HIGH MORPHOLOGICAL DIVERSITY IN NEOPROTEROZOIC VASE-SHAPED MICROFOSSIL ASSEMBLAGES FROM THE CHUAR GROUP, GRAND CANYON: COMPARISONS WITH TESTATE AMOEBAE

Newly discovered vase-shaped microfossil (VSM) assemblages from the >742±6 Ma Chuar Group, Grand Canyon, provide evidence for affinities with testate amoebae. Not only are VSMs exceptionally preserved in Chuar rocks, they exhibit a much higher degree of morphological diversity than was previously known. Using the taxonomy of modern testate amoebae as a guide, we have identified 12 new species of VSMs that augment the eight species already described globally. All of the test characters observed in VSM taxa (e.g., collars; indentations; hexagonal symmetry; lobed, triangular or invaginated apertures; curved necks) are also found in modern testate amoeban taxa, although not always in the same combinations. Some VSM species have characters that are found today in diverse testate amoeban taxa, making it difficult to assess their relationships. A few VSM species, however, have character combinations that closely approximate those found in specific lobose and filose testate amoeban genera, suggesting that at least stem group, and possibly crown group, representatives of these taxa were present 742 Ma.