Glossopteris(etymology: from Ancient Greek γλῶσσα (glôssa, "tongue" ) + πτερίς (pterís, "fern" )) is the largest and best-knowngenusof theextinctPermianorderofseed plantsknown asGlossopteridales(also known as Arberiales, Ottokariales, or Dictyopteridiales). The nameGlossopterisrefers only to leaves, within the framework ofform generaused inpaleobotany(for likely reproductive organs, seeGlossopteridaceae).

Glossopteris
Glossopteris sp.
Scientific classificationEdit this classification
Kingdom: Plantae
Clade: Tracheophytes
Order: Glossopteridales
Family: Glossopteridaceae
Genus: Glossopteris
Brongniart 1828 ex Brongniart 1831
Species
  • G. angustifolia
  • G. brasiliensis
  • G. browniana
  • G. communis
  • G. indica
  • G. occidentalis
Fossils of the gymnospermGlossopteris(dark green) found in all of the southern continents provide strong evidence that the continents were once amalgamated into a supercontinentGondwana

Species ofGlossopteriswere the dominant trees of the middle to high-latitude lowland vegetation across the supercontinentGondwanaduring the Permian Period.Glossopterisfossils were critical in recognizing former connections between the various fragments of Gondwana: South America, Africa, India, Australia, New Zealand, and Antarctica.

Description

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Glossopterissp. LatePermian,Australia. At theRoyal Tyrrell Museum of Palaeontology.

The leaves ofGlossopterisare characterized by their distinctive tongue shape that gives them their name, as well as theirreticulate venation.The leaves were either widely spaced on long stems, or were densely helically arranged on short shoots.

Glossopterisbearing plants grew as woody, seed-bearing trees and shrubs. Their trunks had a maximum diameter of 80 centimetres (2.6 ft), with some likely reaching a height of 30 metres (98 ft).[3]They had a softwood interior resemblingAraucariaceaeconifers.[4]

Seeds were borne on one side of variably branched or fused structures,[5][6][7][8][9][10]andmicrosporangiacontainingpollenwere borne in clusters at the tips of slender filaments.[11]Both the seed- and pollen-bearing organs were partially fused (adnate) to the leaves, or, in some cases, possibly positioned in theaxilsof leaves. The homologies of the flattened seed-bearing structures have remained particularly controversial with some arguing that the fertile organs representmegasporophylls(fertile leaves) whereas others have interpreted the structures as flattened, seed-bearing, axillary axes (cladodes). It is unclear whether glossopterids weremonoeciousordioecious,the fact that only pollen organ bearing leaves and not ovules were found in some layers suggest that at least some species were the latter.[12]

Distribution

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More than 70fossilspecies of this genus have been recognized inIndiaalone,[13]with additional species fromSouth America,Australia,[14][15]Africa,Madagascar[16]andAntarctica.[17][18]Essentially,Glossopteriswas restricted to the middle- and high-latitude parts of Gondwana during the Permian[19]and was an important contributor to the vast Permian coal deposits of the Southern Hemisphere continents.[20]Most northern parts of South America and Africa lackGlossopterisand its associated organs.

However, in recent years a few disparate localities in Morocco, Oman, Anatolia, the western part of the island of New Guinea, Thailand and Laos have yielded fossils that are of possible glossopterid affinity.[21]These peri-gondwanan records commonly occur together with Cathaysian or Euramerican plant species—the assemblages representing a zone of mixing between the strongly provincial floras of the Permian.[22]Apart from those in India and the peri-gondwanan localities, a few other fossils from the Northern Hemisphere have been assigned to this group, but these are not identified with great certainty. For example, specimens assigned toGlossopterisfrom the far east of Russia in the 1960s are more likely to be misdentifications of othergymnospermssuch asPursongia.[23]Confident assignment of fossil leaves toGlossopterisnormally requires their co-preservation with the distinctive segmented roots of this group (calledVertebraria) or with the distinctive fertile organs.[24]In 2018,Glossopterisleaves were reported from mid-Permian (Roadian– earlyWordian) deposits in Mongolia, then located at high latitudes in the Northern Hemisphere, but these fossils were not found in association with other typical glossopterid organs, such as chambered roots or reproductive structures, so the phylogenetic affinities of these leaves remain uncertain.[25]

Chronology

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The Glossopteridales arose in the Southern Hemisphere around the beginning of thePermianPeriod(298.9million years ago),[21]but became extinct during the end-Permian (Changhsingian) mass extinction.[2]The putative persistence ofGlossopterisinto younger strata is commonly invoked on the basis of the distribution of dispersed taeniate bisaccate pollen.[26]However, this category of pollen is known to have been produced by various seed plants, and Triassic examples, in the absence of convincing co-preservedGlossopterisleaves, probably belonged to non-glossopterid groups, such as voltzialean conifers.[27]The distribution ofGlossopterisacross several, now detached, landmasses ledEduard Suess,amongst others, to propose that the southern continents were once amalgamated into a singlesupercontinentPangea.[28]These plants went on to become the dominant elements of the southern flora through the rest of the Permian but disappeared in almost all places at the end of the Permian (251.902million years ago).[29][30][31]The only potentialTriassicrecords areGlossopterisleaves exposed in the banks of the Gopad River nearNidpur,India,[32]but even these records are stratigraphically ambiguous owing to faulting and complex juxtapositioning of Permian and Triassicstrataat Nidpur. Moreover, even if someGlossopterisleaves do persist above the end-Permian extinction horizon, this level pre-dates the Permian-Triassic boundary proper in continental settings of Gondwana by several hundred thousand years[2]and there are no convincing examples ofGlossopterisin confidently dated Triassic strata. Although most modernpalaeobotanytextbooks cite the continuation of glossopterids into later parts of the Triassic and, in some cases into theJurassic,these ranges are erroneous and are based on misidentification of morphologically similar leaves such asGontriglossa,[33]Sagenopteris,orMexiglossa.[34]Glossopterids were, thus, one of the major casualties of theend-Permianmassextinction event.[29]

Taxonomy

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Long considered afernafter its discovery in the 1820s,[35]it was later assigned to thegymnospermssensu lato(i.e.Spermatophyta). The genus is in the orderGlossopteridales,which is placed in the divisionPteridospermatophyta(often informally called "seed ferns" ). In reality, many of the plant groups included within this division are only distantly related to one another, and the relationships of Glossopteridales to other seed plant groups is unclear. Some authors have suggested that the Glossopteridales are closely related toflowering plants,though the evidence for such a relationship is weak.[36]

Glossopterisshould strictly be used to refer to the distinctivespathulatefossil leaves withreticulatevenation,however, the term has also been used to refer to the parent plant as a whole.[37]Leaves ofGlossopterisare associated with reproductive structures belonging to the familyDictyopteridiaceaewithin the Glossopteridales.[38]

The name comes from Ancient Greekγλώσσα(glṓssa'tongue'), because the leaves were tongue-shaped, andπτέρις(pteris'fern, feathery').[citation needed]

Paleoecology

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Reconstruction of trees ofGlossopterisat the Middle Permian Onder Karoo locality in South Africa with male (ai) and female (aii) reproductive organs inset

They are interpreted to have grown in very wet soil conditions,[39][40]similar to the modernBald Cypress.The leaves ranged from about 2 cm to over 30 cm in length.

The profile of glossopterid trees is largely speculative as complete trees have not been preserved. However, based on analogies with modern high-latitude plants, polar-latitudeGlossopteristrees have been suggested to have had a tapered, conical profile like that of aChristmas treeand to have been relatively widely spaced to take advantage of the low-angle sunlight at high latitudes,[3]instead of needles, they had large, broad lance- or tongue-shaped leaves commonly with well differentiated palisade and spongy mesophyll layers.

Glossopteristrees are assumed to have beendeciduous,as fossil leaves are commonly found as dense accumulations representing autumnal leaf banks.[41][42]The broad fossilized growth rings inGlossopteriswoods from Antarctica, then part of Gondwana, reveal that the plants experienced strong growth spurts each spring-summer but underwent the abrupt cessation of growth before each following winter, a transition that could take as little as a month.[43][44]The idea that allGlossopterisspecies are deciduous has been challenged, with an isotopic study finding that AntarcticGlossopterisforests were mixed evergreen-deciduous.[45]

TheGlossopterisbearing plants are likely to have primarily beenwind pollinated.Seeds borne byGlossopterisbearing plants include the generaPlectilospermum,Choanostoma,Pachtestopsis,Illawarraspermum, Lakkosia, LonchiphyllumandHomevaleia.Many of these bear wings, and it is likely that at least some of these werewind dispersed.One speciesChoanostoma verruculosum,may have been adapted to being dispersed by water.[46]

Glossopterisleaves are morphologically simple so there are few characters that can be used to differentiate species.[47]Consequently, many past researchers have considered the PermianGlossopterisflora to be rather homogeneous with the same species distributed throughout theSouthern Hemisphere.However, more recent studies of the more morphologically diverse fertile organs have shown that taxa had more restricted regional distributions and several intra-gondwanan floristic provinces are recognizable. Seeds, much too large to be wind-borne, could not have blown across thousands of miles of open sea, nor is it likely they have floated across vast oceans. Observations such as these led theAustriangeologistEduard Suessto deduce that there had once been a land bridge between these areas. He named this large land massGondwanaland(named after the district in India where the plantGlossopteriswas found). These same observations would also lend support to Alfred Wegener'sContinental drifttheory.

The first Antarctic specimens ofGlossopteriswere discovered by members ofRobert Scott's doomedTerra Novaexpedition.The expedition members abandoned much of their gear in an effort to reduce their load, but kept 35 pounds ofGlossopterisfossils; these were found alongside their bodies.[48]

See also

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References

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  2. ^abcFielding, CR; Frank, TD; Vajda, V; McLoughlin, S; Mays, C; Tevyaw, AP; Winguth, A; Winguth, C; Nicoll, RS; Bocking, M; Crowley, JL (23 January 2019)."Age and pattern of the southern high-latitude continental end-Permian extinction constrained by multiproxy analysis".Nature Communications.10(385): 385.Bibcode:2019NatCo..10..385F.doi:10.1038/s41467-018-07934-z.PMC6344581.PMID30674880.
  3. ^abS. McLoughlinGlossopteris— insights into the architecture and relationships of an iconic Permian Gondwanan plantJ. Bot. Soc. Bengal, 65 (2011), pp. 93-106
  4. ^Weaver, L.; McLoughlin, S.; Drinnan, A.N. (1997). "Fossil woods from the Upper Permian Bainmedart Coal Measures, northern Prince Charles Mountains, East Antarctica".AGSO Journal of Australian Geology and Geophysics.16:655–676.
  5. ^McLoughlin, S (1990). "Some Permian glossopterid fructifications and leaves from the Bowen Basin, Queensland, Australia".Review of Palaeobotany and Palynology.62(1–2): 11–40.Bibcode:1990RPaPa..62...11M.doi:10.1016/0034-6667(90)90015-b.
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  7. ^McLoughlin, S. 1995 Bergiopteris and glossopterid fructifications from the Permian of Western Australia and Queensland. Alcheringa, 19: 175-192.
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