Basal Ceratopsian Research Articles

Endocranial morphology of Liaoceratops yanzigouensis (Dinosauria: Ceratopsia) from Early Cretaceous Jehol Biota of Liaoning in China

ABSTRACT Liaoceratops is a small basal neoceratopsian dinosaur from the Early Cretaceous Jehol Biota of western Liaoning, China. Because its postcranial skeleton is lacking, its behaviour and palaeoecology remain poorly understood. By using computed tomography (CT), we reconstructed the cranial endocast and endosseous labyrinths of an adult individual of Liaoceratops yanzigouensis (PMoL-AD00097). Analysis and comparisons indicate that the brain, olfactory bulb and inner ear of adult Liaoceratops more closely resemble those observed in adult specimens of the basal ceratopsian Psittacosaurus than those in more derived ceratopsians. The relatively large olfactory bulb, discernible floccular lobes, and relatively long semicircular canals suggest that the adult Liaoceratops had a keen sense of smell, a well-developed sensory input for the reflexive stabilisation of gaze and posture, and a nearly horizontal head posture. Based on its relatively short cochlear ducts, adult Liaoceratops likely vocalised at and heard more efficiently to relatively high frequencies than the derived ceratopsian Pachyrhinosaurus and Triceratops. The relatively well-developed semicircular canals suggest that adult Liaoceratops was agile biped and had a similar locomoter mode with adult Psittacosaurus.

Bone histology on Koreaceratops hwaseongensis (Dinosauria: Ceratopsia) from the Lower Cretaceous of South Korea

Koreaceratops hwaseongensis is a basal ceratopsian dinosaur found in the Lower Cretaceous Sihwa Formation (Albian), South Korea. It was found only with the lower part of the body. The right tibia and fibula exhibit poor histological preservation due to microbial degradation. They are characterized by signs of extensive tunneling by microorganisms, which rendered the bone cortex into an amalgam of microscopical globules and foci. Such signs of biodegradation may support the hypothesis that the Lower Cretaceous Korean peninsula had a semi-arid and seasonal wet-dry climate. However, a few remaining traces of histological features like the vasculature and absence/presence of growth marks indicate that the growth pattern of Koreaceratops is very similar to that of a subadult Protoceratops andrewsi. Both species exhibit zonation with some bone remodeling in their tibiae and lines of arrested growth with an extensive bone remodeling in their fibulae. The only histological similarity between Koreaceratops and the more basal ceratopsians Psittacosaurus is the longitudinal and reticular vasculature in their fibulae. These suggest that Koreaceratops is much closer to Protoceratops than Psittacosaurus in terms of phylogeny. The fibula of Koreaceratops shows a constant osseous drift that initially drifted toward the medial axis but abruptly changed to the anterior axis in the final growth interval. In addition, the right tibia's final growth exhibiting an anteromedial osseous drift suggests that Koreaceratops experienced a change in its right hindlimb's biomechanics before death. The number of growth zones in the tibia indicates that Koreaceratops was approximately eight years old when it died.

Testing for a dietary shift in the Early Cretaceous ceratopsian dinosaur Psittacosaurus lujiatunensis

AbstractMany dinosaurs may have shown ecological differentiation between hatchlings and adults, possibly because of the great size differential. The basal ceratopsian Psittacosaurus lujiatunensis is known from thousands of specimens from the Lower Cretaceous of China and these include many so‐called ‘juvenile clusters.’ During the early stages of ontogeny, P. lujiatunensis underwent a posture shift from quadrupedal to bipedal, and a dietary shift has also been postulated. In this study, we made a 2D mechanical analysis of the jaws of a hatchling and an adult to determine the differences between the two systems; we found some differences, but these were only modest. The adult was better suited to feeding on tough plant material than the hatchling, based on its higher values of absolute and relative bite forces and higher values of mechanical advantage, but there were no substantial shifts in jaw shape or function.

Ontogenetic braincase development in Psittacosaurus lujiatunensis (Dinosauria: Ceratopsia) using micro-computed tomography.

Ontogenetic sequences are relatively rare among dinosaurs, with Ceratopsia being one of the better represented clades, and especially among geologically earlier forms, such as Psittacosaurus. Psittacosaurus is a small, bipedal basal ceratopsian abundant in the Lower Cretaceous deposits of Asia, whose cranial and endocranial morphology has been well studied, but only cursory details have been published on the bones surrounding the brain. Using reconstructions created from micro-computed tomography scans of well-preserved skulls from the Barremian–Aptian Yixian Formation, China, we document morphological changes in the braincase of Psittacosaurus lujiatunensis through three growth stages, hatchling, juvenile, and adult, thus providing the first detailed study of ceratopsian braincase morphology through ontogeny. Notable ontogenetic changes in the braincase of P. lujiatunensis include a dramatic relative reduction in size of the supraoccipital, an increase in the lateral expansion of the paroccipital processes and a decrease in the angle between the lateral semicircular canal and the palatal plane. These ontogenetic morphological changes in the braincase relate to expansion of the cranium and brain through growth, as well as reflecting the switch from quadrupedal juveniles to bipedal adults as documented in the changing orientation of the horizontal semicircular canal through ontogeny. Recognition of these patterns in a basal ceratopsian has implications for understanding key events in later ceratopsian evolution, such as the development of the parieto-squamosal frill in derived neoceratopsians.

High-resolution computed tomographic analysis of tooth replacement pattern of the basal neoceratopsian Liaoceratops yanzigouensis informs ceratopsian dental evolution

The dental morphology and tooth replacement pattern of Liaoceratops yanzigouensis, the earliest known neoceratopsian, are important for our understanding of the evolution of the ceratopsian dental system. Here we describe the dental morphology and tooth replacement of Liaoceratops yanzigouensis based on high-resolution computed tomographic (CT) scan data of three specimens including the holotype, the first study for basal ceratopsian. The three-dimensional reconstructions reveal some important new information, including: three teeth in the premaxilla in one side, two more teeth in the dentary than in the maxilla, incipiently developed mesial grooves on some crowns, two generations of replacement teeth within some tooth families; and most functional teeth were under heavy resorption by the replacement process, but still remained functional. Comparisons of tooth pair positions from opposite sides in the four jaw quadrants of three specimens revealed a degree of bilateral symmetry in replacement pattern. Reconstruction of Zahnreihen yields an avergae z-spacing of 2.58 with simultaneous front-to-back tooth replacement. Our study presents the earliest evidence of derived neoceratopsian traits of the complex dental batteries in ceratopsids. Most significantly, our models reveal the tracts of partially resorbed functional teeth which appears to track the growth of the jaws, traits previously undocumented in Ceratopsia.

Postcranial anatomy of Yinlong downsi (Dinosauria: Ceratopsia) from the Upper Jurassic Shishugou Formation of China and the phylogeny of basal ornithischians

Ceratopsia includes some of the best-known ornithischian dinosaurs. Many species are erected based on cranial elements alone, and the postcranial skeletons are either missing or undescribed in many taxa. Here we provide the first detailed postcranial description of Yinlong downsi based on the holotype and eight other well-preserved skeletons. Yinlong downsi from the early Late Jurassic Shishugou Formation of the Wucaiwan area, Xinjiang, China, represents one of the most basal ceratopsians. The detailed study of the postcranial skeleton reveals one feature unique to it among ceratopsians: a blade-like prepubic process of the pubis with an elongate notch near its ventral margin. The postcranial material of Yinlong shares some unique features with that of the ornithischian Stenopelix valdensis from the Early Cretaceous of Germany, and provides further evidence that the latter is a basal ceratopsian. A comprehensive phylogenetic analysis of basal ornithischians was built based on 72 taxa and 380 characters. Most of the characters are illustrated for the first time in order to clarify character states. The new ornithischian phylogeny confirms that Yinlong belongs to Chaoyangsauridae. Chaoyangsaurids and Psittacosaurus form a monophyletic group that is sister to all other ceratopsians. The new phylogeny also supports Stenopelix valdensis as a basal ceratopsian, and Mosaiceratops to be close to Coronosauria. Additionally, the new phylogeny agrees with other recent analyses that place heterodontosaurids as the most basal ornithischians rather than with marginocephalians. Furthermore, Isaberrysaura, which has been hypothesized to be a basal ornithopod, is recovered as one of the most basal stegosaurs for the first time. The former ‘hypsilophodontid’ taxa are recovered within Ornithopoda rather than outside Cerapoda, and Jeholosauridae is shown to be valid in this analysis.

Structure and homology ofPsittacosaurustail bristles

AbstractWe examined bristle‐like appendages on the tail of the Early Cretaceous basal ceratopsian dinosaurPsittacosauruswith laser‐stimulated fluorescence imaging. Our study reveals previously unknown details of these structures and confirms their identification as integumentary appendages. For the first time, we show that most bristles appear to be arranged in bundles and that they exhibit a pulp that widens towards the bristle base. We consider it likely that the psittacosaur bristles are structurally and developmentally homologous to similar filamentous appendages of other dinosaurs, namely the basal heterodontosauridTianyulongand the basal therizinosauroid theropodBeipiaosaurus, and attribute the greater robustness of the bristles ofPsittacosaurusto a higher degree of cornification and calcification of its integument (both skin and bristles). Although the psittacosaur bristles are probably homologous with avian feathers in their origin from discrete cell populations, it is uncertain whether they developed from a follicle, one of the developmental hallmarks of true feathers. In particular, we note a striking resemblance between the psittacosaur bristles and the cornified spine on the head of the horned screamer,Anhima cornuta, an extant anseriform bird. Similar, albeit thinner keratinous filaments of extant birds are the ‘beard’ of the turkey,Meleagris gallopavo, and the crown of the Congo peafowl,Afropavo congensis. All of these structures of extant birds are distinct from true feathers, and because at least the turkey beard does not develop from follicles, detailed future studies of their development would be invaluable towards deepening our understanding of dinosaur filamentous integumentary structures.

Correction: A New Taxon of Basal Ceratopsian from China and the Early Evolution of Ceratopsia

There is an error in the caption title for Fig 6, “The squamosal of Yinlong downsi (IVPP V18641).” Please see the complete, correct Fig 6 caption here. Fig 6 The squamosal of Hualianceratops wucaiwanensis (IVPP V18641).

A New Taxon of Basal Ceratopsian from China and the Early Evolution of Ceratopsia.

Ceratopsia is one of the best studied herbivorous ornithischian clades, but the early evolution of Ceratopsia, including the placement of Psittacosaurus, is still controversial and unclear. Here, we report a second basal ceratopsian, Hualianceratops wucaiwanensis gen. et sp. nov., from the Upper Jurassic (Oxfordian) Shishugou Formation of the Junggar Basin, northwestern China. This new taxon is characterized by a prominent caudodorsal process on the subtemporal ramus of the jugal, a robust quadrate with an expansive quadratojugal facet, a prominent notch near the ventral region of the quadrate, a deep and short dentary, and strongly rugose texturing on the lateral surface of the dentary. Hualianceratops shares several derived characters with both Psittacosaurus and the basal ceratopsians Yinlong, Chaoyangsaurus, and Xuanhuaceratops. A new comprehensive phylogeny of ceratopsians weakly supports both Yinlong and Hualianceratops as chaoyangsaurids (along with Chaoyangsaurus and Xuanhuaceratops), as well as the monophyly of Chaoyangosauridae + Psittacosaurus. This analysis also weakly supports the novel hypothesis that Chaoyangsauridae + Psittacosaurus is the sister group to the rest of Neoceratopsia, suggesting a basal split between these clades before the Late Jurassic. This phylogeny and the earliest Late Jurassic age of Yinlong and Hualianceratops imply that at least five ceratopsian lineages (Yinlong, Hualianceratops, Chaoyangsaurus + Xuanhuaceratops, Psittacosaurus, Neoceratopsia) were present at the beginning of the Late Jurassic.

A psittacosaurid-like basal neoceratopsian from the Upper Cretaceous of central China and its implications for basal ceratopsian evolution.

Psittacosauridae (parrot-beaked dinosaurs) represents the first major radiation of ceratopsians (horned dinosaurs). However, psittacosaurids are divergent from the general morphology found in other ceratopsians, and this has resulted in their uncertain systematic position among ceratopsians. Here we describe a new basal neoceratopsian dinosaur, Mosaiceratops azumai gen. et sp. nov. based on a partial semi-articulated skeleton recovered from the Upper Cretaceous Xiaguan Formation of Neixiang County, Henan Province, China. Although our phylogenetic analysis supports this taxon as the most basal neoceratopsian, Mosaiceratops exhibits many features previously considered unique to the Psittacosauridae among the basal Ceratopsia. These include a relatively highly positioned external naris, a proportionally large premaxilla, the nasal extending ventral to the external naris, slender postorbital and temporal bars, a large notch between the basal tubera, and the edentulous premaxilla. Thus, the discovery of Mosaiceratops reduces the morphological disparity between the Psittacosauridae and other basal ceratopsians. Character optimization suggests that basal neoceratopsians have re-evolved premaxillary teeth; a major reversal previously unknown in any dinosaur clade. The new specimen also highlights the mosaic nature of evolution among early ceratopsians and supports the phylogenetic hypothesis that the Psittacosauridae is a relatively derived clade, rather than the most basal group of the Ceratopsia.

Histology and postural change during the growth of the ceratopsian dinosaur Psittacosaurus lujiatunensis

A few dinosaurs are inferred to have undergone an ontogenetic shift from quadrupedal-to-bipedal posture, or vice versa, based on skeletal allometry. The basal ceratopsian Psittacosaurus lujiatunensis is considered to have been mainly bipedal as an adult. Here we infer a postural shift in this species based on a novel combination of limb measurements and histological data. The forelimb is strongly negatively allometric relative to the hindlimb, and patterns of vascular canal orientation provide evidence that growth of the hindlimb was particularly rapid during the middle part of ontogeny. Histology also makes it possible to determine the ontogenetic ages of individual specimens, showing that the forelimb-to-hindlimb ratio changed rapidly during the first or second year of life and thereafter decreased gradually. Occurrence of an ontogenetic shift from quadrupedality to bipedality was evidently widespread in dinosaurs, and may even represent the ancestral condition for the entire group.

Morphology and Histology of Lattice‐like Ossified Epaxial Tendons in Psittacosaurus (Dinosauria: Ceratopsia)

Abstract:Epaxial tendons play an important role in the study of the musculoskeletal system and locomotory style of dinosaurs. Although the ossified epaxial tendon lattice is fairly well known in Iguanodontoidea, only recently has knowledge of this complex been extended to ceratopsians. This study concerns the gross morphology and microstructure of the tendon lattice in Psittacosaurus, a basal ceratopsian. As in the neoceratopsian Chasmosaurus, the ossified tendons of Psittacosaurus form a three‐layered, lattice‐like structure. The microstructure of the tendons in large psittacosaur individuals retains an early stage of ossification, as in juvenile birds and nestling hadrosaurs, suggesting a slow developmental rate of ossification of the tendons in psittacosaur ontogeny. Comparative study indicates that a lattice‐like arrangement of three‐layered epaxial tendons is widely distributed in Cerapoda. This pattern also extends to Ankylosauria, implying a similar pattern of the epaxial muscles through the ornithischian clade. In addition, comparison with crocodiles implies that the different morphology of ossified tendons in dinosaurs may be associated with adaptive aspects of their paleobiology, not simply a side effect of skeletal ossification. In contrast to the short tendons in quadrupedal Chasmosaurus and Protoceratops, the elongated tendons in Psittacosaurus may be related to the bipedal locomotion characteristic of this taxon.

First Record of a Basal Neoceratopsian Dinosaur from the Late Cretaceous of Kazakhstan

The oldest known ceratopsians come from the Late Jurassic of China (Zhao et al. 1999; Xu et al. 2006). During the Early Cretaceous, the basal ceratopsian Psittacosaurus was among the most common dinosaurs in Asia but more derived basal neoceratopsians were quite rare on that continent (Xu et al. 2002; Makovicky and Norell 2006). Basal neoceratopsians became more abundant in the Late Cretaceous of Mongolia and China, although they are not known in this region from the latest Cretaceous (You and Dodson 2004; Alifanov 2008). In contrast, basal neoceratopsians are rare during the Early Cretaceous in North America but became common and diverse during the Campanian and Maastrichtian (You and Dodson 2004; Chinnery and Horner 2007). Little is known about the evolutionary history of this group in more inland regions of what are now Kazakhstan and adjoining countries. Asiaceratops documents the presence of basal neoceratopsians in the Cenomanian of Uzbekistan (Nessov et al. 1989). Here we report on the first record...

Jaw Mechanics in Basal Ceratopsia (Ornithischia, Dinosauria)

Ceratopsian dinosaurs were a dominant group of herbivores in Cretaceous terrestrial ecosystems. We hypothesize that an understanding of the feeding system will provide important insight into the evolutionary success of these animals. The mandibular mechanics of eight genera of basal ceratopsians was examined to understand the variability in shape of the jaws and the early evolution of the masticatory system in Ceratopsia. Data were collected on lever arms, cranial angles and tooth row lengths. The results indicate that psittacosaurids had higher leverage at the beak and in the rostral part of the tooth row than basal neoceratopsians, but lower leverage in the caudal part of the tooth row. Although the vertebrate mandible is generally considered as a third-class lever, that of basal neoceratopsians acted as a second-class lever at the caudal part of the tooth row, as is also true in ceratopsids. When total input force from the mandibular adductor muscles on both sides of the skull is considered, the largest bite force in basal ceratopsian tooth rows was exerted in the caudal part of the tooth row at the caudal extremity of the zone with near-maximum input force. Medially positioned teeth generate higher leverage than laterally positioned teeth. The largest bite force in all basal ceratopsians is smaller than the maximum input force, a limit imposed by the morphology of the basal ceratopsian masticatory system. In ceratopsids, caudal extension of the tooth row resulted in a much larger bite force, even exceeding the maximum input force.

Comparative anatomy of selected basal ceratopsian dentitions

The dental structure of basal ceratopsians is described. Evolutionary trends in maxillary and dentary teeth of basal ceratopsians include decrease and possible loss of enamel on the occluding side of tooth crowns, increase in the angle of wear facet, development of a prominent primary ridge and deep indentations on mesial and distal sides of the primary ridge, and increase in tooth size in neoceratopsians. Premaxillary teeth in the basalmost ceratopsian Yinlong and basal neoceratopsian Archaeoceratops oshimai exhibit wear facets and denticles along the carina, which imply use for feeding. Maxillary and dentary teeth of basal ceratopsians were probably not as effective in feeding as those in ceratopsids because of the relatively less prominent primary ridges. Some dental characters can be used to identify taxon and tooth position of isolated basal ceratopsian teeth.

A basal ceratopsian with transitional features from the Late Jurassic of northwestern China

Although the Ceratopsia and Pachycephalosauria, two major ornithischian groups, are united as the Marginocephalia, few synapomorphies have been identified due to their highly specialized body-plans. Several studies have linked the Heterodontosauridae with either the Ceratopsia or Marginocephalia, but evidence for these relationships is weak, leading most recent studies to consider the Heterodontosauridae as the basal member of another major ornithischian radiation, the Ornithopoda. Here, we report on a new basal ceratopsian dinosaur, Yinlong downsi gen. et. sp. nov. from the Late Jurassic upper part of the Shishugou Formation of Xinjiang, China. This new ceratopsian displays a series of features transitional between more derived ceratopsians and other ornithischians, shares numerous derived similarities with both the heterodontosaurids and pachycephalosaurians and provides strong evidence supporting a monophyletic Marginocephalia and its close relationship to the Heterodontosauridae. Character distributions along the marginocephalian lineage reveal that, compared to the bipedal Pachycephalosauria, which retained a primitive post-cranial body-plan, the dominantly quadrupedal ceratopsians lost many marginocephalian features and evolved their own characters early in their evolution.

A new species of Psittacosaurus (Dinosauria: Ceratopsia) from the Early Cretaceous Yixian Formation, Liaoning, China

Newly discovered, well-preserved skulls and mandibles from the lowest part of the Early Cretaceous Yixian Formation, western Liaoning Province, China, document the earliest known record of psittacosaurs and provide the basis for recognition of a new species, Psittacosaurus lujiatunensis. This discovery increases the taxonomic diversity of psittacosaurs to eight valid species and extends the stratigraphic range of the family Psittacosauridae from late Barremian-Albian to Hauterivian. Comparative study of the new species with other well-known psittacosaurs indicates that the new taxon is probably the most basal member of the psittacosaur clade now known. This interpretation is in agreement with the temporal distribution of the clade and supports the hypothesis that the Psittacosauridae originated from the basal ceratopsian stem no later than the earliest part of the Cretaceous.