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Chlamyphorus truncatus is the smallest known armadillo, weighing about 100 grams and measuring less than 15 cm from head to tail. It is endemic to central Argentina and the species is named after its unique carapace. This armadillo has almost completely subterranean habits and, unlike all other subterranean mammals, C. truncatus has a carapace composed of osteoderms and cornified scales. Furthermore, the skin and carapace show unique characteristics compared even with other armadillos. Owing to the reduced development of its eyes, it is important to analyse the skin morphology of this species, as well as specialized sensory organs like vibrissae. The aim of this contribution is to describe the histomorphology of the integumentary system of C. truncatus. For this, histological sections of the skin with and without osteoderms were made, and routine histological and immunohistochemical techniques were performed. Furthermore, microCTs were performed on osteoderms to describe their micromorphology. Our results show that the integumentary system presents unique characteristics compared to other armadillos, such as the peculiar skin under the dorsal shield and the flexibility of almost all of its carapace. Furthermore, the modification of the arrangement of hairs in the first pelvic buckler osteoderms may suggest biomechanical adaptations, such as an improvement in the displacement through the tunnels of sandy soils. The skin without osteoderms presents convergent characteristics with that of other subterranean mammals. Furthermore, the vibrissae conserve the structure of the armadillos (the cavernous sinuses extend throughout the follicle‐sinus complex) with a thinning and shortening of the hairs, which are probably linked to passive monitoring of the surrounding environment. Evidently, the adaptations of subterranean mammals to their environment imply structural and functional changes, which are both regressive and progressive in nature. [ABSTRACT FROM AUTHOR]

Although there are problematic earliest Jurassic records, phytosaurs are thought to have become extinct during the Rhaetian. A newly-discovered left paramedian phytosaur osteoderm from a clay pit in Bonenburg, Kreis Höxter, North Rhine-Westphalia, Germany, is the youngest, well-dated phytosaur record. This osteoderm was found in a bone bed (Bone Bed 2) in the Contorta Beds of the Rhaetian Exter Formation. Palynology constrains the age of Bone Bed 2 to the late middle Rhaetian (ca. 203.5 million years ago). The Bonenburg osteoderm cannot be assigned to any named species. It most closely resembles some osteoderms from the Rhaetian of Halberstadt in Central Germany. Phytosaurs survived in Europe to at least the late middle Rhaetian, probably falling victim to the end-Triassic extinction event about two million years later. [ABSTRACT FROM AUTHOR]

Abstract An important component of the Alpine vertebrate record of Late Triassic age derives from the Kössen Formation, which crops out extensively in the eastern Alps. Here, we present an isolated and only partially preserved large rib, which carries an osteoderm on a low uncinate process. Osteological comparison indicates that the specimen likely belongs to a small clade of marine reptiles, Saurosphargidae. Members of the clade are restricted to the western (today Europe) and eastern margins of the Tethys (today China) and were so far known only from the Anisian stage of the Middle Triassic. The assignment of the new find to cf. Saurosphargidae, with potential affinities to the genus Largocephalosaurus from the Guanling Formation of Yunnan and Guizhou Provinces, China, would extend the occurrence of the clade about 35 million years into the Late Triassic.

The skin of many tatrapods is supported by bone structures termed osteoderms. Osteoderms were present in the skin of the first tetrapods that appeared in the Devonian, and were inherited after their fish ancestors. During evolution, osteoderms were lost in many tetrapod lineages. They also appeared de novo several times, for examples, at least five times in amniotes. Osteoderms are present in six families of anuran amphibians, where they are located mainly on the dorsal side of the body. Bony structures also support skin of crocodiles and lizards. Osteoderms were highly developed also in ankylosaurs and stegosaurs, as two lineages of dinosaurs. Skin bones also form the turtle carapace and the armor of extinct placodonts. Among synapsids, osteoderms were present in two Permian species, and among mammals only in extant armadillos and extinct glyptodonts and ground sloths. Osteoderms were lost in such tetrapods as snakes, amphisbaenians, pterosaurs and birds, and most of amphibians and mammals. Osteoderms probably gave rise to gastralia, i.e. the abdominal ribs present in crocodiles, tuatara and many extinct amphibians and reptiles, that protect the guts from damage. In addition to osteoderms, in the skin of many modern amphibians, calcifications, such as lamina calcarea and dermal scales in Apoda, are present. Such calcifications do not contain bone tissue and therefore are not classified as osteoderms, but may have developed through their reduction. Comparative analysis reveals that osteoderms are a plesiomorphic feature of tetrapods, and their loss and reappearance make osteoderms a suitable subject of studies on evolutionary plasticity. [ABSTRACT FROM AUTHOR]

Predation is widely regarded as an important selective force in the evolution and maintenance of dermal armour; yet, the basic premise that predation and armour are strongly linked to each other has proven to be difficult to assess.In this concept, I put forward the fighting‐advantage hypothesis, the view that aggressive interactions with conspecifics, not predation, might have been a key selective pressure in the evolution of dermal armour.Considering intraspecific competition as a potential explanation could not only reveal previously overlooked aspects of the functional and evolutionary significance of dermal armour, but also advance the emerging field of biomimetics in which such knowledge forms the starting point of technological innovation. [ABSTRACT FROM AUTHOR]

An important component of the Alpine vertebrate record of Late Triassic age derives from the Kössen Formation, which crops out extensively in the eastern Alps. Here, we present an isolated and only partially preserved large rib, which carries an osteoderm on a low uncinate process. Osteological comparison indicates that the specimen likely belongs to a small clade of marine reptiles, Saurosphargidae. Members of the clade are restricted to the western (today Europe) and eastern margins of the Tethys (today China) and were so far known only from the Anisian stage of the Middle Triassic. The assignment of the new find to cf. Saurosphargidae, with potential affinities to the genus Largocephalosaurus from the Guanling Formation of Yunnan and Guizhou Provinces, China, would extend the occurrence of the clade about 35 million years into the Late Triassic. [ABSTRACT FROM AUTHOR]

This review describes the formation, structure, and function of bony compartments in antlers, horns, ossicones, osteoderm and the os penis/os clitoris (collectively referred to herein as AHOOO structures) in extant mammals. AHOOOs are extra‐skeletal bones that originate from subcutaneous (dermal) tissues in a wide variety of mammals, and this review elaborates on the co‐development of the bone and skin in these structures. During foetal stages, primordial cells for the bony compartments arise in subcutaneous tissues. The epithelial–mesenchymal transition is assumed to play a key role in the differentiation of bone, cartilage, skin and other tissues in AHOOO structures. AHOOO ossification takes place after skeletal bone formation, and may depend on sexual maturity. Skin keratinization occurs in tandem with ossification and may be under the control of androgens. Both endochondral and intramembranous ossification participate in bony compartment formation. There is variation in gradients of density in different AHOOO structures. These gradients, which vary according to function and species, primarily reduce mechanical stress. Anchorage of AHOOOs to their surrounding tissues fortifies these structures and is accomplished by bone–bone fusion and Sharpey fibres. The presence of the integument is essential for the protection and function of the bony compartments. Three major functions can be attributed to AHOOOs: mechanical, visual, and thermoregulatory. This review provides the first extensive comparative description of the skeletal and integumentary systems of AHOOOs in a variety of mammals. [ABSTRACT FROM AUTHOR]

The anatomy, biochemistry, biomechanics, and evolution of reptile integument have been topics of intense interest in the scientific community for at least two centuries. As such, histological techniques were, and still are, employed to provide a comprehensive understanding of the relationships between tissue structure, function, and the evolution of reptile integument. However, histotechnical preparations of reptile skin present many challenges related to the unique microanatomical configuration of the integument in these animals. Reptilian epidermal scales may be thick and corneous and are often not penetrated well by either processing fluids or embedding media. The reptile dermis is a composite of several different tissue types with a range of biophysical properties creating many problems with tissue processing, sectioning, and staining. Further, lepidosaurs (snakes, lizards, and tuataras) exhibit epidermal modifications associated with the shedding cycle (i.e. ecdysis) that may also create histotechnical artifacts. Here, this study reviews the general skin morphology from crocodilians (alligators, crocodiles, and gharials) and lepidosaurs. Common difficulties encountered while preparing this organ for histological examination are explained and highlighted, and technical solutions and protocols are provided that mitigate these problems. [ABSTRACT FROM AUTHOR]

The presence of osteoderms in the skin of some extinct sloths and in cingulates (armadillos, pampatheres, and glyptodonts) has often been considered a pleisomorphic character of the Xenarthra. While osteoderms are known from the earliest cingulates, they are absent in most sloths including the two extant taxa and only appear late in their fossil record. Osteoderms are currently only reported from five genera of mylodonts and two megatheres, out of the over 100 currently recognized genera of sloths. Consequently, rather than a plesiomorphic character of the Xenarthra, which has been secondarily lost in sloths, it is more likely that osteoderms in sloths are the result of parallel evolution to the cingulates that independently evolved in one, possibly two different sloth clades. [ABSTRACT FROM AUTHOR]

Although it is widely assumed that body armour in animals evolved to thwart predator attacks, assessing the role that predators may play in shaping defensive morphologies has proven to be difficult. Recent studies suggest that body armour might be influenced by additional factors besides predation, and/or even by sexual selection. We investigated variation in dermal armour in 13 populations of armadillo lizards Ouroborus cataphractus, spanning the entire distribution range of the species. We obtained thickness measurements of osteoderms – bony plates embedded in dermal layer of the skin – using micro‐ and nano‐computed tomography. Using these data, we examined the effects of predation pressure/risk and climatic variables on dermal armour variation and addressed sexual and ontogenetic influence. Our results show that climate is the only factor affecting variation in dermal armour. Populations inhabiting more arid environments, characterized by low summer precipitation and mild winter temperatures, are relatively more armoured than those present in less arid environments. In contrast to our expectations, predation pressure or perceived predation risk was not associated with osteoderm thickness. The results of our study support the idea that the evolution of defensive traits might not be driven exclusively by predator–prey interactions, but could be moulded by environmental factors. In particular, we highlight the role of dermal armour as a potentially important mechanism to reduce evaporative water loss in arid environments. [ABSTRACT FROM AUTHOR]

While sexual dimorphism in offensive weaponry is a well-established phenomenon, few studies have looked at sexual differences in defensive body armour. In this study, we investigate sexual dimorphism in the expression of osteoderms – bony elements embedded in the skin – in four species of cordyline lizards by using high-resolution micro-computed tomography. Our results unambiguously show that only in the species with an intermediate phenotype characterized by isolated osteoderms without any clear ecological function do males have a higher degree of osteoderm expression than females. By contrast, no significant sexual differences are present in the species with an armoured phenotype consisting of a continuous layer of imbricating osteoderms. These findings suggest that sexual selection acting on dermal armour might be ubiquitous, but that in the armoured phenotype, its effect is weak because of a stronger selection pressure towards improved defence or physiological function. [ABSTRACT FROM AUTHOR]

Animal body armour is often considered an adaptation that protects prey against predatory attacks, yet comparative studies that link the diversification of these allegedly protective coverings to differential predation risk or pressure are scarce. Here, we examine the evolution of body armour, including spines and osteoderms, in Cordylinae, a radiation of southern African lizards. Using phylogenetic comparative methods, we attempt to identify the ecological and environmental correlates of body armour that may hint at the selective pressures responsible for defensive trait diversification. Our results show that species inhabiting arid environments are more likely to possess elaborated body armour, specifically osteoderms.We did not find any effect of estimated predation pressure or risk on the degree of body armour. These findings suggest that body armour might not necessarily evolve in response to direct interactions with predators, but rather as a result of increased habitat-mediated predation risk. Furthermore, we discuss the possibility that osteoderms might have been shaped by factors unrelated to predation. [ABSTRACT FROM AUTHOR]

Many animal species evolved some form of body armor, such as scales of fish and bony plates or osteoderms of reptiles. Although a protective function is often taken for granted, recent studies show that body armor might comprise multiple functionalities and is shaped by trade-offs among these functionalities. Hence, despite the fact that natural body armor might serve as bio-inspiration for the development of artificial protective materials, focussing on model systems in which body armor serves a solely protective function might be pivotal. In this study, we investigate the osteoderms of Glyptotherium arizonae , an extinct armadillo-like mammal in which body armor evolved as protection against predators and/or tail club blows of conspecifics. By using a combination of micro-computed tomography, reverse-engineering, stress simulations and mechanical testing of 3D printed models, we show that the combination of dense compact layers and porous lattice core might provide an optimized combination of strength and high energy absorption. [ABSTRACT FROM AUTHOR]

An isolated dinosaur osteoderm from the Rumelange-Ottange (Cimalux, formerly Intermoselle) Quarry of the Grand Duchy of Luxembourg is described. The fossil was found in marly-calcareous deposits of the "Marnes sableuses d'Audunle- Tiche", which are Middle Jurassic in age (Humphriesianum Zone, Lower Bajocian). The deposits correspond to an open sea environment with an abundant and diverse marine fauna, including invertebrates, actinopterygians, hybodonts, neoselachians, plough-nose chimaeras, and marine reptiles. The oval, low-keeled osteoderm has a roof-like appearance and is here identified as a thyreophoran dermal scute. It could belong to a basal thyreophoran or, more tentatively, to an early ankylosaur. The specimen was probably a remnant of a floating carcass that drifted over a distance from a land area. The dermal scute from the Ottange- Rumelange Quarry represents the second Jurassic dinosaur reported to date from Luxembourg, and the first one described from the Bajocian. Moreover, it is one of the few non-stegosaurian thyreophoran records of Middle Jurassic age. [ABSTRACT FROM AUTHOR]

The presence of dermal armor is often unambiguously considered the result of an evolutionary predator-prey arms-race. Recent studies focusing predominantly on osteoderms – mineralized elements embedded in the dermis layer of various extant and extinct vertebrates – have instead proposed that dermal armor might exhibit additional functionalities besides protection. Multiple divergent functionalities could impose conflicting demands on a phenotype, yet, functional trade-offs in dermal armor have rarely been investigated. Here, we use high-resolution micro-computed tomography and voxel-based simulations to test for a trade-off between the strength and thermal capacity of osteoderms using two armored cordylid lizards as model organisms. We demonstrate that high vascularization, associated with improved thermal capacity might limit the strength of osteoderms. These results call for a holistic, cautionary future approach to studies investigating dermal armor, especially those aiming to inspire artificial protective materials. [ABSTRACT FROM AUTHOR]

Saltasaurine titanosaurs are characterized by their relatively small size compared to other sauropods, extreme postcranial pneumaticity, and dermal armour covering the body. This group has been reported in the Upper Cretaceous of the Lecho, Allen, and Anacleto formations of Argentina. We describe here a new saltasaurine specimen (MACN-Pv RN 233) from the Campanian of the Angostura Colorada Formation (Río Negro Province) that is represented by eight caudal vertebrae and six osteoderms. This specimen is described in detail and its phylogenetic relationships with the other three known saltasaurines, as well as its implications to the knowledge of caudal vertebra and osteoderm anatomy, are discussed. Our results place MACN-Pv RN 233 more closely related to Saltasaurus loricatus and Rocasaurus muniozi than to Neuquensaurus australis . MACN-Pv RN 233 possesses a combination of features that differ from other saltasaurines, but because of the fragmentary nature of the specimen we decided for the sake of taxonomic stability to not erect a new taxon. This specimen shows the first unambiguous evidence of chevron pneumatisation for a sauropodomorph, implying a broader osteological invasion of the diverticula from the abdominal air sac than previously thought for this group of dinosaurs. MACN-Pv RN 233 preserves two osteoderm morphotypes, one similar to those reported for Neuquensaurus australis and Saltasaurus loricatus . This new specimen expands the distribution of the group to a new geological unit and increases the dinosaur diversity known for the Angostura Colorada Formation. [ABSTRACT FROM AUTHOR]

Microcomputed tomography (μ CT) is a widely used tool in biomedical research, employed to investigate tissues and bone structures of small mammals in vivo. The application of in vivo μ CT scanning in non-medical studies greatly lags behind the rapid advancements made in the biomedical field wherein the methodology has evolved to allow for longitudinal studies and eliminate the need to sacrifice the animal. Ecological and evolutionary studies often involve morphological measurements of a large sample of live animals; however, the potential of in vivo μ CT imaging as a method for data acquisition has yet to be delineated., Here, we describe a protocol for in vivo μ CT imaging of the internal anatomy of reptiles and amphibians, commonly used study organisms in ecological and evolutionary research. We consider the skeletal and extraskeletal (i.e. osteoderms) bones of a lizard as a case study to elucidate the potential of in vivo μ CT imaging. First, we explore the effects of various parameter settings on radiation dose, scan time and image quality. Secondly, we develop a protocol to immobilize and restrain study organisms during scanning without need for the administration of anaesthetics and compare the results of the in vivo protocol to images obtained post-mortem., To immobilize animals, we replace the use of anaesthetics by cooling, thereby allowing the use of previously unsuitable rotating gantry μ CT scanners that are readily available in scientific institutions. The resultant image quality of in vivo μ CT scans is similar to that of post-mortem μ CT scans, especially in the abdominal region. We discuss the effect of tube voltage, distance to X-ray source and metal filtration on radiation dose, and how these parameters could be altered to reduce the cumulative radiation dose while maintaining optimal image quality., The proposed in vivo μ CT protocol offers a new approach to acquire anatomical information for non-biomedical studies. We offer specific suggestions as to how the protocol can be employed to suit a variety of model organisms. [ABSTRACT FROM AUTHOR]

Large ulcerative pits on the external surface of ankylosaur (Dinosauria) osteoderms have been recognized for many years. They have been ascribed without supporting evidence to damage by predator teeth or to disease. The discovery of numerous examples of pitted osteoderms in a monospecific ankylosaur ( Gastonia n.sp.) bone bed in eastern Utah (USA) provided a unique opportunity to study these pits in greater detail. The pits typically are characterized by smooth-walled depressions that disrupt the bone surface, with 43% focal lesions and 57% multifocal. Because ankylosaur osteoderms are analogous to crocodile osteoderms, the possible etiology of the pits was sought among today’s crocodile dermatoses. A modified version of the Istanbul Protocol was used to indicate the degree of certainty for the possible causes. This technique in context of the limited range of response to infection of reptile bone, allows us to narrow the possible causes of pit formation to two. One is ulceration by bacterial or mycological dermatosis; the other is through pressure erosion of the bone surface (cortex) by granuloma formation in the thin skin or at the skin-osteoderm interface. Unfortunately, the biopsies that are critical for differential diagnosis of diseases in modern reptiles cannot be performed on the ankylosaur osteoderms. Therefore, a single definitive etiology for pits in ankylosaurs cannot be identified. [ABSTRACT FROM AUTHOR]

Castellanos described and published about new genera of glyptodonts, according to a phylogenetic scheme mainly based on the evolution of the external surface of the dorsal carapace. Among these new genera, Castellanos proposed Paraglyptodon as the predecessor of Glyptodon , and included within Paraglyptodon all known species of Glyptodontinae recovered from “ horizontes pre-Ensenadenses ”, and within Glyptodon all known species from “ Horizontes pampeanos ”, restricting the latter to the Quaternary. All the species that belong to Paraglyptodon , that is Paraglyptodon chapalmalensis , Paraglyptodon uquiensis , Paraglyptodon dubius , and Paraglyptodon paranensis were established based on one, two or few osteoderms, mostly from the dorsal carapace. Regarding P. paranensis and P. dubius , Oliva and collaborators consider the first as a nomen vanum , representing an indeterminate Glyptodontinae, and the second as a synonym of P . chapalmalensis . Upon re-examination of the holotypes of P . chapalmalensis and P. uquiensis together with their comparison with other well-known specimens of glyptodonts, mainly with Glyptodon (of both juvenile and adult stages), we found the same ornamentation in different sections of the dorsal carapaces, particularly in P. chapalmalensis and in juvenile stages of Glyptodon spp. We could not identify features that would allow us to make a distinction between the holotype of P. uquiensis and Glyptodon spp. Therefore, we consider that a new taxon guide for naming the Upper Chapadmalalan biozone is necessary. The biostratigraphic range of Glyptodon could possibly be extended to the late Pliocene. However, new records and studies are needed to verify the existence of this taxon in the Chapadmalalan Stage/Age in its type locality. [ABSTRACT FROM AUTHOR]

Osteoderms are mineralized structures embedded in the dermis, known for nonavian archosaurs, squamates, xenarthrans, and amphibians. Herein, we compared the osteoderm histology of Brazilian Notosuchia of Cretaceous age using three neosuchians for comparative purposes. Microanatomical analyses showed that most of them present a diploe structure similar to those of other pseudosuchians, lizards, and turtles. This structure contains two cortices (the external cortex composed of an outer and an inner layers, and the basal cortex) and a core in-between them. Notosuchian osteoderms show high bone compactness (>0.85) with varying degrees of cancellous bone in the core. The neosuchian Guarinisuchus shows the lowest bone compactness with a well-developed cancellous layer. From an ontogenetic perspective, most tissues are formed through periosteal ossification, although the mineralized tissues observed in baurusuchid LPRP/USP 0634 suggest a late metaplastic development. Histology suggests that the ossification center of notosuchian osteoderm is located at the keel. Interestingly, we identified Sharpey's fibers running perpendicularly to the outer layer of the external cortex in Armadillosuchus arrudai, Itasuchus jesuinoi, and Baurusuchidae (LPRP/USP 0642). This feature indicates a tight attachment within the dermis, and it is evidence for the presence of an overlying thick leathery layer of skin over these osteoderms. These data allow a better understanding of the osteohistological structure of crocodylomorph dermal bones, and highlight their structural diversity. We suggest that the vascular canals present in some sampled osteoderms connecting the inner layer of the external cortex and the core with the external surface may increase osteoderm surface and the capacity of heat transfer in terrestrial notosuchians., (© 2022 The Authors. Journal of Morphology published by Wiley Periodicals LLC.)

Osteoderms of eight extant and extinct species of crocodylomorphs are studied histologically and morphologically. Most osteoderms display the typical "crocodilian" structure with a woven-fibered matrix surrounded by an upper and a lower parallel fibered matrix. The dorsal ornamentation of those specimens consists of a pit-and-ridge structure, with corresponding remodeling mechanisms. However, an osteoderm of Iberosuchus, studied here for the first time, differs in being nearly devoid of ornamentation; moreover, it shows strong bundles of straight Sharpey's fibers perpendicular to the surface in its lateral and dorsal walls, along with a rough plywood-like structure in its basal plate. This suggests that this osteoderm was more deeply anchored within the dermis than the other osteoderms studied hitherto. This peculiar structure might have been linked to a terrestrial ecology and a specific thermoregulation strategy. Some other notosuchians in our sample do not exhibit ornamentation on their osteoderms, as opposed to neosuchians. Considering current interpretations of osteoderm function(s) in crocodilians, our observations are discussed in reference to possible ecophysiological peculiarities of Notosuchia in general, and Iberosuchus in particular., (© 2022 The Authors. Journal of Morphology published by Wiley Periodicals LLC.)

Among extant mammals, the presence of osteoderms is limited to armadillos (Xenarthra, Dasypodidae), being one of its distinctive features. The osteoderms are articulated to form a carapace that covers their body dorsally. In this paper we study the integumentary structures of the armadillos Chaetophractus vellerosus, Chaetophractus villosus, Euphractus sexcinctus, and Zaedyus pichiy (Euphractinae), Dasypus hybridus, and Dasypus novemcinctus (Dasypodinae) within a comparative framework, aiming to identify patterns common to the family and to the subfamilies Dasypodinae and Euphractinae, as well as peculiarities of each species. Differences between the two subfamilies were observed in the dorsal integument, related to the production of blood cells and the mobility of the carapace. The Euphractinae present more numerous and larger cavities filled with adipose tissue in the osteoderms, as well as more marginal follicles than the Dasypodinae. These provide thermal insulation that could be related to their distribution in cooler climates. The sebaceous glands associated with surface follicles are also more developed in the Euphractinae and could be related to preventing the desiccation of the cornified scales in arid climates. [ABSTRACT FROM AUTHOR]

The calcium (Ca) demand on alligators in active reproduction is significant, yet the source of this additional Ca is unclear. Three possible sources for Ca mobilization are endolymphatic deposits, as in anurans and some lizards; short-lived skeletal medullary bone or analogous deposits, as in birds; or some other source such as the osteoderm layer of the integument or simply mobilization of structural bone. Here, we investigate possible extra-skeletal sources for labile Ca in the reproducing alligator, including endolymphatic Ca deposits, by analogy with anuran amphibian and some reptiles and integumentary osteodermal (scale) Ca deposits. We conducted X-ray image analyses of skulls for the presence of significant endolymphatic Ca deposits. We also examined dermal bone of scutes (osteoderm, scales) from the dorsal integument using both X-ray and histological analyses. Tissues from reproducing females containing mature but unovulated follicles were compared with those from specimens that had nested (laid eggs) or contained eggs within the oviduct at advanced stages of calcification. A small number of immature specimens and an adult male were also compared. No clear differences were observed in endolymphatic deposits between pre- and post-ovulatory specimens. Scute (osteoderm) X-ray density was significantly greater in females with ripe ovarian follicles compared with those that had recently laid (nested) or contained heavily calcified eggs within their oviducts. The latter groups also showed histological evidence of scute resorption compared with the former, suggesting that the scutes play a role in Ca storage during egglay. [ABSTRACT FROM AUTHOR]

Predation has been proposed to be a selective agent in the evolution of morphological antipredator strategies in prey. Among vertebrates, one of the morphological traits that evolved multiple times is body armour, including carapaces, thickened keratinized scales and plates of dermal bone., It has been generally assumed that body armour provides protection against a predatory attack; yet, few explicit tests of the hypothesis exist. Cordylidae, a relatively small family of southern African lizards, show considerable variation in the degree of body armour. Hence, this family provides an opportunity to test the hypothesis that body armour serves as protection against predators., Experiments were conducted to test whether the bite forces of four species of mammalian predators were high enough to penetrate the skins of Karusasaurus polyzonus, Namazonurus peersi, Cordylus cordylus and Cordylus macropholis, as well as those of Ouroborus cataphractus individuals originating from three localities that differed in their predator diversity. Furthermore, histological techniques were used to test whether variation in skin toughness was associated with concomitant changes in the degree of epidermal (i.e. β-keratin) and dermal (i.e. osteoderm) armour., The skin toughness values for four out of five cordylid lizards tested in this study were well below the bite forces of the mammalian predators. In contrast, the thick osteoderms in the dermis of O. cataphractus can withstand bites from several mongoose species. However, the significant variation in body armour that is present between the three populations of O. cataphractus does not seem to be related to predator diversity., It is concluded that body armour can serve as protection against predation in O. cataphractus, but that alternative selection pressures, such as thermoregulation or predation by snakes, presumably underlie variation in defensive morphology in the other cordylid lizards. [ABSTRACT FROM AUTHOR]

Abstract: Alligator is a well-adapted living fossil covered with dorsal armor. This dermal shield consists of bony plates, called osteoderms, interconnected by sutures and non-mineralized collagen fibers, providing a dual function of protection and flexibility. Osteoderm features a sandwich structure, combining an inner porous core and an outer dense cortex, to offer enhancements for stiffness and energy absorbance. In this study, we investigated the multi-scale structure and mechanical behaviors of the American alligator (Alligator mississippiensis) osteoderm. Microcomputed tomography was applied to reveal the complex neurovascular network. Through the observation under optical and scanning electron microscopes, the osteoderm was found to consist of woven bone in the dorsal region and lamellar-zonal bone in the ventral region. Nanoindentation and compressive tests were performed to evaluate the mechanical properties of osteoderms. The varying mineral contents and porosity result in a graded mechanical property: a hard and stiff dorsal cortex gradually transform to a more compliant ventral base. Three protective mechanisms optimized for alligator osteoderms were proposed and elucidated. [Copyright &y& Elsevier]

Abstract: Among titanosaurs, osteoderms are morphologically diverse and have been reported from deposits in South America, Africa, Madagascar, Eurasia and Oceania. In Brazil, titanosaur osteoderms are rare and have only been recorded from Bauru Basin sedimentary rocks. Here, we describe a keeled titanosaur osteoderm, which is the first occurrence of an osteoderm specimen in the São Luís Basin, Northeastern Brazil. This osteoderm is characterized by an external bulb, an internal root, and a very rugose cingulum limiting the external and internal surfaces. These characteristics are typical of Titanosauria dermal bones, and this specimen strengthens the idea that the armored sauropods were present during the early Late Cretaceous of Northeastern Brazil, extending their distribution in the northernmost portion of South America. [Copyright &y& Elsevier]

Predation is widely regarded as an important selective force in the evolution and maintenance of dermal armour; yet, the basic premise that predation and armour are strongly linked to each other has proven to be difficult to assess. In this concept, I put forward the fighting-advantage hypothesis, the view that aggressive interactions with conspecifics, not predation, might have been a key selective pressure in the evolution of dermal armour. Considering intraspecific competition as a potential explanation could not only reveal previously overlooked aspects of the functional and evolutionary significance of dermal armour, but also advance the emerging field of biomimetics in which such knowledge forms the starting point of technological innovation., (© 2022 The Author. Journal of Animal Ecology © 2022 British Ecological Society.)

Abstract: The integument of extant armadillos (Xenarthra, Cingulata) is a unique organ in which complex glandular systems are associated with pilose follicles, dermal ossifications, and cornified scales. Up to date, papers have focused on neither comparative morphology of the skin (dorsal and ventral) nor chronology of the development of interspecific homolog structures. In order to clarify the way in which events occur during development of the integument structures, maturity of other tissues (e.g. skeletal tissues) should be considered. Therefore, we will be able to identify events that have been pre- or post-displaced during ontogenetic development. The aim of this paper is to describe in a developmental and comparative framework the integumentary system of neonates of Dasypus hybridus and Chaetophractus vellerosus. In order to understand the morphology of the different integumentary structures serial histological sections were prepared. Staining techniques included H–E, Masson Trichrome, PAS, orcein and reticulin. To study ossification of postcranial elements, the specimens were cleared and double-stained with alcian blue and alizarin red. Determinations of ossification centers and their progress were recorded through the early uptake of alizarin. The dorsal dermis of neonates from D. hybridus is clearly differentiated into a superficial and deep layer, as in fetuses of Dasypus novemcinctus. In C. vellerosus, however, these layers could not be identified. This suggests a less connective tissue differentiation in the latter species at this stage. Osteoderms in D. hybridus are well differentiated unlike C. vellerosus where no condensations of osteoprogenitory cells are observed. Conversely, pilose follicles and glandular tissues are less developed in D. hybridus. Regarding postcranial elements, ossification centers are less advanced in C. vellerosus than D. hybridus, this is particularly notorious for the vertebral column, sternal, and pelvic girdle elements. Asynchronies between neonates of both species observed on integumentary and postcranial skeletal tissues could match with specific adaptive strategies related to distribution in different environments, and/or different postnatal care. [Copyright &y& Elsevier]

The four types of dermal armour bones/osteoderms and scutes of Balochisauridae and Pakisauridae (Titanosauria) were found as fragmentary in the latest Cretaceous (Maastrichtian) Vitakri Formation of Sulaiman basin in Pakistan. Larger and smaller osteoderms from Pakistan provide a further opportunity for correlation with the armor bones already discovered from Madagascar, Argentina, Brazil, France, Malawi, Romania and Spain. [ABSTRACT FROM AUTHOR]

Abstract: The armadillo has a unique protective bony armor, called the osteoderm, which confers to its shell-like skin distinctive mechanical properties. The top layer of the shell is made out of a dark-brown keratin layer with bimodal size scales. Beneath the keratin layer, the osteoderm consists of hexagonal or triangular tiles having a composition that is the same as bone. The tiles are connected by non-mineralized collagen fibers, called Sharpey’s fibers. The tough and highly mineralized tiles have a tensile strength of approximately 20 MPa and toughness of around 1.1 MJ/m3. In comparison, the hydrated osteoderm has a lower tensile strength of and a toughness of 0.5 MJ/m3. The tensile failure occurs by the stretching and rupture of the Sharpey’s fibers. In a specially designed punch test in which an individual tile is pushed out, the shear strength is , close to the tensile strength of the osteoderm. This surprising result is interpreted in terms of deformation in the Sharpey’s fibers in the hydrated condition. The armadillo shell and a turtle shell are compared, with their corresponding similarities and differences. [Copyright &y& Elsevier]

We describe the extra bony elements, plates, and osteoderms present in species of the genus Brachycephalus. Samples of eight species of Brachycephalus, including seven populations of Brachycephalus ephippium, were examined. The large additional elements associated with the skull (parotic plate) and vertebrae (vertebral and paravertebral plates) all comprise intramembranous bone, similar to that of the frontoparietal or nasal bones of the skull of most of frogs. Additionally, in the dermis of one unnamed species, we discovered and described true osteoderms. We discuss the morphological nature and diversity of theses elements and their importance as evidence of phylogenetic relationship within Brachycephalus. In summary, three distinct conditions of extra bony elements occur in the genus Brachycephalus: (1) bony plates may be present or absent in species of the genus; (2) a few, small bony plates may be developed and these may be represented by (a) paravertebral plates small and restricted to the distal ends of the transverse processes of the presacral IV, (b) parotic plates small and not covering the tops of the squamosals, and (c) ornamented spinal plates on all vertebrae; and (3) well-developed bony plates may be present as (a) paravertebral plates forming a ‘bone-shield’ on the dorsal surface of the trunk, ornamented, and visible through the integument, (b) parotic plates covering the tops of the squamosals, and (c) spinal plates associated with all vertebrae, and ornamented on vertebrate I–VI. Although the phenomenon of miniaturization may be associated with the appearance of new elements in at least some of the species in the genus, the traditional rule may not be universally applicable. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99, 752–767. [ABSTRACT FROM AUTHOR]

Although often overlooked, the integument of many tetrapods is reinforced by a morphologically and structurally diverse assemblage of skeletal elements. These elements are widely understood to be derivatives of the once all-encompassing dermal skeleton of stem-gnathostomes but most details of their evolution and development remain confused and uncertain. Herein we re-evaluate the tetrapod integumentary skeleton by integrating comparative developmental and tissue structure data. Three types of tetrapod integumentary elements are recognized: (1) osteoderms, common to representatives of most major taxonomic lineages; (2) dermal scales, unique to gymnophionans; and (3) the lamina calcarea, an enigmatic tissue found only in some anurans. As presently understood, all are derivatives of the ancestral cosmoid scale and all originate from scleroblastic neural crest cells. Osteoderms are plesiomorphic for tetrapods but demonstrate considerable lineage-specific variability in size, shape, and tissue structure and composition. While metaplastic ossification often plays a role in osteoderm development, it is not the exclusive mode of skeletogenesis. All osteoderms share a common origin within the dermis (at or adjacent to the stratum superficiale) and are composed primarily (but not exclusively) of osseous tissue. These data support the notion that all osteoderms are derivatives of a neural crest-derived osteogenic cell population (with possible matrix contributions from the overlying epidermis) and share a deep homology associated with the skeletogenic competence of the dermis. Gymnophionan dermal scales are structurally similar to the elasmoid scales of most teleosts and are not comparable with osteoderms. Whereas details of development are lacking, it is hypothesized that dermal scales are derivatives of an odontogenic neural crest cell population and that skeletogenesis is comparable with the formation of elasmoid scales. Little is known about the lamina calcarea. It is proposed that this tissue layer is also odontogenic in origin, but clearly further study is necessary. Although not homologous as organs, all elements of the integumentary skeleton share a basic and essential relationship with the integument, connecting them with the ancestral rhombic scale. [ABSTRACT FROM AUTHOR]

Here we describe a pathological osteoderm from the crocodylomorph Diplocynodon hantoniensis (Bouldnor Formation, earliest Oligocene, Isle of Wight, United Kingdom). The specimen bears a porous, erosive branching channel that distorts the surface ornamentation and periosteum over 60% of the preserved dorsal surface area. We diagnose this condition as necrotizing dermatitis: a surficial bacterial or fungal infection that can penetrate the dermal layers to affect the underlaying penosteum of osteoderms. This condition has been previously reported for an extant tortoise and caiman; however, this is the first reported occurrence in the fossil record. [ABSTRACT FROM AUTHOR]

Two series of osteoderms associated with the anterior three-quarters of the presacral vertebral column of the Early Permian temnospondylous amphibian Cacops aspidephorus have important implications for biomechanics of the axial skeleton. An internal series consists of an osteoderm fused to the distal tip of each neural spine. Lying dorsal to the internal series and overlapping each internal osteoderm is a second external series. The orientation of the zygapophyseal facets implies modest lateral flexion with limited coupled axial rotation of the column. However, the osteoderms restricted any possible lateral flexion through their inverted V-shape, strongly angled overlap between each external osteoderm and its neighbouring internal osteoderms, and the presence of a midsagittal flange on the ventral surface of each external osteoderm that fits into grooves on the anterior and posterior edges of the neighbouring internal osteoderms. This configuration allowed vertical flexion of the vertebral column with little lateral flexion. The rod-like nature of osteoderms with the anterior three-quarters of the presacral vertebrae suggests a restricted form of forward movement for Cacops unlike that of other early tetrapods. [ABSTRACT FROM AUTHOR]

Abstract: Titanosaur remains are common findings at the paleontological site of Peirópolis in Uberaba. Among those remains, two osteoderms referred to titanosaur sauropods were reported. Both dermal bones share many features, such as the coarse texture, parallel ventral grooves, lack of the cingulum and presence of a ventral ridge (crest). Armored titanosaurs had wide distribution in the Upper Cretaceous, and have been reported from Argentina, Brazil, France, Madagascar, Malawi, Romania and Spain. In the present work we describe and compare the Brazilian titanosaur osteoderms found thus far. [Copyright &y& Elsevier]

The concentrations of Na, K, Ca, Mg, Ba, Sr, Fe, Al, Mn, Zn, Pb, Cu, Ni, Cr, Co, Se, U and Ti were determined in the osteoderms and/or flesh of estuarine crocodiles (Crocodylus porosus) captured in three adjacent catchments within the Alligator Rivers Region (ARR) of northern Australia. Results from multivariate analysis of variance showed that when all metals were considered simultaneously, catchment effects were significant (P≤0.05). Despite considerable within-catchment variability, linear discriminant analysis (LDA) showed that differences in elemental signatures in the osteoderms and/or flesh of C. porosus amongst the catchments were sufficient to classify individuals accurately to their catchment of occurrence. Using cross-validation, the accuracy of classifying a crocodile to its catchment of occurrence was 76% for osteoderms and 60% for flesh. These data suggest that osteoderms provide better predictive accuracy than flesh for discriminating crocodiles amongst catchments. There was no advantage in combining the osteoderm and flesh results to increase the accuracy of classification (i.e. 67%). Based on the discriminant function coefficients for the osteoderm data, Ca, Co, Mg and U were the most important elements for discriminating amongst the three catchments. For flesh data, Ca, K, Mg, Na, Ni and Pb were the most important metals for discriminating amongst the catchments. Reasons for differences in the elemental signatures of crocodiles between catchments are generally not interpretable, due to limited data on surface water and sediment chemistry of the catchments or chemical composition of dietary items of C. porosus. From a wildlife management perspective, the provenance or source catchment(s) of ‘problem’ crocodiles captured at settlements or recreational areas along the ARR coastline may be established using catchment-specific elemental signatures. If the incidence of problem crocodiles can be reduced in settled or recreational areas by effective management at their source, then public safety concerns about these predators may be moderated, as well as the cost of their capture and removal. [Copyright &y& Elsevier]

Osteoderms (ossified dermal elements) are among the most distinctive features of Titanosauria, a speciose clade of Cretaceous sauropods. Though osteoderms are often described as armor, hollow osteoderms have also been interpreted as mineral storage sites. A new specimen (TMM 45888-1) from the Upper Cretaceous Javelina Formation, Big Bend National Park, Texas, provides insights into osteoderm structure and function. It is oval with a cusp at one end and grooved marginal ornamentation, resembling certain specimens from Argentina but without a keel. It is not divided into bulb and root regions. TMM 45888-1 is the first titanosaur osteoderm from Texas. It cannot be referred to a species but is similar to the osteoderms of Alamosaurus , the only known titanosaur from North America. X-ray CT scans reveal that the interior of TMM 45888-1 is not hollow. Large neurovascular channels connect foramina on the deep, superficial, and marginal faces. The channels are concentrated along the deep face, at the ends, and passing through the center from deep to superficial. The osteoderm was potentially capable of providing mineral storage, localized defense, and display functions based on its vasculature, material properties, and shape. Whole-body defense, vertebral stabilization, and thermoregulation are rejected as functions based on apparent osteoderm scarcity, lack of articulations, and limited superficial vasculature. Osteoderms vary in gross and interior morphology among lithostrotians, necessitating caution when generalizing functions across the clade. [ABSTRACT FROM AUTHOR]

Dermal ossifications (osteoderms, dermal ossicles, osteoscutes) appear independently in various tetrapod lineages. In mammals, however, dermal ossifications are only present in some members of Xenarthra. This clade includes Cingulata (armadillos and their relatives), and Pilosa, including Vermilingua (anteaters) and Folivora (sloths). In extant xenarthrans, osteoderms are invariably present in cingulates whereas they are absent in pilosans. Among extinct sloths, however, a limited number of taxa possessed dermal ossifications. Records of mummified skins of ground sloths bearing osteoderms found in Cueva del Milodón (Southern Chile), with a late Pleistocene age, allowed us to analyze their micro- and macroscopic morphology. The main goal of this study is to closely examine a portion of a mylodontid skin portion using radiography. The arrangement, morphology and internal structure of the ossicles are analyzed and the results are discussed in the context of previous research. The results we obtained indicate that ossicles vary in shape and size, and the integument has four different patterns of arrangement of the ossicles: that is, areas without ossicles, disorganized ossicles, rows, and mosaic areas. The latter has two variants, with clusters of ossicles forming rosettes or stars. Thin sections of the ossicles allowed us to recognize and describe anatomical features of the bone and its mode of growth. Finally, paleobiological and functional considerations of the dermal armor are discussed along with its phylogenetic and chronological implications., (© 2021 Wiley Periodicals LLC.)

Madagascar's endemic ground-dwelling leaf chameleons (Brookesiinae: Brookesia Gray, 1865 + Palleon Glaw, et al., Salamandra, 2013, 49, pp. 237-238) form the sister taxon to all other chameleons (i.e., the Chamaeleoninae). They possess a limited ability of color change, a rather dull coloration, and a nonprehensile tail assisting locomotion in the leaf litter on the forest floor. Most Brookesia species can readily be recognized by peculiar spiky dorsolateral projections ("Rückensäge"), which are caused by an aberrant vertebral structure and might function as body armor to prevent predation. In addition to a pronounced Rückensäge, the Antsingy leaf chameleon Brookesia perarmata (Angel, 1933) exhibits conspicuous, acuminate tubercle scales on the lateral flanks and extremities, thereby considerably enhancing the overall armored appearance. Such structures are exceptional within the Chamaeleonidae and despite an appreciable interest in the integument of chameleons in general, the morphology of these integumentary elements remains shrouded in mystery. Using various conventional and petrographic histological approaches combined with μCT-imaging, we reveal that the tubercle scales consist of osseous, multicusped cores that are embedded within the dermis. Based on this, they consequently can be interpreted as osteoderms, which to the best of our knowledge is the first record of such for the entire Chamaeleonidae and only the second one for the entire clade Iguania. The combination of certain aspects of tissue composition (especially the presence of large, interconnected, and marrow-filled cavities) together with the precise location within the dermis (being completely enveloped by the stratum superficiale), however, discriminate the osteoderms of B. perarmata from those known for all other lepidosaurs., (© 2020 The Authors. Journal of Morphology published by Wiley Periodicals, Inc.)

Associated osteoderms of unique aspect have been found in Ensenadan age deposits near San Pedro, in the Pampean Region of Argentina. Their general shape closely resembles that of mylodontid sloths. They are unique in presenting a homogeneous octahedral shape, contrasting with the heterogeneous shape of other ground sloth osteoderms. The lack of expanded spaces within the bone is shared with some other mylodontid sloths. Histologically, the bone is well vascularized, full of fiber bundles (including Sharpey's fibers), and very similar to the condition in Mylodon darwinii. The lack of individualized fibers near and perpendicular to the external surface suggests a relatively deeper position in the dermis than in the Pleistocene ' Paramylodon ' garbanii. The taxon to which these novel osteoderms belonged is uncertain, but the possible carriers are discussed. • Novel homogenous osteoderms coming from Ensenadan deposits. • Histology of octahedral osteoderm from Folivora. • Independent acquisition of osteoderms in Folivora. [ABSTRACT FROM AUTHOR]

A detailed histological study of Antarctopelta oliveroi , from the Upper Cretaceous of Antarctica, is performed in order to increase our knowledge of the ankylosaur bone histology and its taxonomical and paleobiological implications. The main goals of this contribution are: to infer the ontogenetic stage of the holotype of Antarctopelta oliveroi (MLP 86-X-28-1); to evaluate the degree of interelemental histological variation; to compare its histology with that of other ankylosaurs; to provide information about the phylogenetic affinities of Antarctopelta regarding dermal armor histology; and to evaluate the influence of a high latitude, strongly seasonal ecosystem on the growth of Antarctopelta. The sample includes several postcranial elements from the holotype (e.g. osteoderms, appendicular bones, dorsal ribs, ossified tendons). Bone histology reveals that the specimen was sexually mature at its time of death. Although a distinct Outer Circumferential Layer is not evident in all the sampled elements, the bone microstructure suggests quite slow appositional growth (i.e. most of the growth had already occurred) at the time of death. Primary cortical bone of the sampled elements, mostly composed of fibrolamellar bone tissue interrupted by growth marks, reveals a cyclical growth strategy as reported for other ankylosaurs and non-avian dinosaurs. The bone histology of Antarctopelta indicates that, as with other Southern Hemisphere polar dinosaurs, there are no apparent differences in growth strategy compared with its low latitude relatives. Therefore, no evident physiological modifications appears to be linked with the distribution of ankylosaurs and other non-avian dinosaurs at higher latitudes (>60° S). [ABSTRACT FROM AUTHOR]

Animal body armour is often considered an adaptation that protects prey against predatory attacks, yet comparative studies that link the diversification of these allegedly protective coverings to differential predation risk or pressure are scarce. Here, we examine the evolution of body armour, including spines and osteoderms, in Cordylinae, a radiation of southern African lizards. Using phylogenetic comparative methods, we attempt to identify the ecological and environmental correlates of body armour that may hint at the selective pressures responsible for defensive trait diversification. Our results show that species inhabiting arid environments are more likely to possess elaborated body armour, specifically osteoderms. We did not find any effect of estimated predation pressure or risk on the degree of body armour. These findings suggest that body armour might not necessarily evolve in response to direct interactions with predators, but rather as a result of increased habitat-mediated predation risk. Furthermore, we discuss the possibility that osteoderms might have been shaped by factors unrelated to predation., (© 2018 The Author(s).)

Dermal ossifications, including osteoderms, are present in many vertebrates and are frequently interpreted as a defense against predators. Nevertheless, osteoderms remain ubiquitous in adult crocodilians while being absent in hatchlings, even though adults rarely experience predation. In other biological systems, increased variation, particularly fluctuating asymmetry, have proven useful for identifying biological structures likely to have evolved under relaxed selection, which in turn may inform their function. Therefore, using the keratinous scutes as proxies for the underlying osteoderm morphology, I investigated the average intraspecific variability of geometry and fluctuating asymmetry in dorsal scutes in five species of crocodilians. I first tested for differences in variability of scute length and width, then for differences in bilateral fluctuating asymmetry of scute number, before finally investigating scute distribution patterns for each species compared to hypothetical rectangular and hexagonal scute arrangements. The American crocodile, Crocodylus acutus, shows significantly more asymmetry than other species, which is consistent with relaxed selection on osteoderms in this species. A suspected decrease in intraspecific aggression within Crocodylus acutus, in conjunction with the inferred relaxed selection, suggests that, in general, crocodilian osteoderms function primarily as defensive armor in aggressive encounters with conspecifics. The smooth-fronted caiman, Paleosuchus trigonatus, exhibits increased variation in scute dimensions linked to the mediolateral offset of osteoderms in adjacent rows, possibly resulting in a more rigid carapace. Unfortunately, comparative data on crocodilian behavior, physiology, and development is extremely limited and restricts the ability to explore other potential explanations for the patterns observed, highlighting the need for more research on rare and cryptic crocodylians., (© 2017 Wiley Periodicals, Inc.)

Heterotopic ossification (HO) occurs when soft tissues are inappropriately converted to bony tissue. Several human diseases result in HO with few reliable treatment options. Animal models that naturally produce dermal ectopic bone (i.e., osteoderms), such as crocodilians, have never been utilized as models for studying these disorders in humans. Here, a histological evaluation and staging criteria for osteoderm development is described for the first time in the American alligator (Alligator mississipiensis). Differential staining and immunohistochemistry of alligator scales depict a progressive change during development, where woven bone forms from the differentiated dermis. Bone formation proceeds via intramembranous ossification, which is initiated in part by endothelial cell precursors that undergo endothelial-to-mesenchymal transition and eventually acquire an osteoblast phenotype. As such, the development of osteoderms in the American alligator bears morphological and mechanistic similarities to HO in humans, presenting a potential model for future study of soft tissue mineralization pathologies and providing insight into the morphological and molecular development of osteoderms in other vertebrate lineages. Anat Rec, 2017. © 2017 Wiley Periodicals, Inc. Anat Rec, 301:56-76, 2018. © 2017 Wiley Periodicals, Inc., (© 2017 Wiley Periodicals, Inc.)

Although the evolution and function of "exaggerated" bony projections in ornithischian dinosaurs has been subject to significant debate recently, our understanding of the structure and morphology of their epidermal keratinized coverings is greatly limited. The holotype of Borealopelta , a new nodosaurid ankylosaur, preserves osteoderms and extensive epidermal structures (dark organic residues), in anatomic position across the entire precaudal length. Contrasting previous specimens, organic epiosteodermal scales, often in the form of horn-like (keratinous) sheaths, cap and exaggerate nearly all osteoderms, allowing for morphometric and allometric analyses of both the bony osteoderms and their horny sheaths. A total of 172 osteoderms were quantified, with osteoderm spine length and height being positively allometric with respect to basal length and width. Despite tight correlations between the different measures amongst all other osteoderms, the large parascapular spines represent consistent outliers. Thickness and relative contribution of the keratinized epiosteodermal scales/sheaths varies greatly by region, ranging from 2% to 6% for posterior thoracics, to ∼25% (1.3×) for the parascapular spines-similar to horn sheaths in some bovid analogues. Relative to the bony cores, the horny portions of the spines are strongly positively allometric (slope = 2.3, CI = 1.8-2.8). Strong allometric scaling, species-specific morphology, and significant keratinous extension of the cervicoscapular spines is consistent with elaboration under socio-sexual selection. This marks the first allometric analysis of ornithischian soft tissues., Competing Interests: The author declares no competing interests.