Over 230 million years of Earth's history, dinosaurs became a major terrestrial animal clade and produced one of the most species-rich living tetrapod lineages: birds. Yet, largely because of uncertainty surrounding the phylogeny of early dinosaurs, the tempo and mode of their emergence and initial radiation remain poorly constrained. Here, we reconstruct the initial diversification of dinosaurs through Bayesian tip-dating analyses. Using nine morphological datasets, we estimate that dinosaurs emerged between 250 and 240 Ma, 10 million years before the earliest unambiguous dinosaur fossils. The emergence of the dinosaurs was followed by the rapid appearance and diversification of all major lineages, coinciding with a burst of morphological evolution that peaked in the early Late Triassic. The patterns that we infer are consistent with the expectations under a scenario of evolutionary radiation, in which ecologically disparate lineages rapidly diversify from a single common ancestor. In turn, our results provide a biological explanation for the instability surrounding early dinosaur phylogeny and suggest that the diversity of dinosaurs has been sculpted by multiple rapid radiations following successive mass extinctions in deep time.
The Cretaceous-Paleogene (K-Pg) bolide impact caused the extinction of over half of all plant and animal species. The "fungal infection mammalian-selection" (FIMS) hypothesis, first proposed in 2005, suggested that a post-K-Pg fungal bloom created selective pressures that favored the survival and evolutionary radiation of warm-blooded mammals due to their resistance to fungal diseases, while cold-blooded dinosaurs were at an evolutionary disadvantage. Evidence now indicates that dinosaurs were also endotherms; hence, body temperature alone was unlikely to have predisposed all dinosaurs to fungal infection. The fossil record suggests that avian-like respiratory anatomy was present in archosaurs, the ancestors of all dinosaurs. Here, we update the FIMS hypothesis, drawing on insights from modern bird anatomy and physiology, to suggest that dinosaurs may have been more susceptible to respiratory diseases, including fungal infections, perhaps sufficiently to tip the scales away from a second dinosaur age in a world replete with fungal spores.
Discovery of the "Dueling Dinosaurs" and other significant dinosaur localities from remote and isolated exposures of the Hell Creek Formation in central Montana highlight the complexity of establishing stratigraphic context and correlating Hell Creek Formation fossil localities located within and outside of the type area. Stratigraphic correlation is particularly problematic for the lower two-thirds of the Hell Creek Formation, which generally lacks reliable biostratigraphic or magnetostratigraphic zonation and has no dated ash beds. To address these enduring issues for one of the most significant Upper Cretaceous terrestrial fossil-bearing units in North America, detailed stratigraphic sections were established on the Murray Ranch and on McGinnis Butte in central Montana and correlated with other published Hell Creek Formation localities via magnetostratigraphy, biostratigraphy, and radioisotopic dating of ash beds. Results indicate that the K-Pg boundary is not exposed in the study area; however, high-precision U-Pb CA-TIMS zircon ages for two newly discovered ash beds (66.929 ± 0.020 Ma and 66.850 ± 0.026 Ma, 2σ internal uncertainties) that bracket the "Dueling Dinosaurs" quarry provide the first absolute ages for the lower portion of the Hell Creek Formation anywhere. Bayesian age-stratigraphic modelling places the "Dueling Dinosaurs" depositional age at 66.897 + 0.023/-0.028 Ma and suggests that the age of the base of the formation is ~ 67.102 + 0.710/-0.173 Ma (or older) in the study area. Comparison of stratigraphic architecture within the study area with published sections in the type area suggests that named sandstone marker horizons used for lithostratigraphic and sequence stratigraphic correlation in the type area have limited utility for regional correlation and need to be used with caution.
Numerous lineages of theropod dinosaurs display notable modification of the forelimb, particularly reduction in size and number of digits. Alvarezsauroids are one of the most striking examples of this, exhibiting extreme shortening and increased robusticity of forelimb elements, with a functionally monodactylous manus in late-diverging taxa. These features are generally interpreted as adaptations for digging, possibly as part of a myrmecophagous ecology. Here, we test this hypothesis, using computational range of motion analysis of the shoulder and elbow joints to demonstrate the feasibility of digging behaviours in Mononykus olecranus, a highly specialized alvarezsauroid, and the less specialized Bannykus wulatensis. We find that Bannykus has the capacity for various digging styles and generalized forelimb function, while Mononykus has more restricted motion and may have employed a highly specialized digging style. We also identify similarities in forelimb muscle moment arms between alvarezsaurs and specialized mammalian diggers, supporting adaptation for digging. These findings are consistent with interpretations of insectivory in alvarezsauroids, and suggest increasing specialization to myrmecophagy throughout their evolutionary history, shedding new light on the evolution of this enigmatic clade and the ecological diversity of non-avian theropod dinosaurs.
Postcranial skeletal pneumaticity (PSP) is common in the presacral vertebrae of sauropod dinosaurs, but seemingly rare in their caudal vertebrae. Where identified, evidence for caudal vertebral PSP in sauropods is primarily based on the presence of external features, such as lateral fossae. However, such fossae can only be regarded as unequivocally pneumatic if communication between them and internal pneumatic bone texture can be confirmed. Based upon evidence from internal imaging, caudal vertebral PSP was previously known only in a rebbachisaurid diplodocoid (anterior caudal centrum and neural arch), some somphospondylan titanosauriforms (anterior caudal neural arches only) and saltasaurine titanosaurs (anterior-posterior caudal centra and neural arches). Here, we present novel CT scan data of caudal vertebrae of six Middle-Late Jurassic sauropods, representing several eusauropod lineages. We synthesise these new data with a comprehensive critical appraisal of purported external and internal evidence for caudal vertebral PSP in Sauropodomorpha. Newly sampled specimens of the non-neosauropod eusauropods Cetiosaurus sp. (anterior caudal centrum), 'Cetiosaurus glymptonensis' (middle caudal centrum) and the mamenchisaurid Wamweracaudia keranjei (anterior-middle caudal vertebrae), as well as the dicraeosaurine diplodocoid Dicraeosaurus sattleri (anterior caudal vertebra), are apneumatic. By contrast, the anterior-posterior caudal centra and neural arches of the diplodocine diplodocoid Tornieria africana possess deeply invasive external fossae that communicate with internal pneumatic chambers. Shallow external fossae on the centra and neural arches of at least the anteriormost 24 caudal vertebrae of the brachiosaurid titanosauriform Giraffatitan brancai communicate with internal pneumatic chambers. We observe a repeated pattern of PSP invading the anterior caudal vertebrae, with at least five independent acquisitions and/or reversals within Neosauropoda. Furthermore, for the first time, we demonstrate that extreme caudal vertebral PSP, in which pneumaticity extends into the middle-posterior region of the tail, is not restricted to saltasaurines, with this having also evolved independently in diplodocines and brachiosaurids. Finally, we find that both small- and large-bodied sauropods, including those with relatively short and long tails, evolved (and lost) caudal vertebral PSP. Therefore, the development of caudal vertebral PSP in sauropods does not appear to correspond with changes in body shape or mass. Instead, it might result from the opportunistic nature of pneumatic diverticula. However, given the high degree of inter- and intraspecific plasticity in its phylogenetic and serial distribution, we recognise that the evolution of PSP into the tail of sauropods might have been driven by a set of as-yet unknown, complex selective pressures.
Forelimb reduction has been observed in numerous and disparate non-avian theropod dinosaurs, resulting in the hypothesis that reduced forelimbs evolved convergently. Clades with reduced forelimbs also possess high degrees of cranial robusticity and gigantic body sizes. Here, we provide a novel quantification of forelimb reduction across Theropoda, and create and implement a cranial robusticity scoring system, and analyse this dataset using bivariate and comparative phylogenetic analyses. Results indicate that forelimb reduction is strongly correlated with cranial robusticity and gigantism. Reduced/vestigial forelimbs evolved in at least five theropod lineages in concert with increased cranial robusticity and gigantism. Abelisaurids, carcharodontosaurids and tyrannosaurids show the greatest forelimb reduction relative to the skull. Repeated forelimb reduction across theropods was facilitated by increased cranial robusticity and greater body size that was potentially influenced by an upward trend in prey body size. These events resulted in a shift from subduing prey using grasping forelimbs to using powerful bites and robust skulls.
Fossil remains of the small maniraptoran theropod dinosaur group Troodontidae have so far been documented exclusively from the Laurasian continents, with one exception. A single tooth specimen (DUGF/52), recovered from the Upper Cretaceous Kallamedu Formation in the Cauvery Basin, South India, represents the only known record of this group from Gondwana. Recent field investigations in the same locality have yielded a second, better-preserved troodontid tooth (DUGF/168). This study provides a detailed description of the new specimen and compares both Indian teeth with known troodontid material to clarify their taxonomic affinities. In addition to the qualitative morphological comparisons, quantitative statistical analyses, including principal component analysis (PCA) and discriminant function analysis (DFA), were conducted using seven quantitative variables to support taxonomic assessment. The results reaffirm the previous identification of the specimen DUGF/52 as Troodontidae indet and further assign the new specimen to the same family, showing close morphological resemblance to the North American genus Troodon. The occurrence of this typically Laurasian dinosaur group in the Late Cretaceous deposits of India may reflect either the persistence of a once widespread lineage that became restricted to the Northern Hemisphere following the Laurasia-Gondwana breakup or a later dispersal event from Laurasia to India via Europe and Africa.
Climate highly influenced the distribution of major animal groups that emerged during the Triassic throughout the supercontinent Pangea. The earliest dinosaurs and associated assemblages (Carnian Stage, Late Triassic, ~230 Ma) are recovered along a paleolatitudinal climate belt spanning southern Pangea. However, developmental responses of different amniotic clades to climate across these environments remain unknown. Characterizing developmental variability, presumably driven in part by climatic variability within this belt, helps constrain the climatic ranges that shaped the earliest dinosaurs prior to their worldwide dispersal, while also providing insights into developmental plasticity of Triassic fauna. We analyzed the bone histology of five vertebrate taxa from the Carnian of Zimbabwe, including sauropodomorph and herrerasaurid dinosaurs, a gomphodontosuchine cynodont, a hyperodapedontine rhynchosaur, and a suchian archosaur (?aetosaur) as a proxy to assess probable climatic influence by comparing various growth strategies/metabolisms of these clades across southern Pangea. The dinosaurs are continuously growing individuals that exhibit well-vascularized woven-parallel and parallel-fibered cortical bone with no apparent growth marks. The cynodont is an immature specimen with a well-vascularized fibrolamellar matrix that has anastomosing vascular canals throughout the cortex and a single growth mark, indicating rapid growth. The rhynchosaurian femur and suchian tibia show moderate to poorly vascularized parallel-fibered and woven-fibered matrixes possessing multiple lines of arrested growth along with an external fundamental system, suggesting these were slow-growing individuals that had reached skeletal maturity at the time of death. Comparing this histology to that of similar assemblages from current-day Brazil, Argentina, and India (which fell along the same paleolatitudinal zone during the Triassic), the mid-continent (i.e., Zimbabwean) dinosaurs exhibit continuous uninterrupted growth in contrast to other histologically sampled dinosaurs from different localities along this climatic belt, whereas the Zimbabwean rhynchosaur and suchian exhibit patterns with more frequent cessation of growth than their South American counterparts. Slower-growing Zimbabwean taxa-presumably, more susceptible to climatic stressors-exhibit characteristics suggestive of a less resource-rich environment (e.g., frequent cessations, more interrupted growth) compared with rhynchosaurs and aetosaurs from South America. Taxa with faster growth rates and higher metabolic regimes (i.e., dinosaurs, cynodont) from this same assemblage apparently grew rapidly-and roughly continuously-throughout the year. This is consistent with an overall more arid but less seasonal climate in Zimbabwe compared to the signals recovered in Brazil, Argentina, and India.
Extant birds and the earliest dinosaurs may share fundamental metabolic features essential for aerobic exercise, suggesting that the extraordinary physical performance typical of avian species originated when dinosaurs first appeared during the Carnian Pluvial Episode (CPE). This physiological adaptation is complemented by hyperactive mitochondria that exhibit high oxygen consumption and low reactive oxygen species production. Molecular genomics of fossils, the so-called "Jurassic Genome," indicates that these early dinosaurs possessed compact genomes, 50-60% the size of the human genome, and small cells, implying a highly stringent metabolic regime. We suggest that hyperactive mitochondria, closely associated with compact genomes and small cells, drive theropod adaptation to the hot, dry, and hypoxic environments of the Late Triassic period, ultimately enabling their ecological dominance. Early dinosaurs such as Herrerasaurus are hypothesized to have possessed advanced physiological traits shared with modern birds, including hyperactive mitochondria, compact genomes, small cells, and a developing air-sac system. Collectively, these features most likely may have contributed to exceptional metabolic capacity, locomotor performance, and adaptation to the harsh environment of the CPE.
Many terrestrial vertebrates, both extinct and extant, have widespread or even global distributions. Although vicariance (e.g., through continental fragmentation, sea-level changes) explains some of these patterns, others seemingly require long-distance trans-oceanic dispersal. A key but underexplored factor in this debate is the biological feasibility of such dispersal based on an organism's physiology and biomechanics. We introduce ENHYDROSS, a new mechanistic energetic model that estimates optimal swimming speed and minimum cost of transport for any vertebrate. These allow us to estimate maximum swimming distances and durations. We tested ENHYDROSS on two mammals (elephant, polar bear) and five reptiles, including the Aldabra giant tortoise, saltwater crocodile, ostrich, and two extinct nonavian dinosaurs (Lambeosaurus and Rapetosaurus). For the extinct dinosaurs, we used a broad range of basal metabolic rates to account for different thermophysiological hypotheses. The model's estimates for extant animals align with observed data, while cases of underestimates can be attributed to the effects of ocean currents, as evidenced by estimated passive drifting distances and times under predominantly mild and intermediate currents. ENHYDROSS generally predicts greater swimming capacity than previously proposed models due to assumptions like null-thermogenesis, resulting in lower minimum cost of transport. Applying our model to test the feasibility of extinct dinosaur dispersal between Africa and Europe during the Cretaceous via the Alboran route (the oceanic corridor separating Iberia from Morocco), we found that both hadrosaurs and titanosaurs could plausibly complete the journey, particularly under favorable conditions such as low sea levels, stepping-stone islands, and higher fat reserves. Hadrosaurs showed slightly better swimming efficiency. Dispersal was especially feasible during the early-middle Albian (112.5-107.5 Ma) and latest Cretaceous (72.5-66 Ma), but was unlikely during periods of high sea levels (97.5-77.5 Ma). These results support the possibility of trans-oceanic dinosaur dispersal across distances of up to ~560 km.
Differences in skull and tooth morphology, stomach contents, and estimated bite force between medium-to-large sized (≥100 kg) predatory theropod dinosaurs have long been suspected to correlate with differences in their diets and dietary guilds (e.g., hypercarnivory, piscivory). However, excluding exceptionally rare specimens with associated stomach contents or coprolites, the diets and dietary guilds of these taxa can be difficult to infer in detail. To enable comparisons across a wider array of taxa, especially those lacking stomach contents, an accurate, reliable proxy for diet needs to be employed. Dental microwear texture analysis (DMTA) has been used to investigate the diets of extant and extinct diapsids through examination of micron-scale surface textures. Here, we present a pilot study to determine the utility of DMTA for assessing diet in theropod dinosaurs and whether single teeth can act as a proxy for microwear across the entire dentition. To accomplish this, we examined texture variation along the tooth row in four medium-to-large-bodied theropods: Allosaurus, Ceratosaurus, Irritator, and Tyrannosaurus. Our results suggest that tooth position does affect DMTA and therefore DMT samples should be constrained using the following three guidelines: teeth should be sampled from within a single cranial element (premaxilla, maxilla or dentary); if comparing across elements, samples should be constrained to a single side of the teeth (labial or lingual); and comparisons across the labial surfaces of the dentary and maxillary teeth should be avoided. Our findings imply that taxonomically distinct isolated theropod teeth can be used to infer the dietary ecology of theropod faunal assemblages if constrained sampling occurs.
The first dinosaur to be formally named was Megalosaurus in 1824. Over the subsequent 200 years more than 1,200 different species of dinosaur have been discovered and named. The discoveries come from every continent, but different regions are characterized with different species from different geological time periods. Given this multi-generational collection history, from a wide variety of geographic areas, and representing a huge diversity of animals, it was felt that a new type of visual summary of the current state of our knowledge of dinosaur diversity and discovery history would be much more informative and revealing than a simple list comprised of words and numbers. Using recently published, comprehensive surveys of all known Mesozoic, non-avian dinosaurs, a series of computer-generated, horizontal, stacked, bar-type graphs are used to graphically show how our knowledge of dinosaur diversity has developed over the past 200 years at the decade level. The graphs use clusters of coloured boxes, with individual boxes scaled to the numbers of dinosaurs from a region, to enable comparisons of counts of dinosaur discoveries from different regions within and between decades. The colours are used to identify the countries and regions on an accompanying global map. This analysis of the historical growth in our knowledge of dinosaur diversity is presented in two ways: at the high level of the clades Theropoda, Sauropodomorpha and Ornithischia; and at a lower one with many detailed monophyletic and paraphyletic sub-group levels. As of end of 2025 this survey finds that there are 1,259 reliably known dinosaur species: 428 ornithischians, 366 sauropodomorphs and 465 theropods. From the entire 19th century only 58 dinosaur species can be viewed as having been discovered and still be considered valid today. These 19th century discoveries came from Europe and the United States of America with just three exceptions. Dinosaur discovery and naming rates were very low, typically no more than 10 per decade per major clade, until the 1970s when the decadal counts began to exceed the total 19th century counts for the first time. Discoveries from 1920s began to fully reveal to the true global extent of dinosaur occurrences. The early 2000s saw Argentina and China become the leading countries for new dinosaurs, but Europe and the United States continue to produce new discoveries up to the present.
AbstractThe evolution of feeding performance traits is often inferred to reflect adaptation to dietary resources, but the role of constraint and trade-offs with other traits is rarely explored. Here, we focus on feeding performance in pachycephalosaurs, a group of Late Cretaceous dinosaurs known for their cranial dome. The bony dome is thought to be a sociosexual display structure, but we hypothesize that its presence constrained the space for jaw adductor musculature and reduced the angle of these muscles, thereby reducing feeding performance. We test this by reconstructing the cranial musculature of five phylogenetically and temporally diverse midsized herbivorous dinosaurs: two ornithischians (Heterodontosaurus tucki, Lesothosaurus diagnosticus), one ornithopod (Hypsilophodon foxii), one ceratopsian (Psittacosaurus lujiatunensis), and a pachycephalosaur (Stegoceras validum). Our model of Stegoceras validum-the first for any pachycephalosaur-suggests that its feeding performance was much closer to that of basal ornithischians and ornithopods than expected for a derived Late Cretaceous taxon and contrary to the derived feeding performance of Psittacosaurus lujiatunensis, another marginocephalian. We interpret that the dome constrained pachycephalosaurs to a more plesiomorphic dentition and low-fiber herbivore niche. This may constitute one of the first examples of a sociosexual display structure constraining the evolution of feeding traits. This research also highlights the unclear historical genesis of sociosexually selected structures, especially as to whether they are beneficial structures, costly structures, or "opulent" structures at their most incipient stages.
The first 10 million years (Myr) following the Cretaceous-Paleogene (K-Pg) mass extinction marked a period of global greenhouse conditions and dramatic rise of placental mammals. Because ~80% of known terrestrial sections capturing post-K-Pg mammal recovery come from North America, a substantial knowledge gap exists in the tempo and mode of recovery in Asia, where only 3% of global sites are located and most contain species found nowhere else. We show that isolated Paleocene eutherian assemblages from China (1) exhibited high mean tooth size and disparity early in the Paleocene, (2) shifted in their dental shape in parallel with regional and global environmental changes later in the Paleocene, and (3) achieved maximum dental shape-performance covariation near the end of the first 10 Myr post-K-Pg. This 'brawn before bite' transformation, coupled with prolonged dental shape versus performance variability, favors a scenario whereby many living orders of eutherian mammals were borne out of phenotypically and functionally plastic ancestral assemblages, including those in tropical South China, during the Paleocene. Over the course of Earth's history, five major mass extinctions have shaped life as we know it today. The most recent occurred around 66 million years ago at the end of the Cretaceous Period, leading to the demise of non-avian dinosaurs and ushering in the age of mammals. Most of what we know about how mammals recovered from this mass extinction comes from fossil sites in North America. Far less is known about how ancient mammals in other parts of the world adapted to a dramatically altered environment after the disappearance of large dinosaurs. Tseng, Li and Ting investigated how some of the earliest mammal species in Asia recovered following this global mass extinction. They studied 200 individual teeth from 48 specimens of extinct mammals, including members of the Pantodonta (large herbivorous mammals), Arctostylopidae (stocky herbivorous and omnivorous mammals), and Anagaloidea (a group closely related to rodents). Using high-resolution 3D models of these rare fossil teeth, the researchers quantified variation in tooth shape and function. Their analyses revealed that mammals in East Asia, particularly South China, were already relatively large during the early Palaeocene, the first epoch of the age of mammals. Over the next five million years, their teeth became increasingly specialised for different forms of chewing and food processing, reflecting the likely diversification of diets and ecological niches within mammal communities. The findings also suggest that these early mammals were ecologically flexible, meaning they were able to exploit a wide range of food resources and adapt to changing environmental conditions. As ecosystems recovered and transformed during the first 10 million years after the end-Cretaceous mass extinction, the relationship between tooth shape and function also shifted, indicating changing evolutionary pressures and ecological opportunities. The study by Tseng, Li and Ting helps fill an important gap in our understanding of how biodiversity recovered in different regions of the world following the most recent major mass extinction. Their findings may also inform predictive models and conservation strategies aimed at understanding how modern animals could respond to future biodiversity crises. Insights from the past can help us prepare for the present and future, as rapid climate and environmental change increasingly challenge the coexistence of humans and the natural world.
Mamenchisauridae is a group of long-necked non-neosauropodan eusauropod dinosaurs that were abundant in East Asia during the Middle to Late Jurassic, but their diversity and geographic distribution outside China remain poorly documented. Here we describe Uragasaurus kalasinensis gen. et sp. nov., a new sauropod dinosaur from the Phu Kradung Formation of northeastern Thailand. The new taxon is based on a well-preserved anterior dorsal vertebra exhibiting a distinctive combination of characters, including a unique Y-shaped configuration formed by the intraprezygapophyseal and single intraprezygapophyseal laminae and a camellate internal pneumatic structure within the centrum revealed by computed tomography (CT). Phylogenetic analyses recover the new taxon as an early-diverging member of Mamenchisauridae. This discovery represents the first formally named mamenchisaurid from Thailand and expands the known geographic distribution of the clade in Southeast Asia. The occurrence of this taxon in the Lower part of the Phu Kradung Formation also contributes to understanding faunal succession within the unit, supports an Upper Jurassic age for the lower part of the formation, and improves understanding of sauropod diversity in Southeast Asia during the Jurassic-Cretaceous transition.
A pivotal innovation in the evolution of powered flight in dinosaurs was the triosseal canal-a specialized passage formed by the scapula, coracoid, and furcula that guides the wing-elevation tendon. However, the origins of this structure remained obscure. Here, we applied integrated histological analysis and micro-computed tomography (CT) scanning of a new enantiornithine specimen and the basal ornithuromorph Archaeorhynchus. Our results indicate that the triosseal canal evolved first through paedomorphosis of the coracoscapular joint into a synchondrosis in ornithothoracines and subsequent acquisition of the acrocoracoclavicular joint in ornithuromorphs. The complete lack of a connection between the furcula and coracoid represents one of the crucial skeletal disparities between enantiornithines and ornithuromorphs. We propose that the closure of the triosseal canal in ornithuromorphs markedly improved tendon stability, facilitating a greater range of wing motion and more efficient flight compared to enantiornithines, serving as one of the critical functional triggers responsible for their ecological diversification.
The Tyrannosauridae emerged as the dominant large predators in Laurasia during the Late Cretaceous. Their evolution in North America culminated with the replacement of Albertosaurinae, Daspletosaurinae, and Teratophonei, with masses of 2-3 tonnes, by the giant Tyrannosaurus in the late Maastrichtian, with a mass approaching or exceeding 10 tonnes. The origin of Tyrannosaurus remains enigmatic, but fossils suggest an origin in the Campanian-Maastrichtian of southern Laramidia. Here we describe an unusually large and robust tyrannosaurid tibia from the late Campanian aged Hunter Wash Member of the Kirtland Formation, New Mexico, ~ 74 Ma. The tibia measures 960 mm in length and 128 mm in diameter, ~84% and 78% the dimensions of the largest known Tyrannosaurus, suggesting a mass approaching 5 tonnes, larger than any contemporary tyrannosaur. The Hunter Wash tyrannosaur could potentially represent (i) an unusually large and robust Bistahieversor, (ii) a previously unknown lineage of giant tyrannosaur, or (iii) an early representative of Tyrannosaurini. The tibia's large size, robust proportions, and shape of the distal shaft are most consistent with referral to Tyrannosaurini. The Hunter Wash tyrannosaur emphasizes the marked endemicity of Laramidian dinosaurs; while smaller Albertosaurinae and Daspletosaurini inhabited the north, giant tyrannosaurins occurred in the south.
Triassic pseudosuchians had highly diversified cranial morphologies. These archosaurs occupied diverse ecological roles, ranging from terrestrial predators and herbivores to semiaquatic ambush predators and possible waders. Here, we apply linear cranial morphometrics to assess possible convergences with other sauropsids from the clades Theropoda, Squamata, and Plesiosauria and discuss their paleoecology, based upon what was known for the aforementioned clades. Thus, a total of 34 specimens of Triassic pseudosuchians and theropod dinosaurs were added to a morphometrics dataset originally used to infer the ecology of the enigmatic theropod Spinosaurus aegyptiacus. Principal component analysis and permutational multivariate analyses of variance were used to evaluate morphospace occupation and group differentiation. Our results indicate that linear variables are capable of distinguishing semiaquatic and aquatic taxa from terrestrial taxa, but fail to distinguish between semiaquatic and fully aquatic taxa, and could not distinguish between the different niches of the sampled terrestrial taxa. Phytosaurs cluster close to marine squamates, Qianosuchus mixtus occupies an intermediate position between the phytosaurs and the crocodylomorphs, erpetosuchids plotted near varanids. Beaked pseudosuchians did not cluster close to beaked theropods, with Effigia okeeffeae overlapping with Baryonyx walkeri. The loricatans, and possible synonymous, Decuriasuchus quartacolonia and Prestosuchus chiniquensis overlapped. Some loricatans plot near ornithomimids, and Saurosuchus galilei cluster close to Acrocanthosaurus atokensis. We conclude that convergent morphologies do not necessarily reflect convergent function in Triassic pseudosuchians. The research of their paleoecology would benefit from the integration of morphology and function rather than morphology and convergence, especially with obscure taxa such as the poposauroids.
In this work 40 isolated teeth of theropod dinosaurs from the Cenomanian (Upper Cretaceous) locality of Algora are described. The paleontological area of Algora (Guadalajara province, Spain) provides the highest concentration of macroremains of Cenomanian vertebrates in southwestern Europe. Isolated theropod teeth are the most abundant remains in Algora as far as this group is concerned. Isolated theropod teeth constitute important evidence to analyse theropod diversity, since they are quite common in the fossil record. There have been previous tentative assignations of these theropod teeth to different theropod groups such as Carcharodontosauridae and Abelisauridae. However, in this work we have conducted a more exhaustive and robust analysis with a larger sample size using morphological comparisons using multivariate and cladistic analyses. The results of the analyses carried out in this work support the identification of the isolated teeth of Algora as a theropod abelisaurid, most likely belonging to the subfamily Majungasaurinae. This would further corroborate the presence of this abelisaurid lineage in Europe during the Late Cretaceous, from the Cenomanian onwards.