A silicite horizon corresponding to the global catastrophic event at the Cretaceous–Paleogene boundary was found for the first time in the flysch sequence of the Shapsug section on the southern slope of the Northwest Caucasus. Assemblages of radiolarians and planktonic foraminifers dating the host beds were identified. Mineralogical and analytical data support the presence of tectites, impact minerals, and increased iridium content in the boundary bed of the studied section.
There are important morphological differences between the dominant higher taxa (classes) in associations of radiolarians that inhabited different depths of paleobasins. A similar inversion of dominant radiolarian taxa can be seen in the Early Tournaisian (Mississippian) and the Kungurian (Cisuralian) and may indicate a change in their habitat from deeper conditions dominated by porous Sphaerellaria, to shallower shelf environments, in which spongy-lattice Spumellaria prevailed.
The oldest species of the genus Dvinosaurus Amalitzky, 1921—Dvinosaurus gubini sp. nov.—is described from the Sundyr-1 reference locality of the Sundyr faunal assemblage of Eastern Europe (Upper Permian, Upper Severodvinian, Suchonica vladimiri Assemblage Zone) based on abundant bone material. The diagnostic criteria for the new species are its smaller size compared to other dvinosaurs, the narrowest skull, a short and wide zygomatic bone, and the parasphenoid body with a wider base of the cultriform process, which is well ossified with the basisphenoid; a strongly curved dentary with a well-defined symphysial crest extending downward from the labial side of the symphysial surface and, in some cases, with a single symphysial tusk, a large angle (135°–152°) between the clavicular plate and dorsal process of the clavicle, narrow areas of the interclavicle for insertion of the clavicles, and a narrow entepicondylus of the humerus. The small size, narrow skull, single symphysial tusk, and hypocentrum morphology make the new form similar to the basal Dvinosauria, in particular, to ancestral Trimerorhachidae.
Skeletal morphology of bryozoans of the family Eleidae d’Orbigny, 1852 (Melicerititida, Stenolaemata) and of three of its species from the Middle Callovian (Middle Jurassic) of the Moscow region—Elea lyapini Viskova, 2011, E. troshkovensis Viskova, 2011, and E. taylori Viskova, 2011 was analyzed, confirming that these species belong to the family Eleidae. Along with opercula (calcareous and possibly non-calcareous) and eleozooids (heterozooids), they are characterized by funnel-shaped autozooids, facettes and the distal position of apertures with a straight proximal edge, the absence of peristomes and a number of other characters. This morphology is considered to have resulted from the restructuring of the basic plan of the cylindrical autozooid of tubuliporid bryozoans that happened after the Permian–Triassic crisis at the time of the first radiation of bryozoans during the extensive Callovian transgression.
The morphology and histological structure of the humerus and femora of the stem karaurid salamander Kulgeriherpeton ultimum Skutschas et al., 2018, from the Lower Cretaceous Teete locality, Republic of Sakha (Yakutia) is described. The microanatomical and histological structure of K. ultimum is characterized by the presence of a thick compact primary cortex formed by a parallel-fibered bone; the absence (in the humerus) or presence of a small medullary cavity in the mid-diaphysis; the presence of a medullary cavity expanding towards the epiphyses, which continues in the proximal and distal parts as a complex network of branching canals, partially replaced by erosion bays; the presence of primary vascular canals and growth marks in the primary cortex; the presence of remnants of unresorbed cartilage and the Kashchenko’s line; active secondary remodeling with the formation of erosion bays similar to those in large-sized salamanders (other stem karaurid salamanders and cryptobranchids). Skeletochronological analysis of the humerus of K. ultimum showed that, at the time of the animal’s death, its individual age was 13–16 years, and the absence of a reduction in the distance between cyclic growth marks in the peripheral part of the cortex indicates that it belonged to an actively growing individual that had not reached its maximum possible size. The similarity in the morphology of the humerus and femur of K. ultimum and extant aquatic neotenic salamanders (absence of a dorsal crest on the humerus for the attachment of m. subcoracoscapularis, lower, forward-displaced trochanter of the femur, and shallow ventral fossa (fossa trochanterica) on the femur), as well as the presence of remnants of cartilage and preservation of Kashchenko’s line in the internal structure of limb bones, confirm conclusions about aquatic life style and neotenic nature of stem karaurid salamanders.
Early archosaurs included a range of ecological types—from predators to herbivores and from terrestrial to semi-aquatic forms. Members of the family Ornithosuchidae, traditionally considered active predators, occupy a special position. Their characteristic jaw apparatus structure and the morphology of their postcranial skeleton suggest the development of a unique ecological type among archosaurs, namely, a medium-sized hyperanisodont macrophagous predator. At the same time, some analogs can be noted between ornithosuchids, saber-toothed therapsids, and mammals.
Numerous representatives of the genus Pseudodictyomitra Pessagno, 1977 were studied from the Upper Cretaceous of the Perapedhi Formation (Cyprus). The new species P. venusta sp. nov. is described. The description and stratigraphic range of P. crassa Bragina, 2013 are emended.
Two new species of cornutan stylophora of the genus Phyllocystis are described from the Volkhov Regional Stage (Middle Ordovician, Dapingian) of Baltica. This indicates a biogeographic connection between the Afro-European part of Gondwana and Baltica since the very beginning of the Middle Ordovician. Both species were confined to cold-water, shallow basins with low water mobility. Analysis of the axial symmetry of stylophorans and the location of the hydropore indicates the absence of torsion in their ontogeny and the location of the ambulacral system to the right of their anteroposterior axis. To explain this morphology, two alternative hypotheses are proposed: (1) inversion in the development of right and left coeloms; (2) inverted state of stylophorans compared to other invertebrates, in which respect they resemble chordates in terms of the position of the dorsal and ventral sides.
The shell microstructure of the rare lingulate genus Praeoehlertella Mergl, 2001 from the Famennian of Kazakhstan is studied. The structure of the shell matrix and the secondary granular layer are studied using scanning electron microscope. Imprints of cells of the inner mantle epithelium are discovered.
A new problematic spheromorphic microfossil Gaparella elenae sp. nov. is described from the lower Tommotian (Lower Cambrian) in the Hevte-Tsakhir-Nuruu Ridge, Western Mongolia, and a new combination Gaparella kuanchuanpuensis (Qian, 1977) is proposed. Despite its very peculiar morphology, the genus Gaparella Missarzhevsky in Missarzhevsky and Mambetov, 1981 is usually considered as a junior synonym of the genus Archaeooides Qian, 1977. The taphonomic variability of Mongolian specimens of Gaparella is demonstrated, and their morphology is reconstructed: these were hollow spheres, with a thin perforated double-layered wall; with a system of cavities between the pores, which were scattered on small elevations, with a system of canals in between; the wall may have been organic with an admixture of mineral components. These fossils were probably planktonic filter feeders. Their level of organization appears to be consistent with Porifera; most likely these were juvenile forms.
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：