bluuebunny/crossref_metadata_2025_split huggingface dataset:
Timing of environmental change in Caribbean shallow waters relative to the closure of the Tropical American Seaway: evidence from benthic foraminifera
Authors: Collins Laurel S. 
Published: January 2018

The most significant change in Pliocene oceanic circulation resulted from closure of the Tropical American Seaway between the Caribbean Sea and Eastern Pacific Ocean around 3 Ma. Faunal changes in Caribbean shallow-water marine organisms such as mollusks and corals have been attributed to possible environmental changes associated with this event, including cyclical cooling, initiation of a carbonate regime in the southern Caribbean, and upwelling of deeper waters on the continental shelf, but their occurrences and timing have been unclear.This study uses the ecological and evolutionary record of benthic foraminifera of the upper continental slope to inner continental shelf to investigate environmental change in Caribbean shallow waters with respect to final closure of the interoceanic seaway. Benthic foraminifera are useful as environmental indicators so periods of increased taxonomic turnover should correspond to times of environmental change. Over 100 species commonly occurring in deposits of Caribbean Panama and Costa Rica dated from 6.5 to 1.6 m.y. were taxonomically standardized with existing literature and collections to produce stratigraphic ranges within the Caribbean region.Although an average common species has lived from Early Miocene times until today, an increase in first appearances suggests that an interval of ecological restructuring occurred on the continental shelf to upper slope in latest Miocene time. The last 15 m.y. includes about 45% of the first and last appearances, 70% of which are comparably dated in other Caribbean strata. For the period from 15 to 3 Ma, about 75% of first appearances occurred between 7 and 3 Ma, and more than twice as many occurred between 7 and 5 Ma as occurred before or after that interval. Comparable numbers of continental shelf and slope taxa have first occurrences between 7 and 5 Ma, indicating a general change on the continental shelf to upper slope in the latest Miocene which preceded closure of the interoceanic seaway by 2 to 4 m.y. Few extinctions occurred in the last 7 m.y.; 86% of the common taxa less than 7 m.y. old in Panama and Costa Rica have survived to the present. The appearance of carbonate-loving species in Panama to Costa Rica at 4.6–5.0 Ma and northern Colombia by 5.0 Ma indicates a well established carbonate regime in the southern Caribbean by earliest Pliocene time. Benthic foraminiferal assemblages show no evidence of upwelling in the Panama-Costa Rican region through the Pliocene.The Late Miocene environmental changes in shallow Caribbean waters preceded isotopic changes in open-ocean surface waters that occurred 4 to 3 Ma. Ecological restructuring took place in the latest Miocene, several m.y. before the seaway closed, and any subsequent environmental changes had little effect on benthic foraminifera of the Caribbean continental shelf.
Biostratigraphic investigations help evaluation of the ground-water-flow system near the Savannah River Site, Georgia and South Carolina
Authors: Edwards Lucy E. , Clarke John S. 
Published: January 2018

The Savannah River Site (SRS) has produced and disposed of a variety of potentially hazardous materials since the early 1950's; as a result, ground water is contaminated at several locations on the site. In 1991, the U.S. Geological Survey, in cooperation with the U.S. Department of Energy and the Georgia Department of Natural Resources, began a 6-year study to determine if ground water is flowing from aquifers in South Carolina beneath the Savannah River and into aquifers in Georgia and, if not, under what conditions such flow could occur. A conceptual model based on physical data and a digital ground-water-flow model will be developed to better understand the ground-water-flow system in the study area. Biostratigraphic interpretations will be used to help define the hydrogeologic framework for the conceptual and digital models.The SRS is located in the South Carolina Coastal Plain on the eastern side of the Savannah River, approximately 100 miles upriver from the Atlantic Ocean. In this area, aquifers of Late Cretaceous and Tertiary age are recharged by precipitation. The age and stratigraphic correlation of sediments in the study area have been controversial because existing fossil evidence is sparse, lithologies of adjacent units are commonly similar, and facies changes occur in relatively short distances. These three factors have also complicated understanding of the ground-water-flow system, because clay and silt confining units are more discontinuous updip; therefore identification of ground-water flow paths and delineation of aquifers and confining units are difficult. Detailed biostratigraphy, using marine and nonmarine fossils, is essential to understanding the depositional history of the region and to determining the complex three-dimensional relations of stratigraphic and hydrogeologic units needed for accurate conceptual and ground-water-flow models.Development of the hydrogeologic framework will require data on the geologic, hydrologic, and water-quality characteristics of coastal plain sediments. To provide these data, clusters of seven to ten wells will be constructed at each of seven sites. At each site, a continuous core will be collected from land surface to basement rock, and monitor wells will be installed in each water-bearing zone. The first three cluster sites are located in Georgia along an updip-downdip transect parallel to the Savannah River. The southernmost of the three sites will serve as a biostratigraphic and lithostratigraphic reference section because it will have the thickest section of sediments and will contain marine facies in which a greater abundance of fossil evidence can be expected. Paleoenvironmental data will help predict the continuity of confining units between cluster sites.
Paleoecological affinities of selected Miocene megafossil taxa from the northern intermountain region based on palynological modeling
Authors: Fields Patrick F. , Taggart Ralph E. 
Published: January 2018

Palynological analysis of stratigraphically-controlled samples from a number of localities in the Succor Creek area of the Oregon-Idaho boundary, the Stinking Water flora of eastern Oregon, and the Trapper Creek flora of southern Idaho has proved to be a valuable interpretive tool in the study of these mid-Miocene plant assemblages. Models derived from analysis of the Succor Creek data suggest: 1) paleotopographic trends, 2) patterns of distribution of major forest elements, 3) the role of disturbance and succession, and 4) limits for paleoclimatic reconstruction. These have proved consistent with patterns of megafossil representation at Succor Creek and both megafossil and palynological data at Stinking Water and Trapper Creek. Such models also appear useful in the refinement of ecological affinities of a number of megafossil taxa which occur in these and other Neogene assemblages throughout the northern Intermountain region.Some taxa are quite specific in their affinities, both in terms of vegetational maturity and elevational zonation. Species of Abies, Picea, Pseudotsuga, Thuja and Tsuga appear characteristic of ecologically mature forests at somewhat higher elevations. Such forests are rare at Stinking Water, are best developed in the southern part of the Succor Creek region, and represent the “climax” forests at Trapper Creek. In contrast, broad-leaved taxa, including species of Castanea, Castanopsis, Nyssa, and most Quercus, are reliable indicators of ecologically mature, lower elevation forests.The ecological significance of a number of mixed-mesophytic taxa, including species of Carya, Juglans, Liquidambar, Pterocarya, Sassafras, Tilia, Ulmus, and Zelkova, is ambiguous. Broad-leaved deciduous assemblages dominated by these plants occur as mid-seral recovery stages over a wide range of elevation from lowlands to higher slopes. Ecologically mature forests of these trees tend to be found only at intermediate elevations. At lower elevations they are largely, but not exclusively, replaced in later seral stages by the ecologically mature, low-elevation taxa noted previously; while at higher elevations they are replaced by conifers.Some taxa, most notably Equisetum, Glyptostrobus, Osmunda, and Typha are restricted to very wet habitats, irrespective of elevation. The shade-intolerant Typha forms ephemeral marshes that are rapidly replaced by Glyptostrobus swamps. Lake margins (and riparian settings), over a wide elevational gradient, are characterized by thickets of Acer, Alnus, Arbutus, Populus, Quercus simulata, “Quercus” eoprinus, and Salix. Locally Sequoia occurs in upland settings (i.e. at Payette, Idaho), while Glyptostrobus is more common in lowlands (Stinking Water and northern Succor Creek localities), but can occur in lower frequencies at any paleoelevation. Some taxa, such as Acer medianum appear to be characteristic of mid-seral recovery stages in these wet habitats.
Early morphological diversity in blastozoan echinoderms
Authors: Foote Mike 
Published: January 2018

Morphological diversity (MD) is important for understanding a clade's evolution and for comparing clades to discover evolutionary laws. As the scale of analysis (taxonomic rank) increases, defining a morphological space becomes less tractable, and assessing MD becomes more difficult. Continuous morphometric variables are hard to define for very disparate species, but morphological dissimilarity can be assessed by discrete characters. I use this approach to document the history of MD in the echinoderm subphlylum Blastozoa.About 60 discrete characters were defined, relating to: arrangement and number of thecal plates; shape and symmetry of theca; number, arrangement, form, and plating of ambulacra; arrangement, form, and plating of brachioles; form and plating of attachment structure; nature of respiratory structures; and position of mouth and anus. Character difference for binary and unordered multistate characters is 0 for matches and 1 for mismatches. Ordered multistate characters were scaled so that the maximum character difference was unity. Pairwise dissimilarity between species was measured by the mean character difference. MD in a stratigraphic interval was measured by the mean pairwise dissimilarity among species. Over half of all described genera were represented. MD involves not only the origin of new character states but also the maintenance of primitive states in a clade; therefore, assessment of MD was deliberately not restricted to analysis of novelties! The figures below compare MD to generic diversity based on the Treatise and post-Treatise monographs.Debate persists about the nature and extent of early echinoderm diversification. Most pertinent to this debate, MD in the Cambrian and Lower Ordovician is extremely high compared to taxonomic diversity; there are few taxa sparsely occupying much morphospace. Analysis of clade-shape statistics indicates that the blastozoan clade is bottom-heavy in both aspects of diversity, but more so with respect to MD. The results overall are not sensitive to the details of the time scale, the inclusion of problematic forms, or the number of characters used. The general picture agrees with that advocated by Sprinkle (among others) for the echinoderms as a whole.
The origins and Paleogene history of modern plant communities
Authors: Greenwood David R. , Collinson Margaret E. 
Published: January 2018

Modern plant communities define global Biomes by their structure, floristics and physiognomy. The modern distribution and character of plant communities is determined by climate, large-scale biotic interactions and abiotic factors such as fire and other disturbance history. Biogeographic patterns also reflect past continental movements, dispersal, extinction and speciation events. The past distribution and history of the principal modern plant communities can be traced using key taxa and associations of taxa, and the foliar physiognomy of the biomal communities.The antecedents of many modern types of vegetation can be found in the mixed plant communities of the Cretaceous and earlier. Late Cretaceous angiosperm radiation and K/T extinctions substantially altered these plant communities, setting preconditions for subsequent evolution and the floristic character of terrestrial plant communities. Paleocene vegetation appears intermediate, and the main phase of floristic modernisation appears to have been during the Eocene.Tropical rainforests and deciduous forests of a modern aspect are well represented in Eocene macrofloras at middle and higher palaeolatitudes respectively, in North America, Europe and Australia. These forests partly reflected present day phytogeographic provincialism but many taxa exhibited past cosmopolitanism, having much reduced modern ranges. The presence of “tropical” forests at middle latitudes, well outside their present day latitudinal extent, reflects the Early to Middle Eocene thermal maximum with widespread equable, humid and subhumid climates. At higher latitudes macrofloras reflect deciduous angiosperm vegetation of lower diversity than the middle latitude rainforests. Deciduousness in these forests was probably an adaptation to seasonal darkness beyond the palaeo-Arctic circle, but at intermediate latitudes may have reflected adaptation to greater temperature seasonality. Coniferous forests are represented in Eocene macrofloras from high latitudes and from uplands in the middle latitudes. Grasses are present in some Eocene macrofloras, but grasslands do not appear in the fossil record until the Oligocene or later. They seem to be a response to climatic deterioration and an evolving mammalian biota. Forested and herbaceous wetland communities may have been more diverse and latitudinally more uniform in the Palaeogene than today, but are otherwise quite modern. Post Oligocene history of most plant communities is that of climate altered distribution and floristic extinction.
Comparative paleoecology of Paleogene and Neogene mammalian faunas: guild structure and diversity
Authors: Gunnell Gregg F. , Gingerich Philip D. , Morgan Michele E. , Maas Mary 
Published: January 2018

We examined guild structure and diversity in the mammalian biota of the Paleogene of Wyoming and Montana and the Neogene of Pakistan. Trophic structure was measured as frequency of generic diversity in each of the following trophic categories: insectivore, omnivore, frugivore, herbivore, and carnivore. Trophic categories were inferred from dental morphology.Results are summarized below (see graphs). In Wyoming/Montana, the Paleocene is dominated by herbivores (from the orders Condylarthra, Multituberculata, and Pantodonta) and insectivores (“Proteutheria” and Proprimates). In the early Eocene, herbivores (Perissodactyla, Artiodactyla, and Rodentia), carnivores (Carnivora, Creodonta, and Mesonychia), and insectivores (“Proteutheria,” Proprimates, and Primates) dominate. At the beginning of the Eocene, carnivores and insectivores are more diverse than herbivores, but later, herbivores are more diverse. Adapid primates become an important frugivore element in the early Eocene. Herbivores are the most common group throughout the sequence, ranging from 30% to 75% of all specimens.In the Siwaliks, herbivores (from Proboscidea, Rodentia, Perissodactyla, and Artiodactyla) dominate in generic diversity (70–80%), with artiodactyls consistently representing about 50% of herbivore genera. Circa 16 Ma, rodents appear and become an important herbivore group. At 14 Ma, bovid diversity increases dramatically. Specialized browsers (tragulids, giraffids) and grazers (suids) represent 25% to 35% of herbivore diversity throughout the sequence. Carnivores, represented by creodonts and true carnivores, range from 5% to 20% of generic diversity in the Siwaliks. At 11 Ma, carnivores increase in generic diversity with amphicyonid and hyaenid carnivores dominating the guild. Carnivores and insectivores are never as diverse in the Siwaliks as they are in the early Eocene of North America.
Devonian bryozoan extinction and diversification
Authors: Horowitz Alan S. , Pachut Joseph F. 
Published: January 2018

The names proposed world-wide for Devonian bryozoans have been evaluated with respect to replaced names, synonyms, and nomina dubia [Horowitz and Pachut (1993), Journal of Paleontology, in press]. The resulting list contains 1738 specific names assigned to 199 genera in 45 families. Approximately 75% of Devonian bryozoan species are reported from a single stage. Not more than 10%, and usually 4–6%, of the species reported in any Devonian stage are also reported in the succeeding stage.The largest decrease in observed bryozoan diversity occurs between the Givetian and Frasnian stages, reducing the number of species by 77%, genera by 64%, and families by 42%. These values are less than those reported for the range-through method for the entire fauna of the Permian mass extinction (Raup, 1979) but larger than percentage extinctions (presumably based on range-though data) for four other Phanerozoic mass extinctions tabulated by Valentine and Walker (1987).The range-through method dampens the observed differences in taxonomic diversity among Devonian stages at all taxonomic levels. The range-through number of species/stage is based upon both direct applications of the range-through method and on the assignment of ranges known only to early, middle and late Devonian to include appropriate Devonian stages. Generic and familial diversity increases monotonically from Lochkovian through Givetian stages. Thereafter (Givetian to Frasnian), range-through values for specific (69%), generic (31%), and familial diversity (10%) decrease. Specific and familial decreases across the Givetian-Frasnian boundary are comparable to those reported for non-Permian mass extinctions by Valentine and Walker, but the generic decrease is not as great. These results are consistent with Valentine and Walker's random mass extinction model.Observed bryozoan diversity across the Frasnian-Famennian boundary increases while values calculated using the range-through method decrease by approximately 5–15%. This does not suggest a major bryozoan extinction event. Conversely, the decrease in bryozoan diversity across the Givetian-Frasnian interval is similar to an important Devonian extinction among rugose corals. The reason(s) for these extinctions is not yet clear. With respect to Devonian bryozoans, our inadequate understanding of the cause(s) of mass extinctions and the relatively coarse resolution of the stadial timescale does not permit differentiating between gradual or catastrophic scenarios.
Nothing new under the sun? Tropical vs. temperate patterns in the biogeography of evolutionary innovation
Authors: Jablonski David 
Published: January 2018

Evolutionary novelties do not originate randomly in time and space, but geographic patterns have not been investigated systematically. The present-day latitudinal diversity gradient, manifest at many taxonomic levels, has been taken to suggest that most evolutionary novelties originate in the tropics, but differential extinction could have been as important as differential origination in the accumulation of taxa at low latitudes. Further, a clade's Recent diversity pattern need not reflect its initial geographic distribution. For example, several marine genera that are widespread or mainly tropical today have their oldest representatives recorded as fossils in high paleolatitudes. Are the tropics, in Stenseth's words, a cradle or a museum?The question requires an empirical analysis of the fossil record, but preservation and sampling are highly uneven across the globe over the Phanerozoic. As a first attempt to detect robust patterns, I compared the geographic distribution of the 26 post-Paleozoic marine invertebrate orders having high preservation potential to two datasets likely to reflect preservation and sampling bias (Jablonski and Bottjer 1991): (a) first occurrences of poorly preserved orders (having flimsy or easily disarticulated skeletons, e.g. notaspidean gastropods and comatulid crinoids, n = 16), and (b) all published records of Triassic-Bajocian echinoids (n = 887, first third of Paleozoic-time, with most ordinal originations). First occurrences of well-preserved orders were evenly distributed above and below 30° absolute paleolatitude, contrasting significantly with the poorly preserved orders, which are predominantly extra-tropical in first occurrences (p 0.001, G test). Despite the much more intense collecting and description of fossils at higher paleolatitudes, the Triassic-Bajocian peak in the first occurrence of well-preserved orders falls below 30° paleolatitude, significantly different from the contemporaneous echinoid records, which do appear to reflect collecting intensity (p< 0.005, G test; p < 0.05 for frequency distributions using 10° blocks, Kolmogorov-Smirnov test). The difference increases if the echinoid superorder Microstomata (which contains primitive taxa bearing novelties related to an important shift to deposit-feeding, but not assignable to any presently recognized order) is used instead of its oldest named order, the Cassiduloida; and remains significant if the Lower Triassic is ignored owing to especially poor sampling (p < 0.02). Low paleolatitudes, then, contain significantly more first occurrences of marine invertebrate orders than would be expected from a null hypothesis of sampling and preservation: major novelties appear to have originated preferentially in the tropics. Still unknown is whether the tropics have a higher per-taxon rate of novelty production, but the apparent discordance between within-habitat diversity and ordinal origination along bathymetric gradients sugqests that a simple probabilistic explanation may be inappropriate.