bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparative ecology of bryozoan radiations: origin of novelties in cyclostomes and cheilostomes
Authors: Lidgard Scott , Taylor Paul D. , Jablonski David 
Published: January 2018

The cyclostome and cheilostome bryozoan clades diversified at different times and consequently in different ecological contexts. Cyclostomes began their rebound from a Permo-Triassic bottleneck in the early Jurassic, prior to increases in bioturbation, durgophagous predation, and other ecological changes commonly termed the Mesozoic Marine Revolution. Cheilostomes did not appear until the latest Jurassic and rapid diversification began only in the mid-Cretaceous, when the Mesozoic Revolution was well under way. We compared the radiations of these clades to test for similarities reflecting general patterns in the origin of within-clade novelties, and for differences that might be due to ecological context or clade attributes. We examined the timing and environment of first occurrence of eight morphological novelties that evolved convergently in both clades (ovicells, cylindrical arborescent colony, multilayered encrusting growth [frontal budding s.l.], bilaminate erect colony, fenestrate colony, articulated colony, calcified operculae, avicularia), as well as novelties unique to cheilostomes (cribrimorph and ascophoran grades, and lunulitiform colonies) or to cyclostomes (apertures arranged in fascicles). First occurrences were traced from the literature, BMNH collections, and unpublished data provided by Prof. Dr. E. Voigt; environments were inferred within an onshore-offshore gradient using the protocol of Jablonski and Bottjer (1990).As seen for other invertebrate groups, within-clade novelties were not concentrated in onshore settings for either bryozoan clade, in contrast to the origination patterns at the ordinal level (including the Cheilostomata). Differences in sequence or environment of first occurrence were not obviously related to the Mesozoic Revolution, or to the distinction between zooid- and colony-level characters. Novelties showed a weak tendency to originate in similar sequence and in similar environments for both clades, but these numbers are small. Differences in sequence may partly reflect clade-specific constraints: for example, opercula are considered a prerequisite for the development of avicularia, so that cyclostomes needed to evolve that precursor before avicularia could appear, whereas opercula are primitive (though uncalcified) in cheilostomes and thus did not constitute such a constraint. If avicularia are omitted, the rank-order correlation of novelties becomes marginally significant (p = 0.05, Spearman rank test). The most striking difference is in the temporal pattern of novelty acquisition. In cyclostomes, these are rather evenly spread over 100 Ma, whereas in cheilostomes six of the novelties appeared in the Late Albian-Early Cenomanian during a period of rapid diversification. Despite a slow start, the cheilostome radiation enters an explosive phase that may characterize successful establishment of clades founded late in the Phanerozoic.
Levels of selection: an analysis of the forces driving diversification in the turritellid gastropods
Authors: Lieberman Bruce S. , Allmon Warren D. , Eldredge Niles 
Published: January 2018

This analysis examines the evolution of the greater diversity of non-planktonic species relative to planktonic species in the turritellid gastropods. Two mechanisms for generating diversity gradients in larval types have been proposed in the literature. The first, species selection or the effect hypothesis, focused on the population biology of larval types. The second proposed that factors in development were responsible. Turritellids have been cited as a classic example of species selection. In order to test the validity of these mechanisms for the evolution of the turritellids two phylogenetic models are formulated. One is constructed to fit the predicted evolutionary results if species selection or the effect hypothesis are the operative processes driving diversification. The second model is constructed as if developmental constraints prohibiting the origination of planktonic species in non-planktonic lineages were responsible for the relative increase in non-planktonic species.In order to test these two proposed mechanisms a phylogenetic analysis of the turritellids using molecular sequence data was performed to determine the evolution of larval types in this clade. This is compared to the phylogenetic patterns predicted by the two models. The model asserting the control of species selection or the effect hypothesis is rejected. It is predicted that species with non-planktonic larvae will increase at the expense of planktonic species because planktonic organisms are developmentally more open to change, while developmental change is buffered in the non-planktonics. Once a lineage has become non-planktonic, there is little chance for it to undergo subsequent changes in larval style through phylogenetic time. The process producing this pattern is termed the cell-lineage effect, and it is a mechanism governing changes in the timing of germ line sequestration in organisms. Thus, the fossil and recent turritellid biota will show a bias towards non-planktonic forms due to biases and constraints in development.
The origin of mammals: chronology and paleobiogeography
Authors: Lucas Spencer G. , Hunt Adrian P. 
Published: January 2018

A comprehensive review of the stratigraphic and geographic distribution of the advanced, non-mammalian cynodonts (traversodontids, tritylodontids and tritheledontids) and the Late Triassic-Early Jurassic mammals indicates that: (1) traversodontids were a wholly Triassic group that disappeared during the Rhaetian; during the late Carnian-early Norian they were rare but widespread components of Pangaean land-vertebrate faunas; (2) tritylodontids first appeared in Europe during the Rhaetian, were a cosmopolitan group by the Sinemurian/Pliensbachian and disappeared during the Bathonian; (3) tritheledontids ranged in age from late Carnian to Sinemurian/Pliensbachian and were mostly a New World group; and (4) the oldest mammal is of late Carnian age from West Texas, but there is at least a 10-million-year gap between it and the next oldest mammals from the late Norian of Europe.Advanced cynodont and mammalian distributions of the Late Triassic-Early Jurassic do not suggest Late Triassic paleoprovinciality, but they do support the notion of a cosmopolitan vertebrate fauna during the Sinemurian/Pliensbachian. Proponents of a tritylodontid ancestry of mammals must explain away a 15-million-year-long absence of tritylodontids from the Late Triassic fossil record. In contrast, proponents of a tritheledontid ancestry of mammals need offer no such explanation since tritheledontids and mammals appeared simultaneously during the late Carnian.
Patterns of faunal turnover and diversity in the Wyoming-Montana Paleogene in relation to regional and global events
Authors: Maas M.C. , Gingerich P.D. , Gunnell G. , Krause D.W. 
Published: January 2018

The Bighorn Basin of Wyoming and its northerly extension, the Crazy Mountains Basin of Montana, contain a continuous record of the middle Paleocene through early Eocene mammalian biota. This interval, spanning some eight million years, is subdivided into 18 faunal zones. Durations of the zones, ranging from 0.3 to 0.75 million years, are extrapolated from intrabasinal depositional rates and correlated with the early Tertiary paleomagnetic reversal record. This stratigraphic resolution allows us to document in detail regional diversity and turnover.In the Bighorn and Crazy Mountains basins, standing generic richness (estimated number of genera at the midpoint of an interval) decreased slightly between the Torrejonian and Tiffanian (middle and late Paleocene), increased from the latest Tiffanian and Clarkforkian (latest Paleocene) to the early Wasatchian (early Eocene), and declined during the later Wasatchian.Changes in diversity reflect first and last appearances (including originations, extinctions, and dispersal). Because first and last appearance rates are in part dependent on diversity and the duration of each interval, we plot generic turnover as rate quotients, ratios of observed to expected first or last appearances. Expected turnover rates are calculated from multiple regression of turnover on duration and generic richness. Turnover rates are evaluated in relation to the quality of the fossil record for each interval. Rate quotients show that the slight decline in generic richness in the Bighorn and Crazy Mountains basins between the Torrejonian and Tiffanian resulted from a higher than expected disappearance rate at the end of the Torrejonian. Lower than expected disappearance rates and higher than expected appearance rates in the early Clarkforkian and, particularly, the earliest Wasatchian contributed to the increase in richness during this period. The middle through late Wasatchian decline in generic richness resulted from surprisingly low appearance and high disappearance rates.There was little change in taxonomic composition of faunas between the middle and late Paleocene; faunas from this interval were dominated by archaic groups (e.g., “condylarths”, multituberculates, plesiadapiforms). In contrast, faunal composition changed markedly during the latest Paleocene and the early Wasatchian, with the introduction of major modern groups (e.g., rodents, artiodactyls, perissodactyls, primates) and the decline in diversity of the archaic forms that dominated earlier Paleocene faunas. There is strong evidence that this faunal change was influenced by global climatic factors: climatic warming, beginning in the latest Paleocene, opened new routes for intercontinental dispersal, and had a major effect on worldwide patterns of faunal composition and diversity, including those of the Bighorn and Crazy Mountains basins.
Patterns of loop development in post-Paleozoic terebratulid brachiopods and their evolutionary significance
Authors: Mackinnon David I. 
Published: January 2018

Studies of loop ultrastructure reveal much about both the processes and patterns of loop growth in brachiopods. Such studies also provide useful insight into evolutionary relationships between various main loop-bearing brachiopod taxa. At least five different loop types, two short-looped and three long-looped, are recognisable in Cenozoic Terebratulida.Loop development in short-looped forms is relatively unspectacular and of limited value for evolutionary studies. It consists of the growth of either an undulating transverse ribbon extending between two short crura (in the Family Terebratulidae) or, where crural processes are united (as in most Cancellothyrididae), a ring. In all short-looped forms the loop is derived from, and hence supported solely by, the crura throughout ontogeny.The early stages of loop development in the great majority of post-Paleozoic long-looped brachiopods are similar. A septal pillar, located centrally in the dorsal valve floor, appears generally very early in ontogeny. Rudimentary descending branch elements are generated both from the crura and the flanks of the septal pillar. Rudimentary ascending elements develop at either the ventral or posteroventral edge of the septal pillar and consist firstly of an inverted or steeply inclined and continuously expanding cone or hood which, through resorption of its posteriorly located apex, becomes transformed into a ring. Further growth sees firstly the fusion of the anterior extremeties of adjacent ascending and descending loop elements followed by their progressive anterolateral separation from the septal pillar.Contrasting modes of growth characterise the later stages of loop development in the three main groups of long-looped brachiopods. In Dallinidae, ascending and descending elements detach from the septum to give rise to a long, reflected loop supported only by the crura. In Terebratellidae, a pair of narrow, laterally directed but anteriorly migrating struts anchor the the descending branches to the median septum. These struts, in structural continuity with the median septum, are built up entirely from secondary layer fibres. In Laqueidae, in addition to a pair of septal struts, a pair of anterolaterally migrating vertical bands spanning the gap between adjacent ascending and descending branches provide further support. Unlike the septal struts but like the remaining ascending and descending loop elements, the vertical bands are constructed from both primary and secondary shell layers. Growth line discordancies at the junctions between the vertical bands and contiguous ascending and descending elements indicate the structural integrity of the vertical bands.
Two new carnivorous cynodonts from the Ischigualasto Formation (Upper Triassic) of Argentina
Authors: Martínez Ricardo N. , Forster Catherine A. , May Cathleen L. 
Published: January 2018

Two skulls representing new forms of carnivorous cynodonts were discovered recently in the Upper Triassic (Carnian) Ischigualasto Formation of northwestern Argentina. These specimens are the first complete carnivorous cynodonts described from the Late Triassic of Argentina, and provide critical evidence for the evolution of cranial form between well known Middle Triassic cynodonts, such as Probainognathus, and the first mammals in the latest Triassic.The first skull (PVSJ 422) is proportionately long, with a posterior skull width only 35 per cent of basal skull length (9.5 cm.). Other distinctive features of the skull include the form of the postcanine crowns, which have two cusps posterior to the principal cusp and fine serations on their leading edges, and which overlap each other in an imbricate pattern. Postcanines 5-7 are subequal in size, overlap the dentary laterally, and are substantially larger than postcanines 2-4. The dental formula in the upper jaw is I4-C1-PC7, with the small first postcanine separated fore and aft by small diastemas. As in other advanced eucynodonts, no pineal foramen is present. Some postcranial elements, as yet unstudied, were also found with this specimen.The second skull (PVSJ 411) has broader proportions, the width between quadrates almost half that of basal skull length (7.5 cm.). These proportions, in combination with deep, curved zygomatic arches, resemble other Middle Triassic cynodonts such as Probelesodon. Distinctive features of this skull include bicusped postcanines in the upper jaw similar to those of Probelesodon, and a mandibular symphysis that extends back to the level of the fourth postcanine. The dental formula in the upper jaw is I4-C1-PC6. As in the first skull, a pineal foramen is absent.Several advanced cranial features, such as a fused mandibular symphysis, occur in both skulls and strongly suggest that these new forms belong within the Eucynodontia (Hopson, 1991). Other advanced features, such as the absence of a pineal foramen, further suggest that these new forms are closer to mammals than are traversodontid cynodonts. In contrast, other characters appear to be curiosly primitive, such as a short hard palate in the first skull. These new cynodonts thus may introduce previously unseen features and character combinations to the study of cynodont cranial evolution.
The geological history of polyploidy in woody angiosperms
Authors: Masterson Jane 
Published: January 2018

Polyploidy, the condition where an organism has more than two complete sets of chromosomes, is a common and important evolutionary phenomenon in flowering plants (angiosperms). Estimates of the percentage of angiosperms (approximately 250-300,000 living species) derived from polyploids range from 47-90%. The historical development of polyploidy is currently very poorly understood and whether polyploidy is a major causal factor in angiosperm diversification is widely debated.Many questions about the base chromosome number of angiosperms (important for establishing the extent of polyploidy) and the origin of polyploidy can be addressed using fossil plants. One of the physical effects of polyploidy is a general increase in cell volume; the size of guard cells (leaf epidermal cells that control the opening and closing of the gas exchange pores [stomata]) has been used successfully to determine the relative number of chromosomes present or ploidy level in living Carva (hickories), Betula (birch), Magnolia, and Pvrus (pear). At least two previous studies have used guard cells to estimate ploidy level in fossil taxa (Metasequoia, Sequoia, and Paleorubiaceophyllum).The base haploid chromosome number in angiosperms generally has been assumed to be between n=7-9, but this is apparently based either on the dubious assumption that the most common condition is likely to be primitive (cf. egg laying in mammals) or the inference that because this number is found in many different clades it is likely to be basic in each of these groups. The Gnetales (the living gymnosperms most closely related to angiosperms) have a haploid basic number of 7, but Donoghue and Doyle (1989) find that it is almost equally parsimonious to assume the base number is n=12-14 because of uncertainties over the chromosome number of certain critical extinct outgroups. My guard cell measurements of three angiosperm families (Platanaceae, Magnoliaceae and Lauraceae) provide additional empirical support for the n=7-9 hypothesis and suggest that extinct diploid members existed in the mid-Cretaceous and early Cenozoic floras. These results also falsify the hypothesis that polyploidization triggered the angiosperm radiation in the Cretaceous in these families. Other hypotheses regarding the historical timing of major increases in polyploidy are being tested. These include climatic deterioration and associated modification and mixing of plant distributions during the Eocene and Pleistocene. It may be that polyploids survive major disturbances at a higher rate than diploids because they often have broader ecological tolerances and wider geographic ranges. Thus the accumulation of polyploids in plant families may not occur because they are speciation prone as usually inferred but because they are extinction resistant. My preliminary results in Platanaceae support an increased level of polyploidy after major disturbances.
Paleobotany of the Paleocene St. Stephens site, Berkeley County, South Carolina
Authors: Melchior Robert 
Published: January 2018

Plant fossils including silicified wood, amber and a diverse suite of palynomorphs were recovered from beds of the Rhems and Williamsburg Formations of the Black Mingo group. The Rhems beds are Danian in age and the Williamsburg is Thanetian. Both formations constitute prograding delta sequences. The palynomorph assemblage was recovered from the Rhems Formation and consists of 112 species of pollen and spores of angiosperms, gymnosperms and cryptogams as well as 32 species of fungal spores. Silicified wood represents 10 taxa and the amber is suggestive of two but precise stratigraphic position of these latter fossils is uncertain.An analysis of the ranges of palynomorph taxa within the Rhems Formation yields three assemblages. An assemblage concentrated in the lower, pro-delta beds of the unit is felt to represent a coastal community, a group concentrated in the upper delta-front and topset beds is representative of an inland assemblage and a third group ranges throughout the section. The coastal assemblage is dominated by palms with gymnosperms also being abundant. The inland assemblage consists primarily of a diverse array of dicots associated with the Normapolles group. The long ranging assemblage is associated with both the above groups in about equal numbers. A habitat mosaic consisting of xeric to mesic and hydric elements within the coastal and inland community zones is inferred. Analysis using the modern affinities of the palynomorphs suggests a subtropical, summer dry climate near its meteorological boundary with the tropical zone such as that found in parts of coastal southeast Asia today.Wood taxa from the site include specimens assignable to Podocarpoxylon, Myrica, Fagaceaoxylon, Magnoliaeoxylon, Ulminium, Liquidambar, Nyssoxylon, the Olacaceae, Apocynaceae and possibly the Icacinaceae. Calculated “V” values and anatomical details of these woods correlate well with the habitat mosaic and paleoclimatic implications suggested by the palynomorphs.Infra-red spectra of the ambers suggest affinities of these fossils with the Caesalpiniaceae and the Araucariaceae. Pollen that might be attributable to these groups includes Margocolporites, Rhoipites, and Classopollis (Pagiophyllum).The fungal palynomorphs are both abundant and diverse in some samples from the site. These fossils include both hyphae and conidia in place in the silicified wood and dispersed spores.
Advances in deepsea paleoecology: introduction to the symposium
Authors: Miller W. 
Published: January 2018

This symposium will cover new developments in the ecology and paleoecology of deepsea organisms, based largely on advances in the study of protists, metazoan associations, and biogenic sedimentary structures. Bringing together ecologists and paleoecologists will establish a bridge between workers who have devoted their attention exclusively to the modern biota and those who have only considered fossil evidence from pelagic, turbidite, and related deep basinal rock sequences. Contributors will emphasize patterns and processes from historical or developmental perspectives as well as from experimental or actualistic perspectives, and will attempt to identify the promising directions for future research.Specifically, attention will be focused on benthic organisms and associations, and on biogenic structures, because these entities make up ecologic patterns that are most accessible to study by both biologists and paleontologists. On the biologic side, contributors will review the significance of new discoveries and theories, present summaries of path breaking work on foraminiferids and xenophyophores, and characterize modern organism-sediment interactions and trace associations. Paleontologists will emphasize processes requiring large areas of seafloor and long time spans in their review of the origins of deepsea communities and ichnofacies, large-scale dispersal patterns, long-term ecosystem dynamics, and taphonomy and time-averaging of deepsea fossil deposits. This is the first attempt to bring ecologic and paleoecologic efforts into closer coordination in order to identify the most significant themes in the historical biology of deepwater marine organisms.Some examples of research issues amenable to this kind of coordinated approach include: 1) origination of deepsea inhabitants from shallow marine sources vs. elaboration and diversification of taxa already established in deepwater; 2) importance of small-scale, frequent disturbance vs. large-scale, rare events (turbidity currents, anoxia episodes) in shaping the deepsea biota; 3) taxonomic replacements and invasions at varied spatiotemporal scales; 4) biotic interactions vs. environmental pacing as mechanisms producing community structure; 5) evolutionary importance of allochthonous vs. autochthonous food supplies; 6) relationships between trace fossil assemblages and the development of deepsea ecosystems; 7) the nature and history of linkages between deepsea ecologic systems, and terrestrial and shallow marine systems; and 8) preservation potential of the dominant benthic organisms, and their symbionts or traces, and its implications in paleoecologic reconstructions. In general, combining biologic and paleontologic information should result in more realistic and useful interpretations of ancient biotas (rather than simply the description of more unique fossil finds), as well as an increased awareness of the long-term development of the modern biota (rather than attention directed exclusively to living organisms, short-term processes, and small-scale patterns).