1,721,139 research outputs found
Limb histology of the Triassic stem turtles Proterochersis porebensis Szczygielski & Sulej, 2016 and Proganochelys quenstedtii Baur, 1887 with insights into growth patterns of early turtles
Full text linkData on turtle limb bone histology and microstructure are spotty, especially for Mesozoic taxa, despite significant progress made in recent years. Here we provide first detailed information on the stylopodia of the Late Triassic stem turtles Proganochelys quenstedtii Baur, 1887 from Switzerland and Proterochersis porebensis Szczygielski & Sulej, 2016 from Poland. In both taxa we observed large, internal medullary regions filled with endosteal trabeculae and poorly to moderately vascularized parallel-fibered (grading locally to lamellar) periosteal cortices. Primary vasculature is predominantly longitudinal, in Proterochersis porebensis locally with radial inclination. In large specimens, secondary remodeling is significant in the deeper cortex, but it neither completely obliterates the primary tissue nor reaches the external surface of the bone in either taxon. Comparison of histological data, limb morphology, shell and limb lengths as well as proportions reveal differences in growth patterns between the taxa: Proganochelys quenstedtii seems to grow faster during early life stages than Proterochersis porebensis and attained distinctly larger body sizes earlier in ontogeny, even though the asymptotic body size is roughly the same for both species. Overall, the histological and microstructural characteristics of stylopodial bones of Triassic turtles more closely resemble those of more recent representatives of that group than earlier stem turtles
Editorial: Fossil Record says goodbye to Copernicus – collaboration with Copernicus, a decisive phase in the history of Fossil Record
No full textExtended Data Fig. 2 in Bizarre dermal armour suggests the first African ankylosaur
No full textExtended Data Fig. 2 | XCT-scan image of a longitudinal cross-section through NHMUK PV R37412. White ovals highlight areas where it is possible to see the continuity of cortical and trabecular bone from the spikes to the rod.Published as part of Maidment, Susannah C. R., Strachan, Sarah J., Ouarhache, Driss, Scheyer, Torsten M., Brown, Emily E., Fernandez, Vincent, Johanson, Zerina, Raven, Thomas J. & Barrett, Paul M., 2021, Nature Ecology & Evolution 5 (12) on pages 1576-1581, DOI: 10.1038/s41559-021-01553-6, http://zenodo.org/record/584212
Cranial anatomy of Besanosaurus leptorhynchus Dal Sasso & Pinna, 1996 (Reptilia: Ichthyosauria) from the Middle Triassic Besano formation of Monte San Giorgio, Italy/Switzerland: taxonomic and palaeobiological implications
Full text linkBesanosaurus leptorhynchus Dal Sasso & Pinna, 1996 was described on the basis of a single fossil excavated near Besano (Italy) nearly three decades ago. Here, we re-examine its cranial osteology and assign five additional specimens to B. leptorhynchus, four of which were so far undescribed. All of the referred specimens were collected from the Middle Triassic outcrops of the Monte San Giorgio area (Italy/Switzerland) and are housed in various museum collections in Europe. The revised diagnosis of the taxon includes the following combination of cranial characters: extreme longirostry; an elongate frontal not participating in the supratemporal fenestra; a prominent ‘triangular process’ of the quadrate; a caudoventral exposure of the postorbital on the skull roof; a prominent coronoid (preglenoid) process of the surangular; tiny conical teeth with coarsely-striated crown surfaces and deeply-grooved roots; mesial maxillary teeth set in sockets; distal maxillary teeth set in a short groove. All these characters are shared with the holotype of Mikadocephalus gracilirostris Maisch & Matzke, 1997, which we consider as a junior synonym of B. leptorhynchus. An updated phylogenetic analysis, which includes revised scores for B. leptorhynchus and several other shastasaurids, recovers B. leptorhynchus as a basal merriamosaurian, but it is unclear if Shastasauridae form a clade, or represent a paraphyletic group. The inferred body length of the examined specimens ranges from 1 m to about 8 m. The extreme longirostry suggests that B. leptorhynchus primarily fed on small and elusive prey, feeding lower in the food web than an apex predator: a novel ecological specialisation never reported before the Anisian in a large diapsid. This specialization might have triggered an increase of body size and helped to maintain low competition among the diverse ichthyosaur fauna of the Besano Formation
Osteoderm microstructure of “rauisuchian” archosaurs from South America
Full text linkIn this contribution we analyze and discuss the microanatomy and histology of postcranial osteoderms of a number of "rauisuchians" from different localities of South America (Argentina and Brazil). The studied sample includes osteoderms of Fasolasuchus tenax, Prestosuchus chiniquensis, Saurosuchus galilei and an undetermined rauisuchian from Brazil. The bone microanatomy of the osteoderms is variable: whereas some specimens have a rather compact structure, others show a diploe architecture with a central cancellous core bordered by two compact cortices. Both external and basal cortices are mainly composed of poorly vascularized, fine and coarse parallel-fibred bone and networks of interwoven and mineralized fiber bundles. The internal region of the non-remodeled specimens consists of a well- vascularized core in which the intrinsic fibers exhibit important variations (even in the same specimen), ranging from coarse, parallel-fibred to woven-fibred bone tissues. Lines of arrested growth (LAGs) are well recorded in both basal and external cortices. Differences in the bone microstructure (compact vs. diploe) could be related to the age, sex and reproductive status of the sampled individuals. Hence, age estimation based on the count of LAGs in rauisuchian osteoderms appears to be reliable only in the early stages of ontogeny. The bone microstructure suggests that rauisuchian osteoderms were originated through a mechanism that involves both intramembranous and metaplastic ossifications.Fil: Cerda, Ignacio Alejandro. Universidad Nacional de Rio Negro. Sede Alto Valle. Instituto de Investigaciones en Paleobiologia y Geologia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Desojo, Julia Brenda. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; ArgentinaFil: Scheyer,Torsten M. . Universität Zürich. Paläontologisches Institut und Museum; SuizaFil: Schultze, Cesar Leandro . Universidade Federal do Rio Grande do Sul; Brasi
Extended Data Fig. 4 in Bizarre dermal armour suggests the first African ankylosaur
No full textExtended Data Fig. 4 | Histological thin-section (plane polarized light) showing detail of the spine. A vascular channel can be observed in the top left of the image. The woven bone matrix of the cortex is dominated by primary osteons. Scattered secondary osteons can be observed in the mid and inner cortex. Large resorption cavities lined with lamellar bone can be observed in the trabecular bone of the core (top right). Red arrows indicate growth (=resting) lines.Published as part of Maidment, Susannah C. R., Strachan, Sarah J., Ouarhache, Driss, Scheyer, Torsten M., Brown, Emily E., Fernandez, Vincent, Johanson, Zerina, Raven, Thomas J. & Barrett, Paul M., 2021, Nature Ecology & Evolution 5 (12) on pages 1576-1581, DOI: 10.1038/s41559-021-01553-6, http://zenodo.org/record/584212
Bone shell microstructure of Condorchelys antiqua Sterli, 2008, a stem turtle from the Jurassic of Patagonia
No full textThe histology of the turtle shell has proven to be a valuable source of characters for the study of development and shell origin, as well as early turtles’ lifestyles and systematics. Here we describe and discuss the shell bone microanatomy and histology of Condorchelys antiqua, a stem turtle from the Lower Jurassic of Patagonia. Examination of several elements (including costals, neurals, peripherals and plastral plates) reveals that the shell bones consist of a diploe structure in which the interior area of cancellous bone is framed by external and internal cortices. Whereas the external cortex is mostly composed of structural fiber bundles, histological composition of the internal cortex is more variable, exhibiting structural fiber bundles and/or parallel fibered bone. This histological variation in the internal cortex allows discerning between different types of plates. The cancellous bone is mostly well developed and consists of fine trabeculae composed of secondary lamellar bone tissue. Predominance of structural fiber bundles in the shell bones suggests that metaplasia plays an important role during the development of the shell in this taxon. Comparison with other stem Testudines (including Proganochelys quenstedti, Proterochersis robusta, Kayentachelys sp., Eileanchelys waldmani, and Heckerochelys romani) reveals that the shell histology of C. antiqua resembles more H. romani and E. waldmani than the other stem taxa. The obtained values of compactness of C. antiqua shell bones suggest an aquatic lifestyle for this taxon.Il n’est plus à prouver que l’histologie de la carapace de tortue dans les taxons fossiles est un outil précieux pour résoudre de nombreuses questions concernant l’origine et le développement de la carapace, le mode de vie et la systématique. Nous décrivons et discutons ci-dessous la micro-anatomie et l’histologie de la carapace de Condorchelys antiqua, une souche tortue du Jurassique inférieur de Patagonie. L’observation de plusieurs éléments (notamment les plaques osseuses costales, neurales, périphériques et du plastron) révèle que la carapace consiste en une structure diploë dans laquelle la partie interne de l’os spongieux est entourée par des cortex interne et externe. Bien que le cortex externe soit principalement composé des fibres structurales, la composition histologique du cortex interne est plus variable, montrant des fibres structurelles et/ou pseudo-lamellaires. Cette variation histologique du cortex interne permet de discerner différents types de plaque osseuse. L’os spongieux est principalement bien développé et consiste en fines trabécules composées de tissu osseux lamellaire secondaire. La prédominance des fibres structurelles dans la carapace suggère que la métaplasie de l’os joue un rôle important pendant le développement de la carapace pour ce taxon. Les comparaisons avec d’autres testudinés du groupe souche (incluant Proganochelys quenstedti, Proterochersis robusta, Kayentachelys sp., Eileanchelys waldmani, et Heckerochelys romani) révèlent que l’histologie de la carapace de C. antiqua ressemble plus à celles de H. romani et E. waldmani qu’à celle d’autres taxons souches. Les valeurs de densité de la carapace de C. antiqua suggèrent un mode de vie aquatique.Fil: Cerda, Ignacio Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Universidad Nacional de Río Negro. Sede Alto Valle. Instituto de Investigaciones en Paleobiología y Geología; ArgentinaFil: Sterli, Juliana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Museo Paleontológico Egidio Feruglio; ArgentinaFil: Scheyer, Torsten M.. Universitat Zurich; Suiz
Anatomy, ontogeny, and ecology of Mesosauridae, the first secondarily aquatic amniotes
Full text linkMesosaurier, kleine Reptilien aus dem Unteren Perm, gelten als die frühesten aquatischen Reptilien. Trotz ihrer kurzen Existenz und begrenzten Verbreitung bieten sie wichtige Einblicke in die frühe Amnioten-Evolution. Diese Arbeit fasst vier Artikel zusammen, die Aspekte der Anatomie, Ontogenese und Ökologie von Mesosauridae beleuchten. Kapitel 1 behandelt die Knochenhistologie und Pachyosterosklerose in Mesosaurierknochen, was auf eine vollständig aquatische Lebensweise hinweist. Wir identifizieren auch eine große intraspezifische Variation, die möglicherweise durch unregelmäßige Probenahmeorte beeinflusst wird. Kapitel 2 untersucht die morpho¬logische Variation bei Mesosauriern und deren Umwelt-verteilung basierend auf ihrer Größe. Ontogenetische Veränderungen stehen im Zusammenhang mit dem Wechsel des Ablagerungsmilieus und deuten auf Veränderungen in Ernährung und Lebensraum mit dem Wachstum hin. In Kapitel 3 wird die kaudale Autotomie bei Mesosauriern überprüft und das Vorhandensein kaudaler Bruchebenen bestätigt. Wir schlagen eine stärker von den Extremitäten angetriebene Fortbewegung vor. Unsere Ergebnisse legen nahe, dass kaudale Autotomie ursprünglich in einer breiten Gruppe von Reptilien vorhanden war, anstatt konvergent in verschiedenen Linien entstanden zu sein. Kapitel 4 beschreibt auf Grundlage von Mesosaurier-Exemplaren vier grundlegende axiale Entwicklungs-modelle bei Amnioten und rekonstruiert ihren ursprünglichen Zustand in der Klade. Diese Muster bleiben im Laufe der Zeit relativ stabil, obwohl regionale Einflüsse möglich sind. Diese Erkenntnisse beleuchten wichtige Aspekte der Mesosaurier-Paläontologie und unterstreichen ihre Bedeutung für die Erforschung der Evolution früher Amnioten.The enigmatic mesosaurs were small, reptiles that lived during the Lower Permian period and were the earliest known reptiles to return to living in water. Despite their short existence and restricted geographical distribution, mesosaurs can provide important evidence about the early evolution of amniotes and the colonization of aquatic environments. This thesis regroups four articles published in peer-reviewed journals that investigate aspects of the anatomy, ontogeny, and ecology of Mesosauridae. In Chapter 1, my co-authors and I study bone histology and pachyosterosclerosis in the long bones, vertebrae, and ribs of mesosaurs. Thin sections show a high degree of osteosclerosis in their bones, supporting a fully aquatic lifestyle. We also recover a large intraspecific variation in Mesosauridae, albeit possibly due to irregular sampling locations. In Chapter 2 we examine morphological variation in mesosaurs and the environmental distribution of individuals as a function of size. We highlight ontogenetic changes in mesosaurs associated with a transition across depositional environments, which suggest that mesosaurs underwent diet and life environment change with growth. In Chapter 3, we review the information on caudal autotomy in mesosaurs. We confirm the presence of caudal fracture planes in the clade and propose a more limb-driven propulsion than previously considered. Our results also suggest that caudal autotomy was ancestrally present in a large radiation of reptiles, rather than a feature evolved convergently in multiple lineages. In Chapter 4, based on data in mesosaur specimens, we describe four axial developmental patterns in amniotes and reconstruct their ancestral condition in the clade. We demonstrate that these patterns are relatively stable throughout time, albeit possibly affected by regionalization. These new elements reveal crucial aspects of mesosaur paleontology and substantiate their significance for studying the evolution of early amniotes
(Santa Maria Super sequence, Brazil) from the Middle–Upper Triassic of South America based on microstructural analyses
No full text“Rauisuchia” is a non-monophyletic group of quadrupedal and carnivorous pseudosuchians that inhabited the entire world during the Middle–Upper Triassic period (Anisian/Ladinian–Rhaetian). In South America, “rauisuchians” reached the largest sizes among continental carnivores. Despite their important ecological role, some aspects of their palaeobiology have been poorly examined. Here, we study appendicular bones, dorsal ribs and osteoderms of two genera, the Argentinean Fasolasuchus tenax (PVL 3850, holotype) and the Brazilian Prestosuchus chiniquensis (SNSB-BSPG AS XXV) respectively. The femur of F. tenax is formed by laminar fibrolamellar bone, which is composed of non-fully monorefringent woven-fibred matrix and primary osteons; the dorsal rib has a Haversian bone composition with an external fundamental system recorded and the osteoderm is formed by well-organised parallel-fibred bone. The femur, humerus and fibula of P. chiniquensis are mostly composed of strongly arranged parallel-fibred bone and a laminar vascularisation. The minimal ages obtained correspond to 9 years for F. tenax (based on the maximum number of growth marks in the osteoderm) and 4 years for P. chiniquensis (obtained from the highest count of growth marks in the femur and in the humerus). F. tenax attained somatic and skeletal maturity, while P. chiniquensis was near to reaching skeletal and sexual maturity, but it was somatically immature. The overall rapid growth rate and the high and uniform vascularisation seems to imply that these features are common in most of “rauisuchians”, except in P. chiniquensis.Fil: Ponce, Denis Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación en Paleobiología y Geología; ArgentinaFil: Scheyer, Torsten M.. Universitat Zurich. Instituto Palaontologisches Institut And Museum; SuizaFil: Cerda, Ignacio Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación en Paleobiología y Geología; ArgentinaFil: Desojo, Julia Brenda. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin
Osteoderm histology of Proterochampsia and Doswelliidae (Reptilia: Archosauriformes) and their evolutionary and paleobiological implications
Full text linkPostcranial osteoderms are commonly developed in the major lineages of Archosauriformes, including forms such as proterochampsids and doswelliids. 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 organization, in which two cortices (external and basal) can be differentiated 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 microstructure observed in P. ischigualastensis osteoderms suggests 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 osteoderm formation and also to the development of the external ornamentation. A comparison of our findings with the results of earlier studies on other archosauriforms (phytosaurs and pseudosuchians) reveals that the general osteoderm histology of doswelliids bears a closer resemblance to that of phytosaurs and pseudosuchians than the proterochampsid osteoderm microstructure. If all archosauriform 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.Fil: Cerda, Ignacio Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Rio Negro. Sede Alto Valle. Instituto de Investigaciones en Paleobiologia y Geologia; ArgentinaFil: Desojo, Julia Brenda. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; ArgentinaFil: Trotteyn, Maria Jimena. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Fisicas y Naturales. Instituto de Geologia "Dr. Emiliano Aparicio"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Scheyer, Torsten M.. Palaontologisches Institut und Museum der Universitat Zurich; Suiz
- …
