Dinosaurs Research Articles

Muscle-controlled physics simulations of bird locomotion resolve the grounded running paradox.

Humans and birds use very different running styles. Unlike humans, birds adopt "grounded running" at intermediate speeds-a running gait where at least one foot always maintains ground contact. Avian grounded running is a paradox: Animals usually minimize locomotor energy expenditure, but birds prefer grounded running despite incurring higher energy costs. Using predictive gait simulations of the emu (Dromaius novaehollandiae), we resolve this paradox by demonstrating that grounded running represents an optimal gait for birds, from both energetics and muscle excitations perspectives. Our virtual experiments decoupled effects of posture and tendon elasticity, biomechanically relevant anatomical features that cannot be isolated in real birds. The avian body plan prevents (near) vertical leg postures, making the running style used by humans impossible. Under this anatomical constraint, grounded running is optimal if the muscles produce the highest forces in crouched postures, as is true in most birds. Shared anatomical features suggest that, as a behavior, avian grounded running first evolved within non-avian dinosaurs.

A sauropod tibia with initial fracture from the Middle Jurassic in Yunyang, Chongqing, southwest China

ABSTRACT Among the available palaeopathological results on non-avian dinosaurs, the fracture is the most documented category. Therein, only two sauropod fractured cases have been reported, and no sauropod tibial fracture has been mentioned. In this study, we report a special sauropod tibial fracture from the Middle Jurassic of Yunyang County, Chongqing, southwest China. The morphological observation shows a planar-shaped sauropod tibial fracture, with a rough surface without fracture callus, and does not exhibit other healing manifestations such as swelling. The CT images and energy spectrum data clearly demonstrate the injured cortical bone invaginated into the medullary cavity. Moreover, these data indicate that the tibia fracture is initial, the first valid record of initial fracture in non-avian dinosaurs. This study enhances our knowledge of sauropod limb bone fractures and enriches the pathological information about dinosaur fractures.

Endocranial development in non-avian dinosaurs reveals an ontogenetic brain trajectory distinct from extant archosaurs

Modern birds possess highly encephalized brains that evolved from non-avian dinosaurs. Evolutionary shifts in developmental timing, namely juvenilization of adult phenotypes, have been proposed as a driver of head evolution along the dinosaur-bird transition, including brain morphology. Testing this hypothesis requires a sufficient developmental sampling of brain morphology in non-avian dinosaurs. In this study, we harness brain endocasts of a postnatal growth series of the ornithischian dinosaur Psittacosaurus and several other immature and mature non-avian dinosaurs to investigate how evolutionary changes to brain development are implicated in the origin of the avian brain. Using three-dimensional characterization of neuroanatomical shape across archosaurian reptiles, we demonstrate that (i) the brain of non-avian dinosaurs underwent a distinct developmental trajectory compared to alligators and crown birds; (ii) ornithischian and non-avialan theropod dinosaurs shared a similar developmental trajectory, suggesting that their derived trajectory evolved in their common ancestor; and (iii) the evolutionary shift in developmental trajectories is partly consistent with paedomorphosis underlying overall brain shape evolution along the dinosaur-bird transition; however, the heterochronic signal is not uniform across time and neuroanatomical region suggesting a highly mosaic acquisition of the avian brain form.

Neural canal ridges: A novel osteological correlate of postcranial neuroanatomy in dinosaurs.

In this article, we document the widespread presence of bony ridges in the neural canals of non-avian dinosaurs, including a wide diversity of sauropods, two theropods, a thyreophoran, and a hadrosaur. These structures are present only in the caudal vertebrae. They are anteroposteriorly elongate, found on the lateral walls of the canal, and vary in size and position both taxonomically and serially. Similar bony projections into the neural canal have been identified in extant teleosts, dipnoans, and urodelans, in which they are recognized as bony spinal cord supports. In most non-mammals, the dura mater that surrounds the spinal cord is fused to the periosteum of the neural canal, and the denticulate ligaments that support the spinal cord can pass through the dura and periosteum to anchor directly to bone. The function of these structures in dinosaurs remains uncertain, but in sauropods they might have stabilized the spinal cord during bilateral movement of the tail and use of the tail as a weapon. Of broader significance, this study emphasizes that important new discoveries at the gross anatomical level can continue to be made in part by closely examining previously overlooked features of known specimens.

Earliest evidence of avian primary feathermoult.

Feather moulting is a crucial process in the avian life cycle, which evolved to maintain plumage functionality. However, moulting involves both energetic and functional costs. During moulting, plumage function temporarily decreases between the shedding of old feathers and the full growth of new ones. In flying taxa, a gradual and sequential replacement of flight feathers evolved to maintain aerodynamic capabilities during the moulting period. Little is known about the moult strategies of non-avian pennaraptoran dinosaurs and stem birds, before the emergence of crown lineage. Here, we report on two Early Cretaceous pygostylian birds from the Yixian Formation (125 mya), probably referable to Confuciusornithiformes, exhibiting morphological characteristics that suggest a gradual and sequential moult of wing flight feathers. Short primary feathers interpreted as immature are symmetrically present on both wings, as is typical among extant flying birds. Our survey of the enormous collection of the Tianyu Museum confirms previous findings that evidence of active moult in non-neornithine pennaraptorans is rare and likely indicates a moult cycle greater than one year. Documenting moult in Mesozoic feathered dinosaurs is critical for understanding their ecology, locomotor ability and the evolution of this important life-history process in birds.

Unique functional diversity during early Cenozoic mammal radiation of North America.

Mammals influence nearly all aspects of energy flow and habitat structure in modern terrestrial ecosystems. However, anthropogenic effects have probably altered mammalian community structure, raising the question of how past perturbations have done so. We used functional diversity (FD) to describe how the structure of North American mammal palaeocommunities changed over the past 66 Ma, an interval spanning the radiation following the K/Pg and several subsequent environmental disruptions including the Palaeocene-Eocene Thermal Maximum (PETM), the expansion of grassland, and the onset of Pleistocene glaciation. For 264 fossil communities, we examined three aspects of ecological function: functional evenness, functional richness and functional divergence. We found that shifts in FD were associated with major ecological and environmental transitions. All three measures of FD increased immediately following the extinction of the non-avian dinosaurs, suggesting that high degrees of ecological disturbance can lead to synchronous responses both locally and continentally. Otherwise, the components of FD were decoupled and responded differently to environmental changes over the last ~56 Myr.

Jury remains out on decline of non-avian dinosaurs.

Jury remains out on decline of non-avian dinosaurs.

The evolution of femoral morphology in giant non-avian theropod dinosaurs.

Theropods are obligate bipedal dinosaurs that appeared 230 million years ago and are still extant as birds. Their history is characterized by extreme variations in body mass, with gigantism evolving convergently between many lineages. However, no quantification of hindlimb functional morphology has shown if these body mass increases led to similar specializations between distinct lineages. Here we studied femoral shape variation across 41 species of theropods (n= 68 specimens) using a high-density 3D geometric morphometric approach. We demonstrated that the heaviest theropods evolved wider epiphyses and a more distally located fourth trochanter, as previously demonstrated in early archosaurs, along with an upturned femoral head and a mediodistal crest that extended proximally along the shaft. Phylogenetically informed analyses highlighted that these traits evolved convergently within six major theropod lineages, regardless of their maximum body mass. Conversely, the most gracile femora were distinct from the rest of the dataset, which we interpret as a femoral specialization to "miniaturization" evolving close to Avialae (bird lineage). Our results support a gradual evolution of known "avian" features, such as the fusion between lesser and greater trochanters and a reduction of the epiphyses' offset, independently from body mass variations, which may relate to a more "avian" type of locomotion (more knee-than hip-driven). The distinction between body mass variations and a more "avian" locomotion is represented by a decoupling in the mediodistal crest morphology, whose biomechanical nature should be studied to better understand the importance of its functional role in gigantism, miniaturization and higher parasagittal abilities.

The last ceratosaur of Asia: a new noasaurid from the Early Cretaceous Great Siberian Refugium.

The noasaurid ceratosaur Kiyacursor longipes gen. et sp. nov. is described based on a fragmentary skeleton including cervical vertebra, pectoral girdle, humerus and hind limbs from the Lower Cretaceous (Aptian) Ilek Formation at Shestakovo 1 locality in Western Siberia, Russia. This is the first ceratosaur from the Early Cretaceous of Asia, extending the stratigraphic range of Ceratosauria by 40 Myr on that continent. Kiyacursor shares unique hind limb proportions with Elaphrosaurus and Limusaurus, suggesting improved cursorial ability. These taxa show an ostrich-like specialization of the pes, with a large third metatarsal and greatly reduced second metatarsal. By contrast, all other fast running non-avian theropod dinosaurs have an arctometatarsalian pes, with the third metatarsal strongly reduced proximally. The new taxon lived in the Early Cretaceous ecosystem containing a number of other Jurassic relics, such as stem salamanders, protosuchian and shartegosuchid crocodyliforms, tritylodontid synapsids and docodontan mammaliaforms.

Downsizing a heavyweight: factors and methods that revise weight estimates of the giant fossil whale Perucetus colossus.

Extremes in organismal size have broad interest in ecology and evolution because organismal size dictates many traits of an organism's biology. There is particular fascination with identifying upper size extremes in the largest vertebrates, given the challenges and difficulties of measuring extant and extinct candidates for the largest animal of all time, such as whales, terrestrial non-avian dinosaurs, and extinct marine reptiles. The discovery of Perucetus colossus, a giant basilosaurid whale from the Eocene of Peru, challenged many assumptions about organismal extremes based on reconstructions of its body weight that exceeded reported values for blue whales (Balaenoptera musculus). Here we present an examination of a series of factors and methodological approaches to assess reconstructing body weight in Perucetus, including: data sources from large extant cetaceans; fitting published body mass estimates to body outlines; testing the assumption of isometry between skeletal and body masses, even with extrapolation; examining the role of pachyostosis in body mass reconstructions; addressing method-dependent error rates; and comparing Perucetus with known physiological and ecological limits for living whales, and Eocene oceanic productivity. We conclude that Perucetus did not exceed the body mass of today's blue whales. Depending on assumptions and methods, we estimate that Perucetus weighed 60-70 tons assuming a length 17 m. We calculated larger estimates potentially as much as 98-114 tons at 20 m in length, which is far less than the direct records of blue whale weights, or the 270 ton estimates that we calculated for body weights of the largest blue whales measured by length.

Porphyrin-Based Molecules in the Fossil Record Shed Light on the Evolution of Life

The fossil record demonstrates the preservation of porphyrins (e.g., heme) in organic sediments and the fossilized remains of animals. These molecules are essential components in modern metabolic processes, such as electron transport (cytochromes) and oxygen transport (hemoglobin), and likely originated before the emergence of life. The integration and adaptation of porphyrins and structurally similar molecules (e.g., chlorophylls) are key aspects in the evolution of energy production (i.e., aerobic respiration and photosynthesis) and complex life (i.e., eukaryotes and multicellularity). Here, we discuss the evolution and functional diversity of heme-bound hemoglobin proteins in vertebrates, along with the preservation of these molecules in the fossil record. By elucidating the pivotal role of these molecules in the evolution of life, this review lays the groundwork necessary to explore hemoglobin as a means to investigate the paleobiology of extinct taxa, including non-avian dinosaurs.

Quantifying the effects of exceptional fossil preservation on the global availability of phylogenetic data in deep time.

Fossil deposits with exceptional preservation ("lagerstätten") provide important details not typically preserved in the fossil record, such that they hold an outsized influence on our understanding of biodiversity and evolution. In particular, the potential bias imparted by this so-called "lagerstätten effect" remains a critical, but underexplored aspect of reconstructing evolutionary relationships. Here, we quantify the amount of phylogenetic information available in the global fossil records of 1,327 species of non-avian theropod dinosaurs, Mesozoic birds, and fossil squamates (e.g., lizards, snakes, mosasaurs), and then compare the influence of lagerstätten deposits on phylogenetic information content and taxon selection in phylogenetic analyses to other fossil-bearing deposits. We find that groups that preserve a high amount of phylogenetic information in their global fossil record (e.g., non-avian theropods) are less vulnerable to a "lagerstätten effect" that leads to disproportionate representation of fossil taxa from one geologic unit in an evolutionary tree. Additionally, for each taxonomic group, we find comparable amounts of phylogenetic information in lagerstätten deposits, even though corresponding morphological character datasets vary greatly. Finally, we unexpectedly find that ancient sand dune deposits of the Late Cretaceous Gobi Desert of Mongolia and China exert an anomalously large influence on the phylogenetic information available in the squamate fossil record, suggesting a "lagerstätten effect" can be present in units not traditionally considered lagerstätten. These results offer a phylogenetics-based lens through which to examine the effects of exceptional fossil preservation on biological patterns through time and space, and invites further quantification of evolutionary information in the rock record.

A juvenile bird with possible crown-group affinities from a dinosaur-rich Cretaceous ecosystem in North America

BackgroundLiving birds comprise the most speciose and anatomically diverse clade of flying vertebrates, but their poor early fossil record and the lack of resolution around the relationships of the major clades have greatly obscured extant avian origins.ResultsHere, I describe a Late Cretaceous bird from North America based on a fragmentary skeleton that includes cranial material and portions of the forelimb, hindlimb, and foot and is identified as a juvenile based on bone surface texture. Several features unite this specimen with crown Aves, but its juvenile status precludes the recognition of a distinct taxon. The North American provenance of the specimen supports a cosmopolitan distribution of early crown birds, clashes with the hypothesized southern hemisphere origins of living birds, and demonstrates that crown birds and their closest relatives coexisted with non-avian dinosaurs that independently converged on avian skeletal anatomy, such as the alvarezsaurids and dromaeosaurids.ConclusionsBy revealing the ecological and biogeographic context of Cretaceous birds within or near the crown clade, the Lance Formation specimen provides new insights into the contingent nature of crown avian survival through the Cretaceous-Paleogene mass extinction and the subsequent origins of living bird diversity.

New information on paleopathologies in non-avian theropod dinosaurs: a case study on South American abelisaurids

Studies on pathological fossil bones have allowed improving the knowledge of physiology and ecology, and consequently the life history of extinct organisms. Among extinct vertebrates, non-avian dinosaurs have drawn attention in terms of pathological evidence, since a wide array of fossilized lesions and diseases were noticed in these ancient organisms. Here, we evaluate the pathological conditions observed in individuals of different brachyrostran (Theropoda, Abelisauridae) taxa, including Aucasaurus garridoi, Elemgasem nubilus, and Quilmesaurus curriei. For this, we use multiple methodological approaches such as histology and computed tomography, in addition to the macroscopic evaluation. The holotype of Aucasaurus shows several pathognomonic traits of a failure of the vertebral segmentation during development, causing the presence of two fused caudal vertebrae. The occurrence of this condition in Aucasaurus is the first case to be documented so far in non-tetanuran theropods. Regarding the holotype of Elemgasem, the histology of two fused vertebrae shows an intervertebral space between the centra, thus the fusion is limited to the distal rim of the articular surfaces. This pathology is here considered as spondyloarthropathy, the first evidence for a non-tetanuran theropod. The microstructural arrangement of the right tibia of Quilmesaurus shows a marked variation in a portion of the outer cortex, probably due to the presence of the radial fibrolamellar bone tissue. Although similar bone tissue is present in other extinct vertebrates and the cause of its formation is still debated, it could be a response to some kind of pathology. Among non-avian theropods, traumatic injuries are better represented than other maladies (e.g., infection, congenital or metabolic diseases, etc.). These pathologies are recovered mainly among large-sized theropods such as Abelisauridae, Allosauridae, Carcharodontosauridae, and Tyrannosauridae, and distributed principally among axial elements. Statistical tests on the distribution of injuries in these theropod clades show a strong association between taxa-pathologies, body regions-pathologies, and taxa-body regions, suggesting different life styles and behaviours may underlie the frequency of different injuries among theropod taxa.

Quantitative functional imaging of the pigeon brain: implications for the evolution of avian powered flight.

The evolution of flight is a rare event in vertebrate history, and one that demands functional integration across multiple anatomical/physiological systems. The neuroanatomical basis for such integration and the role that brain evolution assumes in behavioural transformations remain poorly understood. We make progress by (i) generating a positron emission tomography (PET)-based map of brain activity for pigeons during rest and flight, (ii) using these maps in a functional analysis of the brain during flight, and (iii) interpreting these data within a macroevolutionary context shaped by non-avian dinosaurs. Although neural activity is generally conserved from rest to flight, we found significant increases in the cerebellum as a whole and optic flow pathways. Conserved activity suggests processing of self-movement and image stabilization are critical when a bird takes to the air, while increased visual and cerebellar activity reflects the importance of integrating multimodal sensory information for flight-related movements. A derived cerebellar capability likely arose at the base of maniraptoran dinosaurs, where volumetric expansion and possible folding directly preceded paravian flight. These data represent an important step toward establishing how the brain of modern birds supports their unique behavioural repertoire and provide novel insights into the neurobiology of the bird-like dinosaurs that first achieved powered flight.

Escape behaviors in prey and the evolution of pennaceous plumage in dinosaurs

Numerous non-avian dinosaurs possessed pennaceous feathers on their forelimbs (proto-wings) and tail. Their functions remain unclear. We propose that these pennaceous feathers were used in displays to flush hiding prey through stimulation of sensory-neural escape pathways in prey, allowing the dinosaurs to pursue the flushed prey. We evaluated the escape behavior of grasshoppers to hypothetical visual flush-displays by a robotic dinosaur, and we recorded neurophysiological responses of grasshoppers’ escape pathway to computer animations of the hypothetical flush-displays by dinosaurs. We show that the prey of dinosaurs would have fled more often when proto-wings were present, especially distally and with contrasting patterns, and when caudal plumage, especially of a large area, was used during the hypothetical flush-displays. The reinforcing loop between flush and pursue functions could have contributed to the evolution of larger and stiffer feathers for faster running, maneuverability, and stronger flush-displays, promoting foraging based on the flush-pursue strategy. The flush-pursue hypothesis can explain the presence and distribution of the pennaceous feathers, plumage color contrasts, as well as a number of other features observed in early pennaraptorans. This scenario highlights that sensory-neural processes underlying prey’s antipredatory reactions may contribute to the origin of major evolutionary innovations in predators.

Mechanistic phylodynamic models do not provide conclusive evidence that non-avian dinosaurs were in decline before their final extinction

Abstract Phylodynamic models can be used to estimate diversification trajectories from time-calibrated phylogenies. Here we apply two such models to phylogenies of non-avian dinosaurs, a clade whose evolutionary history has been widely debated. Although some authors have suggested that the clade experienced a decline in diversity, potentially starting millions of years before the end-Cretaceous mass extinction, others have suggested that the group remained highly diverse right up until the Cretaceous-Paleogene (K-Pg) boundary. Our results show that model assumptions, likely with respect to incomplete sampling, have a large impact on whether dinosaurs appear to have experienced a long-term decline or not. The results are also highly sensitive to the topology and branch lengths of the phylogeny used. Developing comprehensive models of sampling bias, and building larger and more accurate phylogenies, are likely to be necessary steps for us to determine whether dinosaur diversity was or was not in decline before the end-Cretaceous mass extinction.

The ontogenetic status of a small hadrosauroid dinosaur from the uppermost Cretaceous of Bulgaria, and implications for the paleobiogeography and assembly of European island faunas

During the latest Cretaceous hadrosauroids were the most numerous and taxonomically diverse herbivorous dinosaurs on the European island archipelago, including diminutive non-hadrosaurid hadrosauroids and lambeosaurine immigrants from Asia and, possibly, from North America. In recent years the existence of small-bodied adult hadrosauroids (or ‘island dwarfs’) in the Maastrichtian of Romania and Spain has been confirmed by histological study of their bones. The first fossils attributable to Hadrosauroidea discovered in Bulgaria (from the upper Maastrichtian Kaylaka Formation) are also of diminutive size, but it has been unclear whether the bones belonged to small adults or simply to juveniles. Here, we subjected a tibia, fibula, indeterminate long bone diaphyseal fragment, and six indeterminate bone fragments, which are associated with the hadrosauroid hind limb elements and assumed to had been broken off from one or more of them during excavation, to a histological analysis. The analysis shows that the specimens belong to a young, actively growing individual(s), as evidenced by the presence of highly vascularized primary tissues in the outer cortex, secondary remodelling mostly restricted to certain areas of the bone sections, and absence of annual growth lines or an external fundamental system that would signify skeletal maturity. The bone matrix of the periosteal tissues exhibits high amounts of parallel-fibered and lamellar bone, similar to the long bones of other European island-living non-avian dinosaurs, a feature probably linked to lower growth rates. In general, the histomorphology and size of the Bulgarian hadrosauroid correspond well with ‘late juveniles’ and young ‘subadults’ in the osteohistologically well-studied hadrosauroid Maiasaura peeblesorum. The presence of a medium-sized hadrosauroid in the south-eastern part of the Late Cretaceous European archipelago suggests a dispersal route that allowed large-bodied terrestrial fauna to populate emergent islands in the region.

What do their footprints tell us? Many questions and some answers about the life of non-avian dinosaurs

Dinosaur tracks are considerably common in the fossil record and were described from many areas in the world. They provide a live picture of dinosaur behaviour and offer valuable data about different aspects of the trackmaker paleobiology. The dinosaur ichnological record allows gain information about autopod anatomy, functional adaptations, stance and gaits with which dinosaurs moved. This information, which is often difficult to obtain from the body-fossil record alone, allows making inferences not only concerning the single individuals who produced the footprints, but also within an evolutionary context. Footprints provide also evidences about the abilities that dinosaurs had to swim, run or live with certain pathologies. They also allowed inferring how they move in herds or even made courtship rituals. The study of tracks also enables the reconstruction of paleocommunities including predator–prey interaction. On the other hand, footprints are useful paleoenvironmental indicators, informing about moisture content, bathymetry, paleocurrents, subaqueous substrates, zonations in lacustrine margins, etc. In addition, it has been proposed that dinosaur track assemblages can be related to certain facies (ichnofacies), in order to refine paleoenvironmental reconstructions. Dinosaur tracks can sometimes be in the shadow with respect to the skeletal record. However, the data obtained from the ichnological record complements and completes the knowledge we have about the life of dinosaurs, even showing previously unknown aspects. This work is an overview of the information we can obtain from the study of non-avian dinosaur footprints, trying to answer some questions about their life.

Geologically calibrated mammalian tree and its correlation with global events, including the emergence of humans.

A robust timetree for Mammalia was constructed using the time calibration function of BEAST v1.10.4 and MEGA 11. The analysis involved the application of times of the most recent common ancestors, including a total of 19 mammalian fossil calibration ages following Benton etal. (Palaeontologia Electronica, 2015, 1-106) for their minimum ages. Additionally, fossil calibration ages for Gorilla, Pan, and a geologic event calibration age for otters were incorporated. Using these calibration ages, I constructed a geologically calibrated tree that estimates the age of the Homo and Pan splitting to be 5.69 Ma. The tree carries several significant implications. First, after the initial rifting at 120 Ma, the Atlantic Ocean expanded by over 500 km around Chron 34 (84 Ma), and vicariant speciation between Afrotheria (Africa) and Xenarthra (South America) appears to have commenced around 70 Ma. Additionally, ordinal level differentiations began immediately following the K-Pg boundary (66.0 Ma), supporting previous hypothesis that mammalian radiation rapidly filled ecological niches left vacant by non-avian dinosaurs. I constructed a diagram depicting the relationship between base substitution rate and age using an additional function in BEAST v1.10.4. The diagram reveals an exponential increase in the base substitution rate approaching recent times. This increased base substitution rate during the Neogene period may have contributed to the expansion of biodiversity, including the extensive adaptive radiation that led to the evolution of Homo sapiens. One significant driving factor behind this radiation could be attributed to the emergence and proliferation of C4 grasses since 20 Ma. These grasses have played a role in increasing carbon fixation, reducing atmospheric CO2 concentration, inducing global cooling, and initiating Quaternary glacial-interglacial cycles, thereby causing significant climatic changes.