Affinities of Early Cambrian acritarchs studied by using microscopy, fluorescence flow cytometry and biomarkers

Examination and chemical analysis of extremely well-preserved microfossils from the Lower Cambrian Lukati Formation in Estonia suggests that acritarch s from among the genera Globosphaeridium, Skiagia, Comasphaeridium and Loph osphaeridium have dinoflagellate affinities. The investigation presents a c ombination of transmitted light microscopy, fluorescence microscopy and flo w cytometry, and biomarker analysis that demonstrates a new method for the investigation of problematic organic-walled microfossils. For the chemical analysis, Lukati Formation acritarchs were separated from prasinophycean ta smanitids by size and then divided into two fractions in accordance with th e intensity of their autofluorescence signal. Biomarker molecules were gene rated by pyrolysis directly from isolated acritarch organic walls and studi ed using gas chromatography-mass spectrometry-mass spectrometry (GC-MS-MS) and metastable reaction monitoring (MRM)-GC-MS. The analysis supported prev iously made suggestions that acritarchs include microorganisms of different biological affinities. All acritarch fractions contain the common steranes (cholestane, 24-methylcholestane and 24-ethylcholestane) that are characte ristic molecules for eukaryotes. However, the dinoflagellate-related biomar kers, dinosterane and 4 alpha-methyl-24-ethylcholestane, were concentrated only in the fraction containing highly autofluorescent acritarchs. Addition al chemical analyses of microfossils from the Lower Cambrian Buen Formation of North Greenland confirmed the presence of the dinoflagellate-related bi omarkers at a second Early Cambrian locality. (C) 2000 Elsevier Science B.V . All rights reserved.