Early Diversification

1980 ◽  
Vol 3 ◽  
pp. 86-93
Author(s):  
James Sprinkle
Keyword(s):  
Adaptive Radiation ◽  
Fossil Record ◽  
Early Cambrian ◽  
Early Paleozoic ◽  
Two Stage ◽  
Evolutionary Pattern ◽  
Middle Ordovician ◽  
Early Diversification ◽  
Initial Radiation

The initial explosive radiation of echinoderms in the Cambrian and Ordovician is very likely the single most spectacular evolutionary pattern shown by echinoderms during their long fossil record. This radiation involved 19–20 echinoderm classes and lasted from the Early Cambrian (perhaps latest Precambrian) to the end of the Middle Ordovician. It is important because in many ways this initial radiation determined the entire Paleozoic record for echinoderms. In addition, it is almost a textbook example of a major adaptive radiation (Raup and Stanley, 1978, p. 307, 357–360), and also fits nicely the two-stage metazoan diversification model for the Early Paleozoic outlined by Sepkoski (1979).

Early radiation of echinoderms

1997 ◽  
Vol 3 ◽  
pp. 205-224 ◽  
Author(s):  
James Sprinkle ◽  
Thomas E. Guensburg
Keyword(s):  
Mass Extinction ◽  
Fossil Record ◽  
Early Paleozoic ◽  
Soft Substrate ◽  
Middle Cambrian ◽  
Middle Ordovician ◽  
Late Cambrian ◽  
Low Diversity ◽  
Early Radiation ◽  
Ways Of Life

Echinoderms underwent a major two-part radiation that produced all of the major groups found in the fossil record between the Early Cambrian and the Middle Ordovician. A small initial radiation in the Early and Middle Cambrian produced about nine classes containing low-diversity members of the Cambrian Evolutionary Fauna. These were characterized by primitive morphology, simple ambulacral feeding structures, and the early development of a multiplated stalk or stem for attachment to skeletal fragments on a soft substrate. Several groups became extinct at the end of the Middle Cambrian, leaving the Late Cambrian as a gap of very low diversity in the fossil record of echinoderms with only four classes preserved and very few occurrences of complete specimens, mostly associated with early hardgrounds. The survivors from this interval re-expanded in the Early Ordovician and were joined by many newly evolved groups to produce a much larger radiation of more advanced, diverse, and successful echinoderms representing the Paleozoic Evolutionary Fauna on both hard and soft substrates. At least 17 classes were present by the Middle Ordovician, the all-time high point for echinoderm class diversity, and nearly all of the major ways-of-life (except for deep infaunal burrowing) had been developed. With the rise to dominance of crinoids, many less successful or archaic groups did not survive the Middle Ordovician, and echinoderm class diversity dropped further because of the mass extinction at the end of the Ordovician. This weeding-out process of other less-successful echinoderm groups continued throughout the rest of the Paleozoic, and only five classes of echinoderms have survived to the Recent from this early Paleozoic radiation.

scholarly journals Bradoriids (Arthropoda) and the Cambrian Diversification

Geosciences ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 119
Author(s):  
Mark A. S. McMenamin
Keyword(s):  
Fossil Record ◽  
Evolutionary Dynamics ◽  
Cambrian Explosion ◽  
Early Cambrian ◽  
Middle Ordovician ◽  
High Genus ◽  
Genus Level ◽  
Rapid Ascent

Bradoriids, among the earliest arthropods to appear in the fossil record, are extinct, ostracod-like bivalved forms that ranged from the early Cambrian to the Middle Ordovician. Bradoriids are notable for having appeared in the Cambrian fossil record before the earliest trilobites, and considering their rapid ascent to high genus-level diversity, provide key data for our understanding of the evolutionary dynamics of the Cambrian Explosion. This paper presents a broad review of bradoriid paleobiology. It is hypothesized here that an allele of Antennapedia determines whether bradoriid shields are preplete, amplete, or postplete. The preplete configuration of the shields of Cambroarchilocus tigris gen. nov. sp. nov. suggests that shield rowing motion may have propelled the animal backwards. Arcuate scars attributed here to a microdurophagous predator (Arcuoichnus pierci nov. ichnogen. nov. ichnosp.) occur on the paratype of Cambroarchilocus tigris gen. nov. sp. nov.

scholarly journals The development of Early Paleozoic shell concentrations: evidence from the Cambrian and Ordovician of the Great Basin

1992 ◽  
Vol 6 ◽  
pp. 183-183 ◽  
Author(s):  
Xing Li ◽  
Mary Droser
Keyword(s):  
Great Basin ◽  
Critical Time ◽  
Depositional Environments ◽  
Early Cambrian ◽  
Early Paleozoic ◽  
Lower Paleozoic ◽  
Middle Ordovician ◽  
Physical Scale ◽  
Shell Beds ◽  
Shell Concentrations

Shell concentrations have constituted an important and conspicuous part of the stratigraphic record since the Early Cambrian. The paleontological and stratigraphic significance of shell beds is well understood, primarily from Mesozoic and Cenozoic examples. Lower Paleozoic fossil concentrations, however, have not received much attention. The Cambrian and Ordovician evolutionary radiations were two of the most significant events in the history of life and established the Cambrian and Paleozoic faunas respectively. In order to determine the effect of these radiations on the development of fossil accumulations, a systematic study of early Paleozoic shell beds was conducted in the Great Basin areas of California, Nevada, and Utah.In order to minimize taphonomic variations in original chemical and physical conditions, shell beds were compared from strata deposited in similar depositional environments from similar tectonic settings. Preliminary analysis of the shell beds from relatively pure carbonate facies and mixed carbonate and siliciclastic facies shows: 1) that shell concentrations became a significant stratigraphic feature in the later Early Cambrian; 2) the thickness and lateral extent of the shell beds increase from Early Cambrian to Middle Ordovician; 3) the abundance and internal complexity of the shell beds increase from Early Cambrian to Middle Ordovician; and 4) the Cambrian and Early Ordovician shell beds are primarily, if not exclusively, dominated by trilobites whereas the Middle Ordovician shell beds are dominated by brachiopods and ostracodes.These data show a temporal trend in the development of the early Paleozoic shell beds. The nature of the Cambrian and Ordovician shell beds differs qualitatively and quantitatively. There is an increase in physical scale, abundance, and internal complexity through time. The thickness and abundance of the trilobite beds increase through the Cambrian. Interestingly, although trilobites were still diverse and abundant, they did not commonly generate thick trilobite beds after the Late Cambrian. The early Middle Ordovician is a critical time in the development of early Paleozoic shell beds. A variety of monotaxic and polytaxic shell beds, including 6m thick composite beds, first appeared at this time. While the brachiopods and ostracodes generate laterally extensive, commonly monotaxic, shell beds, the gastropods and bryozoans only formed lenticular concentrations.

scholarly journals Eutherians experienced elevated evolutionary rates in the immediate aftermath of the Cretaceous–Palaeogene mass extinction

2016 ◽  
Vol 283 (1833) ◽  
pp. 20153026 ◽  
Author(s):  
Thomas John Dixon Halliday ◽  
Paul Upchurch ◽  
Anjali Goswami
Keyword(s):  
Phylogenetic Analysis ◽  
Adaptive Radiation ◽  
Mass Extinction ◽  
Fossil Record ◽  
Morphological Evolution ◽  
Placental Mammal ◽  
Stochastic Methods ◽  
Ecological Niches ◽  
Evolutionary Radiation ◽  
Quantitative Analyses

The effect of the Cretaceous–Palaeogene (K–Pg) mass extinction on the evolution of many groups, including placental mammals, has been hotly debated. The fossil record suggests a sudden adaptive radiation of placentals immediately after the event, but several recent quantitative analyses have reconstructed no significant increase in either clade origination rates or rates of character evolution in the Palaeocene. Here we use stochastic methods to date a recent phylogenetic analysis of Cretaceous and Palaeocene mammals and show that Placentalia likely originated in the Late Cretaceous, but that most intraordinal diversification occurred during the earliest Palaeocene. This analysis reconstructs fewer than 10 placental mammal lineages crossing the K–Pg boundary. Moreover, we show that rates of morphological evolution in the 5 Myr interval immediately after the K–Pg mass extinction are three times higher than background rates during the Cretaceous. These results suggest that the K–Pg mass extinction had a marked impact on placental mammal diversification, supporting the view that an evolutionary radiation occurred as placental lineages invaded new ecological niches during the Early Palaeocene.

Coral microatolls and a probable Middle Ordovician example

1990 ◽  
Vol 64 (1) ◽  
pp. 39-43 ◽  
Author(s):  
David R. Kobluk ◽  
Iqbal Noor
Keyword(s):  
Coral Reefs ◽  
Fossil Record ◽  
Scleractinian Coral ◽  
Regional Scale ◽  
Southern Ontario ◽  
Middle Ordovician ◽  
Reef Environments ◽  
Maximum Water ◽  
Water Depths ◽  
Tabulate Corals

A disk-shaped massive colony of Tetradium, from the Middle Ordovician Bobcaygeon Formation in southern Ontario, displays features of a coral microatoll. This is the first pre-Holocene coral microatoll yet described, indicating that some tabulate corals in level-bottom communities were growing as microatolls as do many modern colonial skeleton-secreting organisms.The microatoll therefore is not strictly a Quaternary or even Cenozoic phenomenon, but has a fossil record that may span most of the Phanerozoic. This indicates that the special conditions necessary for microatoll growth have existed outside of reef environments, and were present before the advent of scleractinian coral reefs. It may be possible to use ancient microatolls to estimate absolute water depths at low tide, thereby providing a means for estimating maximum water depths on a local and regional scale.

Early Cambrian Seismic Events and Their Tectonic Significance in Western Zhejiang

2012 ◽  
Vol 524-527 ◽  
pp. 42-48
Author(s):  
Fu Sheng Guo ◽  
Zhao Bin Yan ◽  
Liu Qin Chen
Keyword(s):  
Seismic Event ◽  
Regional Distribution ◽  
Sedimentary Rocks ◽  
Seismic Events ◽  
Time Interval ◽  
Early Cambrian ◽  
Distribution Characteristics ◽  
Early Paleozoic ◽  
Tectonic Events ◽  
Tectonic Significance

The two early Cambrian seismic events could be found from sedimentary rocks at Peilingjiao section of Kaihua County, Baishi and Fangcun sections of Changshan County in western Zhejiang, except for Jiangshan area. The seismic event at Baishi outcrop can be correlated to the second seismic event at Peilingjiao section. Taking Fangcun as epicenter of the second seismic event, the magnitude of paleoseism in western Zhejiang is about 7~7.6. According to investigation on regional distribution of seismic events, the two seismic activities should be regulated by large Kaihua-Chun’an fault, but unrelated with Jiangshan-Shaoxing fault or Changshan-Xiaoshan fault. However, the formation time of Kaihua-Chun’an fault has not yet been determinate. Based on controlling on Silurian, the possible formation age was inferred to early Paleozoic. The distribution characteristics of seismites indicate that the Kaihua-Chun’an fault was already being active during early Cambrian and seismic activities may be response to Sinian tectonic events in western Zhejiang. By the way of analysis on paleoseismic rhythm, the time interval of the two seismic events in western Zhejiang is less than 5.0 Ma, which may be the result of early frequent activities of Kaihua-Chun’an fault.

Occurrence of the siliceous sponge spicule Konyrium (Hexactinellida) in the upper Cambrian of the Mackenzie Mountains, northwestern Canada

2002 ◽  
Vol 76 (3) ◽  
pp. 565-569 ◽  
Author(s):  
Brian R. Pratt
Keyword(s):  
Fossil Record ◽  
Southern China ◽  
South Australia ◽  
Early Cambrian ◽  
Siliceous Sponge ◽  
Sponge Spicule ◽  
Animal Phyla ◽  
Sponge Diversity ◽  
Siliceous Sponges ◽  
Late Neoproterozoic

The fossil record of siliceous sponges—Hexactinellida and demosponge “Lithistida”—hinges upon both body fossils plus isolated spicules mostly recovered from limestones by acid digestion. The earliest record of siliceous sponge spicules extends back to the late Neoproterozoic of Hubei, southern China (Steiner et al., 1993) and Mongolia (Brasier et al., 1997), and body fossils attributed to the hexactinellids have been described from the Ediacaran of South Australia (Gehling and Rigby, 1996); thus they are the oldest-known definite representatives of extant animal phyla. The Early Cambrian saw a remarkable diversification in spicule morphology, with the appearance of an essentially “modern” array of forms (Zhang and Pratt, 1994). While a diversity decline may have occurred with the late Early Cambrian extinction(s), the subsequent Paleozoic and Mesozoic fossil record of spicules shows a relatively consistent range of morphologies (e.g., Mostler, 1986; Bengtson et al., 1990; Webby and Trotter, 1993; Kozur et al., 1996; Zhang and Pratt, 2000). However, because spicule form is not restricted to individual taxa and many sponge species secrete a variety of spicule shapes, it is difficult to gauge true siliceous sponge diversity and to explore their biostratigraphic utility using only isolated spicules.

Early Cambrian multiple-sourced plutonism in the Eastern Sierras Pampeanas, Córdoba, Argentina: Implications for the evolution of the early Paleozoic Gondwana margin

2021 ◽  
Vol 106 ◽  
pp. 103048
Author(s):  
Alina M. Tibaldi ◽  
Juan E. Otamendi ◽  
Alejandro H. Demichelis ◽  
Matías G. Barzola ◽  
Fernando Barra ◽  
...  
Keyword(s):  
Early Cambrian ◽  
Early Paleozoic ◽  
Sierras Pampeanas ◽  
Eastern Sierras Pampeanas ◽  
Gondwana Margin
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