Cambrian Chordates and Vetulicolians

@article{McMenamin2019CambrianCA,
  title={Cambrian Chordates and Vetulicolians},
  author={Mark A. S. McMenamin},
  journal={Geosciences},
  year={2019}
}
  • M. McMenamin
  • Published 26 June 2019
  • Environmental Science
  • Geosciences
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… 

Origin of the Chordate Notochord

TLDR
The history of the formation of two main hypotheses for the origin of the notochord, the signature anatomical structure of chordates, are introduced and the current understandings of embryonic development, molecular profile, and gene regulatory networks ofNotochord and notochords-like structures are summarized.

Serial blockface SEM suggests that stem cells may participate in adult notochord growth in an invertebrate chordate, the Bahamas lancelet

TLDR
For the notochord of adult lancelets, a reasonable interpretation of the data indicates growth of the organ is based on stem cells that self-renew and also give rise to progenitor cells that, in turn, differentiate into lamellar cells.

Incentive disengagement and the adaptive significance of frustrative nonreward

TLDR
This article explores a specific adaptive function hypothesis of frustrative nonreward called the incentive disengagement hypothesis, which is to break an attachment to a site, situation, or stimulus that no longer yields appetitive resources to promote the search for rewards in alternative locations.

Ediacaran Biota

References

SHOWING 1-10 OF 87 REFERENCES

Meiofaunal deuterostomes from the basal Cambrian of Shaanxi (China)

TLDR
It is suggested that a key step in deuterostome evolution was the development of lateral openings that subsequently were co-opted as pharyngeal gills in Saccorhytus, which may help to explain the major gap between divergence times seen in the fossil record and estimates based on molecular clocks.

A Pikaia-like chordate from the Lower Cambrian of China

TLDR
A single specimen of a Lower Cambrian chordate, Cathaymyrus diadexus, new genus and species, that is similar to Pikaia but predates it by about 10 million years (Myr).

A new vetulicolian from Australia and its bearing on the chordate affinities of an enigmatic Cambrian group

TLDR
The hypothesis that the free-swimming vetulicolians are the nearest relatives of tunicates suggests that a perpetual free-living life cycle was primitive for tunicates.

Evidence for gill slits and a pharynx in Cambrian vetulicolians: implications for the early evolution of deuterostomes

TLDR
Evidence is argued that evidence points towards vetulicolians being members of the stem-group deuterostomes; a group best known as the chordates but also including the ambulacrarians (echinoderms, hemichordates), and xenoturbellids.

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

TLDR
Observations support an assignment of the banffiids to the vetulicolians, and 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.

THE SYSTEMATICS AND PHYLOGENETIC RELATIONSHIPS OF VETULICOLIANS

TLDR
It is not possible on current evidence to reach an unequivocal conclusion regarding the phylogenetic position of the vetulicolians, but one possibility is that they are a sister group of arthropods that lost limbs but gained gill structures analogous to those of deuterostomes, but several features remain unexplained by this model.

Yunnanozoon and the ancestry of chordates

The oldest known chordate, Yunnanozoon lividum Hou et al. 1991, from the Chengiang Lagerstatte of Yunnan shows several features in its anatomy that had not been expected to occur at this stage of

Cambrian explosion: Birth of tree of animals

  • D. Shu
  • Geography, Environmental Science
  • 2008

Tentaculate Fossils from the Cambrian of Canada (British Columbia) and China (Yunnan) Interpreted as Primitive Deuterostomes

TLDR
The evidence is suggested that the evidence is more consistent with the ambulacraria being primitive deuterostomes, with specific comparisons being made to the pterobranch hemichordates and pre-radial echinoderms.

Head and backbone of the Early Cambrian vertebrate Haikouichthys

TLDR
Phylogenetic analysis indicates that Haikouichthys somewhat resembles the ammocoete larva of modern lampreys, this is because of shared general craniate characters; adult lampreys and hagfishes (the cyclostomes if monophyletic) are probably derived in many respects.
...