Douglas Burbank
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Chuar Group

  Thus far, work on the Chuar Group has focused on exceptionally well preserved and abundant populations of vase-shaped microfossils (VSMs). This work has shown that VSMs have affinities with the testate amoebae (or ‘thecamoebae’), amoebae that make their own shells, or tests, and today are important components of freshwater and terrestrial ecosystems. Recent phylogenetic trees indicate that some testate amoeban clades are closely related to the animals and fungi. Thus, these fossils provide an important calibration for branching events in the eukaryotic crown group. They also provide the earliest evidence for heterotrophic protists, indicating ecosystem expansion by ~750 Ma. Several VSMs exhibit unusual, semicircular holes in their tests, which may reflect the activity of scavengers or predators, suggesting even broader expansion of food web complexity by this time.
 

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The vase-shaped microfossil, Bonniea dacruchares (left; named after Bonnie Bloeser, the first person to study Chuar Group VSMs), and the modern testate amoeba, Cyphoderia ampulla (right). Photo of C. ampulla courtesy of Ralf Meisterfeld
 

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Several species of VSMs exhibiting semicircular holes in their tests. These may reflect the action of predators or scavengers. If anyone has any particular insight into what may have formed these holes, please contact me.

 

Fossil Abundance

  Vase-shaped microfossils are packed cheek by jowl in numerous meter-scale dolomite nodules near the top of the Chuar Group. Estimated abundances are roughly 1,000 to 4,000 individuals per mm3; the volume of one nodule is estimated to be ~ 125,000 mm3; thus VSMs number on the order of 125-500 x 109 per nodule!!
 

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Thin section view of a nodule showing abundant vase-shaped microfossils.
 

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Typical VSM-packed dolomite nodule, exposed near the top of the Chuar Group. Hammer and backpack for scale. Image courtesy of A. H. Knoll.


 

 

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