Micro- and nano-scale ultrastructure of cell walls in Cryogenian microfossils : revealing their biological affinity

• Recently established protocols and methods in advanced microscopy and spectrometry applied to studies of ancient unicellular organic-walled microfossils of uncertain biological affinities (acritarchs) provide new evidence of the fine ultrastructure of cell walls and their biochemistry that support the interpretation of some such microfossils as photosynthesizing microalgae. The micro-scale and nanoscale ultrastructure of the cell walls of late Cryogenian sphaeromorphic acritarchs from the Chichkan Formation (Kazakhstan) revealed by the advanced techniques and studied originally by Kempe et al. (2005) is here further analyzed and compared to that of modern microalgal analogues. On the basis of such comparison, we interpret the preserved cell wall ultrastructure to reflect original layering and lamination within sublayers of the fossil wall, rather than being a result of taphonomic and diagenetic alteration. The outer thick layer represents the primary wall and the inner layer the secondary wall of the cell, whereas the laminated amorphous sub-layers, 10-20 nm in thickness and revealed by transmission electron and atomic force microscopy, are recognized as trilaminar sheath structure (TLS). Because two-layered cell walls, trilaminar sheaths, and the position of the TLS within the fossil cell wall are characteristic of the mature developmental state in cyst morphogenesis in modern microalgae, we infer that the Chichkan sphaeromorphs are likely resting cells (aplanospores) of chlorophyceaen green microalgae from the Order Volvocales.

Subject headings

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Geologi (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geology (hsv//eng)

Keyword

ultrastructure

cell wall

microfossils

Cryogenian

biological affinity

Historical geology and palaeontology

Historisk geologi och paleontologi

Earth Science with specialization in Historical Geology and Palaeontology

Geovetenskap med inriktning mot historisk geologi och paleontologi

Publication and Content Type

ref (subject category)

art (subject category)