Keywords: Oceanic Anoxic Event, Pliensbachian-Toarcian, carbon isotope excursion, Arctic 30 climate, sea level changes 31 2 The Toarcian Oceanic Anoxic Event (T-OAE) (ca. 182 mya, Early Jurassic) represents one of 32 the best-recognized examples of greenhouse warming, decreased seawater oxygenation and 33 mass extinction. The leading hypothesis to explain these changes is the massive injection of 34 thermogenic or gas hydrate-derived 13 C-depleted carbon into the atmosphere, resulting in a >3 35 per mil negative carbon isotope excursion (CIE), accelerated nutrient input and dissolved 36 oxygen consumption in the oceans. Nevertheless, the lack of a precisely dated record of the T-37 OAE outside low latitudes has led to considerable debate about both its temporal and spatial 38 extent and hence concerning its underlying causes. Here we present new isotopic and 39 lithological data from three precisely dated N Siberian sections, which demonstrate that mass 40 extinction and onset of strong oxygen-deficiency occurred near synchronously in polar and 41 most tropical sites and were intimately linked to the onset of a marked 6‰ negative CIE 42 recorded by bulk organic carbon. Rock Eval pyrolysis data from Siberia and comparisons 43 with low latitudes show that the CIE cannot be explained by the extent of stratification of the 44 studied basins or changes in organic matter sourcing and suggest that the negative CIE 45 reflects rapid 13 C-depleted carbon injection to all exchangeable reservoirs. Sedimentological 46 and palynological indicators show that the injection coincided with a change from cold 47 (abundant glendonites and exotic boulder-sized clasts) to exceptionally warm conditions 48 (dominance of the thermophyllic pollen genus Classopollis) in the Arctic, which likely 49 triggered a rapid, possibly partly glacioeustatic sea-level rise. Comparisons with low latitude 50 records reveal that warm climate conditions and poor marine oxygenation persisted in 51 continental margins at least 600 ky after the CIE, features that can be attributed to protracted 52 and massive volcanic carbon dioxide degassing. Our data reveal that the T-OAE profoundly 53 affected Arctic climate and oceanography and suggest that the CIE was a consequence of 54 global and massive 13 C-depleted carbon injection. 55 56 57
Published data on initial chamber (protoconch) diameter in 507 species, and embryonic shell (ammonitella) diameter in 231 species of Ammonoidea, and embryonic shell (nauta) diameters for 132 species of coiled Nautiloidea, were used to examine evolutionary change in ectocochleate cephalopod reproductive strategies. Palaeotemperatures were found to be a key factor influencing historical changes in the evolution of egg size in ammonoids and nautiloids. A negative relationship was found between egg size and warming of the Earth's climate. Factors related to habitat were also important; in general egg size was larger in cold-water cephalopods. Egg size in Lytoceratina and Phylloceratina in the deep waters of the upper continental slope was much larger than in epipelagic Scaphitidae, as in modern fish and squids. Small eggs and high evolutionary rates helped ammonoids to colonise new habitats and develop high biological diversity, but involved them in planktonic food webs making them more vulnerable to abiotic variability (e.g., climatic changes), ultimately leading to their extinction. Large eggs helped nautiloids to persist through geological history, but at the cost of lower biological diversity, lower evolutionary rates and restricted options for colonising new habitats. Large-egged species such as nautiloids are more vulnerable to ecological, biotic disasters such as the appearance of new predators, including modern fishery. Independence from the planktonic food web is likely to be very important for a taxon's long-term survival over evolutionary history, as demonstrated also by Coelacanthiformes and Elasmobranchia. • Key words: Ammonoidea, Nautiloidea, reproductive strategy, mass extinction, climate change, egg. Vladimir V. Laptikhovsky, Falkland Islands Government Fisheries Department, Stanley, FIQQ 1ZZ, Falkland Islands; vlaptikhovsky@fisheries.gov.fk • Mikhail A. Rogov, Geological Institute of Russian Academy of Sciences, Pyzhevskii Lane 7, Moscow, 119017, Russia; russianjurassic@gmail.com • Svetlana V. Nikolaeva, Paleontological Institute, Russian Academy of Sciences, Moscow, 117997, Russia; 44svnikov@mail.ru • Alexander I. Arkhipkin, Falkland Islands Government Fisheries Department, Stanley, FIQQ 1ZZ, Falkland Islands; aarkhipkin@fisheries.gov.fk Reproductive strategy is an important choice that species face continuously during their evolutionary history. A trade-off exists between fecundity and egg size (numbers vs "quality" of hatchling) because generative production in every species is restricted by body size, available food and longevity (Kasyanov 1999). Understanding these competing strategies led to the idea of r-and K-selection in life histories (MacArthur & Wilson 1967, Pianka 1970. It involves a bet-hedging concept that assumes that maximizing strategies are more advantageous in stable and predictable environments where variance is minimal, while minimizing strategies can enhance long-term fitness in periodically variable environments. Because of this, r-populations tend to inhabit unpredicta...
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