Introducing Zhongjianosaurus.

 

Photograph of Zhongjianosaurus yangi holotype (From Xu & Qin, 2017).

Dromaeosaurids are a group of carnivorous theropods, popularly known as “raptors”. Most of them were small animals, ranging from about 0.7 metres in length to over 7 metres. They had a relatively large skull with a narrow snout and the forward-facing eyes typical of a predator. They also had serrated teeth, and their arms were long with large hands, a semi-lunate carpal, with three long fingers that ended in big claws. The earliest known representatives are from the Lower Cretaceous Jehol Group of western Liaoning, China. The most recent described dromaeosaurid is Zhongjianosaurus yangi. The new taxon was named in honor of  Yang Zhongjian, who is the founder of vertebrate paleontology in China.

The Early Cretaceous Jehol dromaeosaurids not only display a great size disparity, but also show a continuous size spectrum. Zhongjianosaurus represents the ninth dromaeosaurid species reported from the Jehol Biota. It was first reported in 2009, and is notable for its small size (about 25 cm tall), compact body, and extremely long legs.

Zhongjianosaurus yangi holotype. A. right scapulocoracoid in lateral view and furcula in posterior view; B. right humerus in anterior view; C. left ulna and radius in lateral view; D. ‘semilunate’ carpal, metacarpals II and III in ventral view and phalanges II-1 and -2 in lateral view; scale bars equal 5 mm (From Xu & Qin, 2017)

The holotype is an adult individual distinguishable from other microraptorines in possessing many unique features, most of them are present in the forelimbs. For example, the humerus has a strongly offset humeral head, a large fenestra near the proximal end, and a large ball-like ulnar condyle. Zhongjianosaurus also displays several other features which are absent in other Jehol dromaeosaurids. For instance, the uncinate processes are proportionally long and fused to the dorsal ribs, the caudal vertebral transitional point is located anteriorly, and the pes exhibits a full arctometatarsalian condition.

The coexistence of several closely related Jehol dromaeosaurids can be interpreted as niche differentiation. Tianyuraptor have limb proportions and dental morphologies typical of non-avialan carnivorous theropods, suggesting that they were ground-living cursorial predators, meanwhile Microraptor are more likely to have been arboreal or even gliding animals.

References:

Xu X , Qin Z C, 2017, in press. A new tiny dromaeosaurid dinosaur from the Lower Cretaceous Jehol Group of western Liaoning and niche differentiation among the Jehol dromaeosaurids. Vertebrata PalAsiatica

Xu X, 2002. Deinonychosaurian fossils from the Jehol Group of western Liaoning and the coelurosaurian evolution. Ph.D thesis, Beijing: Chinese Academy of Sciences. 1–322

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