Size-Frequency Distributions along a Latitudinal Gradient in Middle Permian Fusulinoideans

Geographic gradients in body size within and among living species are commonly used to identify controls on the long-term evolution of organism size. However, the persistence of these gradients over evolutionary time remains largely unknown because ancient biogeographic variation in organism size is poorly documented. Middle Permian fusulinoidean foraminifera are ideal for investigating the temporal persistence of geographic gradients in organism size because they were diverse and abundant along a broad range of paleo-latitudes during this interval (∼275–260 million years ago). In this study, we determined the sizes of Middle Permian fusulinoidean fossils from three different paleo-latitudinal zones in order to examine the relationship between the size of foraminifers and regional environment. We recovered the following results: keriothecal fusulinoideans are substantially larger than nonkeriothecal fusulinoideans; fusulinoideans from the equatorial zone are typically larger than those from the north and south transitional zones; neoschwagerinid specimens within a single species are generally larger in the equatorial zone than those in both transitional zones; and the nonkeriothecal fusulinoideans Staffellidae and Schubertellidae have smaller size in the north transitional zone. Fusulinoidean foraminifers differ from most other marine taxa in exhibiting larger sizes closer to the equator, contrary to Bergmann's rule. Meridional variation in seasonality, water temperature, nutrient availability, and carbonate saturation level are all likely to have favored or enabled larger sizes in equatorial regions. Temporal variation in atmospheric oxygen concentrations have been shown to account for temporal variation in fusulinoidean size during Carboniferous and Permian time, but oxygen availability appears unlikely to explain biogeographic variation in fusulinoidean sizes, because dissolved oxygen concentrations in seawater typically increase away from the equator due to declining seawater temperatures. Consequently, our findings highlight the fact that spatial gradients in organism size are not always controlled by the same factors that govern temporal trends within the same clade

Permian and Triassic exotic limestone blocks of the Crimea.

Exotic limestone blocks of Permian and Triassic age occur in the Middle Triassic-Middle Jurassic Crimean olistostrome complex of the Maria and Aima River basins and in the Simferopol area. Rich assemblages of small foraminifers, fusulinids, brachiopods, rare ammonoids, and sphinctozoans occur in these blocks. Fossils from Permian blocks indicate the presence of zonal assemblages for the Bolorian, Kubergandian, Murgabian, Midian, Dzhulfian, anal Dorashamian stages. The Neoschwagerina simplex fusulinid zone is extended upward based on the presence in our material of Kubergandian ammonoids with Neoschwagerina simplex Ozawa. Comparison of the fauna from Triassic blocks to assemblages from other regions of the Tethys indicates that the age is Late Triassic Rhaetian corresponding to the Vandaites sturzenbaumi ammonoid zone

Environmental Control on Biotic Development in Siberia (Verkhoyansk Region) and Neighbouring Areas During Permian-Triassic Large Igneous Province Activity

We propose an updated ammonoid zonation for the Permian-Triassic boundary succession (the lower Nekuchan Formation) in the Verkhoyansk region of Siberia: (1) Otoceras concavum zone (uppermost Changhsingian); (2) Otoceras boreale zone (lowermost Induan); (3) Tompophiceras morpheous zone (lower Induan); and (4) Wordieoceras decipiens zone (lower Induan). The Tompophiceras pascoei zone, previously defined between the Otoceras boreale and Tompophiceras morpheous zones, is removed in our scheme. Instead of this the Tompophiceras pascoei epibole zone is proposed for the lower part of the Tompophiceras morpheous zone. New and previously published nitrogen isotope records are interpreted as responses to climatic fluctuations in the middle to higher palaeolatitudes of Northeastern Asia and these suggest a relatively cool climatic regime for the Boreal Superrealm; however the trend towards warming across the Permian-Triassic boundary transition is also seen. The evolutionary development and geographical differentiation of otoceratid ammonoids and associated groups are considered. It is likely that the Boreal Superrealm was their main refugium, where otocerid, dzhulfitid and some other ammonoids survived the major biotic crisis at the end of the Permian. The similarity of ontogenetic development of suture lines of Otoceras woodwardi Griesbach and O. boreale Spath gives some grounds for suggesting a monophyletic origin of the genus Otoceras, having bipolar distribution