Basal Ornithopod Research Articles

Postcranial anatomy of Jeholosaurus shangyuanensis (Dinosauria, Ornithischia) from the Lower Cretaceous Yixian Formation of China

ABSTRACT Jeholosaurus shangyuanensis is a small ornithischian dinosaur from the Lower Cretaceous Yixian Formation of the Lujiatun locality, Liaoning Province, China. Here, we provide the first detailed description of its postcranial skeleton based on the holotype and four other well-preserved skeletons, and compare it with material of other primitive cerapodans. Jeholosaurus can be diagnosed on the basis of one postcranial autapomorphy, relating to the absence of parapophyses from the anterior dorsal vertebrae, and a unique combination of postcranial characters, but its anatomy is otherwise similar to that of many other basal ornithischians. A phylogenetic analysis incorporating these new postcranial data confirms previous suggestions that Jeholosaurus is a basal ornithopod and that it forms a clade with Changchunsaurus and Haya; Koreanosaurus and Yueosaurus might also belong to this clade, though additional material of both will be required to test this hypothesis. The name Jeholosauridae is proposed for this apparently endemic group of Cretaceous East Asian taxa.

Phylogeny, Histology and Inferred Body Size Evolution in a New Rhabdodontid Dinosaur from the Late Cretaceous of Hungary

BackgroundRhabdodontid ornithopod dinosaurs are characteristic elements of Late Cretaceous European vertebrate faunas and were previously collected from lower Campanian to Maastrichtian continental deposits. Phylogenetic analyses have placed rhabdodontids among basal ornithopods as the sister taxon to the clade consisting of Tenontosaurus, Dryosaurus, Camptosaurus, and Iguanodon. Recent studies considered Zalmoxes, the best known representative of the clade, to be significantly smaller than closely related ornithopods such as Tenontosaurus, Camptosaurus, or Rhabdodon, and concluded that it was probably an island dwarf that inhabited the Maastrichtian Haţeg Island.Methodology/Principal FindingsRhabdodontid remains from the Santonian of western Hungary provide evidence for a new, small-bodied form, which we assign to Mochlodon vorosi n. sp. The new species is most similar to the early Campanian M. suessi from Austria, and the close affinities of the two species is further supported by the results of a global phylogenetic analysis of ornithischian dinosaurs. Bone histological studies of representatives of all rhabdodontids indicate a similar adult body length of 1.6–1.8 m in the Hungarian and Austrian species, 2.4–2.5 m in the subadults of both Zalmoxes robustus and Z. shqiperorum and a much larger, 5–6 m adult body length in Rhabdodon. Phylogenetic mapping of femoral lengths onto the results of the phylogenetic analysis suggests a femoral length of around 340 mm as the ancestral state for Rhabdodontidae, close to the adult femoral lengths known for Zalmoxes (320–333 mm).Conclusions/SignificanceOur analysis of body size evolution does not support the hypothesis of autapomorhic nanism for Zalmoxes. However, Rhabdodon is reconstructed as having undergone autapomorphic giantism and the reconstructed small femoral length (245 mm) of Mochlodon is consistent with a reduction in size relative to the ancestral rhabdodontid condition. Our results imply a pre-Santonian divergence between western and eastern rhabdodontid lineages within the western Tethyan archipelago.

A new basal ornithopod dinosaur from the Barremian of Galve, Spain

A partially articulated postcranial skeleton of a small ornithischian dinosaur, Gideonmantellia amosanjuanae nov. gen. et sp., from the Early Cretaceous of Galve (Teruel province, Spain) is described. It was recovered in an outcrop of fluvial red clays from the Camarillas Formation, which is Barremian in age. This partial skeleton is recognised as a new ornithopod taxon by the following autapomorphies: (1) postacetabular process of the ilium with a brevis shelf that is noticeably medially expanded in its cranial part but narrow and horizontal in its caudal part; (2) rod-like prepubic process with its anterior end twisted and expanded; and (3) L-shaped first chevron. Our phylogenetic analysis indicates that Gideonmantellia represents a basal ornithopod taxon more derived than Orodromeus, the “Asian clade” (which includes Haya and others) and Hypsilophodon.

Biological implications of the bone microstructure of the Late Cretaceous Ornithopod Dinosaur Gasparinisaura cincosaltensis

ABSTRACT Here we present the bone histology of Gasparinisaura cincosaltensis, a basal ornithopod from the Late Cretaceous of Patagonia, and discuss its biological implications. The sample includes axial and appendicular elements from several specimens of different ontogenetic stages. The cortex of most bones consists of fibro-lamellar tissue, with mainly longitudinally oriented vascular spaces, which suggests rapid osteogenesis and fast growth. However, the fibro-lamellar bone is commonly interrupted by lines of arrested growth and/or annuli composed of parallel-fibered bone that indicates that the rapid growth was periodic. Although a true outer circumferential layer was not recorded in any of the sampled elements, in several of the larger samples the woven-fibered matrix of the inner and middle cortex grades into a parallel-fibered tissue, which suggests that the attainment of sexual maturity occurred before skeletal maturity. The growth dynamics of Gasparinisaura are similar to those reported in other basal ornithopods. Inter-elemental, as well as intraspecific, variations in histology were observed in Gasparinisaura. Such variation could be the result of sexual dimorphism, or the effect of localized conditions of growth, or perhaps plasticity in growth in response to local environmental conditions.

Vertebrate fossils (Dinosauria) from the Bonnet Plume Formation, Yukon Territory, Canada

Dinosaurs and other terrestrial vertebrates are poorly documented in the Mesozoic of the Canadian polar region. Here, we provide a complete review of the Upper Cretaceous (Maastrichtian) vertebrate fauna of the Bonnet Plume Formation in the northeastern Yukon Territory, Canada, which includes the description of the first newly collected dinosaur bones from this unit in almost half a century. Previously reported fragmentary dinosaur remains collected in the early 1960’s pertain to an indeterminate hadrosaurid. New material includes a poorly preserved forelimb bone and a pedal phalanx. These new remains pertain to at least one species of non-hadrosaurid ornithischian dinosaur, and the humerus is tentatively referred to a small-bodied basal ornithopod. The new vertebrate fossils from the Bonnet Plume Formation provide further evidence of vertebrates from this unit. However, directed field surveys in 2008 and 2009 suggest that vertebrate fossils are not abundant. A review of the known localities of terrestrial Mesozoic vertebrates from the Canadian Arctic indicate that it had a relatively diverse community of terrestrial vertebrates, including dinosaurs, during the Late Cretaceous, but emphasizes our limited knowledge of the Mesozoic Arctic and considerable potential for future exploration and discovery.

Osteological correlates for quadrupedality in ornithischian dinosaurs

The evolution of quadrupedality from bipedal ancestors is an exceptionally rare transition in tetrapod evolution, but it has occurred several times within the herbivorous dinosaur clade Ornithischia. Stegosauria, Ankylosauria, and Ceratopsidae are all uncontroversially quadrupedal, while basal ornithischians and basal ornithopods are uncontroversially bipedal. However, stance in iguanodontian ornithopods, including the hadrosaurs, and in non-ceratopsid ceratopsians is debated because robust osteological correlates of quadrupedality have not been identified. We examine a suite of characteristics that have been previously proposed as osteological correlates for bipedality or quadrupedality in dinosaurs. These include both discrete anatomical features, which we assess as correlates for quadrupedality using character optimization onto a composite cladogram, and proportional ratios, which we assess as correlates by reconstructing nodal ancestral states using squared-change parsimony, followed by optimization. ...

A new basal ornithopod dinosaur (Frenchman Formation, Saskatchewan, Canada), and implications for late Maastrichtian ornithischian diversity in North America

A small, articulated basal ornithopod skeleton from the Frenchman Formation (late Maastrichtian) of Saskatchewan (RSM P 1225.1), previously referred to the taxon Thescelosaurus, differs from both recognized species of this taxon (Thescelosaurus neglectus and Thescelosaurus garbanii). The differences are taxonomically informative and we recognize this specimen as the holotype of a new species, Thescelosaurus assiniboiensis sp. nov., diagnosed by the presence of two autapomorphies, and displaying plesiomorphic traits more similar to those of Parksosaurus, than to those of the other Thescelosaurus species. The Frenchman Formation also harbours an intriguing faunal assemblage in which Thescelosaurus represents one of the most abundant dinosaur taxa, and preserves a relatively high proportion of small (putatively juvenile and subadult) specimens of many dinosaur taxa. Further work that increases the faunal sample from this formation, and that permits quantitative comparisons with contemporary formations, will determine whether or not these differences are well supported, and will determine their ultimate palaeobiological significance. Identification of a third species of Thescelosaurus from the late Maastrichtian of North America suggests that this taxon was more diverse than previously recognized, and shows an increase in diversity from the Campanian through the late Maastrichtian, contrasting the trends seen in most other ornithischian clades. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 163, 1157–1198.

A new ornithischian dinosaur from the Cretaceous Liangtoutang Formation of Tiantai, Zhejiang Province, China

A new ornithischian dinosaur, Yueosaurus tiantaiensis gen. et sp. nov., is erected based on a partial postcranial skeleton from the Liangtoutang Formation (Aptian–Cenomanian) of Zhejiang Province, China. It differs from other ornithischians in possessing the following unique combination of characters: prominent and slightly ventrally directed cervical parapophyses; anteroposteriorly narrow neural spines on caudal vertebrae; scapula with a ventroscapular groove, supraglenoidal buttress, supraglenoid fossa, and a strong anteroventral expansion of the scapular blade. Yueosaurus represents the first basal ornithopod taxon from southeastern China. It expands our understanding of the Cretaceous dinosaurian fauna of Zhejiang Province.

Basal ornithopod (Dinosauria: Ornithischia) teeth from the Prince Creek Formation (early Maastrichtian) of Alaska

A diverse and prolific record of polar dinosaurs comes from the Upper Cretaceous (Campanian–Maastrichtian) sediments of the Prince Creek Formation exposed on Alaska’s North Slope. Previous assignment of basal ornithopod material from this formation has been based solely on teeth, which have either been referred to “hypsilophodontid” indet. or Thescelosaurus sp. Here, we re-examine this material and describe several new specimens, including five isolated premaxillary teeth and three cheek teeth. The premaxillary teeth are most similar to those of Thescelosaurus , whereas the cheek teeth are more similar to its sister taxon Parksosaurus , for which premaxillary teeth are unknown. Referral of this new material to Thescelosaurus would represent the oldest occurrence of this taxon and considerably extend its stratigraphic range. A more likely possibility is that the premaxillary teeth are referable to Parksosaurus, an interpretation that is more parsimonious from a stratigraphic perspective. Intriguingly, one cheek tooth previously referred to as “hypsilophodontid” cannot be referred to either Thescelosaurus or Parksosaurus. Previously, faunal comparisons of the Prince Creek Formation have largely been made with non-contemporaneous formations, including the Campanian-aged Judith River and Aguja formations, or to the latest Maastrichtian Hell Creek Formation. On the basis of age and faunal similarities, a more appropriate comparison should be made with coeval rocks of the Horseshoe Canyon. This study expands our knowledge of Cretaceous ornithischian diversity at polar paleolatitudes and underscores the importance of small, rare, or easily misidentified fossils in paleoecological studies.

A new basal ornithopod (Dinosauria, Ornithischia) from the Late Cretaceous of Mongolia

ABSTRACT Basal ornithopods exhibit a very low diversity in Cretaceous deposits of Asia, with only two diagnostic taxa published to date. A new basal ornithopod, Haya griva, gen. et sp. nov., is described here based on several well-preserved specimens from the Late Cretaceous Javkhlant Formation of Mongolia. Haya is diagnosed by a unique combination of characters, some of which are also present in other Asian Cretaceous basal ornithopods such as a bifid caudal ramus of the jugal and a tapering and beveled predentary. Traits, such as presence of separate maxillary fenestra, otherwise only known in Hypsilophodon, show more homoplastic distributions. Phylogenetic analysis provides weak support for grouping Haya with the Chinese Cretaceous taxa Jeholosaurus and Changchunsaurus, suggesting a greater hidden diversity of such animals in Asia. The most complete prepared specimen of Haya exhibits a sizeable gastrolith mass, representing only the second occurrence among ornithopods.

The postcranial osteology and phylogenetic position of the small ornithischian dinosaur Changchunsaurus parvus from the Quantou Formation (Cretaceous: Aptian–Cenomanian) of Jilin Province, north‐eastern China

Abstract: Ornithopods were the most important group of Cretaceous ornithischians and achieved high levels of abundance and taxonomic diversity. An understanding of the phylogeny, early evolution and diagnosis of the clade is hampered by a shortage of detailed anatomical descriptions of basal taxa. One of the most important basal ornithopod taxa discovered in recent years is Changchunsaurus parvus, from the Quantou Formation (‘middle’ Cretaceous) of Jilin Province, China, represented by excellent cranial and postcranial material. Here, we present the first description of the postcranial anatomy of the holotype specimen of Changchunsaurus and provide comparisons to other basal cerapodans and basal ornithopods. A phylogenetic analysis finds relationships amongst basal ornithopods to be extremely poorly resolved, but supports a sister‐group relationship between Changchunsaurus and Jeholosaurus shangyuanensis from the Yixian Formation (late Barremian–early Aptian) of Liaoning Province, China. Numerous characters distinguish the two taxa, supporting their generic distinction. The proposed sister‐group relationship suggests that an endemic clade of small‐bodied bipedal ornithopods existed in north‐east China during the Early to ‘middle’ Cretaceous.

A new basal ornithopod dinosaur from the Upper Cretaceous of South Korea

A new basal ornithopod dinosaur from the Upper Cretaceous of South Korea

A reappraisal of the Cretaceous non-avian dinosaur faunas from Australia and New Zealand: evidence for their Gondwanan affinities

It has often been assumed that Australasian Cretaceous dinosaur faunas were for the most part endemic, but with some Laurasian affinities. In this regard, some Australasian dinosaurs have been considered Jurassic relicts, while others were thought to represent typical Laurasian forms or endemic taxa. Furthermore, it has been proposed that some dinosaurian lineages, namely oviraptorosaurians, dromaeosaurids, ornithomimosaurians and protoceratopsians, may have originated in Australia before dispersing to Asia during the Early Cretaceous. Here we provide a detailed review of Cretaceous non-avian dinosaurs from Australia and New Zealand, and compare them with taxa from other Gondwanan landmasses. Our results challenge the traditional view of Australian dinosaur faunas, with the majority of taxa displaying affinities that are concordant with current palaeobiogeographic models of Gondwanan terrestrial vertebrate faunal distribution. We reinterpret putative Australian ‘hypsilophodontids’ as basal ornithopods (some of them probably related to South American forms), and the recently described protoceratopsians are referred to Genasauria indet. and Ornithopoda indet. Among Theropoda, the Australian pigmy ‘Allosaurus’ is referred to the typical Gondwanan clade Abelisauroidea. Similarities are also observed between the enigmatic Australian theropod Rapator, Australovenator and the South American carcharodontosaurian Megaraptor. Timimus and putative oviraptorosaurians are referred to Dromaeosauridae. The present revision demonstrates that Australia's non-avian Cretaceous dinosaurian faunas were reminiscent of those found in other, roughly contemporaneous, Gondwanan landmasses, and are suggestive of faunal interchange with these regions via Antarctica.

Стратиграфия Маастрихтских отложений бассейна р. Каканаут (восточная часть Корякского нагорья)

Recent discovery of rich dinosaur fauna at high latitudes in northeastern Russia required the additional investigation of the Kakanaut locality for more precise definition of its age and stratigraphic position. This locality is situated in the southern part of the Koryak Upland, in the Kakanaut River basin near Pekulneyskoe Lake (Chukotka Autonomous Region). In the result of field work 2007-2009, five particular sections were described and joint geological column of the Maastrichtian deposits was composed. In this column three parts were distinguished: the marine siltstone strata, the Kakanaut Formation and the Kokuy strata. The Maastrichtian deposits are covered by effusive-pyroclastic deposits (possibly, early Paleogene in age). The marine siltstone strata contains inocerams and ammonites of the lower and lower part of upper Maastrichtian (Inoceramus (Cataceramus) pilvoensis Sok., Schachmaticeramus shikotanensis (Nagao et Mat.) Schachmaticeramus kusiroensis (Nagao et Mat.). Hypophylloceras marshalli (Shimizu), Diplomoceras sp., Pachydiscus subcompressus Mat.). The Kokuy strata contains remains of the late Maastrichtian-early Palaeocene foraminifers (Rzehakina epigone zone) and of undetermined fragments of ammonites. The Kakanaut Formation are represented by nonmarine volcanogenous-terrigenous sediments. It consists of tuffaceous sandstone and siltstones, tuffs, tuffites and andesite-basaltic rocks and represents lacustrine and fluviodeltaic deposition on near-sea lowland. These deposits contain joint association of fossil plants and dinosaur bones, teeth and eggshell fragments. The dinosaur assemblage represented by basal ornithopods, hadrosaurids, ankylosaurians, neoceratopsians, troodontids, dromaeosaurids and tyrannosaurids. Dinosaur eggshell fragments, belonging to hadrosaurids and non-avian theropods, indicate that at least several dinosaur taxa could reproduce in polar region. The Kakanaut flora includes about 50 taxa. The cycadophytes (Nilssonia, Encephalartopsis) and Ginkgo are very abundant in certain layers. The conifers are represented by mixture of the typical Late Cretaceous elements with an admixture of younger Paleocene elements belonging to families Taxodiaceae, Cupressaceae and Pinaceae. Angiosperms include about 30 species. Families that can be confidently recognized are Platanaceae (Platanus), Cercidiphyllaceae (Trochodendroides), Betulaceae (Corylus), Fagaceae (Fagopsiphyllum), Rosaceae (Peculnea, Arctoterum). Other species appear to belong to ancient groups, without clear phylogenetic links to modern taxa. The age of the fossiliferous beds can be estimated as the beginning of late Maastrichtian. The correlation of the Maastrichtian deposits of different areas at eastern part of Koryak Upland was carried out.

Ichnological evidence for small quadrupedal ornithischians from the basal Cretaceous of SE Asia and North America: implications for a global radiation

Abstract Tracks of small quadrupedal ornithischians with five manual and four pedal digits have been recorded from sedimentary rocks near the Late Jurassic–Early Cretaceous (Tithonian–Berriasian) boundary in NE Thailand and British Columbia. These are compared with larger tracks of gracile, quadrupedal ornithopods from the earliest Cretaceous of Spain and smaller tracks of a quadruped of unknown age from Zimbabwe. The Thai and Canadian tracks are similar to the Early Jurassic (Liassic) ichnogenus Anomoepus and the small ornithopod tracks from the Late Jurassic of Spain. They are the only known post-Liassic ornithischian tracks in which up to five discrete manus digit impressions are clearly visible. Based on strong heteropody (manus much smaller than pes) in all cases we infer an ornithopod trackmaker rather than another ornithischian. The scattered, but widespread earliest Cretaceous occurrence of this ichnotaxon, herein assigned to Neoanomoepus perigrinatus ichnogen. and ichnosp. nov., on the basis of type material from Canada, suggests that these hitherto unknown earliest Cretaceous ichnofaunas may represent a radiation of small basal ornithopods (pes length less than 15 cm), appearing before the widespread radiation of large ornithopods (pes length up to 60 cm or more) later in the Neocomian (Valanginian–Barremian), Aptian–Albian and Late Cretaceous. The primitive condition of the trackmaker is indicated by the pedal and manual morphology, which consists of four and five digits respectively that are not enclosed by well-developed fleshy padding or integument. In contrast, all larger Cretaceous ornithopod tracks, mostly from post-Berriasian strata, have only three pedal digits enclosed in fleshy pads and a manus in which all functional digits are reduced and enclosed by substantial flesh.

The ‘dermal armour’ of the ornithopod dinosaur Hypsilophodon from the Wealden (Early Cretaceous: Barremian) of the Isle of Wight: a reappraisal

The small ornithopod dinosaur Hypsilophodon foxii, from the Early Cretaceous (Barremian) of the Isle of Wight, England, is one of the best known of all dinosaurs; however, the reported presence of dermal armour in this taxon is poorly understood. We reassess the evidence for dermal armour: in all specimens in which they can be identified the plate-like structures formerly identified as armour are associated with the lateral surfaces of the distal sections of the anterior dorsal ribs. Comparison with the ornithopods Talenkauen and Thescelosaurus suggests that these structures do not represent armour, but are instead mineralised cartilaginous intercostal plates. Such plates were probably widespread in basal ornithopods, but have not been recognised to date due to incomplete preservation or variation in the timing and degree of mineralisation.

AN OSSIFIED TENDON TRELLIS IN CHASMOSAURUS (ORNITHISCHIA: CERATOPSIDAE)

The ornithischia and its sister group, the Saurischia, comprise the Dinosauria. Ornithischians (Weishampel, 2004) are a diverse group of primarily quadrupedal herbivores that include such familiar dinosaurs as the armored stegosaurs and ankylosaurs (Thyreophora), as well as the duckbilled hadrosaurs, pachycephalosaurs, and ceratopsians (Cerapoda). The Ceratopsia (You and Dodson, 2004) includes a number of relatively small basal forms such as psittacosaurs and Neoceratopsia, which comprises protoceratopsids and the larger, more derived horned Ceratopsidae. Ossified tendons occur throughout the body of many birds (Vanden Berge and Storer, 1995), but reports in other Saurischia are rare (but see Sereno et al., 2004). However, they occur in nearly all ornithischian dinosaurs except stegosaurs (Sereno and Dong, 1992). The presence of ossified tendons above the sacrum is thought to be a diagnostic character of the Ornithischia (Weishampel, 2004). Many taxa also develop them in association with the caudal and/or thoracic vertebrae. Ossified tendons usually occur in bundles along the epaxial region of the vertebral column and the hypaxial region of the tail in basal ornithopods such as Hypsilophodon Galton, 1974. Similar tendon bundles are known in pachycephalosaurs (Sues and Galton, 1987) and ankylosaurs possess tendons associated with the tail “club” (Coombs, 1995). The ornithopod group Iguanodontoidea (Hadrosauridae and Iguanodontidae plus Protohadros Head, 1998 and Ouranosaurus Taquet, 1976) developed a rhomboidal trellis of ossified tendons (Fig. 1), often considered to be synapomorphic (e.g., Sereno, 1999), along the dorsal side of their vertebral columns (Dollo, 1886; Brown, 1916; Parks, 1920; Lull and Wright, 1942; Norman, 1980, 1986; Prieto-Marquez, 2001; Horner et al., 2004). Note that Hadrosauriformes is synonymous with Iguanodontoidea, but the latter is preferred (Norman, 2004) and used here. Figure 1 — Brachylophosaurus canadensis Sternberg, 1953, MOR 794. Posterior thoracic vertebrae showing the ossified tendon trellis …

A new abelisauroid theropod from northwestern Patagonia

The Argentinean record of abelisauroid theropods begins in the Early Cretaceous (Ligabueino) and spans most of the Late Cretaceous, from Cenomanian (Ilokelesia, Xenotarsosaurus, and Ekrixinatosaurus) to Campanian–Maastrichtian (Abelisaurus, Carnotaurus, Aucasaurus, and Noasaurus). A fragmentary specimen of a theropod dinosaur was collected in 2000 from the middle section of the Lisandro Formation (Turonian?) at Cerro Bayo Mesa, Neuquén Province, Argentina. The fossil-bearing level, which is part of the Lisandro Formation that also yielded the remains of the basal ornithopod Anabisetia saldiviai, corresponds to a reddish, massive mudstone linked with fluvial channel deposits. The theropod identified as MCF-PVPH-237 is an abelisauroid theropod that increases our knowledge about the evolution of South American Abelisauroidea and is the first record of this clade from the Lisandro Formation.