Zhongjianosaurus
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''Zhongjianosaurus'' is a genus of
dromaeosaurid Dromaeosauridae () is a family of feathered theropod dinosaurs. They were generally small to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek ('), meaning ...
belonging to the
Microraptoria Microraptoria (Greek, μίκρος, ''mīkros'': "small"; Latin, ''raptor'': "one who seizes") is a clade of basal dromaeosaurid theropod dinosaurs. The first microraptorians appeared 125 million years ago in China. Many are known for long feather ...
. Believed to hail from the
Yixian Formation The Yixian Formation (; formerly transcribed as Yihsien Formation) is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans the late Barremian and early Aptian stages of the Early Cretaceous. It is known for its ex ...
, specifically the middle of the Jehol Biota, it is the smallest known microraptorine thus far discovered and one of the smallest non-avian
theropod Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...
dinosaurs.


Description

''Zhongjianosaurus'' is distinguishable from other microraptorines in the following
autapomorphies In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to t ...
. Proportionally long ossified uncinate processes are fused to the dorsal ribs. A widely arched
furcula The (Latin for "little fork") or wishbone is a forked bone found in most birds and some species of non-avian dinosaurs, and is formed by the fusion of the two pink clavicles. In birds, its primary function is in the strengthening of the thoracic ...
is present with slender and posteriorly curved clavicular rami. The humeral proximal end is strongly offset medially from the humeral shaft. The internal tuberosity of the humeral proximal end is short. A large fenestra perforates the humeral deltopectoral crest. The humeral ulnar condyle is hypertrophied. The ulna is slightly longer than the humerus. The ulnar olecranon process has a mediolaterally pinched posterior margin. The ulnar distal end bends anteriorly and is strongly expanded laterally. The proximal end of metacarpal II has a strong ventrolateral extension. Metacarpal III is laterally bowed and adorned with a longitudinal ventral groove. Phalanx II-2 is without a proximodorsal lip and lacks strong dorsal arching. The femoral head is stout and lower than the trochanteric crest. The medial condyle of tibiotarsus distal end has a prominent distal extension. The foot shows the arctometatarsalian condition. Metatarsal II is without ginglymi on its distal end. The authors identify the fingers in the
maniraptoran Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the non-avian dinosaurs that were more closely related to them than to ''Ornithomimus velox''. It contains the major subgroups Avialae, Deinonychosauria, Oviraptorosa ...
hand as the second, third and fourth, whereas most researchers see them as the first, second and third so that "metacarpal II" would become metacarpal I etc. The articulated tail has elongate rod-like extensions of the prezygaphophyses and chevrons characteristic of most dromaeosaurids, and these reach almost to the most anterior caudals. The sternum is large, with a maximum anteroposterior length 56% of the femoral length and is long axially in proportion. Bone fusion in the scapula, vertebrae, coracoid, and tarsals suggest that the specimen is a mature adult weighing , making it one of the smallest known non-avian theropods thus far discovered.


Discovery and naming

''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 Liaoning () is a coastal province in Northeast China that is the smallest, southernmost, and most populous province in the region. With its capital at Shenyang, it is located on the northern shore of the Yellow Sea, and is the northernmost ...
,
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
. It was first described by Xu Xing and Qin Zi-Chuan. The genus and specific name honor
Yang Zhongjian Yang Zhongjian, also Yang Chung-chien (; 1 June 1897 – 15 January 1979), courtesy name Keqiang (), also known as C.C. (Chung Chien) Young, was a Chinese paleontologist and zoologist. He was one of China's foremost vertebrate paleontologists. H ...
, 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 The Institute of Vertebrate Paleontology and Paleoanthropology (IVPP; ) of China is a research institution and collections repository for fossils, including many dinosaur and pterosaur specimens (many from the Yixian Formation). As its name suggest ...
, in
Beijing } Beijing ( ; ; ), alternatively romanized as Peking ( ), is the capital of the People's Republic of China. It is the center of power and development of the country. Beijing is the world's most populous national capital city, with over 21 ...
. 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 ''Microraptor'' (Greek, μικρός, ''mīkros'': "small"; Latin, ''raptor'': "one who seizes") is a genus of small, four-winged dromaeosaurid dinosaurs. Numerous well-preserved fossil specimens have been recovered from Liaoning, China. They ...
'' and ''
Sinornithosaurus ''Sinornithosaurus'' (derived from a combination of Latin and Greek, meaning 'Chinese bird-lizard') is a genus of feathered dromaeosaurid dinosaur from the early Cretaceous Period (late Barremian) of the Yixian Formation in what is now China. It ...
''. 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.


Classification

Studies by Xu and Qin place ''Zhongjianosaurus'' in the Dromaeosauridae, and specifically the Microraptoria, based on its synapomorphies. Some studies offer an alternate position as an avialan.


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 In ecology, niche differentiation (also known as niche segregation, niche separation and niche partitioning) refers to the process by which competing species use the environment differently in a way that helps them to coexist. The competitive excl ...
. 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 An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nutri ...
and
arboreal Arboreal locomotion is the Animal locomotion, locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally, but others are exclusively arboreal. Th ...
. 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.


See also

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Timeline of dromaeosaurid research This timeline of dromaeosaurid research is a chronological listing of events in the history of paleontology focused on the dromaeosaurids, a group of sickle-clawed, bird-like theropod dinosaurs including animals like ''Velociraptor''. Since the ...
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2017 in archosaur paleontology The year 2017 in archosaur paleontology was eventful. Archosaurs include the only living dinosaur group — birds — and the reptile crocodilians, plus all extinct dinosaurs, extinct crocodilian relatives, and pterosaurs. Archosaur palaeontology ...


References

{{Taxonbar, from=Q29366656 Early Cretaceous dinosaurs of Asia Microraptorians Feathered dinosaurs Fossil taxa described in 2017