Yarravia is a genus of extinct vascular plants mainly known from fossils found in Victoria, Australia.[1] Originally the rocks in which they were found were considered to be late Silurian in age; more recently they have been found to be Early Devonian (Pragian, around 410 million years ago).[4] Specimens consist only of incomplete leafless stems, some of which bore groups of spore-forming organs or sporangia which were fused, at least at the base.[1]
Fossils of Yarravia were found at a location called the 'Yarra Track', near to the town of Wood's Point, Victoria, Australia.[1] The shale in which they were found, now called the Wilson Creek Shale, was for many years regarded as of late Silurian age. The dating was based on graptolite fossils which were identified as Monograptus uncinatus, which is of early Ludlow age (around 430 to 420 million years ago). These were subsequently described as a new species, M. thomasi, which proved to be of Early Devonian age (Pragian, around 410 million years ago). Rocks of Silurian age do occur in the region and the fossil plant Baragwanathia has been found from both late Silurian and the Early Devonian strata. However, Yarravia was found only in the Devonian shales.[4]
Fossils collected near Rebreuve, Pas-de-Calais Department, northern France, were named Yarravia minor by Danzé-Corsin in 1956. The strata in which they were found were initially considered Pragian, but are now thought to be Emsian (from around 410 to 390 million years ago).
Descriptionedit
Only the uppermost parts of Yarravia have been found in Australia. The stems (axes) were bare, around 2 to 2.5 mm in diameter. The longest pieces were up to 7.5 cm in length. No examples of branching were seen. The internal structure of the stems is not preserved.[1]
The sporangia were borne in a group at the ends of stems. The specimens are flattened, so that the original shape is not entirely clear, but up to five or six upright elongated sporangia appear to have been radially arranged on a base formed by a widening of the stem; there may have been a central space. At the base the sporangia are fused together, but their tips may be free. The entire structure can be described as a 'synangium'. Blackened material inside the sporangia was assumed to have been spores.[1]
Two species were described from the Australian material. In Y. oblonga, the synangium (the group of fused sporangia) was longer than wide, being about 7 mm long by 1.25 mm wide. The tips of the sporangia were free and appear to consist of tissue not containing spores. The synangium of Y. subsphaerica was significantly larger and as long as wide, being about 1 cm in length and width. The tips of the sporangia were less prominent.[1]
Taxonomyedit
The genus Yarravia was named in 1935 by Lang and Cookson, based on fossils found in an Australian locality they called the 'Yarra Track'. Two species were named, Y. oblonga and Y. subsphaerica, referring to the shape of the sporangial heads.[1]
Phylogenyedit
The relationships of Yarravia are uncertain. The genus Hedeia, of similar age, which is known from both Australia and China, had a similar radial cluster of sporangia at the tips of stems; the two genera are distinctive in this way compared to plants from other regions.[5] It has been suggested that Yarravia may simply be Hedeia in a different state of preservation, and that Yarravia is not really synangial.[6] Both genera have been treated as 'rhyniophytes',[7] although other studies regard their placement as uncertain.[8]
Referencesedit
^ abcdefghijLang, W.H. & Cookson, I.C. (1935), "On a Flora, Including Vascular Land Plants, Associated with Monograptus, in Rocks of Silurian Age, from Victoria, Australia", Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, 224 (517): 421–449, Bibcode:1935RSPTB.224..421L, doi:10.1098/rstb.1935.0004, JSTOR 92292
^Edwards, Dianne (2006), "Danziella artesiana, a new name for Zosterophyllum artesianum from the Lower Devonian of Artois, northern France", Review of Palaeobotany and Palynology, 142 (3–4): 93–101, doi:10.1016/j.revpalbo.2006.04.008
^Hao, S.-G. & Gensel, P.G. (1995), "A New Genus and Species, Celatheca beckii, from the Siegenian (Early Devonian) of Southeastern Yunnan, China", International Journal of Plant Sciences, 156 (6): 896–909, doi:10.1086/297312, S2CID 86664097
^ abTims, J.D. & Chambers, T.C. (1984), "Rhyniophytina and Trimerophytina from the early land flora of Victoria, Australia" (PDF), Palaeontology, 27: 265–279, retrieved 2011-12-20
^Hao, S.-G. & Gensel, P.G. (1998), "Some new plant finds from the Posongchong Formation of Yunnan, and consideration of a phytogeographic similarity between South China and Australia during the Early Devonian", Science China Earth Sciences, 41 (1): 1–13, Bibcode:1998ScChD..41....1H, doi:10.1007/bf02932414, S2CID 55451586
^Taylor, T.N.; Taylor, E.L. & Krings, M. (2009), Paleobotany, The Biology and Evolution of Fossil Plants (2nd ed.), Amsterdam; Boston: Academic Press, ISBN978-0-12-373972-8, p. 248
^Kenrick, P. & Crane, P.R. (1997b), "The origin and early evolution of plants on land", Nature, 389 (6646): 33–39, Bibcode:1997Natur.389...33K, doi:10.1038/37918, S2CID 3866183
April 12, 2024
yarravia, genus, extinct, vascular, plants, mainly, known, from, fossils, found, victoria, australia, originally, rocks, which, they, were, found, were, considered, late, silurian, more, recently, they, have, been, found, early, devonian, pragian, around, mill. Yarravia is a genus of extinct vascular plants mainly known from fossils found in Victoria Australia 1 Originally the rocks in which they were found were considered to be late Silurian in age more recently they have been found to be Early Devonian Pragian around 410 million years ago 4 Specimens consist only of incomplete leafless stems some of which bore groups of spore forming organs or sporangia which were fused at least at the base 1 YarraviaTemporal range Pragian Emsian PreꞒ Ꞓ O S D C P T J K Pg NScientific classificationKingdom PlantaeClade TracheophytesStem group Rhyniophytes Genus YarraviaW H Lang amp Cookson 1935 1 SpeciesY oblonga W H Lang amp Cookson 1935 1 Y subsphaerica W H Lang amp Cookson 1935 1 Y minor P Danze Corsin 1956 2 Y gorelovii Ananiev 1960 3 Contents 1 Source of fossils 2 Description 3 Taxonomy 4 Phylogeny 5 ReferencesSource of fossils editFossils of Yarravia were found at a location called the Yarra Track near to the town of Wood s Point Victoria Australia 1 The shale in which they were found now called the Wilson Creek Shale was for many years regarded as of late Silurian age The dating was based on graptolite fossils which were identified as Monograptus uncinatus which is of early Ludlow age around 430 to 420 million years ago These were subsequently described as a new species M thomasi which proved to be of Early Devonian age Pragian around 410 million years ago Rocks of Silurian age do occur in the region and the fossil plant Baragwanathia has been found from both late Silurian and the Early Devonian strata However Yarravia was found only in the Devonian shales 4 Fossils collected near Rebreuve Pas de Calais Department northern France were named Yarravia minor by Danze Corsin in 1956 The strata in which they were found were initially considered Pragian but are now thought to be Emsian from around 410 to 390 million years ago Description editOnly the uppermost parts of Yarravia have been found in Australia The stems axes were bare around 2 to 2 5 mm in diameter The longest pieces were up to 7 5 cm in length No examples of branching were seen The internal structure of the stems is not preserved 1 The sporangia were borne in a group at the ends of stems The specimens are flattened so that the original shape is not entirely clear but up to five or six upright elongated sporangia appear to have been radially arranged on a base formed by a widening of the stem there may have been a central space At the base the sporangia are fused together but their tips may be free The entire structure can be described as a synangium Blackened material inside the sporangia was assumed to have been spores 1 Two species were described from the Australian material In Y oblonga the synangium the group of fused sporangia was longer than wide being about 7 mm long by 1 25 mm wide The tips of the sporangia were free and appear to consist of tissue not containing spores The synangium of Y subsphaerica was significantly larger and as long as wide being about 1 cm in length and width The tips of the sporangia were less prominent 1 Taxonomy editThe genus Yarravia was named in 1935 by Lang and Cookson based on fossils found in an Australian locality they called the Yarra Track Two species were named Y oblonga and Y subsphaerica referring to the shape of the sporangial heads 1 Phylogeny editThe relationships of Yarravia are uncertain The genus Hedeia of similar age which is known from both Australia and China had a similar radial cluster of sporangia at the tips of stems the two genera are distinctive in this way compared to plants from other regions 5 It has been suggested that Yarravia may simply be Hedeia in a different state of preservation and that Yarravia is not really synangial 6 Both genera have been treated as rhyniophytes 7 although other studies regard their placement as uncertain 8 References edit a b c d e f g h i j Lang W H amp Cookson I C 1935 On a Flora Including Vascular Land Plants Associated with Monograptus in Rocks of Silurian Age from Victoria Australia Philosophical Transactions of the Royal Society of London Series B Biological Sciences 224 517 421 449 Bibcode 1935RSPTB 224 421L doi 10 1098 rstb 1935 0004 JSTOR 92292 Edwards Dianne 2006 Danziella artesiana a new name for Zosterophyllum artesianum from the Lower Devonian of Artois northern France Review of Palaeobotany and Palynology 142 3 4 93 101 doi 10 1016 j revpalbo 2006 04 008 Hao S G amp Gensel P G 1995 A New Genus and Species Celatheca beckii from the Siegenian Early Devonian of Southeastern Yunnan China International Journal of Plant Sciences 156 6 896 909 doi 10 1086 297312 S2CID 86664097 a b Tims J D amp Chambers T C 1984 Rhyniophytina and Trimerophytina from the early land flora of Victoria Australia PDF Palaeontology 27 265 279 retrieved 2011 12 20 Hao S G amp Gensel P G 1998 Some new plant finds from the Posongchong Formation of Yunnan and consideration of a phytogeographic similarity between South China and Australia during the Early Devonian Science China Earth Sciences 41 1 1 13 Bibcode 1998ScChD 41 1H doi 10 1007 bf02932414 S2CID 55451586 See e g Hao amp Gensel 1995 op cit p 906 Taylor T N Taylor E L amp Krings M 2009 Paleobotany The Biology and Evolution of Fossil Plants 2nd ed Amsterdam Boston Academic Press ISBN 978 0 12 373972 8 p 248 Kenrick P amp Crane P R 1997b The origin and early evolution of plants on land Nature 389 6646 33 39 Bibcode 1997Natur 389 33K doi 10 1038 37918 S2CID 3866183 Retrieved from https en wikipedia org w index php title Yarravia amp oldid 1170970032, wikipedia, wiki, book, books, library,
