First Reported Cases of Biomechanically Adaptive Bone Modeling in Non-Avian Dinosaurs

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.

Locomotor and postural diversity among reptiles viewed through the prism of femoral microanatomy: Palaeobiological implications for some Permian and Mesozoic taxa

The water-to-land transition by the first tetrapod vertebrates represents a key stage in their evolution. Selection pressures exerted by this new environment on animals led to the emergence of new locomotor and postural strategies that favoured access to different ecological niches and contributed to their evolutionary success. Today, amniotes show great locomotor and postural diversity, particularly among Reptilia, whose extant representatives include parasagittally locomoting erect and crouched bipeds (birds), sub-parasagittal 'semi-erect' quadrupeds (crocodylians) and sprawling quadrupeds (squamates and turtles). But the different steps leading to such diversity remain enigmatic and the type of locomotion adopted by many extinct species raises questions. This is notably the case of certain Triassic taxa such as Euparkeria and Marasuchus. The exploration of the bone microanatomy in reptiles could help to overcome these uncertainties. Indeed, this locomotor and postural diversity is accompanied by great microanatomical disparity. On land, the bones of the appendicular skeleton support the weight of the body and are subject to multiple constraints that partly shape their external and internal morphology. Here we show how microanatomical parameters measured in cross-section, such as bone compactness or the position of the medullocortical transition, can be related to locomotion. We hypothesised that this could be due to variations in cortical thickness. Using statistical methods that take phylogeny into account (phylogenetic flexible discriminant analyses), we develop different models of locomotion from a sample of femur cross-sections from 51 reptile species. We use these models to infer locomotion and posture in 7 extinct reptile taxa for which they remain debated or not fully clear. Our models produced reliable inferences for taxa that preceded and followed the quadruped/biped and sprawling/erect transitions, notably within the Captorhinidae and Dinosauria. For taxa contemporary with these transitions, such as Terrestrisuchus and Marasuchus, the inferences are more questionable. We use linear models to investigate the effect of body mass and functional ecology on our inference models. We show that body mass seems to significantly impact our model predictions in most cases, unlike the functional ecology. Finally, we illustrate how taphonomic processes can impact certain microanatomical parameters, especially the eccentricity of the section, while addressing some other potential limitations of our methods. Our study provides insight into the evolution of enigmatic locomotion in various early reptiles. Our models and methods could be used by palaeontologists to infer the locomotion and posture in other extinct reptile taxa, especially when considered in combination with other lines of evidence.

An insight into cancer palaeobiology: does the Mesozoic neoplasm support tissue organization field theory of tumorigenesis?

BACKGROUND

Neoplasms are common across the animal kingdom and seem to be a feature plesiomorphic for metazoans, related with an increase in somatic complexity. The fossil record of cancer complements our knowledge of the origin of neoplasms and vulnerability of various vertebrate taxa. Here, we document the first undoubted record of primary malignant bone tumour in a Mesozoic non-amniote. The diagnosed osteosarcoma developed in the vertebral intercentrum of a temnospondyl amphibian, Metoposaurus krasiejowensis from the Krasiejów locality, southern Poland.

RESULTS

A wide array of data collected from gross anatomy, histology, and microstructure of the affected intercentrum reveals the tumour growth dynamics and pathophysiological aspects of the neoplasm formation on the histological level. The pathological process almost exclusively pertains to the periosteal part of the bone composed from a highly vascularised tissue with lamellar matrix. The unorganised arrangement of osteocyte lacunae observed in the tissue is characteristic for bone tissue types connected with static osteogenesis, and not for lamellar bone. The neoplastic bone mimics on the structural level the fast growing fibrolamellar bone, but on the histological level develops through a novel ossification type. The physiological process of bone remodelling inside the endochondral domain continued uninterrupted across the pathology of the periosteal part.

CONCLUSIONS

Based on the results, we discuss our case study's consistence with the Tissue Organization Field Theory of tumorigenesis, which locates the causes of neoplastic transformations in disorders of tissue architecture.

The first occurrence of an avian-style respiratory infection in a non-avian dinosaur

Other than repaired fractures, osteoarthritis, and periosteal reaction, the vertebrate fossil record has limited evidence of non-osseous diseases. This difficulty in paleontological diagnoses stems from (1) the inability to conduct medical testing, (2) soft-tissue pathologic structures are less likely to be preserved, and (3) many osseous lesions are not diagnostically specific. However, here reported for the first time is an avian-style respiratory disorder in a non-avian dinosaur. This sauropod presents irregular bony pathologic structures stemming from the pneumatic features in the cervical vertebrae. As sauropods show well-understood osteological correlates indicating that respiratory tissues were incorporated into the post-cranial skeleton, and thus likely had an ‘avian-style’ form of respiration, it is most parsimonious to identify these pathologic structures as stemming from a respiratory infection. Although several extant avian infections produce comparable symptoms, the most parsimonious is airsacculitis with associated osteomyelitis. From actinobacterial to fungal in origin, airsacculitis is an extremely prevalent respiratory disorder in birds today. While we cannot pinpoint the specific infectious agent that caused the airsacculitis, this diagnosis establishes the first fossil record of this disease. Additionally, it allows us increased insight into the medical disorders of dinosaurs from a phylogenetic perspective and understanding what maladies plagued the “fearfully great lizards”.

Growth variability, dimensional scaling, and the interpretation of osteohistological growth data

Osteohistological data are commonly used to study the life history of extant and extinct tetrapods. While recent advances have permitted detailed reconstructions of growth patterns, physiology and other features using these data, they are most commonly used in assessments of ontogenetic stage and relative growth in extinct animals. These methods have seen widespread adoption in recent years, rapidly becoming a common component of the taxonomic description of new fossil taxa, but are often applied without close consideration of the sources of variation present or the dimensional scaling relationships that exist among different osteohistological measurements. Here, we use a combination of theoretical models and empirical data from a range of extant and extinct tetrapods to review sources of variability in common osteohistological measurements, their dimensional scaling relationships and the resulting interpretations that can be made from those data. In particular, we provide recommendations on the usage and interpretation of growth mark spacing/zonal thickness data, when these are likely to be unreliable, and under what conditions they can provide useful inferences for studies of growth and life history.

Polyester or epoxy: assessing embedding product efficacy in paleohistological methods

Histological examination of bone microstructure provides insight into extant and extinct vertebrate physiology. Fossil specimens sampled for histological examination are typically first embedded in an inexpensive polyester resin and then cut into thin sections, mounted on slides, and polished for viewing. Modern undecalcified bone is chemically processed prior to embedding in plastic resin, sectioning, mounting, and polishing. Conversely, small fossil material and modern undecalcified bone are typically embedded in higher priced epoxy resin because these specimen types require final sections near or below 100 µm thick. Anecdotal evidence suggests thin sections made of polyester resin embedded material polished thinner than 100 µm increases likelihood of sample peeling, material loss, and is unsuitable for modern tissue and small fossil material. To test this assertion, a sample of modern bones and fossil bones, teeth, and scales were embedded in either polyester resin or epoxy resin. Embedded specimens were sectioned and mounted following standard published protocol. Thin sections were ground on a lapidary wheel using decreasing grit sizes until tissue microstructure was completely discernible when viewed under a polarizing light microscope. Additionally, eight prepared thin sections (four from polyester resin embedded specimens and four from epoxy resin embedded specimens) were continuously ground on a lapidary wheel using 600 grit carbide paper until peeling occurred or material integrity was lost. Slide thickness when peeling occurred was measured for comparing slide thickness when specimen integrity was lost between the two resin types. Final slide thickness ranged from 38 µm to 247 µm when tissue was identifiable using a polarizing microscope. Finished slide thickness varied between resin types despite similar tissue visibility. However, finished slide thickness appears more dependent on hard tissue composition than resin type. Additionally, we did not find a difference of slide thickness when material was lost between resin types. The results of this preliminary study suggest that polyester resins can be used for embedding undecalcified modern hard tissues and fossilized hard tissues without loss of tissue visibility or material integrity, at least in the short term.

Case study of radial fibrolamellar bone tissues in the outer cortex of basal sauropods

The histology of sauropod long bones often appears uniform and conservative along their evolutionary tree. One of the main aspects of their bone histology is to exhibit a fibrolamellar complex in the cortex of their long bones. Here, we report another bone tissue, the radial fibrolamellar bone (RFB), in the outer cortex of the humeri of a young adult cf. Isanosaurus (Early to Late Jurassic, Thailand) and an adult Spinophorosaurus nigerensis (Early to Middle Jurassic, Niger) that do not exhibit any pathological feature on the bone surface. Its location within the cortex is unexpected, because RFB is a rapidly deposited bone tissue that would rather be expected early in the ontogeny. A palaeopathological survey was conducted for these sampled specimens. Observed RFB occurrences are regarded as spiculated periosteal reactive bone, which is an aggressive form of periosteal reaction. A 'hair-on-end' pattern of neoplasmic origin (resembling a Ewing's sarcoma) is favoured for cf. Isanosaurus, while a sunburst pattern of viral or neoplasmic origin (resembling an avian osteopetrosis or haemangioma) is favoured for Spinophorosaurus. This study highlights the importance of bone histology in assessing the frequency and nature of palaeopathologies. This article is part of the theme issue 'Vertebrate palaeophysiology'.

Dinosaur paleohistology: review, trends and new avenues of investigation

In the mid-19th century, the discovery that bone microstructure in fossils could be preserved with fidelity provided a new avenue for understanding the evolution, function, and physiology of long extinct organisms. This resulted in the establishment of paleohistology as a subdiscipline of vertebrate paleontology, which has contributed greatly to our current understanding of dinosaurs as living organisms. Dinosaurs are part of a larger group of reptiles, the Archosauria, of which there are only two surviving lineages, crocodilians and birds. The goal of this review is to document progress in the field of archosaur paleohistology, focusing in particular on the Dinosauria. We briefly review the "growth age" of dinosaur histology, which has encompassed new and varied directions since its emergence in the 1950s, resulting in a shift in the scientific perception of non-avian dinosaurs from "sluggish" reptiles to fast-growing animals with relatively high metabolic rates. However, fundamental changes in growth occurred within the sister clade Aves, and we discuss this major evolutionary transition as elucidated by histology. We then review recent innovations in the field, demonstrating how paleohistology has changed and expanded to address a diversity of non-growth related questions. For example, dinosaur skull histology has elucidated the formation of curious cranial tissues (e.g., "metaplastic" tissues), and helped to clarify the evolution and function of oral adaptations, such as the dental batteries of duck-billed dinosaurs. Lastly, we discuss the development of novel techniques with which to investigate not only the skeletal tissues of dinosaurs, but also less-studied soft-tissues, through molecular paleontology and paleohistochemistry-recently developed branches of paleohistology-and the future potential of these methods to further explore fossilized tissues. We suggest that the combination of histological and molecular methods holds great potential for examining the preserved tissues of dinosaurs, basal birds, and their extant relatives. This review demonstrates the importance of traditional bone paleohistology, but also highlights the need for innovation and new analytical directions to improve and broaden the utility of paleohistology, in the pursuit of more diverse, highly specific, and sensitive methods with which to further investigate important paleontological questions.

Pain in dinosaurs: what is the evidence?

How far back can we trace behaviour associated with pain? Behaviour is not preserved in the palaeontological record, so, for dinosaurs, we are restricted to what we can deduce from fossilized bones and tracks. This review is a thought experiment using circumstantial evidence from dinosaur fossils and from the behaviour of their extant relatives to describe probable responses of dinosaurs to serious injuries. Searches yielded 196 papers and chapters with: reports of healed serious injuries, and limping gait and injured feet in trackways; information about physiology and behaviour relevant to healing; evidence of evolutionary connections with birds and crocodilians, and their behaviour; and information about relevant aspects of evolution. Clearly, many dinosaurs survived injuries that would have seriously hampered mobility, impairing hunting or escape from predators, and affecting social interactions. Recovery from severe injuries implies pain-mediated responses. Rates of healing seem faster than for other reptiles, possibily aided by warm-bloodedness. Nesting was often communal, raising the possibility of parental and group protection for injured young. The existence of family groups, packs or herds raises the possibility of protection or feeding from pack kills. This is the first study, to our knowledge, of possible pain behaviour and responses to injury in dinosaurs. This article is part of the Theo Murphy meeting issue 'Evolution of mechanisms and behaviour important for pain'.

Ontogenetic changes in the long bone microstructure in the nine-banded armadillo (Dasypus novemcinctus)

Analysis of ontogenetic changes in long bone microstructure aid in vertebrate life history reconstructions. Specifically, osteohistological examination of common fauna can be used to infer growth strategies of biologically uncommon, threatened, or extinct vertebrates. Although nine-banded armadillo biology has been studied extensively, work on growth history is limited. Here we describe long bone microstructure in tibiae and femora of a limited ontogenetic series of nine- banded armadillos (Dasypus novemcinctus) to elucidate patterns of bone growth. The cortex of the smallest individual is composed of compacted coarse cancellous bone (CCCB) and woven tissue. Extensive cortical drift is driven by periosteal erosion and further compaction of trabeculae resulting in an increase in the amount of CCCB. The cortex of the largest specimens is primarily CCCB with thickened endosteal bone and thin outer cortices of lamellar and parallel-fibered tissue. The outer cortices of the largest individuals are interpreted as an external fundamental system (EFS) indicating a cessation of appositional bone growth corresponding to skeletal maturity (i.e. asymptotic or adult size). The EFS forms in femora prior to tibiae, indicating femoral growth rates begin decreasing earlier than tibial in D. novemcinctus. Growth trends in common fauna like the nine-banded armadillo can be used as a foundation for understanding life histories of related, but uncommon or extinct, species of cingulates.

Cancellous bone and theropod dinosaur locomotion. Part I-an examination of cancellous bone architecture in the hindlimb bones of theropods

This paper is the first of a three-part series that investigates the architecture of cancellous ('spongy') bone in the main hindlimb bones of theropod dinosaurs, and uses cancellous bone architectural patterns to infer locomotor biomechanics in extinct non-avian species. Cancellous bone is widely known to be highly sensitive to its mechanical environment, and has previously been used to infer locomotor biomechanics in extinct tetrapod vertebrates, especially primates. Despite great promise, cancellous bone architecture has remained little utilized for investigating locomotion in many other extinct vertebrate groups, such as dinosaurs. Documentation and quantification of architectural patterns across a whole bone, and across multiple bones, can provide much information on cancellous bone architectural patterns and variation across species. Additionally, this also lends itself to analysis of the musculoskeletal biomechanical factors involved in a direct, mechanistic fashion. On this premise, computed tomographic and image analysis techniques were used to describe and analyse the three-dimensional architecture of cancellous bone in the main hindlimb bones of theropod dinosaurs for the first time. A comprehensive survey across many extant and extinct species is produced, identifying several patterns of similarity and contrast between groups. For instance, more stemward non-avian theropods (e.g. ceratosaurs and tyrannosaurids) exhibit cancellous bone architectures more comparable to that present in humans, whereas species more closely related to birds (e.g. paravians) exhibit architectural patterns bearing greater similarity to those of extant birds. Many of the observed patterns may be linked to particular aspects of locomotor biomechanics, such as the degree of hip or knee flexion during stance and gait. A further important observation is the abundance of markedly oblique trabeculae in the diaphyses of the femur and tibia of birds, which in large species produces spiralling patterns along the endosteal surface. Not only do these observations provide new insight into theropod anatomy and behaviour, they also provide the foundation for mechanistic testing of locomotor hypotheses via musculoskeletal biomechanical modelling.

Digging the compromise: investigating the link between limb bone histology and fossoriality in the aardvark (Orycteropus afer)

Bone microstructure has long been known as a powerful tool to investigate lifestyle-related biomechanical constraints, and many studies have focused on identifying such constraints in the limb bones of aquatic or arboreal mammals in recent years. The limb bone microstructure of fossorial mammals, however, has not been extensively described. Furthermore, so far, studies on this subject have always focused on the bone histology of small burrowers, such as subterranean rodents or true moles. Physiological constraints associated with digging, however, are known to be strongly influenced by body size, and larger burrowers are likely to exhibit a histological profile more conspicuously influenced by fossorial activity. Here, we describe for the first time the limb bone histology of the aardvark (Orycteropus afer), the largest extant burrowing mammal. The general pattern is very similar for all six sampled limb bones (i.e., humerus, radius, ulna, femur, tibia, and fibula). Most of the cortex at midshaft is comprised of compacted coarse cancellous bone (CCCB), an endosteal tissue formed in the metaphyses through the compaction of bony trabeculae. Conversely, the periosteal bone is highly resorbed in all sections, and is reduced to a thin outer layer, suggesting a pattern of strong cortical drift. This pattern contrasts with that of most large mammals, in which cortical bone is of mostly periosteal origin, and CCCB, being a very compliant bone tissue type, is usually resorbed or remodeled during ontogeny. The link between histology and muscle attachment sites, as well as the influence of the semi-arid environment and ant-eating habits of the aardvark on its bone microstructure, are discussed. We hypothesize that the unusual histological profile of the aardvark is likely the outcome of physiological constraints due to both extensive digging behavior and strong metabolic restrictions. Adaptations to fossoriality are thus the result of a physiological compromise between limited food availability, an environment with high temperature variability, and the need for biomechanical resistance during digging. These results highlight the difficulties of deciphering all factors potentially involved in bone formation in fossorial mammals. Even though the formation and maintaining of CCCB through ontogeny in the aardvark cannot be unambiguously linked with its fossorial habits, a high amount of CCCB has been observed in the limb bones of other large burrowing mammals. The inclusion of such large burrowers in future histological studies is thus likely to improve our understanding of the functional link between bone growth and fossorial lifestyle in an evolutionary context.

The bone microstructure of polar "hypsilophodontid" dinosaurs from Victoria, Australia

High-latitude (i.e., “polar”) Mesozoic fauna endured months of twilight and relatively low mean annual temperatures. Yet non-avian dinosaurs flourished in this taxing environment. Fossils of basal ornithopod dinosaurs (“hypsilophodontids”) are common in the Early Cretaceous high-latitude sediments of Victoria, Australia, and four taxa have been described; although their ontogenetic histories are largely unexplored. In the present study, eighteen tibiae and femora were utilized in the first multi-specimen ontogenetic histological analysis of Australian polar hypsilophodontids. The sample consists of eleven individuals from the Flat Rocks locality (Late Valanginian or Barremian), and five from the Dinosaur Cove locality (Albian). In both groups, growth was most rapid during the first three years, and skeletal maturity occurred between five and seven years. There is a weak asymptotic trend in a plot of growth mark count versus femur length, with considerable individual variation. Histology suggests two genera are present within the Dinosaur Cove sample, but bone microstructure alone could not distinguish genera within the Flat Rocks sample, or across the two geologically separate (~ 26 Ma) localities. Additional histologic sampling, combined with morphological analyses, may facilitate further differentiation between ontogenetic, individual, and species variation.

Human-Aided Movement of Viral Disease and the Archaeology of Avian Osteopetrosis

The term avian osteopetrosis is used to describe alterations to the skeletal elements of several species of domestic bird, most typically the chicken, Gallus gallus domesticus (L. 1758). Such lesions are routinely identified in animal bones from archaeological sites due to their distinctive appearance, which is characterised by proliferative diaphyseal thickening. These lesions are relatively uncomplicated for specialists to differentially diagnose and are caused by a range of avian leucosis viruses in a series of subgroups. Only some avian leucosis viruses cause the development of such characteristic lesions in osteological tissue. Viraemia is necessary for the formation of skeletal pathology, and avian osteopetrosis lesions affect skeletal elements at different rates. Lesion expression differs by the age and sex of the infected individual, and environmental conditions have an impact on the prevalence of avian leucosis viruses in poultry flocks. These factors have implications for the ways in which diagnosed instances of avian osteopetrosis in archaeological assemblages are interpreted. By integrating veterinary research with archaeological evidence for the presence of avian leucosis viruses across Western Europe, this paper discusses the nature of these pathogens, outlines criteria for differential diagnosis, and offers a fresh perspective on the human-aided movement of animal disease in the past through investigation of the incidence and geographic distribution of avian osteopetrosis lesions from the first century BC to the post-medieval period.

The first specimen of Camarasaurus (Dinosauria: Sauropoda) from Montana: The northernmost occurrence of the genus

A partial skeleton from the Little Snowy Mountains of central Montana is the first referable specimen of the Morrison Formation macronarian sauropod Camarasaurus. This specimen also represents the northernmost occurrence of a sauropod in the Morrison. Histological study indicates that, although the specimen is relatively small statured, it is skeletally mature; this further emphasizes that size is not a undeviating proxy to maturity in dinosaurs, and that morphologies associated with an individual’s age and stature may be more nebulous in sauropods.