bluuebunny/crossref_metadata_2025 huggingface dataset:
Fine-scale temporal variation of the Miocene sticklebackGasterosteus doryssus
Authors: Bell Michael A. , Haglund Thomas R.
Published: July 2016

The fossil stickleback,Gasterosteus doryssus, is highly variable for pelvic girdle structure and the number of dorsal spines. Six “sampling pits” were dug at known stratigraphic positions within a continuous section which contains abundantG. doryssus, and the stratigraphic position of each specimen within each pit was determined. The deposit apparently is composed of annual layers (varves), allowing relatively precise conversion of stratigraphic distance to years. The temporal distribution of phenotypes is heterogeneous but can be grouped into two temporally contiguous, nonheterogeneous sets. However, absence of heterogeneity for pelvic phenotypes within the two groups of pits could be an artifact of small sample size. The number of sample pits was insufficient to determine whether the observed phenotypic heterogeneity among pits represents temporal trends. Differences also occurred between mean temporal distributions of stickleback phenotypes within one of the pits located within a nonheterogeneous set of pits. Thus, there is within-pit temporal heterogeneity that is unresolved by between-pit comparisons, although the sampling pits are separated by an average of only about thirty thousand years. Larger time intervals usually used in paleontology may seriously underestimate evolutionary rates because fine scale reversals of evolutionary trajectory are undetected. Temporal variation inG. doryssusprovides a system in which most limitations of other fossil systems for measuring the rate of evolution can be circumvented. As in virtually all paleontological studies, spatial variation cannot be entirely eliminated as a potential cause of stratigraphic variation.
Estimating Stasis: Can a Null Hypothesis be too Null?
Authors: Levinton Jeffrey S.
Published: July 2016

In a recent contribution, Rightmire (1981) claims that “No significant trends can be observed” in several characters measured in skulls of Homo erectus. While I sympathize with the frustrating problem of small sample size in hominid finds, one must ask the question: could you ever see a trend, given the quality of your information? If sample size is low, if trends are of relatively small magnitude, and if sample variance is high, one can always safely show that nothing (i.e., stasis) has happened. This form of inference falls into a classic statistical trap: attempting to prove statistical homogeneity. You cannot do it without a concomitant estimate of least significant difference, that is, estimating the magnitude of variation within which you cannot distinguish among estimates of a parameter.
Growth rhythms in the brachiopod Rafinesquina alternata from the Late Ordovician of southeastern Indiana
Authors: Rosenberg Gary D.
Published: July 2016

Growth rhythms are described in the accretionary skeletons of Rafinesquina alternata, a Late Ordovician brachiopod from southeastern Indiana. Contiguous growth increments widen and narrow in repeating series, giving the appearance of adjacent clusters of increments. Fourier analyses of growth increment widths and counts of the number of increments within individual clusters yield similar periodicities. Increments vary in width over a period of approximately 19 increments, modulated with a lower amplitude oscillation of 27 increments. The number of increments per cluster falls into two groups; clusters having between 8 and 17 increments outnumber those having between 18 and 30 increments.

All specimens were obtained from a Maysvillian facies of the Dillsboro Formation, previously inferred to represent a shallow subtidal environmental setting. The growth periodicities described here are consistent with this interpretation. The intensity of tidal parameters such as emersion-immersion cycles, substrate shifts, changes in nutrient supply or in oxygen tension declines with depth as would the number of growth increments added each month in response to these factors. Thus, for these specimens, the maximum number of increments per cluster probably approximates the true number of “tidal” days in the Late Ordovician synodic month (period between full moons).

The paleoecological model derived from these analyses can be used in future studies to predict the rate of the earth's rotation and the motion of the moon in the Late Ordovician and, equally importantly, to evaluate the limits of uncertainty of such studies.
The relationship of siphuncle size to emptying rates in chambered cephalopods: Implications for cephalopod paleobiology
Authors: Ward Peter
Published: July 2016

Liquid removal rates in chambers of the living cephalopod Nautilus depend on two factors: the surface area of siphuncular epithelium exposed to liquid in the chambers and the buoyancy of the specimen. In Nautilus made artificially heavy, liquid removal rates are increased as much as five times above neutral buoyancy rates in surface aquaria. Although chamber volume increases faster than siphuncular surface area in successively larger chambers, the increase is small, especially in the last formed dozen chambers. Under conditions of constant liquid removal per unit area of siphuncular epithelium, this means that removal rates of liquid from any two or three successive chambers are nearly constant.

Nautilus shows ranges of chamber volume/siphuncular surface area ratios of .04 cc/mm2 (early, small chambers) to .12–.14 cc/mm2 in late, large chambers. These values are not characteristic of all chambered cephalopods. Comparison of extinct chambered cephalopod taxa with Nautilus indicate a variety of volume/area ratios for similarly sized chambers.
Resolving time in paleobiology
Authors: Behrensmeyer Anna K. , Schindel David
Published: July 2016

Time is so fundamental to the everyday thinking of paleobiologists and geologists that it is seldom given close critical attention. Many of the currently debated issues in evolutionary history—catastrophic extinctions and punctuated vs. gradual morphological change, for instance—include assumptions about time and rate which are seldom made explicit. Methods now exist for calibrating evolutionary patterns through estimates of time components in the fossil and sedimentological records. There is a growing realization that increased precision in defining time frameworks can greatly clarify evolutionary problems. This has helped to stimulate renewed interest in the traditional topic of time and how it is represented in the biological and geological record.
Preservational effects in paleoecological studies: Cretaceous mollusc examples
Authors: Koch Carl F. , Sohl Norman F.
Published: July 2016

The effect of preservational quality on paleoecologic studies is evaluated quantitatively by using data from 83 fossil collections. These collections are from a restricted Cretaceous time interval (Haustator bilira Assemblage Zone) of Maestrichtian Age and are from the Eastern Gulf Coastal Plain Province. In all, 32,335 specimens were identified, resulting in recognition of 643 different taxa. Each collection was categorized into one of six preservational types, ranging from those in which both aragonite and calcite shells are well preserved to those having only calcite shells preserved.

Statistical comparisons reveal that preservation affects the faunal makeup of these collections. Specifically, collections in which both aragonite and calcite are well preserved have more taxa than collections of poorer preservational quality and contain faunal elements not found in other collections.

These two effects can confound paleoecologic studies of endemism, eurytopy vs. stenotopy, species longevity and other studies of the distribution of organisms in space and time. These effects are especially significant for studies based on presence/absence data, such as published faunal lists and selectively collected samples. In such studies, collections of good preservational quality may be interpreted to represent strata of high diversity, taxa having the more durable hard parts will appear to be widespread and long ranging, and taxa that are preserved only in collections of the best preservational quality will appear stenotopic, endemic, and rare.
Is there a characteristic rate of radiation for the insects?
Authors: Wilson Mark V. H.
Published: July 2016

The hypothesis that there is a characteristic rate of exponential radiation for the Insecta is tested for forty-nine of the most diverse family-level taxa in the Coleoptera, Diptera, and Hymenoptera. Data used are estimates of Recent species diversity and age of first appearance in the fossil record, as in the original statement of the hypothesis by Stanley (1979). There is no evidence of a characteristic radiation rate for the insects. A more exact method is proposed for identifying clades that are radiating exponentially. When applied to Stanley's data for the mammalian family Bovidae, it indicates that the Bovidae are not radiating exponentially at a characteristic rate. Future research might emphasize the reliable identification of clades that are radiating exponentially, prior to drawing conclusions about rates that might characterize higher taxa.
Dragons and dinosaurs
Authors: Farlow James O.
Published: July 2016

For paleobiologists interested in extinct carnivorous reptiles, publication of Walter Auffenberg's (1981) 13–month field study of the Komodo dragon (Varanus komodoensis), or ora, as he prefers to call it, provides a useful portrait of a reptile as the top predator of a terrestrial community. A great deal of information about the ora's habitat utilization, activity patterns, diet, social behavior, and reproduction is presented.
Natural rates of growth and longevity ofNautilus belauensis
Authors: Saunders W. Bruce
Published: July 2016

Capture-mark-recapture ofNautilus belauensisin Palau shows that (a) immature animals added an average of 0.1 mm of shell per day at the ventral circumference (projected mean annual increment of 37 mm), but this rate decreases rapidly as maturity is approached; (b) rate of growth line secretion is irregular, ranging from 4 to 8 days per growth line in immature animals; (c) overall weight is an imprecise measure of size and growth inNautilusdue to fluctuations in crop content and chamber liquid; (d) this species is shown to live for at least 4 yr beyond maturity. Age estimates based on the highest growth rate obtained (0.12 mm/day = 43.8 mm/yr) range from 14.5 to 17 yr for seven animals recaptured 45–355 days after release. Combined, these data indicate that the life span ofNautilusmay exceed 20 yr.
Phyletic evolution in theGloborotalia crassaformis(Galloway and Wissler) lineage: a preliminary report
Authors: Arnold Anthony J.
Published: July 2016

A preliminary report is presented documenting the evolution of theGloborotalia crassaformis(Galloway and Wissler) lineage from the Early PlioceneG. cibaoensis(Bermudez) in Hydraulic Piston Core 72/516 on the Rio Grande Rise (western South Atlantic). A new technique, eigenshape analysis, is used to describe the gross changes in morphology, and the use of “Raupian” analysis of expansion rates, angular displacement, position relative to coiling axis, and translation rates of chambers is suggested as a useful vehicle for inferring the geometric causes of observed evolutionary changes. These changes include size increase, decrease in the number of chambers per whorl, inflation, reduction of relative height of aperture, and increase in the peripheral angle. The sequence is judged to be an example of phyletic gradualism.
Equatorward migration of Globorotalia truncatulinoides ecophenotypes through the Late Pleistocene: Gradual evolution or ocean change?
Authors: Lohmann G. P. , Malmgren Björn A.
Published: July 2016

The biogeography of differences in average shape of the modern planktonic foraminifer Globorotalia truncatulinoides (d'Orbigny) exhibits systematic relationships to changes in the ocean's surface environment. Comparison of these shape changes, as they exist today in the Southern Hemisphere, with fossil shapes preserved in a Late Pleistocene record from the South Atlantic Ocean, shows that the biogeography of G. truncatulinoides ecophenotypes has changed markedly through time. Beginning at least 700,000 yr ago and continuing up to the present, there has been a gradual but clear migration of certain morphotypes of G. truncatulinoides toward lower latitudes. The history of this migration bears no simple relationship to the cyclic climatic changes that characterize the Late Pleistocene. We conclude that either (1) phenotypic variants of Gr. truncatulinoides reflect some previously unmeasured, gradually changing aspect of Late Pleistocene oceans, or (2) we are witnessing a gradual evolution of the environment preferences of G. truncatulinoides.
Individuals, hierarchies and processes: towards a more complete evolutionary theory
Authors: Vrba Elisabeth S. , Eldredge Niles
Published: July 2016

Hierarchy is a central phenomenon of life. Yet it does not feature as such in traditional biological theory. The genealogical hierarchy is a nested organization of entities at ascending levels. There are phenomena common to all levels: (1) Entities such as genomic constituents, organisms, demes, and species are individuals. (2) They have aggregate characters (statistics of characters of subparts), but also emergent characters (arising from organization among subparts). Character variation changes by (3) introduction of novelty and (4) sorting by differential birth and death. Causation of introduction and sorting of variation at each level may be (5) upward from lower levels, (6) downward from higher levels, or (7) lodged at the focal level. The term “selection” applies to only one of the possible processes which cause sorting at a focal level. Neo-Darwinian explanations are too narrow, both in the levels (of genotypes and phenotypes) and in the directive process (selection) which are stressed. The acknowledgment of additional, hierarchical phenomena does not usually extend beyond lip service. We urge that interlevel causation should feature centrally in explanatory hypotheses of evolution. For instance, a ready explanation for divergence in populations is “selection of random mutants.” But upward causation from genome dynamics (or downward causation from the hierarchical organism) to the directed introduction of mutants may be more important in a given case. Similarly, a long-term trend is traditionally explained as additive evolution in populations. But sorting among species may be the cardinal factor, and the cause may not be species selection but upward causation from lower levels. A general theory of biology is a theory of hierarchical levels—how they arise and interact. This is a preliminary contribution mainly to the latter question.
The mid-Paleozoic precursor to the Mesozoic marine revolution
Authors: Signor Philip W. , Brett Carlton E.
Published: July 2016

The mid-Paleozoic was punctuated by a rapid radiation of durophagous (shell-crushing) predators. These new predators were primarily placoderm and chondrichthyan fishes but probably also included phyllocarid and eumalacostracan arthropods. Coincident with the radiation of these durophages, beginning in the mid-Devonian, there was an increase in the frequency of predation-resistant morphologies in a variety of marine invertebrate taxa. Among bellerophontid molluscs, disjunct coiling disappeared and umbilici became less common while the frequency of genera with sculpture increased. The abundance of brachiopod genera with spines on one or both valves increased dramatically. Sculpture became more pronounced and common among genera of coiled nautiloids. Inadunate and camerate crinoids showed a marked increase in spinosity, and all three crinoid subclasses tended to develop thicker thecal plates.

Trends toward increasing relative frequencies of predation-resistant features were formed in different ways. Bellerophontid genera lacking predation-resistant features tended to go extinct, leaving the sculptured, tighdy coiled forms as the predominant forms. Among Brachiopoda, the radiation of productids provided the tremendous increase in numbers of spinose genera. Among crinoids, predation-resistant features were acquired through evolution within established clades.

These observations suggest that predation by shell-crushing predators has been an important control on the morphology and composition of the marine invertebrate fauna since at least the Middle Devonian. The mid-Paleozoic radiation of durophages and response of the marine fauna was in many respects similar to events of the Mesozoic Marine Revolution, in effect, the Paleozoic precursor to that event.
Some quantitative methods for studying evolutionary patterns in single characters
Authors: Charlesworth Brian
Published: July 2016

Some statistical methods are described for the detection and estimation of variability in the rate of evolution, from biometrical data on single characters in fossil lineages. The methods were applied to some published examples of protistan and mammalian lineages, extending between 0.8 and 6.4 Myr in duration. Of six cases examined, only one failed to show evidence for significant variation in the rate of evolution, and only four deviated significantly from a random walk pattern, despite significant net evolutionary change in all cases but one.
Functional evolution of the cheek tooth pattern and chewing direction in Tertiary horses
Authors: Rensberger John M. , Forsten Ann , Fortelius Mikael
Published: July 2016

By digitizing the enamel configuration and calculating the overall directional tendencies of the enamel edges in complex equid dental patterns, quantitative changes in functional attributes were traced through a phylogenetic series. Pronounced changes both in the directional emphasis of the enamel edges and in the chewing motion occurred and were interrelated. Two distinct trends were found. From early Eocene to Oligocene, edge alignment became increasingly confined to a single direction, but the teeth retained the phase I and phase II chewing angles characteristic of many primitive herbivorous and omnivorous mammals. The chewing direction in the horizontal plane also remained essentially unchanged. During the Oligocene and the early Miocene, both edge direction and chewing direction remained stable. However, the middle Miocene genus Merychippus represents a stage in which the enamel directional emphasis was lost in transition to a new anteroposterior emphasis, a trend that continued into the late Tertiary equine taxa. Concurrent with this transformation was a loss of all but vestiges of the phase I and II chewing angles in the vertical plane and a shift of the chewing direction in the horizontal plane to an almost transverse movement of the jaw.

In the Oligocene equids, the edges of the labial cusps did attain perpendicularity to the phase I chewing direction, which was oblique to the horizontal plane, but the chewing direction in the horizontal plane was far from perpendicular to the lingual enamel edge direction because the lingual cusps were configured for efficiency in compressive, not shearing, motion that dominated the phase II surfaces. In the later Tertiary the chewing direction and edges attained essentially a perpendicular relationship, which represents the theoretical optimum for a shearing system. The radical change in edge direction in the Miocene probably occurred as a result of an increase in translative movement (longer glide) between the surfaces, making the lingual edges subject to selection for perpendicularity and flattening of the occlusal surface, resulting in a condition where a single edge direction became optimal for all cusps. The extended chewing stroke translation was perhaps the key event initiating the other changes and would have resulted from increased chewing effort accompanying a shift to a diet of mainly grass. The loss of the dual (shearing and compressive) function of the occlusal surface suggests that the earlier diet may have contained significant proportions of other plant parts, such as fruits, seeds, or tender leaves that might be optimally chewed by compressive movements.
Predation and survival among inadunate crinoids
Authors: Lane N. Gary
Published: July 2016

The proposition is presented that the large thecae of many Paleozoic crinoids housed gonads, unlike modern crinoids that have the gonads on the arms or pinnules. Early in their history, inadunate crinoid gonads migrated into a voluminous anal sac, effectively separating them from other vital organs. Excision of the sac by predatory fishes and cephalopods would have been less traumatic than an attack on the theca, and the sac could be more readily regenerated. The pores and slits between plates on inadunate sacs are interpreted as gonopores. Some anal sacs may also have served as brood chambers. The traditional explanation of the sac as a special respiratory structure is discounted.
Alaskan Cretaceous-Tertiary floras and Arctic origins
Authors: Spicer Robert A. , Wolfe Jack A. , Nichols Douglas J.
Published: July 2016

Cretaceous floras in Alaska, when compared to those at mid-latitudes, generally indicate later appearances in Alaska of major clades and major leaf morphologies. Compared to mid-latitude floras, Alaskan Late Cretaceous floras contain few major clades. The Alaskan clades diversified but at a low taxonomic level. Migrational pathways into high latitudes were probably along streams. Similar patterns characterized the Alaskan Tertiary, although some southward migrations of lineages occurred during the Neogene.

Review of other Arctic paleontological data from Ellesmere Island, previously used to suggest that the Arctic was a major center of origin during the Late Cretaceous, indicates that the ages of supposedly substantiating dinoflagellate floras were misinterpreted. When the dinoflagellate data are interpreted according to standard methodology, first occurrences of genera and species groups on Ellesmere are, like the Alaskan occurrences, later than first occurrences at middle latitudes.
Prediction of sample size effects on the measured temporal and geographic distribution patterns of species
Authors: Koch Carl F.
Published: July 2016

Few paleontological studies of species distribution in time and space have adequately considered the effects of sample size. Most species occur very infrequently, and therefore sample size effects may be large relative to the faunal patterns reported. Examination of 10 carefully compiled large data sets (each more than 1,000 occurrences) reveals that the species-occurrence frequency distribution of each fits the log series distribution well and therefore sample size effects can be predicted. Results show that, if the materials used in assembling a large data set are resampled, as many as 25% of the species will not be found a second time even if both samples are of the same size. If the two samples are of unequal size, then the larger sample may have as many as 70% unique species and the smaller sample no unique species. The implications of these values are important to studies of species richness, origination, and extinction patterns, and biogeographic phenomena such as endemism or province boundaries. I provide graphs showing the predicted sample size effects for a range of data set size, species richness, and relative data size. For data sets that do not fit the log series distribution well, I provide example calculations and equations which are usable without a large computer. If these graphs or equations are not used, then I suggest that species which occur infrequently be eliminated from consideration. Studies in which sample size effects are not considered should include sample size information in sufficient detail that other workers might make their own evaluation of observed faunal patterns.
Testing for equality of rates of evolution
Authors: Kitchell Jennifer A. , Estabrook George , MacLeod Norman
Published: July 2016

A new method of data analysis offers a potentially powerful tool for statistically evaluating hypotheses of rate in temporally-ordered evolutionary phenomena. We present a method for bootstrapping time-ordered data sets to test hypotheses of the equality of rate. This method is applicable to both nonrandom and random generative processes. The method is applied to the data of Malmgren et al. (1983) for theGloborotalia plesiotumida–G. tumidaplanktonic foraminiferan lineage and the data of Reyment (1982) for the benthonic foraminiferanAfrobolivina afar. G. plesiotumidais recognizable on the basis of independent data as a species distinct fromG. tumida,its descendant. Evolutionary change rate during the evolution ofG. tumidafromG. plesiotumidais shown to be faster than rates within either species. The pattern of variation exhibited byA. afarincludes a time interval of more rapid change; this more rapid change is observedpost hoc.A bootstrapping model based onpost hocobservations reveals the rate in this time interval to be not significantly faster than expected in suchpost hocintervals.
The evolution of locomotor stamina in tetrapods: circumventing a mechanical constraint
Authors: Carrier David R.
Published: July 2016

Endothermic tetrapods differ dramatically from ectothermic tetrapods in having a great capacity to sustain vigorous locomotion. I suggest that this difference reflects alternative adaptive responses to a mechanical constraint that was an inherent consequence of the vertebrate transition from aquatic to terrestrial modes of locomotion and respiration. The earliest tetrapods may not have been able to walk and breathe at the same time. Their sprawling gait and lateral vertebral bending would have required unilateral contractions of the thoracic musculature that may have interfered with the bilateral movements necessary for breathing. Modern lizards, whose locomotor and respiratory anatomy resembles that of the early tetrapods, provide support for this hypothesis because their breathing is greatly reduced during locomotor activity. Tetrapod lineages that gave rise to modern ectotherms apparently retained the constraint, becoming either highly specialized for burst activity based on anaerobic metabolism or specialized in passive mechanisms of defense against predators. The lineages from which birds and mammals are derived have undergone morphological changes that enable simultaneous running and breathing. In modern tetrapods upright posture is correlated with endothermic metabolism. This correlation may have arisen to circumvent ancestral constraints on locomotor stamina.
Sharovipteryx, a reptilian glider?
Authors: Gans Carl , Darevski Ilja , Tatarinov Leonid P.
Published: July 2016

The unique holotype of the Triassic reptile Sharovipteryx (initially Podopteryx) mirabilis has been reexamined and redescribed, correcting the original account. It is a small lizard-like reptile with an elongate head and densely tubular femur and tibia each longer than the (estimated) intergirdle distance. (Part of the pectoral region has been lost and the remnants remain encased in the matrix.) The matrix retains the impression of portions of the integument, including a patagium that reached from the hindlimbs to the base of the tail. Unlike the original account, the patagium did not extend to the pectoral limbs. Experiments with models indicate that Sharovipteryx could have maintained a shallow glide if the femora were held at a shallow angle to the vertebral column and the tibia and feet extended out at right angles to it, thus stretching the integument. The pectoral limbs (with or without a fringing membrane) might have produced a variable canard; alternatively vertical bending of the tail could have applied drag, each making the glide more stable.
Morphological variation in a colonial marine hydroid: a comparison of size-based and age-based heterochrony
Authors: Blackstone Neil W. , Yund Philip O.
Published: July 2016

In studies of heterochrony, timing of development is generally measured relative to some intrinsic dimension, usually size, which serves as a proxy for time. A complementary approach is to measure timing relative to chronological time, an extrinsic dimension. Here, colony growth of a marine hydroid, Hydractinia echinata, is used to compare size- and age-based approaches to rate heterochronies. Colonies consist of feeding polyps; a basal, encrusting mat; and, in some cases, stolons which extend from the mat. Size is measured by the area covered by the mat and, if present, the stolons. Rate of polyp production was compared between colonies using clonal replicates grown in a common environment. Age-based comparisons employed polyp specific growth rates calculated over the same ontogenetic time interval for each replicate. Specific growth rates for colony area were also calculated; rates-ratios (polyp/area) provided size-based measures of polyp growth, analogous to allometric coefficients commonly used in studies of rate heterochronies. These comparisons show that size can be a misleading referent for between-colony comparisons because the rate of areal growth is not constant among colonies. Size-based measures of changes in developmental rates may provide insight into patterns, but not necessarily processes, of heterochrony. The implications of the pattern-oriented framework of size-based heterochrony should be considered in paleontological studies.
A community-level test of the Mesozoic marine revolution theory
Authors: Aronson Richard B.
Published: July 2016

The Mesozoic marine revolution theory postulates a causal connection between the Cretaceous radiations of durophagous predators and the decline of suspension-feeding echinoderms in shallow-water habitats. In order to test the temporal distribution of dense ophiuroid populations for such a decline, I present a method of calculating the expected distribution of populations or communities in different geologic timespans. This statistical null hypothesis may then be compared with data from the fossil record to draw paleoecological inferences. The model takes into account the relative lengths of time blocks, the decay of sedimentary rock, and changes in shallow sea area through time. Although mass extinctions did not cause the immediate disappearance of shallow-water “brittlestar beds,” brittlestar beds show a significant decline in the Early Cretaceous. Results of several studies suggest that predators were at least partially responsible for reducing the distribution of dense ophiuroid populations.
Diversity-dependent species dynamics: incorporating the effects of population-level processes on species dynamics
Authors: Maurer Brian A.
Published: July 2016

A general model of species dynamics must incorporate the effects of species number on the processes of speciation and extinction. Previous models make specific assumptions about these effects, but do not consider the effects of dynamics of lower level entities on speciation and extinction rates. A hierarchical model is developed which explicitly describes the effects of energy use by species on speciation and extinction rates. The effects of energy use are represented by parameters that characterize the average effects of energy use by each species in the biota on speciation and extinction rates. The dynamics of the model describe a sigmoidal increase in species number over time, as does the logistic model of species dynamics. However, the mechanisms of those dynamics are assumed to be different in the two models. Empirical analysis of a data set on the diversification of fossil Miocene horses suggests that the logistic and hierarchical models have similar descriptive power. The hierarchical model incorporates insights from recent considerations of the nature of a hierarchical theory of biology. Further progress in developing such a theory will depend on the success with which relationships among levels in the biological hierarchy are able to be defined.
Fabricational noise in elephant dentitions
Authors: Roth V. Louise
Published: July 2016

A marked retardation of dental ontogeny characterizes the family Elephantidae. As a consequence of this retardation, elephant teeth are subject to the forces of mastication, eruption, and progression while still in a developing and pliant stage. As specimens described here illustrate, the mechanical forces are often sufficient to deform the gross morphology of dentitions. Morphological variation in elephant teeth can be regarded as “fabricational noise”—revealing information about the dynamic context in which the teeth develop. Accordingly, dental variation is less species-specific in elephants than in other mammals. The fossil record may comprise fewer species of elephants than is generally believed, and trends inferred to reflect rapid evolution within this family may in fact reflect phenotypic plasticity.
Paleoecologic, paleoclimatic, and evolutionary significance of the Oligocene Creede flora, Colorado
Authors: Wolfe Jack A. , Schorn Howard E.
Published: July 2016

Application of multivariate statistical techniques, especially correspondence analysis, results in the recognition of four major communities for the Creede plant assemblages: fir-spruce forest, fir-pine forest, pine-juniper forest or woodland, and mountain mahogany chaparral. Physiognomy of the Creede assemblages indicates a mean annual temperature of <2.5°C. Paleoaltitudinal estimates based on this temperature estimate are inconsistent with physiographic and structural data of post-depositional uplift, unless the climatic effects of a closed basin are factored in; these effects imply that the Creede paleotemperature (and hence paleoaltitude) is applicable to the caldera rim. A variety of data indicate that summers were dry and most precipitation occurred as snow. The stratigraphic sequence of assemblages indicates that significant precipitational change occurred during deposition of the Creede plant-bearing beds.Chamaebatiaria, a shrub that now inhabits dry, open environments, had an ancestral taxon characteristic of the Creede fir-forest communities and strongly indicates a major shift in habitat for this lineage during the Neogene. A second genus,Luetkea, which is now herbaceous, is represented by a probable woody ancestral taxon that was common in the Creede forest communities. Consideration of the adaptive and morphologic histories of the Creede lineages suggests that physiologic adaptation may precede morphologic change. The Creede forest communities have no modern homologues.
Optimized skeletal morphologies of silicoflagellate generaDictyochaandDistephanus
Authors: McCartney Kevin , Loper David E.
Published: July 2016

Several groups of siliceous microorganisms possess a skeletal latticework of interconnected rods. Skeletal configurations of one of these groups, the silicoflagellates, can be produced by a simple mathematical model that minimizes the apical surface area for a given basal area and internal volume. A similar model that minimizes the total length of the skeletal elements, and thus the silica utilization and skeletal weight, produces configurations that are generally less common in silicoflagellates. The diversity of silicoflagellate skeletal morphologies suggests that both the minimization of apical surface area and the conservation of skeletal material may be important factors in skeletal design. The two most important morphologies found in modern oceans, the four-sidedDictyochaand the six-sidedDistephanus, can co-occur in an environment where both factors have some relative importance. However, these models do not explain the range of silicoflagellate skeletal morphology found in nature.
Analysis of clade shape using queueing theory and the fast Fourier transform
Authors: Gilinsky Norman L. , Good I. J.
Published: July 2016

Using queueing theory and the fast Fourier transform, we develop a new approach to analyzing the diversity paths of fossil taxa. The methods employed focus on calculating the probabilities, for each taxonomic group, of arriving at particular values of the diversity at particular times, assuming that diversity paths are random walks. These probabilities, which are represented in probability matrices, allow us to establish a number of null hypotheses that can be used to test for randomness in the diversity paths of the taxonomic groups themselves. As the model employed here is conceptually similar to that employed by Gilinsky and Bambach (1986) in bootstrapping, one consequence of the approach is, in effect, an analytic solution of the bootstrap. A comparison of bootstrapping and analytic results in 15 taxa of marine invertebrates gives nearly identical results. The analytic approach is more general, however, and allows for the calculation of probability matrices under other model assumptions not treated here. We have also applied the probability matrices to a series of tests for nonrandomness as a whole, in contrast to the more usual method of testing particular clade statistics. The familial diversity paths of all 36 extinct orders of marine invertebrates with ten or more families were analyzed. In no case was the null hypothesis of randomness rejected at the 0.05 level. Given the model, and assuming that extinct taxa are representative of all taxa, the familial diversity paths of marine orders appear to behave as random walks.
Constraint and adaptation in the bone-cracking canid Osteoborus (Mammalia: Canidae)
Authors: Werdelin Lars
Published: July 2016

The borophagine canids were bone-cracking scavengers in the Miocene-Pleistocene of North America. In this they parallel the Recent hyenas. This paper analyzes the borophagine adaptation in relation to that of hyaenids, using Osteoborus cyonoides as an example. The emphasis during canid evolution on the posterior molars, which is a derived condition, created a constraint on the adaptation of borophagines. This constraint meant that the borophagines used P4/4 as bone-cracking teeth, whereas hyaenids use P3/3. The latter adaptation has the advantage of separating the bone-cracking teeth from the meat-cutting portion of the dentition, thereby allowing a dual purpose dentition in hyaenids. In borophagines, no such dual purpose was possible, and it is suggested that they were closer to obligate bone-cracking scavengers than Recent hyaenids. Other than the evolution of a specialized bone-cracking tooth, the borophagines adapted to bone cracking by evolving a vaulted and strengthened skull for the dissipation of the strong forces generated during bone cracking. In this they again parallel the hyaenids. Evolution within borophagines involved an elaboration of patterns already set at the group's inception, creating an evolutionary trend which was mediated by the constraint on the bone-cracking morphology. This trend may be due to selection or sorting, or may, under certain assumptions, be stochastic. Other evolutionary trends may also be epiphenomena of constraints that lock morphological evolution.
Sublethal injury and shell repair in Upper Mississippian ammonoids
Authors: Bond Paul N. , Saunders W. Bruce
Published: July 2016

Sublethal injuries recorded in the shells of five Upper Mississippian ammonoid species from the Imo Formation of northwest Arkansas are manifested as repaired shell breaks, which can be categorized as minor, moderate, massive, deep-acute, or as perforations. Overall, 15% of the ammonoids exhibit some form of repaired break. The injuries are distributed as follows: Anthracoceras discus 9%; Fayettevillea bransoni 13%; Fayettevillea friscoense 21%; Rhadinites miseri 24%; Richardsonites mapesi 38%. These figures are substantially lower than in living Nautilus, in which more than one-half of adult specimens exhibit repaired shell breaks. The different frequencies of injuries may reflect species-selective predation, differential abilities to sustain and to repair shell damage, or they may be due to interspecific differences in physical parameters such as shell thickness and body chamber length. The most likely possible perpetrators of the injuries include sharks, other fishes, and cephalopods.
Morphogenesis of uniaxiate graptoloid colonies—a mathematical model
Authors: Urbanek Adam , Uchmański Janusz
Published: July 2016

Morphological gradients in graptoloid colonies are explained by the production and diffusion of a morphogen from the sicula distalwards. Size of the thecae is inversely related to the amount of morphogen present. The graduate decrease of morphogen is given by a set of algebraic equations, and its effect on zooid growth is described by a modified Michaelis-Menten relationship. Changes in size of thecae computed on the basis of these equations fit the changes observed in graptolite colonies. Sets of differential equations are also given to describe the rate of morphogen diffusion and some other processes possibly involved in the development of uniaxiate graptoloid colonies. The suggested basic model of these colonies can be completed by a number of additional assumptions; however, computer experiments reveal that such assumptions do not affect the main properties of the model, namely the appearance of graded series of thecae. New evidence for regeneration of the sicular portion of the broken rhabdosome is presented, providing arguments that morphogen was produced by the siculozooid as a single bolus of secretion. Some local exclusions from the regular size gradient are discussed, and tentative explanations are suggested.
Molecules and the Early Fossil Record
Authors: Valentine James W.
Published: July 2016

The earliest fossil record of animals has long been an enigma. For nearly a century after the appearance ofThe Origin of Species, mineralized trilobites were thought to be among the first organisms to appear as fossils, and as they were considered to be complex life forms, a long previous episode of animal evolution seemed to be indicated. Discovery and description of Tommotian and Vendian faunas, with their small shelly and Ediacaran fossils respectively, provided us with an idea of the nature of organisms in strata that are progressively older than the trilobite-bearing beds. Yet in these older assemblages we do not find the sorts of organisms that might be expected to be precursors to the well-known Phanerozoic clades. The puzzle remains.
Carboniferous-Triassic gastropod diversity patterns and the Permo-Triassic mass extinction
Authors: Erwin Douglas H.
Published: July 2016

Paleozoic and post-Paleozoic marine faunas are strikingly different in composition. Paleozoic marine gastropods may be divided into archaic and modern groups based on taxonomic composition, ecological role, and morphology. Paleozoic assemblages were dominated by pleurotomariids (Eotomariidae and Phymatopleuridae), the Pseudozygopleuridae, and, to a lesser extent, the Euomphalidae, while Triassic assemblages were dominated by the Trochiina, Amberleyacea, and new groups of Loxonematoidea and Pleurotomariina. Several new groups of caenogastropods appeared as well. Yet the importance of the end-Permian mass extinction in generating these changes has been questioned. As part of a study of the diversity history of upper Paleozoic and Triassic gastropods, to test the extent to which taxonomic and morphologic trends established in the late Paleozoic are continued after the extinction, and to determine the patterns of selectivity operating during the extinction, I assembled generic and morphologic diversity data for 396 genera in 75 families from the Famennian through the Norian stages. Within this interval, gastropod genera underwent an adaptive radiation during the Visean and Namurian, largely of pleurotomariids, a subsequent period of dynamic stability through the Leonardian, a broad-based decline during the end-Permian mass extinction, and a two-phase post-extinction rebound during the Triassic. The patterns of generic diversity within superfamily-level clades were analyzed using Q-mode factor analysis and detrended correspondence analysis.

The results demonstrate that taxonomic affinity, previous clade history, generic age, and gross morphology did not determine survival probability of genera during the end-Permian extinction, with the exception of the bellerophontids, nor did increasing diversity within clades or expansion of particular morphologies prior to the extinction facilitate survival during the extinction or success after it. The pleurotomariids diversified during the Lower Permian, but were heavily hit by the extinction. Similarly, trochiform and turriculate morphologies, among those which Vermeij (1987) has identified as having increased predation resistance, were expanding in the late Paleozoic, but suffered similar extinction rates to other nondiversifying clades. Survival was a consequence of broad geographic and environmental distribution, as was the case during background periods.
Cosomys primus: a case for stasis
Authors: Lich Deborah K.
Published: July 2016

The first lower molar length, width, and posterior loop width were analyzed for tenCosomys primuspopulations from horizontal deposits ranging in elevation from 3,000 to 3,295 feet. Sedimentation rates based on radiometric dates for two ashes and rates derived in previous studies suggest that these sediments span an interval of time that ranges from 45,000 to 164,000 years ago. Nonmetric data included the presence of enamel pits, prism folds, and crenulations; the number of triangles; and relative dentine tract heights. Coefficients of variation for the metrics were low, 4 to 7, and a one-way ANOVA revealed no significant differences between any of the populations. Changes in the mean phenotype were less than two phenotypic standard deviations and were not correlated with elevation. The presence of enamel pits, prism folds, and crenulations correlated only with less occlusal wear.

Thus, these microtine rodent populations appear to exhibit stasis over a time period of at least 45,000 and possibly as much as 164,000 years, unless the deposits accumulated more rapidly than previously estimated.
A functional interpretation of the masticatory system and paleoecology of entelodonts
Authors: Joeckel R. M.
Published: July 2016

Entelodonts are medium to large (perhaps 150–750 kg) Oligocene–Miocene bunodont artiodactyls with unique crania but typical artiodactyl postcrania. Functional and ecological interpretations are difficult because there is no clear modern analog to an entelodont in size, dentition, and cranial morphology. Entelodont crania combine primitive and derived features, including laterally expanded zygomatic arch/large temporal fossa (suggesting a large temporalis muscle), unreduced dental formula, long premolar row, fused mandibular symphysis, isognathy, and subcylindrical dentary condyles. Furthermore, the cranium has unique architectural and ontogenetic aspects unparalleled in extant mammals. Canines show heavy, carnivoran-like, apical wear in old individuals, suggesting regular contact with food. Conical premolars and associated diastemata dominate the tooth row. Premolars are often apically worn, in a fashion somewhat like those of carnivorans (e.g.,Crocuta, Borophagus). Molars are low-cusped crushing teeth. Wide gape, indicated by the form of the coronoid process and temporal fossa, facilitated canine and premolar use, probably both in feeding and in social behavior. Jaw mechanics, tooth morphology, and tooth wear are compatible with omnivory and probable scavenging, an intriguing proposition for the hugeDinohyus hollandi.