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Beipiaosaurus inexpectatus

Beipiaosaurus (bye-PEE-oh-SORE-us) was a species of small but primitive therizinosaur closely related to Nothronychus and Therizinosaurus. It lived during the Mid Cretaceous Period 125 million years ago in what is now China, and at one point was the largest known dinosaur with feathers.


In 1996, a humble peasant named Li Yinxian found the fossilzed bones of a dinosaur near the town of Sihetun in China. However, it wasn't until 1999 that the fossils were rediscoverd, examined, and named by paleontologists Xu

File:Beiapiosaurus Skeleton.jpg

Beipiaosaurus Skelton with Feather Indents

Xing, Tang Zhilu, and Wang Xiaolin, and later published in an article in the Nature Magazine. The specimen was named Beipiaosaurus inexpectus, or "unexpected Baipiao lizard". At first, base on the peg-like teeth, scientists thought it was a species of prosauropod, like Plateosaurus, but when more specimens of dinosaurs with long necks, big bodies, extending arms with clawed hands, and theropod-like feet were discovered, they realized Beipiaosaurus was part of a genus of dinosaurs now called therizinosaurs. What makes Beipiaosaurus special, though, is scintists now know that, based off its primitive appearance, therizinosaurs actually evolved from coelurosaurs like dromaeosaurids (Raptors) rather than sauropodomorphs or ornithiscians as thought of previously. It also, from very well-preserved specimens, clued us in that therizinosaurs more than likely had feathers overing their whole bodies.


Like other therizinosaurs, Beipiaosaurus had a long neck and small head for reaching into trees easier, giving itself an almost sauropod's


look. It also had very long arms and wicked claws on each of its fingers for stripping trees of their bark and leaves, and also likely were used for defense against predators. Its body was rather stout, likely ending in a sort of pot-belly, but was much leaner than that of other larger, more evolved therizinosaurs. Beipiaosaurus' jaws started out with a beak in the front and then had peg-like cheek teeth more towards the back, for stripping vegetation more efficiently. However, the teeth weren't very good for


grinding food, which raises the question whether it and other therizinosaurs swallowed gastroliths like sauropods and modern birds and crocodiles do. It grew to be about 7.5 feet (2.6 meters) long, 4 feet (1.3 meters) long, and 100 pounds (45 kilograms) in weight, making it quite small in terms of therizinosaur and dinosau

File:Running Beipiaosaurus.jpg

r standards. Nevertheless, its discovery was an important find in the fossil record for piecing together therizinosaur evolution. As far as we know, Beipiaosaurus had the longest feathers of any known dinosaur, and during the mating season were likely used to attract mates like modern birds do. Being a more primitive therizinosaur also sets it apart from other species related to it. An example is its more slender body and shorter neck. Its legs were also relatively longer than in relatives such as Therizinosaurus, suggesting it was a faster runner. Another feature that makes Baiepiaosaurus unique is its feet, while other, more evolved therizinosaurs had three toes, it had four that were all functional, and gives another hint that it likely evolved from maniraptoran dinosaurs.

In the Media[]

Beipiaosaurus made an appearance in the 13th movie of the Land Before Time series, although one couldn't really tell without some reference. They were also the only therizinosaurs to make a cameo in the series.