Geoscience Reference
In-Depth Information
Gunflintiaand other filaments
Several different genera have been
described of tiny filamentous forms. In
Gunflintia
, which is the most common
Gunflint fossil, the filaments have
thickened partitions (septa) spaced at
irregular intervals so that the individual
cells are of variable size. The cells are
longer than they are wide, 1-5 microns
in diameter, and the filaments are often
over 300 microns long (
8, 9
).
Animikiea
has
closely spaced septa so that individual cells
are wider than they are long, and are from
7-10 microns in diameter. These filaments
may be up to 100 microns long and the
sheath enclosing the filaments has a
granular appearance. The filaments of
Entosphaeroides
have no dividing septa;
they are 5-6 microns in diameter and up to
100 microns long. Finally,
Archaeorestis
differs from the previous three in that
its filaments are branched. It has no
dividing septa, and possesses characteristic
rugose walls. A bulbous swelling of the
filament wall sometimes occurs randomly;
filament diameter ranges from 2-10
microns and filaments are up to 200
microns long. All these filamentous fossils
resemble modern thread-like bacteria,
including both blue-green cyanobacteria
and siderophile (iron-loving) bacteria
living in iron-rich waters today.
Huroniospora
These tiny fossils are spheroidal to
ellipsoidal unattached bodies with a long
axis 1-16 microns long. The thick wall is
sculptured with a reticulate pattern and
they may have a minute aperture at the
restricted end (
8, 9
). They resemble
coccoidal iron-loving bacteria.
Eoastrion
This is one of the best known of the
Gunflint fossils. A variable number of
septate filaments radiate from a central
body and form a characteristic star shape.
Filaments may be single or branched and
are 1.5 microns in diameter, but only 3-18
microns long (
10
). These 'little dawn stars'
can be compared with extant bacteria that
oxidize iron and manganese in their
metabolism.
Kakabekia
This lovely little fossil has a distinctive
threefold structure consisting of a
spheroidal bulb, a slender stipe, and
an umbrella-like crown. The overall length
is about 12-30 microns (
11, 12
) and
11
12
11 The umbrella-shaped bacteria KakabekiaPC. Length
1230 micron.
12 Reconstruction of
Kakabekia.
Search WWH ::
Custom Search