Vase-shaped microfossil (VSM) assemblages from early diagenetic carbonate nodules in >742 ± 6 Ma black shales of the 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, nine new species and eight new genera of VSMs are described, augmenting the eight species and two genera already recognized. Taxa described here areMelanocyrillium hexodiademaBloeser, 1985,Trigonocyrillium horodyskii(Bloeser, 1985) n. comb.,T. fimbriatum(Bloeser, 1985) n. comb.,Cycliocyrillium simplexn. sp.,C. torquatan. sp.,Bonniea dacrucharesn. sp.,B. pytinaian. sp.,Trachycyrillium pudensn. sp.,Palaeoarcella athanatan. sp.,Hemisphaeriella ornatan. sp.,Bombycion micronn. sp., andMelicerion poikilonn. sp. All of the test characters observed in VSM taxa (e.g., collars; indentations; hexagonal symmetry; lobed, triangular or invaginated apertures; curved necks) occur in modern testate amoeban taxa, though not always in the same combinations. Some VSM species have characters found today in diverse extant taxa, making it difficult to assess their relationships. A few species, however, have character combinations that closely approximate those found in specific genera of both lobose and filose testate amoebae, suggesting that at least stem group, and possibly crown group, representatives of these taxa were present ∼742 Ma.These fossils indicate that ecosystems were diverse and complex, that eukaryotic biomineralization had already evolved, and that the last common ancestor of animals+fungi had already appeared by ∼750 Ma.

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Vase-shaped microfossil (VSM) assemblages from early diagenetic carbonate nodules in Ͼ742 Ϯ 6 Ma black shales of the 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, nine new species and eight new genera of VSMs are described, augmenting the eight species and two genera already recognized. Taxa described here are Melanocyrillium hexodiadema Bloeser, 1985, Trigonocyrillium horodyskii (Bloeser, 1985) n. comb., T. fimbriatum (Bloeser, 1985) n. comb., Cycliocyrillium simplex n. sp., C. torquata n. sp., Bonniea dacruchares n. sp., B. pytinaia n. sp., Trachycyrillium pudens n. sp., Palaeoarcella athanata n. sp., Hemisphaeriella ornata n. sp., Bombycion micron n. sp., and Melicerion poikilon n. sp. All of the test characters observed in VSM taxa (e.g., collars; indentations; hexagonal symmetry; lobed, triangular or invaginated apertures; curved necks) occur in modern testate amoeban taxa, though not always in the same combinations. Some VSM species have characters found today in diverse extant taxa, making it difficult to assess their relationships. A few species, however, have character combinations that closely approximate those found in specific genera of both lobose and filose testate amoebae, suggesting that at least stem group, and possibly crown group, representatives of these taxa were present ϳ742 Ma. These fossils indicate that ecosystems were diverse and complex, that eukaryotic biomineralization had already evolved, and that the last common ancestor of animalsϩfungi had already appeared by ϳ750 Ma.

The Testaceafilosia includes amoebae with filopodia and with a proteinaceous, agglutinated or siliceous test. To explore the deeper phylogeny of this group, we sequenced the small subunit ribosomal RNA coding region of 13 species, including the first sequence of an amoeba with an agglutinated test, Pseudodifflugia sp. Phylogenetic analyses using maximum parsimony and maximum likelihood methods as well as neighbor joining method yielded the following results: the order Euglyphida forms a monophyletic lineage with the sarcomonads as sister group. The next related taxa are the Chlorarachnea and the unidentified filose strain N-Por. In agreement with the previous studies the Phytomyxea branch off at the base of this lineage. The Monadofilosa (Testaceafilosia and Sarcomonadea) appear monophyletic. The Testaceafilosia are polyphyletic, because Pseudodifflugia sp. is positioned as the sister taxon to the sarcomonads. Within the order Euglyphida Paulinella branches off first, together with Cyphoderia followed by Tracheleuglypha. In maximum likelihood and neighbor joining analyses, the genus Euglypha is monophyletic. The branching pattern within the order Euglyphida reflects the evolution of shell morphology from simple to complex built test.

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