Changements ontogénétiques dans l’histologie des os longs du cryptobranchidé <i>Eoscapherpeton asiaticum</i> (Amphibians : Caudata) du Crétacé supérieur d’Ouzbékistan

Cet article présente des données histologiques sur les os longs d’individus différents en taille (âge) de la salamandre cryptobranchidée Eoscapherpeton asiaticum basale du Crétacé supérieur (Turonien) d’Ouzbékistan. E . asiaticum ressemble à des membres modernes de Cryptobranchidae par sa taille relativement grande (longueur estimée de son corps jusqu’à 50–60 cm, sa vie aquatique, ses caractères néoténiques). L’analyse de séries de croissance de fémurs démontre une maturation histologique significative pendant l’ontogénie, exprimée par l’apparition progressive d’os à fibres parallèles très organisées dans la partie périphérique du cortex périostique, l’apparition en nombre croissant de traits de remodelage osseux, la résorption progressive du cartilage calcifié dans les zones diaphysales et la formation d’os endochondral soulignant les cavités d’érosion dans le cartilage calcifié, l’épaississement progressif d’un feuillet circonférentiel interne endostéal et une croissance de la vascularité, ainsi que l’apparition d’un réseau vasculaire sous forme de canaux longitudinaux et obliques dans le cortex. Ces changements ontogénétiques dans l’histologie des os longs de E . asiaticum correspondent généralement à ceux observés chez d’autres salamandres, mise à part l’apparition du réseau vasculaire dans le cortex périostique, trait caractéristique des cryptobranchidés, en relation avec la grande taille de leur corps. Selon des données nouvelles, les grands cryptobranchidés du Cénozoïque semblent avoir atteint leur taille plus grande grâce à l’allongement de la période de croissance du squelette.This paper presents histological data on the long bones of different size (age) individuals of the basal cryptobranchid salamander Eoscapherpeton asiaticum from the Upper Cretaceous (Turonian) of Uzbekistan. E . asiaticum is similar to modern members of Cryptobranchidae in being relatively large (estimated body length up to 50–60 cm), aquatic, and neotenic. The analysis of growth series of femora demonstrates a significant histological maturation during ontogeny, expressed by the progressive appearance of highly organized parallel-fibred bone in the peripheral part of the periosteal cortex, appearance and increasing number of bone remodeling features, progressive resorption of calcified cartilage in the diaphyseal areas and formation of endochondral bone lining the erosion cavities in the calcified cartilage, progressive thickening of endosteal inner circumferential layer and increasing of vascularity and appearance of vascular network of longitudinal and oblique canals in the cortex. These ontogenetic changes in the long-bone histology of E . asiaticum generally correspond to those of other salamanders, except the appearance of the vascular network in the periosteal cortex — the feature that is characteristic for cryptobranchids and connected with their large body size. According to new data, the large Cenozoic cryptobranchids appear to have attained their larger size by extending the skeletal growth period.</p

A new relict stem salamander from the Early Cretaceous of Yakutia, Siberian Russia

A new stem salamander, Kulgeriherpeton ultimum gen. et sp. nov., is described based on a nearly complete atlas (holotype) from the Lower Cretaceous (Berriasian–Barremian) Teete vertebrate locality in southwestern Yakutia (Eastern Siberia, Russia). The new taxon is diagnosed by the following unique combination of atlantal characters: the presence of a transversal ridge and a depression on the ventral surface of the posterior portion of the centrum; ossified portions of the intercotylar tubercle represented by dorsal and ventral lips; the absence of a deep depression on the ventral surface of the anterior portion of the centrum; the absence of pronounced ventrolateral ridges; the absence of spinal nerve foramina; the presence of a pitted texture on the ventral and lateral surfaces of the centrum and lateral surfaces neural arch pedicels; the presence of a short neural arch with its anterior border situated far behind the level of the anterior cotyles; moderately dorsoventrally compressed anterior cotyles; and the absence of a deep incisure on the distal-most end of the neural spine. The internal microanatomical organization of the atlas is characterized by the presence of a thick, moderately vascularized cortex and inner cancellous endochondral bone. The recognition of stem salamanders and other vertebrates with Jurassic affinities in the Early Cretaceous high-latitude (paleolatitude estimate N 63–70°) vertebrate assemblage of Teete suggests that: (i) the large territory of present day Siberia was a refugium for Jurassic relicts; (ii) there were no striking differences in the composition of high-latitude Yakutian and mid-latitude Western Siberian Early Cretaceous vertebrate assemblages; and (iii) there was a smooth transition from the Jurassic to Cretaceous biotas in North Asia

Structure, Growth and Histology of Gnathal Elements in <i>Dunkleosteus</i> (Arthrodira, Placodermi), with a Description of a New Species from the Famennian (Upper Devonian) of the Tver Region (North-Western Russia)

A new species of Dunkleosteus, D. tuderensis sp. nov., is named based on an infragnathal from the Famennian of the Tver Region, Russia. CT scanning of the holotype revealed two high-density bony constituents comparable in position and interrelations to components described for coccosteomorph arthrodires, supported by the presence of at least two clusters of large vascular canals marking separate arterial supplies. Coccosteomorph and dunkleosteid pachyosteomorphs exhibit similar growth patterns including labio-basal depositions of vascularized bone in the infragnathals and basally in the supragnathals. In contrast to coccosteomorphs, dunkleosteid reinforcement of the occlusal margins occurred via the formation of dense osteonal bone, in parallel with resorption forming extensive lingual fossae. Active bone remodeling proceeded without a complete reworking of the primary osteonal bone structure and the original arrangement of vascular canals. Due to inconsistent anatomical terminology in gnathal elements of dunkleosteid arthrodires, a revised terminology is suggested and new terms are introduced

Wear patterns and dental functioning in an Early Cretaceous stegosaur from Yakutia, Eastern Russia.

Isolated stegosaurian teeth from the Early Cretaceous high-latitude (palaeolatitude estimate of N 62°- 66.5°) Teete locality in Yakutia (Eastern Siberia, Russia) are characterized by a labiolingually compressed, slightly asymmetrical and mesiodistally denticulated (9-14 denticles) crown, a pronounced ring-like cingulum, as well as a "complex network of secondary ridges". The 63 teeth (found during on-site excavation in 2012, 2017-2019 and screen-washing in 2017-2019) most likely belong to one species of a derived (stegosaurine) stegosaur. Most of the teeth exhibit a high degree of wear and up to three wear facets has been observed on a single tooth. The prevalence of worn teeth with up to three wear facets and the presence of different types of facets (including steeply inclined and groove-like) indicate the tooth-tooth contact and precise dental occlusion in the Teete stegosaur. The microwear pattern (mesiodistally or slightly obliquely oriented scratches; differently oriented straight and curved scratches on some wear facets) suggest a complex jaw mechanism with palinal jaw motion. Histological analysis revealed that the Teete stegosaur is characterized by relatively short tooth formation time (95 days) and the presence of a "wavy enamel pattern". Discoveries of a "wavy enamel pattern" in the Teete stegosaur, in a Middle Jurassic stegosaur from Western Siberia, and in the basal ceratopsian Psittacosaurus, suggest that this histological feature is common for different ornithischian clades, including ornithopods, marginocephalians, and thyreophorans. A juvenile tooth in the Teete sample indicates that stegosaurs were year-round residents and reproduced in high latitudes. The combination of high degree of tooth wear with formation of multiple wear facets, complex jaw motions, relatively short tooth formation time and possibly high tooth replacement rates is interpreted as a special adaptation for a life in high-latitude conditions or, alternatively, as a common stegosaurian adaptation making stegosaurs a successful group of herbivorous dinosaurs in the Middle Jurassic-Early Cretaceous and enabeling them to live in both low- and high-latitude ecosystems