Q2. What are the future works in this paper?
The latter presenting the intriguing possibility that the diversification of marine ecosystems was on a single trajectory that peaked in the Devonian.
The Furongian (late Cambrian) Biodiversity Gap: Real or apparent?
TL;DR: The Furongian gap as mentioned in this paper is defined as the gap between the Cambrian Explosion and the Great Ordovician Biodiversification Event, exemplified by a marked drop in biodiversity.
About: This article is published in Palaeoworld.The article was published on 2019-03-01 and is currently open access. It has received 35 citations till now. The article focuses on the topics: Ordovician & Paleozoic.
Summary (2 min read)
2. Background
- Palaeontologists have long accepted that the fossil record is incomplete but nevertheless adequate to describe and understand the history of life on their planet.
- Some hundred years after publication of the 1st edition of Darwin’s influential work, interest intensified on the adequacy and quality of the fossil record as more complex and sophisticated analyses of the evolution of fossil organisms and their diversity were developed through deep time.
- Raup, in a succession of key papers, developed the concept of time-dependent and timeindependent biases (Raup, 1972, 1976a, 1976b).
- These key factors may provide some explanation for the current dearth of data from this critical interval.
4. Fact or artefact?
- Furongian rocks are known from all major Cambrian palaeocontinents and widely distributed in many regions, such as in Laurentia, South China, Siberia and Baltica.
- This is true for a number of classic areas of Cambrian research from western Gondwana, for example the Barrandian area of Bohemia, Spain and Morocco, together with parts of the Baltic (e.g., Estonia) where the Furongian is poorly represented or consists of shallow-water deposits that are poorly fossiliferous.
- In fact, total and SIB diversity follow comparable trajectories, which seems to fit to occurrence signal, while BC diversity reflects an independent pattern (Fig. 1).
- To avoid inconsistences generated by false positives, the authors ran a two-time data analysis from raw and generalized-differenced data for comparisons (see http://www.graemetlloyd.com/methgd.html for implementation).
- Evidence seems to suggest that, the overall observed diversity (in particular total diversity) may be driven by sampling, sampling does not account for the entire diversity signal; a biological signal is still legible in the fossil record.
5. Natural causes
- Diversity curves based on the Sepkoski Database indicate a high frequency of extinctions during the late Cambrian (Fig. 3).
- The frequency and magnitude of these events, especially when displayed as proportions of extinct genera, are impressive (see e.g., Melott and Bambach, 2012; Erlykin et al., 2018).
- Two globally significant carbon isotope excursions are recognized in the Furongian, the Steptoean Positive carbon Isotope Excursion in the Paibian Stage and the HEllnmaria — Red Tops Boundary Event (HERB) or Top of Cambrian Excursion (TOCE) in provisional Stage 10 (Zhu et al., 2006; Fig. 3 herein).
- The magnitude of the SPICE and the HERB Event in shale successions is, however, subdued compared to the δ13Ccarb excursions recorded in carbonate successions, and the δ13Corg signal is commonly half, or less than half, of the magnitude the δ13Ccarb signal (see Ahlberg et al., in press and references therein).
- The interpretation of the SPICE as a global anoxic event has, however, been questioned, because the presence of benthic faunal elements and bioturbation in almost all SPICE-related sections excludes widespread and persistent anoxia or euxinia, but rather suggest oxic or dysoxic sea floor conditions during most of the SPICE interval (Egenhoff et al., 2015; Wotte and Strauss, 2015).
6. Conclusions
- Currently there is marked interregnum in biodiversity between the high-profile, exceptionally-preserved biotas of the Cambrian Explosion, preserved across a number of Lagerstätten, and the four-fold increase in numbers of families, genera and species during the Great Ordovician Biodiversification Event.
- There are relatively few fossil collections, compared with older and younger strata, through this interval coupled with a lack of taxonomic work on its biotas.
- Extreme fluctuations are present in Furongian environments, providing a barrier to the expansion of the marine ecosystem and its biodiversity.
- That had to wait until the Early Ordovician.
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TL;DR: A review of biodiversity curves of marine organisms indicates that, despite fluctuations in amplitude (some large), a large-scale, long-term radiation of life took place during the early Palaeozoic Era; it was aggregated by a succession of more discrete and regionalized radiations across geographies and within phylogenies.
Abstract: A review of biodiversity curves of marine organisms indicates that, despite fluctuations in amplitude (some large), a large-scale, long-term radiation of life took place during the early Palaeozoic Era; it was aggregated by a succession of more discrete and regionalized radiations across geographies and within phylogenies. This major biodiversification within the marine biosphere started during late Precambrian time and was only finally interrupted in the Devonian Period. It includes both the Cambrian Explosion and the Great Ordovician Biodiversification Event. The establishment of modern marine ecosystems took place during a continuous chronology of the successive establishment of organisms and their ecological communities, developed during the ‘Cambrian substrate revolution’, the ‘Ordovician plankton revolution’, the ‘Ordovician substrate revolution’, the ‘Ordovician bioerosion revolution’ and the ‘Devonian nekton revolution’. At smaller scales, different regional but important radiations can be recognized geographically and some of them have been identified and named (e.g. those associated with the ‘Richmondian Invasion’ during Late Ordovician time in Laurentia and the contemporaneous ‘Boda event’ in parts of Europe and North Africa), in particular from areas that were in or moved towards lower latitudes, allowing high levels of speciation on epicontintental seas during these intervals. The datasets remain incomplete for many other geographical areas, but also for particular time intervals (e.g. during the late Cambrian ‘Furongian Gap’). The early Palaeozoic biodiversification therefore appears to be a long-term process, modulated by bursts in significant diversity and intervals of inadequate data, where its progressive character will become increasingly clearer with the availability of more complete datasets, with better global coverage and more advanced analytical techniques.
46 citations
Cites background from "The Furongian (late Cambrian) Biodi..."
...The Furongian Biodiversity Gap has been recently noted in a number of papers (e.g. Servais & Harper, 2018) and examined in detail (Harper et al. 2019b)....
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...Some of the subsequent benchmark studies during the twentieth and twenty-first centuries have been recently charted by Harper et al. (2019b) in connection with unravelling the Furongian Biodiversity Gap; the studies of Newell (1959), Raup (1972) and Valentine (1973) have been particularly…...
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...Harper et al. (2019b) have discussed this gap in detail, concluding that diversity has been significantly underestimated by a paucity of examined rock, compounded by a distinctive palaeogeography, extreme climates and fluctuating environments....
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...…with exceptional preservation, such as the Burgess Shale in the Canadian Rocky Mountains (e.g. Briggs et al. 1994; Erwin & Valentine, 2013; Briggs, 2015), Chengjiang in South China (e.g. Hou et al. 2017; Yang et al. 2018), Sirius Passet in North Greenland (e.g. Harper et al. 2019a) and others....
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TL;DR: In this paper, molecular clock data suggest with high probability a Cambrian origin of Embryophyta (also called land plants), indicating that their terrestrialization most probably started about 500 Ma.
44 citations
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42 citations
TL;DR: In this paper, a critical analysis of published biodiversity curves and of their own data confirm the traditional view; the Ordovician radiation is a complex, long-term process of multiple biodiversifications of marine organisms.
Abstract: The Ordovician biodiversification is considered one of the most significant radiations in the marine ecosystems of the entire Phanerozoic. Originally recognized as the ‘Ordovician Radiation’, a label retained during most of the 1980s and 1990s, the term ‘Great Ordovician Biodiversification Event’ (GOBE) was coined in the late 1990s and was subsequently adopted by most of the scientific community. The Ordovician biodiversification, has always been considered as a long-term adaptive radiation, resulting in the sum of the different individual diversifications of all groups of marine organisms that occurred diachronously during the entire Ordovician. More recently, based on different palaeontological datasets, comprising data from different palaeogeographical areas, the Ordovician radiation has been interpreted to occur at different times in different places. This is most probably related to the palaeogeography of the Ordovician, when the major palaeocontinents were variously located in low latitudes to develop biodiversity ‘hotspots’ during different time intervals. In particular, some authors, using the potentially biased dataset of the Paleobiology Database (PBDB), have considered the GOBE to be an early Middle Ordovician global bio-event. Accordingly, the GOBE thus apparently corresponds to a relatively short time interval, with dramatic diversity fluctuations resulting in a profound change in marine environments at a global scale, visible by a major pulse in biodiversification of all fossil groups around the world. A critical analysis of the published biodiversity curves and of our own data confirm the traditional view; the Ordovician radiation is a complex, long-term process of multiple biodiversifications of marine organisms. Rapid increases in diversity can be identified for some fossil groups, at regional or palaeocontinental levels, in particular within limited datasets. However, a short, dramatic event that triggered major biodiversity pulses of all fossil groups at a global level at a particular time interval is an oversimplification.
39 citations
TL;DR: The Steptoean Positive Isotopic Carbon Excursion (SPICE) is a prominent chemostratigraphic feature in the Lower Paleozoic. as discussed by the authors quantitatively evaluate the variability in SPICE records, and document that while the excursion is a global signature, its stratigraphic expression is influenced by such conditions as paleolatitude, paleocontinent, water depth, and facies.
21 citations
References
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523 citations
"The Furongian (late Cambrian) Biodi..." refers background in this paper
...…and other themes were expanded by a series of influential papers published in the 1970s against a background of debates on the shape of the Phanerozoic biodiversity curve; did it indicate that biodiversity was in equilibrium throughout geological time (Raup, 1972) or expanding (Valentine, 1973)?...
[...]
...There are errors in dating the length of units, biotic turnover rates are unpredictable, preservation is variable across the phyla, sedimentary facies are unevenly developed through time and their monographic effects (Raup, 1972, 1976a, 1976b)....
[...]
...Clearly, outcrop area, thickness and volume of rock has varied throughout geological time with less available for older formations (Raup, 1972, 1976a, 1976b)....
[...]
...Raup, in a succession of key papers, developed the concept of time-dependent and timeindependent biases (Raup, 1972, 1976a, 1976b)....
[...]
...These and other themes were expanded by a series of influential papers published in the 1970s against a background of debates on the shape of the Phanerozoic biodiversity curve; did it indicate that biodiversity was in equilibrium throughout geological time (Raup, 1972) or expanding (Valentine, 1973)?...
[...]
TL;DR: Modeling supports intuitive and empirical arguments that single-interval taxa, being especially sensitive to variation in preservation and interval length, produce many undesirable distortions of the fossil record, and suggests which rate measures are likely to be most accurate in principle.
Abstract: Mathematical modeling of cladogenesis and fossil preservation is used to explore the expected behavior of commonly used measures of taxonomic diversity and taxonomic rates with respect to interval length, quality of preservation, position of interval in a stratigraphic succession, and taxonomic rates themselves. Particular attention is focused on the independent estimation of origination and extinction rates. Modeling supports intuitive and empirical arguments that single-interval taxa, being especially sensitive to variation in preservation and interval length, produce many undesirable distortions of the fossil record. It may generally be preferable to base diversity and rate measures on estimated numbers of taxa extant at single points in time rather than to adjust conventional interval-based measures by discarding single-interval taxa. A combination of modeling and empirical analysis of fossil genera supports two major trends in marine animal evolution. (1) The Phanerozoic decline in taxonomic...
442 citations
TL;DR: Future assemblies of animals following mass extinction cannot be predicted by analyses of Phanerozoic fossils, and the current global crisis may permanently alter the biosphere’s taxonomic composition by changing the rules of evolution.
Abstract: The fossil record demonstrates that each major taxonomic group has a consistent net rate of diversification and a limit to its species richness. It has been thought that long-term changes in the dominance of major taxonomic groups can be predicted from these characteristics. However, new analyses show that diversity limits may rise or fall in response to adaptive radiations or extinctions. These changes are idiosyncratic and occur at different times in each taxa. For example, the end-Permian mass extinction permanently reduced the diversity of important, previously dominant groups such as brachiopods and crinoids. The current global crisis may therefore permanently alter the biosphere's taxonomic composition by changing the rules of evolution.
376 citations
TL;DR: The SPICE interval is identified as the best characterized ocean anoxic event in the pre-Mesozoic ocean and an extreme example of oxygen deficiency in the later Cambrian ocean, indicating the environmental challenges presented by widespread anoxia may have been a prevalent if not dominant influence on animal evolution in Cambrian oceans.
Abstract: It has been suggested that the Cambrian ocean was oxygen deficient, but physical evidence for widespread anoxia has been lacking Gill et al present sulphur isotope data from Cambrian rocks at six different locations around the world and find a positive sulphur isotope excursion in phase with a large excursion in the marine carbon isotope record, which is thought to be indicative of a global carbon cycle perturbation at the time A prolonged period of anoxia during the Cambrian may explain the previously enigmatic peculiarities seen in the fossil record It has been suggested that the Cambrian ocean was oxygen deficient, but physical evidence for widespread anoxia has been lacking Now, sulphur isotope data from Cambrian rocks at six different locations around the world is presented, with the finding of a positive sulphur isotope excursion in phase with a large excursion in the marine carbon isotope record, which is thought to be indicative of a global carbon cycle perturbation at the time With the help of a box model, these isotope shifts support the idea of large-scale anoxic and sulphidic conditions in the later Cambrian ocean Widespread anoxia in the ocean is frequently invoked as a primary driver of mass extinction as well as a long-term inhibitor of evolutionary radiation on early Earth In recent biogeochemical studies it has been hypothesized that oxygen deficiency was widespread in subsurface water masses of later Cambrian oceans1,2, possibly influencing evolutionary events during this time1,2,3 Physical evidence of widespread anoxia in Cambrian oceans has remained elusive and thus its potential relationship to the palaeontological record remains largely unexplored Here we present sulphur isotope records from six globally distributed stratigraphic sections of later Cambrian marine rocks (about 499 million years old) We find a positive sulphur isotope excursion in phase with the Steptoean Positive Carbon Isotope Excursion (SPICE), a large and rapid excursion in the marine carbon isotope record, which is thought to be indicative of a global carbon cycle perturbation4,5 Numerical box modelling of the paired carbon sulphur isotope data indicates that these isotope shifts reflect transient increases in the burial of organic carbon and pyrite sulphur in sediments deposited under large-scale anoxic and sulphidic (euxinic) conditions Independently, molybdenum abundances in a coeval black shale point convincingly to the transient spread of anoxia These results identify the SPICE interval as the best characterized ocean anoxic event in the pre-Mesozoic ocean and an extreme example of oxygen deficiency in the later Cambrian ocean Thus, a redox structure similar to those in Proterozoic oceans6,7,8 may have persisted or returned in the oceans of the early Phanerozoic eon Indeed, the environmental challenges presented by widespread anoxia may have been a prevalent if not dominant influence on animal evolution in Cambrian oceans
357 citations
"The Furongian (late Cambrian) Biodi..." refers background in this paper
...…for thermally stratified oceans and a distinct temperature gradient from higher to lower latitudes, dramatic sea-level changes, and time intervals of dysoxia or anoxia during parts of the Furongian (e.g., Gill et al., 2011; Babcock et al., 2015; Saltzman et al., 2015 and references therein)....
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...The SPICE event has been characterised as the best anoxic event recorded for pre-Mesozoic oceans and the episodic expansion of depleted bottom waters may have had a dominant influence on the development of marine animals at a critical time in metazoan evolution (Gill et al., 2011)....
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...In most regions, the SPICE can be associated with sea-level oscillations and it is presumed to have been initially triggered by a sea-level rise that brought oxygen-deficient waters onto the shelves (Gill et al., 2011)....
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...These deposits reflect enhanced organic matter burial and suggest that oxygen deficiency was widespread in subsurface water masses in the Furongian (Gill et al., 2011; Saltzman et al., 2015)....
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...The increasing evidence for a anoxia/dysoxia (e.g., Gill et al., 2011) apparently supports the latter hypothesis, but, as reviewed by Taylor (2006), there is also geological evidence consistent with relative sea-level rise and water temperature decline at biomere boundaries (see also Babcock et…...
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TL;DR: In this article, the authors show that species diversity among fossil invertebrates of the Phanerozoic is highly correlated with volume and area of sedimentary rocks and that there is no compelling evidence for a general increase in the number of invertebrate species from Paleozoic to Recent.
Abstract: Species diversity among fossil invertebrates of the Phanerozoic is highly correlated with volume and area of sedimentary rocks. The correlations are statistically significant at the 1% level. The relationship holds even in regions (such as Canada) where the area and volume of rock do not increase through time. These results are interpreted as indicating that the apparent number of species is strongly dependent on sampling and that many of the changes in diversity seen in the Phanerozoic are artifactual. Consequently, there is no compelling evidence for a general increase in the number of invertebrate species from Paleozoic to Recent. This conclusion applies primarily to marine organisms. Diversity may have been in dynamic equilibrium throughout much of this time. A few intervals of the Phanerozoic have consistently fewer invertebrate species than would be predicted from the amount of sedimentary rock available for study. The Silurian, Permian, and Cretaceous stand out in this regard. This may result either from lower than normal diver- sity during these periods or from an unusual abundance of unfossiliferous rocks (evaporites, red beds, etc.).
338 citations
"The Furongian (late Cambrian) Biodi..." refers background in this paper
...Clearly, outcrop area, thickness and volume of rock has varied throughout geological time with less available for older formations (Raup, 1972, 1976a, 1976b)....
[...]
...There are errors in dating the length of units, biotic turnover rates are unpredictable, preservation is variable across the phyla, sedimentary facies are unevenly developed through time and their monographic effects (Raup, 1972, 1976a, 1976b)....
[...]
...Raup, in a succession of key papers, developed the concept of time-dependent and timeindependent biases (Raup, 1972, 1976a, 1976b)....
[...]