''Jianchangosaurus'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

therizinosaur Therizinosaurs (once called segnosaurs) were large herbivorous Theropoda, theropod dinosaurs whose fossils have been found across the Early Cretaceous, Early to Late Cretaceous deposits in Asia and North America. Various features of the forelimbs ...

ian

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

that lived approximately 126

million years ago The abbreviation Myr, "million years", is a unit of a quantity of (i.e. ) years, or 31.556926 teraseconds. Usage Myr (million years) is in common use in fields such as Earth science and cosmology. Myr is also used with Mya (million years ago). ...

during the early part of the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

Period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (or rhetorical period), a concept ...

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 ...

in what is now

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 ...

. The nearly complete juvenile specimen was missing only the distal tail. ''Jianchangosaurus'' was a small, lightly built,

bipedal Bipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning 'two feet' (from Latin ''bis'' 'double' ...

, ground-dwelling

herbivore A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...

, that could grow up to an estimated long and was high at the hips.

Discovery and naming

The holotype specimen, 41HIII-0308A, was discovered on the

Jianchang County Jianchang () is a county of Huludao City in the southwest of Liaoning province, China. It is the largest division of Huludao, with an area of , and population of 600,000, located in mountainous terrain west of that city, serviced by China Nationa ...

, in the western part of

Liaoning Province Liaoning () is a coastal provinces of China, 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 i ...

and purchased by the

Henan Geological Museum The Henan Museum (), located in Zhengzhou, Henan Province, China, is a history and archaeology museum. It has a collection of more than 130,000 pieces of cultural relics through the ages. In addition to its collection of human history the museum ...

noting that some of the elements were repositioned during its preparation. The genus name ''Jianchangosaurus'', means "Jianchang lizard", and is derived from "Jianchang", the name of the county of Liaoning Province,

, where the specimen was found, and the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

word "" () meaning "lizard". The

specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...

''yixianensis'', refers to the Yixian Formation where the specimen was found, and the Latin suffix "-ensis" meaning "originating in". ''Jianchangosaurus'' was described and named by Hanyong Pu, Yoshitsugu Kobayashi, Junchang Lu, Li Xu, Yanhua Wu, Huali Chang, Jiming Zhang, and Songhai Jia in

2013 File:2013 Events Collage V2.png, From left, clockwise: Edward Snowden becomes internationally famous for leaking classified NSA wiretapping information; Typhoon Haiyan kills over 6,000 in the Philippines and Southeast Asia; The Dhaka garment fact ...

and the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

is ''Jianchangosaurus yixianensis''.

Description

The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

specimen of ''Jianchangosaurus'' 41HIII-0308A is a nearly complete skeleton of a single juvenile individual, missing only the distal portion of the tail. ''Jianchangosaurus'' was estimated to have been tall at the hips and approximately long.

Gregory S. Paul Gregory Scott Paul (born December 24, 1954) is an American freelance researcher, author and illustrator who works in paleontology, and more recently has examined sociology and theology. He is best known for his work and research on theropod dino ...

estimated the weight of the holotype specimen around . Jianchangosaurus Restoration

Five sacral vertebrae are present in this genus, a condition that is similar to that of other basal therizinosaurs. The humerus measures in length and is 7% shorter than the scapula. The ulna measures in length and is 78% of the humerus length - which approximates the ratio observed in the basal therizinosaur ''

Falcarius ''Falcarius'' (meaning "sickle cutter") is a genus of primitive therizinosaur dinosaur that lived during the Early Cretaceous period in what is now North America. Its remains were first collected in the Cedar Mountain Formation in 1999, with subs ...

'' (77%). The pubis is 20% longer than the ischium, and it projects anteroventrally and does not exhibit the opisthopubic condition. The tibia () is 1.5 times longer than the femur (), which is the highest ratio known in therizinosaurs, an adaptation which has been strongly correlated with the development of cursorial habits in dinosaurs.

Distinguishing anatomical features

According to Pu et al. 2013, ''Jianchangosaurus'' can be distinguished based on the presence of 27 tightly packed

maxilla The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The t ...

ry teeth; the dorsal border of the

antorbital fenestra An antorbital fenestra (plural: fenestrae) is an opening in the skull that is in front of the eye sockets. This skull character is largely associated with archosauriforms, first appearing during the Triassic Period. Among extant archosaurs, birds ...

is formed by the

nasal Nasal is an adjective referring to the nose, part of human or animal anatomy. It may also be shorthand for the following uses in combination: * With reference to the human nose: ** Nasal administration, a method of pharmaceutical drug delivery ** ...

, and lacrimal, but with the majority of the border formed by the nasal; there is no participation of

jugal The jugal is a skull bone found in most reptiles, amphibians and birds. In mammals, the jugal is often called the malar or zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species. Anatomy ...

in the margin of the antorbital fenestra; a short

diastema A diastema (plural diastemata, from Greek διάστημα, space) is a space or gap between two teeth. Many species of mammals have diastemata as a normal feature, most commonly between the incisors and molars. More colloquially, the condition ...

is present in the anterior tip of the

dentary In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...

; dentary teeth have a concave labial surface and a convex lingual surface (this condition is present for all except six anterior teeth); the lack of prominent hypapophyses in the anterior

dorsal vertebrae In vertebrates, thoracic vertebrae compose the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae. In humans, there are twelve thoracic vertebrae and they are intermediate in size between the cervical ...

; the anterior caudal centra have an oval cross section and the articular facet is as tall as it is wide; the presence of weakly curved manual

ungual An ungual (from Latin ''unguis'', i.e. ''nail'') is a highly modified distal toe bone which ends in a hoof, claw, or nail. Elephants and ungulates have ungual phalanges, as did the sauropods and horned dinosaurs. A claw is a highly modified ungual ...

s with weak flexor tubercles positioned ventral to the articular facet; the ilium is shallow and elongated; the ridge bounding the cuppedicus fossa is confluent with acetabular rim; and there is extensive contact between the pubic apron.

Skull and dentition

The skull is in good preservation and is nearly complete, missing only the ventral lacrimal, the posterior

, the

postorbital The ''postorbital'' is one of the bones in vertebrate skulls which forms a portion of the dermal skull roof and, sometimes, a ring about the orbit. Generally, it is located behind the postfrontal and posteriorly to the orbital fenestra. In some ve ...

, the anterior edge of the quadrate, and the anterior

surangular The suprangular or surangular is a jaw bone found in most land vertebrates, except mammals. Usually in the back of the jaw, on the upper edge, it is connected to all other jaw bones: dentary, angular, splenial and articular The articular bone i ...

bones. ''Jianchangosaurus'' possesses 27 maxillary teeth and approximately 25 to 28 dentary teeth. The researchers observed, however, that at front of the upper jaw the

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has b ...

edentulous Toothlessness, or edentulism, is the condition of having no teeth. In organisms that naturally have teeth, it is the result of tooth loss. Organisms that never possessed teeth can also be described as edentulous. Examples are the members of the ...

and they hypothesized that it was covered by a

rhamphotheca The beak, bill, or rostrum is an external anatomical structure found mostly in birds, but also in turtles, non-avian dinosaurs and a few mammals. A beak is used for eating, preening, manipulating objects, killing prey, fighting, probing for food, ...

. This is also supported by the presence of a series of

foramina In anatomy and osteology, a foramen (;Entry "foramen"
in

along the buccal margin on the lateral surface of the premaxilla. By comparison, in most modern birds, the rhamphotheca grows, and is shed, continuously and in some species its color varies depending on the season. The front portion of the lower jaw is down-turned and in combination with the rhamphotheca on the upper jaw, functioned to pluck food. The skull measures in length, and is 10% longer than the femur, a condition not shared by ''

Beipiaosaurus ''Beipiaosaurus'' is a genus of therizinosauroid theropod dinosaurs that lived in Asia during the Early Cretaceous in the Yixian Formation. The first remains were found in 1996 and formally described in 1999. Before the discovery of ''Yutyrannus ...

''. Derived features present in the skull of this genus strongly suggest adaptations for herbivory. ''Jianchangosaurus'' possesses 27 maxillary teeth and approximately 25 to 28 dentary teeth. The crowns on its teeth diminish in size as they progress toward the posterior of the skull. The teeth on the upper jaw, exhibit the conventional dental morphology - in which the surface of the tooth facing the outside of the mouth is convex. The teeth on the lower jaw possess the reversed morphology, where the surface of the tooth facing the outside is concave. Pu et al. 2013 noted that this dental morphology "likely maximized the biting stress during occlusion to cut fibers of plant material, similar to ornithopods and ceratopsians".

Feather impressions

The impressions of a series of wide and unbranched feathers were discovered with the fossils. Only the distal ends of the feather impressions are visible. Based on their morphology the feathers are considered primitive and bear resemblance to those found along the neck of ''Beipiaosaurus'', which were collected in the same

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondar ...

. The authors noted that the "presence of elongated broad filamentous feathers (EBFF) suggests that they might have been used for visual display".

Ontogenetic stage

The only known ''Jianchangosaurus'' skeleton is that of a juvenile individual. The morphological evidence supporting ontogenetic immaturity consists of the observation that the neurocentral sutures are open (i.e. not fused) in all of the cervical and dorsal vertebrae, as well as in the cervical ribs and in the sacral centra. The scapula and coracoid are also unfused, which the authors indicate may be an ontogenetic feature in ''Jianchangosaurus'' also suggesting that is a juvenile. This condition, however, is also observed in adult basal therizinosaurs.

Classification

Like the primitive ''Falcarius'' and ''Beipiaosaurus'', ''Jianchangosaurus'' was classified as a basal

Phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

analysis suggests that it is more derived than ''Falcarius'' but more primitive than ''Beipiaosaurus''. ''Jianchangosaurus'' is the only known therizinosaur that possesses a tail with caudal centra that are oval in shape. Left

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to d ...

is based on the phylogenetic analysis conducted by Pu et al. 2013, showing the relationships of ''Jianchangosaurus'' as a very primitive therizinosaur. Right cladogram is based on Hartman et al. 2019 which has corroborated the position of ''Jianchangosaurus'':

Notes

References

{{Taxonbar, from=Q13407971 Therizinosaurs Fossil taxa described in 2013 Early Cretaceous dinosaurs of Asia Feathered dinosaurs Yixian fauna Taxa named by Lü Junchang