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Jackson, MS, United States

Harrell T.L.,University of Alabama | Perez-Huerta A.,University of Alabama | Phillips G.,Mississippi Museum of Natural Science
Cretaceous Research | Year: 2016

Cretaceous strata in Alabama and Mississippi (USA) represent one of the most complete records of shallow marine deposition worldwide for the Upper Cretaceous. The age assignment of these strata in the eastern Gulf Coastal Plain is difficult due to the comparative lack of radiometrically datable beds and sometimes conflicting results of biostratigraphy using different taxonomic groups. Numerical age dating using strontium isotope ratios (87Sr/86Sr) preserved in diagenetically resistant fossil shark tooth enameloid had been proposed by previous researchers as a solution to dating some geologic units. Here we apply this methodology to the whole Upper Cretaceous, using teeth of two fossil shark genera (Scapanorhynchus and Squalicorax) collected from variable facies. Shark teeth collected from a bentonite mine in Monroe County, Mississippi, were also analyzed and compared with the radiometric date of the bentonite layer. Results indicate a strong correlation between stratigraphic position of the fossil teeth and numerical age determination based on 87Sr/86Sr content. Furthermore, this method is equally effective for both of the fossil shark genera analyzed in the study. Because of the nearly uniform distribution of strontium in ocean water, numerical age dating using strontium isotope ratios preserved in fossil shark tooth enameloid can be a useful method to employ in the correlation of marine geological strata on both regional and global scales. © 2016 Elsevier Ltd. Source

Yager L.Y.,Mississippi Museum of Natural Science | Miller D.L.,University of Florida | Jones J.,Mississippi State University
Natural Areas Journal | Year: 2010

If fire affects spread of cogongrass (Imperata cylindrica), a non-native grass that displaces native plants, managers can determine best use of resources to restore and maintain the diverse herbaceous groundcovers of longleaf pine-bluestem (Pinus palustris - Andropogon spp. and Schizachyrium spp.) forests of the southeastern United States. In 2003 and 2004, we measured rates of vegetative encroachment of cogongrass into burned and unburned pine-bluestem and pine-shrub forests one and two years post-burning on Camp Shelby Training Site, Mississippi. Linear growth and tiller production were significantly greater in pine-bluestem forests compared to pine-shrub forests for both time periods. Cogongrass growth was not affected by burning in either forest type one-year post-burning, but was significantly greater in burned forests after two years of growth. Two-years post-burning, mean linear growth of cogongrass was 235 cm in burned pine-bluestem, 139 cm in unburned pine-bluestem, 177 cm in burned pine-shrub, and 92 cm in unburned pine- shrub. Tiller production/m2 for 2004 was greatest in pine-bluestem burned plots and least in pine-shrub unburned plots. Linear growth of cogongrass was significantly and positively correlated to percent cover of adjacent herbaceous vegetation but tiller numbers were significantly and negatively correlated to percent cover of adjacent shrubs. Efforts to restore pine-shrub forests to pine-bluestem forest conditions should implement control of cogongrass before and after use of Are. Vigilant control efforts are needed as restoration shifts conditions to those of pine-bluestem forests and increases susceptibility to cogongrass invasion. Source

Taylor P.D.,Natural History Museum in London | James N.P.,Queens University | Phillips G.,Mississippi Museum of Natural Science
Palaeobiodiversity and Palaeoenvironments | Year: 2014

Different cheilostome bryozoan species construct their skeletons from calcite, aragonite, or a combination of these two minerals. Calcite is the primitive biomineral in cheilostomes, but an increasing number of clades since the Late Cretaceous have evolved the ability to biomineralize aragonite. This change in bryozoan mineralogy paralleled the switchover from calcite to aragonite seas. Here, we provide a first test of whether changing bryozoan biomineralogy can be correlated with a particular calcite to aragonite sea transition by comparing the mineralogical composition of bryozoan assemblages from the Eocene with those from the Early Oligocene, a time of major climatic and oceanographical changes that many believe to be a time of transition. Bryozoan assemblages from deposits in Mississippi and western Alabama preserving skeletal aragonite (as indicated by the occurrence of aragonitic molluscs) were sampled, cleaned, and sorted by species for XRD analysis to determine their mineralogy. The hypothesis that the proportion of species employing aragonite increases from the Eocene into the Oligocene through the transition to aragonite seas is not supported by our data. Among 23 Eocene species, 14 (61 %) were found to be calcitic, 7 (30 %) aragonitic and 2 (9 %) bimineralic, whereas among 28 Oligocene species 19 (68 %) were calcitic, 5 (18 %) aragonitic and 4 (14 %) bimineralic. Possible reasons why the expected mineralogical change is lacking include incorrect dating of the calcite to aragonite sea switchover at the Eocene-Oligocene boundary, the compensating effects of cooling at this time favouring calcite over aragonite biomineralization, or high levels of biological control over their mineralogy by the bryozoans. © 2014 Crown Copyright. Source

Strongin K.,University of South Carolina | Taylor C.M.,Texas Tech University | Roberts M.E.,Mississippi Museum of Natural Science | Neill W.H.,Texas A&M University | Gelwick F.,Texas A&M University
American Midland Naturalist | Year: 2011

The Mississippi silverside (Menidia audens), now common throughout the Tennessee-Tombigbee Waterway (TTW) in Mississippi, apparently invaded this highly modified system from the Tennessee River, concurrent with TTW construction (1972-1985). Subsequent decline in distribution and abundance of the native brook silverside (Labidesthes sicculus) led to speculation that dietary competition with M. audens might be occurring. Therefore, diet data from sympatric and allopatric collections of the two silversides at several sites in TTW were analyzed using multivariate statistics and null models to test for significant dietary differences, overlap and niche shifts potentially attributable to habitat alteration. Diet overlap between the two silversides at sites of co-occurrence was greater than expected under the null model. Moreover, intraspecific food habits did not differ between individuals occurring in sympatry and those occurring in allopatry for either silverside. Thus, significant portions of their diet overlapped and neither species has exhibited dietary shifts that would facilitate coexistence. The two species differed significantly along stream size and current velocity gradients, with M. audens preferring the larger, slower moving habitats of the waterway. Unlike L. sicculus, M. audens included the exotic daphnid Daphnia lumholtzi in its diet. Because M. audens capitalized on a wider variety of prey items in the modified TTW environment and because of their previous interactions in other systems, we conclude that the native silverside, L. sicculus, is likely to be replaced by M. audens in lentic TTW habitats. © 2011, American Midland Naturalist. Source

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