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The global diversity of Proterozoic eukaryote fossils is poorly quantified despite its fundamental importance to the understanding of macroevolutionary patterns and dynamics on the early Earth. Here we report a new construction of fossil eukaryote diversity from the Paleoproterozoic to early Cambrian based on a comprehensive data compilation and quantitative analyses. The resulting taxonomic richness curve verifies Cryogenian glaciations as a major divide that separates the “Boring Billion” and Ediacaran periods, with the former characterized by a prolonged stasis, and the latter by greater diversity, more-rapid turnover, and multiple radiations and extinctions. These contrasting evolutionary patterns and dynamics provide a framework to test competing hypotheses on biosphere and geosphere coevolution in the Proterozoic Eon. 

Abstract This work presents a detailed taxonomic study on organic-walled microfossils from the Ediacaran Sete Lagoas Formation (Bambuí Group) at the Barreiro section in the Januária area of the São Francisco basin, Brazil. Seven species are described, includingSiphonophycus robustum(Schopf, 1968),Ghoshia januarensisnew species,Leiosphaeridia crassa(Naumova, 1949),Leiosphaeridia jacutica(Timofeev, 1966),Leiosphaeridia minutissima(Naumova, 1949),Leiosphaeridia tenuissimaEisenack, 1958, and Germinosphaera bispinosaMikhailova, 1986. These taxa are recovered for the first time in the Sete Lagoas Formation. They occur abundantly in the lower portion of the studied section, but onlyGhoshia januarensisis present in the upper part of the studied section, probably due to environmental or taphonomic changes.Leiosphaeridiaspecies, particularlyLeiosphaeridia minutissima, dominate the organic-walled microfossil assemblage. Although most taxa described here have long stratigraphic ranges, they are consistent with a terminal Ediacaran age as inferred from detrital zircon data and tubular fossils (e.g.,CloudinaandCorumbella) from the Sete Lagoas Formation. UUID:http://zoobank.org/7f92b900-0176-4da6-93a3-fd51edb22cbf 

Abstract Macrofossils with unambiguous biogenic origin and predating the one-billion-year-old multicellular fossilsBangiomorphaandProterocladusinterpreted as crown-group eukaryotes are quite rare.Horodyskiais one of these few macrofossils, and it extends from the early Mesoproterozoic Era to the terminal Ediacaran Period. The biological interpretation of this enigmatic fossil, however, has been a matter of controversy since its discovery in 1982, largely because there was no evidence for the preservation of organic walls. Here we report new carbonaceous compressions ofHorodyskiafrom the Tonian successions (~950–720 Ma) in North China. The macrofossils herein with bona fide organic walls reinforce the biogenicity ofHorodyskia. Aided by the new material, we reconstructHorodyskiaas a colonial organism composed of a chain of organic-walled vesicles that likely represent multinucleated (coenocytic) cells of early eukaryotes. Two species ofHorodyskiaare differentiated on the basis of vesicle sizes, and their co-existence in the Tonian assemblage provides a link between the Mesoproterozoic (H.moniliformis) and the Ediacaran (H.minor) species. Our study thus provides evidence that eukaryotes have acquired macroscopic size through the combination of coenocytism and colonial multicellularity at least ~1.48 Ga, and highlights an exceptionally long range and morphological stasis of this Proterozoic macrofossils. 

A thermal component is suggested to be the physical composition of the ejecta of several bright gamma-ray bursts (GRBs). Such a thermal component is discovered in the time-integrated spectra of several short GRBs as well as long GRBs. In this work, we present a comprehensive analysis of ten very short GRBs detected by Fermi Gamma-Ray Burst Monitor to search for the thermal component. We found that both the resultant low-energy spectral index and the peak energy in each GRB imply a common hard spectral feature, which is in favor of the main classification of the short/hard versus long/soft dichotomy in the GRB duration. We also found moderate evidence for the detection of thermal component in eight GRBs. Although such a thermal component contributes a small proportion of the global prompt gamma-ray emission, the modified thermal-radiation mechanism could enhance the proportion significantly, such as in subphotospheric dissipation. 

Sorted by the photon fluences of short Gamma-ray Bursts (SGRBs) detected by the Fermi-Gamma Ray Burst Monitor (GBM), nine brightest bursts are selected to perform a comprehensive analysis. All GRB lightcurves are fitted well by 1 to 3 pulses that are modelled by fast-rising exponential decay profile (FRED), within which the resultant rising time is strongly positive-correlated with the full time width at half maxima (FWHM). A photon spectral model involving a cutoff power-law function and a standard blackbody function (CPL + BB) could reproduce the spectral energy distributions of these SGRBs well in the bursting phase. The CPL’s peak energy is found strongly positive-correlated with the BB’s temperature, which indicates they might be from the same physical origin. Possible physical origins are discussed to account for these correlations. 

Abstract We report the detection of a strong thermal component in the short gamma-ray burst 170206A with three intense pulses in its light curves, throughout which the fluxes of this thermal component exhibit fast temporal variability the same as that of the accompanying nonthermal component. The values of the time-resolved low-energy photon index in the nonthermal component are between about −0.79 and −0.16, most of which are harder than the −2/3 expected in the synchrotron emission process. In addition, we found a common evolution between the thermal component and the nonthermal component, E p , CPL ∝ kT BB 0.95 ± 0.28 and F CPL ∝ F BB 0.67 ± 0.18 , where E p,CPL and F CPL are the peak photon energy and corresponding flux of the nonthermal component, and kT BB and F BB are the temperature and corresponding flux of the thermal component, respectively. Finally, we proposed that the photospheric thermal emission and the Comptonization of thermal photons may be responsible for the observational features of GRB 170206A.