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(Reference retrieved automatically from Web of Science through information on FAPESP grant and its corresponding number as mentioned in the publication by the authors.)

Carbonaceous and siliceous Neoproterozoic vase-shaped microfossils (Urucum Formation, Brazil) and the question of early protistan biomineralization

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Author(s):
Morais, Luana ; Fairchild, Thomas Rich ; Lahr, Daniel J. G. ; Rudnitzki, Isaac D. ; Schopf, J. William ; Garcia, Amanda K. ; Kudryavtsev, Anatoliy B. ; Romero, Guilherme R.
Total Authors: 8
Document type: Review article
Source: JOURNAL OF PALEONTOLOGY; v. 91, n. 3, p. 393-406, MAY 2017.
Web of Science Citations: 12
Abstract

Vase-shaped microfossils (VSMs) occur in dolomitic extraclasts of indeterminate provenance within the basal diamictite of the Neoproterozoic Urucum Formation (Jacadigo Group) of west-central Brazil, having an age constrained between 889 +/- 44 Ma (K-Ar; basement rocks) and 587 +/- 7 Ma (Ar-40/Ar-39 age of early metamorphic cryptomelane in overlying manganese ore). Early isopachous carbonate cement entombed these VSMs, preserving rare direct evidence of original wall composition that is carbonaceous (now kerogenous) in practically all specimens. Some tests are siliceous or composed of a quartz-kerogen mixture; secondary replacement explains some features of these tests, but original biomineralization seems more likely for others. This interpretation, coupled with test morphology, suggests affinity to arcellinid testate amoebae. Five VSM taxa are recognized in the deposit: Cycliocyrillium simplex Porter, Meisterfeld, and Knoll, 2003, and C. torquata Porter, Meisterfeld, and Knoll, 2003, originally described in the Chuar Group (USA), and three new monospecific genera-Palaeoamphora urucumense n. gen. n. sp., Limeta lageniformis n. gen. n. sp., and Taruma rata n. gen. n. sp. Most of the taxonomically important characteristics of these VSMs occur also in extant testate amoebae, but the combinations of some characters, such as organic-walled tests having exceptionally long necks that exhibit terminal apertures (L. lageniformis n. gen. n. sp.), are evidently novel additions to the known diversity of Neoproterozoic VSMs. Evidence of glacially influenced deposition in the conformably overlying Santa Cruz Formation may indicate that the Urucum Formation slightly preceded or was penecontemporaneous with a major Neoproterozoic glaciation, although the VSM-hosting extraclasts must be older, possibly rivaling the age of the testate amoebae of the Chichkan Formation (766 +/- 7 Ma) that are currently regarded as the oldest record of protists in the geological record. (AU)

FAPESP's process: 13/04585-3 - Deciphering the major trends of molecular and morphological evolution in the Amoebozoa
Grantee:Daniel José Galafasse Lahr
Support type: Research Grants - Young Investigators Grants
FAPESP's process: 13/12852-1 - Taphonomy and systematics of Neoproterozoic vase shaped microfossils from Brazil and their paleoecological and phylogenetic significance
Grantee:Luana Pereira Costa de Morais Soares
Support type: Scholarships in Brazil - Doctorate