The Upper Cretaceous (Turonian) Bissekty Formation of Uzbekistan has yielded many isolated bones and teeth representing a variety of non-avian theropod dinosaurs. A pedal phalanx II-2 indicates the presence of a dromaeosaurid theropod that attained a larger body size than any previously known member of that clade. The same formation also yielded a large maxillary fragment that has recently been described as a neovenatorid carcharodontosaurian (Ulughbegsaurus uzbekistanensis). However, this specimen lacks unambiguously diagnostic features of that clade, and its purported carcharodontosaurian characters are either taphonomic artefacts or also shared by dromaeosaurids. Thus, the phylogenetic relationships of Uleghbegsaurus uzbekistanensis remain uncertain. A giant dromaeosaurid occurred together with the medium-sized tyrannosauroid Timurlengia euotica in the Bissekty assemblage.

Dinosaur body fossil material is rare in Scotland, previously known almost exclusively from the Great Estuarine Group on the Isle of Skye. We report the first unequivocal dinosaur fossil from the Isle of Eigg, belonging to a Bathonian (Middle Jurassic) taxon of uncertain affinity. The limb bone NMS G.2020.10.1 is incomplete, but through a combination of anatomical comparison and osteohistology, we determine it most likely represents a stegosaur fibula. The overall proportions and cross-sectional geometry are similar to the fibulae of thyreophorans. Examination of the bone microstructure reveals a high degree of remodelling and randomly distributed longitudinal canals in the remaining primary cortical bone. This contrasts with the histological signal expected of theropod or sauropod limb bones, but is consistent with previous studies of thyreophorans, specifically stegosaurs. Previous dinosaur material from Skye and broadly contemporaneous sites in England belongs to this group, including Loricatosaurus and Sarcolestes and a number of indeterminate stegosaur specimens. Theropods such as Megalosaurus and sauropods such as Cetiosaurus are also known from these localities. Although we find strong evidence for a stegosaur affinity, diagnostic features are not observed on NMS G.2020.10.1, preventing us from referring it to any known genera. The presence of this large-bodied stegosaur on Eigg adds a significant new datapoint for dinosaur distribution in the Middle Jurassic of Scotland.

The problem of the origin of dinosaurs has historically had three dimensions. The first is the question of whether Dinosauria is monophyletic, and of its relationships to other archosaurs. This question was plagued from the beginning by a lack of relevant fossils, an historical burden of confusing taxonomic terms and a rudimentary approach to devising phylogenies. The second dimension concerns the functional and ecological adaptations that differentiated dinosaurs from other archosaurs, a question also marred by lack of phylogenetic clarity and testable biomechanical hypotheses. The third dimension comprises the stratigraphic timing of the origin of dinosaurian groups with respect to each other and to related groups, the question of its synchronicity among various geographic regions, and some of the associated paleoenvironmental circumstances. None of these dimensions alone answers the question of dinosaur origins, and they sometimes provide conflicting implications. Since Dinosauria was named, one or another set of questions has historically dominated academic discussion and research. Paradigms have shifted substantially in recent decades, and current evidence suggests that we are due for more such shifts. I suggest two changes in thinking about the beginning of the “Age of Dinosaurs”: first, the event that we call the (phylogenetic) origin of dinosaurs was trivial compared to the origin of Ornithodira; and second, the “Age of Dinosaurs” proper did not begin until the Jurassic. Re-framing our thinking on these issues will improve our understanding of clade dynamics, timing of macroevolutionary events, and the effects of Triassic climate change on terrestrial vertebrates.

Rare remains of tyrannosauroid dinosaurs from the Aguja Formation in West Texas indicate the presence here of a relatively gracile species, comparable in form and adult size to Appalachiosaurus or subadult albertosaurines, Gorgosaurus and Albertosaurus. Histologic analysis of one of the specimens indicates that the Aguja tyrannosaur attained an adult size substantially smaller than adult albertosaurines (700 kg, 6·5 m body length). The frontal bone is narrow with a wide orbital slot and a bipartite joint for the postorbital, features thought to be diagnostic of Albertosaurinae; but there is a tall sagittal crest and reduced parietal wedge separating the frontals on the midline, features thought to be diagnostic of Tyrannosaurinae. The tall sagittal crest may be a synapomorphy of Tyrannosaurinae, and the Aguja tyrannosaur is herein referred to that clade. However, the unique combination of character states exhibited by the frontal prevents confident attribution to any known species. The Aguja tyrannosaur provides further evidence that North American Campanian tyrannosauroids were remarkably diverse for such large predators, and that each species was apparently endemic to a relatively small geographic province.

Many hypotheses have been proposed for the rise of dinosaurs, but their early diversification remains poorly understood. This paper examines the occurrences, species diversity and abundance of early dinosaurs at both regional and global scales to determine patterns of their early evolutionary history. Four main patterns are clear: (1) sauropodomorph dinosaurs became abundant during the late Norian–Rhaetian of Gondwana and Europe; (2) Triassic dinosaurs of North America have low species diversity and abundance until the beginning of the Jurassic; (3) sauropodomorphs and ornithischians are absent in the Triassic of North America; and (4) ornithischian dinosaurs maintain low species diversity, relative abundance and small body size until the Early Jurassic. No one hypothesis fully explains these data. There is no evidence for a Carnian–Norian extinction event, but sauropodomorphs did become abundant during the Norian in some assemblages. No clear connection exists between palaeoenvironment and early dinosaur diversity, but environmental stress at the Triassic–Jurassic boundary is consistent with changes in North American dinosaur assemblages. Elevated growth rates in dinosaurs are consistent with the gradual phyletic increase in body size. This study demonstrates that early dinosaur diversification was a complex process that was geographically diachronous and probably had several causes.

Jaw fragments bearing teeth from the Barremian of Boca do Chapim (Lisboa e Setubal Province, Portugal), originally considered as crocodilian and identified as Suchosaurus girardi by Sauvage, are redescribed and referred to the spinosaurid dinosaur Baryonyx, on the basis of comparison with Baryonyx walkeri, from the Barremian of England. This extends the geographical distribution of this unusual theropod genus to Portugal.

Baryonyx appears to have been a frequent component of Early Cretaceous dinosaur assemblages in the Iberian region, which may have formed a biogeographical ‘stepping-stone’ for baryonychine dispersal between Europe and Africa.

Casts of forelimb elements of the Cretaceous theropod dinosaur Acrocanthosaurus atokensis were manually manipulated to determine range of motion and infer function. It was found that the humerus can swing posteriorly into a horizontal position but can neither swing laterally to glenoid height nor anteriorly much beyond the glenoid. The forearm can approach but not achieve full extension and right-angle flexion. Pronation and supination are precluded by immobility of the radius relative to the ulna. Motion also seems to be restricted at the wrist. The palm faces medially, and digital movement is subtransverse. All three digits are capable of extreme hyper-extension. Digits I and II converge during flexion. Only digit III can be abducted or adducted. The limited anterior range of brachial motion infers that Acrocanthosaurus first apprehended prey orally, using the forelimb afterwards to secure its grip or deliver fatal blows. Acrocanthosaurus could only manually grasp prey that was beneath its chest, towards which it may have used its mouth to move prey. Struggling prey would have impaled itself further upon the permanently and strongly flexed first ungual. The range of motion in the forelimb of Acrocanthosaurus resembles that of Herrerasaurus and Dilophosaurus, and exceeds that of Tyrannosaurus. Acrocanthosaurus exhibits a greater manual range of motion than ornithomimid and deinonychosaurian coelurosaurs, but less at the shoulder and elbow. Coelurosaurian theropods exhibit reduced digital flexion and hyper-extension, which suggests a change in the use of the manus in coelurosaurs.

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.