Adjusting global extinction rates to account for taxonomic susceptibility

According to when they attained high diversity, major taxa of marine animals have been clustered into three groups, the Cambrian, Paleozoic, and Modern Faunas. Because the Cambrian Fauna was a relatively minor component of the total fauna after mid-Ordovician time, the Phanerozoic history of marine animal diversity is largely a matter of the fates of the Paleozoic and Modern Faunas. The fact that most late Cenozoic genera belong to taxa that have been radiating for tens of millions of years indicates that the post-Paleozoic increase in diversity indicated by fossil data is real, rather than an artifact of improvement of the fossil record toward the present.Assuming that ecological crowding produced the so-called Paleozoic plateau for family diversity, various workers have used the logistic equation of ecology to model marine animal diversification as damped exponential increase. Several lines of evidence indicate that this procedure is inappropriate. A plot of the diversity of marine animal genera through time provides better resolution than the plot for families and has a more jagged appearance. Generic diversity generally increased rapidly during the Paleozoic, except when set back by pulses of mass extinction. In fact, an analysis of the history of the Paleozoic Fauna during the Paleozoic Era reveals no general correlation between rate of increase for this fauna and total marine animal diversity. Furthermore, realistically scaled logistic simulations do not mimic the empirical pattern. In addition, it is difficult to imagine how some fixed limit for diversity could have persisted throughout the Paleozoic Era, when the ecological structure of the marine ecosystem was constantly changing. More fundamentally, the basic idea that competition can set a limit for marine animal diversity is incompatible with basic tenets of marine ecology: predation, disturbance, and vagaries of recruitment determine local population sizes for most marine species. Sparseness of predators probably played a larger role than weak competition in elevating rates of diversification during the initial (Ordovician) radiation of marine animals and during recoveries from mass extinctions. A plot of diversification against total diversity for these intervals yields a band of points above the one representing background intervals, and yet this band also displays no significant trend (if the two earliest intervals of the initial Ordovician are excluded as times of exceptional evolutionary innovation). Thus, a distinctive structure characterized the marine ecosystem during intervals of evolutionary radiation—one in which rates of diversification were exceptionally high and yet increases in diversity did not depress rates of diversification.Particular marine taxa exhibit background rates of origination and extinction that rank similarly when compared with those of other taxa. Rates are correlated in this way because certain heritable traits influence probability of speciation and probability of extinction in similar ways. Background rates of origination and extinction were depressed during the late Paleozoic ice age for all major marine invertebrate taxa, but remained correlated. Also, taxa with relatively high background rates of extinction experienced exceptionally heavy losses during biotic crises because background rates of extinction were intensified in a multiplicative manner; decimation of a large group of taxa of this kind in the two Permian mass extinctions established their collective identity as the Paleozoic Fauna.Characteristic rates of origination and extinction for major taxa persisted from Paleozoic into post-Paleozoic time. Because of the causal linkage between rates of origination and extinction, pulses of extinction tended to drag down overall rates of origination as well as overall rates of extinction by preferentially eliminating higher taxa having relatively high background rates of extinction. This extinction/origination ratchet depressed turnover rates for the residual Paleozoic Fauna during the Mesozoic Era. A decline of this fauna's extinction rate to approximately that of the Modern Fauna accounts for the nearly equal fractional losses experienced by the two faunas in the terminal Cretaceous mass extinction.Viewed arithmetically, the fossil record indicates slow diversification for the Modern Fauna during Paleozoic time, followed by much more rapid expansion during Mesozoic and Cenozoic time. When viewed more appropriately as depicting geometric—or exponential—increase, however, the empirical pattern exhibits no fundamental secular change: the background rate of increase for the Modern Fauna—the fauna that dominated post-Paleozoic marine diversity—simply persisted, reflecting the intrinsic origination and extinction rates of constituent taxa. Persistence of this overall background rate supports other evidence that the empirical record of diversification for marine animal life since Paleozoic time represents actual exponential increase. This enduring rate makes it unnecessary to invoke environmental change to explain the post-Paleozoic increase of marine diversity.Because of the resilience of intrinsic rates, an empirically based simulation that entails intervals of exponential increase for the Paleozoic and Modern Faunas, punctuated by mass extinctions, yields a pattern that is remarkably similar to the empirical pattern. It follows that marine animal genera and species will continue to diversify exponentially long into the future, barring disruption of the marine ecosystem by human-induced or natural environmental changes.

Abstract: Mass extinctions in the past have been characterized by abnormally high species extinction rates within almost all taxa. Attempts to estimate relative rates of extinction and threat among modern taxa, such as insects, plants, and vertebrates, are impeded by differences in the quality of information about each group. Insects and marine groups, for example, have much smaller percentages of known threatened species but also have many more undescribed species than do plants or vertebrates. I tested the possibility that all major groups have equally high rates of extinction and threat. The first test was a model assuming that differences in apparent global extinction and threat rate are caused by two sampling biases that produce artificially low rates in understudied taxa: (1) a common‐species bias in which taxonomists tend to record common (more extinction‐resistant) species first and (2) evaluative neglect, which is a tendency to spend relatively less effort evaluating the extinction and threat status of recorded species in understudied taxa. Global extinction and threat data from a number of groups generally follow the pattern predicted by this model. The second test shows that in direct measurements of extinction and threat between taxa in well‐studied regions, such as the United States and United Kingdom, the apparent global disparity among taxa is greatly reduced. Indeed, many globally understudied taxa, such as insects and other invertebrates, have higher rates of threat than many other taxa, including mammals, in these well‐studied areas. These two tests provide quantitative support for previous suggestions that the wide disparity in rates of species extinction and threat among groups represents an artifactual distortion of the actual rates. Specific suggestions for improved estimates of actual threat include (in order of increasing accuracy): use of well‐studied proxy taxa such as mammals; comparison of threat data among taxa only in well‐studied regions; and, especially important, increased efforts to evaluate the threat status of recorded species of understudied taxa.

Approximate periodicity for peak rates of global extinction during the past 250 m.y. may have resulted from delayed recovery following major extinction events. Two components can be envisioned for such delays: persistence of inimical environmental conditions for some time after the onset of the crisis, and slow restoration of vulnerable taxa. This general hypothesis is consistent with statistical evidence of linkage between measured rates of extinction of marine invertebrate genera for contiguous stages and substages of the geologic column. The nine broad valleys between the “periodic” peak rates for the past 250 m.y. exhibit only three trivial secondary peaks, indicating that, if the pattern is not artifactual, trends in global rates of extinction have not readily been abruptly reversed. Moreover, the smooth observed trends reflect the fact that regional crises tend to remove many species but few genera. To some degree, high rates of extinction that precede peak rates must represent bias of the incomplete fossil record (the Signor-Lipps effect). High rates that immediately follow peak rates also may, to a degree, reflect biological legacy: (1) final extinction of weakened genera or (2) extinction of new genera that contain few species or represent failed evolutionary “experiments.” Nonetheless, there is evidence that protracted intervals of stressful environmental conditions contributed to high rates of extinction preceding or following certain peak intervals, including the Scythian, Cenomanian, Early Paleocene, and Early Oligocene. The reef-building rudists, for example, suffered heavy extinction during both Cenomanian and Turonian time and then failed to recover quickly. The late Neogene record of bivalve molluscs in the Western Atlantic offers a more detailed picture of delayed recovery. Here early intervals of glacial expansion caused heavy extinction, leaving an impoverished, eurythermal fauna that was virtually unaffected by late Pleistocene glacial episodes. The episode of heavy extinction in Late Eocene time exhibits a similar phenomenon on a worldwide scale. Among the planktonic foraminifera, warm-adapted stenothermal species died out, and eurythermal forms predominated throughout Oligocene time; restoration of vulnerable, stenothermal species proceeded gradually during the Miocene Epoch. This example of delayed recovery and others like it following earlier global crises may have prevented such crises from following one another in rapid succession, yielding an appearance of periodicity.

Biotic effects of the Chicxulub impact, K–T catastrophe and sea level change in Texas

The discipline-wide effort to database the fossil record at the occurrence level has made it possible to estimate marine invertebrate extinction and origination rates with much greater accuracy. The new data show that two biotic mechanisms have hastened recoveries from mass extinctions and confined diversity to a relatively narrow range over the past 500 million years (Myr). First, a drop in diversity of any size correlates with low extinction rates immediately afterward, so much so that extinction would almost come to a halt if diversity dropped by 90%. Second, very high extinction rates are followed by equally high origination rates. The two relationships predict that the rebound from the current mass extinction will take at least 10 Myr, and perhaps 40 Myr if it rivals the Permo-Triassic catastrophe. Regardless, any large event will result in a dramatic ecological and taxonomic restructuring of the biosphere. The data also confirm that extinction and origination rates both declined through the Phanerozoic and that several extinctions in addition to the Permo-Triassic event were particularly severe. However, the trend may be driven by taxonomic biases and the rates vary in accord with a simple log normal distribution, so there is no sharp distinction between background and mass extinctions. Furthermore, the lack of any significant autocorrelation in the data is inconsistent with macroevolutionary theories of periodicity or self-organized criticality.

The theoretical framework of Unconventional Petroleum Geology has been gradually established along with the rapid progresses in exploration and development of unconventional petroleum resources. It is now imperative for innovative new insights into the unconventional petroleum sedimentology. Herein,the concept and scientific connotations of "Unconventional Petroleum Sedimentology" are proposed and briefly introduced. The research progresses are summarized for the sedimentology of typical unconventional petroleum resources in China,such as Wufeng-Longmaxi Shale gas in Sichuan Basin and tight oil and shale oil of Yanchang Formation in Ordos Basin. Further research themes and challenges of Unconventional Petroleum Sedimentology are discussed. Sedimentary enrichment of unconventional petroleum resources can be closely related with some critical environmental changes,which would be the result of coupling sedimentology from several geological events such as global or regional tectonic activities,sea(lake) level changes,volcanic eruptions,climate changes,anoxic bottom water,biotic mass extinctions and radiations,and gravity currents. For better understanding of Unconventional Petroleum Sedimentology in future,the Earth Systems Science view and "unconventional" insights should be applied to its research by analyzing geological events in details, which can play an important role in the discovery of new unconventional petroleum resources.

Foraminiferal studies in the Carapita and La Pica formations have provided interesting patterns which could be correlated with paleoceanographic changes brought about by relative sea level changes, among other causes. By their effects on physicochemical parameters, relative sea level changes will affect the character, composition and distribution of marine biofacies. Patterns of foraminiferal abundance and diversity and the appearances and extinctions of species have been used to attempt a characterization of system tracts. This is a part of sequence stratigraphy very poorly understood, especially in deep water environments, where abundance peaks occur at several condensed sections within lowstand system tracts in addition to maximum flooding surfaces. The Carapita Formation is of Early to Middle Miocene age, zones N4 to N14 and correspond to the upper part of the TB1 and TB2 second order cycles of the Hag et al. chart. It was deposited predominantly in bathyal paleoenvironments, though neritic conditions have been determined at the base and summit of this formation. It is unconformably overlain by intercalations of sandstones and shales known as La Pica Formation, of Late Miocene age, deposited on environments ranging from inner neritic to continental. This probably correlates with the lower part of the TB3 supermore » cycle. Both formations were deposited in a foreland basin, formed at the beginning of the Neogene by the southeastward thrusting of the Caribbean plate over the South American continent.« less

AimTo establish a chronology for late Quaternary avian extinction, extirpation and persistence in the Bahamas, thereby testing the relative roles of climate change and human impact as causes of extinction.LocationGreat Abaco Island (Abaco), Bahamas, West Indies.MethodsWe analysed the resident bird community as sampled by Pleistocene (> 11.7 ka) and Holocene (< 11.7 ka) fossils. Each species was classified as extinct (lost globally), extirpated (gone from Abaco but persists elsewhere), or extant (still resident on Abaco). We compared patterns of extinction, extirpation and persistence to independent estimates of climate and sea level for glacial (late Pleistocene) and interglacial (Holocene) times.ResultsOf 45 bird species identified in Pleistocene fossils, 25 (56%) no longer occur on Abaco (21 extirpated, 4 extinct). Of 37 species recorded in Holocene deposits, 15 (14 extirpated, 1 extinct; total 41%) no longer exist on Abaco. Of the 30 extant species, 12 were recovered as both Pleistocene and Holocene fossils, as were 9 of the 30 extirpated or extinct species. Most of the extinct or extirpated species that were only recorded from Pleistocene contexts are characteristic of open habitats (pine woodlands or grasslands); several of the extirpated species are currently found only where winters are cooler than in the modern or Pleistocene Bahamas. In contrast, most of the extinct or extirpated species recorded from Holocene contexts are habitat generalists.Main conclusionsThe fossil evidence suggests two main times of late Quaternary avian extirpation and extinction in the Bahamas. The first was during the Pleistocene–Holocene transition (PHT; 15–9 ka) and was fuelled by climate change and associated changes in sea level and island area. The second took place during the late Holocene (< 4 ka, perhaps primarily < 1 ka) and can be attributed to human impact. Although some species lost during thePHTare currently found where climates are cooler and drier than in the Bahamas today, a taxonomically and ecologically diverse set of species persisted through that major climate change but did not survive the past millennium of human presence.

Biotic recovery after the end-Triassic extinction event: Evidence from marine bivalves of the Neuquén Basin, Argentina

Sea-level change is geographically non-uniform, with regional departures that can reach several times the global average rate of change. Characterizing this spatial variability and understanding its causes is crucial to the design of adaptation strategies for sea-level rise. This, as it turns out, is no easy feat, primarily due to the sparseness of the observational sea-level record in time and space. Long tide gauge records are restricted to a few locations along the coast. Satellite altimetry offers a better spatial coverage but only since 1992. In the Mediterranean Sea, the tide gauge network is heavily biased towards the European shorelines, with only one record with at least 35 years of data on the African coasts. Past studies have attempted to address the difficulties related to this data sparseness in the Mediterranean Sea by combining the available tide gauge records with satellite altimetry observations. The vast majority of such studies represent sea level through a combination of altimetry-derived empirical orthogonal functions whose temporal amplitudes are then inferred from the tide gauge data. Such methods, however, have tremendous difficulty in separating trends and variability, make no distinction between relative and geocentric sea level, and tell us nothing about the causes of sea level changes. Here, we combine observational data from tide gauges and altimetry with sea-level fingerprints of land-mass changes using a Bayesian hierarchical model (BHM) to quantify the sources of sea-level changes since 1960 in the Mediterranean Sea. The Bayesian estimates are provided on 1/4o x 1/4o regular grid. We find that Mediterranean Sea level rose at a relatively low rate from 1960 to 1990, at which point it started rising significantly faster with comparable contributions from sterodynamic sea level (ocean dynamics and thermal expansion) and land-mass changes. (EuroSea Deliverable, D5.2_v2)

Changes in global sea level are important forcing functions upon the quality and quantity of sedimentation within basins. Additional overprints are caused by local to global tectonism. An understanding of the intimate relationships between changes in global sea level and concomitant global tectonism is crucial to the accurate modeling and prediction of secular trends in basin sedimentary response. Previous investigators have qualitatively hypothesized the temporal relationships between plate spreading rates and changes in sea level. In order to quantify and compare the major frequency components of the post-Jurassic global sea-level curve with that of global spreading rates, the published data were converted into the frequency domain by taking the discrete Fourier transform. The resulting power spectral densities delineate the major harmonics of the separate curves. Cross correlation reveals five frequencies common to both changes in global sea level and spreading rates.

Impacts of basin restriction on geochemistry and extinction patterns: A case from the Guadalupian Delaware Basin, USA

Over 40years ago, Raup and Sepkoski identified five episodes of elevated extinction in the marine fossil record that were thought to be statistically distinct, thus warranting the term the "Big Five" mass extinctions. Since then, the term has become part of standard vocabulary, especially with the naming of the current biodiversity crisis as the "sixth mass extinction." However, there is no general agreement on which time intervals should be viewed as mass extinctions, in part because the Big Five turn out not to be statistically distinct from background rates of extinction, and in part, because other intervals of time have even higher extinction rates, in the Cambrian and early Ordovician. Nonetheless, the Big Five represent the five largest events since the early Ordovician, including in analyses that attempt to compensate for the incompleteness of the fossil and rock records. In the last 40years, we have learned a great deal about the causes of many of the major and minor extinction events and are beginning to unravel the mechanisms that translated the initial environmental disturbances into extinction. However, for many of the events, further understanding will require going back to the outcrop, where the patchy distribution of environments and pervasive temporal gaps in the rock record challenge our ability to establish true extinction patterns. As for the current biodiversity crisis, there is no doubt that the rate of extinction is among the highest ever experienced by the biosphere, perhaps the second highest after the end-Cretaceous bolide impact. However (and fortunately), the absolute number of extinctions is still relatively small - there is still time to prevent this becoming a genuine mass extinction. Given the arbitrariness of calling out the Big Five, perhaps the current crisis should be called the "incipient Anthropocene mass extinction" rather than the "sixth mass extinction."

This study extends the Sea-Level Sensitive dynamic model of marine island biogeography by integrating the dynamics of fusion-fission islands during glacial-interglacial cycles with marine island biogeography theory. We discuss the variations in littoral area due to Pleistocene sea-level changes and their effect on the evolutionary rates of splitting, extinction, and merging of populations, as well as on the speciation rates of marine shallow-water organisms. Here, we introduce three different types of fusion-fission islands: Solum islands, i.e., islands that have never been merged with neighbouring islands (at depths shallower than 50 m) during sea-level low stands associated with glacial episodes; Soror islands, i.e., islands that are subjected to fusion-fission cycles due to sea-level changes and thus may be functionally connected or separated depending on the amplitude of sea level changes; and Moliones islands, where two or more islands are functionally connected from a marine point of view, as the seafloor depth separating them is always shallower than 50 m, regardless of sea level. For this study, we selected 324 islands located in temperate and tropical climates, and representative of a broad geographic distribution, which were classified accordingly: 50 Solum islands, 77 islands making up 20 groups of Soror islands, and 197 islands from 34 groups of Moliones islands. Sea-level variation during glacial-interglacial cycles induced changes in the insular littoral area (ILA), resulting in five general types of curves of ILA change herein described. These ILA curves depend on the depth distribution across the shelves, which, in turn, depends on several variables, including the age of the island, the tectonic setting, the presence of submarine and subaerial terraces, and also on the presence/absence of coral reefs. Finally, we provide several predictions on the frequencies of marine population splitting, extinction, and merging events, as well as on the speciation rates of shallow-water marine organisms, according to the respective island types. Highlights We extend the Sea-Level Sensitive dynamic model of marine island biogeography theory to include the special case of fusion-fission islands. The dynamics of fusion-fission islands during glacial-interglacial cycles are relevant to evolutionary and biogeographic studies. We introduce new concepts (Solum, Soror, and Moliones islands) to designate islands according to the impact of glacial episodes and associated sea-level low stands on their marine biota. Five general types of curves of insular littoral area (ILA) change generated by sea-level variations during glacial-interglacial cycles are described. We hypothesize that the frequencies of marine population splitting, extinction, and merging events, as well as the speciation rates of shallow-water marine organisms, vary according to the island type.

The stratigraphic distribution of the different faunal groups of the upper Cenomanian–lower Turonian deposits in the north Eastern Desert, Egypt, is investigated. Variations in species richness, faunal diversity, extinction and origination rates before, during, and after the globally known Oceanic Anoxic Event (OAE) 2 are documented. The OAE2 interval is constrained by the first occurrence of the marker ammonite species Vascoceras cauvini and the last occurrence of Vascoceras proprium, along with the positive δ13C excursions, previously identified from the Wadi El-Burga section. A prominent decline in species richness and diversity, high extinction rates, and low origination rates of the recorded macrofaunal elements are reported during the OAE2 interval. Such faunal bottleneck was attributed to the prevailing major palaeoclimatic and palaeoenvironmental perturbations during that time. Besides oceanic anoxia, changes in sea water palaeotemperature and sea level are discussed. It can be concluded that oceanic anoxia, warming, and /or transgressive episodes were the major driving mechanisms of the faunal crisis reported in the present work.