scholarly journals Current understanding on the Cambrian Explosion: questions and answers

PalZ ◽  
2021 ◽  
Author(s):  
Xingliang Zhang ◽  
Degan Shu
Keyword(s):  
Environmental Changes ◽  
Size Variation ◽  
Progressive Increase ◽  
Cambrian Explosion ◽  
Time Interval ◽  
Early Cambrian ◽  
Ecological Processes ◽  
Questions And Answers ◽  
Evolutionary Event ◽  
History Of

AbstractThe Cambrian Explosion by nature is a three-phased explosion of animal body plans alongside episodic biomineralization, pulsed change of generic diversity, body size variation, and progressive increase of ecosystem complexity. The Cambrian was a time of crown groups nested by numbers of stem groups with a high-rank taxonomy of Linnaean system (classes and above). Some stem groups temporarily succeeded while others were ephemeral and underrepresented by few taxa. The high number of stem groups in the early history of animals is a major reason for morphological gaps across phyla that we see today. Most phylum-level clades achieved their maximal disparity (or morphological breadth) during the time interval close to their first appearance in the fossil record during the early Cambrian, whereas others, principally arthropods and chordates, exhibit a progressive exploration of morphospace in subsequent Phanerozoic. The overall envelope of metazoan morphospace occupation was already broad in the early Cambrian though it did not reach maximal disparity nor has diminished significantly as a consequence of extinction since the Cambrian. Intrinsic and extrinsic causes were extensively discussed but they are merely prerequisites for the Cambrian Explosion. Without the molecular evolution, there could be no Cambrian Explosion. However, the developmental system is alone insufficient to explain Cambrian Explosion. Time-equivalent environmental changes were often considered as extrinsic causes, but the time coincidence is also insufficient to establish causality. Like any other evolutionary event, it is the ecology that make the Cambrian Explosion possible though ecological processes failed to cause a burst of new body plans in the subsequent evolutionary radiations. The Cambrian Explosion is a polythetic event in natural history and manifested in many aspects. No simple, single cause can explain the entire phenomenon.

Theoretical Ecospace for Ecosystem Paleobiology: Energy, Nutrients, Biominerals, and Macroevolution

2013 ◽  
Vol 19 ◽  
pp. 1-20 ◽  
Author(s):  
Andrew M. Bush ◽  
Sara B. Pruss
Keyword(s):  
Ecosystem Dynamics ◽  
Early Cambrian ◽  
Nutrient Cycles ◽  
Earth System ◽  
Ecological Traits ◽  
Ecological Processes ◽  
History Of ◽  
Extinction Selectivity ◽  
Abundance And Diversity ◽  
Selective Extinction

Changes in nutrient cycles and energy fluxes (i.e., ecosystem dynamics) likely drove numerous trends and disruptions in the history of life. Advances in geochemistry offer great insights into paleoecosystem function, as does an understanding of the biogeochemical roles played by ancient organisms. A theoretical ecospace that describes the chemical exchanges between organisms and their environments is presented. Previous descriptions of ecospace principally described spatial and physical aspects of ecology; the new ecospace description broadens the concept to encompass a wider range of ecological processes that control abundance and diversity of fossil organisms. Organisms require materials from the environment for generating energy and building tissues, and these factors are broken down, ultimately specifying particular substances acquired from the environment. Different organisms require specific substances in different amounts depending on factors such as physiology, environmental conditions, etc.; thus, physiological ecospace describes an organism's sensitivity to ecosystem/earth system perturbations and trends. Several examples relating to organisms' requirements for skeletal minerals are reviewed, and a new analysis of extinction selectivity related to ocean acidification is presented. Selective extinction of heavily calcified metazoa is demonstrated to have occurred at least eight times during the Phanerozoic, including the early Cambrian, Frasnian (Late Devonian), and Aptian (Early Cretaceous). Multidimensional structure of ecospace occupation (e.g., correlations among ecological traits) strongly controls the effects of an extinction such that the same kill mechanism applied at different times will affect the ecological composition of the biosphere in a variety of ways.

Origins and Early Evolution of Predation

2002 ◽  
Vol 8 ◽  
pp. 289-318 ◽  
Author(s):  
Stefan Bengtson
Keyword(s):  
Fossil Record ◽  
Cambrian Explosion ◽  
Major Transitions ◽  
Microbial Ecosystems ◽  
Life Itself ◽  
Evolutionary Event ◽  
History Of ◽  
Ultimate Result ◽  
Major Transitions In Evolution ◽  
Theoretical Considerations

Predation, in the broad sense of an organism killing another organism for nutritional purposes, is probably as old as life itself and has originated many times during the history of life. Although little of the beginnings is caught in the fossil record, observations in the rock record and theoretical considerations suggest that predation played a crucial role in some of the major transitions in evolution. The origin of eukaryotic cells, poorly constrained to about 2.7 Ga by geochemical evidence, was most likely the ultimate result of predation among prokaryotes. Multicellularity (or syncytiality), as a means of acquiring larger size, is visible in the fossil record soon after 2 Ga and is likely to have been mainly a response to selective pressure from predation among protists. The appearance of mobile predators on bacteria and protists may date back as far as 2 Ga or it may be not much older than the Cambrian explosion, or about 600 Ma. The combined indications from the decline of stromatolites and the diversification of acritarchs, however, suggest that such predation may have begun around 1 Ga. The Cambrian explosion, culminating around 550 Ma, represents the transition from simple, mostly microbial, ecosystems to ones with complex food webs and second- and higher-order consumers. Macrophagous predators were involved from the beginning, but it is not clear whether they originated in the plankton or in the benthos. Although predation was a decisive selective force in the Cambrian explosion, it was a shaper rather than a trigger of this evolutionary event.

scholarly journals A vanished history of skeletonization in Cambrian comb jellies

2015 ◽  
Vol 1 (6) ◽  
pp. e1500092 ◽  
Author(s):  
Qiang Ou ◽  
Shuhai Xiao ◽  
Jian Han ◽  
Ge Sun ◽  
Fang Zhang ◽  
...  
Keyword(s):  
Sense Organ ◽  
Early Evolution ◽  
Monophyletic Group ◽  
Cambrian Explosion ◽  
Early Cambrian ◽  
Animal Groups ◽  
New Class ◽  
History Of ◽  
Ecological Importance

Ctenophores are traditionally regarded as “lower” metazoans, sharing with cnidarians a diploblastic grade of organization. Unlike cnidarians, where skeletonization (biomineralization and sclerotization) evolved repeatedly among ecologically important taxa (for example, scleractinians and octocorals), living ctenophores are characteristically soft-bodied animals. We report six sclerotized and armored ctenophores from the early Cambrian period. They have diagnostic ctenophore features (for example, an octamerous symmetry, oral-aboral axis, aboral sense organ, and octaradially arranged ctene rows). Unlike most modern counterparts, however, they lack tentacles, have a sclerotized framework, and have eight pairs of ctene rows. They are resolved as a monophyletic group (Scleroctenophora new class) within the ctenophores. This clade reveals a cryptic history and sheds new light on the early evolution of this basal animal phylum. Skeletonization also occurs in some other Cambrian animal groups whose extant members are exclusively soft-bodied, suggesting the ecological importance of skeletonization in the Cambrian explosion.

scholarly journals Darwin's dilemma: the realities of the Cambrian ‘explosion’

2006 ◽  
Vol 361 (1470) ◽  
pp. 1069-1083 ◽  
Author(s):  
Simon Conway Morris
Keyword(s):  
Fossil Record ◽  
Current Work ◽  
Cambrian Explosion ◽  
Molecular Clocks ◽  
Burgess Shale ◽  
Cause And Effect ◽  
Evolutionary Event ◽  
History Of ◽  
Wrong Sort

The Cambrian ‘explosion’ is widely regarded as one of the fulcrum points in the history of life, yet its origins and causes remain deeply controversial. New data from the fossil record, especially of Burgess Shale-type Lagerstätten, indicate, however, that the assembly of bodyplans is not only largely a Cambrian phenomenon, but can already be documented in fair detail. This speaks against a much more ancient origin of the metazoans, and current work is doing much to reconcile the apparent discrepancies between the fossil record, including the Ediacaran assemblages of latest Neoproterozoic age and molecular ‘clocks’. Hypotheses to explain the Cambrian ‘explosion’ continue to be generated, but the recurrent confusion of cause and effect suggests that the wrong sort of question is being asked. Here I propose that despite its step-like function this evolutionary event is the inevitable consequence of Earth and biospheric change.

Disparity and constraint in olenelloid trilobites and the Cambrian Radiation

Paleobiology ◽  
1999 ◽  
Vol 25 (4) ◽  
pp. 459-470 ◽  
Author(s):  
Loren H. Smith ◽  
Bruce S. Lieberman
Keyword(s):  
Morphological Changes ◽  
Early Cambrian ◽  
Morphological Disparity ◽  
Time Period ◽  
Animal Phyla ◽  
Evolutionary Event ◽  
History Of ◽  
Cambrian Radiation ◽  
Active Research ◽  
Morphological Constraint

The Cambrian Radiation marks the appearance of representatives of virtually all major skeletonized phyla in the fossil record and clearly represents a fundamental episode in the history of life. Furthermore, the tempo and mode of this evolutionary event have been the subject of intense debate. One area that has been debated is how so many phylum-level body plans can have evolved in such a geologically brief period. Some have argued that there was enhanced morphological flexibility and fewer evolutionary constraints at this time, leading to greater morphological disparity of Early Cambrian faunas. Others have claimed that this is not true because the evolution of most of the animal phyla significantly predates the radiation or because they failed to detect a signature of decreasing morphological disparity through time. At present, the higher-level patterns of diversification during this time period and the relevant implications for Early Cambrian uniqueness are areas of active research interest and debate. Recognizing this debate, we used both a phylogenetic and a morphometric framework to study whether there is a signature of increasing morphological constraint and decreasing flexibility through time within one of the clades that is a significant constituent of the Early Cambrian biota, specifically, the olenelloid trilobites. In this species-rich clade, we found no evidence that morphological changes were becoming either increasingly constrained or less flexible in one of the dominant Early Cambrian metazoan clades as it passed through the Cambrian Radiation.

scholarly journals Geochemistry of the black rock series of lower Cambrian Qiongzhusi Formation, SW Yangtze Block, China: Reconstruction of sedimentary and tectonic environments

2021 ◽  
Vol 13 (1) ◽  
pp. 166-187
Author(s):  
Hao Liu ◽  
Chan Wang ◽  
Yong Li ◽  
Jianghong Deng ◽  
Bin Deng ◽  
...  
Keyword(s):  
Environmental Changes ◽  
Sedimentary Environment ◽  
Hydrothermal Fluids ◽  
Early Cambrian ◽  
Rock Series ◽  
Yangtze Block ◽  
Tectonic Environment ◽  
Weathering Intensity ◽  
Black Rock Series ◽  
Tectonic System

Abstract The black rock series in the Qiongzhusi Formation contains important geochemical information about the early Cambrian tectonic and ecological environment of the southwestern Yangtze Block. In this paper, major, trace, and rare earth element data are presented in an attempt to reveal the sediment source during the deposition of the early Cambrian Qiongzhusi Formation and to reconstruct the sedimentary tectonic environment and weathering intensity during that time. The basin primarily received continental clastic material with neutral-acidic igneous rocks from a stable source and with a moderate level of maturity during the depositional period of the Qiongzhusi Formation. Furthermore, the strata were weakly influenced by submarine hydrothermal fluids during diagenesis. The reconstruction of the sedimentary environment and weathering intensity shows that P2O5 enrichment and water body stratification occurred due to the effects of upwelling ocean currents during the depositional period of the Qiongzhusi Formation. The combination of upwelling and bottom-water hydrothermal fluids led to environmental changes in the study area, from dry and hot to moist and warm. Last, the reconstruction of the tectonic environment of the Qiongzhusi Formation indicates that deposition occurred in continental slope and marginal marine environments associated with a continental arc tectonic system. These findings provide an essential basis for the comprehensive reconstruction of the early Cambrian sedimentary environment of the Yangtze Block.

scholarly journals Massive hemobilia caused by rupture of gastroduodenal artery pseudoaneurysm, a delayed complication of laparoscopic cholecystectomy: a case report

2021 ◽  
Vol 15 (1) ◽  
Author(s):  
Kurniawan Kurniawan ◽  
I Dewa Nyoman Wibawa ◽  
Gde Somayana ◽  
I Ketut Mariadi ◽  
I Made Mulyawan
Keyword(s):  
Laparoscopic Cholecystectomy ◽  
Gastrointestinal Bleeding ◽  
Abdominal Trauma ◽  
Upper Gastrointestinal Bleeding ◽  
Rare Complication ◽  
Gastroduodenal Artery ◽  
Time Interval ◽  
Artery Pseudoaneurysm ◽  
History Of ◽  
Upper Gastrointestinal

Abstract Background Hemobilia is a rare cause of upper gastrointestinal bleeding that originates from the biliary tract. It is infrequently considered in diagnosis, especially in the absence of abdominal trauma or history of hepatopancreatobiliary procedure, such as cholecystectomy, which can cause arterial pseudoaneurysm. Prompt diagnosis is crucial because its management strategy is distinct from other types of upper gastrointestinal bleeding. Here, we present a case of massive hemobilia caused by the rupture of a gastroduodenal artery pseudoaneurysm in a patient with a history of laparoscopic cholecystectomy 3 years prior to presentation. Case presentation A 44-year-old Indonesian female presented to the emergency department with complaint of hematemesis and melena accompanied by abdominal pain and icterus. History of an abdominal trauma was denied. However, she reported having undergone a laparoscopic cholecystectomy 3 years prior to presentation. On physical examination, we found anemic conjunctiva and icteric sclera. Nonvariceal bleeding was suspected, but esophagogastroduodenoscopy showed a blood clot at the ampulla of Vater. Angiography showed contrast extravasation from a gastroduodenal artery pseudoaneurysm. The patient underwent pseudoaneurysm ligation and excision surgery to stop the bleeding. After surgery, the patient’s vital signs were stable, and there was no sign of rebleeding. Conclusion Gastroduodenal artery pseudoaneurysm is a rare complication of laparoscopic cholecystectomy. The prolonged time interval, as compared with other postcholecystectomy hemobilia cases, resulted in hemobilia not being considered as an etiology of the gastrointestinal bleeding at presentation. Hemobilia should be considered as a possible etiology of gastrointestinal bleeding in patients with history of cholecystectomy, regardless of the time interval between the invasive procedure and onset of bleeding.

Basal Cambrian microfossils from the Yangtze Gorges area (South China) and the Aksu area (Tarim block, northwestern China)

2009 ◽  
Vol 83 (1) ◽  
pp. 30-44 ◽  
Author(s):  
Lin Dong ◽  
Shuhai Xiao ◽  
Bing Shen ◽  
Chuanming Zhou ◽  
Guoxiang Li ◽  
...  
Keyword(s):  
Geographic Distribution ◽  
South China ◽  
Northwestern China ◽  
Cambrian Explosion ◽  
Filamentous Cyanobacteria ◽  
Primary Producers ◽  
Tarim Block ◽  
Eukaryotic Phytoplankton ◽  
History Of ◽  
Wide Geographic Distribution

The basal Cambrian marks the beginning of an important chapter in the history of life. However, most paleontological work on the basal Cambrian has been focused on skeletal animal fossils, and our knowledge about the primary producers—cyanobacteria and eukaryotic phytoplankton (e.g., acritarchs)—is limited. In this research, we have investigated basal Cambrian acritarchs, coccoidal microfossils, and cyanobacteria preserved in phosphorites and cherts of the Yanjiahe Formation in the Yangtze Gorges area (South China) and the Yurtus Formation in the Aksu area (Tarim Block, northwestern China). Our study confirms the occurrence in these two formations of small acanthomorphic acritarchs characteristic of the basal CambrianAsteridium–Comasphaeridium–Heliosphaeridium(ACH) assemblage. These acritarchs include abundantHeliosphaeridium ampliatimi(Wang, 1985) Yao et al., 2005, commonYurtusia uniformisn. gen. and n. sp., and rareComasphaeridium annulare(Wang, 1985) Yao et al., 2005. In addition, these basal Cambrian successions also contain the clustered coccoidal microfossilArchaeophycus yunnanensis(SonginLuo et al., 1982) n. comb., several filamentous cyanobacteria [Cyanonema majusn. sp.,Oscillatoriopsis longaTimofeev and Hermann, 1979, andSiphonophycus robustum(Schopf, 1968) Knoll et al., 1991], and the tabulate tubular microfossilMegathrix longusL. Yin, 1987a, n. emend. Some of these taxa (e.g.,H. ampliatum, C. annulare, andM. longus) have a wide geographic distribution but occur exclusively in basal Cambrian successions, supporting their biostratigraphic importance. Comparison between the stratigraphic occurrences of microfossils reported here and skeletal animal fossils published by others suggests that animals and phytoplankton radiated in tandem during the Cambrian explosion.

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