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 Luükati Formation in Estonia suggests that acritarchs from among the genera Globosphaeridium, Skiagia, Comasphaeridium and Lophosphaeridium have  dinoflagellate affnities. The  investigation  presents  a  combination  of  transmitted  lightmicroscopy,  fluorescence  microscopy and  flow  cytometry,  and  biomarker  analysis  that  demonstrates  a  new  methodfor the investigation of problematic organic-walled microfossils. For the chemical analysis, Lu ̈kati Formation acritarchswere separated from prasinophycean tasmanitids by size and then divided into two fractions in accordance with theintensity  of  their  autofluorescence  signal.  Biomarker  molecules  were generated  by  pyrolysis  directly  from  isolatedacritarch organic walls and studied using gas chromatography–mass spectrometry–mass spectrometry (GC-MS-MS )and  metastable  reaction  monitoring ( MRM )-GC-MS.  The  analysis  supported  previously  made  suggestions  thatacritarchs include microorganisms of diVerent biological aYnities. All acritarch fractions contain the common steranes(cholestane,  24-methylcholestane  and  24-ethylcholestane)  that  are  characteristic  molecules  for  eukaryotes. However,the dinoflagellate-related biomarkers,  dinosterane  and 4a–methyl–24–ethylcholestane, were  concentrated only  in thefraction  containing  highly  autofluorescent  acritarchs.  Additional  chemical  analyses  of  microfossils  from  the  LowerCambrian Buen Formation of North Greenland confirmed the presence of the dinoflagellate-related biomarkers at asecond Early Cambrian locality.