Zhongjianosaurus

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.[1]

Zhongjianosaurus
Temporal range: Early Cretaceous, 125–120 Ma
Zhongjianosaurus yangi
An artist's reconstruction of Zhongjianosaurus yangi
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Saurischia
Suborder: Theropoda
Family: Dromaeosauridae
Clade: Microraptoria
Genus: Zhongjianosaurus
Xu & Qin, 2017
Type species
Zhongjianosaurus yangi
Xu & Qin, 2017

Description

Zhongjianosaurus
Life reconstruction of Zhongjianosaurus yangi based on the holotype skeleton

Zhongjianosaurus is distinguishable from other microraptorines in the following autapomorphies. Proportionally long ossified uncinate processes are fused to the dorsal ribs. A widely arched furcula 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.[1] The authors identify the fingers in the maniraptoran hand as the second, third and fourth,[1] 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 0.31 kg (0.68 lb), making it one of the smallest known non-avian theropods thus far discovered.[1]

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. 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.[1]

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.[1]

Classification

Studies by Xu and Qin place Zhongjianosaurus in the Dromaeosauridae, and specifically the Microraptoria, based on its synapomorphies.[1]

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.[1]

See also

References

  1. ^ a b c d e f g h Xu, Xing; Qin, Zi-Chuan (2017). "A new tiny dromaeosaurid dinosaur from the Lower Cretaceous Jehol Group of western Liaoning and niche differentiation among the Jehol dromaeosaurids" (PDF). Vertebrata PalAsiatica. In press.
Dromaeosaurinae

Dromaeosaurinae is a subfamily of Dromaeosauridae. Most dromaeosaurines lived in what is now the United States and Canada, as well as Mongolia, and possibly Denmark as well. Isolated teeth that may belong to African dromaeosaurines have also been discovered in Ethiopia. These teeth date to the Tithonian stage, of the Late Jurassic Period.All North American and Asian dromaeosaurine dinosaurs from the Late Cretaceous were generally small, no more than 1.8 metres (5.9 ft) long, in Dromaeosaurus and Adasaurus. However, among the dromaeosaurines were the largest dromaeosaurs ever; Dakotaraptor was ~5.5 metres (18 ft) long, Achillobator 6 metres (20 ft), and Utahraptor up to ~7 metres (23 ft).

Eudromaeosauria

Eudromaeosauria ("true dromaeosaurs") is a subgroup of terrestrial dromaeosaurid theropod dinosaurs. They were relatively large-bodied, feathered hypercarnivores (with diets consisting almost entirely of other terrestrial vertebrates) that flourished in the Cretaceous Period.

Eudromaeosaur fossils are known almost exclusively from the northern hemisphere. They first appeared in the early Cretaceous Period (early Aptian stage, about 124 million years ago) and survived until the end of the Cretaceous (Maastrichtian stage, 66 Ma). The earliest known definitive eudromaeosaur is the dromaeosaurine Utahraptor ostrommaysorum, from the Cedar Mountain Formation, dated to 124 million years ago. However, the earlier (143-million-year-old) fossils such as those of Nuthetes destructor and several indeterminate teeth dating to the Kimmeridgian stage may represent eudromaeosaurs.

Graciliraptor

Graciliraptor (meaning "graceful thief") is a genus of theropod dinosaur from the early Cretaceous Period. It is a microraptorine dromaeosaurid.

The type species Graciliraptor lujiatunensis was first named and described in 2004 by Xu Xing and Wang Xiaoling. The generic name is derived from Latin gracilis and raptor. The specific name refers to the village Lujiatun where the fossil site is located. Its fossil, holotype IVPP V 13474, was found in Beipiao, Liaoning Province, China.

Halszkaraptorinae

Halszkaraptorinae is a basal ("primitive") subfamily of Dromaeosauridae that includes the enigmatic genera Halszkaraptor, Mahakala, and Hulsanpes. A comparison of the fossils of Halszkaraptor with the bones of extant crocodilians and aquatic birds revealed evidence of a semiaquatic lifestyle. The group is named after Polish paleontologist Halszka Osmólska.

Hulsanpes

Hulsanpes is a genus of dromaeosaurid theropod dinosaur from Mongolia that lived during the Late Cretaceous.

Itemirus

Itemirus is a genus of theropod dinosaur from the Turonian age of the Late Cretaceous period of Uzbekistan.

Linheraptor

Linheraptor is a genus of dromaeosaurid dinosaur which lived in what is now China in the Late Cretaceous. It was named by Xu Xing and colleagues in 2010, and contains the species Linheraptor exquisitus. This bird-like dinosaur was less than 2 m (6.5 ft) long and was found in Inner Mongolia. It is known from a single, nearly complete skeleton.

Luanchuanraptor

Luanchuanraptor (meaning "Luanchuan thief") is a genus of dromaeosaurid theropod dinosaur from the Late Cretaceous of China. It is based on a partial skeleton from the Qiupa Formation in Luanchuan, Henan. A medium-sized dromaeosaurid, it is the first Asian dromaeosaurid described from outside the Gobi Desert or northeastern China. The fossil material is cataloged as 4HIII-0100 in the Henan Geological Museum and includes four teeth, one frontal, a neck vertebra, one or two back vertebrae, seventeen tail vertebrae, ribs, chevrons, a humerus (upper arm bone), claw and finger bones, partial shoulder and pelvic girdles, and other fragmentary bones from a moderately sized dromaeosaurid. The type species is L. henanensis, described by Lü et al. in 2007.

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 feathers on their legs and may have been semi-arboreal powered fliers, some of which even capable of launching from the ground. Most microraptorians were relatively small; adult specimens of Microraptor range between 77–90 centimetres long (2.53–2.95 ft) and weigh up to 1 kilogram (2.2 lb), making them some of the smallest known dinosaurs.

Neuquenraptor

Neuquenraptor is a genus of dromaeosaurid theropod dinosaurs of the Late Cretaceous of Argentina, one of the first dromaeosaurids found in the Southern Hemisphere.

Ornithodesmus

Ornithodesmus (meaning "bird link") is a genus of small, dromaeosaurid dinosaur from the Isle of Wight in England, dating to about 125 million years ago. The name was originally assigned to a bird-like sacrum (a series of vertebrae fused to the hip bones), initially believed to come from a bird and subsequently identified as a pterosaur. More complete pterosaur remains were later assigned to Ornithodesmus, until recently a detailed analysis determined that the original specimen in fact came from a small theropod, specifically a dromaeosaur. All pterosaurian material previously assigned to this genus has been renamed Istiodactylus.

Pamparaptor

Pamparaptor is an extinct genus of carnivorous deinonychosaur from the late Cretaceous period. It is a basal dromaeosaurid dinosaur with troodontid-like pes which lived during the late Cretaceous period (Turonian to Coniacian stage) in what is now Neuquén province, Patagonia, Argentina. It is known from the holotype MUCPv-1163, an articulated and nearly complete left foot.

The specimen recovered from the Portezuelo Formation (Río Neuquén Subgroup) of Neuquén Group. It was initially considered to be a juvenile specimen of another dromaeosaurid species, Neuquenraptor argentinus. However, it was later re-interpreted as a new genus and named Pamparaptor by Juan D. Porfiri, Jorge O. Calvo and Domenica dos Santos in 2011 and the type species is Pamparaptor micros. The generic name honors Indian Pampas people who lived in central Argentina while "raptor" (robber in Latin). The specific name (micros, meaning "small") refers to the specimen's size (estimated at 0.5 to 0.7 metres (1.6 to 2.3 ft) in length).

Pyroraptor

Pyroraptor (meaning "fire thief") is a genus of dromaeosaurid dinosaur from the Late Cretaceous of what is now southern France, it lived during the late Campanian and early Maastrichtian stages, approximately 70.6 million years ago. It is known from a single partial specimen that was found in Provence in 1992. The animal was named Pyroraptor olympius by Allain and Taquet in 2000.

Saurornitholestinae

Saurornitholestinae is a subfamily of dromaeosaurid dinosaurs. The saurornitholestines currently include three monotypic genera: Atrociraptor marshalli, Bambiraptor feinbergorum, and Saurornitholestes langstoni. All are medium-sized dromaeosaurs from the Late Cretaceous of western North America. The group was originally recognized by Longrich and Currie as the sister taxon to a clade formed by the Dromaeosaurinae and Velociraptorinae. However, not all phylogenetic analyses recover this group.

Shanag

Shanag is a genus of dromaeosaurid theropod dinosaur from the Early Cretaceous Period of Mongolia.

The type species of Shanag is S. ashile. It was named and described by Alan Turner, Sunny Hai-Ching Hwang and Mark Norell in 2007. The generic name refers to the black-hatted dancers in the Buddhist Cham dance. The specific name refers to the Ashile Formation, the old name for the layers where Shanag was found, used by Henry Fairfield Osborn.The holotype of Shanag, IGM 100/1119, was discovered in the Öösh Formation, the stratification of which is uncertain but probably dating to the Berriasian-Barremian. Shanag bears a strong resemblance to basal Chinese dromaeosaurids such as Microraptor and Sinornithosaurus, suggesting a close similarity between the fauna of the Öösh deposits, dated tentatively to 130 million years ago, and the Jehol Biota of China (such as the animals found in the roughly contemporary Yixian Formation), during the Early Cretaceous. The holotype specimen, about six centimetres long, is composed of an associated uncompressed upper and lower jaw fragment, containing a nearly complete right maxilla with teeth, a partial right dentary with teeth and an attached partial splenial.Shanag was a small predator. In 2010 Gregory S. Paul estimated its length at 1.5 metres, the weight at five kilogrammes. Shanag shows a mixture of dromaeosaurid, troodontid and basal avialan traits.Turner et alii assigned Shanag to the Dromaeosauridae. Their cladistic analysis indicated that it was a basal dromaeosaurid but higher in the tree than the Unenlagiinae. Later analyses recovered it in the Microraptorinae.

Unenlagiinae

Unenlagiinae is a subfamily of dromaeosaurid theropods. Unenlagiines are known from South America and Antarctica.

Unquillosaurus

Unquillosaurus (meaning "Unquillo river lizard") is a genus of maniraptoran dinosaur from the Late Cretaceous Period, discovered in Argentina. Known only from a single fossilized pubis (a pelvic bone), its total body length may have reached 2 to 3 metres (6.6 to 9.8 ft).

Variraptor

Variraptor ( VARR-i-rap-tor; "Var thief") is a genus of coelurosaurian theropod dinosaur from the Late Cretaceous of France.

Yurgovuchia

Yurgovuchia is an extinct genus of dromaeosaurid theropod dinosaur known from the Early Cretaceous (probably Barremian stage) of Utah. It contains a single species, Yurgovuchia doellingi. According to a phylogenetic analysis performed by its describers, it represents an advanced dromaeosaurine, closely related to Achillobator, Dromaeosaurus and Utahraptor.

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