the early Jurassic, there were already some fossil materials indicating the existence of stegosaurs, but these fossils were too fragmented or too scattered, so scientists made a lot of assumptions in their understanding of them.

Earth Dragon

This is the case for the Geosaurus discovered in the early Jurassic strata of Dadi Village, Lufeng County, my country.

Scientists only found an incomplete left mandible. In front of the mandible is a predentary bone unique to ornithischian dinosaurs, but there are no teeth on it. There are also fewer teeth in other parts, and they overlap a bit, gradually increasing from front to back. These teeth grow into alveoli, hence the name alveolar teeth. It is precisely because the characteristics of its teeth and predentary bones are similar to those of later stegosaurs that scientists speculate that it is the most primitive stegosaur known so far.

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