Another filamentous alga in the Rhynie
chert
The alga filaments described
here have been seen on a cut face of only one chert sample on an area
of about 1mm2, as
essentially covered by Fig.1. They
seem to be liable to fragmentation, possibly due to partial decay.
Apparently the decay had affected the cells differentially: Most of
them seem to are more or less shrunken but some seem to are not
(Fig.2). Even one of the best-preserved cells (Fig.2) does not reveal
what has happened to its content prior to and during silicification,
and what to think of its fossil content.
Owing
to their rare presence in the Rhynie chert, filamentous algae (other
than
charophytes or cyanobacteria) seem to have been investigated only once
[1] and never since*. The
cell sizes of this alga differ significantly from those of either
species described in [1]. Considering that the narrower cells in Fig.1
may have shrunken, the original width and length seem to be about 20µm
and up to 50µm.
For comparison, the cells of Mackiella
rotundata [1]
are much wider, 28-40µm, and shorter, 23-41µm.
The cells of Rhynchertia punctata
[1] are narrower, 8-16.5µm, and shorter,
16-40µm. Hence, this alga may be regarded as a
not yet described species
Fig.1: Randomly arranged filamentous alga fragments in
chert. Image width 1.3mm.
Fig.2 (below): Detail of Fig.1 (right of the
middle), cells in various states of decay. Image width 0.2mm. Photograph : Gerd Schmahl, Dresden.
Sample in
the collection of Steffen
Koehler, Meissen,
collected decades ago by
Brian Beveridge, Gloucester,
on the now protected site
formerly owned by A.G.
Lyon,
Rhynie, documented here under the label Rh2/301.2
.
* Annotation 2020: Incidentally, this contribution appeared nearly
simultaneously with a
more detailed publication on filamentous algae in the Rhynie chert [2].
That publication concerns a species which seems to be simlar to the present
one.
Size data have been mistaken in [2], Fig.3: The cells in Fig.3a and b are
seen in Fig.3e and k again but their alleged sizes differ by a factor
of 4.
H.-J.
Weiss
2019 2020
[1] David S. Edwards, A.G.
Lyon: Algae from the
Rhynie Chert. Bot. J. Linnean Society 86(1983),
37-55.
[2] C.H. Wellmann, L.E.
Graham, L.A. Lewis: Filamentous
green algae from the Early Devonian Rhynie chert. PalZ 93, 387–393
(2019).
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