title: Mesoproterozoic Archaeoellipsoides:  akinetes of heterocystous cyanobacteria.
abstract: The genus Archaeoellipsoides Horodyski & Donaldson comprises large (up to 135 micrometers long) ellipsoidal and rod-shaped microfossils commonly found in silicified peritidal carbonates of Mesoproterozoic age. Based on morphometric and sedimentary comparisons with the akinetes of modern bloom-forming Anabaena species, Archaeoellipsoides is interpreted as the fossilized remains of akinetes produced by planktic heterocystous cyanobacteria. These fossils set a minimum date for the evolution of derived cyanobacteria capable of marked cell differentiation, and they corroborate geochemical evidence indicating that atmospheric oxygen levels were well above 1% of present day levels 1,500 million years ago.
authors.affiliation: Biological Science Center, Boston University, MA 02215, USA.
authors.forename: S
authors.initials: S
authors.lastname: Golubic
authors.forename: V N
authors.initials: VN
authors.lastname: Sergeev
authors.forename: A H
authors.initials: AH
authors.lastname: Knoll
mesh_terms: D017033:Anabaena; D005075:Biological Evolution; D001900:Boston; D000458:Cyanobacteria; D004783:Environmental Microbiology; D005068:Eutrophication; D005580:Fossils; D019015:Geologic Sediments / Q000032:analysis* / Q000382:microbiology; D009586:Nitrogen Fixation; D010163:Paleontology; D012800:Siberia