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1.
Zootaxa ; 4573(1): zootaxa.4573.1.1, 2019 Mar 29.
Artigo em Inglês | MEDLINE | ID: mdl-31715787

RESUMO

Ostracods from the Upper Oligocene to Lower Miocene Pirabas Formation, Northeastern Amazonia, Pará State, Brazil were examined from one subsurface and four outcrop sections. A total of 119 species were recognized and are illustrated; another 53 species were left in open nomenclature. Twenty-seven of the species are common to the Neogene of Caribbean, another two species are known from areas other than the Caribbean, and one species was already described from the studied unit. This study provides a robust taxonomic database for paleoenvironmental, biostratigraphic and paleogeographic studies and contributes to the knowledge of the paleodiversity of Neogene Ostracods from the Southwestern Atlantic.


Assuntos
Crustáceos , Animais , Brasil , Região do Caribe
2.
Proc Biol Sci ; 285(1888)2018 10 10.
Artigo em Inglês | MEDLINE | ID: mdl-30305432

RESUMO

Molecular phylogenies suggest some major radiations of open-ocean fish clades occurred roughly coincident with the Cretaceous-Palaeogene (K/Pg) boundary, however the timing and nature of this diversification is poorly constrained. Here, we investigate evolutionary patterns in ray-finned fishes across the K/Pg mass extinction 66 million years ago (Ma), using microfossils (isolated teeth) preserved in a South Pacific sediment core spanning 72-43 Ma. Our record does not show significant turnover of fish tooth morphotypes at the K/Pg boundary: only two of 48 Cretaceous tooth morphotypes disappear at the event in the South Pacific, a rate no different from background extinction. Capture-mark-recapture analysis finds two pulses of origination in fish tooth morphotypes following the mass extinction. The first pulse, at approximately 64 Ma, included short-lived teeth, as well as forms that contribute to an expansion into novel morphospace. A second pulse, centred at approximately 58 Ma, produced morphotype novelty in a different region of morphospace from the first pulse, and contributed significantly to Eocene tooth morphospace occupation. There was no significant increase in origination rates or expansion into novel morphospace during the early or middle Eocene, despite a near 10-fold increase in tooth abundance during that interval. Our results suggest that while the K/Pg event had a minor impact on fish diversity in terms of extinction, the removal of the few dominant Cretaceous morphotypes triggered a sequence of origination events allowing fishes to rapidly diversify morphologically, setting the stage for exceptional levels of ray-finned fish diversity in the Cenozoic.


Assuntos
Biodiversidade , Evolução Biológica , Extinção Biológica , Peixes , Fósseis/anatomia & histologia , Animais , Peixes/anatomia & histologia , Oceano Pacífico , Dente/anatomia & histologia , Dente/crescimento & desenvolvimento
3.
Nature ; 556(7701): 366-369, 2018 04.
Artigo em Inglês | MEDLINE | ID: mdl-29643505

RESUMO

Sexual selection favours traits that confer advantages in the competition for mates. In many cases, such traits are costly to produce and maintain, because the costs help to enforce the honesty of these signals and cues 1 . Some evolutionary models predict that sexual selection also produces costs at the population level, which could limit the ability of populations to adapt to changing conditions and thus increase the risk of extinction2-4. Other models, however, suggest that sexual selection should increase rates of adaptation and enhance the removal of deleterious mutations, thus protecting populations against extinction3, 5, 6. Resolving the conflict between these models is not only important for explaining the history of biodiversity, but also relevant to understanding the mechanisms of the current biodiversity crisis. Previous attempts to test the conflicting predictions produced by these models have been limited to extant species and have thus relied on indirect proxies for species extinction. Here we use the informative fossil record of cytheroid ostracods-small, bivalved crustaceans with sexually dimorphic carapaces-to test how sexual selection relates to actual species extinction. We show that species with more pronounced sexual dimorphism, indicating the highest levels of male investment in reproduction, had estimated extinction rates that were ten times higher than those of the species with the lowest investment. These results indicate that sexual selection can be a substantial risk factor for extinction.


Assuntos
Crustáceos/fisiologia , Extinção Biológica , Fósseis , Preferência de Acasalamento Animal , Seleção Genética , Adaptação Fisiológica , Animais , Tamanho Corporal , Crustáceos/anatomia & histologia , Crustáceos/classificação , Feminino , Masculino , Modelos Biológicos , Reprodução , Fatores de Risco , Caracteres Sexuais
4.
PLoS One ; 12(7): e0177791, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-28678866

RESUMO

Assessing the long-term macroevolutionary consequences of sexual selection has been hampered by the difficulty of studying this process in the fossil record. Cytheroid ostracodes offer an excellent system to explore sexual selection in the fossil record because their readily fossilized carapaces are sexually dimorphic. Specifically, males are relatively more elongate than females in this superfamily. This sexual shape difference is thought to arise so that males carapaces can accommodate their very large copulatory apparatus, which can account for up to one-third of body volume. Here we test this widely held explanation for sexual dimorphism in cytheroid ostracodes by correlating investment in male genitalia, a trait in which sexual selection is seen as the main evolutionary driver, with sexual dimorphism of carapace in the genus Cyprideis. We analyzed specimens collected in the field (C. salebrosa, USA; C. torosa, UK) and from collections of the National Museum of Natural History, Washington, DC (C. mexicana). We digitized valve outlines in lateral view to obtain measures of size (valve area) and shape (elongation, measured as length to height ratio), and obtained several dimensions from two components of the hemipenis: the muscular basal capsule, which functions as a sperm pump, and the section that includes the intromittent organ (terminal extension). In addition to the assessment of this primary sexual trait, we also quantified two dimensions of the male secondary sexual trait-where the transformed right walking leg functions as a clasping organ during mating. We also measured linear dimensions from four limbs as indicators of overall (soft-part) body size, and assessed allometry of the soft anatomy. We observed significant correlations in males between valve size, but not elongation, and distinct structural parts of the hemipenis, even after accounting for their shared correlation with overall body size. We also found weak but significant positive correlation between valve elongation and the degree of sexual dimorphism of the walking leg, but only in C. torosa. The correlation between the hemipenis parts, especially basal capsule size and male valve size dimorphism suggests that sexual selection on sperm size, quantity, and/or efficiency of transfer may drive sexual size dimorphism in these species, although we cannot exclude other aspects of sexual and natural selection.


Assuntos
Crustáceos/fisiologia , Fósseis , Genitália/fisiologia , Caracteres Sexuais , Comportamento Sexual Animal/fisiologia , Animais , Tamanho Corporal , Crustáceos/anatomia & histologia , Crustáceos/classificação , Feminino , Genitália/anatomia & histologia , Masculino , Tamanho do Órgão , Especificidade da Espécie
5.
Proc Natl Acad Sci U S A ; 113(49): 14073-14078, 2016 12 06.
Artigo em Inglês | MEDLINE | ID: mdl-27821755

RESUMO

The fossil record of marine animals suggests that diversity-dependent processes exerted strong control on biodiversification: after the Ordovician Radiation, genus richness did not trend for hundreds of millions of years. However, diversity subsequently rose dramatically in the Cretaceous and Cenozoic (145 million years ago-present), indicating that limits on diversification can be overcome by ecological or evolutionary change. Here, we show that the Cretaceous-Cenozoic radiation was driven by increased diversification in animals that transfer sperm between adults during fertilization, whereas animals that broadcast sperm into the water column have not changed significantly in richness since the Late Ordovician (∼450 million years ago). We argue that the former group radiated in part because directed sperm transfer permits smaller population sizes and additional modes of prezygotic isolation, as has been argued previously for the coincident radiation of angiosperms. Directed sperm transfer tends to co-occur with many ecological traits, such as a predatory lifestyle. Ecological specialization likely operated synergistically with mode of fertilization in driving the diversification that began during the Mesozoic marine revolution. Plausibly, the ultimate driver of diversification was an increase in food availability, but its effects on the fauna were regulated by fundamental reproductive and ecological traits.


Assuntos
Biodiversidade , Copulação/fisiologia , Fertilização/fisiologia , Animais , Organismos Aquáticos/genética , Organismos Aquáticos/fisiologia , Evolução Biológica , Ecologia , Fertilização/genética , Fósseis , História Antiga , Masculino , Espermatozoides
6.
Proc Natl Acad Sci U S A ; 112(16): 4885-90, 2015 Apr 21.
Artigo em Inglês | MEDLINE | ID: mdl-25901309

RESUMO

Previous analyses of evolutionary patterns, or modes, in fossil lineages have focused overwhelmingly on three simple models: stasis, random walks, and directional evolution. Here we use likelihood methods to fit an expanded set of evolutionary models to a large compilation of ancestor-descendant series of populations from the fossil record. In addition to the standard three models, we assess more complex models with punctuations and shifts from one evolutionary mode to another. As in previous studies, we find that stasis is common in the fossil record, as is a strict version of stasis that entails no real evolutionary changes. Incidence of directional evolution is relatively low (13%), but higher than in previous studies because our analytical approach can more sensitively detect noisy trends. Complex evolutionary models are often favored, overwhelmingly so for sequences comprising many samples. This finding is consistent with evolutionary dynamics that are, in reality, more complex than any of the models we consider. Furthermore, the timing of shifts in evolutionary dynamics varies among traits measured from the same series. Finally, we use our empirical collection of evolutionary sequences and a long and highly resolved proxy for global climate to inform simulations in which traits adaptively track temperature changes over time. When realistically calibrated, we find that this simple model can reproduce important aspects of our paleontological results. We conclude that observed paleontological patterns, including the prevalence of stasis, need not be inconsistent with adaptive evolution, even in the face of unstable physical environments.


Assuntos
Evolução Biológica , Meio Ambiente , Modelos Biológicos , Característica Quantitativa Herdável , Simulação por Computador , Oceanos e Mares , Isótopos de Oxigênio , Filogenia , Temperatura Ambiente
8.
Proc Natl Acad Sci U S A ; 110(34): 13892-7, 2013 Aug 20.
Artigo em Inglês | MEDLINE | ID: mdl-23924610

RESUMO

Evolutionary processes leading to adaptive radiation regularly occur too fast to be accurately recorded in the fossil record but too slowly to be readily observed in living biota. The study of evolutionary radiations is thereby confronted with an epistemological gap between the timescales and approaches used by neontologists and paleontologists. Here we report on an ongoing radiation of extant Bellamya species (n = 4) from the African Rift Lake Malawi that provides an unusual opportunity to bridge this gap. The substantial molecular differentiation in this monophyletic Bellamya clade has arisen since Late Pleistocene megadroughts in the Malawi Basin caused by climate change. Morphological time-series analysis of a high-resolution, radiocarbon-dated sequence of 22 faunas spanning the Holocene documents stasis up to the middle Holocene in all traits studied (shell height, number of whorls, and two variables obtained from geometric morphometrics). Between deposition of the last fossil fauna (~5 ka) and the present day, a drastic increase in morphological disparity was observed (3.7-5.8 times) associated with an increase in species diversity. Comparison of the rates of morphological evolution obtained from the paleontological time-series with phylogenetic rates indicates that the divergence in two traits could be reconstructed with the slow rates documented in the fossils, that one trait required a rate reduction (stabilizing selection), and the other faster rates (divergent selection). The combined paleontological and comparative approach taken here allows recognition that morphological stasis can be the dominant evolutionary pattern within species lineages, even in very young and radiating clades.


Assuntos
Adaptação Biológica/fisiologia , Biodiversidade , Evolução Biológica , Gastrópodes/anatomia & histologia , Especiação Genética , Modelos Biológicos , Anatomia Comparada/métodos , Exoesqueleto/anatomia & histologia , Animais , Pesos e Medidas Corporais , Gastrópodes/genética , Gastrópodes/fisiologia , Lagos , Malaui , Paleontologia/métodos , Análise de Componente Principal , Especificidade da Espécie
9.
Ecol Lett ; 15(10): 1174-9, 2012 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-22738438

RESUMO

High tropical and low polar biodiversity is one of the most fundamental patterns characterising marine ecosystems, and the influence of temperature on such marine latitudinal diversity gradients is increasingly well documented. However, the temporal stability of quantitative relationships among diversity, latitude and temperature is largely unknown. Herein we document marine zooplankton species diversity patterns at four time slices [modern, Last Glacial Maximum (18,000 years ago), last interglacial (120,000 years ago), and Pliocene (~3.3-3.0 million years ago)] and show that, although the diversity-latitude relationship has been dynamic, diversity-temperature relationships are remarkably constant over the past three million years. These results suggest that species diversity is rapidly reorganised as species' ranges respond to temperature change on ecological time scales, and that the ecological impact of future human-induced temperature change may be partly predictable from fossil and paleoclimatological records.


Assuntos
Biodiversidade , Temperatura Ambiente , Zooplâncton , Animais , Mudança Climática , Ecologia , Previsões , Fósseis , Oceanos e Mares
10.
Evolution ; 66(2): 314-29, 2012 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-22276531

RESUMO

We performed a tree-based analysis of trilobite postembryonic development in a sample of 60 species for which quantitative data on segmentation and growth increments between putative successive instars are available, and that spans much of the temporal, phylogenetic, and habitat range of the group. Three developmental traits were investigated: the developmental mode of trunk segmentation, the average per-molt growth rate, and the conformity to a constant per-molt growth rate (Dyar's rule), for which an original metric was devised. Growth rates are within the normal range with respect to other arthropods and show overall conformity to Dyar's rule. Randomization tests indicate statistically significant phylogenetic signal for growth in early juveniles but not in later stages. Among five evolutionary models fit via maximum likelihood, one in which growth rates vary independently among species, analogous to Brownian motion on a star phylogeny, is the best supported in all ontogenetic stages, although a model with a single, stationary peak to which growth rates are attracted also garners nontrivial support. These results are not consistent with unbounded, Brownian-motion-like evolutionary dynamics, but instead suggest the influence of an adaptive zone. Our results suggest that developmental traits in trilobites were relatively labile during evolutionary history.


Assuntos
Artrópodes/genética , Evolução Biológica , Fósseis , Animais , Artrópodes/anatomia & histologia , Modelos Genéticos , Filogenia
11.
Ecol Evol ; 2(12): 3242-68, 2012 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-23301187

RESUMO

We analyzed published downcore microfossil records from 150 studies and reinterpreted them from an ecological degradation perspective to address the following critical but still imperfectly answered questions: (1) How is the timing of human-induced degradation of marine ecosystems different among regions? (2) What are the dominant causes of human-induced marine ecological degradation? (3) How can we better document natural variability and thereby avoid the problem of shifting baselines of comparison as degradation progresses over time? The results indicated that: (1) ecological degradation in marine systems began significantly earlier in Europe and North America (∼1800s) compared with Asia (post-1900) due to earlier industrialization in European and North American countries, (2) ecological degradation accelerated globally in the late 20th century due to post-World War II economic growth, (3) recovery from the degraded state in late 20th century following various restoration efforts and environmental regulations occurred only in limited localities. Although complex in detail, typical signs of ecological degradation were diversity decline, dramatic changes in total abundance, decrease in benthic and/or sensitive species, and increase in planktic, resistant, toxic, and/or introduced species. The predominant cause of degradation detected in these microfossil records was nutrient enrichment and the resulting symptoms of eutrophication, including hypoxia. Other causes also played considerable roles in some areas, including severe metal pollution around mining sites, water acidification by acidic wastewater, and salinity changes from construction of causeways, dikes, and channels, deforestation, and land clearance. Microfossils enable reconstruction of the ecological history of the past 10(2)-10(3) years or even more, and, in conjunction with statistical modeling approaches using independent proxy records of climate and human-induced environmental changes, future research will enable workers to better address Shifting Baseline Syndrome and separate anthropogenic impacts from background natural variability.

13.
Evol Dev ; 12(6): 635-46, 2010.
Artigo em Inglês | MEDLINE | ID: mdl-21040429

RESUMO

The carapaces of some ostracode taxa bear reticulate skeletal ridges that outline underlying epidermal cells. This anatomy allows one to identify homologous cells across individuals, to infer the modal sequence of cell divisions that occurs over ontogeny, and to identify individuals with variant cell patterns (e.g., additional or missing cell divisions), even in fossils. Here we explore the variational properties and evolutionary history of this developmental system in the deep-sea ostracode genus Poseidonamicus. Using a sample of over 2000 specimens to capture variation in cell division sequence, we show that phenotypic variation in this system is highly structured: some variants, regions of the carapace, and lineages are much more variable than others. Much of the differences in variation among cells can be attributed to the molt stage in which cells take their final form-cell divisions occurring later in ontogeny are more variable than those earlier. Despite ample variation, only two evolutionary changes in the sequence of cell divisions occur over the 40 Myr history of this clade. The evolutionary changes that do occur parallel the two most common intraspecific variants, suggesting that developmental structuring of variation can have long-term evolutionary consequences. Analysis of the most common variant over the last two molt stages suggests that it suffers a fitness disadvantage relative to the modal form. Such normalizing selection may contribute to the evolutionary conservativeness of this developmental system in the Ostracoda.


Assuntos
Evolução Biológica , Divisão Celular , Crustáceos/crescimento & desenvolvimento , Fósseis , Animais
14.
Am Nat ; 176 Suppl 1: S61-76, 2010 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-21043781

RESUMO

Of all of the sources of evidence for evolution by natural selection, perhaps the most problematic for Darwin was the geological record of organic change. In response to the absence of species-level transformations in the fossil record, Darwin argued that the fossil record was too incomplete, too biased, and too poorly known to provide strong evidence against his theory. Here, this view of the fossil record is evaluated in light of 150 years of subsequent paleontological research. Although Darwin's assessment of the completeness and resolution of fossiliferous rocks was in several ways astute, today the fossil record is much better explored, documented, and understood than it was in 1859. In particular, a reasonably large set of studies tracing evolutionary trajectories within species can now be brought to bear on Darwin's expectation of gradual change driven by natural selection. An unusually high-resolution sequence of stickleback-bearing strata records the transformation of this lineage via natural selection. This adaptive trajectory is qualitatively consistent with Darwin's prediction, but it occurred much more rapidly than he would have guessed: almost all of the directional change was completed within 1,000 generations. In most geological sequences, this change would be too rapid to resolve. The accumulated fossil record at more typical paleontological scales (10(4)-10(6) years) reveals evolutionary changes that are rarely directional and net rates of change that are perhaps surprisingly slow, two findings that are in agreement with the punctuated-equilibrium model. Finally, Darwin's view of the broader history of life is reviewed briefly, with a focus on competition-mediated extinction and recent paleontological and phylogenetic attempts to assess diversity dependence in evolutionary dynamics.


Assuntos
Evolução Biológica , Fósseis , Paleontologia/história , Animais , Extinção Biológica , História do Século XIX , Modelos Biológicos , Modelos Estatísticos , Seleção Genética , Fatores de Tempo
15.
Proc Natl Acad Sci U S A ; 106(51): 21717-20, 2009 Dec 22.
Artigo em Inglês | MEDLINE | ID: mdl-20018702

RESUMO

A benthic microfaunal record from the equatorial Atlantic Ocean over the past four glacial-interglacial cycles was investigated to understand temporal dynamics of deep-sea latitudinal species diversity gradients (LSDGs). The results demonstrate unexpected instability and high amplitude fluctuations of species diversity in the tropical deep ocean that are correlated with orbital-scale oscillations in global climate: Species diversity is low during glacial and high during interglacial periods. This implies that climate severely influences deep-sea diversity, even at tropical latitudes, and that deep-sea LSDGs, while generally present for the last 36 million years, were weakened or absent during glacial periods. Temporally dynamic LSDGs and unstable tropical diversity require reconsideration of current ecological hypotheses about the generation and maintenance of biodiversity as they apply to the deep sea, and underscore the potential vulnerability and conservation importance of tropical deep-sea ecosystems.


Assuntos
Biodiversidade , Biologia Marinha , Ecologia
16.
Science ; 325(5941): 733-7, 2009 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-19661426

RESUMO

Evolutionary histories of species and lineages can influence their vulnerabilities to extinction, but the importance of this effect remains poorly explored for extinctions in the geologic past. When analyzed using a standardized taxonomy within a phylogenetic framework, extinction rates of marine bivalves estimated from the fossil record for the last approximately 200 million years show conservatism at multiple levels of evolutionary divergence, both within individual families and among related families. The strength of such phylogenetic clustering varies over time and is influenced by earlier extinction history, especially by the demise of volatile taxa in the end-Cretaceous mass extinction. Analyses of the evolutionary roles of ancient extinctions and predictive models of vulnerability of taxa to future natural and anthropogenic stressors should take phylogenetic relationships and extinction history into account.


Assuntos
Bivalves , Extinção Biológica , Fósseis , Filogenia , Animais , Evolução Biológica , Bivalves/classificação , Bivalves/genética , Biologia Marinha
17.
Ecology ; 90(5): 1291-300, 2009 May.
Artigo em Inglês | MEDLINE | ID: mdl-19537549

RESUMO

In the absence of long-term monitoring data, inferences about extinctions of species and populations are generally based on past observations about the presence of a particular species at specified places and times (sightings). Several methods have been developed to estimate the probability and timing of extinctions from records of such sightings, but they differ in their computational complexity and assumptions about the nature of the sighting record. Here we use simulations to evaluate the performance of seven methods proposed to estimate the upper confidence limit on extinction times under different extinction and sampling scenarios. Our results show that the ability of existing methods to correctly estimate the timing of extinctions varies with the type of extinction (sudden vs. gradual) and the nature of sampling effort over time. When the probability of sampling a species declines over time, many of the methods perform poorly. On the other hand, the simulation results also suggest that as long as the choice of the method is determined by the nature of the underlying sighting data, existing methods should provide reliable inferences about the timing of past extinctions.


Assuntos
Extinção Biológica , Modelos Biológicos , Modelos Estatísticos , Animais , Densidade Demográfica , Viés de Seleção , Especificidade da Espécie
18.
Proc Biol Sci ; 276(1661): 1485-93, 2009 Apr 22.
Artigo em Inglês | MEDLINE | ID: mdl-19324820

RESUMO

Understanding the factors that determine the geographic range limits of species is important for many questions in ecology, evolution and conservation biology. These limits arise from complex interactions among ecology and dispersal ability of species and the physical environment, but many of the underlying traits can be conserved among related species and clades. Thus, the range limits of species are likely to be influenced by their macroevolutionary history. Using palaeontological and biogeographic data for marine bivalves, we find that the range limits of genera are significantly related to their constituent species richness, but the effects of age are weak and inconsistent. In addition, we find a significant phylogenetic signal in the range limits at both genus and family levels, although the strength of this effect shows interoceanic variation. This phylogenetic conservatism of range limits gives rise to an evolutionary pattern where wide-ranging lineages have clusters of species within the biogeographic provinces, with a few extending across major boundaries.


Assuntos
Evolução Biológica , Bivalves/fisiologia , Demografia , Animais , Ecossistema , Fósseis , Modelos Biológicos , Paleontologia
19.
Evolution ; 62(3): 700-10, 2008 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-18081713

RESUMO

Natural selection has almost certainly shaped many evolutionary trajectories documented in fossil lineages, but it has proven difficult to demonstrate this claim by analyzing sequences of evolutionary changes. In a recently published and particularly promising test case, an evolutionary time series of populations displaying armor reduction in a fossil stickleback lineage could not be consistently distinguished from a null model of neutral drift, despite excellent temporal resolution and an abundance of indirect evidence implicating natural selection. Here, we revisit this case study, applying analyses that differ from standard approaches in that: (1) we do not treat genetic drift as a null model, and instead assess neutral and adaptive explanations on equal footing using the Akaike Information Criterion; and (2) rather than constant directional selection, the adaptive scenario we consider is that of a population ascending a peak on the adaptive landscape, modeled as an Orstein-Uhlenbeck process. For all three skeletal features measured in the stickleback lineage, the adaptive model decisively outperforms neutral evolution, supporting a role for natural selection in the evolution of these traits. These results demonstrate that, at least under favorable circumstances, it is possible to infer in fossil lineages the relationship between evolutionary change and features of the adaptive landscape.


Assuntos
Adaptação Biológica/genética , Evolução Biológica , Fósseis , Modelos Genéticos , Fenótipo , Smegmamorpha/genética , Animais , Simulação por Computador , Smegmamorpha/anatomia & histologia , Fatores de Tempo
20.
Proc Natl Acad Sci U S A ; 104(47): 18404-8, 2007 Nov 20.
Artigo em Inglês | MEDLINE | ID: mdl-18003931

RESUMO

The nature of evolutionary changes recorded by the fossil record has long been controversial, with particular disagreement concerning the relative frequency of gradual change versus stasis within lineages. Here, I present a large-scale, statistical survey of evolutionary mode in fossil lineages. Over 250 sequences of evolving traits were fit by using maximum likelihood to three evolutionary models: directional change, random walk, and stasis. Evolution in these traits was rarely directional; in only 5% of fossil sequences was directional evolution the most strongly supported of the three modes of change. The remaining 95% of sequences were divided nearly equally between random walks and stasis. Variables related to body size were significantly less likely than shape traits to experience stasis. This finding is in accord with previous suggestions that size may be more evolutionarily labile than shape and is consistent with some but not all of the mechanisms proposed to explain evolutionary stasis. In general, similar evolutionary patterns are observed across other variables, such as clade membership and temporal resolution, but there is some evidence that directional change in planktonic organisms is more frequent than in benthic organisms. The rarity with which directional evolution was observed in this study corroborates a key claim of punctuated equilibria and suggests that truly directional evolution is infrequent or, perhaps more importantly, of short enough duration so as to rarely register in paleontological sampling.


Assuntos
Evolução Biológica , Fósseis , Modelos Biológicos , Animais , Classificação , Filogenia
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