Search

Osteoderms are dermal ossifications present in several vertebrates and assemble a carapace on armadillos. Here we describe ichnotaxonomically two types of bioerosion traces as well as paleopathologically ulcerative lesions on osteoderms of three specimens of Late Pleistocene Holmesina cryptae armadillos (Xenarthra, Cingulata, Pampatheriidae) found in Lapinha Cave, Iramaia municipality, Bahia State, Brazil. The traces are always on the external surface of the osteoderms, none on endoskeleton elements, which are also different from bites and taphonomic process marks. This is evidence of the biological and syn vivo origin of the traces, making them remarkable and useful to access animal health. Karethraichnus minimum isp. nov. are individual holes interpreted as produced by sand flea sessile females, probably from the Tunga genus, based on already described lesions in living armadillos. This trace reveals a paleoparasitism behavior useful for tracking this relation deep in time in armoured animals. Violinichnus punctatus igen. et isp. nov. is formed by consecutive tiny holes, forming an overall elliptical/violin-like shape. This is attributed to lesions produced by the action of fungi over osteoderms, similar to mycose-like dermatophytosis (ringworm) in modern mammal skin. In contrast, the ulcerative lesions are recorded as necrosis of bone material, producing a corrosive-like disruption on the external surface of the osteoderms formed by irregular pits and exposition of spongy bone. These are ulcerative lesions probably produced by secondary infections by microorganisms such as fungi or bacteria, or even a destructive immunological response. This would begin as a more restricted lesion with several potential agents for this: abrasion from the soil, plants; lesions from intraspecific fights or predation; dermatitis; ectoparasites (e.g., mites, ticks, fleas, mosquitoes) or initial mycosis or bacterial infection. Since a bioerosive process cannot be demonstrated and is rather unlikely for the ulcerative lesions, these structures are not considered trace fossils. It is reasonable to assume that the flea lesion Karethraichnus minimum isp. nov. and fungal lesion Violinichnus punctatus igen. et isp. nov. could lead to an ulcerative lesion. As syn vivo traces, all these are tools to access the health of the animals to which the osteoderm belongs. Further support on ectoparasite and infection studies on living armoured animals would even allow inferences regarding extinct populations and interpretations of ancient ecosystems.

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.

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.

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.

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. Fil: Zurriaguz, Virginia Laura. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Río Negro. Sede Alto Valle. Instituto de Investigaciones en Paleobiología y Geología; Argentina Fil: Martinelli, Agustín Guillermo. Universidade Federal do Rio Grande do Sul; Brasil Fil: Rougier, Guillermo Walter. University of Louisville; Estados Unidos Fil: Ezcurra, Martin Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; Argentina

The pelvic armor elements in the ankylosaurian material from the Upper Cretaceous of Iharkut, Hungary are described here. Among these, a new articulated hip region of a small bodied ankylosaur is referred here to cf. Struthiosaurus sp. It preserves, uniquely among Late Cretaceous European ankylosaurs, an in situ pelvic armor composed of among others four, keeled, oval to circular osteoderms lying centrally and arranged longitudinally above the synsacral neural spines. This is the first indication of this type of pelvic osteoderm arrangement in an ankylosaur, increasing our knowledge on this poorly known part of the ankylosaur skeleton. Some additional pelvic osteoderms are also described that help to reconstruct and distinguish the pelvic armor of the two Late Cretaceous European ankylosaurs Struthiosaurus and Hungarosaurus. Both taxa have some fused parts in the pelvic armor but most probably neither of them had a single, fused pelvic shield as that of the Early Cretaceous Polacanthus. Interwoven texture on the ventral surface of the osteoderms, observed in both European taxa and known in other ankylosaurs (e.g. Polacanthus, Nodosaurus), is suggested here to be a characteristic feature of the non-keeled, fused pelvic armor elements of Ankylosauria.

Until now, only one Cenozoic fossil mammal from the Chilean Precordillera (Arica and Parinacota Region) has been reported, Caraguatypotherium munozi (Mesotheriidae: Notoungulata). In this study, we describe a fourth specimen of C. munozi and a new armadillo species, Epipeltephilus caraguensis (Peltephilidae: Cingulata), both collected from a new site closer to the fossiliferous outcrops of the Caragua area (Serravallian – Tortonian). E. caraguensis differs from other members of the family in having: two sulci in the articular surface of the mobile osteoderm; having a tubular, rough and raised anterior edge; a conspicuous transverse depression; and four widely spaced foramina. This taxon represents the youngest known peltephilid from intermediate latitudes and indicates a wide geographic distribution (Patagonia to Central Andes) of the family just prior to its extinction. The new mesothere specimen is 19% larger than previous records. The revision of the dental features of C. munozi allowed the identification of an ambiguous trait in its original diagnosis, i.e. an enamel fracture was misinterpreted with the presence of a posterior sulcus on the talonid of the m3, suggesting that further taxonomic and systematic revision for the Caragua mesothere is necessary. Although the fossil record from the Caragua area is still scarce, mesotheriines seem to be abundant at this latitude, just as has been observed at several early to late Miocene sites such as Chucal (Chile), Cerdas and Nazareno (Bolivia), as well as in southern regions such as Arroyo Chasico and Mendoza (Argentina). The presence of a new peltephilid species in Caragua sustains the hypothesis of provincialism during the Miocene in intermediate latitudes. Our findings also provide further support for probable faunal movements between intermediate and higher latitudes rather than to lower ones.

Osteoderms are bony deposits that form within the dermal layer of skin in vertebrates. Within geckos, osteoderms are uncommon, only described in Gekko gecko and the genus Tarentola. A previous report of osteoderms in the Afro-Malagasy gekkonid genus Geckolepis has been questioned due to the extreme skin fragility and regional integumentary loss within the group. We re-evaluated the integument anatomy of Geckolepis maculata using µCT scanning, histology, and clearing and staining to verify the presence or absence of osteoderms and, if present, to characterise and compare their morphology to the osteoderms of Gekko gecko and Tarentola, as well as osteoderm diversity within squamates. Osteoderms were confirmed present in Geckolepis maculata; however, these osteoderms are compound, imbricating, squamous elements that are morphologically similar to the dermal ossifications observed in scincids and gerrhosaurids, while G. gecko and Tarentola possess plate-like and granular osteoderms. Our results sugges...

Armored skin resulting from the presence of bony dermal structures, osteoderms, is an exceptional phenotype in gekkotans (geckos and flap-footed lizards) only known to occur in three genera: Geckolepis, Gekko, and Tarentola. The Tokay gecko (Gekko gecko LINNAEUS 1758) is among the best-studied geckos due to its large size and wide range of occurrence, and although cranial dermal bone development has previously been investigated, details of osteoderm development along a size gradient remain less well-known. Likewise, a comparative survey of additional species within the broader Gekko clade to determine the uniqueness of this trait has not yet been completed. Here, we studied a large sample of gekkotans (38 spp.), including 18 specimens of G. gecko, using X-rays and high-resolution computed tomography for visualizing and quantifying the dermal armor in situ. Results from this survey confirm the presence of osteoderms in a second species within this genus, Gekko reevesii GRAY 1831, which exhibits discordance in timing and pattern of osteoderm development when compared with its sister taxon, G. gecko. We discuss the developmental sequence of osteoderms in these two species and explore in detail the formation and functionality of these enigmatic dermal ossifications. Finally, we conducted a comparative analysis of endolymphatic sacs in a wide array of gekkotans to explore previous ideas regarding the role of osteoderms as calcium reservoirs. We found that G. gecko and other gecko species with osteoderms have highly enlarged endolymphatic sacs relative to their body size, when compared to species without osteoderms, which implies that these membranous structures might fulfill a major role of calcium storage even in species with osteoderms.

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.

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.

The osteoderms of Glyptodon reticulatus that do not belong to the cephalic shield, dorsal cuirass, or caudal tube are very variable morphologically. Their histological structure is also variable. Some lack a cancellous bone core, unlike those from the dorsal cuirass. One presents a few large cavities, whereas another is finely cancellous. Some present moderate remodeling and thick collagen fiber bundles. The moderate to high remodeling and the presence of fiber bundles perpendicular to the inner surface in some resemble many dorsal cuirass osteoderms of Glyptodon, but differ from previously described cuirass osteoderms of Glyptotherium. At least the perpendicular bundles may be useful to distinguish those glyptodontine genera. However, these characters do not allow distinction from Panochthus and Doedicurus. Histological distinction from sloth osteoderms is not possible because of the variability in the latter in remodeling degree, presence of large resorption spaces, and of an external fundamental system with fine fiber bundles perpendicular to the bone surface. An osteoderm presents evidence of circumferential lamellar accretion, as in dorsal cuirass osteoderms of Glyptodon. The lack of evidence of woven bone and of circumferential lamellar accretion, non-osteonal lamellar or parallel-fibered bone in another osteoderm suggests primary ossification was mostly metaplastic. This difference from the condition in Dasypus may depend of the time of appearance or body region.

Acaenasuchus geoffreyi is a diminutive armored archosaur from the Upper Triassic Chinle Formation of northern Arizona, U.S.A., with uncertain evolutionary relationships and skeletal maturity. Known only from osteoderms, the taxon has been considered a valid taxon of aetosaur, juvenile specimens synonymous with the aetosaur Desmatosuchus spurensis, or a non-aetosaurian pseudosuchian archosaur. Here, we describe new fossils of Acaenasuchus geoffreyi that represent cranial, vertebral, and appendicular elements as well as previously unknown variations in the dorsal carapace and ventral shield. The skull bones are ornamented with the same anastomosing complex of ridges and grooves found on the paramedian and lateral osteoderms, and the appendicular skeleton resembles that of Revueltosaurus callenderi, Euscolosuchus olseni, aetosaurs, and other armored archosaurs such as erpetosuchids. Histology of osteoderms from the hypodigm of Acaenasuchus geoffreyi shows multiple growth lines, laminar tissue, and low vascularity, evidence that the individuals were close to skeletal maturity and not young juveniles. A revised phylogenetic analysis of early archosaurs recovers Acaenasuchus geoffreyi and Euscolosuchus olsenias sister taxa and members of a new clade that is the sister taxon of Aetosauria. This new phylogeny depicts a broader distribution of osteoderm character states previously thought to only occur in aetosaurs, demonstrating the danger of using only armor character states in aetosaur taxonomy and phylogeny. Acaenasuchus geoffreyi is also a good example of how new fossils can stabilize 'wild card' taxa in phylogenetic analyses and contributes to our understanding of the evolution of the aetosaur carapace. Petrified Forest Museum Association; Friends of Petrified Forest National Park We thank D. and J. Gillette (MNA), P. Holroyd (UCMP), and C. Levitt-Bussian (UMNH) for providing collections and archive access, and for facilitating loans from their institutions. M. Polcyn (SMU) graciously sent us locality information and photographs of SMU 75403. H.-D. Sues provided photographs of and helpful comments on Euscolosuchus olseni, and J. Strotman facilitated the molding, casting, and transfer of casts of USNM 448587 and USNM 448582. P. Holroyd (UCMP) graciously provided permission to histologically section two osteoderms, and A. Lee (Midwestern University) kindly assisted with sectioning. K. Ritterbush (University of Utah) generously provided access to her petrographic microscope imaging system, and the histological slides were imaged by N. Ong. R. Long's field notes are on file in the archives at PEFO and the UCMP and those of Charles Camp are available at the UCMP. Thanks to T. Olson for finding MDM specimens at PFV 211. We thank J. Kirkland and D. DeBlieux (Utah Geological Survey) for permission to include in this study material they collected. The collection and preparation of the specimens from PEFO was funded by the Petrified Forest Museum Association and Friends of Petrified Forest National Park. Silhouettes from phylopic.org in Figure 9 were created by S. Hartman, D. Bogdanov, and Smokeybjb and reused under the Creative Commons Attribution 3.0 Unported license (creativecommons.org/licenses/by/3.0). Thanks to V. Paes Neto and D. Gillette for constructive comments and discussion on aetosaur and glyptodont anatomy, and to A. Turner for help in constraining tree topology in TNT. Comments and suggestions made by M. B. von Baczko and I. Cerda improved the manuscript. This is Petrified Forest National Park Contribution No. 61. The conclusions presented here are those of the authors and do not represent the views of the United States Government.

Abstract: Riostegotherium yanei from the Itaborai Basin, Brazil, is the oldest known Xenarthra. This paper aims to describe the internal morphology of the osteoderms of Riostegotherium yanei from the perspective of histology and micro-CT approaches, expanding the available data on cingulate osteoderm microstructure. Seven osteoderms of R. yanei were used for the internal microstructure description and eight of Dasypus novemcinctus for comparison. The osteoderms of Riostegotherium yanei lacks the diploe-like structure typical of glyptodonts but has a three-layered structure composed of two layers of non-Haversian compact bone enclosing a central layer of primary and secondary osteons. This internal organization is distinct from other Astegotheriini of comparable age, but similar to Dasypus. The 3D reconstruction of Riostegotherium yanei revealed two patterns of internal organization. Pattern 1 of movable osteoderm is composed of large remodeled areas at the base and a more compact bone at the tongue; in Pattern 2 (both movable and buckler), the internal cavities are much smaller, more numerous, and more interconnected to each other. In one buckler osteoderm, the cavities are organized somewhat radially with a compact central region (Pattern 1). Pattern 1 of both movable and buckler osteoderms resemble that of Dasypus.

Osteoderms constitute a morphological system that plays an important role in squamate systematics. However, their study and visualization have always been difficult due to their isolated occurrence in the skin, among the first organs to be removed during the skeletonization process. High-resolution X-ray computed tomography (HRXCT) offers a nondestructive means of visualizing osteoderms both in their natural relationship to each other and to the underlying cranial bones. Although it is often stated that Varanus komodoensis has a "chain mail" of osteoderms, this morphological system was never described in this taxon. Further, given its size, it might be expected that V. komodoensis would present the extreme of osteoderm development in extant varanids, a group that tends to have weakly developed osteoderms or none at all. Indeed, our HRXCT scan of a 19-year-old captive individual reveals an elaborate mesh of cephalic osteoderms that are incredibly numerous and morphologically diverse. We describe this skeletal system and compare it to the cephalic osteoderms in other varanoids. Anat Rec, 302:1675-1680, 2019. © 2019 American Association for Anatomy.

Light and electron microscopy shows the osteoderms of Anguis fragilis to be small, flat disks located in the dermis along the adult trunk: microradiography established the extent of the mineralization. Each osteoderm coincides exactly with an epidermal fold forming the keratinized scales characteristic of the skin of reptiles. Sections perpendicular to the surface show two mineralized layers differing in histological and histochemical characteristics and in fine structure, although both contain collagen fibrils. The structure of each layer can be related to that of the surrounding dermis. The outer superficial layer located in the loose dermis contains few collagen bundles that form a discontinuous sheet at the upper surface of the osteoderms. This superficial layer appears to be constituted of units separated by furrows and is composed of woven fibered bone. The basal plate comprises stratified lamellae formed of parallel-oriented collagen fibrils; the fibrils of successive lamellae lie at right angles. The densely packed collagen fibrils of the basal plate are distributed similarly to those of the dense dermis within which it lies. This layer exhibits structural and histochemical characteristics of a lamellar bone. The presence of two different layers in the osteoderms of Anguis fragilis may reflect their mode of formation, which consists of the deposit of mineral crystals in the preexisting dermal tissue. This mineralization process, considered as a “metaplastic ossification,” may reflect the potentiality retained by the dermis of reptiles to form mineralized structures.

Aetosaurs comprise a clade of quadrupedal, armored, omnivores to herbivores that lived across much of the supercontinent of Pangea during the Late Triassic. Their relative abundance in many units, and the rarity of other Triassic herbivores, points to them as key components of Late Triassic ecosystems. Debate persists about whether they were growing more or less slowly when compared to extant crocodylians, and bone histology is sparsely sampled within the group. We undertook a histological examination of Coahomasuchus chathamensis to address its ontogenetic trajectory and characterize its histology. We sampled a paramedian osteoderm from the holotype specimen, as well as five osteoderms (two paramedian, one lateral, and two of uncertain position) and two incomplete limb bones (radius and fibula), from referred specimens discovered at the type locality. Using these we estimated specimen ages with lines of arrested growth (LAGs) to determine that the study individuals reached from 2 to 7 years old. All of the sampled elements contained woven-fibered bone with extensive vasculature within the internal cortex. In some specimens, more poorly vascularized, parallel-fibered bone is evident externally. The holotype of C. chathamensis represents a juvenile individual, and raises the possibility that the holotype of C. kahleorum is a juvenile as well, complicating aetosaur systematics and diversity. When compared to aetosaurs of similar size, it is clear that C. chathamensis was growing comparatively rapidly, about 3 times the rate of similarly sized specimens of Aetosauroides scagliai from Argentina. This discovery reveals the presence of disparate growth strategies within Aetosauria. Anat Rec, 302:1504-1515, 2019. © 2018 American Association for Anatomy.

In 1940, L.I. Price and A. Oliveira recovered four crocodyliform specimens from the Early Cretaceous Bahia Supergroup (Recôncavo-Tucano Basin). In the present work, we describe four different fossil specimens: an osteoderm, a fibula, a tibia, and some autopodial bones. No further identification besides Mesoeucrocodylia was made due to their fragmentary nature and the reduced number of recognized synapomorphies for more inclusive clades. With exception of the fibula, all other specimens have at least one particular feature, which with new specimens could represent new species. The new specimens described here increase the known diversity of Early Cretaceous crocodyliforms from Brazil. This work highlights the great fossiliferous potential of Recôncavo-Tucano Basin with regard to crocodyliform remains.

One of the most striking features of aetosaurs is the possession of an extensive bony armour composed of dorsal, ventral and appendicular osteoderms. With the purpose of establishing the main histological changes during ontogeny and the degree of histological variation within the armour, we analysed the bone histology of dorsal (paramedian and lateral), ventral and appendicular osteoderms from different taxa from the Late Triassic of South America, including Aetosauroides scagliai, Aetobarbakinoides brasiliensis and Neoaetosauroides engaeus. Histological data support an intramembranous origin for osteoderms. Nevertheless, evidence for metaplastic ossification (i.e. structural fibres) at advanced ontogenetic stages, in at least some elements, is also present. A variant type of parallel fibred bone, which we have named ‘crossed parallel fibred bone’, is characterized for aetosaurs. In this pseudosuchian group, osteoderms exhibit very important microstructural changes during ontogeny, which can be useful for determining ontogenetic stages from isolated elements. Histological data suggest a relatively early onset of sexual maturity among aetosaurs. Microanatomical analysis from different taxa reveal that having high values of compactness is the plesiomorphic condition for Aetosauria. The notably increased compactness of the osteoderms does not appear to be related to size, ontogeny, sex or reproductive status of the individuals. Although a high degree of compactness of osteoderms and other bones has been considered as evidence for an aquatic lifestyle in vertebrates, such an inference contradicts the current concept of a fully terrestrial lifestyle in aetosaurs. Fil: Cerda, Ignacio Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación en Paleobiología y Geología; Argentina Fil: Desojo, Julia Brenda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Departamento Científico de Paleontología de Vertebrados; Argentina Fil: Scheyer, Torsten. Universitat Zurich. Instituto Palaontologisches Institut And Museum; Suiza

It has been hypothesized that the pronounced differences of stegosaur humeral shapes, with large forms having more slender and small forms having more robust humeri, may be explained by a difference in relative centre of mass (COM) placement caused by differing distributions of osteoderms. To test this hypothesis, digital 3-D models of the bones and osteoderms of the Tanzanian stegosaur Kentrosaurus aethiopicus and of the North American stegosaur Stegosaurus armatus were used to create a 3-D computer-aided design life reconstruction. On these models osteoderm placement was varied drastically, recreating both existing and hypothetical forms. These models show that COM position varies somewhat with realistic osteoderm distributions, but insufficiently to explain major differences in humeral shape. The uniform weight distribution between forelimbs and hindlimbs found between the two taxa also casts doubt on the hypothesis that differences in relative COM position caused by other factors than osteoderm distribution can explain differences in humeral robustness.

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.

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.

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.

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., Facultad de Ciencias Naturales y Museo

Although diploglossine osteoderms were mentioned in several systematic and paleontological studies, their morphological variability in single specimens or within species remains paradoxically undescribed. This is mainly the effect of the lack of attention paid hitherto to the morphological and histological characteristics of the tail osteoderms. This study demonstrated that a previously undescribed morphological variability exists in these osteoderms, especially in those resulting from tail regeneration. Indeed, regenerated osteoderms display a plesiomorphic anguid morphology that was previously considered to be absent in Diploglossinae. We also provide the first histological description of diploglossine osteoderms and new information about the obvious differences in growth dynamic between regenerated and nonregenerated osteoderms. These new data raise questions about the usefulness of diploglossine osteoderms in systematic, paleontological, and skeletochronological studies. Our study shows that the exact position on the trunk or on a regenerated or nonregenerated tail of each studied osteoderm must be known in order to avoid mistakes related to their important interspecies and intraspecies variability. J. Morphol. 276:1333–1344, 2015. © 2015 Wiley Periodicals, Inc.

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.

Osteoderms are bone-rich organs found in the dermis of many scleroglossan lizards sensu lato, but are only known for two genera of gekkotans (geckos): Tarentola and Gekko. Here, we investigate their sequence of appearance, mode of development, structural diversity and ability to regenerate following tail loss. Osteoderms were present in all species of Tarentola sampled (Tarentola annularis, T. mauritanica, T. americana, T. crombei, T. chazaliae) as well as Gekko gecko, but not G. smithii. Gekkotan osteoderms first appear within the integument dorsal to the frontal bone or within the supraocular scales. They then manifest as mineralized structures in other positions across the head. In Tarentola and G. gecko, discontinuous clusters subsequently form dorsal to the pelvis/base of the tail, and then dorsal to the pectoral apparatus. Gekkotan osteoderm formation begins once the dermis is fully formed. Early bone deposition appears to involve populations of fibroblast-like cells, which are gradually replaced by more rounded osteoblasts. In T. annularis and T. mauritanica, an additional skeletal tissue is deposited across the superficial surface of the osteoderm. This tissue is vitreous, avascular, cell-poor, lacks intrinsic collagen, and is herein identified as osteodermine. We also report that following tail loss, both T. annularis and T. mauritanica are capable of regenerating osteoderms, including osteodermine, in the regenerated part of the tail. We propose that osteoderms serve roles in defense against combative prey and intraspecific aggression, along with anti-predation functions.

1. 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. 2. 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. 3. 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. 4. 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. 5. 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.

A large osteoderm found in a channel sandstone in the Williams Fork Formation (“Mesaverde Group”) of northwestern Colorado represents the first reported evidence of a large neosuchian crocodyliform in the formation in northwestern Colorado. The osteoderm is of a size and pit pattern that resembles the large alligatoroid Deinosuchus but the thickness and shape of the bone suggest possible affinities with the goniopholidid or pholidosaurid crocodyliform material known from the Campanian of southern Utah; smaller, similar osteoderms from the formation may suggest that this form was relatively abundant as juveniles. Overall faunal similarities of the Williams Fork Formation are closest to the Kaiparowits Formation of southern Utah also, but few lower level taxa can be confirmed from the Williams Fork that are not also known from other areas north and south, suggesting that the Williams Fork vertebrate fauna comes from the southern end of a transition zone between possible latitudinal provinces of Laramidia.

Because pangolins are unique mammals with a body and limbs almost entirely sheathed in hard keratinous overlapping scales and with digging and climbing abilities, the shoulder girdle muscles may differ significantly from those of other mammals including the partially osteoderm-clad armadillos. Therefore, we conducted a functional anatomical study of the shoulder girdle muscles in Chinese pangolins (Manis pentadactyla pentadactyla, Pholidota) and some armadillo species (Dasypodidae). Our CT scans revealed that the pangolin's overlapping scales are hard structures completely encasing the limbs. The armadillo's limbs, however, are covered with small relatively soft non-overlapping scales embedded in the skin, and articulate completely free of the hard osteodermal carapace. The attachments of some shoulder girdle muscles in the pangolin have moved from the surrounding edges of the scapula to the spine, and they, therefore, fully cover the scapula. In addition, some pangolin shoulder girdle muscles cross the shoulder joint to insert on the distal humerus, but this does not occur in armadillos. We cannot rule out the possibility that these muscle modifications represent adaptations for digging and/or climbing in pangolins. Our results and previous literature do not establish specific links between them and locomotive modes. However, we propose that the Chinese pangolin may use its derived muscular features when walking to move its armor-restricted forelimbs more effectively by swinging its head from side to side.

Los aetosaurios son un grupo de arcosaurios pseudosuquios cuadrúpedos y acorazados del Triásico superior. Se Caracterizan por tener una coraza dorsal, una ventral, y osteodermos apendiculares, todos ornamentados. Los aetosaurios fueron propuestos como fósiles guía con base en características distintivas en algunos osteodermos. Por lo tanto, es importante comprender las variaciones intraespecíficas de estos elementos dentro del clado. En la presente contribución, se describen tres tipos de ornamentación en el área medial de los osteodermos paramediales de la coraza dorsal de Aetosauroides scagliai Casamiquela 1960: un “patrón radial”; un “patrón anastomosado”; y uno “intermedio” o “patrón transicional” entre el radial y el anastomosado. Las corazas articuladas de los especímenes PVL 2059 y PVL 2073 muestran los tres tipos de ornamentación, pero con una variación en la posición dentro de la coraza de los osteodermos con estas ornamentaciones. Recientes estudios paleohistológicos en osteodermos de A. scagliai muestran la ausencia de remodelación en los tejidos de los mismos permitiendo la estimación de edad mediante el conteo de LACs (líneas anuales de crecimiento). El PVL 2073 es ligeramente más corto (∼10% en los centros) pero también más joven ontogenéticamente (5 LACs) que el PVL 2059 (10 LACs; y osteodermos ligeramente más anchos). Combinando esta información y comparándola con los cocodrilos actuales (donde los machos son generalmente más grandes que las hembras para una misma edad), concluimos que la variación intraespecífica observada en A. scagliai es compatible con la hipótesis de un dimorfismo sexual. Estos resultados evidencian la necesidad de estudiar las variaciones intraespecíficas en aetosaurios. Aetosaurs are a group of quadrupedal, armoured pseudosuchian archosaurs from the Upper Triassic. They are characterized by dorsal and ventral carapaces, and appendicular osteoderms, all of them ornamented. Aetosaurs have been proposed as index fossils largely based on the distinctiveness of some osteoderms. Therefore, it is important to understand the intraspecific variation of these elements in the clade. In the present contribution, we describe three types of ornamentation on the medial area of paramedian osteoderms in the dorsal armour of Aetosauroides scagliai Casamiquela: the “radial pattern” the “anastomosing pattern”; and an “intermediate” or “transitional pattern”, that is an intermediate between “radial” and “anastomosing” patterns. The articulated dorsal armour preserved in specimens PVL 2059 and PVL 2073 possesses osteoderms carrying all three patterns of ornamentation, but they differ by the position of each type of osteoderm on the carapace. Recent studies on histological thin-sections of osteoderms of A. scagliai reveal the absence of osteoderm tissue remodeling, allowing the estimation of age by counting LAGs (lines of arrested growth). PVL 2073 is slightly shorter (∼10% longer centra) but also ontogenetically younger (5 LAGs) than PVL 2059 (10 LAGs; slightly wider osteoderms). Combining this information and comparing it with that of living crocodiles (where male specimens typically are relatively larger than females of the same age), we conclude that the intraspecific variation observed in A. scagliai is compatible with the hypothesis of sexual dimorphism. These results suggest the need to explore the sources of intraspecific variation in aetosaurs. Fil: Taborda, Jeremías Ramón Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentina Fil: Heckert, Andrew Bittinger. Appalachian State University; Estados Unidos Fil: Desojo, Julia Brenda. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentina

Postcranial osteoderms are commonly developed in the major lineages of Archosauriformes, including forms such as proterochampsids and doswel- liids. Here, we survey the histology of osteoderms of the doswelliids Archeopelta arborensis and Tarjadia ruthae, and the proterochampsids Chanaresuchus bonapartei and Pseudochampsa ischigualastensis to understand better the morphogenesis of these skeletal elements. Whereas, the Doswelliid osteoderms possess a trilaminar organiza- tion, in which two cortices (external and basal) can be dif- ferentiated from an internal core of cancellous bone, these elements are compact structures in proterochampsids. The osteoderms of P. ischigualastensis are avascular and they consist entirely of parallel-fibered bone. Conversely, the osteoderms of C. bonapartei are well vascularized structures composed of zones of woven-fibered bone and annuli of parallel-fibered bone. The rather simple micro- structure observed in P. ischigualastensis osteoderms sug- gests that these elements grew at a constant, low rate. Compared with proterochampsids, doswelliid osteoderms possess a more complex histology, which appears to be linked to variations in the growth rate during the osteo- derm formation and also to the development of the exter- nal ornamentation. A comparison of our findings with the results of earlier studies on other archosauriforms (phyto- saurs and pseudosuchians) reveals that the general osteo- derm histology of doswelliids bears a closer resemblance to that of phytosaurs and pseudosuchians than the proter- ochampsid osteoderm microstructure. If all archosauri- form osteoderms are homologous structures, the closer resemblance of doswellid osteoderm microstructures to that of phytosaurs and pseudosuchians is in agreement with the hypothesis that doswellids are more closely related to archosaurs than proterochampsids. J. Morphol.

Fil: Ponce, Denis A. Universidad Nacional de Río Negro; Argentina Fil: Ponce, Denis A. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Cerda, Ignacio A. Universidad Nacional de Río Negro; Argentina Fil: Desojo, Julia B. División Paleontología Vertebrados, Museo de La Plata, Universidad Nacional de La Plata; Argentina Fil: Cerda, Ignacio A. Instituto de Investigación en Paleobiología y Geología; Argentina Fil: Nesbitt, Sterling J. Department of Geosciences, Virginia Tech; Estados Unidos Osteoderms are common in most archosauriform lineages, including basal forms, such as doswelliids and proterochampsids. In this survey, osteoderms of the doswelliids Doswellia kaltenbachi and Vancleavea campi, and proterochampsid Chanaresuchus bonapartei are examined to infer their palaeobiology, such as histogenesis, age estimation at death, development of external sculpturing, and palaeoecology. Doswelliid osteoderms have a trilaminar structure: two cortices of compact bone (external and basal) that enclose an internal core of cancellous bone. In contrast, Chanaresuchus bonapartei osteoderms are composed of entirely compact bone. The external ornamentation of Doswellia kaltenbachi is primarily formed and maintained by preferential bone growth. Conversely, a complex pattern of resorption and redeposition process is inferred in Archeopelta arborensis and Tarjadia ruthae. Vancleavea campi exhibits the highest degree of variation among doswelliids in its histogenesis (metaplasia), density and arrangement of vascularization and lack of sculpturing. The relatively high degree of compactness in the osteoderms of all the examined taxa is congruent with an aquatic or semi-aquatic lifestyle. In general, the osteoderm histology of doswelliids more closely resembles that of phytosaurs and pseudosuchians than that of proterochampsids.

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 ofBorealopelta, 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.