scholarly journals Cambrian Chordates and Vetulicolians

Geosciences ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 354 ◽  
Author(s):  
McMenamin
Keyword(s):  
Retinoic Acid ◽  
Fossil Record ◽  
Posterior Region ◽  
Early Cambrian ◽  
Anterior Section ◽  
Deuterostome Evolution ◽  
Sudden Appearance ◽  
The Subject ◽  
Range Of Variation

Deuterostomes make a sudden appearance in the fossil record during the early Cambrian. Two bilaterian groups, the chordates and the vetulicolians, are of particular interest for understanding early deuterostome evolution, and the main objective of this review is to examine the Cambrian diversity of these two deuterostome groups. The subject is of particular interest because of the link to vertebrates, and because of the enigmatic nature of vetulicolians. Lagerstätten in China and elsewhere have dramatically improved our understanding of the range of variation in these ancient animals. Cephalochordate and vertebrate body plans are well established at least by Cambrian Series 2. Taken together, roughly a dozen chordate genera and fifteen vetulicolian genera document part of the explosive radiation of deuterostomes at the base of the Cambrian. The advent of deuterostomes near the Cambrian boundary involved both a reversal of gut polarity and potentially a two-sided retinoic acid gradient, with a gradient discontinuity at the midpoint of the organism that is reflected in the sharp division of vetulicolians into anterior and posterior sections. A new vetulicolian (Shenzianyuloma yunnanense nov. gen. nov. sp.) with a laterally flattened, polygonal anterior section provides significant new data regarding vetulicolians. Its unsegmented posterior region (‘tail’) bears a notochord and a gut trace with diverticula, both surrounded by myotome cones.

scholarly journals Cambrian Chordates and Vetulicolians

2019 ◽  
Author(s):  
Mark McMenamin
Keyword(s):  
Retinoic Acid ◽  
Fossil Record ◽  
Evolutionary Dynamics ◽  
Posterior Region ◽  
Early Cambrian ◽  
Anterior Section ◽  
Evolutionary Event ◽  
Sudden Appearance ◽  
Range Of Variation ◽  
Insight Into

Deuterostomes make a sudden appearance in the fossil record during the Early Cambrian. Two deuterostome groups, the chordates and the vetulicolians, are of particular interest for understanding the evolutionary dynamics of the Cambrian evolutionary event. Lagerstätten in China and elsewhere have dramatically improved our understanding of the range of variation in these ancient animals. Cephalochordate and vertebrate body plans are well established at least by Cambrian Series 2. Taken together, roughly a dozen chordate genera and fifteen vetulicolian genera document an explosive radiation of deuterostomes at the base of the Cambrian. A new vetulicolian with a polygonal anterior section and a narrow, unsegmented posterior region (‘tail’) bearing possible myotomes provides new insight into the affinities of the various body plans that emerged during the Early Cambrian. It seems clear that the advent of deuterostomes near the Cambrian boundary involved both a reversal of gut polarity and a two-sided retinoic acid gradient, with a gradient discontinuity at the midpoint of the organism that is reflected in the sharp division of vetulicolians into anterior and posterior sections.

Fossils, molecules and embryos: new perspectives on the Cambrian explosion

Development ◽  
1999 ◽  
Vol 126 (5) ◽  
pp. 851-859 ◽  
Author(s):  
J.W. Valentine ◽  
D. Jablonski ◽  
D.H. Erwin
Keyword(s):  
Fossil Record ◽  
Cambrian Explosion ◽  
Molecular Clocks ◽  
Early Cambrian ◽  
Developmental Systems ◽  
Developmental Control ◽  
Sudden Appearance

The Cambrian explosion is named for the geologically sudden appearance of numerous metazoan body plans (many of living phyla) between about 530 and 520 million years ago, only 1.7% of the duration of the fossil record of animals. Earlier indications of metazoans are found in the Neoproterozic; minute trails suggesting bilaterian activity date from about 600 million years ago. Larger and more elaborate fossil burrows appear near 543 million years ago, the beginning of the Cambrian Period. Evidence of metazoan activity in both trace and body fossils then increased during the 13 million years leading to the explosion. All living phyla may have originated by the end of the explosion. Molecular divergences among lineages leading to phyla record speciation events that have been earlier than the origins of the new body plans, which can arise many tens of millions of years after an initial branching. Various attempts to date those branchings by using molecular clocks have disagreed widely. While the timing of the evolution of the developmental systems of living metazoan body plans is still uncertain, the distribution of Hox and other developmental control genes among metazoans indicates that an extensive patterning system was in place prior to the Cambrian. However, it is likely that much genomic repatterning occurred during the Early Cambrian, involving both key control genes and regulators within their downstream cascades, as novel body plans evolved.

New olenelline trilobites from the Northwest Territories, Canada, and the phylogenetic placement of Judomia absita Fritz, 1973

Zootaxa ◽  
2011 ◽  
Vol 2918 (1) ◽  
pp. 15 ◽  
Author(s):  
I. WESLEY GAPP ◽  
BRUCE S. LIEBERMAN ◽  
MICHAEL C. POPE ◽  
KELLY A. DILLIARD
Keyword(s):  
Phylogenetic Analysis ◽  
New Species ◽  
Northwest Territories ◽  
Phylogenetic Analyses ◽  
Geographic Range ◽  
Early Cambrian ◽  
Phylogenetic Placement ◽  
The Subject ◽  
Three New Species ◽  
One New Species

The Early Cambrian olenelline trilobites are a diverse clade and have been the subject of several phylogenetic analyses. Here, three new species of Bradyfallotaspis Fritz, 1972 (B. coriae, B. nicolascagei, and B. sekwiensis) and one new species of Nevadia Walcott, 1910 (N. saupeae) are described from the Sekwi Formation of the Mackenzie Mountains, Northwest Territories, Canada. In addition, new specimens potentially referable to Nevadia ovalis McMenamin, 1987 were recovered that may expand that species’ geographic range, which was thought to be restricted to Sonora, Mexico. The results of a phylogenetic analysis incorporating several olenelline taxa, including Judomia absita Fritz, 1973 from the Sekwi Formation, are also presented herein. This species has been assigned to various olenelline genera, including Judomia Lermontova, 1951 and Paranevadella Palmer & Repina, 1993. Phylogenetic analysis suggests this species is closely related to Judomia tera Lazarenko, 1960 from Siberia. This phylogenetic relationship provides further support for the hypothesis that a close biogeographic relationship existed between Laurentia and Siberia during the Cambrian.

Rare primitive deuterostomes from the Cambrian (Series 3) of Utah

2015 ◽  
Vol 89 (4) ◽  
pp. 631-636 ◽  
Author(s):  
Simon Conway Morris ◽  
Susan L. Halgedahl ◽  
Paul Selden ◽  
Richard D. Jarrard
Keyword(s):  
New Species ◽  
Fossil Record ◽  
Type Species ◽  
The Body ◽  
New Taxon ◽  
Burgess Shale ◽  
Anterior Section ◽  
Stem Group ◽  
Stratigraphic Range ◽  
New Discovery

AbstractThe fossil record of early deuterostome history largely depends on soft-bodied material that is generally rare and often of controversial status. Banffiids and vetulicystids exemplify these problems. From the Cambrian (Series 3) of Utah, we describe specimens of Banffia episoma n. sp. (from the Spence Shale) and Thylacocercus ignota n. gen. n. sp. (from the Wheeler Formation). The new species of Banffia Walcott, 1911 shows significant differences to the type species (B. constricta Walcott, 1911) from the Cambrian (Series 3, Stage 5) Burgess Shale, notably in possessing a prominent posterior unit but diminished anterior section. Not only does this point to a greater diversity of form among the banffiids, but also B. episoma indicates that the diagnostic median constriction and crossover of either side of the body are unlikely to be the result of taphonomic twisting but are original features. Comparisons extend also to the Cambrian (Series 2) Heteromorphus Luo and Hu in Luo et al., 1999 and, collectively, these observations support an assignment of the banffiids to the vetulicolians. The new taxon T. ignota represents the first discovery of a vetulicystid from beyond China and also significantly extends its stratigraphic range from Series 2 Cambrian into Series 3 Cambrian. Despite overall similarities in bodyplan, T. ignota differs from other vetulicystids in a number of respects, notably the possession of an anterior zone with broad tentacle-like structures. This new discovery is consistent with the vetulicystids representing stem-group ambulacrarians.

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.

The early Mesozoic radiation of dinoflagellates

Paleobiology ◽  
1996 ◽  
Vol 22 (3) ◽  
pp. 329-338 ◽  
Author(s):  
R. A. Fensome ◽  
R. A. MacRae ◽  
J. M. Moldowan ◽  
F. J. R. Taylor ◽  
G. L. Williams
Keyword(s):  
Detailed Analysis ◽  
Fossil Record ◽  
The Past ◽  
Early Mesozoic ◽  
Fossil Evidence ◽  
Evolutionary Radiation ◽  
Molecular Phylogenetic ◽  
Sudden Appearance ◽  
New Evidence

Dinoflagellates are a major component of the marine microplankton and, from fossil evidence, appear to have been so for the past 200 million years. In contrast, the pre-Triassic record contains only equivocal occurrences of dinoflagellates, despite the fact that comparative ultrastructural and molecular phylogenetic evidence indicates a Precambrian origin for the lineage. Thus, it has often been assumed that the dearth of Paleozoic fossil dinoflagellates was due to a lack of preservation or recognition and that the relatively sudden appearance of dinoflagellates in the Mesozoic is an artifact of the record. However, new evidence from a detailed analysis of the fossil record and from the biogeochemical record indicates that dinoflagellates did indeed undergo a major evolutionary radiation in the early Mesozoic.

Cephalopods: biasing agents in the preservation of lobsters

1989 ◽  
Vol 63 (5) ◽  
pp. 621-626 ◽  
Author(s):  
Dale M. Tshudy ◽  
Rodney M. Feldmann ◽  
Peter D. Ward
Keyword(s):  
Fossil Record ◽  
Specific Pattern ◽  
Decapod Crustaceans ◽  
Connective Tissues ◽  
Selective Preservation ◽  
Range Of Variation

Modern Nautilus, in natural and laboratory settings, scavenges both dead and molted decapod crustaceans. Ingestion of palinurid lobster exuviae by Nautilus follows a specific pattern in which the cephalopod consumes the exoskeleton beginning at the posteriormost part of the abdomen and continuing anteriorly. During the ingestion process, the cephalothorax is least likely to be consumed, either because the Nautilus may abandon the remains, or the cephalothorax may become separated from the abdomen at its weakest point, the articulation of the cephalothorax with the abdomen. Examination of 767 fossil lobster specimens from 50 formations, 41 of Cretaceous age, demonstrates that the fossil record of lobsters, the preponderance of which appear to be exuviae, is strongly biased in favor of cephalothoraxes. Observations on Nautilus suggest that anatomically selective scavenging by ancient cephalopods, both nautiloids and ammonoids, may explain, in part, the selective preservation of lobster cephalothoraxes over abdomens. Despite the range of variation in jaw morphologies among ammonoids, probably most could have fragmented and ingested decapod remains. Evidence for selective scavenging in the geologic past is purely circumstantial; no cephalopod bitemarks have been identified on fossil lobster exuviae. Pre-burial decomposition of connective tissues and subsequent disarticulation of the abdomen in the absence of scavenging may also have contributed significantly to the observed anatomical taphonomic bias.

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