Showing papers in "Paleobiology in 1996"
TL;DR: The higher estimates of completeness at smaller geographic scales support previous suggestions that the incompleteness of the fossil record reflects loss of fossiliferous rock more than failure of species to enter the fossilrecord in the first place.
Abstract: The incompleteness of the fossil record hinders the inference of evolutionary rates and patterns. Here, we derive relationships among true taxonomic durations, preservation probability, and observed taxonomic ranges. We use these relationships to estimate original distributions of taxonomic durations, preservation probability, and completeness (proportion of taxa preserved), given only the observed ranges. No data on occurrences within the ranges of taxa are required. When preservation is random and the original distribution of durations is exponential, the inference of durations, preservability, and completeness is exact. However, reasonable approximations are possible given non-exponential duration distributions and temporal and taxonomic variation in preservability. Thus, the approaches we describe have great potential in studies of taphonomy, evolutionary rates and patterns, and genealogy. Analyses of Upper Cambrian-Lower Ordovician trilobite species, Paleozoic crinoid genera, Jurassic bivalve species, and Cenozoic mammal species yield the following results: (1) The preservation probability inferred from stratigraphic ranges alone agrees with that inferred from the analysis of stratigraphic gaps when data on the latter are available. (2) Whereas median durations based on simple tabulations of observed ranges are biased by stratigraphic resolution, our estimates of median duration, extinction rate, and completeness are not biased.(3) The shorter geologic ranges of mammalian species relative to those of bivalves cannot be attributed to a difference in preservation potential. However, we cannot rule out the contribution of taxonomic practice to this difference. (4) In the groups studied, completeness (proportion of species [trilobites, bivalves, mammals] or genera [crinoids] preserved) ranges from 60% to 90%. The higher estimates of completeness at smaller geographic scales support previous suggestions that the incompleteness of the fossil record reflects loss of fossiliferous rock more than failure of species to enter the fossil record in the first place.
249 citations
TL;DR: A global-scale sample of fossil occurrences is analyzed that allows us to determine directly the effects of sample size on the calibration of what is generally thought to be among the most significant global biodiversity increases in the history of life: the Ordovician Radiation.
Abstract: It has long been suspected that trends in global marine biodiversity calibrated for the Phanerozoic may be affected by sampling problems. However, this possibility has not been evaluated definitively, and raw diversity trends are generally accepted at face value in macroevolutionary investigations. Here, we analyze a global-scale sample of fossil occurrences that allows us to determine directly the effects of sample size on the calibration of what is generally thought to be among the most significant global biodiversity increases in the history of life: the Ordovician Radiation. Utilizing a composite database that includes trilobites, brachiopods, and three classes of molluscs, we conduct rarefaction analyses to demonstrate that the diversification trajectory for the Radiation was considerably different than suggested by raw diversity time-series. Our analyses suggest that a substantial portion of the increase recognized in raw diversity depictions for the last three Ordovician epochs (the Llandeilian, Caradocian, and Ashgillian) is a consequence of increased sample size of the preserved and catalogued fossil record. We also use biometric data for a global sample of Ordovician trilobites, along with methods of measuring morphological diversity that are not biased by sample size, to show that morphological diversification in this major clade had leveled off by the Llanvirnian. The discordance between raw diversity depictions and more robust taxonomic and morphological diversity metrics suggests that sampling effects may strongly influence our perception of biodiversity trends throughout the Phanerozoic.
213 citations
TL;DR: The taxonomic composition and diversity of Indo-Pacific reef coral communities that have undergone repeated global change between 125 and 30 Ka (thousand years before present) are examined.
Abstract: One of the most intriguing questions in community ecology remains unanswered: Are ecological communities open assemblages with each species reacting individually to environmental change, or are they integrated units consisting of multispecies assemblages acting in concert? I address this question for marine organisms by examining the taxonomic composition and diversity of Indo-Pacific reef coral communities that have undergone repeated global change between 125 and 30 Ka (thousand years before present).Investigation of community constancy through time relies on two critical questions: (1) Are there significant differences in taxonomic composition among communities from different times? and if not, (2) Are the observed patterns in temporal similarity significantly different from expected patterns resulting from a random sampling of the available within-habitat species pool?Constancy in taxonomic composition and species richness of Pleistocene reef coral assemblages is maintained through a 95-k.y. interval in the raised reef terraces of the Huon Peninsula, Papua New Guinea. Fossil reef coral assemblages show limited membership in species composition despite repeated exposure to marked fluctuations in sea level (up to 120 m) and sea-surface temperatures (up to 6°). During the 95-k.y. interval, the reefs experienced nine cycles of perturbation and subsequent reassembly with similar species composition. Spatial differences in reef coral species composition were greater among the three study sites than among reefs of different ages. Thus local environmental parameters associated with riverine and terrestrial sources had a greater influence on reef coral composition than global climate and sea level changes.The ecological dynamics of reef communities from Papua New Guinea are in marked contrast to those of Quaternary terrestrial and level bottom marine communities which appear to show unlimited community membership on both larger and smaller time scales. Differences in community assembly among ecosystems mean either that coral reefs are fundamentally different or that different ecological patterns and processes are occurring at different temporal scales.
203 citations
TL;DR: There is little indication at the present that symbioses control long-term morphological or ecological patterns within these groups after their appearance, and photosymbiosis may be more a catalyst for the differentiation of major groups than a predictable governor on evolutionary rates.
Abstract: Symbioses are often regarded as an important means for the creation of evolutionary novelty as well as a trigger for the abrupt appearance of higher taxa. The fossil record of foraminifer-algal symbiosis suggests that the appearance of this ecological association contributed to the radiation of Paleogene planktic foraminifera. Isotopic evidence shows that photosymbiosis evolved in synchrony with a major diversification of trochospiral planktic foraminifera about 3.5 m.y. after the end-Cretaceous extinction. In modern planktic foraminifera, photosymbiotic species tend to have more cosmopolitan distributions than asymbiotic foraminifera and a greater ability to withstand periods of nutrient stress. The simultaneous taxonomic radiation and acquisition of photosymbiosis are evidence that the ecological strategy permitted Paleocene foraminifera to expand their niche in pelagic environments by diversifying into low-nutrient surface waters.A comparison of the species longevities of Neogene and Paleogene symbiotic clades suggests that photosymbiosis does not regulate the characteristic rate of taxonomic turnover in clades after they appear. Species longevities are much shorter in Paleocene and Eocene photosymbiotic morphospecies than they are among photosymbiotic Neogene clades; apparently photosymbiosis does not exert a significant control over long-term evolutionary rates. In addition, the absence of a characteristic morphology associated with photosymbiosis in Cenozoic planktic foraminifera suggests that morphology, as with rate of evolutionary turnover, is linked to symbiosis only because of common inheritance instead of a functional relationship. Although the coincidence between the acquisition of photosymbiosis and generic diversification does suggest a linkage between this ecology and the appearance of foraminiferal higher taxa, there is little indication at the present that symbioses control long-term morphological or ecological patterns within these groups after their appearance. Photosymbiosis, and other evolutionary innovations, may be more a catalyst for the differentiation of major groups than a predictable governor on evolutionary rates.
160 citations
TL;DR: The model of budding, the only one in which an ancestor can persist after a branching event, predicts that half or more of extant species have ancestors that are also extant, so the question of how to recognize ancestor-descendant pairs must be carefully considered.
Abstract: Three homogeneous models of species origination and extinction are used to assess the probability that ancestor-descendant pairs are preserved in the fossil record. In the model of cladogenetic budding, a species can persist after it branches and can therefore have multiple direct descendants. In the bifurcation model, a species branches to give rise to two distinct direct descendants, itself terminating in the process. In the model of phyletic transformation, a species gives rise to a single direct descendant without branching, itself terminating in the process. Assuming homogeneous preservation, even under pessimistic assumptions regarding the completeness of the fossil record, the probability of finding fossil ancestor-descendant pairs is not negligible. Even if all species of Phanerozoic marine invertebrates in the paleontologically important taxa had the same probability of preservation, on the order of 1%-10% or more of the known fossil species would be directly ancestral to other known fossil species. However, this is likely to be an underestimate, since the probability of finding ancestor-descendant pairs is enhanced by taxonomic, temporal, and spatial heterogeneities in preservation probability. Moreover, indirect genealogical relationships substantially increase the probability of finding ancestor-descendant pairs. The model of budding, the only one in which an ancestor can persist after a branching event, predicts that half or more of extant species have ancestors that are also extant. Thus, the question of how to recognize ancestor-descendant pairs must be carefully considered.
152 citations
TL;DR: Comparison of the frequencies with which modern African carnivores kill and scavenge ungulates from various size classes with the abundance of these size categories in the assemblage suggests that the Venta Micena hyaena was a bone-cracking scavenger that fed largely on carcasses of ungulate preyed upon and partially consumed by fresh meat-eating carnivores.
Abstract: We report quantitative paleoecologic data on the large mammal assemblage preserved in lower Pleistocene deposits at Venta Micena (Orce, Granada, southeastern Spain). Taphonomic studies show that bones were collected mainly by hyaenids, which transported and deposited them near shallow dens. Differential fragmentation of major long bones was produced by hyaenas as a function of their density and marrow content. Strong selection of prey by carnivores-which pref- erentially killed juveniles, females, and individuals with diminished locomotor capabilities among ungulate prey species of larger body size-is indicated by (1) the abundance of remains of juvenile ungulates in relation to the average weight of adult individuals in each species, (2) attritional mor- tality profiles for ungulate species deduced from crown height measurements, (3) the presence of many metapodials with different osteopathologies in their epiphyses, such as arthrosis, and (4) a biased intersexual ratio of large bovids. Comparison of the frequencies with which modern African carnivores kill and scavenge ungulates from various size classes with the abundance of these size categories in the assemblage suggests that the Venta Micena hyaena (Pachycrocuta brevirostris) was a bone-cracking scavenger that fed largely on carcasses of ungulates preyed upon and partially consumed by fresh meat-eating carnivores such us saber-toothed felids (Homotherium latidens and Megantereon whitei) and wild dogs (Canisfalconeri).
139 citations
TL;DR: In this paper, a detailed analysis of the fossil record and from the biogeochemical record indicates that dinoflagellates did indeed undergo a major evolutionary radiation in the early Mesozoic.
Abstract: Dinoflagellates are a major component of the marine microplankton and, from fossil evidence, appear to have been so for the past 200 million years. In contrast, the pre-Triassic record contains only equivocal occurrences of dinoflagellates, despite the fact that comparative ultrastructural and molecular phylogenetic evidence indicates a Precambrian origin for the lineage. Thus, it has often been assumed that the dearth of Paleozoic fossil dinoflagellates was due to a lack of preservation or recognition and that the relatively sudden appearance of dinoflagellates in the Mesozoic is an artifact of the record. However, new evidence from a detailed analysis of the fossil record and from the biogeochemical record indicates that dinoflagellates did indeed undergo a major evolutionary radiation in the early Mesozoic.
136 citations
TL;DR: While size seems to change gradually through time, morphology gives a rather discontinuous evolutionary pattern for both the upper and lower molar, which suggests that different genetic determinisms and mechanical constraints may act on size and shape.
Abstract: -Size and shape are analyzed for Pliocene lineages of the rodent genus Stephanomys Schaub 1938. Previous phylogenetic studies were based mainly on size variation and descriptive comparisons, without any attempt to quantify shape changes. Hence, on the basis of regular size increase, Stephanomys has been considered a prime example of phyletic gradualism. In order to quantify morphological variation within the lineage, a method for analyzing complex outlines, the elliptic Fourier transform, was applied to tooth contour (upper and lower first molars). It was then possible to compare evolution in size, estimated by tooth area, as well as evolution of shape, represented by Fourier coefficients. While size seems to change gradually through time, morphology gives a rather discontinuous evolutionary pattern for both the upper and lower molar. Such a discrepancy between the evolution of size and shape of a single structure suggests that different genetic determinisms and mechanical constraints may act on size and shape. Hence it may be misleading to infer generalized evolutionary processes from either size or shape alone. S. Renaud, J. Michaux, J-J Jaeger, and J.-C. Auffray. Institut des Sciences de l'Evolution, CC064, Universite Montpellier II, 34095 Montpellier Cedex 05, France Accepted: October 18, 1995
118 citations
TL;DR: It is argued that the study of heterochrony has been bound to an analytical formalism that virtually precludes the recognition of heterotopy, so a new framework for the construction of ontogenetic trajectories is provided and their analysis in a phylogenetic context is illustrated.
Abstract: Heterochrony, change in developmental rate and timing, is widely recognized as an agent of evolutionary change. Heterotopy, evolutionary change in spatial patterning of development, is less widely known or understood. Although Haeckel coined the term as a complement to heterochrony in 1866, few studies have detected heterotopy or even considered the possibility that it might play a role in morphological evolution. We here review the roles of heterochrony and heterotopy in evolution and discuss how they can be detected. Heterochrony is of interest in part because it can produce novelties constrained along ancestral ontogenies, and hence result in parallelism between ontogeny and phylogeny. Heterotopy can produce new morphologies along trajectories different from those that generated the forms of ancestors. We argue that the study of heterochrony has been bound to an analytical formalism that virtually precludes the recognition of heterotopy, so we provide a new framework for the construction of ontogenetic trajectories and illustrate their analysis in a phylogenetic context. The study of development of form needs tools that capture not only rates of development but the space in which the changes are manifest. The framework outlined here provides tools applicable to both. When appropriate tools are used and the necessary steps are taken, a more comprehensive interpretation of evolutionary change in development becomes possible. We suspect that there will be very few cases of change solely in developmental rate and timing or change solely in spatial patterning; most ontogenies evolve by changes of spatiotemporal pattern.
114 citations
TL;DR: In this article, a modified version of Brooks Parsimony analysis was used to distinguish between episodes of vicariance and episodes of dispersal in the Middle Devonian trilobite fauna.
Abstract: Phylogenetic patterns of trilobite clades were used to deduce biogeographic patterns during the Middle Devonian, a time of active plate collision between North America (Laurentia) and other plates, coincident with several major episodes of sea-level rise and fall. The mapping of biogeographic states onto phylogenies for asteropyginid and proetid trilobites indicated that dur- ing their history these trilobite clades often shifted the areas they occupied, and also underwent vicariant differentiation, followed by range expansion, followed by subsequent vicariance. Biogeo- graphic patterns in these individual phylogenies were evaluated and synthesized using a modified version of Brooks Parsimony Analysis, which is discussed. This method makes it possible using cladistic methods to distinguish between episodes of vicariance and episodes of dispersal. Two types of dispersal are recognized herein: (1) the individualistic responses of certain taxa in a single clade that cannot be generalized, i.e., traditional ad hoc dispersal, and (2) those patterns of con- gruent range expansion that are replicated across several clades. The latter are not treated as true dispersal, expansion of a taxon's range over a barrier accompanied by diversification, but rather as a result of the temporary removal of barriers to marine taxa, due either to relative sea-level rise or to the collision of formerly disjunct plates. These are interpreted as changes in the structure of areas, and this type of dispersal is referred to as geo-dispersal. Geo-dispersal was found to have occurred in the Middle Devonian trilobite fauna of Eastern North America. Biogeographic analysis indicated that Eastern North America is a strongly supported area, with the Appalachian and Michigan Basins as sister areas. Armorica and the Canadian Arctic are also sister areas. Congruence was found between area cladograms produced by vicariance and dispersal analyses for Middle Devonian trilobites, suggesting that in some cases the geological processes governing vicariance, such as sea-level changes, were the same as those that caused dispersal.
106 citations
TL;DR: It is shown that there has been stronger predation on various invertebrates in shallow-wa- ter environments since the late Mesozoic marine revolution, and the stalked crinoids may have been unable to cope with increased predation in shelf environments, and they migrated to offshore environments.
Abstract: The number of regenerated arms was counted on specimens of two distinct phenotypes of the stalked crinoid Endoxocrinus parrae (Gervais) from a wide bathymetric range in the Caribbean (178-723 m). In one phenotype, the sample was divided into two groups, one from shallower (< 500 m) depths, the other from deeper (2 500 m); in the other phenotype the group divided at 550 m. In both phenotypes, the frequency of regenerated arms is significantly higher in specimens from shallower water than in those from deeper water. If the regenerated arms in Endoxocrinus parrae were the result of sublethal predation, as previously suggested, then predation intensity is higher in shallow water than deep water. These results are consistent with the idea of the late Mesozoic marine revolution-that there has been stronger predation on various invertebrates in shallow-wa- ter environments since the late Mesozoic. The stalked crinoids may have been unable to cope with increased predation in shelf environments, and they migrated to offshore environments.
TL;DR: In this paper, the authors compare the preservation (taphonomic grade) and age of Chione (bivalve) and fo- raminifera from modern siliciclastic tidal flat sediments of Bahia la Choya, Sonora, Mexico (north-ern Gulf of California).
Abstract: We compare the preservation (taphonomic grade) and age of Chione (bivalve) and fo- raminifera from modern siliciclastic tidal flat sediments of Bahia la Choya, Sonora, Mexico (north- ern Gulf of California). Disarticulated shells of Chione collected from the sediment-water interface of Choya Bay exhibit a substantial range in taphonomic grade and age, several hundred years to -80-125 ka based on Accelerator Mass Spectrometer '4C dates and D-Alloisoleucine/L-Isoleucine values. There is not, however, a one-to-one correspondence between age and taphonomic alteration of Chione: old (or young) valves may be highly altered or they may be relatively pristine. In contrast to Chione, most foraminiferal tests at Choya Bay are quite pristine, which suggests a quite young age, but tests are surprisingly old (up to -2,000 calendar years based on Accelerator Mass Spec- trometer '4C dates). We suggest that following seasonal pulses in reproduction, some foraminiferal tests are rapidly incorporated into a subsurface shell layer by "Conveyor Belt" deposit feeders and preserved there, while the rest of the reproductive pulse rapidly dissolves. Ultimately, some of these buried tests, along with Chione, are transported back to the surface by biological activity and storms. The much greater range of taphonomic grades and ages among Chione shells suggests that they, unlike fora- minifera, are sufficiently large and preservable (low surface/volume ratio and chemical reactivity) to undergo many cycles of degradation, burial, and exhumation before complete destruction. The age of foraminiferal tests indicates that time-averaging of microfossil assemblages at Choya Bay is much more insidious than would be expected considering the relatively pristine state of the tests alone. Based on our studies, the lower limit of temporal resolution of shallow shelf microfossil assem- blages appears to be -1000 years. We caution, however, that each depositional setting (taphofacies) should be evaluated on a case-by-case basis before gross generalizations are made. Indeed, the dis- crepancy between age and taphonomic grade of fossil assemblages at Choya Bay suggests that nei- ther hardpart size or taphonomic grade are infallible indicators of test preservability or likely tem- poral resolution of the host assemblage, and that the dynamics of hardpart input and loss must also be evaluated.
TL;DR: Le terme «quartz» designe une large gamme de materiaux utilises comme matieres premieres au cours du Paleolithique, dont l'importance du potentiel informa- tif que presentent les industries en quartz, et qui, malheureusement, reste souvent sous-exploite.
Abstract: Le terme «quartz» designe une large gamme de materiaux utilises comme matieres premieres au cours du Paleolithique. Afin d'ecarter tout risque d'erreur d'interpretation technologique et afin de faciliter la communication entre chercheurs, il est necessaire que la terminologie utilisee, tant dans le domaine de la petrographie que de la technologie, soit sans ambiguite et acceptee si possible a l'unanimite. Les propositions enoncees ici sont un premier pas vers une homogeneisation de la terminologie. Les caracteristiques de la taille des quartz ainsi que les stigmates de taille qui leur sont specifiques sont ensuite passes en revue ; cette contribution s'appuie evidemment sur un parcours aussi exhaustif que possible de la litterature, mais aussi sur l'experience acquise lors de l'etude de series paleolithiques et sur la pratique experimentale de la taille de ces matieres premieres. Apres un bref etat de la question, et une fois demontree la necessite d'une adaptation, des propositions sont presentees dans le domaine de la methodologie. A titre d'exemple, quelques resultats sont exposes afin de souligner l'importance du potentiel informa- tif que presentent les industries en quartz, et qui, malheureusement, reste souvent sous-exploite.
TL;DR: Hierarchies in natural science are ranked and nested structures such that units at each rank include parts that are units at lower ranks, able to render complexity tractable, by homogenizing units into collectives and by ordering collectives in ranks of increasing inclu- siveness.
Abstract: Hierarchies in natural science are ranked and nested structures such that units at each rank include parts that are units at lower ranks. Hierarchies are able to render complexity tractable, by homogenizing units into collectives and by ordering collectives in ranks of increasing inclu- siveness. Hierarchies contrast with positional structures, such as phylogenetic trees, for in trees all positions are occupied by the same sort of entity-there are no ranked collectives-and positions are specified by the order of appearance or precedence of the entities. In hierarchies, interactions within ranks are most important; in trees, sequences of events along branches are of primary con- cern. As a result hierarchies do, and trees do not, display emergent properties. The value of the hierarchical structure can be lost when ranks are misspecified. A common error is the use of only a fraction of entities that actually occur in a rank, as when genes are considered as a rank below cells, disregarding the remaining cell contents and rendering the nature of cellular organization moot. Misspecification is also common when attributes or processes are used in ranks without indications of the physical entities to which they refer, thus losing track of the proper com- position and ranking of the collectives.
TL;DR: La revision critica tras 20 anos de investigaciones realizadas sobre los materiales plio-pleistocenos of the region of Orce permiten mostrar una idea precisa de los conocimientos actuales y of the potencialidad of la zona, y una cronologia amplia para estas biozonaciones.
Abstract: La revision critica tras 20 anos de investigaciones realizadas sobre los materiales plio-pleistocenos de la region de Orce (Andalucia, Espana) permiten mostrar una idea precisa de los conocimientos actuales y de la potencialidad de la zona. El sector de Orce-Venta Micena y su area adyacente, parte oriental de la cuenca de Guadix-Baza, ha sido objeto de numerosos estudios geologicos, que han permitido establecer la secuencia estratigrafica y situar los munerosos yacimientos paleontologicos y arqueologicos en la serie. Su gran numero y riqueza en micro y macrofauna ha permitido establecer una biozonacion regional, que abarca desde el Plioceno hasta el Pleistoceno medio ; con las tres biozonas del Plioceno (MN15, MN16 y MN17), sucedidas por tres biozonas para el Pleistoceno inferior (zona de Allophaiomys pliocaenicus, zona de Allophaiomys bourgondiae y zona de Stenocranius gregaloides) y la primera zona del Pleistoceno medio con Arvicola cantiana. El estudio de los grandes mamiferos ha puesto en evidencia el "momento Venta Micena", que se corresponde con la Ilegada al sur de la Peninsula Iberica de varias especies africanas y del hombre. Esta fauna se encuentra en las biozonas de micromamiferos representadas por Allophaiomys pliocaenicus y Allophaiomys bourgondiae. Los datos paleomagneticos obtenidos en los yacimientos de las series de Cortess de Baza y de Galera, pertenecientes a la misma unidad geomorfologica indican una cronologia amplia para estas biozonaciones, con los principales yacimientos - Venta Micena, Fuente Nueva -3 y Barranco Leon- proximos en el tiempo y situados en el Pleistoceno inferior. El yacimiento paleontologico de Venta Micena, primer cubil de hienas en campo abierto localizado en Europa, es de una riqueza extraordinaria (1 5 000 restos en 320 m2). Los numerosos estudios realizados precisan su modelo de formacion y aportan interesantes datos sobre los dominios de la arqueozoologia, la tafonomia y la paleoctologia. Paralelamente, el gran esfuerzo consagrado al estudio de algunos restos atribui- dos al genero Homo no ha permitido resolver las enormes dudas sobre su determinacion taxonomica. Las primeras excavaciones sistemâticas realizadas en los yacimientos arqueologicos de Barranco Leon y Fuente Nueva -3 han librado unas industrias liticas, que son una prucha indirecta pero induiscutible de la presencia humana en Andalucia durante el Pleistoceno inferior. Estas aso- ciaciones liticas, todavia numericamente pebres, se caracterizan por la produccion de lascas segun distintos metodos, por la presencia en Fuente Nueva -3 de "pieces esquillees", la rareza de utiles retocados y la ausencia total, por ahora, de bifaces o de deshe- chos caracteristicos de su fabricacion. La continuacion de la excavacion permitirâ proximamente evaluar los datos esenciales sobre el contexto cultural de estos primeros pobladores. La revision general, ha permitido igualmente evaluar algunas deficiencias de la investigacion, como es la necesidad de realizar un estudio de neotectonica y de geomorfologia de la depresion, pero sobretodo ha permitido ver que el sector de Orce no tiene ningun equivalente en Europa y es, por tanto, un punto clave para el estudio del Plio- Pleistoceno del sector occidental de nuestro continente.
TL;DR: In this paper, principal components analysis of Upper Carboniferous (Pennsylvanian) ammonoids (all 117 genera), using 21 variables to measure shell geometry, sculpture and suture complexity, shows that following a sharp decline (∼30%) in generic diversity after the mid-Carboniferous boundary, seven morphotypes persisted throughout the Pennsylvanian (ca. 30 m.y.).
Abstract: Principal components analysis of Upper Carboniferous (Pennsylvanian) ammonoids (all 117 genera), using 21 variables to measure shell geometry, sculpture and suture complexity, shows that following a sharp decline (∼30%) in generic diversity after the mid-Carboniferous boundary, seven morphotypes persisted throughout the Pennsylvanian (ca. 30 m.y.). Six of these were polyphyletically adopted at different times, while the seventh was monopolized by the prolecanitids, a group whose evolution accelerated during the Pennsylvanian and later gave rise to Mesozoic ammonoids. Innovations in suture geometry distinguished at least 17 of 39 (44%) Pennsylvanian ammonoid families. Average suture complexity increased almost threefold; this was achieved by various methods (lobe serration, insertion of umbilical elements, prong subdivision, lobe trifurcation, and secondary bifurcation), which were recurrent and crossed morphotype boundaries. The Pennsylvanian record supports suggestions that Paleozoic ammonoids were confined to a certain suite of basic shell geometries, showing preference for a limited number of sites in the spectrum of available morphospace. However, these morphic constraints did not, with one possible exception (the prolecanitids), control the emergence of increasing sutural complexity during the Pennsylvanian, which occurred among different lineages in all seven morphotypes.
TL;DR: The morphologic radiation of Early Jurassic ammonites following the near extinction at the end of the Triassic is analyzed from 436 species of 156 genera that form a representative sample of morphs occurring worldwide in the first three stages of the Jurassic (Hettangian, Sinemurian, Pliensbachian: 36 subzones, 24 m.y.).
Abstract: The morphologic radiation of Early Jurassic ammonites following the near extinction at the end of the Triassic is analyzed from 436 species of 156 genera that form a representative sample of morphs occurring worldwide in the first three stages of the Jurassic (Hettangian, Sinemurian, Pliensbachian: 36 subzones, 24 m.y.). Morphologic diversity is analyzed independently of taxonomy by processing 18 shape parameters using multivariate analysis and clustering techniques. The morphospace thus defined indicates that morphs fall readily into two groups made up of four and five adjacent morpho-subsets. The temporal pattern of morphospace occupation in the 36 Lower Jurassic subzones displays diversification, depletion (sometimes total), and displacement of successive parts of the morphospace, reflecting a complex history in which morphologic radiation appears to be more than a process of diffusion. The history of the morphologic evolution is tentatively related to sea-level changes and there is a suggestion that morphologic diversity increases during second-order transgressive periods.
TL;DR: The results of this study suggest that mass extinction, long-term biotic interaction, and environ- mental change can all play significant roles in biotic replacements.
Abstract: The macroevolutionary processes underlying large-scale biotic replacements are still poorly understood. Opinion remains divided regarding the roles of mass extinction, biotic inter- action, and environmental perturbations in these replacement events. Previous attempts to test re- placement hypotheses have largely focused on taxonomic diversity patterns. Taxonomic data alone, however, provide little insight about ecological interactions and hence other approaches are needed to understand mechanics of biotic replacements. Here I propose a conceptual model of replacement based on predation-mediated biotic interactions, and attempt a test using analysis of the Cenozoic replacement of the gastropod family Aporrhaidae by a closely related group, the Strombidae. Taxonomic, morphologic, and geographic data analyzed in this study all suggest a replacement of aporrhaids by strombids following the end-Cretaceous mass extinction. While most of the tax- onomic replacement was associated with a mass extinction, some replacement also occurred during background times and was mediated by higher origination rates in strombids rather than by higher extinction rates in aporrhaids. Morphologically, the replacement was largely confined to the portion of the morphospace unaffected by the end-Cretaceous extinction. At a global scale, the geographic overlap between the two groups declined through the Cenozoic, reflecting increasing restriction of aporrhaids to colder, temperate waters while strombids flourished in the tropics. However, at a finer geographic scale a more mosaic pattern of replacement is evident and coincides with Eocene and Oligocene climatic fluctuations. The results of this study suggest that mass extinction, long-term biotic interaction, and environ- mental change can all play significant roles in biotic replacements. Since the relative importance of each factor would vary from one event to another, an understanding of the general nature of large-scale biotic replacements requires a knowledge of the relative intensities of each of these pro- cesses.
TL;DR: A cote des outils sur os indubitables des gisements italiens, a cote de outils as mentioned in this paper is a collection of pieces presenting un bas niveau de modification (par ex. les "outils en os" de Vallonnet, Cueva Morin, Prolom II etc.).
Abstract: A cote des outils sur os indubitables des gisements italiens, il existe beaucoup de cas pour lesquels se pose le probleme de l'identification d'outillage a partir de pieces presentant un bas niveau de modification (par ex. les "outils en os" de Vallonnet, Cueva Morin, Prolom II etc.). Ces difficultes sont dues a l'absence de modeles interpretatifs de reference, a l'insuffisance de donnees actua- listes et aux procedures des archeologues qui ont etudie des pieces selectionnees et non pas des assemblages complets. Les donnees actualistes issues des etudes des activites de carnivores ne permettent pas toujours de definir des criteres diagnostiques precis puisque les referentiels actuels sont essentiellement constitues par des modifications sur restes osseux d'animaux de petite taille (cervides ou bovides de taille moyenne); dans les sites archeologiques, en revanche, il s'agit souvent de restes d'herbivore d'assez grande taille (Bos, Bison). Le site de Bois Roche a fourni un tres abondant assemblage de restes osseux de bovides de grande taille et d'equides. L'exiguite de la salle (qui la rend inhabitable par l'homme), l'abondance de coprolithes, d'os mâches et de diaphyses relativement completes, la presence de dents deciduales d'Hyene et de centaines d'esquilles partiellement digerees et regurgitees, montrent que la grotte etait un repaire d'hyene. La fragmentation des restes osseux est importante et indique un mode de fracturation sur os frais. Plusieurs pieces avec encoches et pseudo-retouches montrent des ressemblances etonnantes avec les traces de percussion intentionnelle et une grande regularite des bords retouches sur la face interne et externe des diaphyses. Il est clair que les carnivores du Pleistocene etaient parfaitement capables de "tailler" des os de grands herbivores (comme Bos et Bison) et de produire des "artefacts" tres semblables a des outils lithiques. Il n'est donc plus possible d'accepter des interpretations d'outils en os peu elabores si l'interpretation ne se fonde pas sur une analyse systematique des modifications et du contexte, sur l'etude taphonomique de l'assemblage complet et l'emploi de criteres diagnostiques definis a partir de referentiels actuels et de sites archeologiques formes par des processus bien identifies.
TL;DR: Analysis of the evolution of the Globorotalia (Fohsella) lineage of planktic foraminifera suggests that reproductive ecology and shell shape have evolved independently in this group, and anagenesis masks at least one speciation event that is apparent only in the isotopic evidence for a change in reproductive ecology.
Abstract: Analysis of the evolution of the Globorotalia (Fohsella) lineage of planktic foraminifera suggests that reproductive ecology and shell shape have evolved independently in this group. The silhouette of fohsellid shells displays a nearly unbroken anagenetic trend, yet isotopic data show that the fohsellids changed their depth of reproduction during the anagenetic evolution of their skeletons. Remarkably, there are no correlations between anagenesis in skeletal shape and the establishment of reproductive isolation. Apparently, anagenesis masks at least one speciation event that is apparent only in the isotopic evidence for a change in reproductive ecology. Although anagenetic trends have been widely cited as evidence for gradual speciation in planktic foraminifera and other microfossil groups, our data suggest that they should not always be considered to record either the tempo or mode of speciation.Speciation was apparently uncoupled from morphological evolution in fohsellids because these evolutionary phenomena occurred in different phases of ontogeny. Gradual morphological changes were associated with the main phase of shell growth of both the ancestor and descendant species in the near-surface ocean. Reproductive isolation occurred when ancestral and descendant populations became established at different depths near the end of the life cycle. Morphological evolution may also be uncoupled from reproductive isolation in other organisms that experience very different selection pressures over the duration of their ontogenies, such as parasites with many hosts, species with multiple phases of metamorphosis, and organisms that broadcast their gametes.
TL;DR: In this article, les fouilles recentes sur le site neolithique recent de Tell Sabi Abyad, Syrie du nord, ont revele des centaines de scellements en argile.
Abstract: Les fouilles recentes sur le site neolithique recent de Tell Sabi Abyad, Syrie du nord, ont revele des centaines de scellements en argile. Nous argumentons que ces scellements ont facilite a Sabi Abyad le stockage communal par une population nomade tres etendue de toute sorte de produits et de creances. Aussi considerons nous que les scellements sont les temoins de la symbiose entre les populations sedentaires et nomades du Neolithique Recent.
TL;DR: Les fouilles de la salle inferieure de la grotte de Yanmburgaz, situee non loin d'Istanbul a l'ouest, ont livre un riche assemblage lithique and une faune dominee par Ursus deningeri.
Abstract: Les fouilles de la salle inferieure de la grotte de Yanmburgaz, situee non loin d'Istanbul a l'ouest, ont livre un riche assemblage lithique et une faune dominee par Ursus deningeri. Les niveaux renfermant ce materiel sont probablement ď âge Pleistocene moyen. L' industrie se compose essentiellement d'outils sur eclats presentant une retouche abrupte souvent extensive et de quelques "choppers" . Ni les bifaces, ni la methode Levallois ne sont presents. Un aspect frappant de l'industrie de la grotte de Yanmburgaz est la variete de methodes employees pour l'obtention des eclats et des supports des outils. La variation technologique de la production des eclats est fortement liee au type de matiere premiere employee.
TL;DR: Faunal abundance and fossil size and shape data from microvertebrate localities in the Upper Cretaceous Judith River Formation of south-central Montana illustrate that even when lo- cated in similar sedimentary facies, concentrations of vertebrate microfossils may exhibit strikingly different taphonomic profiles.
Abstract: Faunal abundance and fossil size and shape data from microvertebrate localities in the Upper Cretaceous Judith River Formation of south-central Montana illustrate that even when lo- cated in similar sedimentary facies, concentrations of vertebrate microfossils may exhibit strikingly different taphonomic profiles. Degrees of microfossil size and shape sorting may vary even among sites from the same sedimentary facies. In some instances, such variations may make it impossible to disregard taphonomic causes for differences sites exhibit in paleofaunal abundances. To limit the possibility that taphonomically generated faunal differences might be mistaken for true differ- ences in paleoecology, comparisons of paleofaunal abundances should be restricted to microver- tebrate sites both from similar sedimentary facies and with similar profiles of fossil sizes and shapes.
TL;DR: In this article, the authors examine the late Pleistocene megafaunal extinctions by testing the only extinction model with strong a priori predictions, the blitzkrieg model, and find that both a reanalysis of Grayson's data and an analysis of new reliable data support a terminal Wisconsin extinction.
Abstract: I examine the late Pleistocene megafaunal extinctions by testing the only extinction model with strong a priori predictions, the blitzkrieg model (Martin 1973; Mosimann and Martin 1975). I first test an assumption of the blitzkrieg and other extinction models that the megafaunal extinctions occurred in the terminal Wisconsin (12-10 Ka). This assumption has been disputed by Grayson (1989, 1991), but I find that both a reanalysis of Grayson's data and an analysis of new reliable data support a terminal Wisconsin extinction.The blitzkrieg model predicts that the ranges of megafauna in North America were constricted as the semicircular front of hunters moved southeastward; hence the extinctions should be time-transgressive from northwest to southeast. I test this prediction in three separate analyses that examine (1) the location of terminal sites for each taxon relative to all their other late Wisconsin fossil sites, (2) the location of terminal sites for each taxon relative to all their other reliably dated late Wisconsin fossil sites, and (3) the spatio-temporal pattern of all the reliably dated terminal Wisconsin sites without regard to taxonomy. The geographic distribution of the megafaunal remains does not support the blitzkrieg hypothesis in any of the three analyses. Moreover, all of the patterns in the data are in a direction opposite to that predicted by the blitzkrieg hypothesis. I examine how these conclusions affect both climatic and predation models, particularly in relation to the testability of other extinction hypotheses.
TL;DR: In this paper, the Mousterien Quina du Perigord et al. define le milieu animal des mousteriens Quina et al., a partir des donnees de trois gisements presentant de longues sequences stratigraphiques.
Abstract: Le but de ce travail est de definir le milieu animal des mousteriens Quina du Perigord a partir des donnees de trois gisements presentant de longues sequences stratigraphiques : le gisement de Combe-Grenal (fouilles F. Bordes), la grotte du Regourdou (fouilles E. Bonifay) et la grotte Vaufrey (fouilles J.-Ph. Rigaud). Les ensembles mousteriens de ces trois gisements ont ete replaces dans la chronologie relative apres consideration de la biostratigraphie des grands mammiferes et des rongeurs ainsi que de la signification paleoclimatique des associations fauniques. Les resultats des travaux de micromorphologie ont ete egalement pris en compte ainsi que quelques datations absolues concernant la grotte Vaufrey. Dans les trois gisements, les niveaux contenant du Mousterien Quina se situent tous au meme niveau de la chronologie relative. Le Mousterien Quina apparait et se developpe lors du Pleniglaciaire du Wurm ancien, stade 4, et disparait au debut du stade isotopique 3. Le milieu, alors largement deboise, convenait aux grands troupeaux d'ongules de milieu ouvert dont la distribution spatiale n'avait rien d'aleatoire. Le Renne occupait, la plupart du temps, la region entre montagne et plaine, la ou les plateaux sont entailles de vallees relativement profondes tandis que les Bovines, surtout representes par le Bison des steppes, et le Cheval se rencontraient principalement dans les regions d'altitude moyenne moins elevee. Les profondes vallees abritees des zones montagneuses offraient au Cerf les meilleurs refuges. Il voisinait alors avec le Bouquetin et le Chamois, chasses des plus hautes altitudes par l'avancee des zones englacees.
TL;DR: L'etude de la frequence des differents elements squelettiques des herbivores, the fracturation des os longs et les courbes de mortalite des populations d'herbivores et de carnivores laissent au contraire clairement entrevoir that les hyenes ont joue un role primordial dans the formation des assemblages osseux.
Abstract: La grotte n°1 de Lunel-Viel (Herault) presente a la fois des traces d'occupation humaine (industrie lithique) et animale (vestiges osseux et coprolithes d'hyene) d'âge pleistocene moyen. L'etude taphonomique du materiel paleontologique a pour principal objectif d'evaluer la part qu'ont joue chacun de ces deux agents dans la mise en place des assemblages osseux. La presence conjointe de coprolithes, d'os ronges d'herbivores (cervides, aurochs, cheval) et de jeunes hyenes a travers toute la stratigraphie, associes a un materiel lithique quantitativement pauvre, prouvent de toute evidence que les hommes n'ont pas ete les seuls occupants de la grotte. L'etude de la frequence des differents elements squelettiques des herbivores, la fracturation des os longs et les courbes de mortalite des populations d'herbivores et de carnivores laissent au contraire clairement entrevoir que les hyenes ont joue un role primordial dans la formation des assemblages osseux.
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TL;DR: The Proterozoic-Cambrian transition is emerging as one of the better calibrated intervals in the pre-Mesozoic geological record and a major obstacle to paleobiological research on early animal evolution.
Abstract: Truth, goes an old proverb, is the daughter of time. Fifty years ago, G. G. Simpson (1944) brought paleontology into the Neodarwinian fold, arguing that evolutionary tempo can be documented in the geological record and used to inform debate about evolutionary mode. Today, increasingly sophisticated paleontological investigations of rate—be it diversification, extinction, migration, morphological change, or divergence in macromolecular sequence—require calibration of the geological time scale with a precision far greater than Simpson could have anticipated. Expanding research on the relationships between environmental history and evolution also requires unprecedented resolution in correlation and geochronometry.
TL;DR: The evolutionary origin of Morozovella angulata from its immediate ancestor, Praemurica uncinata, is preserved in Paleocene sediments from the Gulf of Mexico and represents the beginning of the morozovellid radiation and marks the first appearance of keeled planktonic fo- raminifera after the Cretaceous/Tertiary extinction.
Abstract: The evolutionary origin of Morozovella angulata from its immediate ancestor, Praemurica uncinata, is preserved in Paleocene sediments from the Gulf of Mexico. This event represents the beginning of the morozovellid radiation and marks the first appearance of keeled planktonic fo- raminifera after the Cretaceous/Tertiary extinction. Parallel biometric and isotopic analyses were performed on size-segregated specimens from a succession of stratigraphic horizons. The biometric data reveal a temporal pattern of variation consistent with paedomorphosis. The appearance of angulose juvenile chambers in the otherwise rounded ancestral form (Praemurica uncinata) results in an allometry that becomes more pronounced upsection. At the origin of M. angulata, the juvenile morphology of the ancestor is retained throughout the entire ontogeny. Isotopic analysis of this sequence reveals the gradual acquisition of an increasingly heavy adult 813C signal relative to that of the juvenile, while the 8180 data display no temporal or size-related trends. The temporal in- crease seen in the slope of the 813C/size relationship may reflect the evolution of an increased de- pendency on photosymbionts.
TL;DR: A test and confidence interval for a common upper or lower endpoint in two or more taxa for which the significance level is known is described and illustrated.
Abstract: Statistical inference about the upper and lower endpoints of the stratigraphic ranges of fossil taxa can be based on the pattern of finds. Strauss and Sadler (1989) described a test and confidence interval for a common upper or lower endpoint in two or more taxa. This approach is conservative, in the sense that it provides only an upper bound on the significance level. This paper describes and illustrates a test and confidence interval for which the significance level is known.
TL;DR: An unusual system of fossil lakes in eastern North America is taken advantage of to estimate the time for speciation of endemic semionotid fishes, finding six species in 5000-8000 years, remarkably similar to that estimated for the five cichlids in Lake Nabugabo that diverged from Lake Victoria cichLids in about 4000 years.
Abstract: In this study I take advantage of an unusual system of fossil lakes in eastern North America to estimate the time for speciation of endemic semionotid fishes. Twenty-one species are all found in sedimentary cycle P4, the deposits of a single Early Jurassic lake, in the Towaco Formation of the Newark Basin in New Jersey. To determine the degree of endemism in the fauna from this fossil lake and estimate time for speciation, I surveyed more than 2000 museum specimens from 45 named localities in the Newark Basin and related basins of the Late Triassic to Early Jurassic Newark Supergroup. Six species not found in deposits equal in age to P4 or older are considered to be endemics, eight species occurring in older deposits presumably colonized Lake P4, and evidence for whether the remaining seven species were endemics or colonists is equivocal. The time for the formation, decline, and evaporation of Lake P4, in which P4 sediments were deposited, has been estimated at 21,000-24,000 years. Because all endemic Semionotus first occur in the first third of lake history, the estimated time for speciation of endemics is six species in 5000-8000 years. This rate is remarkably similar to that estimated for the five cichlids in Lake Nabugabo that diverged from Lake Victoria cichlids in about 4000 years.