bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth in encrusting cheilostome bryozoans: II. Circum-Atlantic distribution patterns
Authors: Lidgard Scott
Published: July 2016

Differences in zooid skeletal ontogeny are strongly linked to the distribution of bryozoan species, even along such large-scale environmental gradients as depth and latitude. Three growth patterns broadly characterize zooid formation for encrusting cheilostome bryozoans: zooidal and intrazooidal budding, which facilitate growth in two dimensions at colony margins; and frontal budding, which also permits upward growth in the third dimension. Analyses of skeletal growth patterns of encrusting species present in 230 Recent assemblages from the North Atlantic, Mediterranean, North Sea, and Gulf of Mexico show that species with zooidal budding dominate overwhelmingly at lower latitudes and in shallower water, as assessed by percentages of species within assemblages. In contrast, patterns within moderately diverse fossil assemblages from North America indicate that within the geographic and environmental limits sampled, species with intrazooidal budding once dominated and probably originated in shallow, warm water environments. Intrazooidal budding now occurs with greater relative frequency among species from deeper and higher latitude assemblages. Patterns for frontal budding suggest a slight decrease with increasing depth, but no consistent relationship with latitude. These paleoenvironmental trends occur withn a putatively monophyletic clade and are markedly similar to onshore/offshore trends recognized in other groups of marine benthos, based on patterns of occurrence of supra-specific taxa and novel morphotypes. Results presented here are based on relative dominance of species within assemblages and thus provide a novel comparative test of these previously reported trends.
Antiquity of the chordate pattern of exercise metabolism
Authors: Ruben John A. , Parrish Julia K.
Published: July 2016

Vertebrates and cephalochordates generate significant quantities of lactic acid during intense exercise. This is associated with heavy reliance on anaerobic metabolism for intramuscular ATP formation. We report here exercise-related generation of lactate in the appendicularian Oiko-pleura longicauda (Tunicata: Appendicularia) and in the brittle star Ophioderma panamensis (Echinodermata: Ophiuroidea). The chordate-wide distribution of this pattern of activity metabolism suggests its presence in Early Paleozoic prochordates. The presence of the chordate pattern of activity physiology in Ophioderma suggests that very early (Ediacarian?) deuterostomes may also have generated lactate during intense exercise. Further investigation of activity physiology in other echinoderms is warranted.
Bone histology of the ichthyosaurs: comparative data and functional interpretation
Authors: de Buffrénil Vivian , Mazin Jean-Michel
Published: July 2016

The periosteal cortex in the shaft of limb bones is described histologically in three ichthyosaurian genera,Omphalosaurus, Stenopterygius, andIchthyosaurus. The primary periosteal deposits are composed of typical woven-fibered tissue that was accreted as spongy bone in young individuals, and more or less compact bone in older individuals. During growth, the bone tissue was extensively remodeled with a quantitative imbalance between resorption and redeposition. As a result, the cortex was made cancellous, if previously compact, or still more spongy, if already cancellous. This pattern of remodeling explains why compact cortices are generally lacking in the long bones of ichthyosaurs. The presence of woven-fibered tissue strongly suggests that the limb bones, and probably also the body as a whole, had a rapid postnatal growth in ichthyosaurs, that might have been related to a high, “endotherm-like” metabolic rate. This hypothesis bears on the ecological interpretation of the ichthyosaurs: they could have been capable of sustained, fast swimming and long-range movements, rather than being slow-moving creatures as commonly supposed.
Gross spinal anatomy and limb use in living and fossil reptiles
Authors: Giffin Emily B.
Published: July 2016

The spinal quotient (S.Q.) is an osteologically defined estimate of the enlargement of the spinal cord at limb levels over that at interlimb levels. It is an efficient predictor of limb use in living reptiles and birds and may be used to predict limb function in fossil vertebrates. Among living reptiles, this ratio of limb to interlimb innervation is greatest in arboreal genera, followed by terrestrial sprawlers, aquatic forms, and undulatory forms. Birds show a wide range of brachial S.Q. values that are roughly commensurate with flight ability. S.Q. values for the manipulative forelimbs of some dinosaurs fall well above those of locomotory limbs. Dinosaur hind-limb values are either well within ranges predicted by living reptiles and birds (most taxa), or highly inflated (stegosaurs, sauropods). This inflation may be the result of presence of a glycogen body similar to that of birds. In no case does the lumbosacral S.Q. support the presence of a “sacral brain.”
Biomechanics of the jaw apparatus of the gigantic Eocene birdDiatryma: implications for diet and mode of life
Authors: Witmer Lawrence M. , Rose Kenneth D.
Published: July 2016

Discovery of several new specimens of the gigantic Eocene ground birdDiatryma giganteafrom the Willwood Formation of northwestern Wyoming, has prompted an analysis of its feeding apparatus and an assessment of the mode of life of this unusual bird.Diatrymaexhibits many of the features predicted by biomechanical models to occur in animals delivering large dorsoventral bite forces. Similarly, the mandible ofDiatryma,which was modeled as a curved beam, appears well equipped to withstand such forces, especially if they were applied asymmetrically. Interpretation of these size-independent biomechanical properties in light of the large absolute skull size ofDiatrymasuggests a formidable feeding apparatus. The absence of modern analogues complicates the determination of just how this unique skull morphology correlates with diet. Suggestions thatDiatrymawas an herbivore seem improbable in that they require the postulation of excessively high safety factors in the construction of the skull. The traditional hypothesis ofDiatrymaas a carnivorous bird accords as well or better with the data at hand. Carnivory raises the probability of “accidental” encounter with bones, thus explaining the high safety factors. In fact, the skull and mandible ofDiatrymaare so massive that bone crushing may have been an important behavior.Diatrymacould have been a scavenger. However, limb allometry and phylogenetic interpretation of limb proportions call into question the picture ofDiatrymaas a slow, plodding graviportal animal, suggesting that active predation was within its behavioral repertoire.
Bias of the paleobotanical record as a consequence of variations in the chemical composition of higher vascular plant cuticles
Authors: Tegelaar Erik W. , Kerp Hans , Visscher Henk , Schenck Pieter A. , de Leeuw Jan W.
Published: July 2016

The impact of the variations in the chemical composition of higher vascular plant cuticles on their fossil record is usually not considered in paleobotanical and, more particularly, taphonomic studies. Here we address the subject with reference to the chemical characterization of insoluble cuticular matrices of a large variety of recent and fossil cuticles. The cuticles were analyzed using Curie-point pyrolysis-gas chromatographic techniques. Cuticular matrices of extant higher plants consist either of the biopolyester cutin, the insoluble, non-hydrolyzable polymethylenic biopolymer cutan, or a mixture of both biopolymers. In fossil cuticles an additional cuticular matrix type consisting of cutan and cutin-derived material is recognized. On the basis of the variations in their chemical composition and the different behavior of the cuticular constituents (viz., cutin and cutan) during diagenesis, it is concluded that the paleobotanical record of cuticles will be biased toward taxa originally having a significant amount of cutan in their cuticular matrix.
Probabilities of origination, persistence, and extinction of families of marine invertebrate life
Authors: Gilinsky Norman L. , Good I. J.
Published: July 2016

In this paper we model the process of taxonomic evolution as a Galton-Watson branching process in discrete time and, using maximum likelihood, develop methods to estimate the probabilities of origination, persistence, and extinction of fossil taxa. We use the methods to estimate the probabilities of origination, persistence, and extinction of families (1) within 135 orders of marine invertebrate organisms, (2) within 12 phyla, and (3) within all marine invertebrate life (independently of the suprafamilial classification).

Most orders, including the arcoid bivalves, the dentaloid scaphopods, the orders of chitins, and many others, have relatively low probabilities of familial origination and extinction. The various ammonoid and trilobite orders, and some others, have high probabilities of origination and extinction. Among the phyla, the Archaeocyatha have the highest probabilities of familial origination and extinction, and the Annelida the lowest, with the more typical phyla of shelly organisms clustering near the high end of the probability scale. The Porifera and Protozoa also have low probabilities but not as low as the Annelida. The estimated origination and extinction probabilities for families within all marine invertebrate life are 0.470 and 0.452 per stage, respectively, values that are at the high end of the probability scale. We have also estimated the probabilities of ultimate extinction (extinction of all families) of the supertaxa.

By analyzing the changes of the diversity during each stratigraphic stage separately, we have also determined the trajectories of the estimated origination and extinction probabilities for families within all marine invertebrate life. The estimated origination probability is relatively high in association with the expansion of the Cambrian and Paleozoic evolutionary faunas and declines to more normal levels for the remainder of the Phanerozoic. The trajectory of the estimated extinction probability is from nearly zero early in the Phanerozoic to more normal levels later, showing clearly defined peaks in association with the five Phanerozoic mass-extinction events. The terminal Cretaceous mass extinction is the only one of the five that was not preceded by a monotonic decline of origination probability or by a series of stages with low origination probability. It appears to have been a unique, singular event.

Because the mathematical theory we employ as a model corresponds so closely to the processes of taxonomic evolution as we understand them, we believe that the theory provides a reasonable model of biological reality.
Ecogeography and the Great American Interchange
Authors: Webb S. David
Published: July 2016

When the isthmian land bridge triggered the Great American Interchange, a large majority of land-mammal families crossed reciprocally between North and South America at about 2.5 Ma (i.e., Late Pliocene). Initially land-mammal dynamics proceeded as predicted by equilibrium theory, with roughly equal reciprocal mingling on both continents. Also as predicted, the impact of the interchange faded in North America after about 1 m.y. In South America, contrary to such predictions, the interchange became decidedly unbalanced: during the Pleistocene, groups of North American origin continued to diversify at exponential rates. Whereas only about 10% of North American genera are derived from southern immigrants, more than half of the modern mammalian fauna of South America, measured at the generic level, stems from northern immigrants. In addition, extinctions more severely decimated interchange taxa in North America, where six families were lost, than in South America, where only two immigrant families became extinct.

This paper presents a two-phase ecogeographic model to explain the asymmetrical results of the land-mammal interchange. During the humid interglacial phase, the tropics were dominated by rain forests, and the principal biotic movement was from Amazonia to Central America and southern Mexico. During the more arid glacial phase, savanna habitats extended broadly right through tropical latitudes. Because the source area in the temperate north was six times as large as that in the south, immigrants from the north outnumbered those from the south. One prediction of this hypothesis is that immigrants from the north generally should reach higher latitudes in South America than the opposing contingent of land-mammal taxa in North America. Another prediction is that successful interchange families from the north should experience much of their phylogenetic diversification in low latitudes of North America before the interchange. Insofar as these predictions can be tested, they appear to be upheld.
Growth form in Silurian heliolitid corals: the influence of genetics and environment
Authors: Young Graham A. , Scrutton Colin T.
Published: July 2016

Colony growth form in some Silurian heliolitid corals is analyzed by the measurement of their shape in profile. Data are presented for seven species,Stelliporella parvistella, Heliolites interstinctus, H. megastoma, H. daintreei, H. spongodes, Propora tubulata,andPlasmopora scitafrom three localities in Gotland, Sweden, and three localities in England. Intraspecific growth-form variation is presented on triangle diagrams. These plots allow variation to be compared between species present at each locality and between localities for each species. Results indicate that the overall potential for growth-form variation is genetically controlled and that levels of response to environmental stimuli may differ markedly between species.Stelliporella parvistellais a very plastic species, the only one developing branching growth in addition to other growth forms.Heliolites interstinctusis much less variable, dominantly tabular, domal, and low bulbous in form, but demonstrates a similar response.Propora tubulatahas a tightly constrained bulbous growth form that shows little variation between localities. The other species are represented by few specimens, most of which parallelH. interstinctus.The likely moderating influences of light levels, substrate type, sedimentation rate, energy levels, and other variables on growth-form variation and species range are considered. The main environmental factor including ecophenotypic response is concluded to be sedimentation rate. A close correlation between this factor and growth form inS. parvistellaindicates that form in this species is a particularly sensitive indicator of sedimentation rate and substrate conditions. No simple equations can be made between specific environments and one particular growth form in these corals.
The disparity of the Burgess Shale arthropod fauna and the limits of cladistic analysis: why we must strive to quantify morphospace
Authors: Gould Stephen Jay
Published: July 2016

Three major arguments have been raised against the crucial claim, documented by Whittington and colleagues for the Burgess Shale fauna, and so contrary to traditional views, that disparity of anatomical design reached an early maximum in the history of multicellular life: (1) the presence of many early taxa with low membership and high rank is an artifact of naming; (2) cladistic analysis of Burgess arthropods negates the claim for greater early disparity; and (3) Whittington's argument is a retrospective fallacy based on assigning high rank to differentia only by virtue of their later capacity to define major branches. I show that all these arguments are either false or illogical, and that the claim for increased early disparity is justified: (1) Taxonomic rank is an artifact, but no one has ever based a claim for greater disparity on this false criterion. (2) Cladistics can only deal with branching order, whereas disparity is a phenetic issue. These two legitimate aspects of evolutionary “relationship” are logically distinct. The rooting of a cladogram only illustrates monophyletic ancestry (which no one doubts, as we are not creationists), and cannot measure disparity. (3) The active stabilization of the differentia ofBaupläne(for genetic and developmental reasons only dimly understood) provides a powerful rationale for weighting these characters in considerations of disparity; nothing had so stabilized in the Burgess fauna. If these differentia were steadily changing contingencies, rather than actively stabilized features with “deep” architectural status, then the retrospective argument would be justified. Although the three arguments are wrong, the claim for greater early disparity cannot be confidently established until we develop quantitative techniques for the characterization of morphospace and its differential filling through time. This is a dauntingly difficult problem, much harder than cladistic ordering, but not intractable.
Eocene echinoids, the Suwannee Strait, and biogeographic taphonomy
Authors: Carter Burchard D. , McKinney Michael L.
Published: July 2016

Faunal similarity among regions is often used as a means of identifying regions of endemism in fossil faunas. At least two large-scale taphonomic effects can affect apparent faunal similarity: stratigraphic and facies mismatching. In stratigraphic mismatching, an unconformity represents removal of most or all of a complete assemblage zone in one region, and the constituent taxa are mistakenly interpreted as having never inhabited that region. In facies mismatching, environmental differences between two regions (possibly unrecognized) cause the inference of a barrier that never existed. The two types of mismatching can work in concert if a facies was originally represented in a single stratigraphic interval that has been completely removed from one region. Analysis of faunal similarity via multivariate analysis of individual localities, coupled with comparison of the regions as single samples, may indicate mismatching if the results differ significantly.

We view these two problems as part of a suite of taphonomic effects that are not evident in paleobiological analyses of smaller geographic scope. First, there is ambiguity in the notion of “barrier,” even when a candidate is obvious. Second, barriers in paleobiogeography are often hidden and must be inferred from their effects rather than observed. Third, stratigraphic and facies mismatching produce effects on regional faunas similar to those produced by barriers. Anyone using barriers to explain faunal disruptions should address these three points.

Upper Eocene faunas of central Florida seem taxonomically distinct from those of the remainder of the Gulf Coastal Plain. This has historically been attributed to a known paleogeographic feature, the Suwannee Strait, which acts as a barrier. The amount of dissimilarity of the echinoid faunas is greater than the amount predicted as a result of sampling problems. Comparison of the results of multivariate and whole-region analyses suggests that mismatching of the two faunas, rather than a true barrier, causes the distinction. Principally facies, but also strata are mismatched. Early Late Eocene faunas inhabited terrigenous sands to the north of the strait and carbonate sands to the south and show the highest distinctiveness. Middle Late Eocene faunas inhabited primarily carbonate sands to the south and both carbonate sands and muds to the north. Overall similarity is higher for both local and regional analyses, and the faunas of northern sands are more similar to those of the southern region than to the northern mud faunas. Overall similarity across the strait is highest in the late Late Eocene strata when both regions had carbonate mud and sand facies. The faunas exhibit greater similarity within facies than they do within regions. Upper Late Eocene strata are poorly preserved north of the strait because of post-Eocene erosion.
Conjunction among taxonomic distributions and the Miocene mammalian biochronology of the Great Plains
Authors: Alroy John
Published: July 2016

This paper presents a new means of interpreting the distribution of taxa among taxonomic lists. Traditionally, “similarity” indices have been used to compare lists, and “association” measures have been used to compare taxonomic distributions. It is argued that when sampling regimes are poorly understood, all similarity and association indices are unjustifiable. However, observations that taxa have overlapping (conjunct) or nonoverlapping (disjunct) distributions are universally meaningful. Because greater sampling can only increase the number of known conjunctions and because long lists serve as conjunctional Rosetta Stones, conjunction data sets can be far more reliable than the lists that generate them. One way to account for patterns of conjunction and disjunction is to create theoretical spaces composed of two distributional boundaries or edges for each taxon in each dimension. A parsimonious arrangement of edges implies distributions that always overlap when taxa are conjunct and infrequently overlap when taxa are disjunct. A procedure involving correspondence analysis is shown to minimize the number of implied disjunctions. The method is used to analyze a set of 271 Miocene large-mammal genus lists from the Great Plains region. Biostratigraphic and radiometric data demonstrate that the “best” arrangement of distributional edges is temporal and corresponds to an age-range chart. The edge sequence is calibrated to the radiometric time scale and used to compute a detailed genus-level diversity curve and to redefine the boundaries between Miocene Land-Mammal Ages and Subages in the Great Plains. Each of the Miocene Ages can be divided into two or three Subages. Diversity levels are apparently low throughout the Early Miocene and rise sharply during the Middle Miocene. Significant drops in diversity occurred at about 17.4, 11.6, 8.7, and 6.5 Ma. The base of the Barstovian corresponds to the base of the Middle Miocene, and the Clarendonian straddles the Middle-Late Miocene boundary.
Evolutionary morphology: beyond the analogous, the anecdotal, and the ad hoc
Authors: Fisher Daniel C.
Published: July 2016

Many questions have emerged recently regarding the importance and methodology of analysis of adaptation. Divergent views reflect both problems of definition and more substantive issues of interpretation. Defining the state of adaptation in terms of its contribution to current fitness, rather than origin by natural selection, is essential if natural selection is to be considered anexplanationof adaptation. The context dependency and relativity of fitness apply also to adaptation. Design criteria are essential components of adaptation, but only to the extent that they are subsumed as elements of the causal interactions determining relative reproductive potential. The local, relational, contingent character of adaptation supports only limited reference to improvement. Most long-term patterns of change can be better described as diffusion within a structured design-space than as progressive improvement of design. The analysis of adaptation is part of a broader inquiry into the processes and constraints that control form and the history of changing form. It offers one perspective on how organisms operate on ecological time scales and how their configurations might be maintained or transformed over evolutionary time. Hypotheses concerning adaptation are sometimes tested by reference to predictions concerning the central tendency or trend of some aspect of an anatomical-behavioral system. These can be interpreted with minimal reference to assumptions of optimality if the analysis is viewed in terms of Bayesian inference. However, an alternative and frequently preferable approach to testing relies on limit-oriented predictions. Analysis of adaptation can be visualized as inferring the pattern and nature of interactions comprising the causal plexus that determines fitness. A comprehensive understanding of form and form-change requires that this be integrated with the perspective offered by studies of development, genetics, phylogenetic history, and external perturbations acting on the system.
Gaps in the fossil record
Authors: Holman Eric W.
Published: July 2016

Gaps in the fossil record can be identified in compilations of stratigraphic ranges of lower taxa classified within higher taxa. Statistical properties of such gaps suggest the following conclusions. First, the random sampling model most commonly used to correct for incompleteness in the record is inconsistent with the data. Second, the decline in taxonomic extinction rate during the Phanerozoic is not just an artifact of an increase in the completeness of the record.
Floral diversity, phytogeography, and climatic amelioration during the Early Carboniferous (Dinantian)
Authors: Raymond Anne
Published: July 2016

Phytogeographic analysis of three Early Carboniferous intervals (Tournaisian–early Visean, Visean, and late Visean–early Namurian A) indicates a high level of phytogeographic differentiation in the beginning of the Early Carboniferous that decreases toward the end of this period. Climatic amelioration (warmer or wetter conditions) in the north middle and high latitudes, caused by the collision of Laurussia and Gondwana at the end of the Early Carboniferous, may be responsible for this decrease in phytogeographic provinciality. Toward the end of the Early Carboniferous, a large number of equatorial genera expand their ranges northward, and the average generic diversity of assemblages in the north high latitudes (Siberia) also rises. Both support the hypothesis of climatic amelioration. Northward migration of equatorial forms and the appearance of new genera endemic to Siberia both contributed to the rise in Siberian diversity. Although this trend is not statistically significant, additional evidence of diversity increase in northern high latitudes tied to climatic amelioration comes from the northernmost limit of diverse (≥ 10 genera) assemblages, which rises from 20°N at the beginning to 55°N at the end of the Early Carboniferous. Global plant diversity assessed at the generic level remained constant during the Early Carboniferous. The increase in Siberian diversity was offset by a decrease in equatorial diversity, perhaps due to the loss of pronounced latitudinal climatic gradients between north-middle and equatorial latitudes.
Biogeographic patterns and Plio-Pleistocene extinction of Bivalvia in the Mediterranean and southern North Sea
Authors: Raffi Sergio , Stanley Steven M. , Marasti Raffaella
Published: July 2016

An evaluation of the history of polysyringian species (filibranchs and eulamellibranchs) reveals that the huge early Pliocene bivalve fauna of the Mediterranean Basin (MB) and North Sea Basin (NSB) suffered heavy extinction during late Pliocene and early Pleistocene time. This is evidenced by low survivorship of early Pliocene species in the Recent and by a decline in species richness of the two basins from 323 known early Pliocene species to 198 living species.

Several kinds of evidence indicate that cooling rather than the areal effect of eustatic sea-level lowering was the primary cause of the excessive extinction: (1) heavy Plio-Pleistocene extinction of mollusks was not global but concentrated around the margins of the northern Atlantic—an ocean fringed by polar ice caps; (2) taxa of tropical affinities were most severely affected; (3) heavy extinction occurred in the MB in areas not marked by facies change; (4) in the MB the onset of extinctions coincided with the onset elsewhere, but because of tectonic activity, water depths in the MB were not under tight eustatic control; (5) 14 species present in both the MB and NSB during early Pliocene time are now restricted to waters south of the NSB; and (6) the majority of species common to the two basins during the early Pliocene (eurythermal species) have survived to the present.

Molluscan data support palynological evidence that the climate in the MB was warmer and less seasonal in early Pliocene time than today, when latitudinal temperature gradients are steeper. Molluscan evidence indicates that the North Sea is exceptional in being less seasonal (though cooler) today than in early Pliocene time, and we attribute this anomaly to the local effects of the Gulf Stream, which was strengthened in mid-Pliocene time by the uplift of the Isthmus of Panama.

The heavy extinction in the MB and NSB about 3.2–3.0 ma ago approximately coincided with the earliest deposition of glacial tills in Iceland and with isotopic shifts in the tests of planktonic foraminifers preserved in deep-sea cores. Additional heavy extinction probably coincided with a pulse of severe cooling in late Pliocene time, 2.5–2.4 ma ago. Heavy extinction of mollusks in the MB and NSB continued into the early Pleistocene but not into the middle and late Pleistocene, apparently because by this time it was primarily only eurythermal species that survived. Today the molluscan faunas of the MB and NSB are unusually eurythermal; few species are restricted to a single biogeographic province.
North American mammalian diversity and Eocene–Oligocene extinctions
Authors: Prothero Donald R.
Published: July 2016

Diversity and faunal turnover of North American land mammals are calibrated against the magnetic polarity time scale for million-year intervals for the latest Eocene through late Oligocene. A major, gradual Late Eocene decline in diversity, caused mostly by an extended period of extinction of archaic forms, seems to be related to the worldwide crisis known as the “Terminal Eocene Event.” Along with other evidence of gradual changes in deep-sea microfossils, this evidence argues against a catastrophic explanation for late Eocene extinctions.

Faunal stability characterized the rest of the Oligocene except for a wave of extinctions in the mid-Oligocene (Chadronian-Orellan boundary, about 32.4 ma). This mid-Oligocene event is sudden and severe, occurring in less than 200,000 yr, based on estimates from sedimentation rates calibrated from magnetic polarity interval boundaries. The mid-Oligocene event is found in many paleoclimatic records, but not in all of them. It may be related to the completion of the Circum-Antarctic Current and to increased mid-Oligocene glaciation.
Periodicity of chamber formation in chambered cephalopods: evidence fromNautilus macromphalusandNautilus pompilius
Authors: Ward Peter Douglas
Published: July 2016

The growth rates of ammonites and extinct nautiloids have been estimated in two ways: through analyses of shell growth lines and by analyzing the patterns of oxygen isotopic values from successive septa. In both types of studies, it has been assumed that the amount of time between successive chamber formation events is approximately constant. This assumption has never been tested with living cephalopods, however. To examine this, 10 immatureNautilus pompiliusand two immatureN. macromphaluswere maintained in a surface aquarium for a period of 1 yr and periodically radiographed. The radiographs allowed direct observation of chamber formation events and apertural shell growth. During this observational period 61 separate chamber formation events were observed in the nautiluses. The time between separate chamber formation events increased in successively produced chambers, and varied from a minimum of 2–3 wk in a specimen of 45-mm shell diameter to a maximum of 13–15 wk in a specimen of 132-mm shell diameter. Unlike interval of chamber formation, which increased during ontogeny, rate of apertural shell growth showed no observable rate increase or decrease during ontogeny prior to maturity. With the onset of maturity, as marked by the shell characteristics defined by Collins et al. (1980), apertural shell growth rates dropped markedly, and ceased coincident with the removal of the last volumes of cameral liquid in the last formed, approximated chamber. Both rate of apertural shell growth and septal spacing were affected by degree of shell breakage.
Early Tertiary radiation of marine molluscs and the long-term effects of the Cretaceous-Tertiary extinction
Authors: Hansen Thor A.
Published: July 2016

The Cretaceous–Tertiary (K–T) extinction reduced the gamma diversity of molluscs on the U.S. Gulf Coast from over 500 species in the late Maastrichtian to a little over 100 species in the early Danian. Gamma (total) diversity increased in a series of steps that generally tracked temperature, to a high of around 400 species in the late Middle Eocene, at which time diversity declined in the Late Eocene–Oligocene extinctions. The molluscan radiation occurred in at least two distinct phases: 1) an Initial Radiation Phase in which certain families underwent unusually high speciation, apparently filling ecological niches vacated by the extinction, followed by extinction of many of the species in these families in the late Danian; and, 2) a Secondary Radiation Phase where gamma diversity gradually increased and new genera gradually appeared. The fact that the gamma diversity of molluscs did not reach pre-extinction levels before the next extinction in the Late Eocene suggests that molluscan faunas may spend much of their evolutionary time recovering from these extinctions.
Spatial resolution in subfossil molluscan remains: Implications for paleobiological analyses
Authors: Miller Arnold I.
Published: July 2016

The ability of paleobiologists to draw paleoecological inferences based on spatial faunal variability within a single stratigraphic interval depends ultimately on the spatial resolving power of the fossil record. This paper evaluates the potential spatial resolution of fossil assemblages by examining modern skeletal remains of molluscs on a benthic transect, along which there is a marked decrease in seagrass cover, in Smuggler's Cove, St. Croix, U.S. Virgin Islands. The sampling transect began in a Thalassia-covered area approximately three meters deep, extended into slightly deeper water with lighter seagrass cover, and ended on an open, bioturbated sandy tract at a depth of nearly six meters.

Two-way cluster analysis and polar ordination of 37 samples of molluscan remains, taken at 10-meter intervals along the 360-meter transect, reveal patterns of variation that are shown by correlation analyses and consideration of the autecologies of individual species to be related to measured changes in vegetation. There is a transition from dominance primarily by epifaunal gastropods living on seagrass blades to dominance by infaunal, burrowing bivalves as grass cover becomes lighter. Some non-systematic variability exists in faunal distributional patterns within areas where the environment does not vary systematically, but this does not mask the regular faunal transitions related to environmental changes. Correspondence between the dead and live faunas is difficult to ascertain because of the scarcity of live fauna in collected samples.

The results suggest that spatial faunal transitions in fossil remains at even the fine scale evaluated in this study are potentially preservable in the fossil record.
Patterns of generic extinction in the fossil record
Authors: Raup David M. , Boyajian George E.
Published: July 2016

Analysis of the stratigraphic records of 19,897 fossil genera indicates that most classes and orders show largely congruent rises and falls in extinction intensity throughout the Phanerozoic. Even an ecologically homogeneous sample of reef genera shows the same basic extinction profile. The most likely explanation for the congruence is that extinction is physically rather than biologically driven and that it is dominated by the effects of geographically widespread environmental perturbations influencing most habitats. Significant departures from the congruence are uncommon but important because they indicate physiological or habitat selectivity. The similarity of the extinction records of reef organisms and the marine biota as a whole confirms that reefs and other faunas are responding to the same history of environmental stress.
Trophic diversity in past and present guilds of large predatory mammals
Authors: Van Valkenburgh Blaire
Published: July 2016

Trophic diversity within guilds of terrestrial predators is explored in three modern and two ancient communities. The modern communities span a range of environments including savannah, rainforest, and temperate forest. The paleocommunities are North American, Orellan (31–29 Ma), and late Hemphillian (7–6 Ma), respectively. The predator guilds are compared in terms of: 1) species richness; 2) the array of feeding types; and 3) the extent of morphological divergence among sympatric species. Feeding type is determined from dental measurements that reflect the proportion of meat, bone, and non-vertebrate foods in the diet. Measurements include estimates of canine shape, tooth size, cutting blade length, and grinding molar area. Morphological divergence among sympatric predators is measured by calculating Euclidean distances among species in a six-dimensional morphospace. Results indicate that the number of predator and prey species are roughly correlated in both ancient and modern communities. Two of the predator guilds, the late Hemphillian and modern Yellowstone, contain relatively few species and appear to be the result of extinction without replacement. Despite differences in history, age, and environment, the extent of morphological divergence within guilds does not differ significantly for the sampled communities. It is clear that the basic pattern of adaptive diversity in dental morphology among coexisting carnivores was established at least 32 million years ago. It appears that interspecific competition for food has acted similarly to produce adaptive divergence among sympatric predators in communities that differ widely in time, space, and taxonomic composition.
Diversification and germ-line determination
Authors: Buss Leo W.
Published: July 2016

The species richness of extant metazoan phyla displays a strong association with the ontogenetic timing of germ-line determination. Taxa with early ontogenetic determination of the germ-line are characterized by low species number relative to taxa with late or variable determination. A test for a similar association in fossil taxa is compromised by the fact that all phyla displaying early determination of the germ-line are small, soft-bodied groups which lack a reliable fossil record. To the extent that this correlation reflects causality, patterns of evolutionary diversification have been decidedly non-random. The fact that ontogenetic timing of germ-line determination defines the extent to which genetic variation arising during the course of ontogeny may be inherited suggests a possible causal foundation for the pattern.
Modeling bivalve diversification: the effect of interaction on a macroevolutionary system
Authors: Miller Arnold I. , Sepkoski J. John
Published: July 2016

The global diversification of the class Bivalvia has historically received two conflicting interpretations. One is that a major upturn in diversification was associated with, and a consequence of, the Late Permian mass extinction. The other is that mass extinctions have had little influence and that bivalves have experienced slow but nearly steady exponential diversification through most of their history, unaffected by interactions with other clades. We find that the most likely explanation lies between these two interpretations. Through most of the Phanerozoic, the diversity of bivalves did indeed exhibit slow growth, which was not substantially altered by mass extinctions. However, the presence of “hyperexponential bursts” in diversification during the initial Ordovician radiation and following the Late Permian and Late Cretaceous mass extinctions suggests a more complex history in which a higher characteristic diversification rate was dampened through most of the Phanerozoic. The observed pattern can be accounted for with a two-phase coupled (i.e., interactive) logistic model, where one phase is treated as the “bivalves” and the other phase is treated as a hypothetical group of clades with which the “bivalves” might have interacted. Results of this analysis suggest that interactions with other taxa have substantially affected bivalve global diversity through the Phanerozoic.
Shell coiling in some larger foraminifera: general comments and problems
Authors: De Renzi Miquel
Published: July 2016

The logistic model provides a useful geometric description of coiling for larger Foraminifera. This model represents a spiral in polar coordinates by means of a logistic equation. The model describes the spires of the genera Alveolina, Nummulites, and Assilina very well. The logistic model is a consequence of allometric growth in these genera. The spires of Nummulites do not fit the logarithmic spiral model well, because the model does not accommodate ontogenetic change of form. Computer simulations using the logistic model also show the very different morphologies of the genus Alveolina. The model allows study of geometrical constraints on test form and of pathways followed by the evolution of the genus (or genera). The logistic model describes ontogenetic change in the organism's functional requirements. The main physiological requirements are nourishment, general exchanges of matter and energy with the environment, and light for the photosynthetic symbionts that live in the cytoplasm of these larger Foraminifera. All these functions require suitable area/volume ratios, that mandate changes of form during growth. The possible biological meaning of the parameters of the model is explored. The use of the more meaningful parameters is proposed in statistical multivariate studies.
The ontogeny ofPteranodonand other pterosaurs
Authors: Bennett S. Christopher
Published: July 2016

Immature specimens of the Late Cretaceous pterosaurPteranodonwere identified using three size-independent criteria: (1) fusion of various cranial and postcranial elements; (2) degree of epiphyseal ossification; and (3) bone grain or degree of ossification of limb-bone shafts. Immature individuals make up 15% of available specimens ofPteranodonand do not differ significantly in size from mature individuals. This and the extensive fusion of the mature skeleton suggest thatPteranodonhad determinate growth. The bone of limb-bone shafts of immature individuals is fibro-lamellar bone, which suggests that they grew rapidly to adult size. The size-independent criteria can also be used to identify immature and mature individuals of other pterosaur taxa, and other large pterodactyloids also probably exhibited rapid determinate growth.
Decay and preservation of polychaetes: taphonomic thresholds in soft-bodied organisms
Authors: Briggs Derek E. G. , Kear Amanda J.
Published: July 2016

A series of experiments was carried out to investigate the nature and controls (oxygen, microbial populations, agitation) on the degradation of soft tissues. Decay was monitored in terms of morphological change, weight loss, and change in chemical composition in the polychaete Nereis virens. Polychaetes include a range of tissue types of differing chemical composition and preservation potential: muscle, cuticle, setae, and jaws. Regardless of conditions, all the muscle had broken down and fluid loss through the ruptured cuticle had reduced the carcass to two dimensions within 8 days at 20°C. In most cases some cuticle, in addition to the jaws and setae, remained after 30 days. Where oxygen was completely eliminated, the rate of decay of the more volatile issues was significantly reduced. The degree of both osmotic uptake of water by the carcass and changes in water pH differed depending on whether the system was open or closed to oxygen diffusion. Autolytic and chemical processes are not sufficient to fully degrade the carcass in the absence of bacteria. Where internal bacteria are present, the presence or absence of water column bacteria made little difference to decay rate. Initial degradation (in the first 3 days) affects mainly the lipid fraction and the collagen of the cuticle. Later decay reduces the nonsoluble protein and increases the relative proportion of refractory structural components (tanned chitin and collagen) to more than 95% by day 30. Thus, only the sclerotized tissues are likely to survive beyond 30 days in the absence of early diagenetic mineralization. The sequence of degradation predicted from the relative decay resistance of macromolecules in the sedimentary record (protein → carbohydrate → lipid) is not, therefore, a consistent indicator of the preservation potential of structural tissues which incorporate them.

The experiments reveal five stages in the decay of polychaete carcasses; whole/shriveled, flaccid, unsupported gut, cuticle sac, jaws and setae. All are represented in the fossil record. This allows an estimation of how far decay proceeded before it was halted by the fossilization process. The most complete preservations occur in the Cambrian where the Burgess Shale preserves evidence of muscle tissues. Traces of the gut and cuticle are more widely preserved, as at Mazon Creek, Grès à Voltzia, Solnhofen, and Hakel. Preservation varies within Konservat-Lagerstätten. The most common whole body preservation includes only the more recalcitrant tissues, jaws (where present) and setae, with an impression of the body outline. The stage of decay can be used as a taphonomic threshold, to provide an indication of how significantly the diversity of an exceptionally preserved biota is likely to have been reduced by taphonomic loss.
The promise of paleobiology as a nomothetic, evolutionary discipline
Authors: Gould Stephen Jay
Published: July 2016

During the past 20 years, paleobiology has established the foundations of a nomothetic science based upon evolutionary theory. This radical break with a past philosophy based on irreducible historical uniqueness is still impeded by (1) overreliance upon the inductivist methodology that embodied this previous philosophy, and (2) an unadventurous approach to biology that attempts passively to transfer the orthodoxies of microevolutionary theory across vast stretches of time and several levels of a hierarchy into the domain of macroevolution. I analyze the major trends of recent invertebrate paleobiology in the light of these two impediments. The formulation, by paleobiologists and with paleobiological data, of new macroevolutionary theories should end the subservience of passive transfer and contribute, in turn, to the formulation of a new, general theory of evolution that recognizes hierarchy and permits a set of unifying principles to work differently at various levels.
Is a new and general theory of evolution emerging?
Authors: Gould Stephen Jay
Published: July 2016

The modern synthesis, as an exclusive proposition, has broken down on both of its fundamental claims: extrapolationism (gradual allelic substitution as a model for all evolutionary change) and nearly exclusive reliance on selection leading to adaptation. Evolution is a hierarchical process with complementary, but different, modes of change at its three major levels: variation within populations, speciation, and patterns of macroevolution. Speciation is not always an extension of gradual, adaptive allelic substitution to greater effect, but may represent, as Goldschmidt argued, a different style of genetic change—rapid reorganization of the genome, perhaps non-adaptive. Macroevolutionary trends do not arise from the gradual, adaptive transformation of populations, but usually from a higher-order selection operating upon groups of species, while the individual species themselves generally do not change following their geologically instantaneous origin. I refer to these two discontinuities in the evolutionary hierarchy as the Goldschmidt break (between change in populations and speciation) and the Wright break (between speciation and trends as differential success among species).

A new and general evolutionary theory will embody this notion of hierarchy and stress a variety of themes either ignored or explicitly rejected by the modern synthesis: punctuational change at all levels, important non-adaptive change at all levels, control of evolution not only by selection, but equally by constraints of history, development and architecture—thus restoring to evolutionary theory a concept of organism.