bluuebunny/crossref_metadata_2025 huggingface dataset:
Patterns of evolutionary tempo and mode in the radiation ofMelanopsis(Gastropoda; Melanopsidae)
Authors: Geary Dana H.
Published: July 2016

The Paratethyan basins of eastern Europe and western Asia became isolated from marine influence in the Late Miocene, and were the sites of several remarkable endemic radiations of brackish and freshwater organisms. Here I describe the patterns of tempo and mode before and during the radiation of the gastropodMelanopsisin the Pannonian basin of eastern and central Europe, and I explore the underlying mechanisms of evolutionary change.

The most ancient melanopsid species in this area,M. impressa, was present in freshwater areas marginal to the basin well before the radiation. Widely spaced samples ofM. impressaindicate that this species underwent a period of stasis lasting at least 7 m.y. The end of stasis corresponded with the extinction of the last of the normal marine fauna in the basin, suggesting that the lack of other fauna and/or reduced salinity in the basin permitted expansion of the melanopsids from the basin margins into the basin proper. Stasis ended with the onset of changes in size, shouldering, and ontogeny, which led eventually toM. fossilis. Change occurred over a 2-m.y. interval; a series of intermediates is present for all three characters. Within-sample correlations provide no evidence that the three characters are constructionally linked; instead they appear to be changing independently. The mode of change in theM. impressa–M. fossilislineage appears to have been anagenetic. Alterations in the rate and direction of selection (and/or genetic links between characters) are probably required to explain the overall slowness of the change.

Most Pannonian basin melanopsid species arose by rapid cladogenesis in the Middle Pannonian Stage. Physical factors in the basin probably influenced the timing of this diversification; contrasting patterns of variation and diversity between two melanopsid clades suggest that intrinsic factors influenced the extent of diversification.
Postmortem changes in strength of gastropod shells: evolutionary implications for hermit crabs, snails, and their mutual predators
Authors: LaBarbera Michael , Merz Rachel Ann
Published: July 2016

Calliostoma ligatumshells inhabited by hermit crabs were weaker than shells inhabited by snails collected at the same locality. When shells ofC. ligatumwere loaded repetitively to 80% of their predicted failure load, hermit crab-inhabited shells showed an immediate drop in shell strength followed by a progressive further loss of shell strength over the next 18 days. SnailinhabitedC. ligatumshells exhibited a decrease in strength after 9 days, but returned to initial values within 18 days of loading.

Hermit crabs thus bear shells significantly weaker than they were when borne by the gastropods that produced them. Reported similarities in vulnerability of gastropods and hermit crabs to shell-crushing predators may be artifacts of the metric (critical size) used to compare vulnerabilities. Hermit crabs probably were a significant factor in the diversification of durophagous predators in the Mesozoic, supplying a prey base identical in size and shape to gastropods but with significantly lower resistance to crushing. The unpredictability of strength in hermit-crab inhabited shells may maintain the apparently inefficient indiscriminate attacks common among durophagous predators.
Flight characteristics of Triassic and Jurassic Pterosauria: an appraisal based on wing shape
Authors: Hazlehurst Grant A. , Rayner Jeremy M. V.
Published: July 2016

The mass, wingspan, and wing area of pterosaurs were reconstructed. Mass was estimated by determining volume and multiplying by avian density. This method was considered appropriate only for smaller pterosaur species because there is evidence for lower density in larger species. These reconstructions were used to compare the wing shapes of Triassic and Jurassic pterosaurs with those of birds. Pterosaurs had wings of below-average loading and above-average aspect compared to the avian mean. This wing design was compatible with relatively slow and highly efficient flight, with high maneuverability. Wing area depends on the reconstruction model adopted; wings attached to the hindlimb principally reduced aspect, and secondarily reduced loading, which would improve take-off performance at the expense of efficiency. The wing shape and cranial feeding adaptations of pterosaurs were most compatible with a marine or aerial predatory adaptive zone. The reconstructed pterosaurs show a limited range of wing shape compared to birds. This may partly reflect preservational bias favoring species living in marine or lagoonal environments, but this is not a complete explanation because there is a lack of pterosaurs with wings of high loading like the marine ducks and auks. Structural, physiological, or adaptive factors may have limited pterosaur wing shape.
Patterns of temporal change in single morphological characters of a Miocene stickleback fish
Authors: Bell Michael A. , Baumgartner Jeffrey V. , Olson Everett C.
Published: July 2016

Patterns of temporal variation of six characters in a Miocene stickleback (Gasterosteus doryssus) are presented. Most pairs of characters tend to be correlated, but these correlations account for only about 26% of the observed variation, and thus the characters are studied separately. All character state frequencies exhibit temporal heterogeneity, and their means have temporal trends. Regardless of these overall trends, reversals of the trends cause end members of four time series not to differ significantly from each other. We argue that most observed temporal variation represents intrapopulation evolutionary change. Although most time series have somewhat stepped patterns, complete stasis is absent. Gradual variation is predominant, and in one case is nearly linear, but very rapid evolutionary bursts are also seen. The most rapid stratigraphic change appears to represent a local extinction, followed by recolonization by a differentiated population, but another episode of rapid change probably represents evolution in situ by means of standard neo-Darwinian mechanisms, without involvement of “macromutations” or true saltation. The irregular patterns and great magnitude of phenotypic change that are observed indicate that conventional paleontological samples may miss important evolutionary phenomena and are not comparable to shorter-term evolution in extant populations.
Ontogenetic regulatory mechanisms and evolution of mellitid lunules (Echinoidea, Clypeasteroida)
Authors: Telford Malcolm
Published: July 2016

Lunules have evolved independently in several groups of clypeasteroids, including the Rotulidae, Astriclypeidae, Mellitidae and Scutasteridae. In this paper, only the monophyletic assemblage Monophorasteridae plus Mellitidae is considered. Lunules result from modifications of the growth patterns of test plates which bring about changes in relative growth in specific directions. It is unnecessary to postulate resorption of the test. Ambulacral lunules, which are known to have hydrodynamic functions, originated as part of a series of changes: 1) bifurcation of food grooves, 2) formation of pressure drainage channels, 3) lobulation of the ambitus (as inMonophoraster), 4) complete lunule formation. The anal lunule shares the hydrodynamic function but arose separately, as a developmental aberration. The position of the periproct is highly variable but it is most commonly located at the junction of suture lines, at plate corners. InScutellait is located between the first and second post-basicoronal plates. InMonophorasterthe periproct is located further forward, between the first post-basicoronal plates, and the small anal lunule occupies the junction point between first and second post-basicoronals. It is hypothesized that the anal lunule originated as an all-or-nothing event following the forward migration of the periproct and failure to resume normal plate growth at the sutural junction point between first and second post-basicoronal plates. Its walls were derived from paired interambulacral supports. The hypothesis is discussed in connection with the ontogenetic formation of the anal lunule in living mellitid sand dollars.
Developmental regulation and morphological saltation in the heteromorph ammonite Nipponites
Authors: Okamoto Takashi
Published: July 2016

Nipponites, a Late Cretaceous nostoceratid ammonite, shows a peculiar meandering shell growth in the middle-late stage. Assuming neutral buoyancy, and a constant aperture angle relative to the sea bottom, meandering growth of this ammonite was modeled by computer simulation. In this model, the meandering shell growth is controlled by regulation of life orientation. The remarkable similarity in the coiling modes and rib obliquity patterns between the computer-simulated and actual specimens strongly suggests a free living mode of life in Nipponites with an approximately neutral buoyancy. The simulation also suggests that morphological saltation from a simple helicoid form like Eubostrychoceras japonicum to a meandering shell form like Nipponites occurred abruptly without any intermediate form by minor change of the upper and lower limits of growth direction.
Survivorship in the Bivalvia: comparing living and extinct genera and families
Authors: Gilinsky Norman L.
Published: July 2016

George Gaylord Simpson was one of the first paleontologists to apply survivorship analysis to the study of fossil taxa. His finding that the survivorship curve for extant bivalve genera plotted above that for extinct genera led him to conclude that bivalve genera are drawn from at least two distinct distributions of longevities, and formed the fundamental basis for his influential concepts of horotelic and bradytelic evolutionary rates. Survivorship curves presented in this paper show the same pattern of disjunct survivorship in genera from the Treatise on Invertebrate Paleontology and in families from Sepkoski's compendium.

Some of the observed differences between survivorship curves are artificial, occurring because long-lived genera and families are more likely to survive to the Recent than short-lived genera and families. The living fauna thus contains a disproportionate number of long-lived genera and families, and the survivorship curve for the living fauna is expected to lie above that for the extinct fauna for this reason alone—even if all longevities are drawn from the same distribution. Recognition of this bias led Raup (1975) to question the significance of the survivorship patterns presented by Van Valen (1973), and Stanley's (1984) acceptance of Raup's argument led him to dismiss the survivorship pattern discovered by Simpson. But statistical analysis using bootstrapping shows that this bias accounts for only a small proportion of the difference between survivorship curves. Other biases considered, such as “pull of the Recent,” “asymmetrical range truncation,” and erroneous concatenation of stratigraphic ranges, do not account for the pattern either. Although still other biases, as yet unknown, cannot definitively be ruled out, it appears that the longevities of extinct and living bivalve taxa are meaningfully different, and that the fundamental causes are biological.
An unusual pattern of divergence between two fossil gastropods: ecophenotypy, dimorphism, or hybridization?
Authors: Geary Dana H.
Published: July 2016

The temporal dimension of fossil sequences provides a critical component to the study of intraspecific dynamics and species formation. Here I report on the branching and subsequent morphological evolution of two gastropods (Melanopsis fossilisandM. vindobonensis) from the Late Miocene of the Pannonian basin in eastern and central Europe. Although morphological divergence between species is rapid, intermediates between the two species co-occur with typical individuals for approximately 1 m.y. and then disappear. The long-term persistence of intermediates followed by their ultimate disappearance is a pattern that, to my knowledge, has not been previously observed.

Distinguishing genetic from ecophenotypic influences on shell form in freshwater prosobranchs is difficult. Nevertheless, consideration of the temporal, geographic, lithologic, and paleoecologic patterns of this sequence suggests that the morphologic differences betweenM. fossilisandM. vindobonensishad some genetic basis. Whether these forms were initially morphs of a single species or two species with some hybridization between them is impossible to determine. In either case, the morphological changes that resulted inM. vindobonensiswere rapid, but the attainment of complete isolation betweenM. fossilisandM. vindobonensisapparently did not occur until approximately 1 m.y. later.
Variation between groups in evolutionary rates: a statistical test of significance
Authors: Raup David M. , Marshall Larry G.
Published: July 2016

The statistical significance of differences in evolutionary rate between major taxonomic groups is evaluated using conventional chi-square techniques on stratigraphic range data. Romer's (1966) compilation of stratigraphic ranges of fossil mammals is used to determine whether orders differ significantly from each other in generic origination and extinction rates. The evolutionary histories of 2180 genera (primarily Cenozoic in age) are analyzed. Chi-square testing shows that significantly high or low (P ≥ 0.99) extinction or origination occurs in 15% of the testable cases. Significantly high or low evolutionary turnover in a taxon (orders in this case) we term taxotely. Significantly high turnover rate is equivalent to Simpson's tachytely and significantly low turnover is equivalent to his bradytely.

In the mammal data set, taxotely is largely attributable to the influence of South American endemics. Some of the effect is interpreted as an artifact of biases in the fossil record (or its study) and some is attributed to real biological aspects of mammalian evolution.
On the relationship of the myotome to the axial skeleton in vertebrate evolution
Authors: Lauder George V.
Published: July 2016

The traditional belief that vertebrae must alternate in position with the segmented body musculature (myotomes) to allow bending of the axial skeleton is evaluated in terms of the patterns of development and structure of gnathostome vertebrae. The key functional parameter allowing lateral bending of the axial skeleton is the intersegmental position of both the neural and haemal arches, not the centrum. The intersegmental position of both the centrum and arches in tetrapods is the result of a secondary association of the centrum with the primary intersegmental position of the neural and haemal arches. The pattern of vertebral ontogeny and structure in primitive gnathostomes suggests that a causal link between sclerotomic resegmentation during amniote development and the presence of intersegmental vertebrae in the adult is spurious and corroborates the hypothesis that the process of resegmentation evolved as a method of redistributing large volumes of sclerotome cells during development. Patterns of vertebral construction in lower vertebrates are related to fast-start performance and the use of the body as a hybrid oscillator during locomotion.
Some distributional models for fossil animals
Authors: Tipper John C.
Published: July 2016

Models for the areal distribution of marine animals may be formulated in such a way that their validity can be tested statistically. Five such models are described here: in each case the distributions of the individual taxa are made functions of depth of water, oceanicity, and substrate type.

The simplest model proposes that benthic species are substrate-dependent: it can be verified by a series of χ2 tests. Benthic species can also be seriated along an environmental gradient: this second model can be tested by using a Monte Carlo simulation procedure. The third model proposes that planktic species are to some degree stratified in the water column, and hence that their remains are distributed additively in the underlying sediments: tests on modern and sub-fossil data sets indicate that realistic versions of this model are probably valueless for most geological work. The final models are extensions of the additive model: they are used here to demonstrate the importance of selecting an appropriate model and, in particular, of knowing the mode of life of each species before the model is selected.
Paleontological data and molecular phylogenetic analysis
Authors: Smith Andrew B. , Littlewood D. T. J.
Published: July 2016

Molecular data are becoming an indispensable tool for the reconstruction of phylogenies. Fossil molecular data remain scarce, but have the potential to resolve patterns of deep branching and provide empirical tests of tree reconstruction techniques. A total evidence approach, combining and comparing complementary morphological, molecular and stratigraphical data from both recent and fossil taxa, is advocated as the most promising way forward because there are several well-established problems that can afflict the analysis of molecular sequence data sometimes resulting in spurious tree topologies. The integration of evidence allows us to: (1) choose suitable taxa for molecular phylogenetic analysis for the question at hand; (2) discriminate between conflicting hypotheses of taxonomic relationship and phylogeny; (3) evaluate procedures and assumptions underlying methods of building trees; and (4) estimate rates of molecular evolution in the geological past. Paleontology offers a set of independent data for comparison and corroboration of analyses and provides the only direct means of calibrating molecular trees, thus giving insight into rates of molecular evolution in the geological past.
Morphological disparity in Ordovician-Devonian crinoids and the early saturation of morphological space
Authors: Foote Mike
Published: July 2016

It has been argued that many clades originating in the early Paleozoic filled their design space rapidly while still at low taxonomic diversity. Standardization of morphology for analytical purposes facilitates testing of this claim. Here I document evolutionary patterns of morphological disparity in Ordovician-Devonian crinoids, using a set of 75 discrete characters covering the principal features of the crinoid stem, cup, tegmen, and arms. Disparity is measured as the average dissimilarity among species, the range of morphospace occupied, and the number of realized character-state combinations. Comparison with generic richness reveals that the full range of form was essentially attained by the early part of the Caradocian, long before the time of maximal taxonomic diversity. Despite subsequent taxonomic diversification, the variety of crinoid form did not expand appreciably; increased diversity was accommodated by the evolution of variations upon the spectrum of designs established earlier. The data discussed here do not definitively imply specific sources of constraint, but the effective stasis in disparity supports previous arguments that some morphological limits were reached early in crinoid history.
The promotion and prevention of recoiling in a maximally snaillike vermetid gastropod: a case study for the centenary of Dollo's Law
Authors: Gould Stephen Jay , Robinson Betsey A.
Published: July 2016

The Neogene speciesPetaloconchus sculpturatuspresents a contradiction in terms, for it grows whorl “packages” of nearly perfect regularity, but ranks within the most geometrically irregular family of uncoiled gastropods, the Vermetidae. We perform a first biometric study of vermetids (only possible because sufficient regularity of growth permits us to number and identify whorls) to specify and characterize the factors on both sides of this “exquisite tension” between promotion and prevention of recoiling. Promoting factors include the older phyletic heritage of preserved dextral coiling, and the more immediate vermetid (or specifically petaloconchid) features of growth toward open spaces (where regular coiling might proceed in an unimpeded fashion); radular excision of discordant feeding tubes with shaping of the resulting scar so that growth may proceed in conformity with previous whorls; and locking of subsequent whorls upon a keel formed by longitudinal bead-rows of the previous whorl. Preventing factors include prominent phyletic heritage of all vermetids—maximal early irregularity enjoined by discordance between larval and subsequent growth (with teleoconch wrapping itself around the protoconch), thus precluding an ordered substrate to act as a foundation for regular whorl “packages” of intermediary growth—and a set of features specific to this lineage and acting as geometric constraints. In this category, we particularly document the exceedingly low rate of whorl expansion and the consequently wide umbilical space that produces a shell akin to winding a cylindrical coil of narrow-diameter rope around the periphery of a wide circular platform. This complex combination of promoting and preventing factors produces a shell that is tantalizingly close to fully regular, but cannot truly reattain this previous phyletic state—thus providing a fine example of Dollo's Law at the centenary of his formation of irreversibility.
Volatility and the Phanerozoic decline of background extinction intensity
Authors: Gilinsky Norman L.
Published: July 2016

The well-known decline of global background extinction intensity was caused by the sorting of higher taxonomic groups. Two factors were responsible. First, probabilities of familial origination and extinction in these groups (taxonomic orders) were highly correlated. Groups whose families had high probabilities of origination and extinction tended to have highly volatile diversity paths and, consequently, short life spans. Second, orders with high probabilities of familial origination and extinction were rarely replaced by new high-turnover orders. Thus, because high-turnover orders tended to become extinct without replacement, the global background extinction intensity declined. Since familial origination and extinction probabilities are correlated, global background origination intensity inevitably declined as well. As a consequence of these processes, virtually all groups of organisms now living have low probabilities of familial origination and extinction.

Simulations of branching evolution were used to obtain the expected relationships among probabilities (of origination and extinction), volatilities, and longevities for the entire range of possible probabilities, and these relationships were compared to those obtained from the empirical record. In the simulations, only the probabilities of origination and extinction were specified, so volatilities and clade longevities were determined entirely by the probabilities. The similarity between results obtained by simulation and those obtained by analysis of the empirical record further supports the inference that the observed decline of background extinction (and origination) intensity can be explained largely by the loss of high-probability groups to induced volatility.
Comparing the stratigraphic record to estimates of phylogeny
Authors: Huelsenbeck John P.
Published: July 2016

The age of first occurrence of taxa remains an underutilized source of information in phylogenetic analysis. In this paper I develop a method whereby one can measure the fit of the stratigraphic record to an estimated phylogenetic tree. The method works as follows: (1) each of the internal nodes excluding the root node of a phylogenetic tree is visited, (2) the oldest age of first occurrence for the taxa above the node is compared to the oldest age of first occurrence for the sister node, and (3) if the age above the node is the same age or younger than the age below the node, then the node is stratigraphically consistent. A measure of the total fit of the stratigraphic record to the tree is the proportion of nodes that are stratigraphically consistent (expressed as the stratigraphic consistency index, SCI). This measure of stratigraphic fit is sensitive to errors in phylogenetic estimation as well as to missing lineages (or parts of lineages). The significance of the fit of the stratigraphic record to the tree can be determined through a permutation approach that generates the null distribution for SCI under the hypothesis that the stratigraphic fit is no better than would be expected at random. The method is applied to several studies taken from the literature. Almost all published trees had significant SCI values, meaning the trees fit the stratigraphic record quite well. Applications of stratigraphic consistency for determining the confidence that should be placed in a phylogenetic estimate, for determining the root of a tree, and as a modified optimality criterion for estimating phylogenetic trees are discussed.
Early Mesozoic (Late Triassic-Early Jurassic) Tethyan brachiopod biofacies: possible evolutionary intra-phylum niche replacement within the Brachiopoda
Authors: Sandy Michael R.
Published: July 2016

Distributions of brachiopods from low-latitude paleogeographic settings, primarily in the Tethyan Ocean of southern Europe, with additional data from North America allow some observations on the bathymetric distribution of early Mesozoic brachiopod orders. Norian and latest Triassic (Rhaetian) brachiopod biofacies are dominated in shallowest waters by short-looped terebratulids (Terebratulidina) while spire-bearing athyrids (Athyrida) are common components of deeper-water environments in the latest Triassic. In the late Early Jurassic (Pliensbachian), shallow-water brachiopod faunas are dominated by rhynchonellids, short-looped terebratulids are commoner in relatively deeper shelf waters, and spiriferids and long-looped terebratulids (Terebratellidina) are abundant in deeper-water shelf environments.

Following the end-Triassic extinction event there appears to be niche-replacement in deep-water shelf environments of Late Triassic athyrids by spiriferids and long-looped terebratulids in the Early Jurassic. Rhynchonellids appear to have diversified into shallowest water environments; specialized short-looped terebratulids may have occupied deeper-water niches that resulted ultimately in the success of the enigmatic Pygopidae later in the Jurassic and Cretaceous.
CerioShell: a computer program designed to simulate variation in shell form
Authors: Stone J. R.
Published: July 2016

I describe a mathematical model of shells that incorporates simple morphometric measurements, which can be obtained easily from sectioned specimens. The model reconstructs form (size and shape) by describing the path in space traversed by, and the changes in dimensions of, a shell aperture during accretionary growth. The model contains parameters that independently affect components of these two aspects of shell form in directions radially away from (or toward) and along a coiling axis. I also describe a computer program, CerioShell, that uses the mathematical model to graphically simulate shell forms. The program permits the viewing of images from different three-dimensional orientations, using various graphical representations, and provides dimensions of the images it generates. Together, the model and the program allow one to investigate the effects that changes in modes of growth would have on shell form.
The life orientation of concavo-convex brachiopods: overturning the paradigm
Authors: Lescinsky Halard L.
Published: July 2016

Concavo-convex brachiopods are generally assumed to have lived with their convex valves against the sediment. This orientation is based primarily on the a priori assumption that the upturned commissure would prevent fouling of the brachiopods' mantle cavity. Here, I present epibiontic and taphonomic evidence from orthids and nonproductid strophomenids that concavo-convex brachiopods lived in the reverse life orientation, with the convex valve on top.

Ten testable epibiontic and taphonomic criteria are proposed to establish the uppermost valve during encrustation and whether epibionts encrusted primarily live or dead hosts. The criteria are evaluated for 11 collections of Ordovician and Devonian nonproductid concavo-convex brachiopods that contain a total of over 500 brachiopods and 4000 epibionts. In all cases, the results support a convex-up orientation and the encrustation of live hosts. Five criteria concern epibiont growth patterns and show that (1) epibionts predominate on convex valves, (2) epibionts are not restricted to shell margins, (3) distinct exposed and cryptic faunas, as predicted theoretically and described in previous studies, exist on convex and concave valves respectively, (4) epibiont colonies were often truncated by the commissures and hinges of live hosts, and (5) growth patterns of some epibionts indicate live hosts. Five taphonomic criteria show that (1) concavo-convex shells have greater epibiont cover than other morphologies, (2) internal surfaces of disarticulated specimens are rarely encrusted, (3) interiors of articulated specimens are rarely mud-filled, (4) standard taphofacies indicators suggest little postmortem exposure, and (5) sedimentological reconstructions suggest rapid burial.

Convex-up brachiopods suggest that the Paleozoic mud bottoms they lived on were probably firmer than usually assumed and that a more complex functional interpretation of concavo-convexity is required. Hydrodynamic stability was important to many concavo-convex, plano-convex, and unequally bi-convex brachiopods. Brachiopods with these morphologies probably lived in the more stable orientation on their concave or flat valve. Productid brachiopods, although also concavo-convex, lived convex valve down and are ecologically distinct from earlier concavo-convex taxa. Productids were anchored, semi-infaunally, by spines and were more similar to Mesozoic oysters in orientation and shell function.
The evolutionary bootstrap: a new approach to the study of taxonomic diversity
Authors: Gilinsky Norman L. , Bambach Richard K.
Published: July 2016

The evolutionary bootstrap is a new approach to the analysis of patterns of taxonomic diversity. In general, the evolutionary bootstrap works by surveying the diversity history of a taxon, learning its dynamic properties, and then generating randomly large numbers of artificial diversity histories based upon what was learned. The distribution of artificial—or bootstrapped—diversity histories approximates the distribution of diversity histories that were possible for taxa with the dynamic properties of the real taxon, and serves as a paleontological null hypothesis for studying statistically the diversity history of the real taxon.

Two null hypotheses were established, the additive and the multiplicative. The additive null hypothesis assumes that the amount of diversity change that occurs in a higher taxon during an interval of time isindependentof the number of member subtaxa present at the beginning of the interval. The multiplicative null hypothesis, in contrast, assumes that the amount of diversity change that occurs isdependentupon the number of member subtaxa present at the start. Thus the two null hypotheses represent end members of a diversity-independent/diversity-dependent continuum of possibilities.

Detailed analyses using the evolutionary bootstrap, in conjunction with the clade statistics of Gould et al. (1977), show that several of the 17 higher taxa studied have diversity histories that are statistically significantly different from the random expectation under one or both null hypotheses. Analyses of multiple taxa in aggregate also reveal several properties of diversity histories that are statistically significantly different from random. Real taxa tend to have higher uniformities and lower maximum diversities than expected under the multiplicative null hypothesis. They have lower uniformities, higher maximum diversities, and longer durations than expected under the additive null hypothesis. And, they have lower centers of gravity than expected under either null hypothesis. Overall, the results provide a possible statistical verification of the process of taxonomic (traditionally, adaptive) radiation and suggest the need to consider deterministic explanations for observed diversity patterns.
Biogenic and diagenetic Sr/Ca in Plio-Pleistocene fossils of the Omo Shungura Formation
Authors: Sillen Andrew
Published: July 2016

Under conditions of normal calcium metabolism, strontium/calcium ratios (Sr/Ca) have been shown to reflect the trophic level of contemporary and recent terrestrial fauna. These ratios therefore offer a potential means of studying fossil ecosystems and the diet of prehistoric humans. In cases in which suitable controls have demonstrated the preservation of biogenic Sr/Ca, it has been possible to investigate the proportionate importance of meat vs. vegetable foods in the diets of prehistoric humans. However, diagenetic change after interment has made it impossible to discern biogenic Sr/Ca in faunal and human skeletons over 15,000 y b.p. A procedure is investigated for the analysis of biogenic and diagenetic apatite in vertebrate fossils, on the basis of solubility differences among carbonate, hydroxy-, and fluorapatites. When applied to the 2 ma b.p. fauna of the Omo Basin (Ethiopia), distinct characterization of the herbivore, omnivore, and carnivore fauna in conformity with trophism was discerned, in spite of anomalous Sr/Ca of one highly specialized carnivore,Homotherium.Possible metabolic and/or taphonomic explanations of this anomaly are discussed, and future basic research into the solubility profile procedure is outlined.
Quantitative Variation in Elephant Dentitions: Implications for the Delimitation of Fossil Species
Authors: Roth V. Louise
Published: July 2016

Dental measurements are commonly used in the diagnosis of fossil elephant species, yet elephant teeth develop slowly, within a highly dynamic context that enhances opportunities for physical deformation (or its subtler manifestation, quantitative phenotypic variation). This paper examines intraspecific variation in elephant teeth and compares it with variability in other mammals (83 species in 7 orders). I conclude that (1) male elephants tend to have slightly larger cheek teeth than females, though the difference is not marked; (2) of the full complement of six cheek teeth per jaw quadrant, no single tooth consistently varies less than the others (so on this basis, for taxonomic decisions no tooth is preferable to the customarily used M3 = tooth VI); (3) single-population samples vary less than more inclusive, geographically heterogeneous samples of elephant teeth; (4) although differential wear and eruption are important sources of variation in dental measurements, complete elephant teeth are consistently more variable in length and width than the cheek teeth of other mammals; (5) variability in dental dimensions of recognized fossil species of elephants is in general not grossly inconsistent with variability noted in modern elephants, but there are some exceptions. With the information and guidelines presented here, consideration of variability, and assessment of the statistical power permitted by available samples, can enhance confidence and precision in the delimitation of species and provide a firmer basis for macroevolutionary inferences.
Growth rates of pterobranchs and the lifespan of graptolites
Authors: Rigby Susan , Dilly P. Noel
Published: July 2016

Pterobranchs are the closest living relatives of graptolites. Their skeleton is constructed from the same material, and in a homologous manner. Growth rates of the pterobranch Cephalodiscus gracilis are described for the first time and, along with rhabdopleuran growth rates, they are used to estimate the amount of time invested by a graptolite colony in growing its rhabdosome. This is a measure of minimum age. The significance of age calculations is shown for individuals and large communities of graptoloids. Large individuals can be shown to be much older than the time it would have taken them to settle through seawater and so it is shown that graptoloids moved up, as well as down, through the water column. Life tables constructed for biserial graptoloids from the Utica shale in Quebec, Canada, suggest that these graptoloids died from constant environmental stress. Graptoloid length can thus be a function of environment and should only cautiously be considered to be of taxonomic significance.
The potentials and limitations of dicotyledonous wood anatomy for climatic reconstructions
Authors: Wheeler Elisabeth A. , Baas Pieter
Published: July 2016

The incidences of selected features of dicotyledonous wood that are believed to be of ecologic and/or phylogenetic significance (distinct growth rings, narrow and wide vessel diameter, high and low vessel frequencies, scalariform perforations, tangential vessel arrangement, ring porosity, and helical wall thickenings) were plotted through time (Cretaceous–Recent). There are marked differences between the Cretaceous and Tertiary in the frequency of all wood anatomical features. Incidences of features that are associated with markedly seasonal climates in extant floras do not approach modern levels until the Neogene. Correlations of wood anatomical features with ecology do not appear to have been constant through time, because in the Cretaceous different features provide conflicting information about the climate. Throughout the Tertiary the southern hemisphere/tropical and the northern hemisphere/temperate regions differed in the incidences of ecologically significant features and these differences are similar to those in the Recent flora. Possibilities for reliably using dicotyledonous wood for climatic reconstructions appear restricted to the Tertiary and Quaternary. However, at present the fossil wood record for most epochs and regions is too limited to permit detailed reconstructions of their past climate.
Numerical experiments with model monophyletic and paraphyletic taxa
Authors: Sepkoski J. John , Kendrick David C.
Published: July 2016

The problem of how accurately paraphyletic taxa versus monophyletic (i.e., holophyletic) groups (clades) capture underlying species patterns of diversity and extinction is explored with Monte Carlo simulations. Phylogenies are modeled as stochastic trees. Paraphyletic taxa are defined in an arbitrary manner by randomly choosing progenitors and clustering all descendants not belonging to other taxa. These taxa are then examined to determine which are clades, and the remaining paraphyletic groups are dissected to discover monophyletic subgroups. Comparisons of diversity patterns and extinction rates between modeled taxa and lineages indicate that paraphyletic groups can adequately capture lineage information under a variety of conditions of diversification and mass extinction. This suggests that these groups constitute more than mere “taxonomic noise” in this context. But, strictly monophyletic groups perform somewhat better, especially with regard to mass extinctions. However, when low levels of paleontologic sampling are simulated, the veracity of clades deteriorates, especially with respect to diversity, and modeled paraphyletic taxa often capture more information about underlying lineages. Thus, for studies of diversity and taxic evolution in the fossil record, traditional paleontologic genera and families need not be rejected in favor of cladistically-defined taxa.
Levels of selection and macroevolutionary patterns in the turritellid gastropods
Authors: Lieberman Bruce S. , Allmon Warren D. , Eldredge Niles
Published: July 2016

This analysis examines the evolution of the greater diversity of species with non-planktonic larval types relative to species with planktonic larval types in the turritellid gastropods. This sort of trend has been documented in both the fossil and recent biota of several gastropod families. Two mechanisms for generating diversity gradients in larval types have been proposed in the literature. The first, species selection, focuses on the population biology of larval types. The second proposes that factors in development that are mediated by organismal adaptation are responsible. Turritellids have been cited as a classic example of species selection. In order to examine the relevance of these two proposed mechanisms, a phylogenetic analysis of the turritellids using molecular sequence data was performed to determine the evolution of larval types in this clade. The resultant phylogeny suggests that species selection is not the only process driving the trend toward increasing numbers of non-planktonic species through time. Developmental processes, apart from those involving organismal adaptation (except in the trivial sense), are implicated as playing a role in this trend. In particular, these processes may involve changes in the timing of germ-line sequestration in organisms. Germ-line sequestration governs how accessible organisms are to heritable variation during ontogeny. Embryological evidence from gastropods suggests that non-planktonic species have early germ-line sequestration relative to planktonic species, making them more resistant to developmental change. Thus, non-planktonic lineages will only rarely revert to a planktonic larval mode.
The first 2 million years after the Cretaceous-Tertiary boundary in east Texas: rate and paleoecology of the molluscan recovery
Authors: Hansen Thor A. , Farrell Benjamin R. , Upshaw Banks
Published: July 2016

Analysis of molluscan collections from a 3+ m.y. interval around the Cretaceous–Tertiary (K–T) interval in east Texas suggests that molluscs suffered an extinction at or near the K–T boundary, followed by a prolonged period of stress which lasted through the P0 and P1a planktic foraminiferal zones. The stressed period was characterized by low species richness, low abundances of individuals, high species turnover and a dominance of deposit feeders. Species richness and the relative abundance of deposit feeders generally track the 13C depletion curve suggesting that the stress was caused by a lack of primary production. A stable, relatively diverse, suspension feeding molluscan community was reestablished less than two million years after the K–T boundary. The total number of species within the habitat did not recover to Cretaceous levels within the study interval.
Hierarchies in biology and paleontology
Authors: Valentine James W. , May Cathleen L.
Published: July 2016

Hierarchies in natural science are ranked and nested structures such that units at each rank include parts that are units at lower ranks. Hierarchies are able to render complexity tractable, by homogenizing units into collectives and by ordering collectives in ranks of increasing inclusiveness. Hierarchies contrast with positional structures, such as phylogenetic trees, for in trees all positions are occupied by the same sort of entity—there are no ranked collectives—and positions are specified by the order of appearance or precedence of the entities. In hierarchies, interactions within ranks are most important; in trees, sequences of events along branches are of primary concern. As a result hierarchies do, and trees do not, display emergent properties.

The value of the hierarchical structure can be lost when ranks are misspecified. A common error is the use of only a fraction of entities that actually occur in a rank, as when genes are considered as a rank below cells, disregarding the remaining cell contents and rendering the nature of cellular organization moot. Misspecification is also common when attributes or processes are used in ranks without indications of the physical entities to which they refer, thus losing track of the proper composition and ranking of the collectives.
Morphological diversification of Ptychopariida (Trilobita) from the Marjumiid biomere (Middle and Upper Cambrian)
Authors: Sundberg Frederick A.
Published: July 2016

Ptychopariid trilobites from the Marjumiid biomere of Laurentia underwent a statistically significant morphological diversification that is concordant with proposed adaptive radiations of trilobites in each of the Cambrian biomeres. An analysis of a subset consisting of the biomere's most characteristic taxa, the Asaphiscacea, Raymondinacea, and Marjumiacea, also illustrates this morphological diversification. In detail, the total data set and subset show a limited range of morphologies near the base of the biomere and a large increase in range in the upper portion of the biomere.

Regional assemblages from the Appalachians, Great Basin, and Texas were also studied to determine if they too show the larger-scale macroevolutionary patterns of trilobites from Laurentia as a whole. The regional assemblages illustrate similar, butnot identical, morphological diversifications, which are also similar to the overall Laurentian pattern. Subsets of the characteristic taxa also show this diversification. These results suggest that regional assemblages can be used to investigate these larger-scale macroevolutionary patterns.

Causal mechanisms for the diversification patterns are not clear. Potential mechanisms include: (1) endemic evolution of new morphologies in Laurentia; (2) migration of new morphologies, including intra- and inter-continental migrations; and (3) environmental controls over the distribution of morphologies. Likely causes for the morphological diversification and its similarity among regions probably include aspects of all three mechanisms.
Limited membership in Pleistocene reef coral assemblages from the Huon Peninsula, Papua New Guinea: constancy during global change
Authors: Pandolfi John M.
Published: July 2016

One of the most intriguing questions in community ecology remains unanswered: Are ecological communities open assemblages with each species reacting individually to environmental change, or are they integrated units consisting of multispecies assemblages acting in concert? I address this question for marine organisms by examining the taxonomic composition and diversity of Indo-Pacific reef coral communities that have undergone repeated global change between 125 and 30 Ka (thousand years before present).

Investigation of community constancy through time relies on two critical questions: (1) Are there significant differences in taxonomic composition among communities from different times? and if not, (2) Are the observed patterns in temporal similarity significantly different from expected patterns resulting from a random sampling of the available within-habitat species pool?

Constancy in taxonomic composition and species richness of Pleistocene reef coral assemblages is maintained through a 95-k.y. interval in the raised reef terraces of the Huon Peninsula, Papua New Guinea. Fossil reef coral assemblages show limited membership in species composition despite repeated exposure to marked fluctuations in sea level (up to 120 m) and sea-surface temperatures (up to 6°). During the 95-k.y. interval, the reefs experienced nine cycles of perturbation and subsequent reassembly with similar species composition. Spatial differences in reef coral species composition were greater among the three study sites than among reefs of different ages. Thus local environmental parameters associated with riverine and terrestrial sources had a greater influence on reef coral composition than global climate and sea level changes.

The ecological dynamics of reef communities from Papua New Guinea are in marked contrast to those of Quaternary terrestrial and level bottom marine communities which appear to show unlimited community membership on both larger and smaller time scales. Differences in community assembly among ecosystems mean either that coral reefs are fundamentally different or that different ecological patterns and processes are occurring at different temporal scales.