Australia: The Land Where Time Began

A biography of the Australian continent 

Cambrian Explosion - Lophophorata

Fossil forms of all classes and 14 of the 27 orders of brachiopods have been found in the Cambrian, 10 of the orders appear in the explosion faunas, and all but 1 of the Cambrian orders (Lingulida) are extinct. This is the common pattern of early morphological disparity achievement, and taxonomic breadth, which has been followed over geological time by the loss of major clades. According to the authors1 a large portion of what is now called Stage 2 of the Cambrian was recognised originally in Siberia as the Tomotian stage, characterised by phosphatic sclerites, produced by basal or marginal accretion, that were mm-sized, tommotiids. Scleritomes of several tommotiids that were fully articulated have now been recovered. Eccentrotheca, a tommotiid, had a tubular scleritome, the individual sclerites being fused together and was probably cemented to the substrate (Skovsted et al., 2008); it has been interpreted as a lophophorate tube. Partial scleritomes of Paterimitra, another tommotiid, have revealed that it was conical and that it was also attached to a hard substrate (Skovsted, Holmer et al., 2009). The mineralogy of the organophosphatic shells of tommotiids shows strong similarity to certain brachiopods (Balthasar et al., 2009). A model in which the tommotiids are stem lophotrochozoans of various affinities is suggested by this mineralogy, with the bivalve condition of the skeletons of bivalves originating from the progressive simplification of a benthic, tubular filter feeder that has a composite scleritome; visualisation of the tommotiid animal has been as a stem phoronid in a tube (Skovsted, Balthasar et al., 2009; Skovsted, Brock et al., 2009). Tommotiid sclerites may have achieved a considerable range of scleritome types in the Cambrian, as tommotiid sclerites are quite diverse, and as more specimens are evaluated it is likely the phylogenetic conjectures could change.

Sources & Further reading

  1. Erwin, Douglas H., & Valentine, James W., 2013, The Cambrian Explosion: The Construction of Animal Biodiversity, Roberts & Co., Greenwood Village, Colorado

Author: M. H. Monroe
Last Updated 12/05/2014
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