bluuebunny/crossref_metadata_2025 huggingface dataset:
Functional and phylogenetic interpretation of enamel microstructure in rhinoceroses
Authors: Rensberger John M. , Koenigswald Wighart v.
Published: July 2016

Worn enamel surfaces of the cheek teeth in fossil and recent rhinoceroses are characterized by fine, parallel ridges aligned perpendicular to the enamel-dentin interface. We show that these ridges result from an unusual enamel ultrastructure in which a primitively horizontal layering of the prisms has become vertical. The new structure apparently appeared between early and middle Eocene, at the time when the superfamilies of perissodactyls were rapidly diverging. Similar modifications of the enamel structure occurred in certain parts of the cheek teeth in tapiroids, chalicotherioids and brontotherioids, but hardly at all in the equids. The modified enamel structure, where it occurs in groups other than rhinocerotoids, is associated with lophs but not cusps. Experimental evidence shows that the modified enamel is more resistant to wear than the unmodified enamel. The consistent association with thin lophs rather than cusps suggests that the modified enamel evolved to prolong the life of the lophs, where occlusal pressures are highest and attrition greatest. The dominance of modified enamel in rhinocerotoids correlates with the higher degree of compression of the cusps and extreme lophodonty in this group. The absence of modified enamel structure in the equids, even in the ectoloph, correlates with the lesser importance of the ectoloph in equids relative to brontotherioids, chalicotherioids and rhinocerotoids.
Paleophytochemistry: Implications Concerning Plant Evolution
Authors: Niklas Karl J.
Published: July 2016

Chemical analyses of fossil plants and their associated sediments are currently providing the paleobotanist with biochemical information relevant to the reconstruction of taxonomic relationships. The isolation and chemical identification of various plant pigments from fossils, such as flavonoids and carotenoids (compounds that give flowers their characteristic colors), steroids, fatty acids, and a host of plant phenolic acids, provide the opportunity to characterize the specific paleophytochemical profiles of fossil species.
Cenozoic Birds
Authors: Feduccia Alan
Published: July 2016

Birds have traditionally been termed the best known group of vertebrates. This cliché, however, relates to the fact that living species are well described, even to the subspecies level. Birds are well known because they are diurnal (therefore easily observed) and because of their aesthetic appeal—birds are beautiful. Because of this appeal, birds have been subject to persistent scrutiny by amateur and professional naturalists alike, and their study has consequently contributed to the development of not only evolutionary thought, but also such diverse fields as ecology, behavior and even comparative physiology. However, while these disciplines have advanced, our understanding of bird phylogeny and evolution has simply not kept pace and the relationships of the higher categories of birds are still very poorly understood.
A Radical Look at Fish-Tetrapod Relationships
Authors: Thomson Keith Stewart
Published: July 2016

No one needs reminding that we are well into a revolutionary phase in the study of evolution, systematics, and the interrelationships of organisms. To belabor the metaphor a little, to the thesis of Darwinian evolution and Mayrian systematics has been added a new cladistic antithesis which says that the search for ancestors is a fool's errand, that all we can do is determine sister group relationships of monophyletic taxa based on the analysis of derived characters. Consequently, our attention should be focused upon patterns which can be delineated, discussed, and modified in the light of new data, rather than upon processes which may only be the subject of untestable hypotheses. It is a change in approach that is not easy to accept for, in a sense, it runs counter to what we have all been taught, and it is particularly difficult for the paleontologist to accept because a major feature of the approach is a concentration upon living rather than on fossil forms. In fact, fossils are, in general, either difficult to use or irrelevant, or both, in terms of new attempts to set out the relationships of the major groups of organisms. The subject of this brief notice is a critically important new addition to the literature on this growing, dare I say evolving, subject.
The role of spines in preventing structural damage to echinoid tests
Authors: Strathmann Richard R.
Published: July 2016

Living echinoids provide a structural analogue to the rigid thecae of many extinct echinoderms and are here used to examine some consequences of the increased rigidity and decreased number of plates which occurred in several lineages of echinoderms. A special feature of the echinoids is the large spines which protect the echinoid tests from failure under impact. The spines absorb energy or spread loads because the spines break or the tissue connecting the spine to the test is stretched or torn. Spines that absorb impacts might be superfluous in echinoderms encased in a rigid test or theca if they have flexible stems or are in low energy habitats, but spines should be useful to stemless thecate echinoderms on hard substrata. In the absence of spines, a flexible theca of overlapping plates might be superior to a rigid theca. Greater rigidity does not necessarily provide greater protection.

Tracts of podial pores are sites of weakness in all tests examined [Eucidaris tribuloides(Lamarck),Echinometra viridisAgassiz,Diadema antillarumPhilippi,Lytechinus variegatus(Lamarck),Tripneustes ventricosus(Lamarck)]. Therefore arrangement of pores affects strength of rigid thecae. Sutures are stronger than plates in most species examined, but cracks cross sutures, and tests ofE. tribuloidesfrequently break along sutures. It is not yet proven that sutures increase toughness of rigid tests by relieving stress on plates or stopping cracks. If resisting failure under impact is important, then preconditions for acquiring rigidity are life in a low energy habitat or accessory structures which absorb or spread impacts.
Ralph Gordon Johnson 1927–1976
Authors: Schopf Thomas J. M.
Published: July 2016

Ralph Gordon Johnson was born July 5, 1927 at Oak Park, Illinois. He died September 23, 1976, in Chicago, Illinois, of cancer, after an illness of about 2 months.

For the past twenty years, Ralph Gordon Johnson contributed significantly in three areas of paleobiology: understanding the dynamics of benthic marine communities, exploring the mode of formation of fossil assemblages, and describing the remarkably preserved Mazon Creek fauna.
Biological interaction between fossil species: character displacement in Bermudian land snails
Authors: Schindel David E. , Gould Stephen Jay
Published: July 2016

Poecilozonites (Gastrelasmus) is an important component of the endemic land snail fauna of Pleistocene Bermuda. The type species P. circumfirmatus Redfield usually occurs in sympatry with its congener P. discrepans Pfeiffer, though each species is found alone at several localities. The species are less alike morphologically where they occur together than where they are allopatric. This allopatric convergence and sympatric divergence strongly suggests the biological interaction known as character displacement, often documented for living populations. The relatively complete fossil record of Bermuda offers advantages for studying this phenomenon. Collections can be made from a variety of microhabitats occupied through time. Statistical analysis of 1,600 individuals collected from more than 100 localities indicates that interspecific variation is primarily a function of the presence or absence of a congener and depends to a lesser degree on microhabitat. P. circumfirmatus undergoes a smaller morphological change between allopatry and sympatry than does P. discrepans. Study of relative abundances suggests that P. discrepans may have been competitively inferior, though no functional bases for differences between the species are known.
Phenetic variability and functional morphology of erect cheilostome bryozoans from the Danian (Palaeocene) of Denmark
Authors: Thomsen Erik
Published: July 2016

Fragments of cheilostome and cyclostome bryozoans are the most common fossils in the mound structures commonly found in the Lower Danian limestones of southern Scandinavia. Sedimentological investigations and measurement of colony morphology combined with flume channel experiments indicate that: 1) The mounds were affected by unidirectional currents which created relatively high current velocities on the upstream flanks and summits, and low velocities on the downstream flanks and in the basins. 2) Colonies with slender stems and thin walls dominated in areas with low current velocities and those with thick stems and thick walls dominated in areas with high velocities. 3) The specific variability of the stem diameter was mainly controlled by the geometrical arrangement of the zooids. In general, species with a bilamellar arrangement of the zooids show high variability, whereas species with a radial arrangement show small variability. 4) Variation in the wall thickness is primarily related to the mode of growth of the individual zooids. In the ascophorans deposition was confined to the external surface of the stems. On the other hand, in the coilostegoid anascans the secondary skeletal material was deposited on all the internal surfaces of the zooids as well as on the external side of the cryptocyst. Cuticles do not seem to have been present in the secondary thickened part of the frontal wall of either the coilostegoid anascans or the ascophorans. 5) Calcareous material was deposited predominantly on the lower and older portions of the colony.
A model for estimating standing crop in ancient communities
Authors: Kranz Peter M.
Published: July 2016

The paleoecologist has been hampered in his studies of ancient communities by an inability to obtain reasonable estimates of standing crops and diversities. Finding the diversity of an ancient community is no simple matter, because a fossil assemblage is a mixture of living and recently dead individuals from that community. Considerable numbers of each group may be missing. The relationship of the elements in a fossil population for an individual species can be expressed as follows: F = Fl + Fd, where F is the average number of fossil individuals collected per unit area, Fl is the part of the sample produced by the burial of live individuals, and Fd is the part produced by the individuals already dead at the time of burial. Fl is a product of the standing crop S (number of individuals per unit area), multiplied by the probability of failure P (proportion of the standing crop which can be expected to fail to escape anastrophic burial), or Fl = (S) (P). Fd is the product of the death rate D (number of individuals which die per age-class time unit) multiplied by the residence time R (average length of time expressed in age-class time units that the remains of an individual will persist after death), or Fd = (D) (R). The probability of failure, residence time, and death rate can all be estimated from modern communities; the death rate can also be estimated from the fossils. Thus, the standing crop of an individual species can be expressed as follows:

This equation can be modified to eliminate the need to estimate D, as follows
where i is the subscript indicating the number of the specific age class where the youngest is 1 and oldest is n. Once the standing crop for each species in the community has been estimated, a meaningful diversity can be calculated. Study of the model reveals that in populations where high-early mortality is the rule the likelihood of error in estimating population parameters is lower than for constant and low-early mortality populations.
Preservation and paleoecology of a Middle Ordovician hardground community
Authors: Brett Carlton E. , Liddell W. David
Published: July 2016

Limestone beds in the Middle Ordovician (Trentonian) Bobcaygeon Formation, exposed near Kirkfield, Ontario, exhibit irregular, bored and encrusted surfaces indicative of early lithification. These hardgrounds were formed in extensively burrowed carbonate sediments and their hummocky surface topographies were inherited, in part, from a pre-existing pattern of burrow tunnels. A diverse community, including bryozoans, brachiopods, crinoids, edrioasteroids, and paracrinoids, colonized these hard substrates. In addition, most surfaces are riddled with small, cylindrical boreholes (Trypanites) which represent dwellings of soft-bodied organisms. Some hardground surfaces were inhabited by multiple generations of organisms. Remains of the older generations of encrusters were strongly abraded and nearly obliterated. Superimposed upon these worn remnants are well-preserved remains of rather fragile organisms, e.g. complete hybocystitid crinoids and edrioasteroids. Evidently, certain hardground surfaces were rapidly buried by muds, resulting in the in situ preservation of the last generation of attached organisms.

Slightly differing subcommunities of organisms inhabited various microhabitats provided by the irregular hardground surfaces. Thus, the relative abundance of bryozoans and echinoderms encrusting the roofs of small crevices differs from that on the exposed upper surfaces of the hardgrounds. This is the geologically oldest known hardground community in which microhabitat subdivision can be recognized. However, polarity between the subcommunities is not as pronounced as in geologically younger hard substrate faunas.
Role of ideas in advancing paleontology
Authors: Krohn Ingrid M.
Published: July 2016

Modern biological principles and mathematical techniques applied to fossil data may contribute to a rigorous theoretical framework for the analysis of macroevolutionary trends. Such cross-fertilization may also serve to correct interpretative biases common in paleontological literature.
Fossil macromolecules from cephalopod shells: characterization, immunological response and diagenesis
Authors: Westbroek P. , van der Meide P. H. , van der Wey-Kloppers J. S. , van der Sluis R. J. , de Leeuw J. W. , de Jong E. W.
Published: July 2016

The EDTA-soluble fractions extracted from rostra of two late Cretaceous belemnites (Cephalopoda),GonioteuthisandBelemnitella, were divided into an humic acid and a fulvic acid fraction (the latter was absent inBelemnitella). The extracts are compared with preparations from shells of two recent cephalopods,Nautilus pompiliusandSepia officinalis.Use was made of immunology, amino acid analysis, pyrolysis mass spectrometry and some other techniques.

The fulvic acid fraction ofGonioteuthis, a mixed peptide-like saccharide-like substance, produced confluent immunodiffusion patterns with an EDTA-solubleNautilusextract against anti-Nautilusrabbit serum. The humic acid ofGonioteuthisdid not contain D-alloisoleucine and its amino acid composition was very similar to that of the EDTA-insoluble fraction ofNautilus.This humic acid was enriched in polyphenol, which may be due to chemical reaction of peptides and carbohydrates during diagenesis. It is concluded that both fractions ofGonioteuthisare original belemnite materials that have undergone only minor alterations during diagenesis.

This is an exploratory study of biochemical compounds derived from fossils, with particular emphasis on immunological methods.
Selection pressure for high body temperatures: implications for dinosaurs
Authors: McGowan C.
Published: July 2016

An understanding of the thermal strategies of extant animals is a prerequisite for any useful discussion on the possible thermal strategies of dinosaurs. Of cardinal importance is the identification of the selection pressures that have resulted in the evolution of high body temperatures. Although different selection pressures have probably been operational in different organisms, enhanced muscle power may have been a prime factor.

Many dinosaurs, including the ornithomimids, carnosaurs and hadrosaurs possess cursorial features suggesting high activity levels, which in turn suggest the possession of high body temperatures. Even if it is denied that high body temperatures are a prerequisite for speed, it cannot be denied that muscular activity liberates large quantities of heat, and most dinosaurs, by virtue of their small area to volume ratio, must have maintained constant, and sometimes high, body temperatures. This thermal strategy, described as inertial homeothermy, does not require a high (mammalian/avian) rate of metabolism, and most dinosaurs were probably not endothermic.

The smallest dinosaurs (e.g.Compsognathus) were probably too small to have been able to maintain constant body temperatures in the absence of external insulation. Perhaps they were feathered, like their close relativeArchaeopteryx.Presence of feathers inArchaeopteryxis compelling evidence for endothermy.

The largest dinosaurs, the sauropods, had an exceedingly small area to volume ratio, that probably imposed limitations on their rate of heat dissipation. This in turn may have restricted their rate of muscular activity; there are also sound mechanical reasons why they should have been relatively inactive. It is therefore concluded that sauropods probably maintained relatively low body temperatures.
Resolution of life habits using multiple morphologic criteria: Shell form and life-mode in turritelliform gastropods
Authors: Signor Philip W.
Published: July 2016

Shell form is not strictly linked to life habits in modern marine turritelliform gastropods. To test the usefulness of various morphological characters in determining life-mode, I present a set of predictions giving the expected distribution of characters occurring in turritelliform snails with three different life-modes. Burrowing species should lack sculpture, possess columellar folds and a flat whorl profile, and have an orthocline or prosocline aperture. Mobile epifaunal forms should have sculpture, a rounded whorl profile, a displaced tangential aperture and a smooth columella. Sedentary forms should resemble epifaunal forms but have non-tangential apertures. These predictions were tested with a sample of 105 Recent marine species. Each hypothesis was found to be a statistically valid generalization and in 92 of the species (88%) the life habits were correctly predicted. Accuracy may be further improved by considering additional features such as ratchet sculpture and disjunct or open coiling. These patterns of shell form can be used to interpret fossil species as burrowers, or as sedentary or active epifaunal forms. For example, the unusual Devonian murchisoniid gastropod Ptychocaulus verneuili is interpreted as an active burrower.

The relatively imperfect relationship between shell form and life-mode in turritelliform gastropods, as compared to the Bivalvia, apparently results in part from the behavioral complexity of the Gastropoda. Gastropods have a repertoire of activities which would place them in different life-modes at different times; snail morphology reflects this complexity.
Variation and dynamics of a fossil antelope population
Authors: Kurtén Björn
Published: July 2016

656 mandibles and isolated teeth of the bovid Pachytragus solignaci Robinson from two localities in the Miocene Beglia Formation, Gafsa, Tunisia, have been individually aged on the basis of ontogenetic development and state of dental wear. The sample probably represents normal but seasonally restricted mortality. Life table analysis indicates an annual mortality rate of 25–30%, increasing in old animals. Dental dimensions are affected by stabilizing selection which sets in as the tooth comes into function, earlier mortality being nonselective in that respect.
The Whitehead Institute Symposium on Forces Molding the Genome
Authors: Schopf Thomas J. M. , Harrison Richard
Published: July 2016

I. Many believe that sooner or later molecular biology will mechanistically provide the precise genotypic basis for phenotypic change. This in turn will provide the basis for attacking several major evolutionary problems posed by paleontology, including the following:

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There are approximately 30 phylum-level taxa in the animal kingdom, and yet in the “fast” version of evolutionary history, many of then arose 600 Myr ago in a very short period of time (of order <30 Myr). In terms of basic body plan and inferred ecology, these sponges, clams, arthropods, etc. were seemingly as different then as they are now. It is as though the rate of morphologic change was much more rapid during that interval than during the nearly 600 Myr since then. Even the “slow” version of evolutionary history (which allows for an additional unfossilized record of about 500 Myr) demands an answer to what has controlled the development of major evolutionary Bauplans.

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Some morphologic traits (though probably not individual species) persist for immense periods of geologic time—the general shape of the horseshoe crab, for example, or the bristle patterns of taxa of meiofaunal “worms” living among sand grains. What is the developmental rationale for these persistent traits? In short, what is the molecular basis for genetic and morphologic canalization?

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The general pattern of species specialization proceeds unabated overtime, but every once in a while the developmental clock is reset. Organisms which are sexually mature but with simplified or “primitive” morphology arise de novo, and these lineages then form the stock of unspecialized forms from which future specializations evolve. What is the molecular basis for resetting the developmental clock?

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Reproductive isolation may arise “accidentally” through genomic changes unrelated to changes in the local environment. To the extent this is true, speciation has a largely accidental component. Knowledge of the rate and type of genomic change is critical for an evaluation of this idea.
Introduction to the Symposium on Tempo and Mode of Evolution from Micropaleontological Data
Authors: Berggren William A. , Casey Richard E.
Published: July 2016

The concept of punctuated equilibria was introduced by Eldredge and Gould (1972) as an interpretation of the sequential occurrence of species as actually observed in the fossil record. The pattern of sudden appearance of a new species followed by little or no morphological change during the remainder of the species' existence contrasts with phyletic gradualism, the pattern of slower, more evenly distributed change which was long considered to be the principal mode of species formation (Simpson 1944). The question of which is the dominant pattern of evolutionary change has continued as an actively debated theme in much of the paleontological literature of the past decade.
Biogeographic and ecologic perspective on polycystine radiolarian evolution
Authors: Casey Richard E. , Wigley Cynthia R. , Perez-Guzmán Ana Maria
Published: July 2016

Polycystine radiolarians axe the most widely distributed (geographically and geologically) of the well-preserved microzooplankton. To correctly interpret the tempo and mode of radiolarian microevolution, speciation and macroevolution, the zoogeography and ecological niches of extant, and paleozoogeography and paleoecological niches of extinct subspecies, species and higher taxa of the studied lineages should be carefully considered. Such studies of the Stichocorys and Lamprocyrtis lineages suggest that allopatric speciation as peripheral isolates is important. Sympatric speciation is also a possible mode of evolution in these lineages. Hybridization may play a role in the evolution of one subspecies and one species. Allopatrically evolved subspecies and species require some time to inhabit their maximum geographical range after evolving in an isolated and peripheral part of that “environment,” whereas the supposedly sympatrically evolved forms do not. Cooling trends and water mass reorganization may be related to the speciation events. Similar, but much less controlled, studies on a macroevolutionary scale (evolution above the species level, essentially the “family” level) suggest that there have been about half a dozen periods of major adaptive breakthroughs resulting in quantum, or macro, evolution. Global coolings and the initiations of “new” cold-water spheres and related water masses appear to have allowed these macroevolutionary steps during the Ordovician, Devonian-Carboniferous, Permian, and early Neogene. Ecological pressure from diatoms and planktonic foraminiferans appears to have been related to macroevolutionary events bounding the Cretaceous-Tertiary transition.
When and how did plants and animals take to the land?
Authors: Thomas R. D. K.
Published: July 2016

The origin and diversification of terrestrial communities has long been associated with the Devonian. The earliest known substantial assemblage of land plants and animals preserved in or close to their original habitats is still that of the Rhynie Chert peat bog, from Scotland, which is of Siegenian age.
Paleobiologic significance of fossulae in North American Late Ordovician solitary rugose corals
Authors: Elias Robert J.
Published: July 2016

Three features that provide information on the paleobiologic significance of fossulae in North American Late Ordovician solitary rugose corals are (1) irregularities in shape and position of the outer wall, (2) discontiguous septal growth lamellae, and (3) foreign objects incorporated into interseptal chambers within the corallum. Outer wall irregularities indicate that portions of a polyp could detach from the calice and could contract and expand radially by a significant amount and for prolonged periods of time during ontogeny, especially in the vicinity of the alar and cardinal fossulae. Discontiguous lamellae indicate that the polyp could detach from septa and contract laterally, especially in the cardinal fossula. This began with the onset of maturity and probably reflects reproductive activity. Ostracodes are the most common foreign objects in these coralla and are usually situated within or near the cardinal and alar fossulae. In the most likely hypothesis accounting for their presence, a live ostracode entered the calice when one side of the polyp temporarily detached from the corallum and contracted radially. It became trapped upon expansion and reattachment of the soft parts. The polyp moved upward in its corallum by detachment and uplift of the aboral surface. In a less likely hypothesis, the ostracode was captured by the coral for food and came to rest on the floor of the central cavity. It was incorporated into an interseptal chamber when the polyp moved upward in its corallum by atrophy of the aboral surface and formation of a new base above the object. In either hypothesis, portions of the polyp in the cardinal and alar fossulae probably functioned throughout ontogeny for water circulation in the central cavity, and for the intake of food and/or ejection of undigested material through the mouth. Taxonomic, stratigraphic, and paleobiogeographic variability in frequencies of the three features may indicate differences in the necessity and/or ability of polyps to perform these functions involving the fossulae. This could be a reflection of environmental and/or genetic factors.
Morphology and morphologic diversity of mid-Carboniferous (Namurian) ammonoids in time and space
Authors: Saunders W. Bruce , Swan Andrew R. H.
Published: July 2016

Morphologic analysis of 281 species of ammonoids from Great Britain, the North American mid-continent, and the South Urals, at eight successive levels within the Namurian Series (ca. 18 Myr duration), using bivariate plots and principal-components analysis, permits definition of morphologic diversity and identification of morphotypic patterns in time and space. Namurian ammonoids exhibit the same general range of shell geometry that characterizes ammonoids as a whole; there were few post-Namurian innovations in the basic geometry of planispiral ammonoids. Within this overall range of geometry, there are eight preferred morphotypes: two were phylogenetically monopolized by long-ranging forms; three were generalized and reoccur in successive horizons; two others were homeomorphically utilized at different times by different lineages; and one represents morphologic innovation followed by radiation. Such patterns seem to represent combined effects of function, phylogeny, and ecology. Synchronous variations in isolated successions suggest global controls such as eustatic sea-level fluctuations, whereas provincial differences in diversity may be attributable to paleogeographic and ecologic factors. We predict that the Namurian record of ammonoid morphologic diversity and change will be found to be distinctive and differentiable from earlier and later intervals.
Paedomorphosis and the evolution of the Dipnoi
Authors: Bemis William E.
Published: July 2016

Paedomorphosis has played an important evolutionary role in several vertebrate lineages, yet there are few studies in which fossils have been used to document this evolutionary pattern directly. The unusually good fossil record of lungfishes offers an excellent opportunity to do this. An approach to recognizing paedomorphic character complexes in fossil lineages is formalized, and the interdependence of ontogenetic and phylogenetic studies is reemphasized. Concordant evolutionary changes in seven characters representing a variety of organ systems are discussed. For example, in Devonian lungfishes, the tail is heterocercal, endochondrally ossified bones are present, and the fin rays are similar to those of other Osteichthyes. Recent lungfishes have protocercal tails, suppression of endochondral ossification, and greatly reduced fin rays. The data suggest that paedomorphosis played a pervasive role in the evolution of lungfishes and give further evidence for the evolutionary importance of heterochrony.
Predation on fossil and Recent ophiuroids
Authors: Aronson Richard B.
Published: July 2016

The frequency of sublethal damage was examined in two ophiuroid species, Palaeocoma milleri and ?Ophioderma tenuibrachiata (Ophiodermatidae), from a shallow-water Jurassic “starfish bed.” None of 60 specimens was regenerating arms, a result that agrees with four previous studies of Paleozoic and early Mesozoic ophiuroids. By contrast, 66.1 percent of a living Ophioderma brevispinum population from Belize were regenerating one or more arms. For living populations of Ophiothrix oerstedi, the natural injury frequency was high at sites where the field mortality of tethered individuals was high. All predators that have been observed feeding on ophiuroids cause sublethal injuries, which would appear as regenerating arms in the fossil record. These results support the hypothesis that predation pressure on ancient ophiuroid populations was low and increased after the Jurassic.
Lyellian curves and mean taxonomic durations
Authors: Pease Craig M.
Published: July 2016

The mean taxon duration, , and the 50 percent point of the Lyellian curve, T50, are directly proportional to one another: . However, there is a disagreement in the literature over the correct value of the proportionality constant, C. Various authors have claimed that C ≈ 1.44, C = 2.00 and C ≈ 2.89. I critically examine the assumptions underlying these three choices of C and argue that C ≈ 1.44, which is based on an exponential model of survivorship, is more widely applicable than the other values of C.
Apical skeletons of sea urchins (Echinodermata: Echinoidea): two methods for inferring mode of larval development
Authors: Emlet Richard B.
Published: July 2016

Recent data from mollusks suggest that mode of larval development may have important consequences for rates of speciation and extinction of marine organisms. The present study examines two methods that may be used to infer mode of development in the tests of fossil and Recent echinoids: genital pore size and crystallographic patterns of apical plates. Extant species with known modes of development were examined, and the following hypotheses were tested. 1) Species that produce large eggs and have nonfeeding larval development have larger genital pores than species that produce small eggs and have feeding larval development. 2) Orientations of crystallographic axes (c-axes) of genital and ocular plates differ in species with differing modes of development and can be used to infer mode of development. Genital pore size was found to be strongly dependent on body size within a species. For some taxa, pairwise interspecific comparisons of the relationships between genital pore size and body size support the hypothesis of larger genital pores for species with nonfeeding larval development. However, in multiple comparisons of linear regressions, species with nonfeeding larval development always overlapped other species with feeding larval development. An examination of the allometry of genital pore growth showed some species with nonfeeding larval development differed from those with feeding larval development; other species with differing modes of development could not be distinguished on the basis of allometric growth parameters. Orientations of c-axes of genital plates were found to be accurate indicators of mode of development, but orientations of c-axes of ocular plates were not. Among regular echinoids, 71 of 72 species supported the hypothesis that orientation of c-axes of genital plates is indicative of mode of development. Among 19 spatangoid echinoids studied, orientations of c-axes of genital plates generally allowed separation of species with differing modes of development. This method cannot be used to infer modes of development in taxa with reduced numbers of genital plates such as some spatangoids, some cassiduloids, and all clypeasteroids. Taxonomic differences in c-axis orientations require that inferences be made from comparisons between species within families.
Geographical restriction as a guide to the causes of extinction: the case of the cold northern oceans during the Neogene
Authors: Vermeij Geerat J.
Published: July 2016

Geographical restriction to refuges implies the regional extinction of taxa in areas of the previous range falling outside the refuge. A comparison of the circumstances in the refuge with those in areas from which the taxa were eliminated is potentially informative for pinpointing the causes of extinction. A synthesis of data on the geographical and stratigraphical distributions of cool-water molluscs of the North Pacific and North Atlantic Oceans during the late Neogene reveals four patterns of geographical restriction, at least two of which imply that climatic cooling was not the only cause of extinction during the last several million years. These four patterns are (1) the northwestern Pacific restriction, involving 15 taxa whose amphi-Pacific distributions during the late Neogene became subsequently restricted to the Asian side of the Pacific; (2) the northwestern Atlantic restriction, involving six taxa whose early Pleistocene distribution is inferred to have been amphi-Atlantic, but whose present-day and late Pleistocene ranges are confined to the northwestern Atlantic; (3) a vicariant Pacific pattern, in which many ancestral amphi-Pacific taxa gave rise to separate eastern and western descendants; and (4) the circumboreal restriction, involving six taxa whose early Pleistocene distribution, encompassing both the Atlantic and Pacific Oceans, became subsequently limited to the North Pacific. Like the Pliocene extinctions in the Atlantic, previously studied by Stanley and others, the vicariant Pacific pattern is most reasonably interpreted as having resulted from regional extinction of northern populations in response to cooling. The northwestern Pacific and Atlantic restrictions, however, cannot be accounted for in this way. In contrast to the northeastern margins of the Pacific and Atlantic, the northwestern margins are today characterized by wide temperature fluctuations and by extensive development of shore ice in winter. Northeastern, rather than northwestern, restriction would be expected if cooling were the overriding cause of regional extinction. Among the other possible causes of extinction, only a decrease in primary productivity can account for the observed northwestern and circumboreal patterns of restriction. Geographical patterns of body size and the distribution of siliceous deposits provide supporting evidence that primary productivity declined after the Miocene in the northeastern Pacific, but remained high in the northwestern Pacific, and that productivity in the Pacific is generally higher than it is in the Atlantic. The patterns of geographical restriction in the northern oceans thus provide additional support to previous inferences that reductions in primary productivity have played a significant role in marine extinctions.
The articulate brachiopod hinge mechanism: morphological and functional variation
Authors: Carlson Sandra J.
Published: July 2016

Functional consequences of the variation in geometry and morphology of the articulate brachiopod hinge mechanism are poorly understood, despite the fact that hinge structures have considerable importance in brachiopod taxonomy. Jaanusson (1971) proposed that the ability to resorb shell material during growth, particularly in the hinge structures, can be used to distinguish two groups within the articulates, the deltidiodonts and the cyrtomatodonts. He considered the two groups to be morphologically distinct, “natural” phylogenetic groups, separated by a “functional discontinuity.” In order to test the morphological, functional, and phylogenetic implications of shell resorption, comparisons of the hinge-system geometry and diductor muscle moment are made here between deltidiodont and cyrtomatodont brachiopods. A truss network composed of landmarks relevant to the valve opening mechanism is constructed to characterize hinge-system geometry. The function of the hinge mechanism is analyzed in the context of valve opening, and diductor muscle force, effort lever arm, and moment are compared between deltidiodonts and cyrtomatodonts. The distribution of resorption among brachiopods is investigated with respect to a phylogenetic hypothesis proposed by Williams and Rowell (1965a).

Deltidiodont brachiopods are morphologically more variable than cyrtomatodonts, and a greater proportion of the variability is correlated with size. Deltidiodonts and cyrtomatodonts employ different strategies to open the valves; deltidiodont lever arms are relatively longer, whereas cyrtomatodont diductor muscles have relatively larger cross-sectional areas. The greatest muscle moment in deltidiodont hinge systems is realized in the maintenance of a gape angle; in the cyrtomatodont system, it is achieved at the initiation of a gape. Although they are morphologically and functionally distinct, it is doubtful that the two groups are separated by a “functional discontinuity.” Because the phylogenetic relationships among brachiopod orders are not yet resolved, the status of shell resorption as a homologue is still unclear. Resorption is manifest in at least some members of each major group of articulates (except the pentameraceans); it is likely that resorption has evolved independently several times in brachiopod evolution, in part because of the increased morphological flexibility it confers.
Paleozoic dipnoan phylogeny: functional complexes and evolution without parsimony
Authors: Campbell K. S. W. , Barwick R. E.
Published: July 2016

Attempts at understanding evolutionary relationships among Paleozoic Dipnoi (lungfish) using cladistic methodology have proved totally unsatisfactory (Miles 1977; Marshall 1987). We attempt to reconstruct the relationships between the better known genera using a method that involves the recognition of lineages based on evolving functional complexes, particularly those involved with food reduction and respiration. Within these broadly defined lineages, we have defined sub-lineages based on evolutionary patterns shown by structures that have been stratigraphically dated; such patterns are found inter alia in the roofing bones and the external dermal bones of the mandible. A number of new suborders and families are recognised; genera for which further morphological data are required before they can be assigned to a higher taxon are indicated; two generic synonyms are recognised.

In appendices, short descriptions are given of two new genera—Pillararhynchus from the Gogo Formation (Upper Devonian) of Western Australia, and Sorbitorhynchus from the Emsian of Guangxi, China.
Arm autotomy and arm branching pattern as anti-predatory adaptations in stalked and stalkless crinoids
Authors: Oji Tatsuo , Okamoto Takashi
Published: July 2016

Arm autotomy was induced in a living specimen of Metacrinus rotundus (Echinodermata: Crinoidea). An arm was autotomized at a ligamentary articulation known as a cryptosyzygy, following incision by scissors distal to the break point. Although sessile stalked crinoids cannot entirely escape from a predatory attack by arm autotomy and they do not have an active defense, arm autotomy at cryptosyzygies reduces damage and arm loss by effective distribution, and by minimizing trauma and facilitating subsequent regeneration.

The paradigmatic distribution of cryptosyzygies in which arm loss is set at a minimum, compared with the actual distribution, shows that these two patterns are similar and that actual specimens successfully reduce arm loss by the effective distribution of cryptosyzygies. The crinoid branching pattern also affects arm loss, and two different paradigms are discussed: anti-predatory and harvesting. Arm branching patterns of various isocrinids have tended toward the anti-predatory configuration from the Jurassic to the Recent, suggesting that the isocrinids have coped with increased predation. Shallow-water comatulids generally adopt the anti-predatory paradigm in their branching pattern, whereas many deep-water, stalked crinoids adopt a harvesting paradigm, reflecting that shallow-water comatulids receive more predatory attacks than do deep-water crinoids.
Biogeography and paleobiology
Authors: Jablonski David , Flessa Karl W. , Valentine James W.
Published: July 2016

In the past decade paleobiologists have applied the techniques of both ecological and historical biogeography, although vicariance/cladistic approaches have as yet had minimal impact. The traditional focus of paleobiogeographic study has been the province, a statistical entity defined by clusters of range endpoints of individual taxa. The study of such provinces has been useful in inferring past continental positions (although ambiguities remain that must be resolved using independent geological criteria) and in understanding the role of past global geographies in regulating biotic diversity through changes in the numbers and extent of provinces. This approach can be complemented by the treatment of geographic ranges of taxa as irreducible or emergent traits with far-reaching evolutionary effects upward and downward within a genealogical hierarchy. Temperature tolerances in benthic marine organisms appear to be by-products of selection for enzyme structures imparting favorable activity levels within the normal temperature range rather than direct products of selection for resistance to temperature extremes. Thus geographic range endpoints, which are also influenced by dispersal capability and the resulting scale of gene flow among disjunct populations, are not direct products of selection. However, themagnitudesof geographic ranges of species and clades behave as emergent properties and significantly influence taxonomic survivorship during background and mass extinctions in ways that are not extrapolations of effects at lower hierarchical levels. Biogeography shapes macroevolutionary patterns of origination and extinction during times of normal, background extinction and mass extinction. Preferential extinction among regions or among endemic rather than widespread clades can result in strong biases in the nature of the survivors of mass extinctions, with taxa being lost not because of selection against attributes of individual organisms but because of higher-order patterns of geographic selectivity.
Biases in the durations and diversities of fossil taxa
Authors: Pease Craig M.
Published: July 2016

The theoretical framework developed here delineates the biological and paleontological circumstances under which the observed durations and diversities of fossil taxa will be significantly affected by three time-dependent sampling biases. The pull of the Recent and the loss of fossiliferous sediments shorten the observed durations of ancient taxa, as compared to the observed durations of Recent taxa. By contrast, the duration truncation mechanism lengthens the observed durations of ancient, as compared to more recent, taxa. Both the pull of the Recent and loss of fossiliferous sediments decrease the observed diversity of ancient, as compared to contemporary, communities.

This theoretical framework is built on four parameters: the extinction and origination rates q and p; the fossilization rate, v; and the fossil loss rate, h. I derive formulas for the observed durations and diversities of fossil taxa in terms of these parameters and develop a method of estimating these parameters. The estimation procedure is applied to the bivalve families, and I provide statistical evidence for the conclusion that q – p < 0 for bivalve families, and hence that bivalve diversity has been increasing through time. The theory predicts that a certain fraction of an extinct fauna will be represented by only one fossil, and hence will have an observed duration of zero. As the record becomes poorer, this fraction increases. For bivalves I assume that families known from only one stage have an observed duration of zero, and exploit this assumption to estimate h and v/p.

To evaluate the errors made in applying the model to the bivalves, I estimate several parameters in two different ways and find the estimates to be consistent. Additionally, I argue that the errors caused by the simplifying assumptions of the model are less than the sampling errors inherent in estimating p, q, h, and v.
An interpretation of high montane conifers in western Tertiary floras
Authors: Axelrod Daniel I.
Published: July 2016

Megafossil remains of conifers allied to taxa of the high montane fir-spruce-hemlock-white pine zone often occur in relatively lowland Tertiary floras together with taxa typical of the mixed-conifer and broadleaved sclerophyll forest zones. Even though these forests are now separated in elevation by fully 1,000 m and in distance by 10–20 km or more, it has been generally accepted that the structures of the high montane conifers were transported to the basins of deposition from distant, high mountains. Several lines of evidence show that montane conifers were regular members of both mixed-conifer and montane conifer forests. They were restricted to higher elevations in the late Neogene–Quaternary; as summers became drier and hotter, the germinating seedlings failed to become established in the mixed-conifer forest zone. They were further isolated from the broadleaved sclerophyll zone, which was confined to lower levels as winters became colder and snow more frequent.
Septum morphology and bathymetry in cephalopods
Authors: Westermann Gerd E. G. , Ward Peter
Published: July 2016

Nautilus pompilius at Fiji lives abundantly to about 600 m depth while the shell implodes between 730–900 m when sunk in a cage. From this, and the average parameters of the septum, its tensile strength is calculated to 110–140 MPa. This is markedly higher than the latest value from direct tensile tests (78 MPa). In recent pressure tests by Saunders and Wehman with dry shells from the Philippines, implosion occurred at pressure equivalents to 310–680 m depth, without significant correlation with septal thickness. We attribute this excessive range and non-correlation to structural damage by postnecrotic processes. The recalculated tensile strength from their original data is 56–137 MPa; the higher values are compatible with our values for septal nacre of Nautilus and Spirula (c. 155 MPa). Septal curvature and thickness in orthocones thus remain useful guides to bathymetry.