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Journal articles on the topic 'Theropoda'

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Published: 4 June 2021
Last updated: 14 June 2025

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1

Button, Khai, Hailu You, James I. Kirkland, and Lindsay Zanno. "Incremental growth of therizinosaurian dental tissues: implications for dietary transitions in Theropoda." PeerJ 5 (December 11, 2017): e4129. http://dx.doi.org/10.7717/peerj.4129.

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Previous investigations document functional and phylogenetic signals in the histology of dinosaur teeth. In particular, incremental lines in dentin have been used to determine tooth growth and replacement rates in several dinosaurian clades. However, to date, few studies have investigated the dental microstructure of theropods in the omnivory/herbivory spectrum. Here we examine dental histology of Therizinosauria, a clade of large-bodied theropods bearing significant morphological evidence for herbivory, by examining the teeth of the early-diverging therizinosaurian Falcarius utahensis, and an isolated tooth referred to Suzhousaurus megatherioides, a highly specialized large-bodied representative. Despite attaining some of the largest body masses among maniraptoran theropod dinosaurs, therizinosaurian teeth are diminutive, measuring no more than 0.90 cm in crown height (CH) and 0.38 cm in crown base length (CBL). Comparisons with other theropods and non-theropodan herbivorous dinosaurs reveals that when controlling for estimated body mass, crown volume in therizinosaurians plots most closely with dinosaurs of similar dietary strategy as opposed to phylogenetic heritage. Analysis of incremental growth lines in dentin, observed in thin sections of therizinosaurian teeth, demonstrates that tooth growth rates fall within the range of other archosaurs, conforming to hypothesized physiological limitations on the production of dental tissues. Despite dietary differences between therizinosaurians and hypercarnivorous theropods, the types of enamel crystallites present and their spatial distribution—i.e., the schmelzmuster of both taxa—is limited to parallel enamel crystallites, the simplest form of enamel and the plesiomorphic condition for Theropoda. This finding supports previous hypotheses that dental microstructure is strongly influenced by phylogeny, yet equally supports suggestions of reduced reliance on oral processing in omnivorous/herbivorous theropods rather than the microstructural specializations to diet exhibited by non-theropodan herbivorous dinosaurs. Finally, although our sample is limited, we document a significant reduction in the rate of enamel apposition contrasted with increased relative enamel thickness between early and later diverging therizinosaurians that coincides with anatomical evidence for increased specializations to herbivory in the clade.
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2

Rowe, Timothy. "The Early History of Theropods." Short Courses in Paleontology 2 (1989): 100–112. http://dx.doi.org/10.1017/s2475263000000891.

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Theropods have traditionally been portrayed as extinct bipedal predators built along the lines of such celebrated terrors as Tyrannosaurus, Deinonychus, and Allosaurus. The earliest theropods indeed fit that image, and all of them are decidedly extinct. However, it has become increasingly apparent that living birds trace their genealogy to those extinct theropods (Ostrom, 1976; Gauthier, 1986; Gauthier and Padian, 1985 and this volume), and that any adequate consideration of the evolutionary history of Theropoda must assess the lineage as a whole, instead of arbitrarily focusing on the Mesozoic forms alone. When the approximately 8,600 living avian descendants of the ancestral theropod are taken into account, together with the various extinct Mesozoic and Cenozoic taxa, theropods display a far greater range of size, form, behavior, and diet than we ever pictured in our traditional image.
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3

Gatesy, Stephen M. "Caudofemoral musculature and the evolution of theropod locomotion." Paleobiology 16, no. 2 (1990): 170–86. http://dx.doi.org/10.1017/s0094837300009866.

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Living crocodilians and limbed lepidosaurs have a large caudofemoralis longus muscle passing from tail to femur. Anatomical and electromyographic data support the conclusion that the caudofemoralis is the principal femoral retractor and thus serves as the primary propulsive muscle of the hind limb. Osteological evidence of both origin and insertion indicates that a substantial caudofemoralis longus was present in archosaurs primitively and was retained in the clades Dinosauria and Theropoda. Derived theropods (e.g., ornithomimids, deinonychosaurs, Archaeopteryx and birds) exhibit features that indicate a reduction in caudofemoral musculature, including fewer caudal vertebrae, diminished caudal transverse processes, distal specialization of the tail, and loss of the fourth trochanter. This trend culminates in ornithurine birds, which have greatly reduced tails and either have a minute caudofemoralis longus or lack the muscle entirely.As derived theropod dinosaurs, birds represent the best living model for reconstructing extinct nonavian theropods. Bipedal, digitigrade locomotion on fully erect limbs is an avian feature inherited from theropod ancestors. However, the primitive saurian mechanisms of balancing the body (with a large tail) and retracting the limb (with the caudofemoralis longus) were abandoned in the course of avian evolution. This strongly suggests that details of the orientation (subhorizontal femur) and movement (primarily knee flexion) of the hind limb in extant birds are more properly viewed as derived, uniquely avian conditions, rather than as retentions of an ancestral dinosaurian pattern. Although many characters often associated with extant birds appeared much earlier in theropod evolution, reconstructing the locomotion of all theropods as completely birdlike ignores a wealth of differences that characterize birds.
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4

Hendrickx, Christophe, Ricardo Araújo, and Octávio Mateus. "The non-avian theropod quadrate I: standardized terminology with an overview of the anatomy and function." PeerJ 3 (September 17, 2015): e1245. http://dx.doi.org/10.7717/peerj.1245.

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The quadrate of reptiles and most other tetrapods plays an important morphofunctional role by allowing the articulation of the mandible with the cranium. In Theropoda, the morphology of the quadrate is particularly complex and varies importantly among different clades of non-avian theropods, therefore conferring a strong taxonomic potential. Inconsistencies in the notation and terminology used in discussions of the theropod quadrate anatomy have been noticed, including at least one instance when no less than eight different terms were given to the same structure. A standardized list of terms and notations for each quadrate anatomical entity is proposed here, with the goal of facilitating future descriptions of this important cranial bone. In addition, an overview of the literature on quadrate function and pneumaticity in non-avian theropods is presented, along with a discussion of the inferences that could be made from this research. Specifically, the quadrate of the large majority of non-avian theropods is akinetic but the diagonally oriented intercondylar sulcus of the mandibular articulation allowed both rami of the mandible to move laterally when opening the mouth in many of theropods. Pneumaticity of the quadrate is also present in most averostran clades and the pneumatic chamber—invaded by the quadrate diverticulum of the mandibular arch pneumatic system—was connected to one or several pneumatic foramina on the medial, lateral, posterior, anterior or ventral sides of the quadrate.
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5

Zelenitsky, Darla K., François Therrien, and Yoshitsugu Kobayashi. "Olfactory acuity in theropods: palaeobiological and evolutionary implications." Proceedings of the Royal Society B: Biological Sciences 276, no. 1657 (2008): 667–73. http://dx.doi.org/10.1098/rspb.2008.1075.

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This research presents the first quantitative evaluation of the olfactory acuity in extinct theropod dinosaurs. Olfactory ratios (i.e. the ratio of the greatest diameter of the olfactory bulb to the greatest diameter of the cerebral hemisphere) are analysed in order to infer the olfactory acuity and behavioural traits in theropods, as well as to identify phylogenetic trends in olfaction within Theropoda. A phylogenetically corrected regression of olfactory ratio to body mass reveals that, relative to predicted values, the olfactory bulbs of (i) tyrannosaurids and dromaeosaurids are significantly larger, (ii) ornithomimosaurs and oviraptorids are significantly smaller, and (iii) ceratosaurians, allosauroids, basal tyrannosauroids, troodontids and basal birds are within the 95% CI. Relative to other theropods, olfactory acuity was high in tyrannosaurids and dromaeosaurids and therefore olfaction would have played an important role in their ecology, possibly for activities in low-light conditions, locating food, or for navigation within large home ranges. Olfactory acuity was the lowest in ornithomimosaurs and oviraptorids, suggesting a reduced reliance on olfaction and perhaps an omnivorous diet in these theropods. Phylogenetic trends in olfaction among theropods reveal that olfactory acuity did not decrease in the ancestry of birds, as troodontids, dromaeosaurids and primitive birds possessed typical or high olfactory acuity. Thus, the sense of smell must have remained important in primitive birds and its presumed decrease associated with the increased importance of sight did not occur until later among more derived birds.
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6

Agnolin, Federico L., and Fernando E. Novas. "Unenlagiid theropods: are they members of the Dromaeosauridae (Theropoda, Maniraptora)?" Anais da Academia Brasileira de Ciências 83, no. 1 (2011): 117–62. http://dx.doi.org/10.1590/s0001-37652011000100008.

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In the present paper we analyze the phylogenetic position of the derived Gondwanan theropod clade Unenlagiidae. Although this group has been frequently considered as deeply nested within Deinonychosauria and Dromaeosauridae, most of the features supporting this interpretation are conflictive, at least. Modification of integrative databases, such as that recently published by Hu et al. (2009), produces significant changes in the topological distribution of taxa within Deinonychosauria, depicting unenlagiids outside this clade. Our analysis retrieves, in contrast, a monophyletic Avialae formed by Unenlagiidae plus Aves.
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7

Balanoff, Amy M., Xing Xu, Yoshitsugu Kobayashi, Yusuke Matsufune, and Mark A. Norell. "Cranial Osteology of the Theropod Dinosaur Incisivosaurus gauthieri (Theropoda: Oviraptorosauria)." American Museum Novitates 3651 (July 25, 2009): 1–35. http://dx.doi.org/10.1206/644.1.

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8

Bates, Karl T., Roger B. J. Benson, and Peter L. Falkingham. "A computational analysis of locomotor anatomy and body mass evolution in Allosauroidea (Dinosauria: Theropoda)." Paleobiology 38, no. 3 (2012): 486–507. http://dx.doi.org/10.1666/10004.1.

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We investigate whether musculoskeletal anatomy and three-dimensional (3-D) body proportions were modified during the evolution of large (>6000 kg) body size in Allosauroidea (Dinosauria: Theropoda). Three adaptations for maintaining locomotor performance at large body size, related to muscle leverage, mass, and body proportions, are tested and all are unsupported in this analysis. Predictions from 3-D musculoskeletal models of medium-sized (Allosaurus) and large-bodied (Acrocanthosaurus) allosauroids suggest that muscle leverage scaled close to isometry, well below the positive allometry required to compensate for declining muscle cross-sectional area with increasing body size. Regression analyses on a larger allosauroid data set finds slight positive allometry in the moment arms of major hip extensors, but isometry is included within confidence limits. Contrary to other recent studies of large-bodied theropod clades, we found no compelling evidence for significant positive allometry in muscle mass between exemplar medium- and large-bodied allosauroids. Indeed, despite the uncertainty in quantitative soft tissue reconstruction, we find strong evidence for negative allometry in the caudofemoralis longus muscle, the single largest hip extensor in non-avian theropods. Finally, we found significant inter-study variability in center-of-mass predictions for allosauroids, but overall observe that consistently proportioned soft tissue reconstructions produced similar predictions across the group, providing no support for a caudal shift in the center of mass in larger taxa that might otherwise reduce demands on hip extensor muscles during stance. Our data set provides further quantitative support to studies that argue for a significant decline in locomotor performance with increasing body size in non-avian theropods. However, although key pelvic limb synapomorphies of derived allosauroids (e.g., dorsomedially inclined femoral head) evolved at intermediate body sizes, they may nonetheless have improved mass support.
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9

XI-JIN, ZHAO, ROGER B. J. BENSON, STEPHEN L. BRUSATTE, and PHILIP J. CURRIE. "The postcranial skeleton ofMonolophosaurus jiangi(Dinosauria: Theropoda) from the Middle Jurassic of Xinjiang, China, and a review of Middle Jurassic Chinese theropods." Geological Magazine 147, no. 1 (2009): 13–27. http://dx.doi.org/10.1017/s0016756809990240.

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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.
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10

BRUSATTE, STEPHEN L., DANIEL J. CHURE, ROGER B. J. BENSON, and XING XU. "The osteology of Shaochilong maortuensis, a carcharodontosaurid (Dinosauria: Theropoda) from the Late Cretaceous of Asia." Zootaxa 2334, no. 1 (2010): 1. http://dx.doi.org/10.11646/zootaxa.2334.1.1.

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Large-bodied theropod dinosaurs from the Early-mid Cretaceous of the northern continents (Laurasia) are poorly known. One of the most complete and intriguing theropods from this interval is Shaochilong maortuensis Hu, 1964 from the Turonian (< 92 Ma) Ulansuhai Formation of Inner Mongolia, China. The phylogenetic placement of Shaochilong has long been a subject of debate, as it has been referred to several disparate theropod groups (e.g., Megalosauridae, Allosauridae, Tyrannosauroidea, Maniraptora). In a recent taxonomic reassessment, Shaochilong was identified as the first Asian member of Carcharodontosauridae, a clade of allosauroid theropods that was once thought to be restricted to Gondwana and includes some of the largest terrestrial predators to ever live. However, the characters supporting such a placement were only briefly discussed, and a full anatomical description of Shaochilong has yet to be presented. We provide a detailed osteological description of the lectotype and paralectotype series, show that Shaochilong is a small-bodied and short-snouted carcharodontosaurid, and highlight numerous cranial features shared with other carcharodontosaurids. We argue that the vicariant hypothesis of allosauroid biogeography, in which lineages split in concert with the fragmentation of Pangaea, is poorly supported. Finally, large-scale patterns of theropod evolution and faunal replacement are discussed, and it is argued that allosauroids persisted as large-bodied predators later in the Cretaceous than previously thought.
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11

Averianov, A. O., and A. V. Lopatin. "A New Theropod Dinosaur (Theropoda, Dromaeosauridae) from the Late Cretaceous of Tajikistan." Doklady Earth Sciences 499, no. 1 (2021): 570–74. http://dx.doi.org/10.1134/s1028334x21070047.

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12

Marsh, Adam D., and Timothy B. Rowe. "A comprehensive anatomical and phylogenetic evaluation of Dilophosaurus wetherilli (Dinosauria, Theropoda) with descriptions of new specimens from the Kayenta Formation of northern Arizona." Journal of Paleontology 94, S78 (2020): 1–103. http://dx.doi.org/10.1017/jpa.2020.14.

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AbstractDilophosaurus wetherilli was the largest animal known to have lived on land in North America during the Early Jurassic. Despite its charismatic presence in pop culture and dinosaurian phylogenetic analyses, major aspects of the skeletal anatomy, taxonomy, ontogeny, and evolutionary relationships of this dinosaur remain unknown. Skeletons of this species were collected from the middle and lower part of the Kayenta Formation in the Navajo Nation in northern Arizona. Redescription of the holotype, referred, and previously undescribed specimens of Dilophosaurus wetherilli supports the existence of a single species of crested, large-bodied theropod in the Kayenta Formation. The parasagittal nasolacrimal crests are uniquely constructed by a small ridge on the nasal process of the premaxilla, dorsoventrally expanded nasal, and tall lacrimal that includes a posterior process behind the eye. The cervical vertebrae exhibit serial variation within the posterior centrodiapophyseal lamina, which bifurcates and reunites down the neck. Iterative specimen-based phylogenetic analyses result in each of the additional specimens recovered as the sister taxon to the holotype. When all five specimens are included in an analysis, they form a monophyletic clade that supports the monotypy of the genus. Dilophosaurus wetherilli is not recovered as a ceratosaur or coelophysoid, but is instead a non-averostran neotheropod in a grade with other stem-averostrans such as Cryolophosaurus ellioti and Zupaysaurus rougieri. We did not recover a monophyletic ‘Dilophosauridae.’ Instead of being apomorphic for a small clade of early theropods, it is more likely that elaboration of the nasals and lacrimals of stem-averostrans is plesiomorphically present in early ceratosaurs and tetanurans that share those features. Many characters of the axial skeleton of Dilophosaurus wetherilli are derived compared to Late Triassic theropods and may be associated with macropredation and an increase in body size in Theropoda across the Triassic-Jurassic boundary.
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Chiarenza, Alfio Alessandro, and Andrea Cau. "A large abelisaurid (Dinosauria, Theropoda) from Morocco and comments on the Cenomanian theropods from North Africa." PeerJ 4 (February 29, 2016): e1754. http://dx.doi.org/10.7717/peerj.1754.

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We describe the partially preserved femur of a large-bodied theropod dinosaur from the Cenomanian “Kem Kem Compound Assemblage” (KKCA) of Morocco. The fossil is housed in the Museo Geologico e Paleontologico “Gaetano Giorgio Gemmellaro” in Palermo (Italy). The specimen is compared with the theropod fossil record from the KKCA and coeval assemblages from North Africa. The combination of a distally reclined head, a not prominent trochanteric shelf, distally placed lesser trochanter of stout, alariform shape, a stocky shaft with the fourth trochanter placed proximally, and rugose muscular insertion areas in the specimen distinguishes it fromCarcharodontosaurus,DeltadromeusandSpinosaurusand supports referral to an abelisaurid. The estimated body size for the individual from which this femur was derived is comparable toCarnotaurusandEkrixinatosaurus(up to 9 meters in length and 2 tons in body mass). This find confirms that abelisaurids had reached their largest body size in the “middle Cretaceous,” and that large abelisaurids coexisted with other giant theropods in Africa. We review the taxonomic status of the theropods from the Cenomanian of North Africa, and provisionally restrict the Linnean binominaCarcharodontosaurus iguidensisandSpinosaurus aegyptiacusto the type specimens. Based on comparisons among the theropod records from the Aptian-Cenomanian of South America and Africa, a partial explanation for the so-called “Stromer’s riddle” (namely, the coexistence of many large predatory dinosaurs in the “middle Cretaceous” record from North Africa) is offered in term of taphonomic artifacts among lineage records that were ecologically and environmentally non-overlapping. Although morphofunctional and stratigraphic evidence supports an ecological segregation between spinosaurids and the other lineages, the co-occurrence of abelisaurids and carcharodontosaurids, two groups showing several craniodental convergences that suggest direct resource competition, remains to be explained.
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Dal Sasso, Cristiano, Simone Maganuco, and Andrea Cau. "The oldest ceratosaurian (Dinosauria: Theropoda), from the Lower Jurassic of Italy, sheds light on the evolution of the three-fingered hand of birds." PeerJ 6 (December 19, 2018): e5976. http://dx.doi.org/10.7717/peerj.5976.

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The homology of the tridactyl hand of birds is a still debated subject, with both paleontological and developmental evidence used in support of alternative identity patterns in the avian fingers. With its simplified phalangeal morphology, the Late Jurassic ceratosaurian Limusaurus has been argued to support a II–III–IV digital identity in birds and a complex pattern of homeotic transformations in three-fingered (tetanuran) theropods. We report a new large-bodied theropod, Saltriovenator zanellai gen. et sp. nov., based on a partial skeleton from the marine Saltrio Formation (Sinemurian, lowermost Jurassic) of Lombardy (Northern Italy). Taphonomical analyses show bone bioerosion by marine invertebrates (first record for dinosaurian remains) and suggest a complex history for the carcass before being deposited on a well-oxygenated and well-illuminated sea bottom. Saltriovenator shows a mosaic of features seen in four-fingered theropods and in basal tetanurans. Phylogenetic analysis supports sister taxon relationships between the new Italian theropod and the younger Early Jurassic Berberosaurus from Morocco, in a lineage which is the basalmost of Ceratosauria. Compared to the atrophied hand of later members of Ceratosauria, Saltriovenator demonstrates that a fully functional hand, well-adapted for struggling and grasping, was primitively present in ceratosaurians. Ancestral state reconstruction along the avian stem supports 2-3-4-1-X and 2-3-4-0-X as the manual phalangeal formulae at the roots of Ceratosauria and Tetanurae, confirming the I–II–III pattern in the homology of the avian fingers. Accordingly, the peculiar hand of Limusaurus represents a derived condition restricted to late-diverging ceratosaurians and cannot help in elucidating the origin of the three-fingered condition of tetanurans. The evolution of the tridactyl hand of birds is explained by step-wise lateral simplification among non-tetanuran theropod dinosaurs, followed by a single primary axis shift from digit position 4 to 3 at the root of Tetanurae once the fourth finger was completely lost, which allowed independent losses of the vestigial fourth metacarpal among allosaurians, tyrannosauroids, and maniraptoromorphs. With an estimated body length of 7.5 m, Saltriovenator is the largest and most robust theropod from the Early Jurassic, pre-dating the occurrence in theropods of a body mass approaching 1,000 Kg by over 25 My. The radiation of larger and relatively stockier averostran theropods earlier than previously known may represent one of the factors that ignited the trend toward gigantism in Early Jurassic sauropods.
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Sakamoto, Manabu. "Jaw biomechanics and the evolution of biting performance in theropod dinosaurs." Proceedings of the Royal Society B: Biological Sciences 277, no. 1698 (2010): 3327–33. http://dx.doi.org/10.1098/rspb.2010.0794.

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Despite the great diversity in theropod craniomandibular morphology, the presence and distribution of biting function types across Theropoda has rarely been assessed. A novel method of biomechanical profiling using mechanical advantage computed for each biting position along the entirety of the tooth row was applied to 41 extinct theropod taxa. Multivariate ordination on the polynomial coefficients of the profiles reveals the distribution of theropod biting performance in function space. In particular, coelophysoids are found to occupy a unique region of function space, while tetanurans have a wide but continuous function space distribution. Further, the underlying phylogenetic structure and evolution of biting performance were investigated using phylogenetic comparative methods. There is a strong phylogenetic signal in theropod biomechanical profiles, indicating that evolution of biting performance does not depart from Brownian motion evolution. Reconstructions of ancestral function space occupation conform to this pattern, but phylogenetically unexpected major shifts in function space occupation can be observed at the origins of some clades. However, uncertainties surround ancestor estimates in some of these internal nodes, so inferences on the nature of these evolutionary changes must be viewed with caution.
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16

Currie, P. J. "Cranial anatomy of Stenonychosaurus inequalis (Saurischia, Theropoda) and its bearing on the origin of birds." Canadian Journal of Earth Sciences 22, no. 11 (1985): 1643–58. http://dx.doi.org/10.1139/e85-173.

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The discovery in recent years of additional skull material of the rare carnivorous dinosaur Stenonychosaurus inequalis prompts the first thorough description of this animal. This species, known only from the Upper Cretaceous strata of North America, is closely related to, but distinct from, the two described species of Saurornithoides from Mongolia. A derived characteristic, an inflated parasphenoid capsule, is found in both the saurornithoidids and ornithomimids, strongly suggesting shared ancestry. The middle ear cavity is well defined and is connected to at least two systems of sinuses in the skull bones. Periotic sinuses like these have not been described in theropods, and their presumed absence has been used as evidence against theropod ancestry of birds. Although these and other cranial characteristics of Stenonychosaurus do not prove that birds descended from theropods, they strengthen the claim that small carnivorous dinosaurs are more plausible bird ancestors than either pseudosuchians or crocodiles:
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Baron, Matthew G., and Paul M. Barrett. "A dinosaur missing-link? Chilesaurus and the early evolution of ornithischian dinosaurs." Biology Letters 13, no. 8 (2017): 20170220. http://dx.doi.org/10.1098/rsbl.2017.0220.

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The enigmatic dinosaur taxon Chilesaurus diegosuarezi was originally described as a tetanuran theropod, but this species possesses a highly unusual combination of features that could provide evidence of alternative phylogenetic positions within the clade. In order to test the relationships of Chilesaurus , we added it to a new dataset of early dinosaurs and other dinosauromorphs. Our analyses recover Chilesaurus in a novel position, as the earliest diverging member of Ornithischia, rather than a tetanuran theropod. The basal position of Chilesaurus within the clade and its suite of anatomical characters suggest that it might represent a ‘transitional’ taxon, bridging the morphological gap between Theropoda and Ornithischia, thereby offering potential insights into the earliest stages of ornithischian evolution, which were previously obscure. For example, our results suggest that pubic retroversion occurred prior to some of the craniodental and postcranial modifications that previously diagnosed the clade (e.g. the presence of a predentary bone and ossified tendons).
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Currie, Philip J., and Xi-Jin Zhao. "A new carnosaur (Dinosauria, Theropoda) from the Jurassic of Xinjiang, People's Republic of China." Canadian Journal of Earth Sciences 30, no. 10 (1993): 2037–81. http://dx.doi.org/10.1139/e93-179.

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In 1987, a Sino-Canadian expedition known as the Dinosaur Project (China – Canada – Alberta – Ex Terra) discovered a large theropod skeleton in the Upper Jurassic Shishugou Formation of the Junggar Basin in northwestern China. The well-preserved skeleton lacks much of the tail and most of the arms, but is otherwise nearly complete. The new genus and species, Sinraptor dongi, represents a poorly understood stage of theropod evolution, even though a related form, Megalosaurus, was the first dinosaur described and named (by W. Buckland in 1824). Sinraptor has a large pneumatopore in the jugal, a pronounced postorbital rugosity, a relatively long intertemporal bar in which the postorbital appears very short in lateral aspect, and a pneumatic palatine. It is more advanced than Piatnitzkysaurus from Argentina, less derived than Allosaurus, and shows its strongest similarities to Yangchuanosaurus. The preorbital skull length of Sinraptor is relatively longer than in Yangchuanosaurus, but the skull is relatively lower. A specimen from Sichuan recently described as "Yangchuanosaurus" hepingensis represents a second species of Sinraptor. Sinraptor and Yangchuanosaurus are united in a new family of theropods, the Sinraptoridae.
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De Ricqlès, A. J., K. Padian, J. R. Horner, E. T. Lamm, and N. Myhrvold. "Osteohistology ofConfuciusornis sanctus(Theropoda: Aves)." Journal of Vertebrate Paleontology 23, no. 2 (2003): 373–86. http://dx.doi.org/10.1671/0272-4634(2003)023[0373:oocsta]2.0.co;2.

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20

Machado, Elaine Batista, and Alexander Wilhelm Armin Kellner. "Notas sobre Spinosauridae (Theropoda, Dinosauria)." Anuário do Instituto de Geociências 28, no. 1 (2005): 158–73. http://dx.doi.org/10.11137/2005_1_158-173.

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Spinosaur remains were collected in Africa, Europa, Asia and Brazil, coming from deposits with ages ranging from the Late Jurassic to the Late Cretaceous. Although having a wide distribution - both geographically and temporally - little is actually known about the group since most specimens are incomplete. Up to now, only eight species were described. Spinosauridae is divided into the Baryonychinae (Suchomimus + Baryonyx + Cristatosaurus) and Spinosaurinae (Spinosaurus+ Angaturama + Irritator). Only in Africa members of both clades were found. One possible scenario that could explain the spinosaurid distribution, suggests that forms related to Baryonyx (the most primitive member of this clade) dispersed from Europe to Northern Africa, where Spinosaurinae were originated. Later, members of the Spinosaurinae further spread to South America.
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White, Matt A., Phil R. Bell, Alex G. Cook, Stephen F. Poropat, and David A. Elliott. "The dentary ofAustralovenator wintonensis(Theropoda, Megaraptoridae); implications for megaraptorid dentition." PeerJ 3 (December 15, 2015): e1512. http://dx.doi.org/10.7717/peerj.1512.

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Megaraptorid theropods were an enigmatic group of medium-sized predatory dinosaurs, infamous for the hypertrophied claw on the first manual digit. Megaraptorid dentition is largely restricted to isolated teeth found in association with skeletal parts; however, thein situmaxillary dentition ofMegaraptorwas recently described. A newly discovered right dentary pertaining to theAustralovenatorholotype preservesin situdentition, permitting unambiguous characterisation of the dentary tooth morphology. The new jaw is virtually complete, with an overall elongate, shallow profile, and fifteen visiblein situteeth at varying stages of eruption.In situteeth confirmAustralovenatorexhibited modest pseudoheterodonty, recurved lateral teeth with a serrate distal carina and reduced mesial carina, similar to other megaraptorids.Australovenatoralso combines of figure-of-eight basal cross-section with a lanceolate shape due to the presence of labial and lingual depressions and the lingual twist of the distal carina. Computed tomography and three-dimensional imagery provided superior characterisation of the dentary morphology and enabled an accurate reconstruction to a pre-fossilised state. The newly established dental morphology also afforded re-evaluation of isolated theropod teeth discovered at theAustralovenatorholotype locality and from several additional Winton Formation localities. The isolated Winton teeth are qualitatively and quantitatively similar to thein situdentary teeth ofAustralovenator, but are also morphometrically similar to Abelisauridae, Allosauridae, Coelophysoidea, Megalosauridae and basal Tyrannosauroidea. Qualitative characters, however, clearly distinguish the teeth ofAustralovenatorand the isolated Winton teeth from all other theropods. Evidence from teeth suggests megaraptorids were the dominant predators in the Winton Formation, which contrasts with other penecontemporaneous Gondwanan ecosystems.
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Feduccia, Alan. "FANTASY VS REALITY: A Critique of Smith et al.'s Bird Origins." Open Ornithology Journal 9, no. 1 (2016): 14–38. http://dx.doi.org/10.2174/1874453201609010014.

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Adherents of the current orthodoxy of a derivation of birds from theropod dinosaurs, criticize the commentary by Feduccia (2013, Auk, 130) [1 - 12] entitled “Bird Origins Anew” as well as numerous papers by Lingham-Soliar on theropod dermal fibers, using numerous mischaracterizations and misstatements of content, and illustrate their own misconceptions of the nature of the debate, which are here clarified. While there is general agreement with the affinity of birds and maniraptorans, the widely accepted phylogeny, advocating derived earth-bound maniraptorans giving rise to more primitive avians (i.e. Archaeopteryx), may be “topsy-turvy.” The current primary debate concerns whether maniraptorans are ancestral or derived within the phylogeny, and whether many maniraptorans and birds form a clade distinct from true theropods. Corollaries of the current scheme show largely terrestrial maniraptoran theropods similar to the Late CretaceousVelociraptorgiving rise to avians, and flight originatingviaa terrestrial (cursorial) “gravity-resisted,” as opposed to an arboreal “gravity-assisted” model. The current dogma posits pennaceous flight remiges in earth-bound theropods having evolved in terrestrial theropods that never flew. As part of the orthodoxy, fully feathered maniraptorans such as the tetrapteryx glidersMicroraptorand allies, are incorrectly reconstructed as terrestrial cursors, when in reality their anatomy and elongate hindlimb feathers would be a hindrance to terrestrial locomotion.The same is true of many early birds, exemplified by reconstruction of the arboreally adaptedConfuciusornisas a terrestrial predator, part of the overall theropodan scheme of birds evolving from terrestrial dinosaurs, and flight from the ground up. Both sides of this contentious debate must be constantly aware that new fossil or even molecular discoveries on birds may change current conclusions.
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Carrano, Matthew T., and Scott D. Sampson. "The Phylogeny of Ceratosauria (Dinosauria: Theropoda)." Journal of Systematic Palaeontology 6, no. 2 (2008): 183–236. http://dx.doi.org/10.1017/s1477201907002246.

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Carrano, Matthew T., Roger B. J. Benson, and Scott D. Sampson. "The phylogeny of Tetanurae (Dinosauria: Theropoda)." Journal of Systematic Palaeontology 10, no. 2 (2012): 211–300. http://dx.doi.org/10.1080/14772019.2011.630927.

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Carrano, Matthew T., Roger B. J. Benson, and Scott D. Sampson. "The phylogeny of Tetanurae (Dinosauria: Theropoda)." Journal of Systematic Palaeontology 10, no. 3 (2012): 599. http://dx.doi.org/10.1080/14772019.2012.713753.

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Balanoff, Amy M., and Mark A. Norell. "Osteology of Khaan mckennai (Oviraptorosauria: Theropoda)." Bulletin of the American Museum of Natural History 372 (December 28, 2012): 1–77. http://dx.doi.org/10.1206/803.1.

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Agnolin, Federico L., and Agustín G. Martinelli. "Did oviraptorosaurs (Dinosauria; Theropoda) inhabit Argentina?" Cretaceous Research 28, no. 5 (2007): 785–90. http://dx.doi.org/10.1016/j.cretres.2006.10.006.

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Guinard, Geoffrey. "Forelimb shortening of Carcharodontosauria (Dinosauria: Theropoda): an update on evolutionary anterior micromelias in non-avian theropods." Zoology 139 (April 2020): 125756. http://dx.doi.org/10.1016/j.zool.2020.125756.

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BRUSATTE, STEPHEN L., ROGER B. J. BENSON, PHILIP J. CURRIE, and ZHAO XIJIN. "The skull of Monolophosaurus jiangi (Dinosauria: Theropoda) and its implications for early theropod phylogeny and evolution." Zoological Journal of the Linnean Society 158, no. 3 (2010): 573–607. http://dx.doi.org/10.1111/j.1096-3642.2009.00563.x.

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Novas, Fernando E. "The tibia and tarsus in Herrerasauridae (Dinosauria, incertae sedis) and the origin and evolution of the dinosaurian tarsus." Journal of Paleontology 63, no. 5 (1989): 677–90. http://dx.doi.org/10.1017/s0022336000041317.

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The tarsus and distal end of the tibia are described in Herrerasauridae, a family that includes the oldest known dinosaurs. This tarsal configuration is compared to those of more advanced dinosaurs and to other archosaurs. Through phylogenetic analysis of the morphological characters, a picture emerges of the evolutionary changes in the ankles of early dinosaurs.The tibia of the herrerasaurids has a quadrangular distal articular surface, with a shallow ventrolateral notch. This morphology is strikingly similar to that of the lagosuchid thecodontsPseudolagosuchusandLagosuchusand represents the most primitive tibial condition known for Dinosauria.Aside from the derived states possessed by Theropoda, Sauropodomorpha, and Ornithischia, respectively, it was impossible to recognize synapomorphies in tibiotarsal anatomy shared by these groups exclusive of Herrerasauridae. The transverse broadening of the distal end of the tibia seems to have been attained independently by ornithischians, theropods, and sauropodomorphs.The tarsus of herrerasaurids is characterized by an astragalus with a small but conspicuous lateroventral depression, by a pyramidal calcaneum with a ventromedial projection that articulates into the cavity of the astragalus just mentioned, and by a posterolaterally directed calcaneal tuber. These characters are also seen inLagosuchus(a close relative of dinosaurs), in the prosauropodRiojasaurusand, insofar as the astragalus is concerned, in the primitive dinosaurWalkeria, which suggests that dinosaurs of different lineages shared the same tarsal condition.By definition, this type of articulation between the astragalus and calcaneum follows the “crocodile-reversed” tarsal condition, suggesting that the tarsus in lagosuchids and dinosaurs could be derived from the “crocodile-reversed” pattern present in Ornithosuchidae andEuparkeria. In contrast, the mesotarsal ankle of lagosuchids and dinosaurs lacks the synapomorphies of the “crocodile-normal” ankle present in Crocodylia, Rauisuchidae, Aetosauria, and other archosaurs.It is concluded that Herrerasauridae retained the primitive tibiotarsal condition for Dinosauria, from which those of the Ornithischia, Sauropodomorpha, and Theropoda were derived. Furthermore, tibiotarsal anatomy supports monophyly of Dinosauria.
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Langer, Max C., Jonathas S. Bittencourt, and Cesar L. Schultz. "A reassessment of the basal dinosaur Guaibasaurus candelariensis, from the Late Triassic Caturrita Formation of south Brazil." Earth and Environmental Science Transactions of the Royal Society of Edinburgh 101, no. 3-4 (2010): 301–32. http://dx.doi.org/10.1017/s175569101102007x.

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ABSTRACTThe dinosaur record of the Santa Maria beds of Rio Grande do Sul (Mid–Late Triassic; south Brazil) includes the herrerasaur Staurikosaurus pricei, and two basal members of the sauropodomorph lineage: Saturnalia tupiniquim and Unaysaurus tolentinoi. The most enigmatic of the saurischian taxa is, however, Guaibasaurus candelariensis, previously regarded as either a basal theropod or a basal sauropodomorph. This study provides a detailed anatomical revision of all specimens originally referred to G. candelariensis by Bonaparte and co-authors, including its type-series and a more recently excavated partial postcranium. Although coming from different sites, these specimens share a unique combination of traits, and at least one possible autapomorphic feature of the pelvis, which support the inclusivity and uniqueness of the species. G. candelariensis was a medium-sized (nearly 2 m long) biped with an intriguing mix of plesiomorphic and derived (eusaurischian/theropod) features. Phylogenetic studies reveal weak support for the nesting of G. candelariensis within Theropoda, but this affinity is bolstered by various traits it shares with neotheropods. The Norian age of G. candelariensis corroborates previous studies that suggest the continuous radiation of more basal dinosauromorphs until the end of the Triassic, after the appearance of the three main dinosaur clades.
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Holtz, Thomas R. "Phylogenetic taxonomy of the Coelurosauria (Dinosauria: Theropoda)." Journal of Paleontology 70, no. 3 (1996): 536–38. http://dx.doi.org/10.1017/s0022336000038506.

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Phylogenetic taxonomy, that component of phylogenetic systematics concerned with the verbal representation (rather than the reconstruction or estimation) of phylogenetic relationships, was developed by de Queiroz and Gauthier (1990, 1992, 1994). Under phylogenetic taxonomy, all taxon names are names of clades (i.e., an ancestor and all of that ancestor's descendants). De Queiroz and Gauthier (1990, 1992, 1994) described three possible ways of denning clade names within the phylogenetic taxonomic system: 1) node-based definitions (Figure 1.1), of the form “the most recent common ancestor of Taxon A and Taxon B, and all of that ancestor's descendants”; 2) stem-based definitions (Figure 1.2), of the form “Taxon A and all taxa sharing a more recent common ancestor with Taxon A than with Taxon B”; and 3) apomorphy-based definitions (Figure 1.3), of the form “the first taxon with derived character X and all of that ancestor's descendants.” Bryant (1994) noted that, while the first two definition types will always be stable, apomorphy-based definitions are potentially confusing if that derived character is found to occur in more than one lineage (i.e., is homoplastic). Under the phylogenetic system of taxonomy, definitions of taxon names are independent with respect to previous diagnosis (as particular character states may be found to occur in other lineages or in more inclusive clades) and composition (as particular member taxa may subsequently be found to lie outside the defined clade boundary). This paper is the initial work in an ongoing study by Holtz and Padian (1995, in preparation) to clarify the phylogenetic taxonomy of major clades of theropods and related taxa.
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BARRETT, PAUL M. "THE DIET OF OSTRICH DINOSAURS (THEROPODA: ORNITHOMIMOSAURIA)." Palaeontology 48, no. 2 (2005): 347–58. http://dx.doi.org/10.1111/j.1475-4983.2005.00448.x.

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Evans, David C., Derek W. Larson, Thomas M. Cullen, and Robert M. Sullivan. "“Saurornitholestes” robustus is a troodontid (Dinosauria: Theropoda)." Canadian Journal of Earth Sciences 51, no. 7 (2014): 730–34. http://dx.doi.org/10.1139/cjes-2014-0073.

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The holotype of Saurornitholestes robustus (SMP VP-1955) from the upper Kirtland Formation (De-na-zin Member), originally identified as a dromaeosaurid, is here re-identified as an indeterminate troodontid theropod. The frontal has no diagnostic dromaeosaurid characters, but is shown to have several features unique to troodontids among deinonychosaurs, including the shallow lateral wall defining the fossae for the olfactory system, the exclusion of the supratemporal fossa from the dorsal surface of the frontal, and a raised orbital rim. The size and morphology of SMP VP-1955 is also consistent with better-known troodontid material from the late Campanian of Alberta, and as preserved, the Kirtland specimen is indistinguishable from comparable Alberta material. The revised identification of SMP VP-1955 provides the first non-dental skeletal record of a troodontid from the Kirtland Formation, and a rare record of this clade from the Kirtlandian land-vertebrate age.
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Senter, Phil. "Comparison of forelimb function betweenDeinonychusandBambiraptor(Theropoda: Dromaeosauridae)." Journal of Vertebrate Paleontology 26, no. 4 (2006): 897–906. http://dx.doi.org/10.1671/0272-4634(2006)26[897:coffbd]2.0.co;2.

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Tahara, Rui, and Hans C. E. Larsson. "Cranial pneumatic anatomy ofOrnithomimus edmontonicus(Ornithomimidae: Theropoda)." Journal of Vertebrate Paleontology 31, no. 1 (2011): 127–43. http://dx.doi.org/10.1080/02724634.2011.539646.

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Claessens, Leon P. A. M., and Mark A. Loewen. "A redescription ofOrnithomimus veloxMarsh, 1890 (Dinosauria, Theropoda)." Journal of Vertebrate Paleontology 36, no. 1 (2015): e1034593. http://dx.doi.org/10.1080/02724634.2015.1034593.

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Liao, Chun-Chi, Lindsay E. Zanno, Shiying Wang, and Xing Xu. "Postcranial osteology of Beipiaosaurus inexpectus (Theropoda: Therizinosauria)." PLOS ONE 16, no. 9 (2021): e0257913. http://dx.doi.org/10.1371/journal.pone.0257913.

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Beipiaosaurus inexpectus, from the Lower Cretaceous Yixian Formation (Sihetun locality, near Beipiao), Liaoning, China, is a key taxon for understanding the early evolution of therizinosaurians. Since initial publication in 1999, only the cranial elements of this taxon have been described in detail. Here we present a detailed description of the postcranial skeletal anatomy of the holotype specimen of B. inexpectus, including two never before described dorsal vertebrae from the anterior half of the series. Based on these observations, and comparisons with the postcranial skeleton of therizinosaurian taxa named since the most recent diagnosis, we revised the diagnostic features for B. inexpectus adding three new possible autapomorphies (PII-3 shorter than PIII-4, subequal length of the pre- and postacetabular portions of the ilium, and equidimensional pubic peduncle of ilium). Additionally, we also propose three possible synapomorphies for more inclusive taxa (Therizinosauroidea and Therizinosauridae) and discuss implications for evolutionary trends within Therizinosauria. The newly acquired data from the postcranial osteology of the holotype specimen of B. inexpectus sheds light on our understanding of postcranial skeletal evolution and identification of therizinosaurians.
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Griffin, Christopher T. "Large neotheropods from the Upper Triassic of North America and the early evolution of large theropod body sizes." Journal of Paleontology 93, no. 5 (2019): 1010–30. http://dx.doi.org/10.1017/jpa.2019.13.

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AbstractLarge body sizes among nonavian theropod dinosaurs is a major feature in the evolution of this clade, with theropods reaching greater sizes than any other terrestrial carnivores. However, the early evolution of large body sizes among theropods is obscured by an incomplete fossil record, with the largest Triassic theropods represented by only a few individuals of uncertain ontogenetic stage. Here I describe two neotheropod specimens from the Upper Triassic Bull Canyon Formation of New Mexico and place them in a broader comparative context of early theropod anatomy. These specimens possess morphologies indicative of ontogenetic immaturity (e.g., absence of femoral bone scars, lack of co-ossification between the astragalus and calcaneum), and phylogenetic analyses recover these specimens as early-diverging neotheropods in a polytomy with other early neotheropods at the base of the clade. Ancestral state reconstruction for body size suggests that the ancestral theropod condition was small (~240 mm femur length), but the ancestral neotheropod was larger (~300–340 mm femur length), with coelophysoids experiencing secondary body size reduction, although this is highly dependent on the phylogenetic position of a few key taxa. Theropods evolved large body sizes before the Triassic–Jurassic extinction, as hypothesized in most other ancestral state reconstructions of theropod body sizes, but remained rare relative to smaller theropods until the Jurassic.
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Van Valkenburgh, Blaire, and Ralph E. Molnar. "Dinosaurian and mammalian predators compared." Paleobiology 28, no. 4 (2002): 527–43. http://dx.doi.org/10.1666/0094-8373(2002)028<0527:dampc>2.0.co;2.

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Theropod dinosaurs were, and mammalian carnivores are, the top predators within their respective communities. Beyond that, they seem distinct, differing markedly in body form and ancestry. Nevertheless, some of the same processes that shape mammalian predators and their communities likely were important to dinosaurian predators as well. To explore this, we compared the predatory adaptations of theropod dinosaurs and mammalian carnivores, focusing primarily on aspects of their feeding morphology (skulls, jaws, and teeth). We also examined suites of sympatric species (i.e., ecological guilds) of predatory theropods and mammals, emphasizing species richness and the distribution of body sizes within guilds. The morphological comparisons indicate reduced trophic diversity among theropods relative to carnivorans, as most or all theropods with teeth appear to have been hypercarnivorous. There are no clear analogs of felids, canids, and hyaenids among theropods. Interestingly, theropods parallel canids more so than felids in cranial proportions, and all theropods appear to have had weaker jaws than carnivorans. Given the apparent trophic similarity of theropods and their large body sizes, it was surprising to find that species richness of theropod guilds was as great as or exceeded that observed among mammalian carnivore guilds. Separation by body size appears to be slightly greater among sympatric theropods than carnivorans, but the magnitude of size difference between species is not constant in either group. We suggest that, as in modern carnivoran guilds, smaller theropod species might have adapted to the threats posed by much larger species (e.g., tyrannosaurs) by hunting in groups, feeding rapidly, and avoiding encounters whenever possible. This would have favored improved hunting skills and associated adaptations such as agility, speed, intelligence, and increased sensory awareness.
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Souza, Geovane Alves de, Marina Bento Soares, Arthur Souza Brum, et al. "Osteohistology and growth dynamics of the Brazilian noasaurid Vespersaurus paranaensis Langer et al., 2019 (Theropoda: Abelisauroidea)." PeerJ 8 (September 15, 2020): e9771. http://dx.doi.org/10.7717/peerj.9771.

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Although the knowledge of bone histology of non-avian theropods has advanced considerably in recent decades, data about the bone tissue patterns, growth dynamics and ontogeny of some taxa such as abelisauroids are still limited. Here we describe the bone microstructure and growth dynamics of the Brazilian noasaurine Vespersaurus paranaensis using five femora and six tibiae and quantify the annual growth marks through retrocalculation of missing ones to estimate ontogenetic ages. The femoral series comprises four femoral histological classes (FHC I-IV), varying from two annuli or LAGs to seven LAGs. Femora show that sexual maturity was achieved around the seventh to tenth year of life, whereas the tibiae suggest it was earlier (around three to five years old). Tibiae represent three histological classes (THC I-III) displaying from three to nine LAGs. Two tibiae (THC III) exhibit an external fundamental system indicating that these specimens reached full skeletal size. The heterogeneous maturity observed in Vespersaurus hind limb bones could result from differential allometry scaling between femora and tibiae length with the body length. The predominant parallel-fibered bone matrix suggests that Vespersaurus grew more slowly than most theropods, including other abelisauroids, in a pattern shared with the noasaurines Masiakasaurus knopfleri from Madagascar and CPPLIP 1490 from Brazil. This deviation from the typical theropod growth pattern may be mainly correlated with small body size, but also may related to resource limitation imposed by the arid climate prevailing in southwestern Gondwana during Cretaceous. Moreover, given the ecological and phylogenetic similarities among these taxa, such features would probably be apomorphic within Noasauridae.
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SMITH, NATHAN D., PETER J. MAKOVICKY, WILLIAM R. HAMMER, and PHILIP J. CURRIE. "Osteology of Cryolophosaurus ellioti (Dinosauria: Theropoda) from the Early Jurassic of Antarctica and implications for early theropod evolution." Zoological Journal of the Linnean Society 151, no. 2 (2007): 377–421. http://dx.doi.org/10.1111/j.1096-3642.2007.00325.x.

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Gold, Maria Eugenia Leone, Stephen L. Brusatte, and Mark A. Norell. "The Cranial Pneumatic Sinuses of the TyrannosauridAlioramus(Dinosauria: Theropoda) and the Evolution of Cranial Pneumaticity in Theropod Dinosaurs." American Museum Novitates 3790, no. 3790 (2013): 1–46. http://dx.doi.org/10.1206/3790.1.

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Carrano, Matthew T., and Jonah Choiniere. "New information on the forearm and manus ofCeratosaurus nasicornisMarsh, 1884 (Dinosauria, Theropoda), with implications for theropod forelimb evolution." Journal of Vertebrate Paleontology 36, no. 2 (2016): e1054497. http://dx.doi.org/10.1080/02724634.2015.1054497.

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45

Zanno, Lindsay E., Khishigjav Tsogtbaatar, Tsogtbaatar Chinzorig, and Terry A. Gates. "Specializations of the mandibular anatomy and dentition ofSegnosaurus galbinensis(Theropoda: Therizinosauria)." PeerJ 4 (March 29, 2016): e1885. http://dx.doi.org/10.7717/peerj.1885.

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Definitive therizinosaurid cranial materials are exceptionally rare, represented solely by an isolated braincase and tooth in the North American taxonNothronychus mckinleyi, the remarkably complete skull of the Asian taxonErlikosaurus andrewsi, and the lower hemimandibles ofSegnosaurus galbinensis. To date, comprehensive descriptions of the former taxa are published; however, the mandibular materials ofS. galbinensishave remained largely understudied since their initial description in 1979. Here we provide a comprehensive description of the well-preserved hemimandibles and dentition ofS. galbinensis(MPC-D 100/80), from the Upper Cretaceous Bayanshiree Formation, Gobi Desert, Mongolia. The subrectangular and ventrally displaced caudal hemimandible, extreme ventral deflection of the rostral dentary, and edentulism of the caudal dentary ofS. galbinensisare currently apomorphic among therizinosaurians. Unique, unreported dental traits including lingually folded mesial carinae, development of a denticulated triangular facet on the distal carinae near the cervix, and extracarinal accessory denticles, suggest a highly specialized feeding strategy inS. galbinensis. The presence of triple carinae on the distalmost lateral tooth crowns is also unique, although may represent an abnormality. Contrasted with the simplistic dentition of the contemporaneous therizinosauridE. andrewsi, the dentition ofS. galbinensisis indicative of niche partitioning in food acquisition, processing, or resources among known therizinosaurids inhabiting Asian ecosystems in the Late Cretaceous. Although not quantitatively correlated with diet, this suite of specializations is otherwise unique among theropod dinosaurs and supports derived inferences of facultative or obligate herbivory in therizinosaurids, ultimately adding novel information to our understanding of ecomorphology in theropods.
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SENTER, PHIL. "FORELIMB FUNCTION IN ORNITHOLESTES HERMANNI OSBORN (DINOSAURIA, THEROPODA)." Palaeontology 49, no. 5 (2006): 1029–34. http://dx.doi.org/10.1111/j.1475-4983.2006.00585.x.

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47

MAKOVICKY, PETER J., MARK A. NORELL, JAMES M. CLARK, and TIMOTHY ROWE. "Osteology and Relationships of Byronosaurus jaffei (Theropoda: Troodontidae)." American Museum Novitates 3402 (March 2003): 1–32. http://dx.doi.org/10.1206/0003-0082(2003)402<0001:oarobj>2.0.co;2.

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MAKOVICKY, PETER J., MARK A. NORELL, JAMES M. CLARK, and ROWE TIMOTHY. "Osteology and Relationships of Byronosaurus jaffei (Theropoda: Troodontidae)." American Museum Novitates 3402 (March 2003): 1–32. http://dx.doi.org/10.1206/0003-0082(2003)402<1:oarobj>2.0.co;2.

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Turner, Alan H., Diego Pol, and Mark A. Norell. "Anatomy ofMahakala omnogovae(Theropoda: Dromaeosauridae), Tögrögiin Shiree, Mongolia." American Museum Novitates 3722, no. 3722 (2011): 1–66. http://dx.doi.org/10.1206/3722.2.

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Kirkland, James I., and Douglas G. Wolfe. "First definitive therizinosaurid (Dinosauria; Theropoda) from North America." Journal of Vertebrate Paleontology 21, no. 3 (2001): 410–14. http://dx.doi.org/10.1671/0272-4634(2001)021[0410:fdtdtf]2.0.co;2.

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