Beipiaosaurus is a genus of therizinosauroid theropod dinosaur from the Early Cretaceous of China. Before the discovery of Yutyrannus, it was among the largest dinosaurs known from direct evidence to be feathered.
The exact classification of therizinosaurs had in the past been hotly debated, since their prosauropod-like teeth and body structure indicate that they were generally herbivorous, unlike typical theropods. Beipiaosaurus, being considered to be a primitive therizinosauroid, has features which suggest that all therizinosauroids, including the more derived Therizinosauridae, to be coelurosaurian theropods, not sauropodomorph or ornithischian relatives as once believed.
Discovery[]
In 1996, the peasant Li Yinxian discovered a skeleton of a theropod dinosaur near the village of Sihetun. In the May 27, 1999, issue of the journal Nature the discovery was announced and the type species Beipiaosaurus inexpectus named and described by Xu Xing, Tang Zhilu and Wang Xiaolin. The generic name Beipiaosaurus translates as "Beipiao lizard" after Beipiao, a city in China near the location of its discovery. Beipiaosaurus is known from a single species, B. inexpectus, the specific name, meaning "unexpected" in Latin, referring to "the surprising features in this animal".
The holotype (type specimen) of Beipiaosaurus inexpectus, holotype IVPP V11559, was recovered in the Jianshangou Beds of the Yixian Formation in Liaoning Province, China. The specimen was collected in sediment deposited during the Aptian stage of the Cretaceous period, approximately 125 to 124 million years ago. This specimen is housed in the collection of the Institute of Vertebrate Paleontology and Paleoanthropology, in Beijing, China. It consists of a partial, sub-adult, skeleton that is largely disarticulated. A significant number of fossilized bones were recovered, including: cranial fragments, a mandible, teeth, three cervical vertebrae, four dorsal vertebrae, four dorsal ribs, two sacral vertebrae, twenty-five caudal vertebrae, a pygostyle, three chevrons, an incomplete furcula and scapula, two coracoids, a complete forelimb, a partial forelimb, both ilia, an incomplete pubis, an incomplete ischium, a femur, both tibiae (one incomplete), an incomplete fibula, an astragalus, a calcaneum, several tarsals, metatarsals, and unguals, and remains of the integument, including feathers.
A second specimen, STM 31-1, a partial skeleton, was described by Xu et al. in 2009, which preserved a significant covering of unique, elongated feathers. This specimen consisted of a complete skull, a sclerotic ring, the mandible, the atlas and axis bones, nine additional cervical vertebrae, dorsal vertebrae, seventeen cervical ribs, twelve dorsal ribs, both scapulae and coracoids, one complete humerus and proximal humerus, one complete radius and distal radius, one complete ulna and distal ulna, carpals, and some metacarpals. The rear of the skull of this specimen was badly crushed.
Appearance[]
Like other therizinosaurs, Beipiaosaurus had a long neck and small head for reaching into trees easier, giving itself an almost sauropod 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 dinosaur 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 Media[]
Beipiosaurus appear in the thirteenth film in the Land Before Time series, The Land Before Time XIII: The Wisdom of Friends, wherein they are referred to as "Yellow Bellies", in reference to the color of their large bellies. They have much smaller claws than those of the real animals, lack proper tails, and are generally far more similar to the recently extinct dodo than actual Beipiaosaurus.