Guadalupian (Middle Permian) megaspores from a permineralised peat in the Bainmedart Coal Measures, Prince Charles Mountains, Antarctica

Abstract

A unique Guadalupian (mid-Permian) megaspore assemblage has been recovered from permineralised peats capping a coal seam in the Bainmedart Coal Measures, Prince Charles Mountains, East Antarctica. The megaspores are exquisitely preserved in three-dimensions and reveal the presence of at least three lycopsid species for which the macrofossil record is at present scant. The megaspores are assigned to three existing genera and in each case represent new species. Duosporites lambertensis sp. nov. and Banksisporites antarcticus sp. nov. are rare and predominantly laevigate trilete megaspores, but D. lambertensis sp. nov. has sparse grana or spinules and a shallow furrow bordering the contact faces, whereas B. antarcticus sp. nov. lacks ornament, has unmodified contact faces and has a more rounded amb. Singhisporites hystrix sp. nov. is the most abundant megaspore in the assemblage and is densely ornamented with elaborately branched, pointed processes. Scanning electron microscopy and X-ray synchrotron tomography reveal a spongy exosporium and no obvious mesosporium; microspores attributable to Lundbladispora sp. adhere to the ornament of S. hystrix sp. nov. — these forms likely representing the microspores and megaspores, respectively, of the same biological species. Although of low diversity, the megaspore assemblage is of similar generic composition to those known from Permian sediments of the Mahanadi Graben, India, and appears typical of high-latitude Gondwanan Glossopteris-dominated peat-forming communities. This lends support to previous palaeogeographic reconstructions of Gondwana that place the Antarctic Lambert Graben as the southern (up-slope) extension of the Mahanadi Graben prior to dispersal of the southern continents.

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Research papers
Guadalupian (Middle Permian) megaspores from a permineralised peat in the
Bainmedart Coal Measures, Prince Charles Mountains, Antarctica
Ben J. Slatera,⁎, Stephen McLoughlinb, Jason Hiltona
aSchool of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
bDepartment of Palaeobotany, Swedish Museum of Natural History, Stockholm, Sweden
a b s t r a c ta r t i c l ei n f o
Article history:
Received 14 May 2011
Received in revised form 12 July 2011
Accepted 15 July 2011
Available online xxxx
Keywords:
Permian
Antarctica
Gondwana
peat
lycopsid
megaspore
A unique Guadalupian (mid-Permian) megaspore assemblage has been recovered from permineralised peats
capping a coal seam in the Bainmedart Coal Measures, Prince Charles Mountains, East Antarctica. The
megaspores are exquisitely preserved in three-dimensions and reveal the presence of at least three lycopsid
species for which the macrofossil record is at present scant. The megaspores are assigned to three existing
genera and in each case represent new species. Duosporites lambertensis sp. nov. and Banksisporites antarcticus
sp. nov. are rare and predominantly laevigate trilete megaspores, but D. lambertensis sp. nov. has sparse grana
or spinules and a shallow furrow bordering the contact faces, whereas B. antarcticus sp. nov. lacks ornament,
has unmodified contact faces and has a more rounded amb. Singhisporites hystrix sp. nov. is the most abundant
megaspore in the assemblage and is densely ornamented with elaborately branched, pointed processes.
Scanning electron microscopy and X-ray synchrotron tomography reveal a spongy exosporium and no
obvious mesosporium; microspores attributable to Lundbladispora sp. adhere to the ornament of S. hystrix sp.
nov. — these forms likely representing the microspores and megaspores, respectively, of the same biological
species. Although of low diversity, the megaspore assemblage is of similar generic composition to those
known from Permian sediments of the Mahanadi Graben, India, and appears typical of high-latitude
Gondwanan Glossopteris-dominated peat-forming communities. This lends support to previous palaeogeo-
graphic reconstructions of Gondwana that place the Antarctic Lambert Graben as the southern (up-slope)
extension of the Mahanadi Graben prior to dispersal of the southern continents.
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
The macrofossil record of lycopsids in Antarctica extends back to at
least the Middle Devonian (Grindley et al., 1980; McLoughlin and
Long, 1994; Xu and Berry, 2008) and continues well into the
Cretaceous (Cantrill, 2001) and, on the basis of dispersedmicrospores,
the group probably persisted in Antarctica into the mid-Cenozoic
(Truswell and Macphail, 2009). Previous studies have concluded that
heterosporous lycopsids constituted a relatively minor component of
Gondwanan Permian peat-forming ecosystems (Diessel, 1992; Glass-
pool, 2000, 2003), although they were locally important in wetland
communities in the early part of the period (Anderson et al., 1999).
This is in marked contrast to their great abundance in peat-forming
communities in the Carboniferous of Europe and North America
(Bateman et al., 1992) and the Permian of China (Wang and Chen,
2001). Although lycopsid macrofossils are relatively rare in Middle to
Late Permian Gondwanan peats, especially those in eastern Gondwana,
research on Triassic strata from the Prince Charles Mountains (PCMs)
demonstrates a resurgence in the abundance of lycopsids following
the P-Tr boundary based on microspore, megaspore and macrofossil
remains (McLoughlin et al., 1997; Lindström and McLoughlin, 2007;
Vajda and McLoughlin, 2007).
The study of fossil megaspores from Gondwana began tentatively
in the 1860's (Carruthers, 1869), but remained confined to a few
isolated studies until the first detailed account by Surange et al.
(1953), which documented mounted Indian megaspores using
reflected light microscopy(Pant andMishra, 1986). Although lycopsid
microspores have been widely employed in Permian biogeography
and biostratigraphy (e.g. Foster, 1982; Césari and Gutiérrez, 2000),
megaspores have remained a somewhat under-utilised tool but they
are likely to have equivalent palaeo-biogeographical and stratigraph-
ical significance and they have found application for local strati-
graphic correlation in some Indian basins (Maheshwari & Tewari
1987; Tewari et al., 2004, 2007, 2009; Tewari, 2008). Furthermore,
their diversity and abundance offer clues to lycopsid diversity in the
source palaeovegetation even in the absence of macrofossil and
microspore evidence (e.g. Bateman and Hilton, 2009).
Thisstudyinvestigatesmegasporespreservedinsilicifiedpeatsfrom
the Bainmedart Coal Measures in the PCMs, East Antarctica. Earlier
studies have investigated the palynology and palaeobotany of the
Review of Palaeobotany and Palynology 167 (2011) 140–155
⁎ Corresponding author. Tel.: +44 1214146151; fax: +44 12144942.
E-mail address: bxs574@bham.ac.uk (B.J. Slater).
0034-6667/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.revpalbo.2011.07.007
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BainmedartCoalMeasures,fromwhichmegasporesfromsiltstonesthat
alternate with coal seams in the Toploje Member were illustrated but
not systematically described by McLoughlin et al. (1997). Megaspores
have also been recovered from the overlying Lower Triassic Ritchie
Member (lower Flagstone Bench Formation) by McLoughlin et al.
(1997)andfromtheUpperTriassicMcKelveyMember(upperFlagstone
INDIA
AUSTRALIA
EAST ANTARCTICA
1
2
3
4
5
PERMIAN BASIN
1
2
3
4
5
MANAHADI BASIN
GODAVARI BASIN
TRANSANTARCTIC MOUNTAINS
SYDNEY BASIN
BOWEN BASIN
PRINCE
CHARLES
MOUNTAINS
ANTARCTIC
PENINSULA
NORTH
NEW ZEALAND
SOUTH
NEW ZEALAND
NEW GUINEA
CAMPBELL
PLATEAU
A
(FB)
Pagadroma Gorge
Snow and ice
2 km
(GG)
Glossopteris Gully
(DT)
(T)
PCM 14
PCM 9
(T)
(RC)
PCM 2
PCM 3
PCM 15
(Pr)
(RC)
B
Battye Glacier
(Pr)
Radok Lake
(Pr)
N
Fault
Collection area
Snow and ice coverage
Flagstone Bench Formation (FB)
Glossopteris Gully Member (GG)
Dragons Teeth Member (DT)
Toploje Member (T)
Radok Conglomerate (RC)
Precambrian metamorphics
and Intrusives (Pr)
Water (lakes and streams)
Fig. 1. A, Map of the position of the Prince Charles Mountains in the Middle Permian in relation to other Glossopteris dominated Permian basins in Gondwana and B, geological map of
the Radok lake area, Prince Charles Mountains, Antarctica. Modified from Anderson (1977), Lawver and Scotese (1987) and McKelvey and Stephenson (1990).
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Bench Formation) by Cantrill and Drinnan (1994). The megaspores
documented here represent the oldest megaspores systematically
described from Antarctica to date, and their significance lies in their
exceptional uncompressed preservation within a permineralised peat.
Exquisite preservation of the mire-dwelling plants in this deposit
revealscrypticelementsof theflorathatarenotpreservedelsewherein
the Lambert Graben succession.
2. Occurrence and geological setting
Samples were collected from the northern Prince Charles Moun-
tains, Antarctica, at several sites along an exposure of silicified peat
that crops out over a strike extent of c. 3 km (Fig. 1B). The silicified
peat is up to 40 cm thick and constitutes the uppermost part of a coal
seam that caps the Toploje Member in the lower part of the
Bainmedart Coal Measures (Fig. 2). The silicified peat is dated as
Roadian–Wordian (Guadalupian: Middle Permian) based on palyno-
logical correlation to the Australian Didecitriletes ericianus Zone
(Lindström and McLoughlin, 2007). Siderite-rich lacustrine sediments
of the Dragons Teeth Member overlie the silicified peat layer (Fielding
and Webb, 1996). The Bainmedart Coal Measures constitute the
middle unit of the Permian-Triassic Amery Group and consist of a
series of cyclic sandstones, siltstones and coals interpreted to have
been deposited in high-energy braided fluvial systems alternating
with extensive low-energy floodbasin mires (Fielding and Webb,
1996; McLoughlin et al., 1997; McLoughlin and Drinnan, 1997a,
1997b; Lindström and McLoughlin, 2007).
The strongly cyclic nature of sedimentation within the Bainmedart
Coal Measures has been attributed to the influence of Milankovitch-
induced climatic forcing by Fielding and Webb (1996). Conformably
overlying the Bainmedart Coal Measures is the Flagstone Bench
Formation, which completely lacks coals and hosts typical Triassic
palynoassemblages and macrofossils (Cantrill et al., 1995; McLoughlin
et al., 1997). McLoughlin et al. (1997) and Lindström and McLoughlin
>320 m
RADOK
CONGLOMERATE
303 m
TOPLOJE
MEMBER
15-25 m
D. T. MBR
c. 880 m
GLOSSOPTERIS
GULLY MEMBER
349 m
GRAINGER
MEMBER
548.5 m
McKINNON
MEMBER
> 550 m
RITCHIE
MEMBER
>139.5
m
JETTY MEMBER
THICKNESSUNIT BOUNDARY CRITERIA
>72 m McKELVEY MBR
Concealed/faulted contact
Transition from lithic sst and
conglomerates to thick qtz-felds
sst and coal
Distinctive package of
sideritic/limonitic
sandstones and shales
Prominent silicified peat bed
(*source of studied material)
Top of last major coal below
thick sandstone succession
Base of first major coal
above thick sandstone
succession
Top of last major coal
Erosional surface
Transition from siltstone- to
sst-dominated succession
Contact concealed/faulted.
(Transition to interbedded
iron-stained, sits.-sst-congl.
succession)
FLAGST. BENCH Fm
BAINMEDART COAL MEASURES
*
Norian
Early-Middle
Triassic
Early
Triassic
Changh-
singian
Wuchia-
pingian
Capitanian
Wordian
Roadian
Kungurian
(part)
AGE
Fig. 2. Stratigraphic column showing the position of the silicified peat bed. Ages after Lindström and McLoughlin (2007), depths after McLoughlin and Drinnan (1997a, b).
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(2007)concludedthatthisbasinincorporatesararecontinuousPermo-
Triassic continental succession and that the Bainmedart Coal Measures
host a continuous record of plant remains through the Middle and Late
Permian. The disappearance of coals at the top of the Bainmedart Coal
Measures(end-Permian)wasinterpretedtorepresentatransitionfrom
humid (in the Permian) to increasingly arid environments in (the
Triassic: McLoughlin et al., 1997; Lindström and McLoughlin, 2007).
The Bainmedart Coal Measures were deposited within half-grabens
that form part of the Lambert Graben system (Fedorov et al., 1982;
Stagg, 1985; McLoughlin and Drinnan, 1996). The Lambert Graben has
been considered to represent the southern (up-slope) extension of the
Mahanadi Graben (or less likely the Godavari Graben) in India since
palaeogeographic reconstructions place the eastern margin of India
adjacent to this part of Antarctica prior to the breakup of Gondwana
(Fedorov et al., 1982; Holdgate et al., 2005; Veevers, 2004; Harrowfield
et al., 2005; Bogor, 2011; see Fig. 1A).
DuringtheMiddlePermian,Antarcticaoccupiedpolarlatitudesanda
centralpositionintheSouthernHemispheresupercontinentGondwana
(Fig. 1A). Gondwana was composed of Antarctica, Australia, New
Zealand,Africa,Madagascar,India,Arabia,SouthAmericaandaseries of
smaller peripheral terranes at this time (Lottes and Rowley, 1990).
During the Early and Middle Permian, the northern PCMs lay at c. 65–
70°S (McLoughlin et al. 1997). This position endows Antarctica with a
key role in understanding the history of the Gondwanan biota. It
provides evidence of the highest-latitude southern forests of the
Permian and its location may have enhanced its role as a dispersal
corridor between the various middle-latitude Gondwanan phytogeo-
graphic subprovinces (Ryberg, 2010).
Plate I. Scanning electron micrographs of Duosporites lambertensis sp. nov. All from site PCM 15. Scale bars=100 μm for 1–3; 10 μm for 4.
1.
2.
Proximal view of megaspore (NRMS089516) showing notably sunken margin of contact areas.
Proximal view of holotype (NRMS089517) showing very fine felt-like ornament, and subtle swellings on the polar regions of the contact faces that may correspond to
papillae on a concealed inner body.
Enlargement of labrae from Pl. I, 2, showing sinuosity at the pole.
Enlargement from Pl. I, 2 showing fine ornament and a weak ridge at perimeter of contact surface.
3.
4.
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3. Materials and methods
Samples from several localities exposing the silicified peat layer
(Fig. 1B) were bulk-macerated in cold 30% HF for 2 weeks. The released
debris was separated from the HF solution using a 150 micron nylon
sieve. The macerated material was then retained in a petri dish with
distilled water for examination with a binocular microscope using
incident and transmitted light. Megaspores were picked with a fine
camel hair brush then mounted on SEM stubs, coated with gold and
studied using a Hitachi S-4300 field emission scanning electron
microscope at the Swedish Museum of Natural History. Spore
morphological terminology used in this study is that of Playford and
Dettmann (1996). All measurements and dimensions provided are
taken from dried specimens illustrated with SEM. Individual mega-
spores shrink to c. 80% of their original (wet) size when dehydrated.
Some additional megaspore cross-sections were recorded in thin-
sections of the permineralised peat (see Holdgate et al., 2005, Fig. 14K)
prepared either with the acetate peel technique (Galtier and Phillips,
1999) or ground thin-sectioning (Hass and Rowe, 1999).
The ornamentation, microspores and internal structures of one
megaspore species were also studied using synchrotron-based X-ray
tomographic microscopy (SRXMT) at the TOMCAT beamline of the
SwissLightSourceatthePaulScherrerInstitute,Switzerland.Specimens
were mounted on 3 mm diameter brass stubs and examined using
the technique outlined by Donoghue et al. (2006). Slice data derived
from the scans (Hintermüller et al., 2010) were then analysed and
Plate II. Scanning electron micrographs of Banksisporites antarcticus sp. nov. Scale bars=100 μm for 1–3; 10 μm for 4.
1.
2.
3.
4.
Proximal view of holotype (NRMS089515; site PCM 15) showing laevigate contact.
Proximal view of megaspore (NRMS089527; site PCM2) showing incomplete development of ridge bounding contact areas.
Oblique view of megaspore (NRMS089518; site PCM 15) showing distal surface (bottom) and lack of curvaturae ridges connecting labrae.
Microfoveolate outer wall of the holotype.
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manipulatedusingAvizosoftwareforcomputedtomography.Thisisthe
most detailed study of megaspores using synchrotron X-ray tomogra-
phy to date, and the first such investigation of post-Carboniferous
megaspores, thus building on the work of Glasspool et al. (2009).
Illustrated specimens are prefixed NRMS or CPC and are stored in
the palaeobotanical collections of the Swedish Museum of Natural
History, Stockholm, and the Commonwealth Palaeontological Collec-
tion, Geoscience Australia, Canberra, respectively.
4. Systematic palaeobotany
4.1. Genus Duosporites Høeg et al., 1955, emend. Glasspool (2003)
4.1.1. Duosporites lambertensis B. J. Slater, S. McLoughlin et J. Hilton sp.
nov. (Plate I, 1–2)
Specific diagnosis: Amb subtriangular, laesurae slightly sinuous and
extending almost to megaspore margin. Labrae broad and rounded,
broadening towards the equator. Curvaturae ridges delimiting contact
areas are marked by short spines or grana. Curvaturae ridges bounded
proximally by a wide, shallow furrow surrounding the domed polar
regionof contactfaces.Bothhemispheres almostlaevigatebutbearing
irregularly spaced, very fine grana and spinula.
Holotype: NRMS089517.
Location, unit and age: Site PCM 15, 1.8 km east of Radok Lake, Northern
PCMs,EastAntarctica;uppermostToplojeMember(Roadian–Wordian),
Bainmedart Coal Measures, Amery Group, Lambert Graben.
Etymology: Named after the Lambert Graben, Antarctica.
Abundance and distribution: Rare (n=2) in the uppermost Toploje
Member.
Description: The description is based on two specimens recovered
from one locality (PCM 15) exposing the silicified peat layer.
The megaspores are trilete, with a convexly subtriangular amb
(Plate I, 1–2). The equatorial diameter is 400–500 μm. The labrae
exhibit one or two slight folds near the pole (Plate I, 3) but are
otherwise straight, extending to the equator or locally projecting as
a weak marginal extension (Plate I, 1–2). Labrae are laevigate–
microfoveolate, 20–30 μm wide for most of their length but
broadening to 60 μm equatorially, c. 20–30 μm high, and of
consistent height across most of the proximal surface, but tapering
abruptly near the margin of the contact areas (Plate I, 1–2). The
curvaturae ridges are distinct and marked by a low file of spinula or
grana (b1.5 μm high; Plate I, 4). Each curvaturae ridge is flanked on
the proximal side by a shallow but wide (50–80 μm wide) furrow,
which surrounds the domed (convex) polar region of the contact
area. Proximal and distal ornamentation of the megaspore is
undifferentiated, consisting of irregular, sparse grana and spinula
typically b0.5 μm wide and b1 μm high. The spore wall is a dense,
porous network of sporopollenin threads (Plate I, 4). The inner
spore body is subtriangular and 230–325 μm in equatorial diameter
and may possess proximal papillae based on the presence of several
weak swellings expressed on the contact faces of the outer spore
wall (Plate I, 2).
Remarks and comparisons: The megaspores are assigned to Duospor-
ites (Høeg et al., 1955 emend. Glasspool, 2003) on the basis of their
subtriangular amb, the extension of the trilete rays to the
megaspore margin and the mostly laevigate nature of the spore
wall; features that are distinctive of this genus. Although only
represented by two specimens, the new taxon can be distinguished
from all other species of Duosporites by its possession of sparsely
spinulose ornament across the entire surface of the megaspore and
by the ridge of short grana and spinula surrounding the contact face
and demarcating the curvaturae ridges. These features are consid-
ered autapomorphic to the species resulting in the erection of
Duosporiteslambertensis sp. nov.
Duosporites lambertensis sp. nov. differs from Duosporites
congoensis Høeg et al., 1955, emend. Glasspool, (Glasspool, 2003)
in the distribution of very short spines across the entire exine
surface endowing it with an almost felt-like texture. In addition, the
furrow surrounding the contact faces is proportionally wider, which
gives the polar regions of the contact faces a more pronounced
domed appearance. The trilete rays are less sinuous than those of D.
congoensis, being straighter near the equator and only having one
or two folds near the pole. The spinulose ornament is similar to that
of Duosporites trivedii (Dijkstra, 1955) Piérart, 1959, emend Glass-
pool, 2003. However the ornament of D. lambertensis (b0.5 μm wide
and b1 μm high) is much smaller than that of D. trivedii (with
verrucae 10–20 μm in basal diameter). Considering their morphol-
ogy, size and age, the megaspores are most likely derived from a
lycopsid (e.g. Glasspool, 2003).
4.2. Genus BanksisporitesDettmann, 1961, emend. Glasspool, 2003
4.2.1. Banksisporites antarcticus B. J. Slater, S. McLoughlin et J.
Hilton sp. nov.
Specific diagnosis: Amb subcircular; laesurae straight to slightly
sinuous, extending to the equator, which is marked by the curvaturae
ridges. Labrae consistent in width throughout their length. Curvaturae
ridges distinct to faint. Exine mostly smooth but with sparse short
grana across the entire megaspore.
Holotype. NRMS089515.
Location, unit and age: Site PCM 15, 1.8 km east of Radok Lake
(Fig. 1B), Northern PCMs, Antarctica; uppermost Toploje Member
Plate III. Scanning electron microscope images of Singhisporites hystrix sp. nov. Scale bars=250 μm for 1 and 3; 100 μm for 2, 4, 5; 50 μm for 6).
1.
2.
3.
4.
5.
6.
Proximal view of megaspore: NRMS089368, site PCM 3 (scale bar=250 μm).
Proximal view of holotype (CPC34312; site PCM 14) showing slight compression of proximal ornament (scale bar=100 μm).
Detail of the contact areas, laesurae and arcuate rim; NRMS089391, site PCM 9 (scale bar=250 μm).
Ornamentation on contact surface; NRMS089404, site PCM 9 (scale bar=100 μm).
Sharply defined change in ornamentation height and structure along arcuate rim connecting equatorial ends of labrae; NRMS089383, site PCM 9 (scale bar=100 μm).
Coarsely spongeous outer spore wall and complex sculptural elements of the proximal surface; NRMS089429, site PCM 2 (scale bar=50 μm).
Plate IV. Scanning electron microscope images of the ornament of Singhisporites hystrix sp. nov. Scale bars=200 μm for 1; 50 μm for 2; 10 μm for 3; 20 μm for 4. (see on page 8)
1.
2.
3.
4.
Distal sculptural elements with arrow indicating adhering microspore; NRMS089428, site PCM 2 (scale bar=200 μm).
Enlargement of ornamentation showing stilt-like basal attachment of the flared sculptural elements to the outer spore wall from Pl. IV, 1 (scale bar=50 μm).
Section through spore wall across the contact face showing ribbon-like and branched/reticulate sculptural elements; CPC34314, site PCM 14 (scale bar=10 μm).
Section through the distal surface spore wall showing taller, stouter, longitudinally ribbed ornamentation; NRMS089541, site PCM 2 (scale bar=20 μm).
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Plate III.
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Plate IV. (caption on page 6).
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(Roadian–Wordian), Bainmedart Coal Measures, Amery Group,
Lambert Graben.
Etymology: Named after the Antarctic continent where the specimens
were found.
Abundanceanddistribution:CommonintheuppermostToplojeMember.
Description: The description is based on N10 specimens. The mega-
spores are trilete with a circular to subcircular amb (Plate II, 1–2) and
broadly elliptical polar outline. The equatorial diameter range is 400–
600 μm and the polar diameter is c. 500 μm. The contact areas form a
broad smooth dome. The laesurae are slightly sinuous near the pole,
but are otherwise straight, extending to the equator (Plate II, 1–2).
The labrae are laevigate–microfoveolate, b25 μm wide and b50 μm
high; their height is consistentapart from their abrupt truncation atthe
equator(PlateII,1–2).Thecontactareasarenormallydelimitedbyalow
curvaturae ridge b10 μm high and b10 μm wide (Plate II, 1–2) but in a
few cases this feature is not developed (Plate III, 3). Both proximal and
distal (Plate II, 3) surfaces are essentially laevigate but very sparse
sculptural elements on both surfaces include b1 μm diameter, b1 μm
highgranaorspinulaemergingfromamicrofoveolateexine(PlateII,4).
Remarks and comparisons: The megaspores are assigned to Banksisporites
astheyexhibitthediagnosticfeaturesofthisgenusincludingasubcircular
amb, straight–sinuous trilete rays that do not extend beyond the contact
area,andmoreorlesssmoothproximalanddistalsurfaces(seeDiscussion
and emendation of this genus by Glasspool, 2003). The present species
differs from other members of the genus by possessing very sparse short
grana acrosstheentire surfaceand laesuraethataremoreorless uniform
in width and height extending to the margins of the megaspore.
Banksisporites antarcticus sp. nov. differs from Banksisporites endo-
sporitiferus (Singh, 1953) Tewari and Maheshwari, 1992, emend.
Glasspool 2003 in the dimensions of labrae, which widen peripherally
in B. endosporitiferus but remain more or less of uniform width in B.
antarcticus. Banksisporites antarcticus is distinct from Banksisporites
indicus (Singh, 1953) Glasspool, 2003, since the former lacks verrucae.
LaesuraeofB.antarcticusarealsoproportionallylonger,extendingtothe
equator, whereas in B. indicus the laesurae reach a maximum of 80% of
the megaspore radius. The labrae of B. indicus also taper in height and
width with distance from the pole, a feature that is not evident in B.
antarcticus. The curvaturae ridges of B. antarcticus are also much lower
(b10 μm high) and less consistently developed than those of B. indicus
(up to 40 μm high). In this respect B. antarcticus shares similarities with
Banksisporitesrotundus(Singh,1953)Glasspool,2003initspossession of
a low arcuate ridge (which is even less well defined in B. rotundus).
Banksisporites antarcticus differs from B. rotundus in the possession of
sparsegranaonboththeproximalanddistalsurfaces,whichareabsentin
B. rotundus. A wide range of GondwananMesozoic megaspores has been
assignedtoBanksisporites(BattenandKovach,1990;Tosolinietal.,2002)
butthesecanbedistinguishedfromB.antarcticusbythecharacteroftheir
labrae, curvaturae ridges, micro-ornament and dimensions.
Plate V. Scanning electron microscope images of microspores adhering to the surface of Singhisporites hystrix. Scale bars=100 μm for 1; 10 μm for 2, 3; 50 μm for 4.
1.
2.
3.
4.
Enlargement of megaspore's proximal ornamentation with attached microspores indicated by arrows; NRMS089538, site PCM 2 (scale bar=100 μm).
Enlargement from Pl. V, 1 showing proximal face and contact surfaces of microspore (scale bar=10 μm).
Enlargement from Pl. V, 1 showing distal surface of microspore (scale bar=10 μm).
Microspores entrapped within the ornamentation of Singhisporites hystrix; NRMS089413 (scale bar=50 μm).
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4.3. Genus Singhisporites Potonié, 1956, emend. Glasspool, 2000
4.3.1. Singhisporites hystrix B. J. Slater, S. McLoughlin et J. Hilton sp. nov.
Specific diagnosis. Amb circular to subcircular. Laesurae straight,
extending 60–80% distance to equator. Contact areas sunken,
delimited by sharply defined change in ornamentation along the
arcuate rim connecting the equatorial ends of labrae. Contact areas
bearing branched or reticulate, slender, sinuous, ribbon-like or bush-
like sculptural elements, which branch to mostly pointed tips. Distal
surface bearing complex ribbon-like or flared, multiple-branched or
reticulate sculptural elements connected to the exine by a spongy
pedestal structure. Distal ornament of uniform height but sculptural
elements are more than twice the height of those on the contact faces.
Outer spore wall coarsely spongeous.
Holotype. CPC34312.
Location, unit and age: Found in samples from all exposures of the
silicified peat bed listed herein, 1.8 km east of Radok Lake (Fig. 1B),
Northern PCMs, Antarctica; uppermost Toploje Member (Roadian–
Wordian), Bainmedart Coal Measures, Amery Group, Lambert Graben,
Etymology: Derived from the Latin for porcupine due to its spiny
appearance.
Abundance and distribution: Abundant (N50 specimens) in the Toploje
Member permineralised peat layer. Similar megaspores, but assigned
to other species of Singhisporites (Potonié, 1956, emend. Glasspool,
2000) have been found in the Permian of India, Australia and South
Africa (Glasspool, 2003). This is the first record of the genus in
Antarctica.
Description: The trilete megaspores have a circular amb (Plate III, 1–2:
Plate VI, 1–2). The equatorial diameter is 600–800 μm and the polar
diameter is approximately 500 μm (Plate III, 1–2). The polar outline is
broadly elliptical, with contact areas forming a low pyramid (Plate III,
3). The laesurae are straight and extend 60–80% of the distance to the
equator. The labrae are b15 μm wide, b20 μm high, and are commonly
surmounted by flared, multiple-branched, sculptural elements
b35 μm in height. The contact areas are sunken, and are delimited
by a sharply defined change in ornamentation along the arcuate rim
connecting the equatorial ends of the labrae (Plate III, 3, 5). The
contact areas bear solitary, clustered, branched or reticulate, slender,
sinuous, sculptural elements 1–3 μm wide, b33 μm high and spaced
10–25 μm apart (Plate III, 4). The distal surface of the megaspore bears
complex, multiple-branched or reticulate flared, ribbon-like or
cylindrical sculptural elements(Plate III, 5). Thesesculpturalelements
are 10–20 μm wide, 20–70 μm long at the base, flaring to 80 μm wide
apically, 60–100 μm high and are spaced 10–30 μm apart (Plate III, 5–
6; Plate IV, 1–2). The outer spore wall is typically 25–35 μm thick and
coarsely spongeous (Plate III, 6; Plate IV, 3–4). The inner spore wall is
apparently closely adpressed to the outer wall and is densely
structured, being 1–3 μm thick and forming a sheet fused to the
inner surface of the exine (Plate IV, 3–4). Tomographic imaging
reveals that the sculptural ornament is of a uniform maximum height
above the surface of the megaspore wall in areas other than the
contact faces (Plate VI, 1–4).
Microspores: Asingletypeofmicrosporeoccurslocallytrappedbetween
themegasporesculpturalelementsofthiskindofmegaspore(PlateIV,1,
4; Plate V, 1; Plate VI, 5, 6; Plate VII, 5). Trapped microspores are trilete
and 45–50 μm in equatorial diameter (Plate V, 2). The laesurae are
straight to slightly sinuous, extending around 60% of the distance to the
equator and are flanked by labrae (Plate VII, 3). The proximal
ornamentation is sparsely spinose and proximal spines are b1 μm wide
and b1.5 μm high (Plate V, 2). The distal surfaces of the microspores are
densely ornamented with spines, bacula, or elongate, branched, ribbon-
likesculpturalelements,typicallyb5 μmwideandb2.5 μmhigh(PlateV,
3–4). A prominent cingulum extends from the margins of the contact
area and is 20–50 μm wide, and commonly has spinose extensions 1–
2 μm long (Plate V, 2–4). The spore wall is finely spongeous.
Remarks and comparison: These trilete megaspores are assigned to
Singhisporites Potonié emend. Glasspool (2000) on the basis that their
laesurae do not extend beyond the contact areas, the limits of which
are defined by a change in the height and complexity of ornamen-
tation along the arcuate rim (Plate VI, 8). The new species differs from
other Singhisporites in the evenly distributed and uniform height
(apart from the contrast between the contact areas and the rest of the
exine) of dense, elaborate ornament on all specimens. The ornament
differs from other species of Singhisporites in the marked difference
between the ornament of the contact face and distal surface; the
processes of the contact face are flattened, shorter and always ribbon-
like, whereas the larger distal processes are wider, more three-
dimensionally branched or cylindrical, commonly forming tubes, with
each process mounted on a pedestal structure. The ornament along
the arcuate rim is commonly fused to varying degrees to form a
curtain, although this feature demonstrates considerable intraspecific
variation. It is clear from the x-ray tomographic images that flanking
the labrae there are two consistently thick pads of tissue overlain by
Plate VI. Computed tomographic images of Singhisporites hystrix sp. nov., NRMS089351, site PCM 15, generated from attenuation-based synchrotron-radiation X-ray tomographic
microscopy (SRXTM). (Scale bars=100 μm for 1–4; 10 μm for 5–8).
1.
2.
3.
4.
5.
6.
7.
8.
Polar view showing thick elaborate ornament and dense internal body. Pale line denoted by arrow indicates outline of underlying mounting medium.
Polar view image compiled from fewer tomographic sections than Pl. I.1 and showing granular texture of inner body.
Equatorial view showing inner body positioned near proximal pole.
Equatorial view (polar section) compiled of a small number of tomographic sections showing the contrast in stature between proximal and distal ornament.
Enlargement of distal ornament showing sections of two adhering microspores (arrowed).
Enlargement of complex distal ornament and an adhering microspore (arrowed).
Enlargement of complex distal ornament.
Enlargement of the relatively flat proximal surface of megaspore in polar section. Arrows indicate margins of contact areas defined by marked changes in ornament
stature.
Plate VII. Attenuation-based synchrotron-radiation X-ray tomographic microscopy (SRXTM) images (single sections) of Singhisporites hystrix sp. nov., NRMS089351. (Scale
bars=100 μm for 1–3, 7; 10 μm for 4–6, 8). (see on page 12)
1.
2.
3.
4.
5.
6.
7.
8.
Polar section showing small sunken pads of wall tissue supporting ornament that flank the labrae.
Polar section showing contrast in size of proximal (upper) versus distal (lower) ornament.
Transverse section roughly through the proximal surface showing well-defined labrae flanking the laesurae.
Polar section showing enlargement of internal granular body.
Enlargement of microspore (arrowed) entrapped by ornament of the distal surface.
Enlargement of distal spore wall showing robust branching sculptural elements.
Tangential section through portion of distal spore wall (central fibrous feature) surrounded by transverse sections of complex-branched distal ornament.
Enlargement of polar section through proximal surface showing thickened pads (supporting sculpture) immediately flanking the labrae.
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1
2
3
4
5
6
7
8
Plate VI.
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1
2
3
4
56
7
8
Plate VII. (caption on page 10).
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sculptural elements (Plate VII, 1, 8). The sunken bases of these
thickened pads are not clear in the SEM images. The x-ray
tomographic images also reveal the presence of a potential inner
body (Plate VI, 1–3; Plate VII, 4). However this feature is granular in
nature rather than smooth and is eccentrically positioned and of
irregular shape, and so may represent an aggregation of fine organic
debris that has entered the spore via the laesurae. FollowingGlasspool
(2000), the inner body is disregarded as a useful taxonomic character.
Singhisporites hystrix differs from Singhisporites surangei (Singh,
1953) Potonié, 1956 emend. Glasspool, 2000 in several aspects. In S.
hystrix, the labrae are more pronounced and are never undulate as in
some S. surangei specimens. Labrae in S. hystrix are similar to those of
S. tubbus Glasspool, 2000 in being distinct, high and narrow but the
ornament of the latter is distinct in consisting of short, flattened
processes with ragged margins. The contact faces and all other surfaces
in S. hystrix are ornamentated in all cases, and this differs from many S.
surangei specimens, which lack areas of ornament. The ornament of S.
hystrix is also stouter and has branched, pointed tips (Plate IV, 4),
comparedtothemoreroundedtipsevidentinS.surangei.Thelatteralso
lacksthepedestalattachmentbasesofthesculpturalelements(PlateIV,
1–2). The ornament forms a uniform height around S. hystrix and is
denserthanthatofSinghisporitesradialis(BharadwajandTewari,1970),
a megaspore that also displays uniform ornament distribution. The
ornament also differs from the thick fleshy processes of S. radialis
(BharadwajandTewari,1970)inbeingribbonlike.Singhisporiteshystrix
differs from all other Singhisporites in the difference between ornament
on the contact faces and the distal surface. In S. hystrix, the processes
covering the contact faces are shorter than the distal ornament and
always ribbon-like in structure (Plate III, 4; Plate IV, 3), whereas the
larger distal processes are attached to the exine by a pedestal-like
structure, are cylindrical (or otherwise three-dimensionally branched)
and commonly form hollow tubular structures (Plate III, 3; Plate IV, 4;
Plate VI, 4–7; Plate VII, 2, 6, 7). The ribbon-like ornament on the contact
facescanappearasspinule-likehollowtubesindegraded(PlateIII,2)or
over-macerated specimens.
Singhisporites was established by Potonié (1956), and later, Glass-
pool (2000, 2003) designated the genera Mammilaespora (Pant and
Srivastava, 1961), Triapipellitis (Kar, 1968), Singraulispora (Pant and
Mishra, 1986), Ancorisporites (Pant and Mishra, 1986) and Ramispina-
tispora (Pant and Mishra, 1986) to be junior synonyms of Singhispor-
ites.WealsoconsiderthatRamispinatisporamahanadiensisTewarietal.
(2009) should be reassigned to Singhisporites Potonié emend. Glass-
pool (2000), on the basis that Glasspool (2003) showed that all
members of Ramispinatispora have equivalent ornamental characters
toSinghisporites.The specimenassigned to R.mahanadiensis by Tewari
et al. (2009), however, does display characteristic features, such as
entangled web-like ornamentation, to warrant its distinction at the
specific level from other representatives of the genus. The other two
species referred to Ramispinatispora from the Ib-River Coalfield by
Tewari et al. (2009), namely Ramispinatispora indica and Ramispina-
tispora nautiyalii, were previously transferred to Singhisporites indica
and Singhisporites nautiyalii respectively by Glasspool (2003) and we
agreewiththese reassignments. Furthermore,the specimenidentified
as Singhisporites baculatus (Kar) by Tewariet al. (2009, Fig. 4.3) should
be considered a junior synonym of Singhisporites surangei since
Singhisporites baculatus was only separated on the basis of possession
of a dark inner body, a feature that Glasspool (2000) concluded is not
specifically diagnostic since it is variable between specimens and can
be affected by taphonomic processes and the degree of oxidation
during preparation. Here we formally transfer R. mahanadiensis
Tewari,Mehrotra, Meenaet Pillai(Tewarietal.,2009) toSinghisporites
in accordance with the conclusions of Glasspool (2000, 2003).
Microspores adhering to the ornament of Singhisporites hystrix sp.
nov. are similar to dispersed examples of Lundbladispora sp. (Visscher
et al., 2004) in their sub-rounded shape, possession of a granular to
spinose or baculate ornamented distal surface and narrow cingulum.
They most likely represent the microspores of the same parent plant
as S. hystrix. Other species of Singhisporites, including Singhisporites
grandis and Singhisporites nautiyalii, have also been reported to have
microspores adhering to their surface ornament. Entrapment of
microspores in the elaborate ornament of the megaspores may have
been part of their reproductive strategy.
4.3.2. Singhisporites mahanadiensis (Tewari, Mehrotra, Meena et Pillai)
B. J. Slater, S. McLoughlin et J. Hilton comb. nov.
Basionym: Ramispinatispora mahanadiensis, Tewari, R., Mehrotra, N.C.,
Meena, K.L. and Pillai, S.S.K. 2009. Permian Megaspores from Kuraloi
Area, Ib-River Coalfield, Mahanadi Basin, Orissa. Journal of the
Geological Society of India, 74, p. 673, Fig. 3 (18–19).
Location, unit and age: Permian of Kuraloi area, Ib-River Coalfield,
Mahanadi Basin, Orissa, India.
Remarks: It has been deemed necessary to transfer Ramispinatispora
mahanadiensis to Singhisporites on the basis of Glasspool's (2003)
assertion that Ramispinatispora is a junior synonym of Singhisporites
based on the characters of its ornamentation.
5. Discussion
Three species of lycopsid megaspore have been identified from the
genera Duosporites, Banksisporites and Singhisporites within a single
layer of Permian permineralised peat from the PCMs, Antarctica. This
indicates the presence of at least three whole-plant lycopsids in the
source flora (for recent synthesis see Bateman and Hilton, 2009). No
previously reconstructed whole-plant lycopsids have megaspores
belonging to these morphogenera so it is difficult to further evaluate
their systematic position within the Lycopsida or the growth
architecture of the plants that produced these megaspores (see
Bateman et al., 1992; Bateman, 1994; Bateman and Hilton, 2009). The
lycopsid affinity of these megaspores is based on the sculptural spines
on the surfaces of the megaspores (known only from lycopsids), the
wall ultrastructure and the widespread development of heterospory
in this group (Pant and Mishra, 1986; Jha and Tewari, 2003; Jha et al.
2006; Tewari et al. 2007; Tewari and Jha, 2007). The lycopsids that
contributed to the peats of the Bainmedart Coal Measures were
probably herbaceous, since large arborescent lycopsids have not been
recorded after extensive sectioning of the peats. The upper tier
vegetation of the mire community was apparently dominated by
glossopterid and cordaitalean gymnosperms (Holdgate et al., 2005).
Apart from South Africa and South America, where some arborescent
forms are known in moderate abundance in the Early Permian
(Anderson and Anderson, 1985; Guerra-Sommer and Cazzulo-
Klepzig, 2000), lycopsids have been considered relatively insignificant
components of the high-latitude Gondwanan Permian floras (Shi
et al., 2010). The apparent dearth of lycopsid macrofossils may be due
to the diminutive size and fragile architecture of many lycopsids
in high-latitude Gondwanan peat-forming communities. Axes and
leaves of one such herbaceous lycopsid have been identified in the
silicified peat of the Toploje Member (Holdgate et al., 2005) but will
be morefully describedelsewhere (SlaterandMcLoughlin, researchin
progress). Schwendemann et al. (2010) describedanotherherbaceous
lycopsid from Upper Permian strata of the central Transantarctic
Mountains, and Townrow (1968) described a small selaginellalean
plant from the Late Permian of eastern Australia. Dispersed lycopsid
megaspores have been widely reported from Permian Gondwanan
strata and assigned to several dozen species. Collectively, these data
suggest that heterosporous lycopsids were widespread but cryptic
and not necessarily uncommon ground-storey elements of the
Permian vegetation of Gondwana in somcble habitats.
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Synchrotron-based X-ray tomography currently reveals architec-
tural features with a resolution similar to or slightly lower than that
obtainable from SEM. The shape and distribution of sculptural
elements are well resolved. Details of the spore wall structure
(Plate VI, 5, 6, 8; Plate VII, 4–8) are slightly less clear than achievable
with TEM. The advantage of the former technique is that internal
architecture is discernable without the need to break or section the
specimen. Further, SEM can later be undertaken on the same
specimen to obtain high resolution images of the outer surface
morphology if necessary. With anticipated improvements in resolu-
tion to nanometre range, X-ray tomography is likely to become an
increasingly valuable analytical tool for precision palyno-taxonomic
studies.
5.1. Reproductive biology
Megaspores are generally considered to have lesser dispersive
potential in comparison to microspores due to their larger size and
production in smaller numbers (Bateman and DiMichele, 1994;
Playford and Dettmann, 1996). The branched ornamentation of
Singhisporites hystrix, apart from facilitating entrapment of micro-
spores, might also have aided hydrochory (flotation in water), thus
promoting wider dispersal (Tewari et al., 2009). This might explain
the higher abundance of S. hystrix within the peat layer in comparison
to other megaspore taxa. The trilete microspores found adhering
sporadically to the S. hystrix ornamentation are all of one kind and are
likely to be biologically affiliated with the megaspore since they were
found attached only to that species. Pant and Mishra (1986) noted
microspores entrapped within the extended ornamentation of
specimens of ‘Mammilaespora grandis’ (now Singhisporites grandis;
see Glasspool, 2000, 2003) and ‘Ramispinatispora nautiyalii’ (now
Singhisporites nautiyalii; see Glasspool, 2000, 2003), and concluded
that long elaborate sculptural elements may serve to trap affiliated
microspores, improving the chances of fertilisation. The ornamenta-
tion of S. grandis and S. nautiyalii is similar to that of S. hystrix,
indicating this strategy of microspore entrapment to be common
within the genus where it presumably reflects a selective advantage
for reproduction in water and retention of the microspore on the
megaspore.
5.2. Taphonomy
Whereas Late Permian peats from the central Transantarctic
Mountains appear to represent small lenses or rafted (allochthonous)
wedges of peat (Taylor et al., 1989), the Middle Permian example in
the PCMs represents a peat mire community preserved in situ that
extends as a single layer exposed over several kilometres along strike
(Fielding and Webb, 1996). Beyond this, little detailed work has yet
beenundertaken on thefloristiccomposition ortaphonomic historyof
the Toploje Member silicified peat. The silicified peat layer represents
the autochthonous and hypautochthonous remains of a Permian
glossopterid-dominated mire flora, from which Holdgate et al. (2005)
illustrated its major biotic components and outlined the relative
proportions of plant organs within the deposit. Lycopsids represented
b0.1% of the peat constituents by volume. Understanding the
formation of this organic deposit has importance since it provides
an in situ window into the ecology of these southern high latitude
mire communities and permits confident biological attribution and
quantification ofisolated remainsin thewidespread andeconomically
important Permian Gondwanan coals that are otherwise interpreted
from strongly altered (chemically and structurally) coal macerals.
The megaspores described here are very well preserved. The
apparently rapid silicification process has largely prevented compres-
sion of the megaspores so they retain their original three-dimensional
structure. There is also little evident damage to the megaspore
structure through pyrite crystal growth that commonly reduces the
qualityofpreservation.Thesource of silicacontributingto thisdeposit
has yet to be determined. Many similar deposits of silicified plant
remains are associated with hydrothermal activity (surficial hot
springs)where organicremains are permineralised through silica ions
attaching to free hydrogen bonds in the partially degraded plant
tissues and thence via infilling of pore spaces by additional
precipitation of silica from solution (Jefferson, 1987; Channing and
Edwards, 2009). Examples of this include the Devonian Rhynie Chert
in Aberdeenshire, Scotland (Trewin, 2003), the yet to be located
lagerstätte of Early Mississippian to Middle Pennsylvanian age that
has yielded ex situ chert nodules on the Yorkshire coastline (Stevens
et al., 2010), and from the Late Jurassic San Agustín Farm Lagerstätten
from the Deseado Massif in Patagonia, Argentina (Guido et al., 2010).
The formation of algal mats and resultant changes in pH conditions of
lacustrine or lagoonal environments has also been highlighted as a
potential mechanism for silicification (Francis, 1984; Falcon-lang
et al., 2011). However, substantial quantities of algal palynomorphs
have not yet been identified in the PCM deposits (McLoughlin et al.,
1997; Lindström and McLoughlin, 2007). Other sites preserve
permineralised plant remains in volcaniclastic sediments where
abundant silica is available from the breakdown of volcanic glass
and unstable silicates. Examples of this type of silicification include
the Cerro Cuadrado fossil forest in Patagonia (Stockey, 1975), the
Glossopteris-bearing permineralised peat of the Fort Cooper Coal
Measures, northeastern Australia (Gould and Delevoryas, 1977) and
the Grand-Croix permineralised plants from central France (Galtier,
2008). Since no volcanigenic sediments are associated with the
silicified peat deposit in the PCMs, an alternative mechanism must
explain their preservation. The overlying lacustrine sediments of the
Dragons Teeth Member (Fielding and Webb, 1996), which cap the
silicified peats, indicate the presence of a persistent lake environment
that may have experienced fluctuating alkalinity due to strong
seasonality at high latitudes during the Permian. This could have
created conditions of varying silica solubility within the lake waters,
and resulted in siliceous envelopment of the detritus on the lake floor
(Stigall et al., 2008), although such radical seasonal swings in
alkalinity are typically associated with semi-arid environments, both
modern (Hesse, 1989) and ancient (Wheeler and Textoris, 1978).
Fluctuating alkalinity has been shown to be an important factor in
modern siliceous preservation of marsh plants surrounding hot
springs at Yellowstone National Park in Wyoming, USA (Channing
and Edwards, 2009). The silicification evident in Jurassic high-latitude
lacustrine sediments of Antarctica from the Kirkpatric Basalt has been
attributed to microbial mat induced silicification (Stigall et al., 2008),
and may have parallels to the conditions operating in the PCMs,
although microbial laminae have not been detected in the latter
deposits.
5.3. Palaeogeography
The central position of Antarctica within Gondwana during the
Permian endows it with a pivotal role in understanding the relation-
ships between the dispersed Gondwanan biotas (Ryberg, 2010). The
PCM permineralised peat represents the remains of southern high-
latitude forest mires. Palaeogeographic reconstructions place the
Lambert Graben (in which the Bainmedart Coal Measures were
deposited) adjacent to the Mahanadi Graben in India prior to the
breakup of Gondwana (Fedorov et al., 1982; Stagg, 1985; Veevers
2004; Bogor, 2011), although there is also an alternative case for the
Godavari Graben being positioned adjacent to the Lambert Graben
based on similarities in coal deposits (Holdgate et al., 2005). Previous
studies of the Permian megaspore assemblages from the Mahanadi
Graben have uncovered the genera Singhisporites and Banksisporites in
common with the PCM silicified peat, suggesting a strong phytogeo-
graphic link. However, both of these genera are also reported from
sediments of the Godavari Graben (Tewari and Jha, 2007).
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6. Conclusions
1. Three species of dispersed megaspore have been identified from
the Permian flora of the PCMs (Singhisporites hystrix sp. nov.,
Duosporites lambertensis sp. nov. and Banksisporites antarcticus sp.
nov.). These indicate the presence of at least three whole-plant
species of presumably herbaceous heterosporous lycopsid.
2. Microspores of Lundbladispora sp. adhering to the ornament of
Singhisporites hystrix are interpreted as the microspores of the
same whole-plant species, with this tendency for entrapped
microspores within the ornament of the megaspore being common
within the genus and presumably part of its reproductive strategy.
3. This pioneering attempt at X-ray tomography of megaspores has
demonstrated that internal features such as sunken exinal
thickenings flanking the labrae can be observed that would
otherwise be missed in SEM images of the external surface.
Another advantage of using synchrotron tomography is that the
specimens can be removed following the procedure and then be
studied using SEM at a later time.
4. The unusual taphonomic conditions resulting in early silicification
of this in situ peat layer in the PCMs has preserved the megaspores
in an excellent condition, devoid of compression and free from
pyritisation. The absence of volcanogenic features lends support to
a model of silicification based on seasonal fluctuations in the
alkalinity of lake waters that subsequently covered the peats.
5. Previous palaeogeographic reconstructions that place the Indian
Mahanadi Graben adjacent to the Lambert Graben of Antarctica
during the Middle Permian are here supportedby the identification
of shared megaspore genera.
Acknowledgements
This research was supported by the Natural Environment Research
Council, U.K. (NE/H5250381/1 to BJS) and the Synthesys programme of
theEUtosupportresearchonmuseumcollections(SE-TAF-4827toBJS).
The Australian Antarctic Division provided financial and logistical
support for collecting the specimens via Antarctic Science Advisory
Council Project 509; Profs D. Cantrill and A. Drinnan helped collect
material in the field on two Antarctic expeditions. Thanks also to Else
Marie Friis and Anna Lindström (NRM), and Marco Stampanoni and
Federica Marone (Paul Sherrer Institute) for aid in the Synchrotron
tomography work (supported by the European Union FP6, project
number20100167,toP.C.J.Donoghue,S.BengstonandE.M.Friisandthe
European Community — Research Infrastructure Action under the FP7
“Capacities” Specific Programme). Robert Mill (Royal Botanic Gardens,
Edinburgh) provided valuable advice on Latin nomenclature. SM
acknowledges funding support from a Swedish Research Council (VR)
grant and an Australian Research Council Linkage grant.
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