Basal Tetanuran Research Articles

Theropod teeth from the Middle-Upper Jurassic Shishugou Formation of northwest Xinjiang, China

ABSTRACT Sixteen isolated theropod teeth were discovered in two areas in the upper Middle–lower Upper Jurassic Shishugou Formation of the Xinjiang Uyghur Autonomous Region, northwest China. This sample can be divided on the basis of qualitative features and simple quantitative metrics into seven tooth morphotypes, each of which probably represents a distinct taxon. Three of the morphotypes may be attributable to theropods already known from the Shishugou Formation, namely the alvarezsauroid Haplocheirus and the basal tetanurans Monolophosaurus and Sinraptor. The other four morphotypes, however, appear to represent new taxa, taking the known theropod diversity of the Shishugou Formation from six species to at least ten. One of the new taxa is probably a dromaeosaurid. Another appears to represent a troodontid or a relative of the potentially troodontid-like Paronychodon, itself so far known only from isolated teeth. Of the remaining two taxa, one appears to be a basal tetanuran or tyrannosauroid, whereas the other either belongs to one of these same groups or represents a ceratosaur. The probable deinonychosaurian teeth in our sample are among the oldest fossils known for this clade, and highlight the diversity of coelurosaurs in the Shishugou Formation.

The evolution of large-bodied theropod dinosaurs during the Mesozoic in Asia

The fossil record of large-bodied, apex carnivorous theropod dinosaurs in Eastern Asia is now among the best understood in the world, thanks to new discoveries and reinterpretations of long-neglected fossils. Asia boasts the most complete record of Middle Jurassic theropods globally, as well as one of the best-studied Late Cretaceous theropod faunas, and new research is helping to fill what was previously a 60-million-year gap in the Early-mid Cretaceous fossil record of large Asian predators. In general, the bio-geographic affinities of large-bodied Asian theropods over time were intimately related to physical geography, and progressively more derived theropod clades evolved large body size and occupied the apex predator niche throughout the Jurassic and Cretaceous. During the Middle Jurassic, largely endemic clades of basal tetanurans were prevalent in Asia, whereas during the Late Jurassic mid Cretaceous more derived “intermediate” tetanuran theropods with cosmopolitan affinities occupied the large predator role, including sinraptorids, spinosauris, and carcharodontosaurians. Finalli, during the final 20 million years of the Cretaceous, more derived, bird-like coelurosaurs attained large body size. Foremost among these were the tyrannosaurids, a radiation of northern (Asian and North American) megapredators whose ascent into the apex predator niche was a delayed event restricted to the Campanian-Masastrichian. As Asia is the focus of intense ongoing dinosaur fieldwork, our undestarnding of large-bodied theropod evolution will continue to be refined with future discoveries.

A Large Abelisauroid Theropod Dinosaur from the Early Cretaceous of Libya

Despite increasingly intensive paleontological sampling, Cretaceous terrestrial vertebrates from continental Africa remain relatively poorly known, frustrating efforts to characterize paleoecosystems in the region, as well as the paleobiogeography of the southern continents during this interval. Here we describe the partial skeleton of a large-bodied theropod dinosaur from the Early Cretaceous (early Aptian, ~125-120 Ma) of Libya. The specimen consists of associated elements (two incomplete dorsal vertebrae, a proximal caudal centrum, a partial proximal caudal neural arch, the distal right femur, and the mostly complete right tibia) and is referable to the widespread ceratosaurian clade Abelisauroidea. The discovery adds to the growing record of abelisauroids from mainland Africa, and firmly establishes the presence of the clade on the continent prior to its final separation from South America. Indeed, the age of the Libyan theropod predates or is penecontemporaneous with the accepted timing of fragmentation of most major Gondwanan landmasses, supporting the hypothesis that abelisauroids could have dispersed throughout the southern continents before land connections between these areas were severed. Moreover, the considerable size of the Libyan form challenges assertions that abelisauroids were ecologically subordinate to basal tetanuran theropods in Early and middle Cretaceous paleoenvironments of Gondwana.

A New Large-Bodied Theropod Dinosaur from the Middle Jurassic of Warwickshire, United Kingdom

Previously undocumented postcranial material from the Chipping Norton Limestone Formation (Middle Jurassic: Lower Bathonian) of Cross Hands Quarry, near Little Compton, Warwickshire represents a new large-bodied theropod dinosaur, distinct from the contemporaneous Megalosaurus bucklandii. Cruxicheiros newmanorum gen. et sp. nov. is diagnosed by a single autapomorphy, the presence of a proximomedially inclined ridge within the groove that marks the lateral extent of the posterior flange of the femoral caput (trochanteric fossa). C. newmanorum shows three tetanuran features: widely separated cervical zygapophyses, a swollen ridge on the lateral surface of the iliac blade and an anterior spur of the caudal neural spines. However, due to fragmentary preservation its affinities within Tetanurae remain uncertain: phylogenetic analysis places it as the most basal tetanuran, the most basal megalosauroid (= spinosauroid) or the most basal neotetanuran.

Non-avian theropod dinosaurs from the early Late Cretaceous of central Europe

Quantitative and qualitative analyses of isolated teeth and postcranial elements of non-avian theropod dinosaurs from the Upper Cretaceous (Santonian) Csehbánya Formation, Iharkút (western Hungary) indicate that these remains represent multiple dinosaur groups. Based on comparative and statistical analyses, 58 teeth and tooth fragments are identified as belonging to medium-sized basal tetanuran theropods that may have represented the top-predator of the terrestrial Iharkút ecosystem. These teeth are almost identical with the two ‘ Megalosaurus pannoniensis’ teeth from the lower Campanian of Muthmannsdorf (Austria) and show a notable similarity to teeth of the Middle Jurassic M. bucklandii and the Lower Cretaceous ‘ M. dunkeri’ from England. A single pedal ungual phalanx is interpreted as the oldest European occurrence of Late Cretaceous abelisaurids, as suggested by a ventral groove and bifurcated grooves laterally bordering a convex, triangular area. Small-bodied paravian theropods are found to be the best represented group in Iharkút, including teeth, caudal vertebrae, a metacarpal III, manual phalanges, and a fragmentary left tibia. A particularly notable paravian remain is a complete left scapulocoracoid possessing a unique pneumatic foramen ventral to the coracoid foramen. This specimen is assigned to Pneumatoraptor fodori n. g. et sp. Finally, numerous postcranial elements of Theropoda indet. were recovered, including a fragmentary sacrum that offers new insights into the sacral pneumaticity of theropods. The presence of these theropods in the Santonian Iharkút ecosystem provides the first evidence that during the early Late Cretaceous the Mediterranean archipelago was inhabited by both Gondwanan and Euramerican members of theropod dinosaurs. Consistent with data available for other archosaurian taxa, the close relationship of the basal tetanuran teeth with much older forms suggests that the Iharkút area may have functioned as a refugium in the early Late Cretaceous Mediterranean archipelago.

The skull of Monolophosaurus jiangi (Dinosauria: Theropoda) and its implications for early theropod phylogeny and evolution

The Middle Jurassic was a critical time in the evolution of theropod dinosaurs, highlighted by the origination and initial radiation of the large-bodied and morphologically diverse Tetanurae. Middle Jurassic tetanurans are rare, but have been described from Europe, South America and China. In particular, China has yielded a number of potential basal tetanurans, but these have received little detailed treatment in the literature. Chief among these is Monolophosaurus jiangi, known from a single skeleton that includes a nearly complete and well-preserved skull characterized by a bizarre cranial crest. Here, we redescribe the skull of Monolophosaurus, which is one of the most complete basal tetanuran skulls known and the only quality source of cranial data for Middle Jurassic Chinese theropods. The cranial crest is atomized into a number of autapomorphic features and several characters confirm the tetanuran affinities of Monolophosaurus. However, several features suggest a basal position within Tetanurae, which contrasts with most published cladistic analyses, which place Monolophosaurus within the more derived Allosauroidea. Cranial characters previously used to diagnose Allosauroidea are reviewed and most are found to have a much wider distribution among Theropoda, eroding an allosauroid position for Monolophosaurus and questioning allosauroid monophyly. The use of phylogenetic characters relating to theropod cranial crests is discussed and a protocol for future use is given. The systematic position of Guanlong wucaii is reviewed, and a basal tyrannosauroid affinity is upheld contrary to one suggestion of a close relationship between this taxon and Monolophosaurus. (C) 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2010, 158, 573-607.

The evolution of large-bodied theropod dinosaurs during the Mesozoic in Asia

The fossil record of large-bodied, apex carnivorous theropod dinosaurs in Eastern Asia is now among the best understood in the world, thanks to new discoveries and reinterpretations of long-neglected fossils. Asia boasts the most complete record of Middle Jurassic theropods globally, as well as one of the best-studied Late Cretaceous theropod faunas, and new research is helping to fill what was previously a 60-million-year gap in the Early-mid Cretaceous fossil record of large Asian predators. In general, the biogeographic affinities of large-bodied Asian theropods over time were intimately related to physical geography, and progressively more derived theropod clades evolved large body size and occupied the apex predator niche throughout the Jurassic and Cretaceous. During the Middle Jurassic, largely endemic clades of basal tetanurans were prevalent in Asia, whereas during the Late Jurassic-mid Cretaceous more derived “intermediate” tetanuran theropods with cosmopolitan affinities occupied the large predator role, including sinraptorids, spinosaurids, and carcharodontosaurians. Finally, during the final 20 million years of the Cretaceous, more derived, bird-like coelurosaurs attained large body size. Foremost among these were the tyrannosaurids, a radiation of northern (Asian and North American) megapredators whose ascent into the apex predator niche was a delayed event restricted to the Campanian-Maastrichtian. As Asia is the focus of intense ongoing dinosaur fieldwork, our understanding of large-bodied theropod evolution will continue to be refined with future discoveries.

A description ofMegalosaurus bucklandii(Dinosauria: Theropoda) from the Bathonian of the UK and the relationships of Middle Jurassic theropods

Megalosaurus bucklandii (Dinosauria: Theropoda), the oldest named dinosaur taxon, from the Bathonian (Middle Jurassic) of England, is a valid taxon diagnosed by a unique character combination of the lectotype dentary. Abundant referred material is described and several autapomorphies are identified: ventral surfaces of first and third to fifth sacral centra evenly rounded, ventral surface of second sacral centrum bearing longitudinal, angular ridge; dorsally directed flange around midheight on the scapular blade; an array of posterodorsally inclined grooves on the lateral surface of the median iliac ridge; anteroposteriorly thick ischial apron with an almost flat medial surface; and complementary groove and ridge structures on the articular surfaces between metatarsals II and III. A new phylogenetic analysis focuses on basal tetanurans and includes 41 taxa, six of which have never been included in a cladistic analysis, and 213 characters, 29 of which are new. This is the first phylogenetic analysis to focus on basal tetanuran relationships, and it reveals several new results. Megalosauroidea (= Spinosauroidea) includes two clades, basal to the traditional content of Megalosauridae + Spinosauridae. These comprise Xuanhanosaurus, Marshosaurus, Condorraptor + Piatnitzkysaurus and Chuandongocoelurus + Monolophosaurus. Almost all large-bodied Middle Jurassic theropods are megalosauroids, but Poekilopleuron is an allosauroid. Megalosauroids show geographical differentiation among clades, indicating the development of endemic theropod faunas across Pangaea during the Middle Jurassic. Notably, megalosaurids are not known from outside of Europe during this epoch. Megalosauroids are less diverse and abundant during the Late Jurassic, when most theropods are neotetanurans and allosauroids dominate the large-bodied predator niche. This indicates faunal turnover between the Middle and Late Jurassic.

The postcranial skeleton ofMonolophosaurus jiangi(Dinosauria: Theropoda) from the Middle Jurassic of Xinjiang, China, and a review of Middle Jurassic Chinese theropods

AbstractThe Middle Jurassic was a critical time in the evolution of theropod dinosaurs, highlighted by the origination and radiation of the large-bodied and morphologically diverse Tetanurae. Middle Jurassic tetanurans are rare but have been described from Europe, South America and China. In particular, China has yielded a number of potential basal tetanurans, but these have received little detailed treatment in the literature. Here we redescribe the postcranial skeleton of one of the most complete Chinese Middle Jurassic theropods,Monolophosaurus. Several features confirm the tetanuran affinities ofMonolophosaurus, but the possession of ‘primitive’ traits such as a double-faceted pubic peduncle of the ilium and a hood-like supracetabular crest suggest a basal position within Tetanurae. This conflicts with most published cladistic analyses that placeMonolophosaurusin a more derived position within Allosauroidea. We review the Middle Jurassic record of Chinese theropods and compareMonolophosaurusto other Middle Jurassic theropods globally. These comparisons suggest thatMonolophosaurusandChuandongocoelurusformed an endemic theropod clade limited to the Middle Jurassic of Asia. Other Middle Jurassic Chinese theropods deserve further study.

The first definitive carcharodontosaurid (Dinosauria: Theropoda) from Asia and the delayed ascent of tyrannosaurids

Little is known about the evolution of large-bodied theropod dinosaurs during the Early to mid Cretaceous in Asia. Prior to this time, Asia was home to an endemic fauna of basal tetanurans, whereas terminal Cretaceous ecosystems were dominated by tyrannosaurids, but the intervening 60 million years left a sparse fossil record. Here, we redescribe the enigmatic large-bodied Chilantaisaurus maortuensis from the Turonian of Inner Mongolia, China. We refer this species to a new genus, Shaochilong, and analyze its systematic affinities. Although Shaochilong has previously been allied with several disparate theropod groups (Megalosauridae, Allosauridae, Tyrannosauroidea, Maniraptora), we find strong support for a derived carcharodontosaurid placement. As such, Shaochilong is the first unequivocal Asian member of Carcharodontosauridae, which was once thought to be restricted to Gondwana. The discovery of an Asian carcharodontosaurid indicates that this clade was cosmopolitan in the Early to mid Cretaceous and that Asian large-bodied theropod faunas were no longer endemic at this time. It may also suggest that the ascent of tyrannosaurids into the large-bodied dinosaurian predator niche was a late event that occurred towards the end of the Cretaceous, between the Turonian and the Campanian.

A Jurassic ceratosaur from China helps clarify avian digital homologies

Theropods have traditionally been assumed to have lost manual digits from the lateral side inward, which differs from the bilateral reduction pattern seen in other tetrapod groups. This unusual reduction pattern is clearly present in basal theropods, and has also been inferred in non-avian tetanurans based on identification of their three digits as the medial ones of the hand (I-II-III). This contradicts the many developmental studies indicating II-III-IV identities for the three manual digits of the only extant tetanurans, the birds. Here we report a new basal ceratosaur from the Oxfordian stage of the Jurassic period of China (156-161 million years ago), representing the first known Asian ceratosaur and the only known beaked, herbivorous Jurassic theropod. Most significantly, this taxon possesses a strongly reduced manual digit I, documenting a complex pattern of digital reduction within the Theropoda. Comparisons among theropod hands show that the three manual digits of basal tetanurans are similar in many metacarpal features to digits II-III-IV, but in phalangeal features to digits I-II-III, of more basal theropods. Given II-III-IV identities in avians, the simplest interpretation is that these identities were shared by all tetanurans. The transition to tetanurans involved complex changes in the hand including a shift in digit identities, with ceratosaurs displaying an intermediate condition.

Evidence for avian intrathoracic air sacs in a new predatory dinosaur from Argentina.

BackgroundLiving birds possess a unique heterogeneous pulmonary system composed of a rigid, dorsally-anchored lung and several compliant air sacs that operate as bellows, driving inspired air through the lung. Evidence from the fossil record for the origin and evolution of this system is extremely limited, because lungs do not fossilize and because the bellow-like air sacs in living birds only rarely penetrate (pneumatize) skeletal bone and thus leave a record of their presence.Methodology/Principal FindingsWe describe a new predatory dinosaur from Upper Cretaceous rocks in Argentina, Aerosteon riocoloradensis gen. et sp. nov., that exhibits extreme pneumatization of skeletal bone, including pneumatic hollowing of the furcula and ilium. In living birds, these two bones are pneumatized by diverticulae of air sacs (clavicular, abdominal) that are involved in pulmonary ventilation. We also describe several pneumatized gastralia (“stomach ribs”), which suggest that diverticulae of the air sac system were present in surface tissues of the thorax.Conclusions/SignificanceWe present a four-phase model for the evolution of avian air sacs and costosternal-driven lung ventilation based on the known fossil record of theropod dinosaurs and osteological correlates in extant birds:(1) Phase I—Elaboration of paraxial cervical air sacs in basal theropods no later than the earliest Late Triassic.(2) Phase II—Differentiation of avian ventilatory air sacs, including both cranial (clavicular air sac) and caudal (abdominal air sac) divisions, in basal tetanurans during the Jurassic. A heterogeneous respiratory tract with compliant air sacs, in turn, suggests the presence of rigid, dorsally attached lungs with flow-through ventilation.(3) Phase III—Evolution of a primitive costosternal pump in maniraptoriform theropods before the close of the Jurassic.(4) Phase IV—Evolution of an advanced costosternal pump in maniraptoran theropods before the close of the Jurassic.In addition, we conclude:(5) The advent of avian unidirectional lung ventilation is not possible to pinpoint, as osteological correlates have yet to be identified for uni- or bidirectional lung ventilation.(6) The origin and evolution of avian air sacs may have been driven by one or more of the following three factors: flow-through lung ventilation, locomotory balance, and/or thermal regulation.

The cranial anatomy of the coelophysoid theropod Zupaysaurus rougieri from the Upper Triassic of Argentina

Zupaysaurus rougieri is a theropod dinosaur that is known from an almost complete skull and limited postcranial material (e.g., axial elements, scapulocoracoid, tibia, astragalocalcaneum), from the Los Colorados Formation (La Esquina Fauna, Norian), NW Argentina. This taxon was originally interpreted as a basal tetanuran, but is actually a member of the Coelophysoidea. Zupaysaurus differs from other basal dinosaurs in the presence of the following cranial apomorphies: a maxillary-jugal ventral margin describing an obtuse angle in lateral view, a horizontal ramus of the maxilla with parallel dorsal and ventral margins, a notch at the base of the ascending process of the maxilla, and a sigmoid ventral process of the squamosal. Furthermore, the skull of this theropod reveals anatomical novelties (e.g., pneumatic lacrimal, maxillary fenestra, oval orbit, wide contact between squamosal and quadratojugal) absent in any other Triassic dinosaur hitherto described, including remaining coelophysoids. Interestingly, these features resemble morphological aspects of more derived theropods, approaching some traits of tetanuran and ceratosaurian neotheropods. In this regard, a redescription of the skull of Zupaysaurus and comparisons with basal neotheropods, mainly coelophysoids, is presented here in order to provide a better cranial anatomical record for this Triassic theropod and insights to their early cranial evolution.

The Anatomy and Systematics of Eustreptospondylus Oxoniensis, A Theropod Dinosaur from the Middle Jurassic of Oxfordshire, England

Recent work on theropod phylogeny has concentrated on the interrelationships of taxa that lie close to the ancestry of birds (coelurosaurs), whereas only a small number of studies have investigated the evolution of more primitive theropods (e.g. basal tetanurans). Ghost lineages implied by theropod phylogenies suggest that the Middle Jurassic was an important time in tetanuran evolution, witnessing the initial radiation and diversification of the clade. However, Middle Jurassic theropod specimens are rare and often incomplete.The holotype specimen of Eustreptospondylus oxoniensis, from the Middle Oxford Clay (upper Callovian) of Oxfordshire, England, represents the most complete Middle Jurassic theropod specimen from Europe. This taxon therefore has the potential to shed much needed light on basal tetanuran evolution at a critical time in the clade's history. Although several previous authors considered the anatomy and systematics of Eustreptospondylus, none of these accounts provided a comprehensive description and their utility is therefore limited.Here, we provide a detailed redescription of Eustreptospondylus and confirm its phylogenetic position as a basal member of Spinosauroidea. The taxon exhibits several anatomical features that appear to be incipient versions of the highly specialized character states found in more derived members of the clade (e.g. development of the premaxillary/maxillary embayment). The results of this work also suggest that Spinosauroidea may have originated in the Middle Jurassic of Europe, later dispersing to Gondwana.

Post-cranial remains of ‘coelurosaurs’ (Dinosauria, Theropoda) from the Late Jurassic of Tanzania

Small theropod post-cranial material from Tendaguru, Tanzania, the only known Late Jurassic theropod locality in the Southern Hemisphere, is reviewed. Material originally described as ‘coelurosaurs’ includes at least one taxon of basal tetanuran and one taxon of small abelisauroid. Together with the abelisauroid Elaphrosaurus and the presence of a larger ceratosaur in Tendaguru, this material indicates that ceratosaurs were an important faunal element of Late Jurassic East African theropod faunas. One bone furthermore shares derived characters with the holotype of the poorly known Middle Jurassic Australian theropod Ozraptor and allows the identification of the latter as the oldest known abelisauroid, thus indicating an early divergence of ceratosaurids and abelisauroids within ceratosaurs. Abelisauroids might have originated in Gondwana and represent important faunal elements of Cretaceous Gondwanan theropod faunas in general.

Osteology and relationships of a new theropod dinosaur from the Middle Jurassic of Patagonia

Abstract: A new taxon of theropod dinosaur is described as Condorraptor currumili gen. et sp. nov., from the Middle Jurassic (Callovian) Cañadón Asfalto Formation of Chubut Province, Argentinean Patagonia. The taxon is represented by a single fragmentary postcranial skeleton. Although incompletely known, Condorraptor is the second most complete theropod from the Middle Jurassic of Gondwana. The new taxon is characterized by the absence of a posterior incision between the fibular condyle and the medial side of the proximal articular end of the tibia, the pleurocoels in the anterior cervicals being situated posteroventral to the parapophyses, and the presence of a pronounced ‘step’ between the distal articular facet and shaft of Mt IV. Pneumatic features of the vertebral column show strong variation between the left and right side. Condorraptor gen. nov. can be referred to the Tetanurae and is a representative of a global radiation of basal tetanurans in the Early to Mid Jurassic.

Braincase structure of the Middle Jurassic theropod dinosaurPiatnitzkysaurus

The braincase of the Middle Jurassic basal tetanuran theropod Piatnitzkysaurus floresi is described in detail. It exhibits several probable autapomorphic characters of this taxon, including the extremely shortened and narrow basipterygoid processes, the presence of parasphenoid recesses that seem to communicate with each other, and basipterygoid recesses that are approximately as long anteroposteriorly as they are high. The braincase of Piatnitzkysaurus shows two possible synapomorphies with the enigmatic European Middle Jurassic theropod Piveteausaurus, a subrectangular pituitary fossa that is wider than high and the transverse span between the basipterygoid processes being smaller than the width of the basal tubera. A noteworthy aspect of the braincase of Piatnitzkysaurus is the high number of accessory pneumatic recesses, which indicates that the presence of an anterior and dorsal tympanic recess, and possibly also of subcondylar and basipterygoid recesses is plesiomorphic for tetanurans. In contrast, the bones enclosing the brain (e.g., laterosphenoid, prootic, supraoccipital) are very massive and lack internal pneumatic chambers, as they are present in later tetanurans.

Material referred to Megalosaurus (Dinosauria: Theropoda) from the Middle Jurassic of Stonesfield, Oxfordshire, England: one taxon or two?

Megalosaurus bucklandii von Meyer, 1832 is one of the most widely known, but poorly understood, of all theropod dinosaurs. It was recently claimed that the large theropod material from the Stonesfield Slate of Oxfordshire, which is usually attributed solely to M. bucklandii , represents not one, but two taxa on the basis of differences in the scapulocoracoids, ilia and femora. Here we evaluate this claim following examination of almost all relevant examples of these elements from the UK. A consistent suite of four differing femoral character states cannot be accounted for by sexual, ontogenetic or individual variation, and supports the presence of two morphotypes that probably represent distinct taxa. However, other purported differences between these two morphotypes are shown to be either ambiguous or erroneous. One taxon (‘morphotype B’, corresponding to that represented by one of the paralectotypes of M. bucklandii ) appears to be a basal tetanuran, whereas the other (‘morphotype A’) cannot be confidently assigned to any major theropod clade. Phylogenetic analyses of theropod interrelationships should not include any nominal species of Megalosaurus until a full taxonomic appraisal of this material has been completed.