A giant tyrannosaur from the Campanian-Maastrichtian of southern North America and the evolution of tyrannosaurid gigantism.

Tyrannosaurid dinosaurs dominated as predators in the Late Cretaceous of Laurasia, culminating in the evolution of the giant Tyrannosaurus rex, both the last and largest tyrannosaurid. Where and when Tyrannosaurini (T. rex and kin) originated remains unclear. Competing hypotheses place tyrannosaurin origins in Asia, or western North America (Laramidia). We report a new tyrannosaurin, Tyrannosaurus mcraeensis, from the Campanian-Maastrichtian Hall Lake Formation of New Mexico, based on a fossil previously referred to T. rex. T. mcraeensis predates T. rex by ~ 6-7 million years, yet rivaled it in size. Phylogenetic analysis recovers T. mcraeensis as sister to T. rex and suggests Tyrannosaurini originated in southern Laramidia. Evolution of giant tyrannosaurs in southern North America, alongside giant ceratopsians, hadrosaurs, and titanosaurs suggests large-bodied dinosaurs evolved at low latitudes in North America.

Exceptionally preserved stomach contents of a young tyrannosaurid reveal an ontogenetic dietary shift in an iconic extinct predator.

Tyrannosaurids were large carnivorous dinosaurs that underwent major changes in skull robusticity and body proportions as they grew, suggesting that they occupied different ecological niches during their life span. Although adults commonly fed on dinosaurian megaherbivores, the diet of juvenile tyrannosaurids is largely unknown. Here, we describe a remarkable specimen of a juvenile Gorgosaurus libratus that preserves the articulated hindlimbs of two yearling caenagnathid dinosaurs inside its abdominal cavity. The prey were selectively dismembered and consumed in two separate feeding events. This predator-prey association provides direct evidence of an ontogenetic dietary shift in tyrannosaurids. Juvenile individuals may have hunted small and young dinosaurs until they reached a size when, to satisfy energy requirements, they transitioned to feeding on dinosaurian megaherbivores. Tyrannosaurids occupied both mesopredator and apex predator roles during their life span, a factor that may have been key to their evolutionary success.

Putative avian teeth from the Late Cretaceous of Alberta, Canada, are more likely from crocodilians.

Isolated teeth, previously referred to Aves, are more common than other bird fossils from the Late Cretaceous of Alberta. However, there are no known morphological synapomorphies that distinguish isolated bird teeth, and features of these teeth are generally shared with those of non-avian theropods and crocodilians. Here, specimens ranging from Late Santonian to Late Maastrichtian in age are described and qualitatively categorized into morphotypes, most of which strongly resemble teeth of extant juvenile and some fossil crocodilians. Variation within this sample of teeth may therefore reflect the heterodont dentition of crocodilians, rather than avian species diversity. Quantitative analysis Principal Component Analysis was mostly uninformative, with limited overlap between putative avian teeth and those of known Cretaceous birds, crocodilians, and non-avian theropods. The reassignment of these putative avian teeth to Crocodylia has important ramifications for our understanding of the evolutionary history of Cretaceous birds.

"Dragons" on the landscape: Modeling the abundance of large carnivorous dinosaurs of the Upper Jurassic Morrison Formation (USA) and the Upper Cretaceous Dinosaur Park Formation (Canada).

Counts of the number of skeletal specimens of "adult" megaherbivores and large theropods from the Morrison and Dinosaur Park formations-if not biased by taphonomic artifacts-suggest that the big meat-eaters were more abundant, relative to the number of big plant-eaters, than one would expect on the basis of the relative abundance of large carnivores and herbivores in modern mammalian faunas. Models of megaherbivore population density (number of individuals per square kilometer) that attempt to take into account ecosystem productivity, the size structure of megaherbivore populations, and individual megaherbivore energy requirements, when combined with values of the large theropod/megaherbivore abundance ratio, suggest that large theropods may have been more abundant on the landscape than estimates extrapolated from the population density versus body mass relationship of mammalian carnivores. Models of the meat production of megaherbivore populations and the meat requirements of "adult" large theropods suggest that herbivore productivity would have been insufficient to support the associated number of individuals of "adult" large theropods, unless the herbivore production/biomass ratio was substantially higher, and/or the large theropod meat requirement markedly lower, than expectations based on modern mammals. Alternatively, or in addition to one or both of these other factors, large theropods likely included dinosaurs other than megaherbivores as significant components of their diet.

Osteology and reassessment of Dineobellator notohesperus, a southern eudromaeosaur (Theropoda: Dromaeosauridae: Eudromaeosauria) from the latest Cretaceous of New Mexico.

Dromaeosaurids (Theropoda: Dromaeosauridae), a group of dynamic, swift predators, have a sparse fossil record, particularly at the end of the Cretaceous Period. The recently described Dineobellator notohesperus, consisting of a partial skeleton from the Upper Cretaceous (Maastrichtian) of New Mexico, is the only diagnostic dromaeosaurid to be recovered from the latest Cretaceous of the southwestern United States. Reinterpreted and newly described material include several caudal vertebrae, portions of the right radius and pubis, and an additional ungual, tentatively inferred to be from manual digit III. Unique features, particularly those of the humerus, unguals, and caudal vertebrae, distinguish D. notohesperus from other known dromaeosaurids. This material indicates different physical attributes among dromaeosaurids, such as use of the forearms, strength in the hands and feet, and mobility of the tail. Several bones in the holotype exhibit abnormal growth and are inferred to be pathologic features resulting from an injury or disease. Similar lengths of the humerus imply Dineobellator and Deinonychus were of similar size, at least regarding length and/or height, although the more gracile nature of the humerus implies Dineobellator was a more lightly built predator. A new phylogenetic analysis recovers D. notohesperus as a dromaeosaurid outside other previously known and named clades. Theropod composition of the Naashoibito Member theropod fauna is like those found in the more northern Late Cretaceous North American ecosystems. Differences in tooth morphologies among recovered theropod teeth from the Naashoibito Member also implies D. notohesperus was not the only dromaeosaurid present in its environment.

A non-avian dinosaur with a streamlined body exhibits potential adaptations for swimming.

Streamlining a body is a major adaptation for aquatic animals to move efficiently in the water. Whereas diving birds are well known to have streamlined bodies, such body shapes have not been documented in non-avian dinosaurs. It is primarily because most known non-avian theropods are terrestrial, barring a few exceptions. However, clear evidence of streamlined bodies is absent even in the purported semiaquatic groups. Here we report a new theropod, Natovenator polydontus gen. et sp. nov., from the Upper Cretaceous of Mongolia. The new specimen includes a well-preserved skeleton with several articulated dorsal ribs that are posterolaterally oriented to streamline the body as in diving birds. Additionally, the widely arched proximal rib shafts reflect a dorsoventrally compressed ribcage like aquatic reptiles. Its body shape suggests that Natovenator was a potentially capable swimming predator, and the streamlined body evolved independently in separate lineages of theropod dinosaurs.

The appendicular myology of Stegoceras validum (Ornithischia: Pachycephalosauridae) and implications for the head-butting hypothesis.

In this study, we use an exceptional skeleton of the pachycephalosaur Stegoceras validum (UALVP 2) to inform a comprehensive appendicular muscle reconstruction of the animal, with the goal of better understanding the functional morphology of the pachycephalosaur postcranial skeleton. We find that S. validum possessed a conservative forelimb musculature, particularly in comparison to early saurischian bipeds. By contrast, the pelvic and hind limb musculature are more derived, reflecting peculiarities of the underlying skeletal anatomy. The iliotibialis, ischiocaudalis, and caudofemoralis muscles have enlarged attachment sites and the caudofemoralis has greater leverage owing to the distal displacement of the fourth trochanter along the femur. These larger muscles, in combination with the wide pelvis and stout hind limbs, produced a stronger, more stable pelvic structure that would have proved advantageous during hypothesized intraspecific head-butting contests. The pelvis may have been further stabilized by enlarged sacroiliac ligaments, which stemmed from the unique medial iliac flange of the pachycephalosaurs. Although the pubis of UALVP 2 is not preserved, the pubes of other pachycephalosaurs are highly reduced. The puboischiofemoralis musculature was likely also reduced accordingly, and compensated for by the aforementioned improved pelvic musculature.

Morphology and distribution of scales, dermal ossifications, and other non-feather integumentary structures in non-avialan theropod dinosaurs.

Modern birds are typified by the presence of feathers, complex evolutionary innovations that were already widespread in the group of theropod dinosaurs (Maniraptoriformes) that include crown Aves. Squamous or scaly reptilian-like skin is, however, considered the plesiomorphic condition for theropods and dinosaurs more broadly. Here, we review the morphology and distribution of non-feathered integumentary structures in non-avialan theropods, covering squamous skin and naked skin as well as dermal ossifications. The integumentary record of non-averostran theropods is limited to tracks, which ubiquitously show a covering of tiny reticulate scales on the plantar surface of the pes. This is consistent also with younger averostran body fossils, which confirm an arthral arrangement of the digital pads. Among averostrans, squamous skin is confirmed in Ceratosauria (Carnotaurus), Allosauroidea (Allosaurus, Concavenator, Lourinhanosaurus), Compsognathidae (Juravenator), and Tyrannosauroidea (Santanaraptor, Albertosaurus, Daspletosaurus, Gorgosaurus, Tarbosaurus, Tyrannosaurus), whereas dermal ossifications consisting of sagittate and mosaic osteoderms are restricted to Ceratosaurus. Naked, non-scale bearing skin is found in the contentious tetanuran Sciurumimus, ornithomimosaurians (Ornithomimus) and possibly tyrannosauroids (Santanaraptor), and also on the patagia of scansoriopterygids (Ambopteryx, Yi). Scales are surprisingly conservative among non-avialan theropods compared to some dinosaurian groups (e.g. hadrosaurids); however, the limited preservation of tegument on most specimens hinders further interrogation. Scale patterns vary among and/or within body regions in Carnotaurus, Concavenator and Juravenator, and include polarised, snake-like ventral scales on the tail of the latter two genera. Unusual but more uniformly distributed patterning also occurs in Tyrannosaurus, whereas feature scales are present only in Albertosaurus and Carnotaurus. Few theropods currently show compelling evidence for the co-occurrence of scales and feathers (e.g. Juravenator, Sinornithosaurus), although reticulate scales were probably retained on the mani and pedes of many theropods with a heavy plumage. Feathers and filamentous structures appear to have replaced widespread scaly integuments in maniraptorans. Theropod skin, and that of dinosaurs more broadly, remains a virtually untapped area of study and the appropriation of commonly used techniques in other palaeontological fields to the study of skin holds great promise for future insights into the biology, taphonomy and relationships of these extinct animals.

A thing with feathers.

Michael Benton and colleagues reminisce about the discovery of Sinosauripteryx, the first feathered dinosaur.

A partial oviraptorosaur skeleton suggests low caenagnathid diversity in the Late Cretaceous Nemegt Formation of Mongolia.

The Nemegt Formation of the Gobi Desert of Mongolia has produced one of the most abundant and diverse oviraptorosaur records globally. However, the caenagnathid component of this fauna remains poorly known. Two caenagnathid taxa are currently recognized from the Nemegt Formation: Elmisaurus rarus and Nomingia gobiensis. Because these taxa are known from mostly non-overlapping material, there are concerns that they could represent the same animal. A partial, weathered caenagnathid skeleton discovered adjacent to the holotype quarry of Nomingia gobiensis is referable to Elmisaurus rarus, revealing more of the morphology of the cranium, mandible, pectoral girdle, and pubis. Despite metatarsals clearly exhibiting autapomorphies of Elmisaurus rarus, overlapping elements are identical to those of Nomingia gobiensis, and add to a growing body of evidence that these taxa represent a single morphotype. In the absence of any positive evidence for two caenagnathid taxa in the Nemegt Formation, Nomingia gobiensis is best regarded as a junior synonym of Elmisaurus rarus. Low caenagnathid diversity in the Nemegt Formation may reflect broader coexistence patterns with other oviraptorosaur families, particularly oviraptorids. In contrast to North America, competition with the exceptionally diverse oviraptorids may have restricted caenagnathids to marginal roles in Late Cretaceous Asian ecosystems.

Dinosaur biodiversity declined well before the asteroid impact, influenced by ecological and environmental pressures.

The question why non-avian dinosaurs went extinct 66 million years ago (Ma) remains unresolved because of the coarseness of the fossil record. A sudden extinction caused by an asteroid is the most accepted hypothesis but it is debated whether dinosaurs were in decline or not before the impact. We analyse the speciation-extinction dynamics for six key dinosaur families, and find a decline across dinosaurs, where diversification shifted to a declining-diversity pattern ~76 Ma. We investigate the influence of ecological and physical factors, and find that the decline of dinosaurs was likely driven by global climate cooling and herbivorous diversity drop. The latter is likely due to hadrosaurs outcompeting other herbivores. We also estimate that extinction risk is related to species age during the decline, suggesting a lack of evolutionary novelty or adaptation to changing environments. These results support an environmentally driven decline of non-avian dinosaurs well before the asteroid impact.

Maniraptoran pelvic musculature highlights evolutionary patterns in theropod locomotion on the line to birds.

Locomotion is a fundamental aspect of palaeobiology and often investigated by comparing osteological structures and proportions. Previous studies document a stepwise accumulation of avian-like features in theropod dinosaurs that accelerates in the clade Maniraptora. However, the soft tissues that influenced the skeleton offer another perspective on locomotory adaptations. Examination of the pelvis for osteological correlates of hind limb and tail musculature allowed reconstruction of primary locomotory muscles across theropods and their closest extant relatives. Additionally, the areas of pelvic muscle origins were quantified to measure relative differences within and between taxa, to compare morphological features associated with cursoriality, and offer insight into the evolution of locomotor modules. Locomotory inferences based on myology often corroborate those based on osteology, although they occasionally conflict and indicate greater complexity than previously appreciated. Maniraptoran pelvic musculature underscores previous studies noting the multifaceted nature of cursoriality and suggests that a more punctuated step in caudal decoupling occurred at or near the base of Maniraptora.

A fast-growing basal troodontid (Dinosauria: Theropoda) from the latest Cretaceous of Europe.

A characteristic fauna of dinosaurs and other vertebrates inhabited the end-Cretaceous European archipelago, some of which were dwarves or had other unusual features likely related to their insular habitats. Little is known, however, about the contemporary theropod dinosaurs, as they are represented mostly by teeth or other fragmentary fossils. A new isolated theropod metatarsal II, from the latest Maastrichtian of Spain (within 200,000 years of the mass extinction) may represent a jinfengopterygine troodontid, the first reported from Europe. Comparisons with other theropods and phylogenetic analyses reveal an autapomorphic foramen that distinguishes it from all other troodontids, supporting its identification as a new genus and species, Tamarro insperatus. Bone histology shows that it was an actively growing subadult when it died but may have had a growth pattern in which it grew rapidly in early ontogeny and attained a subadult size quickly. We hypothesize that it could have migrated from Asia to reach the Ibero-Armorican island no later than Cenomanian or during the Maastrichtian dispersal events.

A new ankylosaurid skeleton from the Upper Cretaceous Baruungoyot Formation of Mongolia: its implications for ankylosaurid postcranial evolution.

A new articulated postcranial specimen of an indeterminate ankylosaurid dinosaur from the Upper Cretaceous (middle-upper Campanian) Baruungoyot Formation from Hermiin Tsav, southern Gobi Desert, Mongolia includes twelve dorsal vertebrae, ribs, pectoral girdles, forelimbs, pelvic girdles, hind limbs, and free osteoderms. The new specimen shows that Asian ankylosaurids evolved rigid bodies with a decreased number of pedal phalanges. It also implies that there were at least two forms of flank armor within Ankylosauridae, one with spine-like osteoderms and the other with keeled rhomboidal osteoderms. Unique anatomical features related to digging are present in Ankylosauridae, such as dorsoventrally flattened and fusiform body shapes, extensively fused series of vertebrae, anteroposteriorly broadened dorsal ribs, a robust humerus with a well-developed deltopectoral crest, a short robust ulna with a well-developed olecranon process, a trowel-like manus, and decreased numbers of pedal phalanges. Although not fossorial, ankylosaurids were likely able to dig the substrate, taking advantage of it for self-defence and survival.

Ejection fraction and mortality: a nationwide register-based cohort study of 499 153 women and men.

AIMS: We investigated the sex-based risk of mortality across the spectrum of left ventricular ejection fraction (LVEF) in a large cohort of patients in Australia. METHODS AND RESULTS: Quantified levels of LVEF from 237 046 women (48.1%) and 256 109 men undergoing first-time, routine echocardiography (2000-2019) were linked to 119 232 deaths (median 5.6 years of follow-up). Overall, 17.6% of men vs. 8.3% of women had an LVEF <50%. An LVEF <40% was associated with the highest crude cardiovascular-related and all-cause mortality at 5 years (∼20-30% and ∼ 40-50%, respectively). Thereafter, actual cardiovascular-related and all-cause mortality at 5 years in both sexes steeply improved to a nadir LVEF of 65.0-69.9% (reference group). Below this LVEF level, the adjusted hazard ratio (HR) for cardiovascular-related mortality for a LVEF of 55.0-59.9% was 1.36 [95% confidence interval (CI) 1.16-1.59; P < 0.001] in women and 1.21 (95% CI 1.05-1.39; P = 0.008) in men. In women, an LVEF of 60.0-64.9% was also associated with a HR 1.33 (95% CI 1.16-1.52; P < 0.001) for cardiovascular-related mortality. These associations were most striking in women and men aged <65 years and were replicated in those with suspected heart failure (32 403 cases aged 65.2 ± 16.1 years, 57.0% women). For pre-existing heart failure (33 738 cases aged 67.6 ± 16.9 years, 46.5% women), the specific threshold of increased mortality was at and below 50.0-54.9%. CONCLUSIONS: Among patients investigated for suspected or established cardiovascular disease, we found clinically relevant sex-based differences in the distribution and mortality associated with an LVEF <65.0-69.9%. Specifically, they suggest a greater risk of mortality at higher LVEF levels among women.

A new two-fingered dinosaur sheds light on the radiation of Oviraptorosauria.

Late Cretaceous trends in Asian dinosaur diversity are poorly understood, but recent discoveries have documented a radiation of oviraptorosaur theropods in China and Mongolia. However, little work has addressed the factors that facilitated this diversification. A new oviraptorid from the Late Cretaceous of Mongolia sheds light on the evolution of the forelimb, which appears to have played a role in the radiation of oviraptorosaurs. Surprisingly, the reduced arm has only two functional digits, highlighting a previously unrecognized occurrence of digit loss in theropods. Phylogenetic analysis shows that the onset of this reduction coincides with the radiation of heyuannine oviraptorids, following dispersal from southern China into the Gobi region. This suggests expansion into a new niche in the Gobi region, which relied less on the elongate, grasping forelimbs inherited by oviraptorosaurs. Variation in forelimb length and manus morphology provides another example of niche partitioning in oviraptorosaurs, which may have made possible their incredible diversity in the latest Cretaceous of Asia.

Author Correction: First Ornithomimid (Theropoda, Ornithomimosauria) from the Upper Cretaceous Djadokhta Formation of Tögrögiin Shiree, Mongolia.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

A Problematic Tyrannosaurid (Dinosauria: Theropoda) Skeleton and Its Implications for Tyrannosaurid Diversity in the Horseshoe Canyon Formation (Upper Cretaceous) of Alberta.

Several published censuses have noted the presence of two tyrannosaurids, Daspletosaurus sp. and Albertosaurus sarcophagus, within the Upper Cretaceous Horseshoe Canyon Formation of Alberta. Although A. sarcophagus is known from more than a dozen major discoveries in these strata, Daspletosaurus sp. is known from just a single problematic skeleton (lacking most of the skull) of a young individual. Here we describe and figure this skeleton, and marshal a variety of osteohistologic, morphometric, and phylogenetic methods to accurately determine its taxonomic status. Although none of these methods individually provides convincing evidence regarding the affinities of the specimen, together (and including other historical and biostratigraphic considerations) they strongly imply that the skeleton instead pertains to a young A. sarcophagus. In this way, we show that only a single species of tyrannosaurid is definitively present in the Horseshoe Canyon Formation, greatly simplifying interpretations of tyrannosaurid evolution and ecology in this setting. Anat Rec, 303:673-690, 2020. © 2019 The Authors. The Anatomical Record published by Wiley Periodicals, Inc. on behalf of American Association of Anatomists.

Histology of Caenagnathid (Theropoda, Oviraptorosauria) Dentaries and Implications for Development, Ontogenetic Edentulism, and Taxonomy.

The fossil record of caenagnathid oviraptorosaurs consists mainly of their fused, complexly sculptured dentaries, but little is known about the growth and development of this diagnostic structure. Previous work has suggested that the ridges and grooves on the occlusal surface are either the vestiges of teeth and their alveoli or were adaptations to increase shearing action during mastication. In addition, the distinctiveness of the dentaries has led to their use for species-level taxonomy, without a complete understanding of their variation through ontogeny. Here, we describe additional caenagnathid mandibles from the Dinosaur Park Formation of Alberta, Canada, and perform histological analyses to assess relative ontogenetic stage and the nature of the occlusal elaborations. The results show that the mandibular symphysis is synostosed early in ontogeny and does not accurately reflect ontogenetic stage in caenagnathids. In contrast, the presence of cyclical growth marks in a large specimen shows that mandibles can be used for relative histological maturity estimation. Histological features of the ridges of bone surrounding the lingual groove indicate that they are not the vestiges of tooth-bearing tissues and that caenagnathids did not lose their teeth through ontogeny as suggested in previous work. Instead, increased secondary remodeling in these structures is consistent with their use for food processing. Unexpectedly advanced maturity in a small specimen suggests that at least three caenagnathid species of varying body sizes coexisted in the Dinosaur Park Formation. These results stress the necessity of histological analysis when assessing maturity or ontogenetic trends in fossil material. Anat Rec, 303:918-934, 2020. © 2019 Wiley Periodicals, Inc.

The Anatomical and Functional Evolution of the Femoral Fourth Trochanter in Ornithischian Dinosaurs.

The femoral fourth trochanter is the attachment site of the caudofemoralis musculature, which is the primary hindlimb retractor in most non-avian dinosaurs. Early ornithischian dinosaurs are uniquely characterized by a fourth trochanter with a prominent pendant process. Throughout the evolution of ornithischians, the fourth trochanter repeatedly converged on two major morphological changes: (1) the distal migration of the trochanter down the femoral shaft and (2) the loss of the pendant process. Both changes, as well as the original evolution of the pendant form, relate to a single major functional shift emphasizing caudofemoral leverage. Direct evidence of muscle scarring across the surface of the pendant process affirms that it served to extend the attachment of the primary caudofemoralis brevis tendon distally. A proximally located fourth trochanter is the basal condition in dinosaurs and other archosaurs, and the development of a pendant process lengthened the functional lever arm with regard to the insertion of the caudofemoralis. This adaptation afforded improved mechanical advantage, perhaps beneficial in the context of the newly assumed herbivorous diets of basal ornithischians. As some derived ornithischians increased in body size, a high-leverage system with a more distal caudofemoralis attachment evolved. In some groups, the fourth trochanter as a whole descended down the femur, eventually reaching a point where the pendant process was unnecessary. Sauropodomorphs, the other great lineage of dinosaur herbivores, converged on the same high-leverage distal fourth trochanter arrangement, but without first transitioning through a prominent pendant form. Anat Rec, 303:1146-1157, 2020. © 2019 Wiley Periodicals, Inc.