bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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.
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.
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:
—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.—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?—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?—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.
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.
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.
Evolution of the coral-zooxanthellae symbiosis during the Triassic: a geochemical approach
Authors: Stanley George D. , Swart Peter K. 
Published: July 2016

Scleractinian corals first appeared during Triassic time in tropical shallow water environments. Controversy surrounds the paleoecology of scleractinian corals of the Late Triassic. Were they like their living counterparts, capable of supporting reefs, or had they not yet coevolved the important association with zooxanthellae that facilitated reef growth and construction? Indirect evidence suggests that some Upper Triassic corals from the Tethys played important constructional roles as reef builders within tropical carbonate complexes of the Tethys. To evaluate this idea, we have employed a geochemical approach based on isotope fractionation to ascertain if Late Triassic corals once possessed zooxanthellae.We have determined evidence for the ancient presence of algal symbiosis in 13 species of Triassic scleratinians from reef complexes in Turkey and northern Italy. In contrast, two higher latitude Jurassic species used as a control group for isotope analysis, lacked isotopic indications of symbiosis. These findings, together with stratigraphic and paleoecologic criteria, support the contention that Late Triassic scleractinian corals inhabiting shallow-water carbonate complexes of the Tethys were predominantly zooxanthellate, like their living counterparts from present day reefs.We view the zooxanthellate condition in calcifying reef organisms as a necessary prerequisite for constructional reef development. Our results emphasize the power of stable isotope studies in helping to answer paleobiological questions.