No abstract

No abstract

The East African Rift System (EARS) has played a central role in our understanding of human origins and vertebrate evolution in the late Cenozoic of Africa. However, the distribution of fossil sites along 3 the rift is highly biased toward its northern extent, and the types of paleoenvironments are primarily restricted to fluvial and lacustrine settings. Here we report the discovery of the first fossil sites from the Urema Rift at Gorongosa National Park (central Mozambique) at the southern end of the EARS, and reconstruct environmental contexts of the fossils. In situ and surface fossils from the lower member of the Mazamba Formation, estimated to be of Miocene age, comprise mammals, reptiles, fishes, invertebrates, palms, and dicot trees. Fossil and geological evidence indicates a coastal-plain paleoenvironmental mosaic of riverine forest/woodland and estuarine habitats that represent the first coastal biomes identified in the Neogene EARS context. Receiving continental sediment from source terranes west of today's Urema Graben, estuarine sequences accumulated prior to rifting as compound incised-valley fills on a low-gradient coastal plain following transgression. Modern environmental analogues are extremely productive habitats for marine and terrestrial fauna, including primates. Thus, our discoveries raise the possibility that the Miocene coastal landscapes of Gorongosa were ecologically-favorable habitats for primates, providing relatively stable maritime climate and ecosystem conditions, year-round freshwater availability, and food both from terrestrial and marine sources. The emerging fossil record from Gorongosa is beginning to fill an important gap in the paleobiogeography of Africa as no fossil sites of Neogene age have previously been reported from the southernmost part of the EARS. Furthermore, this unique window into past continentalmargin ecosystems of central Mozambique may allow us to test key paleobiogeographic hypotheses during critical periods of primate evolution.

No abstract

Trophic position is a fundamental characteristic of animals, yet it is unknown in many extinct species. In this study, we ground-truth the 15 N/ 14 N ratio of enameloid-bound organic matter (δ 15 N EB ) as a trophic level proxy by comparison to dentin collagen δ 15 N and apply this method to the fossil record to reconstruct the trophic level of the megatooth sharks (genus Otodus ). These sharks evolved in the Cenozoic, culminating in Otodus megalodon , a shark with a maximum body size of more than 15 m, which went extinct 3.5 million years ago. Very high δ 15 N EB values (22.9 ± 4.4‰) of O. megalodon from the Miocene and Pliocene show that it occupied a higher trophic level than is known for any marine species, extinct or extant. δ 15 N EB also indicates a dietary shift in sharks of the megatooth lineage as they evolved toward the gigantic O. megalodon , with the highest trophic level apparently reached earlier than peak size.

It is well known that a subtle nonlinearity can occur during clumped isotope analysis of CO2 that - if remaining unaddressed - limits accuracy. The nonlinearity is induced by a negative background on the m/z 47 ion Faraday cup, whose magnitude is correlated with the intensity of the m/z 44 ion beam. The origin of the negative background remains unclear, but is possibly due to secondary electrons. Usually, CO2 gases of distinct bulk isotopic compositions are equilibrated at 1000 °C and measured along with the samples in order to be able to correct for this effect. Alternatively, measured m/z 47 beam intensities can be corrected for the contribution of secondary electrons after monitoring how the negative background on m/z 47 evolves with the intensity of the m/z 44 ion beam. The latter correction procedure seems to work well if the m/z 44 cup exhibits a wider slit width than the m/z 47 cup. Here we show that the negative m/z 47 background affects precision of dual inlet-based clumped isotope measurements of CO2 unless raw m/z 47 intensities are directly corrected for the contribution of secondary electrons. Moreover, inaccurate results can be obtained even if the heated gas approach is used to correct for the observed nonlinearity. The impact of the negative background on accuracy and precision arises from small imbalances in m/z 44 ion beam intensities between reference and sample CO2 measurements. It becomes the more significant the larger the relative contribution of secondary electrons to the m/z 47 signal is and the higher the flux rate of CO2 into the ion source is set. These problems can be overcome by correcting the measured m/z 47 ion beam intensities of sample and reference gas for the contributions deriving from secondary electrons after scaling these contributions to the intensities of the corresponding m/z 49 ion beams. Accuracy and precision of this correction are demonstrated by clumped isotope analysis of three internal carbonate standards. The proposed correction scheme can be easily applied if the slit width of the m/z 49 Faraday cup is bigger than that of the m/z 47 cup.

AI Ca Lotus White dover KEY WORDSMn N Nodulation P Pasture legumes Root morphology Soil pH SUMMARY Effects of increasing rates of lime (0, 900, 1725, and 3000 kg Ca(OH)ffha producing soil pH of 4.0, 4.7, 5.1 and 5.6) and P (50, 150, 250 and 350 kg P/ha) on top and root yield, root morphology and chemical composition of lotus (Lotus pedunculatus Cav.) and white clover (Trifolium repens L.), were studied, using an acid soil in a greenhouse experiment.Increasing rates of applied lime and phosphate resulted in substantial increases in top yields of both species but concomitant increases in root yield were small. In the unlimed soil, lotus out-yielded (tops and roots) white clover at all P levels. However, in the three limed treatments, white clover clearly outyielded lotus. Yield response curves to applied P levelled offat the two highest lime rates for lotus but not for white dover.Nodulation and N content of white clover increased significantly with increasing lime applications, but for lotus there was a significant decrease in nodulation at the highest lime rate. Increased P rates had a small stimulatory effect on nodutation in both species.Of the total root weight, the percentage contribution of the tap and primary lateral root fractions was smaller and that of the secondary plus tertiary lateral roots was greater for lotus than for white clover although root length per unit weight tended to be larger for white dover at the two highest lime rates. Furthermore, lotus possessed longer and more numerous root hairs than white clover. Lime applications significantly decreased the percentage contribution of the tap and primary lateral roots to the total root weight and increased the percentage contribution of the secondary plus tertiary lateral roots.A1 and Mn contents of tops and roots of both species decreased with increasing lime rates. There was a highly significant negative correlation between relative yield and AI content of lotus and white clover tops. In comparison with the limed treatments, in the unlimed treatments a greater percentage of total P, AI, Mn and N content accumulated in the roots of both species. In addition, lotus accumulated a much greater percentage AI in its roots than white clover. 241Plant and Soil 62, 241-254 (1981).

No abstract