Thecamoebians (Testate Amoebae) Straddling the Permian-Triassic Boundary in the Guryul Ravine Section, India: Evolutionary and Palaeoecological Implications

Abstract

Exceptionally well-preserved organic remains of thecamoebians (testate amoebae) were preserved in marine sediments that straddle the greatest extinction event in the Phanerozoic: the Permian-Triassic Boundary. Outcrops from the Late Permian Zewan Formation and the Early Triassic Khunamuh Formation are represented by a complete sedimentary sequence at the Guryul Ravine Section in Kashmir, India, which is an archetypal Permian-Triassic boundary sequence [1]. Previous biostratigraphic analysis provides chronological control for the section, and a perspective of faunal turnover in the brachiopods, ammonoids, bivalves, conodonts, gastropods and foraminifera. Thecamoebians were concentrated from bulk sediments using palynological procedures, which isolated the organic constituents of preserved thecamoebian tests. The recovered individuals demonstrate exceptional similarity to the modern thecamoebian families Centropyxidae, Arcellidae, Hyalospheniidae and Trigonopyxidae, however, the vast majority belong to the Centropyxidae. This study further confirms the morphologic stability of the thecamoebian lineages through the Phanerozoic, and most importantly, their apparent little response to an infamous biological crisis in Earth’s history.

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

“…; Singh et al . ) and as VSMs are a polyphyletic categorization, taxonomic differences are also likely. The wide variety of preservational windows available for Neoproterozoic VSMs, including those documented herein, suggest that it was not the closing of a taphonomic window, but other factors (perhaps changing ecosystem preferences to lacustrine environments, extinction, or selection for non‐testate amoeba) that led to the disappearance of characteristic high diversity Neoproterozoic VSM assemblages from the fossil record.…”

“…There is a Phanerozoic fossil record of testate amoebae, but these fossils differ in their morphology, taxonomy and taphonomy from those found in the Neoproterozoic (Singh et al . ).…”

Testate Amoebae in the 407-Million-Year-Old Rhynie Chert

“…The Phanerozoic fossil record of terrestrial amoebozoans is meager, comprising a handful of well-documented records (e.g., [35] and references therein; [36]). Until now, the oldest widely accepted fossils of terrestrial arcellinids came from upper Permian fluvial rocks that contain species assigned to the families Arcellidae, Centropyxidae, Plagiopyxidae, Difflugidae, and Trigonopyxidae [36,37]. Freshwater species of the families Centropyxidae and Difflugiidae have also been recorded from Upper Triassic amber [38], and Centropyxidae, Difflugiidae, Hyalosphenidae, and Phryganellidae occur in Cretaceous amber and non-marine shales from Canada, US, and Europe ( [30] and references therein; [35]).…”

Erugomicula, a new genus of Arcellinida (testate lobose amoebae)

“…Stratigraphic range. Although some arcellinidan species have been found in sediments dating as far back as the Permian (Singh et al, 2015), the type species of the new genus Erugomicula bidens has, to date, only been observed in Holocene lacustrine sediments (Medioli and Scott, 1983).…”