Junggaria was a genus of rhyniophyte-like land plants known from fossils found in China in Upper Silurian strata (Přídolí, around 430 to 420 million years ago). It bore leafless dichotomously or pseudomonopodially branching axes, some of which ended in spore-forming organs or sporangia of complex shape. The genus Cooksonella, found in Kazakhstan from deposits of a similar age, is considered to be an illegitimate synonym.[1]
Junggaria spinosa was first described as a new species by Dou in 1983,[2] from four fossil specimens found in the Wutubulake Formation, Xinjiang, China, now dated to the Late Silurian (Přídolí, around 430 to 420 million years ago). Further specimens were found later and a more detailed description was published in 1993 by Cai et al.[1]
The specimens are fragmentary so that a full reconstruction is difficult. It appears that the sporophyte of Junggaria spinosa had 'pseudomonopodial' branching, i.e. the leafless stems (axes) divided into two branches in such a way that one continued as the 'main' stem and the other became a side or lateral branch. Lateral branches divided dichotomously up to twice, terminating in spore-forming organs or sporangia. Stems varied in width from around 1.1 mm to 2.5 mm. Most of the stems were smooth but some bore hair-like structures up to 0.1 mm in diameter and 0.5 mm long. A darker central strand was observed on some stems, but the internal structure is not known.[1]
Schematic representation of two sporangia of Junggaria spinosa as they appear in fossil specimens. Based on Fig. 6 in Cai, Dou & Edwards (1993). Scale bar is 1 mm.
In the flattened fossils, the sporangia consist of a central, roughly circular area, on average 2 mm in diameter, smoothly connected to the end of the stem on which they were borne. Around the top and sides of the central area there is a border, around 1 mm wide, which is not connected to the stem and ends abruptly. The border varies in shape, sometimes being uniform, sometimes lobed; it appears to consist of two layers separated by a 'filling'. The layers appear separated into two 'valves' in some specimens. Cai et al. say that it is difficult to reconstruct the three-dimensional structure of a sporangium before preservation; it may have been more-or-less spherical or it may already have been compressed from side to side before being fossilized. They concluded that "[t]hese unique and somewhat bizarre sporangia ... defy our understanding", but that the most surprising feature was their complexity relative to other Silurian species such as Salopella, Cooksonia or Steganotheca.[1]
Relationship with Cooksonellaedit
The new genus and species Cooksonella sphaericanom. illeg. was created by Senkevich in 1978 for plants found in Kazakhstan.[3] The sediments in which the fossils were found are now also regarded as from the Přídolí. The description of C. sphaerica is considered by Cai et al. to be sufficiently similar to the Chinese specimens to regard them as the same species. The different preservation of the Kazakhstan specimens allowed the presence of a central strand of tracheids to be demonstrated, showing that C. sphaerica is a vascular plant.[1]
Senkevich's name is illegitimate, because the genus name Cooksonella had already been used for a different fossil. Hence Cai et al. were unable to rename Dou's Junggaria spinosa as Cooksonella sphaerica.[1] A new genus name is required under the International Code of Botanical Nomenclature, but as of April 2011[update] does not appear to have been created, so that forms such as "Cooksonella sphaerica/Junggaria spinosa" will be found in the literature.[4]
Phylogenyedit
Junggaria has some affinities with the rhyniophytes in that it has leafless dichotomizing stems with terminal sporangia and appears to have xylem.[1] Rhyniophytes or paratracheophytes are part of the group from which the true vascular plants or tracheophytes are believed to have evolved.[5] However, features of the sporangium led Cai et al. to make comparisons with genera such as Renalia, Sartilmania and some species of Cooksonia.[1] These have been placed within the tracheophytes, basal to lycophytes (modern clubmosses and allies).[6] The relationships of Junggaria/Cooksonella remain uncertain.
Referencesedit
^ abcdefghCai, C.-Y.; Dou, Y.-W. & Edwards, D. (1993), "New Observations on a Pridoli Plant Assemblage from North Xinjiang, Northwest China, with Comments on its Evolutionary and Palaeogeographical Significance" (PDF), Geological Magazine, 130 (2): 155–170, Bibcode:1993GeoM..130..155C, doi:10.1017/S0016756800009821
^* Dou, Y.-W. & Sun, Z.-H. (1983), "Devonian Plants", Palaeontological Atlas of Xinjiang, Vol. II. Late Palaeozoic Section (in Chinese), Beijing: Geological Publishing House, cited in Cai, Dou & Edwards 1993
^Senkevich, M.S. (1978), "New Devonian psilophytes from Kazakhstan", Ezheg. Vses. Paleontol. Obshchestva (in Russian), 21: 288–298, cited in Edwards, D.; Fanning, U. & Chaloner, W.G. (1985), "Evolution and Environment in the Late Silurian-Early Devonian: The Rise of the Pteridophytes", Philosophical Transactions of the Royal Society B, 309 (1138): 147–165, Bibcode:1985RSPTB.309..147E, doi:10.1098/rstb.1985.0076, JSTOR 2396357
^See e.g. Gensel, Patricia G. (2008), "The Earliest Land Plants", Annu. Rev. Ecol. Evol. Syst., 39: 459–77, doi:10.1146/annurev.ecolsys.39.110707.173526, p. 469
^Gerrienne, P. & Gonez, P. (2011), "Early evolution of life cycles in embryophytes: A focus on the fossil evidence of gametophyte/sporophyte size and morphological complexity", Journal of Systematics and Evolution, 49: 1–16, doi:10.1111/j.1759-6831.2010.00096.x, S2CID 29795245
^Crane, P.R.; Herendeen, P. & Friis, E.M. (2004), "Fossils and plant phylogeny", American Journal of Botany, 91 (10): 1683–99, doi:10.3732/ajb.91.10.1683, PMID 21652317
April 14, 2024
junggaria, genus, rhyniophyte, like, land, plants, known, from, fossils, found, china, upper, silurian, strata, přídolí, around, million, years, bore, leafless, dichotomously, pseudomonopodially, branching, axes, some, which, ended, spore, forming, organs, spo. Junggaria was a genus of rhyniophyte like land plants known from fossils found in China in Upper Silurian strata Pridoli around 430 to 420 million years ago It bore leafless dichotomously or pseudomonopodially branching axes some of which ended in spore forming organs or sporangia of complex shape The genus Cooksonella found in Kazakhstan from deposits of a similar age is considered to be an illegitimate synonym 1 JunggariaTemporal range Late Late Silurian PreꞒ Ꞓ O S D C P T J K Pg NScientific classificationKingdom PlantaeClade PolysporangiophytesClade TracheophytesStem group RhyniophytesGenus JunggariaY W DouSpeciesJ spinosa Y W DouSynonyms Cooksonella M S Senkevich nom illeg Contents 1 Description 2 Relationship with Cooksonella 3 Phylogeny 4 ReferencesDescription editJunggaria spinosa was first described as a new species by Dou in 1983 2 from four fossil specimens found in the Wutubulake Formation Xinjiang China now dated to the Late Silurian Pridoli around 430 to 420 million years ago Further specimens were found later and a more detailed description was published in 1993 by Cai et al 1 The specimens are fragmentary so that a full reconstruction is difficult It appears that the sporophyte of Junggaria spinosa had pseudomonopodial branching i e the leafless stems axes divided into two branches in such a way that one continued as the main stem and the other became a side or lateral branch Lateral branches divided dichotomously up to twice terminating in spore forming organs or sporangia Stems varied in width from around 1 1 mm to 2 5 mm Most of the stems were smooth but some bore hair like structures up to 0 1 mm in diameter and 0 5 mm long A darker central strand was observed on some stems but the internal structure is not known 1 nbsp Schematic representation of two sporangia of Junggaria spinosa as they appear in fossil specimens Based on Fig 6 in Cai Dou amp Edwards 1993 Scale bar is 1 mm In the flattened fossils the sporangia consist of a central roughly circular area on average 2 mm in diameter smoothly connected to the end of the stem on which they were borne Around the top and sides of the central area there is a border around 1 mm wide which is not connected to the stem and ends abruptly The border varies in shape sometimes being uniform sometimes lobed it appears to consist of two layers separated by a filling The layers appear separated into two valves in some specimens Cai et al say that it is difficult to reconstruct the three dimensional structure of a sporangium before preservation it may have been more or less spherical or it may already have been compressed from side to side before being fossilized They concluded that t hese unique and somewhat bizarre sporangia defy our understanding but that the most surprising feature was their complexity relative to other Silurian species such as Salopella Cooksonia or Steganotheca 1 Relationship with Cooksonella editThe new genus and species Cooksonella sphaerica nom illeg was created by Senkevich in 1978 for plants found in Kazakhstan 3 The sediments in which the fossils were found are now also regarded as from the Pridoli The description of C sphaerica is considered by Cai et al to be sufficiently similar to the Chinese specimens to regard them as the same species The different preservation of the Kazakhstan specimens allowed the presence of a central strand of tracheids to be demonstrated showing that C sphaerica is a vascular plant 1 Senkevich s name is illegitimate because the genus name Cooksonella had already been used for a different fossil Hence Cai et al were unable to rename Dou s Junggaria spinosa as Cooksonella sphaerica 1 A new genus name is required under the International Code of Botanical Nomenclature but as of April 2011 update does not appear to have been created so that forms such as Cooksonella sphaerica Junggaria spinosa will be found in the literature 4 Phylogeny editJunggaria has some affinities with the rhyniophytes in that it has leafless dichotomizing stems with terminal sporangia and appears to have xylem 1 Rhyniophytes or paratracheophytes are part of the group from which the true vascular plants or tracheophytes are believed to have evolved 5 However features of the sporangium led Cai et al to make comparisons with genera such as Renalia Sartilmania and some species of Cooksonia 1 These have been placed within the tracheophytes basal to lycophytes modern clubmosses and allies 6 The relationships of Junggaria Cooksonella remain uncertain References edit a b c d e f g h Cai C Y Dou Y W amp Edwards D 1993 New Observations on a Pridoli Plant Assemblage from North Xinjiang Northwest China with Comments on its Evolutionary and Palaeogeographical Significance PDF Geological Magazine 130 2 155 170 Bibcode 1993GeoM 130 155C doi 10 1017 S0016756800009821 Dou Y W amp Sun Z H 1983 Devonian Plants Palaeontological Atlas of Xinjiang Vol II Late Palaeozoic Section in Chinese Beijing Geological Publishing House cited in Cai Dou amp Edwards 1993 Senkevich M S 1978 New Devonian psilophytes from Kazakhstan Ezheg Vses Paleontol Obshchestva in Russian 21 288 298 cited in Edwards D Fanning U amp Chaloner W G 1985 Evolution and Environment in the Late Silurian Early Devonian The Rise of the Pteridophytes Philosophical Transactions of the Royal Society B 309 1138 147 165 Bibcode 1985RSPTB 309 147E doi 10 1098 rstb 1985 0076 JSTOR 2396357 See e g Gensel Patricia G 2008 The Earliest Land Plants Annu Rev Ecol Evol Syst 39 459 77 doi 10 1146 annurev ecolsys 39 110707 173526 p 469 Gerrienne P amp Gonez P 2011 Early evolution of life cycles in embryophytes A focus on the fossil evidence of gametophyte sporophyte size and morphological complexity Journal of Systematics and Evolution 49 1 16 doi 10 1111 j 1759 6831 2010 00096 x S2CID 29795245 Crane P R Herendeen P amp Friis E M 2004 Fossils and plant phylogeny American Journal of Botany 91 10 1683 99 doi 10 3732 ajb 91 10 1683 PMID 21652317 Retrieved from https en wikipedia org 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