2. The Devonian is a geologic period and system
of the Paleozoic Era spanning from the end of
the Silurian Period, about 419.2 ± 3.2 Mya
(million years ago), to the beginning of the
Carboniferous Period.
Devonian period is also known as “ mother of
diversification” ,because maximum
diversification of land plant occurred during
this period ,except angiosperms all forms
were present.
3. The Rhynie Chert in Scotland is a Devonian
age deposit containing fossils of both
zosterophylls and trimerophytes, some of the
earliest vascular plants. This indicates that
prior to the start of the Devonian, the first
major radiations of plants had already
happened. The oldest known vascular plants
in the Northern Hemisphere are from the
Devonian Period.
4. Harlan P. Banks
He was the first to
propose abandoment of
the Psilophytales, which
had become a repository
for all types of unrelated
early plants. In its place
he established three
subdivisions ,-
Rhyniophytina
Zosterophyllophytina
Trimerophytina
5. Rhyniophytina can be characterised by
dichotomously branched, naked aerial axes
with terminal sporangia.
The aerial axes arise from horizontal,
dichotomizing rhizomes that bear rhizoids ;
no true roots are known.
Spores are all of the same morphological
type, and hence the plants are considered
homosporous.
6. Only the sporophyte
phase of cooksonia is
currently known (i.e.
the phase which
produce spores rather
than gametes).
7. “First vascular land
plant” .(devonian).
Terminating first
hemispherical
sporangia.
It could survive
unfavourable
condition i.e. oxygen
evolve from hydrosphere
to the atmosphere, in this
way ozone layer was
formed.
8. The Rhynie chert is an
Early Devonian
sedimentary deposit
exhibiting extraordinary
fossil . It is exposed near
the village of Rhynie,
Aberdeenshire, Scotland.
The Rhynie chert
contains exceptionally
preserved plant, fungus,
lichen and animal
material preserved in
place by an overlying
volcanic deposit.
9. Rhynie chert section
Section of Rhynie chert
showing closely spaced
upright axes and
matrix (Devonian).
10. Trench exposing Rhynie
chert bed.
This fossil bearing rock
consists of a fine
grained chert that is
now regarded as
coming from the upper
part of the lower
devonian, and dated at
approximately 400
million yrs ago.
11. Robert Kidston (1917-
1921)
Kidston and Lang (1917-
1921), described four
plant taxa,
Rhynia major
R. gwynne-vaughanii
Hornea lignieri and
Asteroxylon mackiei
All of the RHYNIE CHERT
gametophytes contain
conducting cells and
mycorrhizal.
12. The gametophytes of
Rhynia are
dioicous,bearing male
and female
gametangia, antheridia
and archegonia on
different axes. A
significant finding is
that the axes were
vascular.
13. R. Major (Aglaophyton
major)
Its new name is
Aglaophyton major (by D.S.
EDWARDS 1986) and best
known plant from Rhynie
chert.
Rhynia are all small plants,
lacking leaves and roots,
and bearing terminal
sporangia on branching
axes, approximately 18 cm
in height and branches
dichotomously. It appears
to have a creeping rhizome.
Sporangia are fusiform
14. Life history
Suggested life history of
Aglaophyton major showing
stages in the development
of the dimorphic
gametophytes.
Mature sporophyte bear
sporangia with spores of
two types.
Blue spores develop into
antheridiophores and
orange spores develop into
archegoniophores(From
Taylor et al , 2005)
15. The Lyonophyton rhyniensis is the
gametophyte of A. major, i.e. unisexual
antheridiophore – gametophytes that bear
antheridia and archegoniophores –
gametophytes that bears archegonia (Remy
and Hass ,1996)
16. A. major
Aglaophyton major. (A)
Whole plant
reconstruction showing
rhizome and vertical
axes. (B) Cross section
showing "protostele", (C)
sporangium in
longitudinal section with
spores inside. (D)
Lyonophyton rhyniensis,
the suggested
gametophyte of
Aglaophyton.
17. (A) Whole plant reconstruction,
and (B) schematic protostele in
transverse section
Rhynia gwynne-vaughanii has
a distinct protostele composed
of distinct phloem and xylem
cells. The cortex is composed
of parenchyma with abundant
air spaces that resemble the
spongy mesophyll of leaves and
so may have functioned for
photosynthesis. Sporangia are
generally fusiform and located
at branch tips. The presence of
terminal sporangia and
possible archegonia on the
same plant have raised the
possibility of a bryophyte-like
life history.
18. The gametophyte phase is called Remyophyton
delicatum (Kerp et al ,2004) and consists of a dense
cluster of greater than 200 unbranched axes, 0.2-0.7
mm in diameter with the basal region represented by
globular prothalli (protocorms) bearing rhizoids.
Gametophytes are unisexual –either
archegoniophores or antheridiophores.
Archegoniophores are larger (10-15 mm long) and
bear massive archegonia with long protruding neck .
Antheridiophores are smaller (4-8 mm long) with
stalked antheridia arising from the flattened upper
surface .
Conducting tissue is made up of” s” type element.
19. (A) Whole plant reconstruction;
(B) schematic protostele; (C)
sporangia. (D) Langiophyton
mackiei, the suggested
gametophyte of Horneophyton.
A vascular plant with
dichotomously-branched
above-ground axes that
terminate in sporangia. This
plant differs from all other
Rhynie Chert plants in having
a corm-like base bearing
numerous rhizoids.
Furthermore,Horneophyton
also appears to have a free-
living gametophyte,
Langiophyton (Figure D).
Although poorly known, this
vascular plant was probably
about 6 cm tall with cup-like
terminal structures bearing
archegonia. Horneophyton
and Langiophyton are linked
by epidermal features and
the detail of conducting
cells.merous rhizoids.
20. Reconstruction of Asteroxylon
mackiei (devonian)
Most complex element in
the Rhynie chert flora.
It is characterised by
numerous small flaps of
tissue(leaflike appendages
or enations) that cover the
aerial stem ,as well as a
more complex central strand
and conducting system.
Asteroxylon mackiei was
homosporous like the other
rhynie chert plants,but the
sporangia were located
laterally along the stem ,not
apically,as in the other
taxa.
The gametophyte of A.
mackiei remain unknown.
21. Suggested reconstruction of
Nothia aphylla (devonian)
From Daviero-Gomez et
al,(2004).
It had branching
horizontal underground
stems (rhizomes) and
leafless aerial stems
(axes) bearing lateral and
terminal spore-forming
organs (sporangia). Its
aerial stems were covered
with small 'bumps'
(emergences), each
bearing a stoma.
The plant described as
Kidstonophyton discoides
is possibly the male
gametophyte of Nothia
aphylla
22. The zosterophyllophytes (or zosterophylls)
are the second major group of vascular plants
established by Banks (1975),as the
Zosterophyllophytina.
Zosterophyllophytes characterised from the
other early vascular plant is the presence of
sporangia that are borne laterally along the
stem; they may either be sessile or attached
by short branches.
23. All Zosterophyllophytes are homosporus
,although the size range of the spores can be
rather extensive in some devonian forms, e.g.
are Barinophyton and Protobarinophyton(each
sporangium contains both large and small
spores.
24. (A). A detail of the stem (B)
shows that it had a protostele.
Zosterophyllum, an
early Devonian plant,
has a naked axis, some
sterile and some fertile
25. Sawdonia ornata
The axes are 3 - 10 mm
wide (mostly 5 mm or less)
and they show, like the
previous plant,
pseudomonopodial
branching.
The side axes are borne
alternating left and right,
growing at a rather sharp
angle but bending till they
grow nearly parallel to the
main axis. It is striking that
the main axis and the side
branches are lie in one
plane.
: Reconstruction of the
plant after Gensel &
Andrews (1984)
26. Sawdonia is a member
of the zosterophylls.
This group is thought to
have some relationship
to the lycopods, either as
lycopod ancestors or as
their sister group.
numerous spiny enations
that typically cover the
surface of these plants
27. Trimerophytopsida (or Trimeropsida) is a class of
early vascular plants from the Devonian,
informally called trimerophytes. It contains
genera such as Psilophyton. This group is
probably paraphyletic, and is believed to be the
ancestral group from which both the ferns and
seed plants evolved.
Genera:- Psilophyton, Trimerophyton
†
29. Fossil and
reconstruction both are
showing.
Pertica quadrifaria (the
type species of the
genus) was described in
1972 from compression
fossils found in the
Trout Valley Formation
of northern Maine, USA.
terminal branchlets
bore masses of erect
paired, ellipsoidal
sporangia in distinctive
tight clusters.
30. Psilophyton is a genus of extinct vascular plants.
Described in 1859, it was one of the first fossil
plants to be found which was of Devonian age
(about 420 to 360 million years ago). Specimens
have been found in northern Maine, USA; Gaspé
Bay, Quebec and New Brunswick, Canada; the
Czech Republic; and Yunnan, China. Plants lacked
leaves or true roots; spore-forming organs or
sporangia were borne on the ends of branched
clusters. It is significantly more complex than
some other plants of comparable age (e.g.
Rhynia) and is thought to be part of the group
from within which the modern ferns and seed
plants evolved
31. Psilophyton dawsonii
P. princeps
P. crenulatum
P. dapsile
P. primitivum
P. forbesii is the largest known species of
Psilophyton.
Psilophyton is a genus of trimerophytes, the early
land plant group that we think is derived from the
rhyniophytes and which we believe gave rise to most
of the later vascular plant groups (except the
lycopods), including the ferns, horsetails and
progymnosperms. Progymnosperms in turn gave rise
to the seed plants, including, ultimately angiosperms
32. Its sporangia are
clustered together and
have a twisting
dehisence mechanism.
33. P. dawsonii is one species
that shows internal anatomy.
Here you see the axis in
cross section.
The central area is the
mesarch protostele that
characterizes this group.
Protoxylem strands are a
little difficult to make out,
but they occur at several
spots along the center of the
axis.
Outside the xylem is a zone
where tissues are poorly
preserved, which probably
represents the phloem and
possibly inner cortical zones.
The band of tissue to the
outside of this is the cortex,
with a uniseriate epidermis
on the surface.
34. . There are a variety of
species of Psilophyton
that vary in features of
their branching and
presence or absence of
enations, and other
characters
35. P. princeps, the first-
discovered species,
differed from
P. dawsonii in having
spines on the stems and
larger sporangia.
Reconstructions suggest
a height of around
60 cm. Its stems were
bare of spines but
marked by longitudinal
striations. Compared to
P. dawsonii, P.princeps
. had a greater
distinction between
main stems and side
branches, which may be
considered an 'advanced'
feature.
36. By the Devonian Period, colonization of the land
was well underway. Before this time, there was no
organic accumulation in the soils, resulting in
soils with a reddish color. This is indicative of the
underdeveloped landscape, probably colonized
only by bacterial and algal mats.
By the start of the Devonian, early terrestrial
vegetation had begun to spread. These plants did
not have roots or leaves like most plants today,
and many had no vascular tissue at all. They
probably spread vegetatively, rather than by
spores or seeds, and did not grow much more
than a few centimeters tall. These plants included
the now extinct zosterophylls and trimerophytes.
37. By the Late Devonian, lycophytes, sphenophytes,
ferns, and progymnosperms had evolved. Most of
these plants have true roots and leaves, and
many grew quite tall.
The progymnosperm Archaeopteris was a large
tree with true wood. It was the oldest known tree
until the 2007 identification of Wattieza in 2007.
By the end of the Devonian, the first seed plants
had appeared. This rapid appearance of so many
plant groups and growth forms has been called
the "Devonian Explosion." Along with this
diversification in terrestrial vegetation structure,
came a diversification of the arthropods.
38. Thomas N. Taylor
H.P. Banks
Taylor and taylor
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