Swedish Museum of Natural History
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Revisiting the molluscan fauna from the Cambrian (Series 2, stages 3–4) Xinji Formation of North China
No full textA diverse group of molluscs from the Cambrian Series 2, Stages 3–4 Xinji Formation of the North China Block (NCB) is described, based on more than 4500 specimens from three well-studied sections in Shaanxi and Henan provinces, along the southern and southwestern margin of the NCB. Twenty molluscan species are identified, including one bivalve, three stem group gastropods, and 16 additional helcionelloids. Among these, six helcionelloid species are reported from the NCB for the first time, and one new species, Parailsanella luonanensis sp. nov. is proposed. This diverse molluscan fauna shares a large number of species with contemporaneous faunas of South Australia (15), Antarctica (7), Laurentia (6), Siberia (3) and South China (1). Faunal similarities are even greater on a generic level. The striking similarities of the molluscan faunas of North China, South Australia and Antarctica strongly support the hypothesis that the NCB was situated close to Eastern Gondwana, most likely close to South Australia in the Cambrian Epoch 2. In addition, well-preserved shell attachment muscle scars were observed in the helcionelloid Figurina figurina, with two pairs of symmetrical, continuous, band-like muscle scars, which are obviously different from the musculature of both gastropods and monoplacophorans. Because of this unique musculature, these characteristic Cambrian cap-like molluscs are assigned to the Helcionelloida rather than to the Gastropoda or Monoplacophora. A diverse group of molluscs from the Cambrian Series 2, Stages 3–4 Xinji Formation of the North China Block (NCB) is described, based on more than 4500 specimens from three well-studied sections in Shaanxi and Henan provinces, along the southern and southwestern margin of the NCB. Twenty molluscan species are identified, including one bivalve, three stem group gastropods, and 16 additional helcionelloids. Among these, six helcionelloid species are reported from the NCB for the first time, and one new species, Parailsanella luonanensis sp. nov. is proposed. This diverse molluscan fauna shares a large number of species with contemporaneous faunas of South Australia (15), Antarctica (7), Laurentia (6), Siberia (3) and South China (1). Faunal similarities are even greater on a generic level. The striking similarities of the molluscan faunas of North China, South Australia and Antarctica strongly support the hypothesis that the NCB was situated close to Eastern Gondwana, most likely close to South Australia in the Cambrian Epoch 2. In addition, well-preserved shell attachment muscle scars were observed in the helcionelloid Figurina figurina, with two pairs of symmetrical, continuous, band-like muscle scars, which are obviously different from the musculature of both gastropods and monoplacophorans. Because of this unique musculature, these characteristic Cambrian cap-like molluscs are assigned to the Helcionelloida rather than to the Gastropoda or Monoplacophora. This research was also supported by funds from the National Key Research and Development Program (Grant 2017YFC0603101), Natural Science Foundation of China (Grants 41621003 and 41890840), the Strategic Priority Research Program of Chinese Academy of Sciences (Grant XDB26000000), 111 Project (D17013)</p
First discovery of Small Shelly Fossils and new occurrences of brachiopods and trilobites from the early Cambrian (Stage 4) of the Swedish Caledonides, Lapland
No full textNew fossil discoveries are reported from the Grammajukku Formation at Luobákte south of Lake Torneträsk in northern Swedish Lapland, including a fauna of Small Shelly Fossils (SSF) from a limestone bed in the uppermost part of the formation and new occurrences of brachiopods and trilobites in siltstones of the lower part of the formation. The moderately diverse SSF fauna is the first of its kind reported from the Swedish Caledonides and includes the first record of the tommotiid Lapworthella schodackensis and the bradoriid spine Mongolitubulus spinosus from Baltica, together with fragmentary specimens of Bradoria sp. and remains of one additional bradoriid arthropod, a protoconodont and a helcionelloid mollusc. In addition, the limestone bed yields abundant specimens of the brachiopods Botsfordia cf. caelata and Eoobolus cf. priscus and an unidentified ellipsocephalid trilobite. Lower down in the Grammajukku Formation, specimens of both brachiopod taxa, orthothecid hyoliths, the trilobite Ellipsocephalus cf. gripi and an unidentified holmiid trilobite were found at several levels in a siltstone, previously regarded as unfossiliferous. These discoveries markedly increase the known diversity of the palaeobiota from the Grammajukku Formation in northern Lapland and provide new insights into the biostratigraphy and palaeoenvironment of the lower Cambrian in Scandinavia and the palaeobiogeography of Cambrian faunas in general
Palynofacies analysis for interpreting paleoenvironment and hydrocarbon potential of Triassic–Jurassic strata in the Sichuan Basin, China
No full textThe Sichuan Basin is one of the largest petroliferous basins in China. The continental fluvial‒lacustrine sediments of the Upper Triassic Xujiahe Formation and the Lower Jurassic Zhenzhuchong Formation yield diverse fossil organisms and host one of the most important gas reservoirs in thebasin. However, paleontological implication for the paleoenvironment and hydrocarbon source is less documented. Here, we report, for the first time for this basin, results from palynofacies analyses combined with thermal alteration data in the Early Mesozoic deposit of the Qilixia section, northeastern Sichuan Basin. The results show that, organic matters in sediments are dominated by phytoclasts, with less abundant palynomorphs and a few amorphous organic matters (AOMs). Four palynofacies assemblages were identified, reflecting depositional settings in a general proximal and oxicfluvial‒deltaic environment, with two distal-proximal sedimentary cycles. The prominent dominance of opaque phytoclasts within the lower Zhenzhuchong Formation may be related to frequent wildfires across the Triassic-Jurassic transition. Palynofacies data (especially the relative abundanceof opaque phytoclasts) may reflect 405 kyr eccentricity cyclicity pattern. The palynofacies and thermal alteration index (TAI), combined with geochemical data indicate the presence of type III kerogen in mature to post-mature phases, suggesting gas potential of the Xujiahe and Zhenzhuchong formations in the northeastern Sichuan Basin. This study provides significant implications for better understanding the paleoenvironment variationsduring the Triassic-Jurassic transition and the future gas exploration in this area.Also funded by the National Science Foundation of China (NSFC41702004, 41790454, 41572014, 41688103), Strategic PriorityResearch Program (B) of the Chinese Academy of Sciences(XDB18000000, 26000000), the State Key Laboratory ofPalaeobiology and Stratigraphy (20172103, 20191103)</p
Palaeoneurology and palaeobiology of the dinocephalian Anteosaurus magnificus
No full textDinocephalians (Therapsida), some of the earliest amniotes to have evolved large body size, include the carnivorous Anteosauria and mostly herbivorous Tapinocephalia. Whilst the palaeoneurology of the Tapinocephalia has been investigated in Moschognathus whaitsi, that of the Anteosauria remains completely unknown. Here we used X-ray micro-Computed Tomography to study, for the first time, the palaeoneurology of Anteosaurus magnificus. Compared to Moschognathus, we reconstruct Anteosaurus as an agile terrestrial predator based on the enlarged fossa for the floccular lobe of the cerebellum and semicircular canals of the inner ear. A major difference between the two genera resides in the orientation of the braincase, as indicated by the angle between the long axis of the skull and the plane of the lateral semicircular canal. This angle is 25° in Anteosaurus, whereas it is 65° in Moschognathus, which suggests that the braincase of the latter was remodelled as an adaptation to head-butting. This is consistent with less cranial pachyostosis and the retention of a large canine in Anteosauria, which suggests that dentition may have been used for intraspecific fighting and display in addition to trophic interactions. The evolution of a thick skull, horns, and bosses in tapinocephalids parallels the evolutionary reduction of the canine, which lead to a shift of the agonistic function from the mouth to the skull roof, as observed in extant social ungulates. Similarly, tapinocephalians may have developed complex social behaviour. Thisresearch was conducted with financial support from the PalaeontologicalScientific Trust (PAST) and its scatterlings projects; the NationalResearch Foundation of South Africa (NRF) African Origins Platform;and the DST-NRF Centre of Excellence in Palaeosciences (CoE inPalaeosciences).</p
Instalment of the margarosanite group, and data on walstromite–margarosanite solid solutions from the Jakobsberg Mn–Fe deposit, Värmland, Sweden
No full textThe margarosanite group (now officially confirmed by IMA-CNMNC) consists of triclinic Ca-(Ba, Pb) cyclosilicates with three-membered [Si3O9]6- rings (3R), with the general formula AB2Si3O9, where A = Pb, Ba, Ca and B = Ca. A closest-packed arrangement of O atoms parallel to (101) hosts Si and B cations in interstitial sites in alternating layers. The 3R layer has three independent Si sites in each ring. Divalent cations occupy three independent sites: Ca in B occupies two nonequivalent sites, Ca1 (8-fold coordinated), and Ca2 (6-fold coordinated). A (=Ca2) is occupied by Pb2+ (or Ba2+) in 6+4 coordination, or 6+1 when occupied by Ca; this third site occurs within the 3R-layer in a peripheral position. Three minerals belong to this group: margarosanite (ideally PbCa2Si3O9), walstromite (BaCa2Si3O9) and breyite (CaCa2Si3O9). So far, no solid solutions involving the Ca1 and Ca2 sites have been described. Therefore, root names depend on the composition of the Ca3 site only. Isomorphic replacement at the Ca3 sites has been noted. We here report data on a skarn sample from the Jakobsberg Mn-Fe oxide deposit, in Värmland (Sweden), representing intermediate compositions on the walstromite-margarosanite binary, in the range ca. 50–70% mol.% BaCa2Si3O9. The plumbian walstromite is closely associated with celsian, phlogopite, andradite, vesuvianite, diopside and nasonite. A crystal-structure refinement (R1 = 4.8%) confirmed the structure type, and showed that the Ca3 (Ba, Pb) site is split into two positions separated by 0.39 Å, with the Ba atoms found slightly more peripheral to the 3R-layers
Cleaning up the record – revised U-Pb zircon ages and new Hf isotope data from southern Sweden
No full textTen samples of orthogneisses and granitoids from the Eastern Segment of the Sveconorwegian Orogen in southern Sweden, previously dated by ID-TIMS on zircon, have been dated anew using SIMS spot analysis of individual zircon grains, leading to more reliable and in most cases also more precise revised magmatic crystallization ages. A gneissic monzonite within the Protogine Zone south of Alvesta in Småland yields a revised U-Pb age of ca. 1725 Ma, four samples of orthogneiss from Skåne all yield revised ages between 1690 and 1700 Ma, while two samples of coarse-grained granitoid gneiss in the same region yield ages between 1680 and 1690 Ma. These revised ages are between 15 and 250 m.y. older than previously obtained TIMS ages. Two samples of the Gumlösa-Glimåkra granite along the Protogine Zone in northern Skåne and one sample of related syenite yield ages around 1220 Ma, similar but more precise compared to the previous ages. The U-Pb zircon data have been complemented by Hf isotope analysis by LA-ICP-MS on the same zircon grains, and previously obtained initial Sr and Nd whole-rock isotope data have been recalculated to the revised crystallization ages. The Sr isotope data scatter, while the revised initial εNd values fall between +1 and +2 for the older granitoids and orthogneisses, and close to 0 for the 1220 Ma intrusives along the Protogine Zone. Initial εHf in magmatic undisturbed zircons shows relatively little spread within each sample, between 2 and 4 Epsilon units, disregarding occasional outliers, with average values for the 1725 - 1680 Ma rocks falling between +3and +5.5, and at ca. +1.5 in the 1220 Ma rocks. In spite of the limited variation, there is a covariation between initial εNd and initial εHf in the older rocks, suggesting either mixing between two isotopically distinct magma sources, or one magma source which is isotopically heterogeneous. The isotopic signatures of the 1220 Ma intrusives along the Protogine Zone is indicative of juvenile mantle input totheir magmas, rather than pure crustal melting
Historical population declines prompted significant genomic erosion in the northern and southern white rhinoceros ( Ceratotherium simum )
No full textLarge vertebrates are extremely sensitive to anthropogenic pressure, and their populations are declining fast. The white rhinoceros (Ceratotherium simum) is a paradigmatic case: this African megaherbivore has suffered a remarkable decline in the last 150 years due to human activities. Its subspecies, the northern (NWR) and the southern white rhinoceros (SWR), however, underwent opposite fates: the NWR vanished quickly, while the SWR recovered after the severe decline. Such demographic events are predicted to have an erosive effect at the genomic level, linked to the extirpation of diversity, and increased genetic drift and inbreeding. However, there is little empirical data available to directly reconstruct the subtleties of such processes in light of distinct demographic histories. Therefore, we generated a whole-genome, temporal data set consisting of 52 resequenced white rhinoceros genomes, representing both subspecies at two time windows: before and during/after the bottleneck. Our data reveal previously unknown population structure within both subspecies, as well as quantifiable genomic erosion. Genome-wide heterozygosity decreased significantly by 10% in the NWR and 36% in the SWR, and inbreeding coefficients rose significantly by 11% and 39%, respectively. Despite the remarkable loss of genomic diversity and recent inbreeding it suffered, the only surviving subspecies, the SWR, does not show a significant accumulation of genetic load compared to its historical counterpart. Our data provide empirical support for predictions about the genomic consequences of shrinking populations, and our findings have the potential to inform the conservation efforts of the remaining white rhinoceroses
