bluuebunny/crossref_metadata_2025_split huggingface dataset:
Phenotypic evolution in a lineage of the Eocene ostracod Echinocythereis
Authors: Reyment Richard A. 
Published: July 2016

Two speciation events occurred in the Eocene lineage beginning with Echinocythereis isabenana Oertli (Aragon, Spain). After a long period of stasis in ornament and shape/size, this species underwent a relatively rapid decrease in size, accompanied by ornamental changes. The transition required about 30,000 yr. The new species E. aragonensis Oertli is significantly smaller (20% decrease in size). The lateral papillation is denser and less regular, the papillae being significantly smaller than in the ancestral form. This ornament gradually yields to increasing frequencies of individuals with reduced papillae superimposed on a progressively better developed network of filaments. This change, which is regionally valid, is ultimately replaced by fully expressed reticulations, on which minute pustules may occur; this development typifies the third species, E. posterior Oertli. Some ornamental characteristics of E. aragonensis are anticipated in rare individuals of E. isabenana. Ornamental features of E. posterior appear in late larvae of E. isabenana. Generally, E. aragonensis and E. posterior do not differ significantly in size. A trend toward smaller carapaces in the upper samples of E. posterior could be related to ecophenotypic effects.All species are highly polymorphic for both shape and ornament; the morphs are not sharply bounded and are mostly of uncertain evolutionary status. The transition from isabenana to aragonensis is heralded by a sharp rise in the coefficient of variation for length measures of the carapace. There is a pronounced multivariate morphometric discontinuity between isabenana and the descendant forms, which are largely multivariately homogeneous. The isabenana-aragonensis transition could have occurred by selection or by random genetic drift. Both models can be accommodated by the data; however, the weight of evidence favors the former hypothesis. Evolution in the Echinocythereis lineage seems to have occurred by two different mechanisms. The first transition was rather rapid, with many disjunct features. The second was slow, the changes being more of degree than of kind.
The enigmatic Ediacaran (late Precambrian) genusRangeaand related forms
Authors: Jenkins Richard J. F. 
Published: July 2016

The late Precambrian genusRangeaGürich, 1929, a frond-like fossil composed of repeated foliate elements, is one of the first discovered forms belonging to the now widely known soft-bodied assemblages characterizing the Ediacaran Period.Rangeaoccurs together with the generaPteridiniumGürich, 1933, andErniettaPflug, 1966, in the lower parts of the Nama Group, Namibia (South West Africa).Investigation of the preservation and structure ofRangea, utilizing a methodology similar to that established by Wade (1968, 1971), indicates that it was probably a colonial octocoral consisting of a large tapering primary polyp, or oozoid, and a number of leaf-shaped, conjoined fronds which bore the feeding polyps; it is suggested to belong to a group of early Ediacaran anthozoans which provide a fossil link between the still living Telestacea and Pennatulacea. Similar investigations ofPteridiniumandErniettadisclose that their structure is different fromRangeaand does not support ideas that they are related to it.
Prolonged stability in local populations of Cerion agassizi (Pleistocene-Recent) on Great Bahama Bank
Authors: Gould Stephen Jay 
Published: July 2016

Long-term persistence of patterns in geographic variation within species is an interesting and puzzling phenomenon. I present a well-defined natural experiment in the land snail Cerion agassizi from the islands of Great Bahama Bank. C. agassizi is the best-known fossil of the ca. 120,000 years BP dunes of New Providence, Cat and Eleuthera Islands; populations have survived on Cat and Eleuthera. During the Wisconsin glacial advance, all these islands joined together in an emergent bank. Presence of the same species on two islands at two times permits a test for both time signatures (does change occur in the same manner on both islands) and island signatures (do aspects of shell phenotypes remain constant on each island through time).Factor and discriminant analyses establish morphological separations among fossil populations of the three islands. These differences occur along pathways specified by well-known covariance sets in the complex allometric ontogeny of Cerion. By these routes, small variations in the geometry of growth may be magnified to large differences in external appearance. I found a time signature, probably attributable to introgression of modern populations by Cerion glans on both Cat and Eleuthera. Despite the intermediate period of emergence and joining of all islands, I also found an island signature in the preservation through time, on both Cat and Eleuthera, of the differentia that separate fossil populations. The basic distinctions of the two islands, expressed as patterns of covariance in growth, have been stable for at least 120,000 years.
The role of anoxia in the decay and mineralization of proteinaceous macro-fossils
Authors: Allison Peter A. 
Published: July 2016

Actualistic experiments have quantified rate of anaerobic decay and associated mineralization around proteinaceous macro-organisms. Carcasses of the polychaete wormNereisand the eumalacostracansNephropsandPalaemonwere buried in airtight glass jars filled with sediment and water from marine, brackish, and lacustrine environments. Over a period of 25 weeks the contents were examined to determine the state of decay and were chemically analyzed to monitor early diagenetic mineralization (two methods for such analysis are reviewed). Decay processes were active in the experimental conditions despite anoxia and had virtually destroyed the carcasses within 25 weeks. However, decay-rate in the sulfate-reducing marine system was greater than in the methanogenic freshwater environments. Petrological and geochemical analyses of the organic remains identified discrete layers of authigenic iron monosulfide (a pyrite precursor) on the surface of the decayingNephropscuticle within weeks of initiating the experiment. Chemical analysis of decomposing flesh showed a marked increase in pore-water calcium content with time.The results clearly show that anoxia is ineffective as a long-term conservation medium in the preservation of soft-bodied fossils. However, decay-induced mineralization can be very rapid so that even a slight reduction in decay rate can lead to improved levels of fossil preservation. Traditionally, stagnation and rapid burial are considered to be the main prerequisites for the preservation of soft-bodied fossils and the formation ofKonservat-Lagerstätten. Clearly these factors are only important in that they promote early diagenetic mineralization. This is the only way to halt information loss through decay.
Swimming capabilities of Mesozoic marine reptiles: implications for method of predation
Authors: Massare Judy A. 
Published: July 2016

Body shape and mode of swimming were major factors that affected the swimming capabilities of Mesozoic marine reptiles. By estimating the total drag and the amount of energy available through metabolism, the maximum sustained swimming speed was calculated for 115 marine reptile specimens. Calculated sustained swimming speeds range from 1.8 to 2.7 m/sec, but are probably too high by as much as a factor of two. Mesozoic marine reptiles were probably much slower than modern toothed whales. The diversification of fast, agile teleost fish in the Cretaceous may have therefore contributed to the decline of the marine reptiles.Long-bodied reptiles appear to have had slower sustained swimming speeds than deep-bodied forms of the same length. For a given length, ichthyosaurs were probably faster sustained swimmers than plesiosaurs, and plesiosaurs were probably faster sustained swimmers than crocodiles and mosasaurs. This suggests that the long-bodied forms probably used an ambush technique to capture prey, to maximize the range of possible prey and to minimize competition with the faster pursuit predators.
Macroevolutionary differences between the two major clades of Neogene planktonic foraminifera
Authors: Stanley Steven M. , Wetmore Karen L. , Kennett James P. 
Published: July 2016

Being of especially high quality, the Neogene fossil record of planktonic foraminifera offers special opportunities for assessing patterns of extinction and speciation. A variety of metrics indicates that within this group the mean duration of lineages has been much shorter (rate of extinction has been higher) for the globorotaliid clade than for the globigerinid clade. Furthermore, in the globorotaliid clade rates of extinction and speciation have not been closely linked to changes in diversity, but rather have been relatively high even at times when diversity has undergone little change. Thus, the globorotaliid clade has undergone more rapid evolutionary turnover than the globigerinid clade. Data for living species reveal that neither geographic range nor temperature tolerance is the primary factor controlling lineage duration. On the other hand, there is evidence that lineages marked by low abundance (small population size) are relatively short-lived. The reason that globorotaliid lineages have generally survived for shorter intervals, on the average, may be that their populations have been less abundant and less stable. Usually they live deeper in the water column, where food is often sparse, and many flourish only in areas of upwelling. Furthermore, the globorotaliids lack symbiotic algae for nutritional support. The same ecological factors may have accelerated speciation in the globorotaliid clade, by causing species to be patchily distributed. Thus, population size and structure have been more important than geographic range in determining rates of extinction and speciation. This parallels the situation for Neogene marine bivalves.For planktonic foraminifera, as for Western Atlantic Bivalvia, the normal pattern of extinction was reversed in late Pliocene time, apparently in response to climatic cooling. The globigerinids suffered a sudden pulse of extinction. The deeper dwelling globorotaliids fared better; probably many of their species benefited from elevation of the seasonal thermocline into the photic zone. At the same time, rate of speciation declined in the globorotaliid clade, which supports the idea, inferred from the evolutionary history of marine bivalves, that an increase in the size and stability of populations should depress both rate of extinction and rate of speciation.
Interpreting the diet of extinct ruminants: the case of a non-browsing giraffid
Authors: Solounias Nikos , Teaford Mark , Walker Alan 
Published: July 2016

Modern ruminant species have traditionally been placed in three broad dietary categories (browsers, grazers and intermediates) based on their observed feeding habits. Shape analysis of premaxillary outlines of 31 species of ruminants shows that their premaxillae differ according to their dietary category. Browsers have pointed premaxillae and grazers square ones. Intermediate feeders have intermediate outlines.The Miocene giraffidSamotherium boissierihas always been viewed as a specialized browser similar to the modern okapi,Okapia johnstoni. However, the premaxillary shape ofS. boissierifalls very close to the mean of the grazers and is most similar to that of the African buffalo (Syncerus caffer), a committed grazer.Quantitative analyses of the microscopic wear patterns on the molars reveal significant differences between three modern species from the three dietary groups.S. boissierihas more microscopic scratches on its teeth than either the modern giraffeGiraffa camelopardalis(a browser) or Grant's gazelleGazella granti(an intermediate feeder). In this respect, it is indistinguishable from the wildebeestConnochaetes taurinuswhich is a committed grazer.Both of these analyses suggest that this extinct giraffid was a grazer, although we cannot rule out the possibility that it was an intermediate feeder. It was definitely not a specialized browser as are both living members of the Giraffidae.
Real and random patterns associated with molluscan spatial and temporal distributions
Authors: Russell Michael P. , Lindberg David R. 
Published: July 2016

The species-level properties of geographic range and geologic duration are often used as variables in evolutionary studies. However, estimates of species duration are not independent of estimates of geographic range. Before these properties are used in macroevolutionary hypotheses, error associated with these estimates must be quantified. This error may lead to spurious inferences of evolutionary processes. To assess the error associated with estimates of geographic range and geologic duration, we modeled various sampling regimes and calculated the bias associated with these estimates.We present three analyses which document the bias associated with estimates of geographic range and geologic duration. First, we find a positive correlation between local abundance and geographic range for a sample of 180 species of Recent prosobranch gastropods from the northeastern temperate Pacific Ocean. Therefore, geographically short-ranging species are less likely to be represented in the fossil record than geographically long-ranging species because of their local rarity. Second, we demonstrate that the chance of underestimating the geographic range of a species is acute for species with restricted spatial distributions, further compounding the problem of documenting their distribution in space and time. Third, we present a simulation which quantifies the degree of autocorrelation between geographic range and geologic duration for different levels of sampling resolution and spatial distributions of fossil localities.
Phyletic gradualism and punctuated equilibrium in the late Neogene planktonic foraminiferal clade Globoconella
Authors: Wei Kuo-Yen , Kennett James P. 
Published: July 2016

Substantial geographic coverage in paleontological study is essential in testing evolutionary models of phyletic gradualism and punctuated equilibrium. We present a multivariate morphometric study of the late Neogene planktonic foraminiferal clade Globoconella using specimens from four Deep Sea Drilling Project sites (DSDP 284, 207A, 208, and 588) along a latitudinal traverse in the southwest Pacific.During the Late Miocene (7 Ma to 5 Ma), populations of the ancestral species Globorotalia (Globoconella) conomiozea formed a geographic cline showing continuous morphological variation from the temperate sites (DSDP 284 and 207A) to the warm subtropical sites (DSDP 208 and 588). Populations living to the south had higher conical angle and fewer chambers in the final whorl compared to the northern populations. Nevertheless, populations across the entire cline exhibited a coherent, directional trend towards having larger conical angle and fewer chambers through time. At the Miocene/Pliocene boundary, the intensification of the Tasman Front (Subtropical Divergence) possibly isolated the peripheral populations in the warm subtropics from the central stocks of the temperate water masses. The evolutionary trends became decoupled: the central populations gradually lost their keel and transformed into G. (G.) sphericomiozea, while the peripheral populations in the warm subtropical areas retained their keel and evolved into a flattened species, G. (G.) pliozea.The gradual transformation of G. (G.) conomiozea terminalis (a form retaining a keel) into G. (G.) sphericomiozea (a form lacking a keel) occurred during an interval of about 0.2 m.y., with all measured morphologic variables showing continuous and steady changes. The evolution of the central populations follows the model of phyletic gradualism. In peripheral populations, the origin of the descendant species G. (G.) pliozea from the ancestor G. (G.) conomiozea terminalis occurred very rapidly within an interval of less than 0.01 m.y. The population size of G. (G.) pliozea was small at the incipient stage at about 5.05 Ma, but increased rapidly to become dominant during the next 0.2 m.y. when the ancestral species G. (G.) conomiozea terminalis became locally extinct. Following speciation, G. (G.) pliozea exhibited morphological stasis for about 0.6 m.y., until the central stock form G. (G.) puncticulata migrated back to the warm subtropics; during the next 0.5 m.y. of their sympatry, there is no sign of hybridization between these two sister species. The evolution of G. (G.) pliozea follows the model of punctuated equilibrium.The evolution of the Globoconella clade shows both phyletic gradualism and punctuated equilibrium. These two “alternative” evolutionary models complement each other rather than being mutually exclusive. Both models are indispensable towards providing a complete picture of the evolution of Globoconella.
The reflection of deciduous forest communities in leaf litter: implications for autochthonous litter assemblages from the fossil record
Authors: Burnham Robyn J. , Wing Scott L. , Parker Geoffrey G. 
Published: July 2016

To assess the degree to which forest litter reflects the source forest, three 1-ha plots of temperate deciduous forest were mapped and litter accumulating in these forests was sampled. Identity, position, and diameter of all stems 2 cm or larger diameter at breast height are known for each forest. Composition of the leaf litter is governed by two key factors: (1) abscised leaves are deposited primarily on the forest floor directly underneath the canopy that produced them, and (2) the leaf mass of a species is highly correlated with its stem cross-sectional area. These factors produce autochthonous litter samples that correspond closely in composition to the forest within a circle of canopy-height radius or less. Even relatively small litter samples (350 leaves) consistently contained all the common species in the local area. However, the rarer tree species were seldom recovered in the litter samples. Correlation coefficients for litter mass and basal area by species are typically over .80.These observations have three important implications for interpreting autochthonous compression-fossil assemblages. First, approximate relative abundances of locally dominant and subdominant forest taxa can be obtained from relatively small samples of autochthonous compression-fossil assemblages. Second, representation of rare forest species, even in large fossil samples, will be fortuitous. For this reason, complete species lists and consistent estimates of richness cannot be derived directly from most existing samples of autochthonous compression-fossil assemblages. Third, the strong tendency for leaves to fall beneath the canopy of the tree that sheds them suggests that properly sampled autochthonous fossil leaf assemblages may yield information on crown size of individual trees and the spatial distribution of individuals and species, aspects of vegetational structure that have been thought accessible only in well-preserved “fossil forests” with standing trunks.
On the declining extinction and origination rates of fossil taxa
Authors: Pease Craig M. 
Published: July 2016

The per-stage extinction rate is the product of the per-taxon extinction rate and stage length, and the per-stage origination rate is defined similarly. These rates decline from ancient to recent times because of the pull of the Recent, because there is more young than old fossiliferous rock, and because average stage length increases from the recent to the past. More specifically, the present model assumes that the graphs of ln(per-stage extinction rate) and ln(per-stage origination rate) versus geologic time have slope zero in the absence of sampling biases, and shows how sampling biases cause both these graphs to appear to have slope min(h,q) + s in the distant past, where h and q are the fossil loss and actual per-taxon extinction rates, and the stratigraphic constant, s, quantifies how stage length changes through time.Although the per-stage rates of bivalve families and marine invertebrate genera decline toward the recent, the magnitudes of these declines are entirely consistent with what the present model predicts sampling biases will produce. Hence there is no need to postulate a biological explanation for these patterns.
The importance of phylogenetic analysis for the assessment of species turnover: a case history of Paleocene mammals in North America
Authors: Archibald J. David 
Published: July 2016

During the latest Cretaceous and the Paleocene in western North America, disappearance rates for mammalian genera track appearance rates, both reaching their peak in the early Paleocene (Puercan) following the extinction of non-avian dinosaurs. Some of the disappearances during this time were pseudoextinctions that resulted when ancestral species disappeared during speciation.Species-level cladistic analyses and a well-constrained biostratigraphic framework are required to study this form of pseudoextinction. Cladistic analyses show that monophyly cannot be established or rejected for some species because these species lack autapomorphies (uniquely derived character states) that unite their constituent members. Such taxa, termed metaspecies, are potential ancestors to species and higher clades with which they share a node in the cladogram.A hypothetical species-level cladistic analysis coupled with three different hypothetical biostratigraphies shows how different models of speciation (bifurcation, budding, or anagenesis) result in very different patterns of true versus pseudoextinction. Depending on the speciation model, true extinction can be overestimated by as much as a factor of four, raising the specter of mass extinction. Species-level studies for three early Tertiary mammalian taxa—taeniodont eutherians, taeniolabidid multituberculates, and periptychid ungulates—use the same procedures. They show that almost 25% of disappearances during the early Paleocene (Puercan) for species in the analysis were pseudoextinctions of metaspecies. Budding and anagenetic-like peripatric speciation, but not bifurcation, are seen in the three examples.Equating disappearance to true extinction can profoundly affect interpretations of faunal turnover, especially during mass extinctions or major faunal reorganizations. Some authors use pseudoextinction to describe the taxonomic rather than evolutionary disappearance of nonmonophyletic groups. Pseudoextinction, as used here refers only to the evolutionary disappearance of metaspecies via speciation. Both usages seem appropriate but should not be confounded.