Palaeoworld最新文献

This study analyzed 14 stratigraphic sections exposing the Devonian–Carboniferous boundary interval in the North Urals, representing different facies from shallow-water carbonate platform to bathyal, in order to assess the possibility of recognizing regional levels corresponding to the base of the conodont zones S. sulcata and Protognathodus kockeli. The base of the S. sulcata Zone is regionally recognized by the first appearances of the conodonts Siphonodella sulcata (Huddle), S. semichatovae Kononova and Lipnjagov and Patrognathus crassus Kononova and Migdisova, roughly correlated with the first appearance of the foraminifer Tournayellina pseudobeata Reitlinger and Kulagina, and with the first appearances of the ostracods Cribroconcha primaris Kochetkova, Chamishaella grekoffi Tchizhova, Glyptolichvinella spiralis (Jones and Kirkby), Armilla uralica Sobolev, Calcarofera ex gr. media Schornikov, Compositocostata cumina Sobolev, Spinoalacia tschigovae Sobolev, Richterina latior Rabien. The base of the S. sulcata Zone occurs in the interval between two positive inorganic carbon isotope excursions. The base of the Protognathodus kockeli Zone is marked by the first appearance of Protognathodus kockeli (Bischoff) in a very narrow facies belt on the slope of the carbonate platform, recognized regionally by the onset of the last phase of the positive inorganic carbon isotope excursion, the beginning of the transgression after the terminal Famennian regression, the beginning of the unilocular foraminifera Bisphaera bloom and probably the appearance of the ostracods Monoceratina sp. 1. The level corresponding to the base of Pr. kockeli Zone is poorly supported biostratigraphically, but is characterized by clear isotope-stratigraphic and cyclostratigraphic data, although the eustatic signal may be obscured in places by local tectonics.

The Zipf distribution is widespread in physical and biological systems on the modern Earth; whether such distributions existed in the ancient Earth-life system, however, remains understudied. Here I demonstrate that per-capita change rates (PCCRs) of the atmospheric CO₂ level, global average temperature, genus richness, and body size during the Phanerozoic exhibited Zipf distributions. Statistical analyses, including the goodness-of-fit test, likelihood-ratio test, and complementary cumulative distribution function (CCDF), support these Zipf distributions. Moreover, correlation analyses show that these environmental variables and biological metrics are correlated while their PCCRs are not, suggesting that Zipf distributions in PCCRs are unlikely to directly connect to each other; instead, there probably existed a set of common but unknown factors responsible for these systematic Zipf distributions in PCCRs. The results in this study offer new perspectives on the evolutionary patterns of the ancient Earth-life system.

Although gastropods are one of the most studied mollusk groups, fossil records of heterobranch microgastropods are scarce. Here, nine species of heterobranch microgastropods are described from the early Eocene Cambay Shale of the Cambay Basin, including 8 new species: Ringicula knolli n. sp., Cylichna (Cylichna) ypresiana n. sp., Aliculastrum suratense n. sp., Odostomia concavata n. sp., Megastomia canaliculata n. sp., Megastomia carinata n. sp., Costosyrnola taptiensis n. sp., and Cingulina eamesi n. sp. This new fauna is discussed here with respect to its associated lithology, faunal association, and habitat and feeding preferences. A low diversity microgastropod fauna composed predominantly of eurytopic genera in association with similar eurytopic macro-mollusks indicates a restricted marginal marine condition. Eight out of the nine species described here are endemic. On the other hand, apart from Cingulina and Costosyrnola, which have a poor fossil record, the reported genera were widespread during the early Eocene. The heterobranchs are characterized by planktotrophic larval development, believed to benefit large scale dispersal. As the strong endemism of the species does not support this hypothesis, it is suggested here that the isolated and restricted nature of the basin could have facilitated rapid speciation in the fauna.