Vase‐shaped microfossils from the Tonian Callison Lake Formation of Yukon, Canada: taxonomy, taphonomy and stratigraphic palaeobiology

Abstract

Vase-shaped microfossils (VSMs), interpreted as the remains of testate amoebae, are found in late Tonian sedimentary rocks around the world. Here we explore the taxonomy, taphonomy and stratigraphical occurrence of VSMs from the Callison Lake Formation of the Coal Creek inlier, Yukon, Canada. Found in silicified black shale horizons and stromatolitic dolostone, sedimentological data suggest these VSMs inhabited a series of marine embayments characterized by lagoonal and/or shelf interior depositional environments. The fossiliferous strata have recently been dated with Re-Os geochronology at c. 753-740 Ma, which indicates they are not only coeval with diverse VSM assemblages described in the Chuar Group of Grand Canyon, Arizona, but also provides supportive evidence for the early diversification of eukaryotic clades prior to the Sturtian age Snowball Earth event (c. 717-660 Ma). Petrographic examination of well-preserved specimens reveal taxa comparable to those from the Chuar Group, as well as two previously undescribed species. Species overlapping with Chuar Group VSMs are Bonniea dacruchares, Bonniea pytinaia, Cycliocyrillium simplex, Cycliocyrillium torquata, Melanocyrillium hexodiadema and Palaeoarcella athanata. New taxa described here are Bonniea makrokurtos and Cycliocyrillium rootsi. Energy dispersive x-ray spectroscopic data reveal that the Callison Lake microfossils are preserved through a variety of taphonomic pathways, including silicification, infilling, authigenic mineralization and dolomitization. We explore the utility of M. hexodiadema as a latest Tonian biostratigraphical marker and examine the role of Callison Lake sequence stratigraphy as a control on the distribution and abundance of VSMs in the Coal Creek inlier and other global sedimentary successions.

Phylogenomics and Morphological Reconstruction of Arcellinida Testate Amoebae Highlight Diversity of Microbial Eukaryotes in the Neoproterozoic

“…The Organoconcha ancestral is comparable to the genus Paleoarcella from the Chuar Group [32], in general shape and form, while additionally showing a hypothetical organic composition, as has been previously speculated for Paleoarcella and other VSMs [9,33]. The Glutinoconcha reconstructed ancestral shares many similarities with the genus Cycliocyrillium, described originally for the Chuar Group in the Grand Canyon, USA (730 mya [9,27,32], later reported for both the Urucum Formation in Central Brazil (889-706 mya [11]) and the Callison Lake Formation in Canada (756-740 mya [10]). These are oval shaped in lateral view, with a circular aperture, for which there are diverging interpretations about the original composition: some authors arguing for an agglutinated shell [11], while others argue for an originally organic shell [32]; alternatively, the genus Trigonocyrillium, also described for the Chuar Group [9,32], has very similar overall shape.…”

“…The presence of a hard part also increases possibilities of fossilization: examples of fossil shells range from Foraminifera, widely used as index fossils in the Phanerozoic, to the lesser known but older vase-shaped microfossils (VSMs) found as far back as the Tonian period in the Neoproterozoic (1,000-720 million years ago) [9]. Recent studies have demonstrated that Neoproterozoic microfossils are more common, abundant, and diverse than previously thought [10][11][12], thus indicating that the planet was supporting eukaryotic life before and during Snowball Earth events (Cryogenian period) [13]. However, interpreting the phylogenetic affinities of Neoproterozoic microfossils is still an ongoing exercise.…”

After the boring billion and before the freezing millions: evolutionary patterns and innovations in the Tonian Period

“…Important Tonian microfossils that have the potential to shed light on evolutionary innovations include the following: (1) various ornamented acritarchs such as Trachyhystrichosphaera ( Figure 3A), Culcitulisphaera, and Cerebrosphaera, which are widely accepted as eukaryotic organisms [33][34][35][36][37]; (2) multicellular eukaryotes such as Proterocladus ( Figure 3B), which has been interpreted as a siphonous green alga [38]; Palaeovaucheria ( Figure 3C) and Jacutianema, which have been interpreted as putative xanthophytes or members of the stramenophiles ( [39,40], but see [41]); and Cheilofilum, which has been compared with the extant ascomycete fungus Annellophora ( [42], but see [41]); (3) vase-shaped microfossils or VSMs ( Figure 3D) that have been interpreted as members of amoebozoans and rhizarians [43][44][45]; (4) apatitic scale microfossils or ASMs ( Figure 3E) that are interpreted as remains of biomineralizing eukaryotes [46].…”

Insights into vase-shaped microfossil diversity and Neoproterozoic biostratigraphy in light of recent Brazilian discoveries

“…Morphologically, VSMs are hollow structures, approximately 100 microns in maximum dimension, with a single aperture; they may be discoidal, spheroidal to ovoid, or vase-to flask-shaped, with organic or diagenetically (and possibly biogenically) mineralized walls, some possibly covered originally by scales and some with a collar or neck-like oral extension (Bloeser et al, 1977;Knoll and Vidal, 1980;Knoll and Calder, 1983;Green et al, 1988;Turner et al, 1998;Martí Mus and Moczydłowska, 2000;Porter and Knoll, 2000;Sergeev and Schopf, 2010;Strauss et al, 2014;Cohen et al, 2017;Moczydłowska et al, 2017;Morais et al, 2017;Riedman et al, 2017). Most are preserved as casts and molds (Bloeser et al, 1977;Knoll and Vidal, 1980;Knoll and Calder, 1983;Bloeser, 1985;Porter and Knoll, 2000;Sergeev and Schopf, 2010;Riedman et al, 2017), although carbonaceous remains of originally organic test walls have been reported as rare occurrences in some assemblages (Knoll and Calder, 1983;Bloeser, 1985; Morais et al-Vase-shaped microfossil diversity and biostratigraphy Knoll et al, 1991;Cohen et al, 2017;Riedman et al, 2017) but predominate in the Urucum Formation (Morais et al, 2017). It is widely accepted (although not necessarily correct) that the 18 described species of VSMs form a polyphyletic grouping, possibly related to extant testate amoebae found within the Rhizaria and Amoebozoa (Schopf, 1992;Porter and Knoll, 2000;Porter et al, 2003).…”