Testate amoebae in the Neoproterozoic Era: evidence from vase-shaped microfossils in the Chuar Group, Grand Canyon

By S. Porter, Andrew H. Knoll. Paleobiology, 2000

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Abstract Vase-shaped microfossils (VSMs) occur globally in Neoproterozoic rocks, but until now their biological relationships have remained problematic. Exceptionally preserved new populations from the uppermost Chuar Group, Grand Canyon, Arizona, display details of morphology and taphonomy that collectively point to affinities with the testate amoebae. The fossils are tear-shaped tests, ∼20–300 μm long and ∼10–200 μm wide, that are circular in transverse section, expand aborally toward a rounded or slightly pointed pole, and taper orally toward a “neck” that ends in a single aperture. Apertures may be circular, hexagonal, triangular, or crenulate, and may be rimmed by a distinct collar. Approximately 25% of the Chuar VSMs are curved, such that the oral and aboral poles do not lie opposite each other. Tests are preserved as mineralized casts and molds, commonly coated with organic debris or iron minerals, but they were originally composed of nonresistant organic matter. Approximately 1% have a “honeycomb-patterned” wall attributable to the original presence of mineralized scales whose bases were arranged regularly in the test wall. Scale-bearing testate amoebae, such as members of the Euglyphidae, are essentially identical to the honeycomb VSMs, and a close relationship between other Grand Canyon VSMs and additional testate amoebae, both lobose and filose, is likely. The VSM population therefore most likely represents a multispecies assemblage whose spatial association reflects a common habitat and/or taphonomic circumstances that favor test preservation. The assignment of these fossils to the testate amoebae strengthens the case for a major diversification of eukaryotic organisms by mid-Neoproterozoic times and, more significantly, provides the earliest morphological evidence for heterotrophic eukaryotes in marine ecosystems.

Subfields: Atmospheric Science, Molecular Biology, Paleontology

View Paper: https://www.semanticscholar.org/paper/963c85d0ad2ce167191838b61efb3f62fa3e26b7

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Citations in the corpus

Biomineralization and Evolutionary History (2003, neutral): “At present, the oldest inferences of protistan biomineralization come from vaseshaped tests preserved in 742±6 million year old rocks of the Chuar Group, Grand Canyon, Arizona (Porter and Knoll 2000; Porter et al. 2003).”
The hierarchical structure of organisms: a scale and documentation of a trend in the maximum (2001, background): “…1997) Grypania; spirally coiled eukaryotic cell 3a Han and Runnegar 1992 Negaunee Fm., Michigan 2100 (Han and Runnegar 1992) to 1850 (Porter and Knoll 2000) Bangiophyte red alga; unbranched uniseriate filaments 3b Butterfield et al. 1990 Hunting Fm., Somerset Island, Canada 1250 to…”
The Laurentian record of Neoproterozoic glaciation, tectonism, and eukaryotic evolution in Death Valley, California (2013, background): “The former exhibit oval or spheroidal shapes extending into a neck or tapering to a point and share features reported previously for VSMs (Marti-Mus and Moczydlowska, 2000; Porter and Knoll, 2000) (Figs.”
The Proterozoic Record of Eukaryotes (2015, background): “…as a crown group Vaucherian (chromalveolate) alga, ca. 800Ma Proterocladus, interpreted as a crown group green alga (Butterfield 2004; 2011), and ca. 742Ma VSM taxa from the Chuar and Callison Lake formations representing amoebozoans and rhizarians (Porter and Knoll 2000; Strauss et al. 2014).”
A review of current testate rhizopod (thecamoebian) research in Canada (2002, background): “Recently, a well preserved PALAEO 2789 21-5-02 multispecies fauna made up of the molds of testate amoebae characterized by tests comprised of scales and proteinaceous walls has been reported from neoproterozoic rocks of the Chuar Group, Grand Canyon Arizona (Porter and Knoll, 2000).”
The rise of predators (2011, background): “1B and 1C; Porter and Knoll, 2000; Porter et al., 2003); the mid-Neoproterozoic Tenuocharta cloudii, a multicellular, sheet-like fossil whose calcareous cell walls may refl ect primary (Horodyski and Mankiewicz, 1990) or early diagenetic (Knoll, 2003) mineralization; and ca. 650 Ma millimeter- to…”
The oxygenation of the atmosphere and oceans (2006, neutral): “The transport of organic matter into the deep oceans was also augmented by the development of organisms such as the vase-shaped microfossils (VSM) with tests consisting of 1 to more than 10 m m silica scales (Porter & Knoll 2000; Porter et al .”
The Evolution of Plant Body Plans—A Biomechanical Perspective (2000, background): “By late Mesoproterozoic or early Neoproterozoic time, the major radiation events distinguishing modern-day eukaryote lineages had already taken place (Knoll, 1995; Porter and Knoll, 2000).”
A basin redox transect at the dawn of animal life (2012, background): “This apparent radiation includes the first unequivocal appearances of groups such as the vase-shaped microfossils, interpreted to be related to lobose, and perhaps filose, testate amoebae (Porter and Knoll, 2000; Porter et al., 2003), scale microfossils of uncertain phylogenetic affinity (Cohen et a”