bluuebunny/crossref_metadata_2025 huggingface dataset:
Mississippian pelmatozoan community reorganization: a predation-mediated faunal change
Authors: Waters Johnny A. , Maples Christopher G.
Published: July 2016

Crinoid genera of the subclass Camerata generally dominated Late Silurian through Middle Mississippian pelmatozoan echinoderm assemblages. This dominance reached a peak during the early and middle Mississippian (Kinderhookian-Meramecian), but abruptly ended at the close of the Genevievian Stage (=lowermost Chesterian) in eastern North America. During the Genevievian Stage, crinoids of the subclass Inadunata became taxonomically more diverse but a few camerates, especiallyPlatycrinitesandBatocrinus,continued to be numerically dominant in many pelmatozoan assemblages. In eastern North America, platycrinids and batocrinids were reduced drastically near the Genevievian-Gasperian boundary. So obvious is this faunal change that, until recently, the Meramecian-Chesterian Series boundary was recognized as the last occurrence ofPlatycrinites penicillus.The sudden and drastic decline of numerically dominant platycrinids and batocrinids in eastern North America suggests a mass extinction, but is better interpreted as a range contraction and loss of dominance. Platycrinids, in particular, continued to be significant components of pelmatozoan assemblages in Europe and Asia long after the end of the Genevievian Stage. We infer that this reorganization of pelmatozoan assemblages in eastern North America was a product of predation, siliciclastic tolerance, and current-energy preference, with predation playing a major role. Reorganization resulted in post-Genevievian dominance by (1) cladid crinoids, (2) camerate crinoids that were cladid homeomorphs, and (3) the blastoidPentremites.Foraminifera, conodonts, corals, brachiopods, bryozoans, and other echinoderm groups were affected little, if any, during this same time.
The evolution of larval morphology during the post-Paleozoic radiation of echinoids
Authors: Wray Gregory A.
Published: July 2016

The post-Paleozoic radiation of echinoids entailed a rapid diversification not only of adult morphology, but also of larval morphology. The timing, order, and phylogenetic distribution of evolutionary transformations in echinopluteus larvae are reconstructed here under maximum parsimony assumptions from a large neontological data base. Many echinoid larval apomorphies apparently evolved within the Paleozoic stem lineage and were subsequently retained during much of the crown-group radiation. This suite of apomorphies includes most (and perhaps all) of the skeletal elements and some features of soft anatomy such as vibratile lobes. Other features apparently arose or were modified during the post-Paleozoic radiation. These include skeletal features such as arm-rod structure and length, and soft structures such as epaulettes and skeletal muscles. Transformational hypotheses of this kind can be supported or rejected with further neontological data, and many can potentially be tested from fossil evidence. Many post-Paleozoic transformations in echinopluteus structure may be adaptive. For example, increases in arm length and flattening of arm ectoderm may increase feeding rate and efficiency, and both types of transformation have occurred several times within the crown group. Relational hypotheses of this nature can be tested through comparative functional studies in extant echinoplutei. Parallel evolutionary losses of feeding in echinoplutei are accompanied by loss or modification of characteristic structures. This suggests that developmental constraints do not fully explain the conservation of these structures in planktotrophic echinoplutei. Comparisons of larval and adult morphology over congruent time intervals demonstrate that the origin of many orders was accompanied by a suite of synapomorphies in larval morphology that was subsequently conserved. Many details of echinopluteus morphology are therefore of taxonomic significance. Intraordinal patterns of larval diversity, however, vary considerably. That larval morphology has diversified independently of adult morphology indicates that mosaic evolution has occurred within the life cycle and suggests that echinoid larvae and adults can and do respond to selection independently. Taken together, these findings underscore the complex ways in which complex life cycles can evolve.
The Broken-Stick model as a null hypothesis for crinoid stalk taphonomy and as a guide to the distribution of connective tissue in fossils
Authors: Baumiller Tomasz K. , Ausich William I.
Published: July 2016

Lengths of crinoid stalk segments consisting of multiple columnals (pluricolumnals) from the Fort Payne Formation of south-central Kentucky (Mississippian) were tested for uniformity using simulations. The results indicate that stalk segment lengths are too uniform to have been produced by a random process operating on homogeneous stalks.

The most parsimonious explanation for the uniformity of pluricolumnal lengths is based on analogy with stalks of living isocrinids. The stalks of these crinoids are organized into multicolumnal segments of approximately uniform length: columnals within each segment are connected by “through-going” ligament and “intercolumnal” ligament. The articulation between segments, however, consists of only intercolumnal ligament. Preliminary results from experiments on Recent carcasses indicate that the latter is the primary plane of disarticulation following death.

The preservational pattern of the Mississippian stalks suggests that their ligamentary organization was similar to that of the isocrinids. Since the plane of primary disarticulation in isocrinids corresponds to the autotomy plane, Mississippian crinoids also may have been capable of autotomizing their stalks.
Evolutionary trends in the articulate brachiopod hinge mechanism
Authors: Carlson Sandra J.
Published: July 2016

Evolutionary patterns in the articulate brachiopod hinge are investigated and this empirical example is used as a model to examine evolutionary trends and evolutionary constraints. Several features of the hinge-system geometry exhibit persistent directional change from the Cambrian to the Recent and result in increased mechanical advantage in opening the valves. These geometric changes are reflected also in general features of shell morphology and growth and in patterns of familial diversity through time. Specific, identifiable constraints on brachiopod morphology and function related to the position of the pedicle and muscles and nature of the hinge line and hinge structures may be said to direct the observed trends. The pattern of evolutionary change among all articulate brachiopods is most satisfactorily accommodated by a diffusion model of morphological change. Examined independently, the deltidiodonts (with noninterlocking hinge structures) appear to reflect a process of directional selection through time, whereas change in the cyrtomatodont hinge mechanism (with interlocking teeth and sockets) may reflect the incidental effects of selection for increasing mantle-cavity volume rather than increasing diductor (opening) muscle moment. The “transition” from deltidiodont to cyrtomatodont hinge structures over the course of brachiopod evolutionary history may be interpreted from at least two distinctly different perspectives. Paleoecologically, this transition appears to reflect a habitat shift from soft sediment to hard, rocky substrates. Phylogenetically, the transition reflects the process of evolution: deltidiodonts persist as their modified descendants, the cyrtomatodonts. Investigating the acquisition of evolutionary novelties over time, or the transition from primitive to derived morphological features, may be the most informative approach to follow in studying evolutionary trends.
Functional analysis of archaeocyathan skeletal morphology and its paleobiological implications
Authors: Savarese Michael
Published: July 2016

A biomechanical study of archaeocyathan (phylum Archaeocyatha) skeletal construction was undertaken in order to compare its function with that of poriferans. Flume experiments were conducted on three cylindrical, brass models of regular archaeocyathans. Two of these, the porous-septate and aporous-septate models (i.e., possessing septa either with or without pores), represent an ontogenetic series; regular archaeocyathans (class Regulares) typically exhibit a reduction in septal porosity as they grow and many have aporous septa as adults. The third model is aseptate and represents a morphology that is not found in the fossil record. All models exhibit passive entrainment of flow during flume testing, a phenomenon on which modern sponges depend for suspension feeding. Flow direction through the models is consistent with predictions of the spongiomorph-affinity hypothesis. The three models behave quite differently, however. The aseptate model is least effective at passive entrainment. Although some fluid exits the top of the central cavity (or osculum), a great deal of fluid is entrained out the top of the intervallum and also leaks out the outer wall. Flow induction from the oscula of the septate models is augmented when compared to the aseptate model. The porous-septate model exhibits slight leakage from the outer wall, and a dye-rich plume exits the top of the intervallum. Alternatively, the aporous-septate model exhibits no outer-wall leakage and no entrainment from the intervallum. These differences in flow pattern between the porous- and aporous-septate models suggest a hitherto unknown function for septa. Imperforate septa prohibit the migration of fluid through the intervallum to the low-pressure, downstream side where leakage occurs. The ontogenetic shift in septal porosity, common to many archaeocyathan species, may be a mechanism by which outer-wall leakage is avoided later in life. Archaeocyathans would have encountered progressively higher ambient current velocities as their height increased through growth. Outer-wall leakage is not a problem at low velocities or small sizes, but leakage becomes serious at higher velocities when tall, adult morphologies are attained.
African origin of caviomorph rodents is indicated by incisor enamel microstructure
Authors: Martin Thomas
Published: July 2016

The same three subtypes of derived multiserial Hunter-Schreger bands are found in the incisor enamel of African phiomorph rodents from the late Eocene-early Oligocene and the oldest South American Caviomorpha from the Deseadan (late Oligocene). The synapomorphies contained therein, especially arrangement and orientation of interprismatic matrix, make an African origin of the Caviomorpha very probable. A North American origin of the Caviomorpha is thus rejected, as only primitive pauciserial Hunter-Schreger bands have been observed in possible ischyromyoid caviomorph ancestors. A multiserial Schmelzmuster apparently never evolved in the North American rodent fauna.
Morphological optimization in the largest living foraminifera: implications from finite element analysis
Authors: Song Yan , Black R. Gary , Lipps Jere H.
Published: July 2016

Benthic foraminifera have attained gigantic sizes many times throughout geologic history. To understand the selective processes underlying foraminiferal gigantism, we used a computer-based, three-dimension, solid finite element model to analyze the mechanical strength of different discoid forms, including two of the largest living foraminifera—Cycloclypeus carpenteriBrady andMarginopora vertebralisQuoy and Gaimard. These two species enlarge by cyclic, planar growth, resulting in slightly biconvex (C. carpenteri) and slightly biconcave (M. vertebralis) forms. As the tests enlarge, the maximum stresses induced by a standard bending moment decrease in both species. Such stress-reducing growth plans apparently allow growth to extraordinarily large sizes and allow volume to increase with minimal lowering of the surface-to-volume ratio, a critical functional factor in ensuring increased surface area for photosynthesis by endosymbionts contained within the tests and for chemical exchange by the foraminifera with the external environment. Of the two species,M. vertebralishas a stronger construction and a lower surface-to-volume ratio. These features indicate optimal constructional solutions to environmental constraints (degree of turbulence and light availability) in their disparate natural habitats:M. vertebralisin the mechanically rigorous inter- to subtidal, andC. carpenterion the light-minimal and hydraulically quieter, deeper sea beds. We conclude that morphological design in larger foraminifera is constrained by a biomechanical factor, and that gigantism and biomechanical optimization are demonstrably related.
Stratophenetic tracing of phylogeny using SIMCA pattern recognition technique: a case study of the late Neogene planktic foraminiferaGloboconellaclade
Authors: Wei Kuo-Yen
Published: July 2016

The Plio-Pleistocene planktic foraminiferal sequence of theGloborotalia(Globoconella)puncticulata-inflataclade in Deep Sea Drilling Project Site 588, dated at 4.36 Ma to 0.05 Ma, records the branching history of theG. inflatalineage from the ancestralG. puncticulatalineage. The gradational nature of the divergence and the enormous morphological variability inherent in theG. inflatalineage have elicited different views on taxonomy and phylogeny of this clade. A pattern recognition technique, soft independent modeling of class analog (SIMCA), was used as an objective quantitative stratophenetic methodology to reconstruct the phylogenetic history.

Typical specimens of two species,G. puncticulataandG. inflata,were identified from a stratigraphic level dated at 2.76 Ma. Principal component models were built to characterize the morphometric patterns of the two morphotypes using SIMCA. TheGloboconellaspecimens of the next lower and higher adjacent stratigraphic levels were evaluated against the models and classified into one of the two morphotypes. The newly classified specimens were then used to build new models for further tracing of lineages in lower and upper sections, respectively. Progression of such training and classification procedures through stratigraphic intervals resulted in a reconstruction of the evolutionary patterns of the two lineages. Cladogenesis gave rise to the descendant lineage,G. inflata,at about 3.5 Ma. The two co-existing species,G. inflataandG. puncticulata,differ only in size and show similarity in most characters at the beginning of their divergence. Other characters began to diverge later, at various rates. The gradients between planktic and benthic foraminiferal δ18O values show a continuous increase during the late Pliocene. The succession fromG. puncticulatatoG. inflataduring the same time correlates with the progressively increased vertical stratification in temperature of surface waters.Globorotalia puncticulatabecame extinct at 2.35 Ma when the temperature gradient further increased, corresponding to the onset of extensive glaciation in the Northern Hemisphere.
Rates of evolution
Authors: Stanley Steven M.
Published: July 2016

For some higher taxa, species can be identified in the fossil record with a high degree of reliability. The great geological durations of species indicate that phyletic evolution is normally so slow that little change occurs within a lineage during 105–107 generations. Failure to recognize sibling species in the fossil record has no bearing on this conclusion because they embody virtually no morphological change. Although slowness is the rule, we have no more precise assessment of morphological rates of phyletic evolution for any major taxon. Morphological data that have been assembled to assess rates of phyletic evolution have been meager, unrepresentative, and predominantly reflective of nothing more than body size. Net selection pressures within long segments of phylogeny—even ones that embrace large amounts of evolution—are infinitesimal and seemingly unsustainable against random fluctuations. This suggests that natural selection operates in a highly episodic fashion.

Rates of adaptive radiation and extinction at the species level can be estimated for many taxa and, from them, rates of speciation in adaptive radiation. Species selection should universally tend to increase rate of speciation and decrease rate of extinction, yet these rates are positively correlated in the animal world, apparently because they are linked by common controls: both rate of speciation and rate of extinction seem to increase with level of stereotypical behavior and to decrease with dispersal ability. Only a few “supertaxa” have been able to combine high rates of speciation with moderate rates of extinction.
Patterns of evolution in the Archean and Proterozoic Eons
Authors: Knoll Andrew H.
Published: July 2016

Problems of taphonomy and sampling adequacy hinder direct evolutionary interpretations of pattern in the Precambrian paleontological record; however, molecular studies of microbial phylogeny and comparative physiological and ecological investigations of living microorganisms can be combined with geological research to establish patterns of early evolution. The Late Proterozoic record of planktonic algae resembles those of Phanerozoic plants, animals, and microplankton in its patterns of diversification and turnover, as well as in the importance of major extinction events in shaping the course of evolution. Late Proterozoic eukaryotes thus appear to be discussable in terms of the macroevolutionary issues that have become central to Phanerozoic paleobiology. In contrast, evolutionary patterns in Precambrian prokaryotes appear to be different from those of plants and animals, a possible consequence of their differing systems of genetic organization and recombination.
Competition and the morphology, ecology, and evolution of acorn barnacles: an experimental test
Authors: Dungan Michael L.
Published: July 2016

Recent ideas about the role of competition in the ecology and evolution of acorn barnacles are based partly on relationships between morphology and the outcome of competition for space. One hypothesis is that present distributions and patterns of evolutionary diversification and decline among acorn barnacles reflect the competitive exclusion and replacement of solid-walled forms by those with tubiferous skeletal structure. An alternate view is that large barnacles generally outcompete smaller ones, independent of differences in skeletal structure, with predation and disturbance favoring the ecological and evolutionary success of small barnacles. Field experiments and observations in the Gulf of California suggested that the small, solid-walled species, Chthamalus anisopoma, competitively exlcudes the larger, tubiferous Tetraclita stalactifera confinis on the lower part of the shore. Greater tolerance to aerial exposure appears to allow Tetraclita to occupy a high intertidal refuge above Chthamalus. A common denominator among several cases of competitive exclusion in acorn barnacles is the greater settlement density of the competitive dominant, not its morphology. Morphological considerations alone are insufficient to predict or explain the outcome of competition between barnacle species.
Why are larger Foraminifera large?
Authors: Hallock Pamela
Published: July 2016

Delayed maturation and growth to large sizes are only advantageous under stable environmental conditions where food resources are limited. Specialization to algal symbiosis is also highly advantageous under those conditions if sunlight is available. The coevolution of these two characteristics has occurred many times in many foraminiferal lineages. These traits are sometimes associated with increased embryon size and suppression of sexual reproduction, which are also characteristics most advantageous under stable environmental conditions. Specialization for these traits, ensuring success in warm, shallow, stable, oligotrophic environments, often dooms the species or lineage to extinction when conditions change.
Patterns of phylogeny and rates of evolution in fossil horses: hipparions from the Miocene and Pliocene of North America
Authors: MacFadden Bruce J.
Published: July 2016

In North America, hipparion horses consisted of four distinct genera, Hipparion, Neohipparion, Nannippus, and Cormohipparion, known from the medial Miocene to the late Pliocene, ca. 15.5–2 ma ago. The speciation mode is determined for 10 of the 16 valid hipparion species; 50% (5) seem to have resulted from anagenesis and 50% (5) from cladogenesis. Roughly contemporaneous species of the four hipparion genera seem to proceed through similar evolutionary stages of cranial and dental characters. The mean hipparion species longevity is 3.3 ma (N = 16); the mean generic longevity is 8.4 ma (N = 4). Only two species become extinct in less than 2 ma; extinction occurs at a rate of ca. 470 μmacarthurs for species with durations between 2 and 5 ma. For selected dental characters, mean evolutionary rates (for the 16 species) were between .08 darwins (d) and .03 d with crown height evolving most rapidly. Despite the commonly held notion that fossil horses evolved rapidly, these data suggest normal or average (horotelic) evolution for hipparions, which is not surprising because they were already established in the grazing adaptive zone during their history.
Ammonoid early internal shell structure: its bearing on early life history
Authors: Tanabe Kazushige , Ohtsuka Yasuo
Published: July 2016

Morphologic analysis was made on early whorls of two Paleozoic and 43 Mesozoic ammonoid species to obtain basic data on early life history. A positive linear relationship between protoconch and ammonitella sizes is recognized among the species examined. Total rotation angle of the ammonitella (ammonitella angle) seems to be independent of ammonitella size but has a significant negative linear relation with whorl expansion rate. This supports the model that the embryonic shell of ammonoids consists of gas-filled protoconch and the succeeding body whorl up to the primary varix. Growth analysis of siphuncle diameter in the early post-embryonic stage also indicates that the shell growth rates of the species hatched from large-sized eggs were smaller than those of species hatched from small-sized eggs.
The relationship of trabecular architecture to inferred loading patterns in the third metacarpals of the extinct equids Merychippus and Mesohippus
Authors: Thomason J. J.
Published: July 2016

The internal structures of the third metacarpals of Merychippus and Mesohippus are assessed from thin sections and from radiographs, and systems of trabeculae differing in orientation and density are described. The principal forces transmitted to the articular surfaces of these bones are reconstructed and are used to estimate the pressure of contact on each surface. The major correlations made between the structure and the function of the third metacarpal of Equus (Thomason, 1985a) are also observed in this bone in Merychippus and Mesohippus. More important, the differences in trabecular structure among the recent and fossil bones may be interpreted in terms of the differences in inferred function. Thus the functional interpretation of the internal structure of fossil bones may reasonably be attempted.
Locomotor diversity within past and present guilds of large predatory mammals
Authors: Van Valkenburgh Blaire
Published: July 2016

The impact of environment, interspecific competition, and, to a lesser extent history, on the structure of the guild of large predatory mammals is explored in one fossil and four Recent communities. Two aspects are emphasized: (1) the number of species within each guild and (2) the extent of locomotor convergence as inferred from morphology among the constituent species. Locomotor behavior reflects habitat choice, hunting mode, and escape strategy, all of which appear to be important avenues of adaptive divergence among coexisting predators.

Locomotor behavior in extinct and extant predators is determined from body weight and five measured characteristics of the postcranial skeleton, including ungual shape, elbow shape, and limb proportions. Results indicate that levels of morphologic and inferred ecologic similarity between large predators are higher in the tropical grassland guild of East Africa than in the equivalent guilds of either tropical or temperate forest. This may be due to the great density and diversity of terrestrial herbivores in the productive grasslands. The fossil guild, from the Late Chadron–Orellan (Oligocene) of North America, appears most similar to the tropical forest guilds, but the predators seem to have been slower and more robust than their modern counterparts. Since the Orellan represents an early stage in the evolution of large, fissiped carnivores, both ancestry and time could have influenced Orellan guild structure.
Testing for historical patterns of change: a case study with frog pectoral girdles
Authors: Emerson Sharon B.
Published: July 2016

Evolutionary morphologists and paleontologists have long questioned whether there are general historical patterns to the distribution of morphological types. Few studies have rigorously addressed that question. This study tests the decoupling hypothesis, which predicts an increase in the number of morphological constraints with a reduction in the number of independent elements. Eight cases of historical transformation of the epicoracoid cartilages of frogs were selected for analysis. Similar morphological shape changes occurred across the independently derived historical transformations as determined by a triangle analysis of shape. These results support the decoupling hypothesis and indicate that there may be generalized historical pathways of structural change. This finding is important for the development of a predictive theory in evolutionary morphology.
Computed tomography ofArchaeopteryx
Authors: Haubitz B. , Prokop M. , Döhring W. , Ostrom J. H. , Wellnhofer P.
Published: July 2016

Application of computed tomography to the most recently recognized specimen ofArchaeopteryxdemonstrates the potential of this technique for paleontological issues. Contrary to earlier interpretations of these specimens, the results of computed tomography appear to show the presence of an avian-like doubled-headed quadrate bone in this earliest true bird.
Alpha, beta, or gamma: where does all the diversity go?
Authors: Sepkoski J. John
Published: July 2016

Global taxonomic richness is affected by variation in three components: within-community, or alpha, diversity; between-community, or beta, diversity; and between-region, or gamma, diversity. A data set consisting of 505 faunal lists distributed among 40 stratigraphic intervals and six environmental zones was used to investigate how variation in alpha and beta diversity influenced global diversity through the Paleozoic, and especially during the Ordovician radiations. As first shown by Bambach (1977), alpha diversity increased by 50 to 70 percent in offshore marine environments during the Ordovician and then remained essentially constant for the remainder of the Paleozoic. The increase is insufficient, however, to account for the 300 percent rise observed in global generic diversity. It is shown that beta diversity among level, soft-bottom communities also increased significantly during the early Paleozoic. This change is related to enhanced habitat selection, and presumably increased overall specialization, among diversifying taxa during the Ordovician radiations. Combined with alpha diversity, the measured change in beta diversity still accounts for only about half of the increase in global diversity. Other sources of increase are probably not related to variation in gamma diversity but rather to appearance and/or expansion of organic reefs, hardground communities, bryozoan thickets, and crinoid gardens during the Ordovician.
The Late Devonian extinction event: evidence for abrupt ecosystem collapse
Authors: McGhee George R.
Published: July 2016

The Late Devonian extinction event was not geologically “instantaneous,” in that extinctions during the epoch are not concentrated into a single sharp pulse at the end of the Frasnian. Extinction rates are elevated for a period of at least 2 to 4 m.y. during the middle and late phases of the Frasnian, with maximum rates occurring generally 2 m.y. before the terminal Frasnian. Neither was the Late Devonian biotic crisis a “gradual” event. In the analysis of the evolution of ecosystems, it is misleading to consider the pattern of extinction rates alone. Frasnian marine ecosystems flourished during the same time interval characterized by elevated extinction rates because origination rates of new species are higher, per time interval, than corresponding extinction rates. This pattern of relative origination/extinction rates abruptly reversed during the latest Frasnian—precipitating a rapid loss of species diversity. Within limits of current stratigraphic correlation, the ecosystem collapse appears to have occurred simultaneously in such widespread geographic regions as New York State (U.S.A.) and the southern Urals (U.S.S.R.).

In viewing the Late Devonian event from an ecological perspective, the most important question is not “What triggered the elevated extinction rates?”, but rather “What was the inhibiting factor that caused the cessation of new species originations?”
Trilobite diversity patterns in an Upper Cambrian stage
Authors: Westrop Stephen R.
Published: July 2016

Recovery of trilobite faunas following a mass extinction during the Upper Cambrian Sunwaptan Stage (equal to the “Ptychaspid Biomere”) involved increases in both within-habitat (alpha) diversity and in levels of biofacies differentiation. This pattern parallels, at a lower hierarchical level, the global increase in Phanerozoic marine invertebrate species richness (Sepkoski et al. 1981), which was influenced by changes in provinciality and in alpha diversity. Diversification slowed markedly in subtidal shelf carbonate habitats in the upper half of the stage, but continued in carbonate shelf margin environments, possibly due to higher rates of immigration from off-shelf sites. Trilobite clades appearing early in the stage have low centers of gravity, reflecting high immigration rates during and shortly after an interval of mass extinction. Expansion of shallow-water carbonate deposition in the upper half of the stage was accompanied by the spread of carbonate bank biofacies. Families occurring in these biofacies gradually increased in species richness and tended to have high centers of gravity.
Taphonomic bias and the evolutionary history of the family Cidaridae (Echinodermata: Echinoidea)
Authors: Greenstein Benjamin J.
Published: July 2016

The class Echinoidea apparently originated during the Ordovician Period and diversified slowly through the Paleozoic Era. The clade then mushroomed in diversity beginning in Late Triassic time and continued expanding into the present. Although this evolutionary history is generally accepted, the taphonomic overprint affecting it has not been explored. To gain a more accurate perception of the evolutionary history of the group, I have compared the diversity history of the family Cidaridae (Echinodermata: Echinoidea) with the preservational style of fossil type species using literature-derived data. The Cidaridae apparently originated in Middle Triassic time and diversified slowly through the Neocomian (Early Cretaceous). Diversity was maintained through the remainder of the Cretaceous and Tertiary Periods, reflecting the diversity history of the subclass. Characterization of the preservational style of type fossil material for the family revealed the following breakdown of preservational states: 60% of species were described on the basis of disarticulated skeletal material, primarily spines; 20% based on intact coronas denuded of spines, apical system, Aristotle's lantern and peristomial plates; 10% based on large coronal fragments; and 10% based on other skeletal elements. This distribution may represent the effect of a disarticulation threshold on the condition of echinoid carcasses before final burial and suggests that preservation of intact specimens may be very unlikely. For cidaroids, previous work has suggested that this threshold is likely to be reached after 7 days of decay.

Comparison of the diversity history of the Cidaridae with the preservation data reveals that characteristic patterns of taphonomic overprint have affected the group since its origination in Middle Triassic time, and the nature of that overprint has changed over time: the early diversity history of the group is characterized by occurrences of fragmented fossil material, with spines predominant; further radiation of the group in mid-Jurassic time coincided with an increase in modes of preservation, ranging between exceptionally well-preserved material and disarticulated skeletal elements. Finally, type material is more rarely described from younger stratigraphic intervals (Miocene–Pleistocene) and consists predominantly of disarticulated skeletal elements and coronal fragments larger than an interambulacrum in size. Intact, denuded coronas are noticeably lacking.

The number of type species of Cidaridae described in each stratigraphic interval has not been consistent during post-Paleozoic time. Middle Triassic, Malm (Upper Jurassic), Senonian (Upper Cretaceous) and Eocene series yielded significantly (α= .05) higher numbers of type specimens per million years, while the Lias (Lower Jurassic), Dogger (Mid-Jurassic), Lower Cretaceous and Paleocene yielded significantly (α= .05) lower numbers of type specimens per million years. This may be the result of a combination of taxonomic, sampling, and geographical biases.
Ten years in the library: new data confirm paleontological patterns
Authors: Sepkoski J. John
Published: July 2016

A comparison is made between compilations of times of origination and extinction of fossil marine animal families published in 1982 and 1992. As a result of ten years of library research, half of the information in the compendia has changed: families have been added and deleted, low-resolution stratigraphic data have been improved, and intervals of origination and extinction have been altered. Despite these changes, apparent macroevolutionary patterns for the entire marine fauna have remained constant. Diversity curves compiled from the two data bases are very similar, with a goodness-of-fit of 99%; the principal difference is that the 1992 curve averages 13% higher than the older curve. Both numbers and percentages of origination and extinction also match well, with fits ranging from 83% to 95%. All major events of radiation and extinction are identical. Therefore, errors in large paleontological data bases and arbitrariness of included taxa are not necessarily impediments to the analysis of pattern in the fossil record, so long as the data are sufficiently numerous.
Evolution of sexually dimorphic characters in peccaries (Mammalia, Tayassuidae)
Authors: Wright David B.
Published: July 2016

Cladistic analysis of osteological and dental characters in a monophyletic group of Miocene and younger tayassuids demonstrates a pattern of changes in the degree of sexual dimorphism in canine tooth diameter and zygomatic arch width, and in phenotypic correlations between these characters. Primitively, tayassuids have canine teeth that are sexually dimorphic and discretely bimodal in size, and zygomatic arches that are narrow in both sexes. Many late Miocene and Pliocene tayassuids have broad, winglike zygomatic processes. In some species, these processes are large in both sexes, but in others, those of females are much smaller than those of males. The presence of large processes in both sexes is primitive relative to the condition of strong sexual dimorphism. In five separate clades, the zygomatic processes of both sexes become reduced in size, and the degree of sexual dimorphism in canine size becomes reduced as well. The pattern is congruent with predictions derived from a theoretical model of the evolution of sexual dimorphism, and it further indicates the emergence of a new phenotypic correlation between two previously uncorrelated characters, canine size and zygoma size. The advent of this new correlation coincides with the advent of pronounced sexual dimorphism in zygomatic processes. Although such a pattern could be explained by genetically modifying phenotypic expression of homologous characters in one sex or the other, an epigenetic modification of expression is equally plausible: the evolution of sexual dimorphism in homologous characters could be accomplished by placing phenotypic expression of an originally monomorphic character under the control of steroid sex hormones. This hypothesis is consistent with evidence from many vertebrate groups, and it provides testable predictions.
Implosion of living Nautilus under increased pressure
Authors: Kanie Yasumitsu , Fukuda Yoshio , Nakayama Hideaki , Seki Kunihiro , Hattori Mutsuo
Published: July 2016

In a hyperbaric chamber, a living mature specimen of Nautilus pompilius withstood a hydrostatic pressure of 8.05 MPa (80.5 kg/cm2) equivalent to 785 m deep in the sea. Thereafter it was killed instantly by implosion of the shell. Before implosion, the animal reacted physiologically to increasing pressure. Therefore, the depth of 785 m can be assigned the depth limit of N. pompilius. The result bears on critical interpretations on the paleoecology and paleobiology of extinct nautiloids and ammonoids with similar shells.
Temporal variation in extinction risk and temporal scaling of extinction metrics
Authors: Foote Mike
Published: July 2016

Many areas of paleobiological research require reliable extinction metrics. Branching-and-extinction simulations and data on Phanerozoic marine families and genera are used to investigate the relationship between interval length and commonly used extinction metrics. Normalization of extinction metrics for interval length is problematic, even when interval length is known without error, because normalization implicitly assumes some model of variation in extinction risk within an interval. If extinction risk within an interval were constant, or if it varied but played no role in the definition of stratigraphic intervals, then Van Valen's time-normalized extinction metric would provide a measure of average extinction risk that is effectively unbiased by interval length. When extinction risk varies greatly within an interval and interval boundaries are drawn at times of heavy extinction, extinction metrics that normalize for interval length are negatively correlated with interval length. Despite its intuitive appeal, the per-taxon extinction rate (proportional extinction per million years) is biased by interval length under a wide range of extinction models.

Empirically, time-normalized extinction metrics for Phanerozoic families and genera are negatively correlated with interval length. This is consistent with an extinction model in which many times of very low risk are punctuated by a few times of very high risk which in turn determine stage boundaries. Origination and extinction patterns are similar, but origination intensity varies less among stages than extinction intensity. This observation has at least two plausible explanations: that origination episodes are more protracted than extinction episodes, and that biologic groups do not respond in unison to origination opportunities the way they seem to respond during extinction events. For families and genera, there is enough variation in extinction intensity among stages that stage length can be ignored when studying certain extinction patterns over the entire Phanerozoic.
Possible propulsion modes in Graptoloidea: a new model for graptoloid locomotion
Authors: Melchin Michael J. , DeMont M. Edwin
Published: July 2016

The mode of locomotion of any swimming animal is constrained by its size, architecture, and phylogenetic history. Considering these factors and the range of locomotory systems used by extant zooplankton, the range of possible modes of locomotion for graptoloids can be effectively limited. Three assumptions have been made: (1) graptoloids did not use a mode of locomotion unknown among modern organisms; (2) all graptoloids employed essentially the same mode of locomotion except, possibly, in their early growth stages; and (3) graptoloids did not rely entirely on passive buoyancy—no extant zooplankton groups in the size range of the graptoloids do. Structures that increase buoyancy or drag are often found in actively swimming zooplankton. They enhance feeding efficiency and reduce sinking rates during nonswimming periods.

The modes of locomotion utilized by extant zooplankton groups are ciliary propulsion, elongate body undulation, jet propulsion, rowing with skeletonized appendages, and rowing or undulation with muscular appendages. Of these, all but the last can be rejected for the graptoloids on the basis of scale or architecture. It is concluded that graptoloids probably used a rowing or undulatory motion with muscular appendages for swimming. Using a pterobranch model for the graptoloid zooids, the lophophore is considered an unlikely propulsive structure because the design requirements would conflict with those of a ciliarly suspension-feeding organ. Winglike, lateral extensions of the muscular cephalic shield, the same structure used for creeping locomotion in the benthic pterobranchs, is regarded as the most likely propulsive organ, analogous to the pteropod swimming wings.
The ammonoid suture problem: relationships between shell and septum thickness and suture complexity in Paleozoic ammonoids
Authors: Saunders W. Bruce
Published: July 2016

The most widely cited explanation for the functional enigma of sutural complexity in ammonoids, the Buckland hypothesis, has related septal folding and fluting to buttressing, providing increased shell strength against implosion, along with increased efficiency and decreased weight in shell and septum construction. In Paleozoic ammonoids, sutures ranged from simple to extremely complex. Comparison of shell and septum thickness (in polished sections) with sutural complexity in 49 Paleozoic ammonoid genera (Middle Devonian–Upper Permian) indicates that no significant reduction in either septum thickness or shell thickness accompanied a one-hundred-fold increase in sutural complexity. These preliminary results fail to support the Buckland hypothesis, suggest there may have been alternative incentives for increasing sutural complexity, and add support to views that septal fluting may have been related to buoyancy control.
Functional significance of regular archaeocyathan central cavity diameter: a biomechanical and paleoecological test
Authors: Savarese Michael
Published: July 2016

Theoretical and experimental biomechanical approaches are used to test the effect regular archaeocyathan central cavity diameter has on the generation of passive flow through the skeleton. These results are then used to predict a correspondence between gross morphology and paleoenvironmental occurrence. Previous work has demonstrated that regular archaeocyathan morphology generates passive flow, via Bernoulli and viscous entrainment effects, through its porous walls for suspension feeding, a phenomenon that occurs in modern sponges. Efficacy of entrainment depends upon the area of the excurrent pore (i.e., central cavity) over which the ambient flow is moving. Consequently, archaeocyaths should have maximized their central cavity diameters.

Five-centimeter-long, conical and cylindrical acrylic pipes with varying end diameters were tested in a flume to document the relative effects of Bernoulli and viscous entrainment. Each pipe was oriented perpendicular to the flow direction in a uniform flow field, and fluorescein dye was injected at the pipe's mid-length for flow visualization. Models with different-sized apertures consistently exhibit dye movement to the larger opening and greater dye entrainment speeds than models with identically sized apertures, thereby suggesting that viscous entrainment effects are significant and operating in concert with Bernoulli effects. To test for similar effects in archaeocyaths, four brass models were constructed with varying central cavity diameters. Both volume flux and excurrent flow speed of the exiting water increased as the central cavity diameter increased. An analysis of the morphologies that occur in nature confirm these results. Regular archaeocyaths most commonly have central cavity diameters close to their outer wall diameter, thereby maximizing the excurrent pore area.

These results have implications for archaeocyathan paleoecology. Environments with low-magnitude currents should support individuals with larger central cavity diameters than higher energy settings. Data on the occurrence of morphotypes within bioherms of varying flow energies from South Australia support this prediction.
Oxygen isotope variability in juvenile dinosaurs (Hypacrosaurus): evidence for thermoregulation
Authors: Barrick Reese E. , Showers William J.
Published: July 2016

Small terrestrial vertebrates are not capable of maintaining a constant body temperature (±2°C) without a relatively high metabolism. The amount of temperature variability during bone growth can be determined using oxygen isotopes from bone phosphate because fractionation of oxygen isotopes between body fluid and bone phosphate is dependent upon temperature. Fluctuation of body temperature during the early phase of growth in juvenile ectotherms should result in high intra- and interbone isotopic variability, whereas juvenile endotherms should have low isotopic variability resulting from the maintenance of homeothermy. Analyses of juvenile Hypacrosaurus individuals indicate a pattern of low isotopic heterogeneity suggestive of endothermy.
Phyletic gradualism in a European Plio-PleistoceneMimomyslineage (Arvicolidae, Rodentia)
Authors: Chaline Jean , Laurin Bernard
Published: July 2016

The European Plio-PleistoceneMimomys(Hintonia)occitanus-ostramosensislineage of arvicolid rodents appears to present a genuine case of gradual evolution. Analysis of numerous dental samples recorded from 3 to 1.5 ma by several biometrical methods led to the following conclusions: samples from the whole geographical area order into a morphological continuum (chronomorphocline); the successive populations in the trend show important overlap of their variation; and the absence of stasis or any interruption in the trend, combined with its unidirectionality, suggests genuine phyletic gradualism. The chronomorphocline is characterized by an important increase in tooth hypsodonty, by the progressive and continuous development of lateral enamel tracks. Four phases of evolution can be recognized in the lineage, the rates of morphological changes being variable and related to climatic fluctuations (Reuverian, Pretiglian, Tiglian, Eburonian). Morphological changes are initiated by environmental fluctuations, although the polarity of climatic change is not a determining factor. Environmental changes act as stimulus and release drift processes. Phyletic gradualism occurring over such a wide area implies extensive gene flow, and suggests that only general, not local, environmental components act to produce the observed morphological changes.
Ontogeny and heterochrony in the ostracode Cavellina Coryell from Lower Permian rocks in Kansas
Authors: Schweitzer Peter N. , Kaesler Roger L. , Lohmann G. P.
Published: July 2016

Animals evolve by changing their form and by changing the rate at which they develop. Since evolution of development through time may be directly related to the adaptation of their life histories, study of ontogeny in fossils may yield information about the ecology of extinct animals. We need to know how to measure animals' ontogeny and at what taxonomic level structural differences overshadow differences in development. Two closely related species of the Permian ostracode Cavellina were compared to determine how much of the morphological difference between them is due to differences in their ontogenies. Most of the difference is not related to ontogeny. They also differ in a way that could be explained by heterochrony, although this difference is secondary in importance to the structural difference. These findings suggest that ecological adaptation might best be studied by examining the changes in development that occur within species through time and space.