138-631: Marginocephalia ( / ˌ m ɑːr dʒ ə n oʊ s ə ˈ f æ l i ə / Latin: margin-head) is a clade of ornithischian dinosaurs that is characterized by a bony shelf or margin at the back of the skull. These fringes were likely used for display. This clade was officially defined in the PhyloCode by Daniel Madzia and colleagues in 2021 as "the smallest clade containing Ceratops montanus , Pachycephalosaurus wyomingensis , and Triceratops horridus ". There are two clades included in Marginocephalia:
276-469: A follicle , but instead arise from discrete cell populations that exhibit continuous growth. A 2016 study by Ji Qiang and colleagues was published in the Journal of Geology. Their conclusion was that these were actually highly modified scales because the morphology and anatomy did not resemble feathers. A darkened soft-tissue structure was also found near the jugal horn; this may represent a keratinous sheath or
414-459: A nomen dubium . Xu Xing , another Chinese paleontologist, named a new species of Psittacosaurus in 1997, based on a complete skull with associated vertebrae and a forelimb. This material was recovered in Gansu Province , near the border with Inner Mongolia. This species is named P. mazongshanensis after the nearby mountain called Mazongshan (Horse Mane Mountain) and has been described in
552-567: A Chinese specimen, SMF R 4970, which most likely comes from the Yixian Formation of Liaoning Province , China. The specimen, which is not yet assigned to any particular species, was likely illegally exported from China and was purchased in 2001 by the Senckenberg Museum in Germany . It was described while awaiting repatriation; previous repatriation attempts were unsuccessful. Most of
690-493: A bulbous vertical ridge down the centre of each tooth. Both upper and lower jaws sport a pronounced beak, formed from the rostral and predentary bones, respectively. The bony core of the beak may have been sheathed in keratin to provide a sharp cutting surface for cropping plant material. As the generic name suggests, the short skull and beak superficially resemble those of modern parrots. Psittacosaurus skulls share several adaptations with more derived ceratopsians, such as
828-521: A crushed skull and fragmentary lower jaw, Young named Psittacosaurus osborni , distinguished by its small size and lack of a sagittal crest on the parietal. The second species, P. tingi , was named for partial lower jaws and teeth, which Young only tentatively referred to Psittacosaurus instead of Protiguanodon . Both specimens, stored in the Institute of Vertebrate Paleontology and Paleoanthropology as IVPP RV31039 and IVPP RV31040 respectively, come from
966-593: A dinosaur, which was given the nickname of "Red Mesa skeleton". The location of discovery is also known as the Oshih locality of the Khukhtek Formation , of Early Cretaceous Aptian to Albian age. The specimen, catalogued as AMNH 6254, was described in 1924 by Osborn, only partially prepared, who gave it the name Psittacosaurus mongoliensis , describing its parrot-like beak on the suggestion of fellow American paleontologist William King Gregory . Osborn demonstrated
1104-633: A distinct group from stegosaurs in the 1920s despite many members being known for decades before, with the group now encompassing a broad array of heavy, quadrupedal ornithischians with extensive armour covering their body and skull. The fifth recognized major subgroup of ornithischians is Pachycephalosauria , which was first named in 1974 after being confused for a long time with the theropod Troodon on account of their similarly omnivorous and unique teeth. Pachycephalosaurians are unique for their tall, thickened skulls and small, bipedal bauplan, suggesting that their domes were for sexual display or combat in
1242-740: A form of agonistic behavior . The frills of ceratopsians are incredibly diverse. They may have been used for protective purposes as the frill sometimes splays over the neck. However, some say that the frill would have provided little protection from other large dinosaurs such as Tyrannosaurus . Other possible functions include intraspecific communication for mating purposes or as a visual display of territorial protection, as seen in many common day organisms such as red-breasted robins. The frills also could have been used for species recognition purposes, as they seem to develop fairly early in life. There has also been evidence that ceratopsians care for their young, as bone-beds have been found of adult individuals with
1380-521: A horny sheath of keratin. The teeth are arranged in batteries for easy replacement and have serrations which may have been useful for cutting up vegetation. Marginocephalia evolved several methods for breaking down vegetation. Pachycephalosaurs had especially large abdomens with broad girths and elongate sacral ribs suggesting the presence of a large stomach. This is presumed to have been useful for breaking down tough vegetation through bacterial fermentation . Another adaptation for advanced vegetation digestion
1518-405: A jugal horn and a thin parietal-squamosal shelf that extends back and up into a frill. This frill could have been used for anchoring jaw muscles, as well as for display. The horns were likely used for establishing dominance, or defending territories. It is also possible they were a factor in sexual display and species recognition. One of the basalmost members of this group is Psittacosaurus , which
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#17328525155091656-459: A keratinous beak . The premaxillary teeth and the first lower tooth in Heterodontosaurus are enlarged into sizeable canines. In later ornithopods, the skulls are more elongate and sometimes fully rectangular, with a very large nasal opening, and a thin, elongate palpebral that can extend the entire way across the orbit. Teeth are almost always absent from the premaxilla, the antorbital fossa
1794-499: A narrower skull overall. The ischium bone of the pelvis is also longer than the femur , which differs from other species in which these bones are known. The type specimen has a skull length of 13.2 centimetres (5.2 in) and a femoral length of 13 centimetres (5.1 in), but is not fully grown. An adult P. neimongoliensis was probably smaller than P. mongoliensis , with a proportionately longer skull and tail. P. ordosensis can be distinguished by numerous features of
1932-436: A natural Dinosauria, which has been supported since. The first cladistic studies on Ornithischia were published simultaneously in 1984 by David B. Norman , Andrew R. Milner, and Paul C. Sereno . These studies differed somewhat in their results, but found that Iguanodon was closer to hadrosaurs than other ornithopods, followed by Dryosaurus , Hypsilophodon and then Lesothosaurus and its relatives. While
2070-459: A natural cross-section to compare them to modern animals, showing that dinosaurian dermal layers evolved in parallel to those in many other large vertebrates. The collagen tissue fibres in Psittacosaurus are complex, virtually identical to all other vertebrates in structure but having an exceptional thickness of about forty layers. As the sections of dermis were collected from the abdomen, where
2208-697: A nest of juveniles, although some refute this as viable evidence of care for young. There have also been bone-beds found with hundreds of adult ceratopsians, indicating herd activity. A few specimens have been found with puncture wounds, supporting the use of horns as protective or combative weapons. Other research examining juvenile ceratopsians reveals a change in horn morphology over time, suggesting frills and horns could have been used for intraspecific communication of age. Horns also could have been used for thermoregulation as indicated by isotope analysis , as aid in knocking down vegetation, or for horn-locking agonistic behavior. The study of sexual dimorphism in dinosaurs
2346-617: A new Chinese species of Psittacosaurus was found in the Aptian-Albian Qingshan Formation of Shandong Province , southeast of Beijing . C. C. Young called it P. sinensis to differentiate it from P. mongoliensis , which had originally been found in Mongolia. Fossils of more than twenty individuals have since been recovered, including several complete skulls and skeletons, making this the most well-known species after P. mongoliensis . Chinese paleontologist Zhao Xijin named
2484-655: A new locality, Ulan Osh, where a disarticulated specimen of Psittacosaurus mongoliensis was found, and in 1948 they revisited the sites of the American expeditions and excavated fragmentary postcrania from Oshih and Ondai Sair. The material from these expeditions was taken to the Paleontological Institute of Moscow . Soviet excavations near Kemerovo in Siberia also discovered a partial skull and skeleton of multiple individuals referrable to Psittacosaurus . This material
2622-517: A new species after his mentor, C. C. Young, in 1962. However, the type specimen of P. youngi (a partial skeleton and skull) was discovered in the same rocks as P. sinensis and appears to be very similar, so P. youngi is generally considered a junior synonym of that better-known species. As with P. guyangensis and P. osborni , You and Dodson (2004) listed it as valid in a table, but not in their text. In 1988, Zhao and American paleontologist Paul Sereno described P. xinjiangensis , named after
2760-606: A preliminary manner. Unfortunately, the skull was damaged while in the care of the Chinese Institute of Vertebrate Paleontology and Paleoanthropology (IVPP), and several fragments have been lost, including all of the teeth. The remains were found in the Lower Xinminbao Formation , which have not been precisely dated, although there is some evidence that they were deposited in the late Barremian through Aptian stages. Sereno suggested in 2000 that P. mazongshanensis
2898-480: A published length of about 16 centimetres (6.3 in). P. meileyingensis has the shortest snout and neck frill of any species, making the skull nearly circular in profile. The orbit (eye socket) is roughly triangular, and there is a prominent flange on the lower edge of the dentary, a feature also seen in specimens of P. lujiatunensis , and to a lesser degree in P. mongoliensis , P. sattayaraki , and P. sibiricus . The complete type skull, probably adult,
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#17328525155093036-544: A robust beak. One individual was found preserved with long filaments on the tail, similar to those of Tianyulong . Psittacosaurus probably had complex behaviours, based on the proportions and relative size of the brain. It may have been active for short periods of time during the day and night, and had well-developed senses of smell and vision. Psittacosaurus was one of the earliest ceratopsians, but closer to Triceratops than Yinlong . Once in its own family, Psittacosauridae, with other genera like Hongshanosaurus , it
3174-417: A single known species. The difference is most likely due to artifacts of the fossilisation process. While Psittacosaurus is known from hundreds of fossil specimens, most other dinosaur species are known from far fewer, and many are represented by only a single specimen. With a very high sample size, the diversity of Psittacosaurus can be analysed more completely than that of most dinosaur genera, resulting in
3312-441: A skin flap. A 2021 study of SMF R 4970 examined its cloaca , the first one known from a non-avian dinosaur. The positioning of the individual when it died is oriented obliquely, so the structure can be seen better in the right side. Psittacosaurus' cloaca is comparable to those of crocodilians, with discrete lateral lips that converge anteriorly, giving the cloaca a v-shape anatomy. It also shows resemblance to that of birds, with
3450-520: A synonym of P. mongoliensis , but noted it was tentative because of the presence of multiple valid psittacosaur species in Inner Mongolia. Young also described the species P. tingi in the same 1931 report which contained P. osborni . It is based on several skull fragments. He later synonymised the two species under the name P. osborni . You and Dodson (2004) followed this in a table, but Sereno regarded both species as synonyms of P. mongoliensis ;
3588-408: A table in the latter reported P. tingi as a nomen dubium , however. The front half of a skull from Guyang County in Inner Mongolia was described as Psittacosaurus guyangensis in 1983. Disarticulated postcranial remains representing multiple individuals were found at the same locality and were assigned to the species. While it differs from the type specimen of P. mongoliensis , it falls within
3726-510: A time that are replaced as they are worn down. As they evolved, pachycephalosaurs evolved much thicker and advanced skull roofs including dome forms with horn-like ornamentation. Some research suggests these domes were used like helmets for protection while head-butting members in intraspecific combat. Some research suggests their necks were not strong enough to support such an impact. Flat-headed pachycephalosaur specimens have been found in Asia, and there
3864-429: A triangular skull that had large circular orbits on the sides. This suggests that early ornithischians had relatively huge eyes that faced laterally. The forelimbs of early ornithischians are considerably shorter than their hindlimbs. A small forelimb such as those present in early ornithischians would not have been useful for locomotion, and it is evident that early ornithischians were bipedal dinosaurs. The entire skeleton
4002-443: A unique skull anatomy that is unlike any other ornithischian. The bones of the top of the skull are thickened and in many taxa expanded significantly to form round bony domes as the top of the head, as well as possessing small nodes or elongate spikes along the back edge of the skull. Many taxa are only known from these thick skull domes, which are fused from the frontal and parietal bones. As in many other ornithischians,
4140-428: Is 13.7 centimetres (5.5 in) long. The dentary of P. sattayaraki has a flange similar to that found in P. mongoliensis , P. sibiricus , P. lujiatunensis and P. meileyingensis , although it is less pronounced than in those species. The material appears to be roughly the same size as P. sinensis . The frontal bone of P. neimongoliensis is distinctly narrow compared to that of other species, resulting in
4278-408: Is 30% smaller than P. mongoliensis . The largest are P. lujiatunensis and P. sibiricus , although neither is significantly larger than P. mongoliensis . Psittacosaurus postcranial skeletons are more typical of a 'generic' bipedal ornithischian. There are only four digits on the manus ('hand'), as opposed to the five found in most other ornithischians (including all other ceratopsians), while
Marginocephalia - Misplaced Pages Continue
4416-463: Is a genus of extinct ceratopsian dinosaur from the Early Cretaceous of what is now Asia , existing between 125 and 105 million years ago . It is notable for being the most species -rich non-avian dinosaur genus. Up to 12 species are known, from across China , Mongolia , Russia , and Thailand . The species of Psittacosaurus were obligate bipeds at adulthood, with a high skull and
4554-409: Is a fossa in front of the eye, as in P. mongoliensis . The jugal bones flare outwards widely, making the skull wider than it is long, as seen in P. sinensis . Widely flared jugals are also found in P. sibiricus . Overall, this species is thought to exhibit several primitive characteristics compared to other species of Psittacosaurus , which is consistent with its greater geological age. P. gobiensis
4692-540: Is an extinct clade of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds . The name Ornithischia , or "bird-hipped", reflects this similarity and is derived from the Greek stem ornith- ( ὀρνιθ- ), meaning "bird", and ischion ( ἴσχιον ), meaning "hip". However, birds are only distantly related to this group, as birds are theropod dinosaurs. Ornithischians with well known anatomical adaptations include
4830-409: Is box-like, while the snout tapers to a point. The nasal opening is small, the antorbital fossa that opens from the side of the skull into the palate is large, shallow and triangular, the orbit is large and round and has a palpebral creating a brow, and the lower jaw has a large mandibular fenestra . The skulls of Emausaurus and Scelidosaurus , two early members of
4968-421: Is close to sexual maturity, it is likely that the umbilicus probably retained throughout this individual's life and that Psittacosaurus had its umbilicus at least until sexual maturity. It is uncertain whether the umbilicus is present in mature or nearly mature individuals of all non-avian dinosaurs. Skulls of P. mongoliensis are flat on top, especially over the back of the skull, with a triangular depression,
5106-537: Is especially prominent in Ceratopsia, where only the primitive Psittacosaurus is bipedal. All the derived forms were strong quadrupeds, although their stance is controversial. Some think they were fairly columnar, with front limbs erect under the body, which would have been more efficient for speed. Others think the legs were more sprawling, as evidenced by the shape of the forelimb bones. Although not as fast, this posture would have been efficient for grazing vegetation on
5244-404: Is great controversy on the meaning of these flat heads. Recent research suggests the flat heads could be a juvenile state before developing the dome shape in the adult stage. It could also be evidence of sexual dimorphism with the female being more flat-headed. Ceratopsians , or "horned-faces", differ from pachycephalosaurs in the presence of a rostral bone, or beak. They are also known for having
5382-495: Is incredibly difficult. The varying size and intricacy of margins in Marginocephalia have shown many signs of sexual dimorphism. Although the intricate frills of marginocephalians sometimes seem to present with dimorphic features, many doubt the validity of these claims. Stegoceras validum , a pachycephalosaur, can be segregated into two groups based on the size and shape of their skulls. These two group classifications separated
5520-472: Is much debate over whether these filaments found in specimens of Tianyulong , Psittacosaurus , and Kulindadromeus may have been primitive feathers . Ornithischia is a very large and diverse group of dinosaurs, with members known from all continents, habitats, and a very large range of sizes. They are primarily herbivorous browsers or grazers, but some members may have also been opportunistic omnivores. Ornithischians are united by multiple features of
5658-499: Is no convincing evidence which shows these structures to be homologous to the structurally different integumentary filaments of theropod dinosaurs". However, they found that all other feather-like integument from the Yixian Formation could be identified as feathers. In 2008, another study was published describing the integument and dermis of Psittacosaurus sp., from a different specimen. The skin remains could be observed by
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5796-433: Is not assumed that they belong to the same species. More than 200 specimens of Psittacosaurus have been found in the Yixian Formation, which is famous for its fossils of feathered dinosaurs . The vast majority of these have not been assigned to any published species, although many are very well preserved and some have already been partially described. Nearly 100 Psittacosaurus skeletons were excavated in Mongolia during
5934-408: Is now considered to be senior synonym of the latter and an early offshoot of the branch that led to more derived forms. The genera closely related to Psittacosaurus are all from Asia, with the exception of Aquilops , from North America . The first species was either P. lujiatunensis or closely related, and it may have given rise to later forms of Psittacosaurus . Psittacosaurus is one of
6072-513: Is one of the most species-rich dinosaur genera from Asia. Ceratopsians later evolved into very large quadrupeds with elaborate facial horns such as Triceratops , Styracosaurus , and Centrosaurus . There was no change in richness of species throughout the Cretaceous before the Cretaceous-Paleogene extinction . Marginocephalians have simple, peg-like teeth surrounded by rhamphotheca,
6210-508: Is reduced and round to slit-like, the tip of the snout is sometimes flared to form a broad beak. Members of the ornithopod family Hadrosauridae show further adaptations, including the formation of dental batteries where teeth are continuously replaced, and in many genera the development of prominent cranial crests formed by multiple different bones of the skull. Pachycephalosauria , at one time thought to be close to ornithopods and now known to be related instead to ceratopsians , show
6348-586: Is regarded as Aptian-Albian in age. A second species described in 1988 by Sereno and Zhao, along with two Chinese colleagues, was P. meileyingensis from the Jiufotang Formation , near the town of Meileyingzi, Liaoning Province , northeastern China. This species is known from four fossil skulls, one associated with some skeletal material, found in 1973 by Chinese scientists. The age of the Jiufotang in Liaoning
6486-588: Is related to the many possible functions of the bony skull margins. Some possible functions of the variably shaped and sized margins are to ward off predators, display, ritualized combat, defense of territory, or establishing social ordering. Both pachycephalosaurs and ceratopsians show evidence of interspecific communication , and there may be evidence of intraspecific communication. Pachycephalosaurs, with their dome-shaped heads, are commonly thought to have used their thick skulls for butting into each other. Their brains and vertebrae are positioned in ways to protect from
6624-692: Is seen in Ceratopsians, which evolved features to improve their chewing apparatus. Derived ceratopsians have vertical grinding surfaces on their teeth to maximize break-down of tough vegetation. There is also evidence of advanced adductor musculature that extends from a large coronoid process on the mandible up to the ceratopsian frill, which would increase chewing force. Pachycephalosaurs had gastroliths to help in digestion of food, but only primitive ceratopsians, such as Psittacosaurus , have been found to have gastroliths. Marginocephalian remains reveal significant evidence of being social creatures, much of which
6762-650: Is the oldest available name, the researchers argued that because the type specimen of P. lujiatunensis was better preserved, the correct name for this species should be P. lujiatunensis rather than P. houi , which would normally have priority. P. gobiensis is named for the region it was found in 2001, and first described by Sereno, Zhao and Lin in 2010. It is known from a skull and partial articulated skeleton with gastroliths. Many other specimens either cannot be determined to belong to any particular species, or have not yet been assigned to one. These specimens are generally all referred to as Psittacosaurus sp., although it
6900-434: Is the presence of 23 vertebrae between the skull and pelvis, unlike the 21 or 22 in the other species where the vertebrae are known. P. xinjiangensis is distinguished by a prominent jugal 'horn' that is flattened on the front end, as well as some features of the teeth. The ilium , one of the three bones of the pelvis, also bears a characteristically long bony process behind the acetabulum (hip socket). An adult femur has
7038-592: Is unknown, but in the neighbouring province of Inner Mongolia, it has been dated to about 110 Ma, in the Albian stage of the Early Cretaceous. French paleontologist Eric Buffetaut and a Thai colleague, Varavudh Suteethorn , described a partial upper and lower jaw from the Aptian-Albian Khok Kruat Formation of Thailand in 1992, giving it the name P. sattayaraki . In 2000, Sereno questioned
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#17328525155097176-565: The Aptian to Albian stages of the Early Cretaceous Period , or approximately 125 to 100 mya. Fossil remains of over 75 individuals have been recovered, including nearly 20 complete skeletons with skulls. Individuals of all ages are known, from hatchlings less than 13 centimetres (5.1 in) long, to very old adults reaching nearly 2 metres (6 ft 7 in) in length. In a 2010 review, Sereno again regarded P. osborni as
7314-631: The Greek word sauros ("lizard"). This name refers to the ancient Hongshan culture of northeastern China, who lived in the same general area in which the fossil skull of Hongshanosaurus was found. The type and only named species, H. houi , honours Hou Lianhai , a professor at the IVPP in Beijing, who curated the specimen. Genus and species were both named by Chinese paleontologists You Hailu , Xu Xing, and Wang Xiaolin in 2003. Sereno (2010) regarded its distinct proportions as due to crushing and compression of
7452-544: The Hongshanosaurus skulls. He regarded Hongshanosaurus as a junior synonym of Psittacosaurus , and potentially the same as P. lujiatunensis . He did not synonymise the two species because of difficulties with the holotype skull of H. houi , instead considering new combination P. houi a nomen dubium within Psittacosaurus . Sereno's hypothesis was supported by a morphometric study in 2013, which found P. houi and P. lujiatunensis to be synonymous. While P. houi
7590-518: The Ilek Formation of Siberia, which ranges from the Barremian to Aptian stages of the Early Cretaceous. Individuals of this species could grow up to 2.5 meters in length, making it one of the largest members of the genus. P. lujiatunensis , named in 2006 by Chinese paleontologist Zhou Chang-Fu and three Chinese and Canadian colleagues, is one of the oldest-known species, based on four skulls from
7728-568: The Jurassic Period and became more common in the Cretaceous. They are basally small facultative quadrupeds while derived members of the group are large obligate quadrupeds. Primitive marginocephalians are found in Asia, but the group migrated upwards into North America. Pachycephalosaurs , or "thick-headed reptiles", have primitive features that include basally small sized bodies, obligate bipedalism, and simple teeth with one row in operation at
7866-609: The Late Jurassic , encompassing a diverse array of bodyforms from the small, bipedal Psittacosaurus up to the very large, quadrupedal, horned and frilled ceratopsids like Torosaurus , which has the longest skull of any terrestrial vertebrate. Ornithopods, which range from the Early Jurassic in some studies until the end of the Cretaceous with continuous diversity, are generally bipedal and unarmoured, though some later groups like Hadrosauridae evolved complex dental anatomy in
8004-793: The Ordos prefecture of the Inner Mongolia Autonomous Region. The type specimen is a nearly complete skeleton, including part of the skull. However, only the skull, lower jaw, and foot have been described. Three other specimens were referred to this species but remain undescribed. Like P. neimongoliensis , this species was discovered in the Eijnhoro Formation. Sereno (2010) found the species as described to be indistinguishable from P. sinensis , another small species, but suggested that additional study of P. ordosensis might reveal diagnostic features. He provisionally designated P. ordosensis
8142-715: The Psittacosaurus biochron . In 1922 , American paleontologist Henry Fairfield Osborn took part in the Third Asiatic Expedition of the American Museum of Natural History to discover fossils and geologic formations from the Cretaceous and Tertiary of Mongolia . In the Oshih Formation of the Artsa Bogdo Basin, Wong, the Mongolian chauffeur, discovered a nearly complete skull , jaws , and skeleton of
8280-531: The Qingshan Formation . Of this material, the nearly complete skeleton and skull IVPP V738 was described as the type of the new species Psittacosaurus sinensis , which was found in a red layer 10 mi (16 km) northwest of Rongyang City in Shandong . Yang also assigned 11 other specimens to the taxon, considering it to be the most diverse Psittacosaurus species known at the time. It was distinguished from
8418-588: The Xinjiang Autonomous Region in which it was discovered. Several individuals of different ages were discovered in the early 1970s by Chinese paleontologists and described by Sereno and Zhao, although the holotype and most complete skeleton belonged to a juvenile. An adult skeleton was later discovered at a different locality in Xinjiang. These specimens come from the upper part of the Tugulu Group , which
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#17328525155098556-621: The Xinpongnaobao Formation . An additional tooth, partial hand , and fragments of vertebrae and limbs were found in the same locality, with the tooth being referred to Protiguanodon and the remainder of the material being uncertain. Additional Psittacosaurus material from possibly the same locality was described later in 1953 by Birger Bohlin , who considered the remains to likely belong to P. mongoliensis . The Soviet Expeditions into Mongolia from 1946 to 1949 uncovered more material of Psittacosaurus . In 1946 they discovered
8694-441: The antorbital fossa , on the outside surface of the maxilla (an upper jaw bone). A flange is present on the lower edge of the dentary (the tooth-bearing bone of the lower jaw), although it is not as prominent as in P. meileyingensis or P. major (= P. lujiatunensis ). P. mongoliensis is among the largest known species. The skull of the type specimen, which is probably a juvenile, is 15.2 centimetres (6 in) long, and
8832-493: The ceratopsians or "horn-faced" dinosaurs (e.g. Triceratops ), the pachycephalosaurs or "thick-headed" dinosaurs, the armored dinosaurs ( Thyreophora ) such as stegosaurs and ankylosaurs , and the ornithopods . There is strong evidence that certain groups of ornithischians lived in herds, often segregated by age group, with juveniles forming their own flocks separate from adults. Some were at least partially covered in filamentous (hair- or feather- like) pelts, and there
8970-464: The dorsal (upper) surface of the tail. These were confirmed by the authors, as well as an independent scientist, to not represent plant material. The bristle-like integumentary structures extend into the skin nearly to the vertebrae, and were likely circular or tubular before being preserved. Under ultraviolet light , they gave off the same fluorescence as scales, providing the possibility they were keratinized . The study stated that, "at present, there
9108-464: The jugal (cheek) bone on the outside of the skull. The jugals flare out sideways, forming ' horns ' proportionally wider than in any other known Psittacosaurus species except P. sibiricus and P. lujiatunensis . Because of the flared cheeks, the skull is actually wider than it is long. A smaller 'horn' is present behind the eye , at the contact of the jugal and postorbital bones, a feature also seen in P. sibiricus . The mandible (lower jaw) lacks
9246-483: The quadrate bones . Osborn created the new family Psittacosauridae for Psittacosaurus , which he considered possibly related to Ankylosauria , while he placed Protiguanodon within the family Iguanodontidae as the only member of the new subfamily Protiguanodontinae . Osborn published an additional description of the specimens of Protiguanodon and Psittacosaurus in 1924 , citing his previous study as naming both to be members of Psittacosauridae, and considering
9384-725: The Barremian Andakhuduk Formation of Mongolia. It is named after Amitabha Buddha . The species of Psittacosaurus vary in size and specific features of the skull and skeleton, but share the same overall body shape. The best-known— P. mongoliensis —can reach 2 metres (6.5 ft) in length. The maximum adult body weight was most likely over 20 kilogrammes (44 lb) in P. mongoliensis . Several species approach P. mongoliensis in size ( P. lujiatunensis , P. neimongoliensis , P. xinjiangensis ), while others are somewhat smaller ( P. sinensis , P. meileyingensis ). The smallest known species, P. ordosensis ,
9522-496: The addition of horns above each orbit and on the top of the snout, as well as substantial elongation of the frill and in many genera the development of two large parietal fenestrae forming holes in the frill. The skull and frill elongation makes the skulls of Torosaurus and Pentaceratops the largest of any known terrestrial vertebrate, at over 2 m (6.6 ft) long. Early ornithischians were relatively small dinosaurs, averaging about 1–2 meters in body length, with
9660-600: The armoured group Thyreophora , show similarities in the box-like skull that tapers to the front. The antorbital fossa is smaller and forming an elongate oval in both taxa, and the palpebral which is elongate and slender in Lesothosaurus is widened in Emausaurus and completely incorporated into the skull as a flat bone in Scelidosaurus . Skulls in members of the thyreophoran group Stegosauria are much longer and lower, with
9798-413: The associated femur is 16.2 centimetres (6.4 in) in length. Other specimens are larger, with the largest documented femur measuring about 21 centimetres (8.25 in) long. P. sinensis is readily distinguished from all other species by numerous features of the skull. Adult skulls are smaller than those of P. mongoliensis and have less teeth. Uniquely, the premaxillary bone contacts
9936-630: The best assignment for the type material may be Ceratopsia incertae sedis . Two new species of Psittacosaurus were described by Canadian Dale Russell and Zhao in 1996. The first was named P. neimongoliensis , after the Mandarin Chinese name for Inner Mongolia. It is based on a nearly complete fossil skeleton, including most of the skull, found in the Early Cretaceous Ejinhoro Formation with seven other individuals. Russell and Zhao also named P. ordosensis in 1996, after
10074-399: The body was covered in scales . Larger scales were arranged in irregular patterns, with numerous smaller scales occupying the spaces between them, similarly to skin impressions known from other ceratopsians, such as Chasmosaurus . A series of what appear to be hollow, tubular bristle-like structures, approximately 16 centimetres (6.3 in) long, were also preserved, arranged in a row down
10212-417: The bristles as being most similar to the quills of Tianyulong , and the sparsely distributed elongated broad filamentous feathers (EBFFs) of Beipiaosaurus . Similar, non-feather-derived bristles are found in a few extant birds such as the "horn" on the horned screamer and the "beards" of turkeys ; these structures differ from feathers in that they are unbranched, heavily cornified and do not develop from
10350-399: The dorsal lobe being homologous to the birds' cloacal protuberance. A 2022 study of SMF R 4970 identified it as an approximately 6–7 year old subadult by comparing its femoral length to that of similarly-aged specimens of P. lujiatunensis , and found that it preserves the first umbilicus (belly button) known from a non-avian dinosaur (the oldest known from an amniote ). Because the specimen
10488-1094: The early evolution of ornithopods considerably, and showing that the evolution of ornithischians was far from definitive. Below are the cladograms of Sereno, Butler and colleagues, and Dieudonné and colleagues, restricted to the major clades of Ornithischia, Heterodontosauridae, Lesothosaurus and Pisanosaurus . Sereno, 1986 Lesothosaurus Stegosauria [REDACTED] Ankylosauria [REDACTED] Pachycephalosauria [REDACTED] Ceratopsia [REDACTED] Heterodontosauria Ornithopoda [REDACTED] Butler et al., 2008 Pisanosaurus Heterodontosauridae Lesothosaurus Stegosauria [REDACTED] Ankylosauria [REDACTED] Ornithopoda [REDACTED] Pachycephalosauria [REDACTED] Ceratopsia [REDACTED] Dieudonné et al., 2021 Lesothosaurus Stegosauria [REDACTED] Ankylosauria [REDACTED] Ornithopoda [REDACTED] Ceratopsia [REDACTED] Pachycephalosauria (incl. heterodontosaurids ) [REDACTED] When Ornithischia
10626-512: The femur is 22.3 cm (8.75 in) in length. It is also distinguished by its neck frill , which is longer than any other species, at 15 to 18% of skull length. A very striking feature of P. sibiricus is the number of 'horns' around the eyes, with three prominences on each postorbital, and one in front of each eye, on the palpebral bones. Similar horns found on the postorbital of P. sinensis are not as pronounced but may be homologous . The jugal has extremely prominent 'horns' and may contact
10764-512: The form of batteries of teeth. Stegosaurs are comparatively limited, restricted to a primarily Jurassic group of moderate to large, quadrupedal herbivores with two rows of vertical plates ornamenting their spine, which possibly did not go extinct until the Late Cretaceous, though at the time of Marsh Stegosauria was used for all armored and quadrupedal taxa, many of which are now separated into Ankylosauria . Ankylosaurs were only recognized as
10902-452: The form of head-butting or flank-butting. Some taxa, particularly those at one point groupt together in the ornithopod family Hypsilophodontidae , are now recognized to not fall within any of the major ornithischian groups, and either be outside Genasauria, or on the basal stem of Neornithischia outside Cerapoda. Following the publication of the PhyloCode to provide rules and regulations on
11040-402: The fossil record, such as behaviour, or colouration. Therefore, actual species diversity may be much higher than currently recognised in this and other dinosaur genera. As some species are known only from skull material, species of Psittacosaurus are primarily distinguished by features of the skull and teeth. Several species can be recognised by features of the pelvis as well. In the 1950s,
11178-467: The four-toed hindfoot is very similar to many other small ornithischians. The skull of Psittacosaurus is highly modified compared to other ornithischian dinosaurs of its time. Extremely tall in height and short in length, the skull has an almost round profile in some species. The portion in front of the orbit (eye socket) is only 40% of total skull length, shorter than any other known ornithischian. The lower jaws of psittacosaurs are characterised by
11316-937: The ground. Less is known about bipedal pachycephalosaur locomotion, although they must have had a fairly broad girth in order to make room for their enlarged gut. The cladogram below follows a 2009 analysis by Zheng and colleagues. Stenopelix Wannanosaurus Goyocephale Homalocephale Pachycephalosauridae Micropachycephalosaurus Chaoyangsaurus Psittacosauridae Liaoceratops Archaeoceratops Leptoceratopsidae Coronosauria Cladogram after Butler et al. , 2011. Wannanosaurus Goyocephale Homalocephale Pachycephalosauridae Micropachycephalosaurus Chaoyangsaurus Stenopelix Yinlong Psittacosauridae Liaoceratops Archaeoceratops Leptoceratopsidae Coronosauria [REDACTED] [REDACTED] [REDACTED] Ornithischia Ornithischia ( / ˌ ɔːr n ə ˈ θ ɪ s k i . ə / )
11454-468: The group Predentata to unite ornithopods, stegosaurs, and Ceratopsia within Dinosauria, but with additional work and new discoveries the unnatural nature of Dinosauria came to be accepted, and the names Seeley proposed found common use. After further decades, in 1974 Robert T. Bakker and Peter M. Galton provided new evidence in support of the grouping of ornithischians and saurischians together within
11592-429: The hand. In addition, the antorbital fenestra , an opening in the skull between the eye socket and nostril , was lost during the evolution of Psittacosauridae, but is still found in most other ceratopsians and in fact most other archosaurs . It is considered highly unlikely that the fifth digit or antorbital fenestra would evolve a second time. In 2014, the describers of a new taxon of basal ceratopsian published
11730-399: The hollow opening, or fenestra , seen in other species, and the entire lower jaw is bowed outwards, giving the animal the appearance of an underbite . The skull of an adult P. sinensis can reach 11.5 centimeters (4.5 in) in length. P. sibiricus is the largest-known species of Psittacosaurus . The skull of the type specimen is 20.7 centimetres long (8.25 in), and
11868-450: The impact of head-butting. Also, the columnar structure found in bone remains is consistent with models used to recreate the practice of head-butting. However, some pachycephalosaurs such as Stygimoloch have vascularization in the skull cap that would not have supported head-butting behavior. Thus, the heads could have been used as ornamentation or to butt into the softer flank of other pachycephalosaurs for intraspecific communication or as
12006-404: The jugals, which have very prominent 'horns'. It is also the smallest known species. One adult skull measures only 9.5 centimeters (3.75 in) in length. The type skull of P. lujiatunensis measures 19 cm (7.5 in) in length, while the largest-known skull is 20.5 centimetres (8 in) long, so this species was similar in size to P. mongoliensis and P. sibiricus . There
12144-425: The large size of its skull by Sereno, Zhao and two colleagues in 2007. You and colleagues described an additional specimen and concurred that it was distinct from P. lujiatunensis . P. major was originally characterised by a proportionately large skull, which was 39% of the length of its torso, compared to 30% in P. mongoliensis , and other features. However, a 2013 study utilising morphometric analysis showed that
12282-501: The largest horned ornithischians were around 8.5 m (28 ft) and 11 t (11 long tons; 12 short tons), and the largest crested ornithischians were around 15 m (49 ft) and 13.5 t (13.3 long tons; 14.9 short tons). Much of the knowledge of early ornithischian anatomy comes from Lesothosaurus , which is a taxon known from multiple skulls and skeletons from the Early Jurassic of Lesotho . The rear of its skull
12420-531: The limbs may represent disruptive coloration . The specimen also had dense clusters of pigment on its shoulders, face (possibly for display), and cloaca (which may have had an antimicrobial function, though this has been disputed ), as well as large patagia on its hind legs that connected to the base of the tail. Its large eyes indicate that it also likely had good vision, which would have been useful in finding food or avoiding predators. The authors pointed out that there might have been variation in coloration across
12558-399: The lower beds of the Yixian Formation , near the village of Lujiatun. While this bed has been dated differently by different authors, from 128 Ma in the Barremian stage, to 125 Ma in the earliest Aptian, revised dating methods have shown them to be about 123 million years old. P. lujiatunensis was contemporaneous with another psittacosaurid species, Hongshanosaurus houi , which
12696-438: The most completely known dinosaur genera. Fossils of hundreds of individuals have been collected so far, including many complete skeletons. Most age classes are represented, from hatchling through to adult, which has allowed several detailed studies of Psittacosaurus growth rates and reproductive biology . The abundance of this dinosaur in the fossil record has led to the labelling of Lower Cretaceous sediments of east Asia
12834-458: The opisthopubic pelvis evolved a fourth time, in the clade Dromaeosauridae , but this is controversial, as other authors argue that dromaeosaurids are mesopubic. It has also been argued that the opisthopubic condition is basal to maniraptorans (including among others birds, therizinosauroids and dromaeosaurids), with some clades having later experienced a reversal to the propubic condition. The first recognition of an herbivorous group of dinosaurs
12972-474: The origins of the group and the relationships of primitive taxa like Pisanosaurus and members of Silesauridae may sometimes be found to be ornithischians outside this core grouping. Madzia and colleagues also provided a composite cladogram of Ornithischia to illustrate the consensus of internal divisions, which can be seen below. Ornithischia has been defined as all taxa closer to Iguanodon than Allosaurus or Camarasaurus . Genasauria has been defined as
13110-520: The other known species by a shorter and wider snout, and an overall smaller size at 675 mm (26.6 in). Yang also revised the classifications of the other species of Psittacosaurus . Following similar conclusions to Rozhdestvensky, Yang considered Protiguanodon to be a junior synonym of Psittacosaurus , but retained the species as separate giving former Protiguanodon mongoliense the new species name Psittacosaurus protiguanodonensis , as otherwise both it and Psittacosaurus mongoliensis would have
13248-420: The palate. The skulls are known from many early ornithopods and some heterodontosaurids , showing similar general features. Skulls are relatively tall with shorter snouts, but the snout is elongated in some later taxa like Thescelosaurus . The orbit and antorbital fossa are large, but the nasal opening is small, and while teeth are present in the premaxilla, there is a toothless front tip that likely formed
13386-743: The phylogenetics of Ornithischia was published in 2008 by Richard J. Butler and colleagues, including many primitive ornithischians and members from all of the major subgroups, to test some of the hypotheses given previously about ornithischian evolution and the relationships of the groups. Thyreophora was found to be a supported group, as well as the clade of pachycephalosaurs and ceratopsians that Sereno named Marginocephalia in 1986. Some taxa considered earlier to be ornithopods, like heterodontosaurids, Agilisaurus , Hexinlusaurus and Othnielia , were instead found to be outside of both Ornithopoda and Ceratopsia, but still closer to those two groups than thyreophorans. The early Argentinian taxon Pisanosaurus
13524-413: The premaxilla, both features also seen in the possibly related P. sinensis . There is a flange on the dentary of the lower jaw, similar to P. mongoliensis , P. meileyingensis , and P. sattayaraki . It can be told apart from the other species of Psittacosaurus by a combination of 32 anatomical features, including six that are unique to the species. Most of these are skull details, but one unusual feature
13662-547: The range of individual variation seen in other specimens of that species and is no longer recognised as a valid species. You and Dodson (2004) included P. guyangensis in a table of valid taxa, but did not include it as such in their text. Seventeen species have been referred to the genus Psittacosaurus , although only nine to eleven are considered valid today. This is the highest number of valid species currently assigned to any single non-avian dinosaur. In contrast, most other dinosaur genera are monospecific , containing only
13800-569: The range of the animal, depending on differences in the light environment. The authors were unable to determine which species of Jehol Formation Psittacosaurus the specimen belonged to due to the way the skull is preserved, but ruled out P. mongoliensis , based on hip features. Another 2016 study used laser-stimulated fluorescence imaging to analyze the internal structure of the bristles. The highly cornified bristles were arranged in tight clusters of three to six individual bristles, with each bristle being filled with pulp. The authors considered
13938-490: The recognition of more species. Most extant animal genera are represented by multiple species, suggesting that this may have been the case for extinct dinosaur genera as well, although most of these species may not have been preserved. In addition, most dinosaurs are known solely from bones and can only be evaluated from a morphological standpoint, whereas extant species often have very similar skeletal morphology but differ in other ways which would not normally be preserved in
14076-560: The relationships within Ornithischia with greater detail was that of Sereno in 1986 , who provided features that supported the evolution of all ornithischian groups and shared similarities with earlier studies. Sereno found that Lesothosaurus was the most primitive ornithischian, with all other ornithischians united within the clade Genasauria, which has two subgroups. The first subgroup, Thyreophora , unites ankylosaurs and stegosaurs along with more primitive taxa like Scelidosaurus , while
14214-596: The same species name. Contrasting Rozhdestvensky, Yang retained the earlier Chinese species P. osborni and P. tingi as separate from P. mongoliensis , but not separate from each other, making P. tingi a junior synonym of P. osborni . Following his new breakdown of species, Yang described the distribution of the genus Psittacosaurus : P. sinensis was the only species known from Shandong; P. osborni and possibly P. mongoliensis were both known from Haratologay (also known as Tebch); P. mongoliensis and P. protiguanodonensis were both known form Oshih; and P. mongoliensis
14352-483: The scales were eroded, the tissue may have assisted with the musculature of the stomach and intestines and offered protection against predators. As described in a 2016 study, examination of melanosomes preserved in the specimen of Psittacosaurus preserved with integument indicated that the animal was countershaded , likely related to living in a dense forest habitat with little light, much like many modern species of forest-dwelling deer and antelope; stripes and spots on
14490-420: The second subgroup, Cerapoda , contained ornithopods, ceratopsians, pachycephalosaurs, and small primitive forms. One group of the small primitive forms considered to be cerapodans by Sereno, Heterodontosauridae , has since been found to be a group of very early ornithischians of similar evolutionary status as Lesothosaurus , although this result is not definitive. The first large-scale numerical analysis of
14628-459: The separate status of Protiguanodontinae as uncertain. Further preparation of the skeleton of AMNH 6254 showed significant similarities in the skeletons of Psittacosaurus and Protiguanodon , including the number of teeth, the number of pre-caudal vertebrae , and other details of the skull and skeleton. Osborn also referred the specimen AMNH 6261 from the Oshih Formation to Psittacosaurus , so
14766-501: The skull and skeleton. P. youngi was considered to be most similar to P. sinensis , but separated them to bring the count of members of Psittacosauridae to one genus and five species. Many later expeditions by various combinations of Mongolian, Russian, Chinese, American, Polish, Japanese, and Canadian paleontologists also recovered specimens from throughout Mongolia and northern China. In these areas, Psittacosaurus mongoliensis fossils are found in most sedimentary strata dating to
14904-411: The skull, limbs, and hip, were unrelated to other dinosaurs, and so he proposed that Dinosauria was an unnatural grouping of two independently-evolved suborders , Saurischia and Ornithischia. It is from the anatomy of the hip that Seeley chose the name Ornithischia, referencing the bird-like anatomy of the ischium bone. Many researchers did not follow the division of Seeley at first, with Marsh naming
15042-471: The skull, teeth, and skeleton, including especially the presence of a predentary and palpebral , an increased number of sacral vertebrae , the absence of gastralia , and an opisthopubic pubis . Early ornithischians ranged around 1–2 m (3.3–6.6 ft) in length, with them increasing in size over time so that the largest armoured ornithischians were around 7.5 m (25 ft) and 9 t (8.9 long tons; 9.9 short tons),
15180-473: The skull. While Osborn considered Protiguanodon and Psittacosaurus separate based on the lack of horns on the jugal bones in Protiguanodon , a general dissimilarity in the skeletons, and wide geographic separation of the two specimens, Gregory suggested in correspondence that the Protiguanodon specimen could represent a juvenile of Psittacosaurus , based on similarities in size, the parietal bones , and
15318-654: The smallest clade containing Ankylosaurus , Iguanodon , Stegosaurus , and Triceratops . Heterodontosaurus tucki ( Heterodontosauridae ) [REDACTED] Huayangosaurus taibaii ( Huayangosauridae ) Stegosaurus stenops ( Stegosauridae ) [REDACTED] Mymoorapelta maysi Polacanthus foxii ( Polacanthinae ) [REDACTED] Nodosaurus textilis Panoplosaurus mirus ( Panoplosaurini ) Struthiosaurus austriacus ( Struthiosaurini ) Psittacosaurus Psittacosaurus ( / ˌ s ɪ t ə k ə ˈ s ɔːr ə s / SIT -ə-kə- SOR -əs ; " parrot lizard ")
15456-429: The snout is short and tapering, the nasal opening is small, the antorbital fossa is sometimes absent, and there are premaxillary teeth, though only three. The two palpebrals are also incorporated into the skull roof as in thyreophorans, rather than free. Ceratopsians, the sister group to pachycephalosaurs, also display many cranial adaptations, most importantly the evolution of a bone called the rostral that forms
15594-560: The species have been recognised as the results of the deformation of the skull after fossilisation. Sereno (2010) remained unconvinced of its validity. Beginning in the 1950s, Russian paleontologists began excavating Psittacosaurus remains at a locality near Shestakovo village in Kemerovo Oblast in Western Siberia . Two other nearby localities were explored in the 1990s, one of which produced several complete skeletons. This species
15732-500: The species population in half, which is highly indicative of sexual dimorphism. However, some report that the two groups may actually represent two separate species. Protoceratops , a type of ceratopsian, also shows signs of sexual dimorphism. However, their frills don't seem to develop until later in life, and may be coordinated with sexual maturity. In general, primitive marginocephalians were bipedal or facultative quadrupedal , and derived individuals were obligate quadrupedal. This
15870-438: The study of Norman placed ceratopsians between Hypsilophodon and more derived ornithopods, the study of Sereno placed ceratopsians with ankylosaurs and stegosaurs. It has since been recognized by that ceratopsians are closer to ornithopods than the armoured ankylosaurs and stegosaurs, but the relationships of some groups are still in states of change, with some more consistent results than others. An early study that looked at
16008-583: The summers of 2005 and 2006 by a team led by Mongolian paleontologist Bolortsetseg Minjin and American Jack Horner from the Museum of the Rockies in Montana . Although only P. mongoliensis has been described from Mongolia so far, these specimens are still in preparation and have not yet been assigned to a species. P. amitabha was named by Napoli et al. in 2019 from a complete skull and partial skeleton. recovered in
16146-431: The supposed differences between P. lujiatunensis and P. major were due to differences in preservation and crushing. The study concluded that both represented a single species. A third species of Lujiatun psittacosaur, the first to be named, was described as Hongshanosaurus houi in 2003. The generic name Hongshanosaurus was derived from the Mandarin Chinese words 紅 ( hóng : "red") and 山 ( shān : "hill"), as well as
16284-420: The sutures separating skull bones are almost completely obliterated by surface texturing, and there is bony armour above the orbits, and at the top and bottom corners of the back of the skull. Teeth are sometimes absent from the premaxilla, and both the upper and lower jaws have deeply inset teeth creating large cheeks. Ankylosaurs also have very extensive and complicated network of sinuses, formed by bone growth in
16422-524: The taxon was unique based on the short and deep snout, and the broad rear skull, as well as by lacking teeth in the premaxilla . In the same paper, Osborn also described another new taxon he considered similar to Psittacosaurus , Protiguanodon mongoliense , which was found in the same expedition but from the Ondai Sair Formation . The holotype of Protiguanodon , AMNH 6253, included a nearly complete skeleton found articulated, and partial remains of
16560-609: The teeth of the two taxa could be compared. It was mentioned in 1932 by American paleontologist Roy Chapman Andrews that AMHN 6254 was the only good specimen that could be found at Oshih, with only one additional skull and jaws of an adult, and two hatchling skulls, having been found in a later revisit to the locality in 1923. Following the discovery of material of psittacosaurids in Haratologay in Inner Mongolia , Yang Zhongjian described two additional species in 1932. Known from
16698-469: The thick-skulled Pachycephalosauria and the horned Ceratopsia . All members of Marginocephalia were primarily herbivores (though pachycephalosaurs are speculated to have been omnivorous). They basally used gastroliths to aid in digestion of tough plant matter until they convergently evolved tooth batteries in Neoceratopsia (or "new Ceratopsia") and Pachycephalosauria . Marginocephalia first evolved in
16836-565: The top beak opposite the predentary. The jugal bones flare to the sides to create a pentagonal skull seen from above, the nasal opening is closer to the top of the snout than the teeth, and while the snout tapers in some taxa, it is very deep and short in Psittacosaurus . The ceratopsian palpebral is generally triangular, and the back edge of the skull roof forms a flat frill that is enlarged in more derived ceratopsians. The ceratopsian family Ceratopsidae progresses on these features with
16974-399: The unique rostral bone at the tip of the upper jaw, and the flared jugal (cheek) bones. There is still no sign of the bony neck frill or prominent facial horns which would develop in later ceratopsians. Bony horns protrude from the skull of P. sibiricus , but these are thought to be an example of convergent evolution . The integument , or body covering, of Psittacosaurus is known from
17112-401: The use of taxonomic names for groups, the internal classification of Ornithischia was revised by Daniel Madzia and colleagues in 2021 to provide a framework of definitions and taxa for other studies to follow and modify from. They names the new clade Saphornithischia to unite heterodontosaurids with more derived ornithischians to encompass the concept of the well-supported clear ornithischians, as
17250-464: The validity of this species, citing its eroded and fragmentary nature, and noted an absence of features characteristic of the genus Psittacosaurus . However, in 2002 the original authors published new images of the fossil which seem to show teeth in the lower jaw that exhibit the bulbous vertical ridge characteristic of psittacosaurs. Other authors have also defended its validity, while some continue to regard it as dubious. Sereno (2010) proposed that
17388-661: The width at the back being greater than the height in Stegosaurus . The snout and lower jaw are long and deep, and in some genera the premaxilla does not have any teeth. As in Scelidosaurus , the palpebral forms the top border of the orbit as a flat brow bone, but the antorbital fossa is reduced to the point of absence in some genera. Ankylosaurs , the other group of armoured ornithischians, have very robust, immobile skulls, with three significant features that separate them from other groups. The antorbital fossa, supratemporal fenestra and mandibular fenestra are all closed,
17526-588: Was "opisthopubic", meaning that the pubis pointed down and backwards ( posterior ), parallel with the ischium (Figure 1a). Additionally, the ilium had a forward-pointing process (the preacetabular process) to support the abdomen. This resulted in a four-pronged pelvic structure. In contrast to this, the saurischian pelvis was "propubic", meaning the pubis pointed toward the head ( anterior ), as in ancestral reptiles (Figure 1b). The opisthopubic pelvis independently evolved at least three times in dinosaurs (in ornithischians, birds and therizinosauroids ). Some argue that
17664-461: Was a nomen dubium , with no unique features that separate it from any other species of Psittacosaurus . However, more recent authors have noted that it can be distinguished by its proportionally long snout compared to other species of Psittacosaurus , as well as a prominent bony protuberance, pointing outwards and downwards, on the maxilla of the upper jaw. The maxillary protuberance is also now missing. Other features originally used to distinguish
17802-546: Was also named by Osborn in 1923. Psittacosaurids were basal to almost all known ceratopsians except Yinlong and perhaps the Chaoyangsauridae . While Psittacosauridae was an early branch of the ceratopsian family tree, Psittacosaurus itself was probably not directly ancestral to any other groups of ceratopsians. All other ceratopsians retained the fifth digit of the hand, a plesiomorphy or primitive trait, whereas all species of Psittacosaurus had only four digits on
17940-403: Was described by Soviet paleontologist Anatoly Rozhdestvensky in 1955 , who also proposed that Protiguanodon mongoliense , Psittacosaurus osborni , and Psittacosaurus tingi were junior synonyms of Psittacosaurus mongoliensis . In 1958 , Yang published a paper on the dinosaurs of Laiyang , in which he described multiple discoveries of Psittacosaurus from a collection of localities of
18078-407: Was first named, Seeley united the orders Ornithopoda and Stegosauria of Marsh's taxonomy within the new group. Ceratopsia was then recognized as a unique group related to ornithopods and stegosaurs by Marsh by 1894, with each of the three suborders still being recognized as distinct groups today. Ceratopsians are recognized as group that grew in diversity later in the Cretaceous after evolving in
18216-466: Was found in the same beds. It is potentially synonymous with H. houi ; Sereno (2010), who proposed that Hongshanosaurus is a synonym of Psittacosaurus , opted to leave P. lujiatunensis and H. houi separate species due to the inadequacies of the latter's type specimen. One nearly complete skeleton of P. lujiatunensis from the same lower beds of the Yixian Formation had previously been classified in its own species, Psittacosaurus major , named for
18354-436: Was found to be the most primitive ornithischian, but while overall results agreed with earlier studies and showed some stability, areas of the evolutionary tree were found to be problematic, and with potential for later change. In 2021 , a new phylogenetic study was published authored by Paul-Emile Dieudonné and colleagues that instead found Heterodontosauridae to nest alongside Pachycephalosauria within Marginocephalia, changing
18492-500: Was lightly built, with a largely fenestrated skull and a very stout neck and trunk. The tail is nearly half of the dinosaurs' overall length. The long tail presumably acted as a counterbalance and as a compensating mechanism for shifts in the creature's center of gravity. The hindlimbs of early ornithischians show that the tibia is considerably longer than the femur, a feature that suggests that early ornithischians were adapted for bipedality, and were fast runners. The ornithischian pelvis
18630-401: Was named P. sibiricus in 2000 in a scientific paper written by five Russian paleontologists, but credit for the name is officially given to two of those authors, Alexei Voronkevich and Alexander Averianov . The remains were not completely described until 2006. Two nearly complete, articulated skeletons and a variety of disarticulated material from other individuals of all ages are known from
18768-517: Was named Orthopoda in 1866 by Edward Drinker Cope , a name that is now recognized as a synonym of Ornithischia. Discussions on the taxonomy of dinosaurs by Othniel Charles Marsh identified two major groups of herbivorous dinosaurs, Ornithopoda and Stegosauria , containing genera from a broad geographic and stratigraphic distribution. While often these groups were placed within Dinosauria, Harry Govier Seeley suggested instead in 1888 that ornithopods and stegosaurs, which shared many features in
18906-581: Was possibly known from Kemerovo. Further discoveries in the Qingshan Formation of Laiyang in 1958 were described by Zhao Xijin in 1962 , giving the new name Psittacosaurus youngi for the specimen BPV.149 in the Beijing Museum of Natural History . Known for a complete skull, partial vertebral series and partial pelvis, P. youngi was distinguished by Zhao by having the shortest skull of all species, vertebral and tooth counts, and various features of
19044-411: Was small-bodied (one metre (3 ft 3 in) long) and differs from other species of Psittacosaurus by "significant, but structurally minor, details." These include the presence of a pyramidal horn on the postorbital , a depression on the postorbital-jugal contact, and enamel thickness. P. mongoliensis was a contemporary. Psittacosaurus is the type genus of the family Psittacosauridae, which
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