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Zhongjianosaurus is a genus of dromaeosaurid belonging to the Microraptoria. Believed to hail from the Yixian Formation, specifically the middle of the Jehol Biota, it is the smallest known microraptorine thus far discovered and one of the smallest non-avian theropod dinosaurs.

Description

Zhongjianosaurus was first reported in 2009 when a new species based on a specimen consisting of a partial postcranial articulated skeleton was recovered from the lake deposits in Sihedang, Lingyuan County, in western Liaoning. It was first described by Xu Xing and Qin Zi-Chuan. The genus and specific name honor Yang Zhongjian, China's founder of vertebrate paleontology. The holotype specimen, labelled as IVPP V 22775, is currently housed in the Institute of Vertebrate Paleontology and Paleoanthropology, in Beijing.

The specimen's remains preserve the four most posterior cervical vertebrae (likely 7-10 in regards to placement). Seven dorsal vertebrae are known, while eight dorsal ribs are known from the left side of the specimen in comparison to the five preserved for the right side. Five left uncinate processes are preserved as well. The caudal series of vertebrae are represented by 26 articulated caudal vertebrae, probably missing only the first caudal vertebra, likely making a full count of 27 caudal vertebrae in the tail. The sternum is represented by what is probably the left sternal plate. Five left sternal ribs are preserved, more than are seen in the related genera Microraptor and Sinornithosaurus. The furcula is preserved as well, as are the scapulae and coracoids, which are fused. The forelimbs of Zhongjianosaurus are represented by both humeri, the left ulna, the left radius, and a partial left manus. The specimen's hindlimbs meanwhile, are represented by both femora, both tibiotarsi, and portions of both feet.

Studies by Xu and Qin place Zhongjianosaurus in the Dromaeosauridae, and specifically the Microraptoria, based on its synapomorphies.

Paleobiology

The discovery of Zhongjianosaurus in the Yixian Formation, in addition to eight other dromaeosaurids suggests that there was a sufficient amount of niche partitioning. The varying size of the different dromaeosaurids likely indicates that they focused on different types of prey and that many were specific about what type of prey they consumed. Niche partitioning may also have been aided by differentiation in habitat preferences. Zhongjianosaurus was, in view of its small size, possibly omnivorous and arboreal. However, a full understanding of niche differentiation of Jehol dromaeosaurids probably will require a full dataset of the tempo-spatial distribution of the many Jehol dromaeosaurid fossils and a better understanding of their ecology before such conclusions can be fully drawn.

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