Rhynie chert
1631677
224916583
2008-07-11T00:03:53Z
Dysmorodrepanis
303688
/* Arthropods */
[[Image:Rhynie chert.jpg|thumb|300px|Hand sample of the Rhynie Chert from Rhynie, Scotland.]]
{{coord|display=title|57|20|12|N|002|50|29|W}}
The '''Rhynie chert''' is an Early [[Devonian]] [[Lagerstätte]]
found near the village of [[Rhynie]], [[Aberdeenshire]], [[Scotland]], containing exceptionally preserved plant, fungus, lichen and animal material [[petrified]] in three dimensions by covering with fast-setting volcanic minerals. The bulk of the fossil bed consists of primitive [[plant]]s (which had [[xylem|water-conducting cells]] and [[spores|sporangia]], but no true [[leaf|leaves]]), along with [[arthropod]]s, lichens, algae and fungi.
This fossil bed is remarkable for two reasons. Firstly, the age of the site ([[Pragian]], [[Devonian|Early Devonian]], formed about {{Ma|410|}}<ref>{{cite journal|author=Rice, C. M., Ashcroft, W. A., Batten, D. J., Boyce, A. J., Caulfield, J. B. D., Fallick, A. E., Hole, M. J., Jones, E., Pearson, M. J., Rogers, G., Saxton, J. M., Stuart, F. M., Trewin, N. H. & Turner, G.|year=1995|title=A Devonian auriferous hot spring system, Rhynie, Scotland|journal=Journal of the Geological Society, London|volume=152|pages=229–250|doi=10.1144/gsjgs.152.2.0229}}</ref><ref>http://www.bgs.ac.uk/nigl/pdf_downloads/2004AnnualReport.pdf</ref>) places it at an early stage in the colonisation of land. Secondly, these [[chert]]s are famous for their exceptional state of [[ultrastructure|ultrastructural]] preservation, with individual cell walls easily visible in polished specimens. [[Stomata]] have been counted and [[lignin]] remnants detected in the plant material, and the breathing apparatus of [[trigonotarbids]] (known as [[book lung]]s) can be seen in cross-sections. Fungal [[hypha]]e can be seen entering plant material, acting as decomposers and [[mycorrhiza]]l [[symbiosis|symbionts]].
==Conditions of formation==
The chert was formed when silica-rich water from volcanic springs rose rapidly and [[petrifaction|petrified]] the early terrestrial [[ecosystem]], ''in situ'' and almost instantaneously, in much the same fashion that organisms are petrified by hot springs today<ref name=Trewin1996/> - although the astounding fidelity of preservation has not been found in recent deposits.<ref name=Trewin2003/> Hot springs, with temperatures between 90–120{{oC}},<ref name=Trewin1996/> were active in a number of episodes; the water had probably cooled to under 30{{oC}} before it reached the fossilised organisms.<ref name=Trewin2004/> Their activity is preserved in 53 beds, 80mm thick on average, over a 35.41m sequence,<ref name=Powell2000>{{cite journal|doi=10.1144/GSL.SP.2000.180.01.23|title=Palaeoecology and plant succession in a borehole through the Rhynie cherts, Lower Old Red Sandstone, Scotland|year=2000|author=Powell, C. L.|journal=Geological Society London Special Publications|volume=180|pages=439}}</ref> interbedded with sands, shales and [[tuff]]s - which speak of local volcanic activity.<ref name=Rice2002>{{cite journal
| author = Rice, C.M.
| coauthors = Trewin, N.H.; Anderson, L.I.
| year = 2002
| title = Geological setting of the Early Devonian Rhynie cherts, Aberdeenshire, Scotland: an early terrestrial hot spring system
| journal = Journal of Geological Society
| volume = 159
| issue = 2
| pages = 203
| url = http://jgs.lyellcollection.org/cgi/content/abstract/159/2/203
| accessdate = 2008-05-15
| format = abstract
| doi = 10.1144/0016-764900-181
}}</ref> Deposition was very rapid.<ref name=Wellman2006/> The fluids originated from a shallowly dipping extensional fault system to the west, which bounded an extensional half-[[graben]].<ref name=Rice2002/>
Fossils were formed as silica formed in the hot springs themselves;<ref name=Trewin1996/> when silica-rich water flooded the surrounding areas;<ref name=Trewin1996/> and when it permeated into the surrounding soil.<ref name=Trewin1996/> The texture of the sinter formed resemble those found today in freshwater streams at [[Yellowstone]] which are typically alkaline (pH 8.7) and tepid (20-28{{oC}}).<ref name=Trewin2003/> The springs were periodically active, and flowed into an alluvial plain containing small lakes.<ref name=Powell2000/> By analogy with Yellowstone, the chert itself probably formed in a marshy area towards the latter end of the extent of outwash from the springs.<ref name=Trewin2004/> Living vegetation covered around 55% of the land area, with litter covering 30% and the remaining 15% of the ground being bare.<ref name=Trewin2004/>
A braided<ref name=Fayers2003>{{cite journal | author = Fayers | year = 2003 | doi = 10.1017/S0263593300000729 | title = A review of the palaeoenvironments and biota of the Windyfield chert | journal = Transactions of the Royal Society of Edinburgh Earth Sciences | volume = 94 }}
:Contains useful reconstructions of both the plant associations, and the regional setting.</ref> river flowing to the north periodically deposited the sandy layers found in cores when it flooded its banks.<ref name=Trewin2004>{{cite journal
| author = Trewin, N.H.
| coauthors = Wilson, E.
| year = 2004
| title = Correlation of the Early Devonian Rhynie chert beds between three boreholes at Rhynie, Aberdeenshire
| journal = Scottish Journal of Geology
| volume = 40
| issue = 1
| pages = 73–81
| doi = 10.1144/0036-9276/01-239
| doi_brokendate = 2008-06-23
}}</ref>
Sedimentary textures which appear to have formed in the hydrothermal vents themselves are preserved with a brecciated texture;<ref name=Trewin1996/> "geyserite", a sediment with a botryoidal form reminiscent of modern vent margins, is also found.<ref name=Trewin1996/> Spores collected from within surrounding rocks had been heated to different degrees, implying a complex history of local heating by volcanic processes.<ref name=Wellman2006>{{cite journal|doi=10.1017/S0263593300001449|title=Spore assemblages from the Lower Devonian ‘Lower Old Red Sandstone’ deposits of the Rhynie outlier, Scotland|year=2006|author=Wellman, Charles H.|journal=Transactions of the Royal Society of Edinburgh Earth Sciences|volume=97}}</ref>
==Preservation==
===Plants===
The preservation of plants varies from perfect three dimensional cellular [[permineralisation]] to flattened charcoal films. <ref name=Trewin1996>{{cite journal|titleo=The Rhynie cherts: an early Devonian ecosystem preserved by hydrothermal activity|journal=Ciba Found Symp. |year=1996|volume=202|pages=131–45|pmid=9243014}}</ref> On occasion, plants may have their vertical axes preserved in growth position, with [[rhizoid]]s still attached to [[rhizome]]s; even the [[plant litter]] is preserved.<ref name=Trewin1996/>
Plants were only found on the land - none lived in the water of lakes or hot springs.<ref name=Powell2000/> ''[[Rhynia]]'' typically grew on sandy surfaces, and is often preserved there in life position; ''[[Horneophyton]]'' grew on {{wict|sinter}}, the sediment formed by the hot springs. These two colonisers were subsequently joined by other genera.<ref name=Powell2000/>
The time between sinter deposition events was too short to allow the populations to develop to climax communities, and correspondingly early colonisers appear most frequently, pseudo-randomly, in logged sequences.<ref name=Trewin2004/>
Plants demonstrate best the great value of the exceptional preservation of the Rhynie chert. The presence of soft tissue, including [[parenchyma]], is not observed elsewhere in the fossil record<ref name=Edwards2003/> until the advent of amber in the [[Triassic]].{{Verify source|date=May 2008}} This allows the study of structures such as the air spaces ''behind'' [[stomata]], whereas the conventional record at its best allows no more than the counting of stomata.<ref name=Edwards2003/> It has also enabled [[paleobotanist]]s to firmly deduce that plants such as ''Agalophyton'' were'' not'' aquatic, as once believed.<ref name=Edwards2003/> Further, as plants are preserved in situ, it permits the study of exactly how and ''why'' the branching patterns of the early plants emerged, whereas the conventional record only showed that branching was present.<ref name=Edwards2003>{{cite journal|doi=10.1017/S0263593300000778|title=Embryophytic sporophytes in the Rhynie and Windyfield cherts|year=2003|author=Edwards, Dianne|journal=Transactions of the Royal Society of Edinburgh Earth Sciences|volume=94}}</ref> The analysis of rhizomes and rhizoids makes it possible to discern which plants had an active water uptake system (e.g. ''Horneophyton''), and which were likely to have colonised waterlogged surfaces (''Asteroxylon'').<ref name=Edwards2003/> In some cases, it is possible to see different mechanisms of repairing wounds, and to deduce that they were caused by fungal or bacterial infection.<ref name=Edwards2003/>
The preservation of spores attached to [[sporangia]] allows spore genera to be matched with their producers - something that is otherwise very difficult to do.<ref name=Wellman2003>{{cite journal|doi=10.1017/S0263593300000791|title=Spores of the Rhynie chert plant Horneophyton lignieri (Kidston and Lang) Barghoorn and Darrah, 1938|year=2003|author=Wellman, Charles H.|journal=Transactions of the Royal Society of Edinburgh Earth Sciences|volume=94}}</ref> The chert also allows the identification of the gametophyte phases of species such as ''[[Aglaophyton]]''.<ref name=Taylor2005>{{cite journal|doi=10.1073/pnas.0501985102|title=Life history biology of early land plants: Deciphering the [[gametophyte]] phase|year=2005|author=Taylor, T. N.|journal=Proceedings of the [[United States National Academy of Sciences|National Academy of Sciences]]|volume=102|pages=5892|pmid=15809414}}</ref>
Analysis of spores shows that the flora was lacking in some elements common elsewhere at this time, likely due to its setting in a mountainous region, rather than in a lowland flood plain like most other fossil deposits.<ref name=Wellman2004/> However, the spores, which are distinctive enough to permit their producing organism to be identified - are identical to those found elsewhere in "normal" environments.<ref name=Wellman2004/> There is no clear-cut evidence that the plants of the Rhynie assemblage were specifically adapted to stressed environments,<ref name=Powell2000/> and it is likely that the flora in fact represents those members of the global fauna that happened to be capable of colonising and surviving a hot spring environment by virtue of fortuitous preadaptions.<ref name=Wellman2004/>
===Algae===
The only alga to have been found in the Rhynie chert is the charophyte ''[[Palaeonitella]]'',<ref name=Trewin2003/> which inhabited the alkaline freshwater pools towards the end of the sinter apron.<ref name=Kellman2003>{{cite journal|doi=10.1017/S0263593300000808|title=Charophyte algae from the Rhynie chert|year=2003|author=Kelman, Ruth|journal=Transactions of the Royal Society of Edinburgh Earth Sciences|volume=94}}</ref>
===Arthropods===
As a result of its exquisite preservation, the Rhynie chert boasts the most diverse non-marine fauna of its time.<ref name=Trewin2004/> Typical members of the Rhynie chert arthropod fauna include the [[crustacean]] ''[[Lepidocaris]]'', the [[euthycarcinoid]] ''[[Heterocrania]]'',<ref name=Trewin2003>{{cite journal
| author = Trewin, N.H.
| coauthors = Fayers, S.R.; Kelman, R.
| year = 2003
| title = Subaqueous silicification of the contents of small ponds in an Early Devonian hot-spring complex, Rhynie, Scotland
| journal = Canadian Journal of Earth Sciences
| volume = 40
| issue = 11
| pages = 1697–1712
| url = http://article.pubs.nrc-cnrc.gc.ca/ppv/RPViewDoc?_handler_=HandleInitialGet&articleFile=e03-065.pdf&journal=cjes&volume=40
| accessdate = 2008-05-15
| doi = 10.1139/e03-065
}}</ref> the [[springtail]] ''[[Rhyniella praecursor]]'', the [[Opiliones|harvestman]] ''[[Eophalangium sheari]]''<ref name=Dunlop2007>{{cite journal
| author = Dunlop, J.A.
| coauthors = Anderson, L.I.; Kerp, H.; Hass, H.
| year = 2007
| title = A harvestman (Arachnida: Opiliones) from the Early Devonian Rhynie cherts, Aberdeenshire, Scotland
| journal = Earth and Environmental Science Transactions of the Royal Society of Edinburgh
| volume = 94
| issue = 04
| pages = 341–354
| doi = 10.1017/S0263593300000730
}}</ref>, [[pseudoscorpion]]s, [[Acari]] (mites), and [[trigonotarbid]]s.<ref name=Wellman2004>{{cite journal
| doi=10.1098/rspb.2004.2686|pmid=15255055|title=Palaeoecology and palaeophytogeography of the Rhynie chert plants: evidence from integrated analysis of ''in situ'' and dispersed spores|year=2004|author=Wellman, Charles H.|journal=Proceedings of the Royal Society B Biological Sciences|volume=271|pages=985}}</ref>
The oldest known [[insect]] (''[[Rhyniognatha hirsti]]''), which resembles the modern springtails, was found in the Rhynie chert,<ref>{{cite journal|doi=10.1038/291317a0|title=A new assessment of ''Rhyniella'', the earliest known insect, from the Devonian of Rhynie, Scotland|year=1981|author=Whalley, Paul|journal=Nature|volume=291|pages=317}}</ref> pushing dates for the origination of insects back to the Silurian period.<ref name=Engel2004>{{cite journal|doi=10.1038/nature02291|title=New light shed on the oldest insect|year=2004|author=Engel, Michael S.|journal=Nature|volume=427|pages=627}}</ref>
===Fungi===
Fungi known from the Rhynie chert include the [[chytridiomycetes]],<ref name=Taylor1992>{{cite journal
| author = Taylor, T.N.
| coauthors = Remy, W.; Hass, H.
| year = 1992
| title = Fungi from the Lower Devonian Rhynie chert: Chytridiomycetes
| journal = American Journal of Botany
| volume = 79
| issue = 11
| pages = 1233–1241
| url = http://links.jstor.org/sici?sici=0002-9122(199211)79:11%3C1233:FFTLDR%3E2.0.CO;2-B
| accessdate = 2008-05-15
| doi = 10.2307/2445050
}}</ref> [[ascomycetes]],<ref name=Taylor2005>{{cite journal
| doi=10.3852/mycologia.97.1.269
| title=Perithecial ascomycetes from the 400 million year old Rhynie chert: an example of ancestral polymorphism
| year=2005
| author=Taylor, T.N.
| journal=Mycologia
| volume=97
| pages=269
}}</ref> oomycota (Peronosporomycetes)<ref name=Kriggs2007>{{cite journal|doi=10.1111/j.1469-8137.2007.02008.x|title=Fungal endophytes in a 400-million-yr-old land plant: infection pathways, spatial distribution, and host responses|year=2007|author=Krings, Michael|journal=New Phytologist|volume=174|pages=648}}</ref> and glomeromycetes;<ref name=Berbee2007/> indeed the only fungal groups ''not'' yet known from the Rhynie are the Zygomycota (although they may have formed lichens - see later), and the Basidiomycota,<ref name=Kriggs2007/> the latter of which may not even have evolved by Rhynie time.<ref name=Berbee2007/>{{rp|Fig. 1}}
The Chytridiomycetes, or Chytrids, are a basal group of fungi, closely related to the true fungi.
The chytrids display a range of behaviour in the Rhynie chert. {{wict|Eucarpic}} and {{wict|holocarpic}} forms are known - i.e. some forms grew specialised fruiting bodies while others did not show specialisation in this fashion.<ref name=Taylor1992/> {{wict|Saprotrophy}} may be present, and parasitism is common; one individual has even been found parasitising a germinating gametophyte..<ref name=Taylor1992/> The fungi were aquatic, and grew in both plants and algae; they are also found preserved "loose" in the chert matrix.<ref name=Taylor1992/> Their flagellate spores are preserved.<ref name=Taylor1992/>
===Cyanobacteria===
In the rare instances that [[cyanobacteria]] are found in the fossil record, their presence is usually the subject of much controversy, for their simple form is difficult to distinguish from inorganic structures such as bubbles.
However, ''bona fide'' cyanobacteria are preserved in the Rhynie chert. The aquatic organisms are thought to belong to the [[Oscillatoriales]] section on the basis of [[biomarker]] absence.<ref name=Krings2007>{{cite journal | author = Krings | year = 2007 | doi = 10.1016/j.revpalbo.2007.05.002 | title = A filamentous cyanobacterium showing structured colonial growth from the Early Devonian Rhynie chert | journal = Review of Palaeobotany and Palynology | volume = 146 | pages = 265 }}</ref> The fossils are filamentous, around 3 μm in diameter, and grew on plants and the sediment itself. They occasionally form structured colonies which go on to create [[microbial mats]].<ref name=Krings2007/>
===Lichens===
A new genus of lichen, ''Winfrenatia'', has been recovered from the Rhynie chert. The lichen comprises a thallus, made of layered, aseptate hyphae; a number of depressions are formed on its top surface. Each depression contains a net of hyphae holding a sheathed cyanobacterium. The fungus appears to be related to the Zygomycetes, and the photobiont resembles the {{wict|coccoid}} [[Gloeocapsa]] and [[Chroococcidiopsis]].<ref name=Taylor1997>{{cite journal|title=A cyanolichen from the Lower Devonian Rhynie chert|author=Taylor, T.N.;Hass, H; Kerp, H|year=1997|journal=Am J Bot|volume=84|pages=992|doi=10.2307/2446290}}</ref>
==Interactions==
The Rhynie chert, by preserving a snapshot of an ecosystem ''in situ'' in high fidelty, gives a unique opportunity to observe interactions between species and kingdoms. There is evidence of parasitic behaviour by fungi on algae ''[[Palaeonitella]]'', provoking a [[hypertrophy|hypertrophic]] response.<ref name=Taylor1992/> Herbivory is also evident, judging by boring and piercing<ref name=Labanderia2007>{{cite journal | author = Labandeira, CONRAD| year = 2007 | doi = 10.1111/j.1744-7917.2007.00152.x | title = The origin of herbivory on land: Initial patterns of plant tissue consumption by arthropods | journal = Insect Science | volume = 14 | pages = 259}}</ref> wounds in various states of repair, and the mouthparts of arthropods.<ref name=Kenrick2000>{{cite book
| author = Kenrick, P.
| coauthors = Crane, P.R.
| year = 2000
| title = The Origin And Early Evolution Of Plants On Land
| journal = Shaking the Tree: Readings from Nature in the History of Life
| url = http://books.google.com/books?hl=en&lr=&ie=UTF-8&id=M6yF0pU4eCsC&oi=fnd&pg=PA217&ots=sdZaNyvWU5&sig=dSdcQnOPIRsiNEbZ-US657yTR0g
| format = Google books
| accessdate = 2008-05-16
}}</ref>
[[Coprolite]]s - fossilised droppings - give a useful insight of what animals ate, even if the animals cannot be identified. Coprolites found in the Rhynie chert are typically between 0.5 and 3 mm in size, and contain a variety of contents.<ref name=Habgood2007>{{cite journal
| author = Habgood, K.S.
| coauthors = Hass, H.; Kerp, H.
| year = 2003
| title = Evidence for an early terrestrial food web: coprolites from the Early Devonian Rhynie chert
| journal = Earth and Environmental Science Transactions of the Royal Society of Edinburgh
| volume = 94
| issue = 04
| pages = 371–389
| doi = 10.1017/S0263593300000754
| publisher = Cambridge University Press
| url = http://journals.cambridge.org/abstract_S0263593300000754
| accessdate = 2008-05-15
| format = abstract
}}</ref> Analysis of coprolites allows the identification of different feeding modes, including detritovory and herbivory; some coprolites are so densely packed with spores that it is possible that these made up a substantial proportion of some organisms' diets.<ref name=Habgood2007/>
Plants responded to fungal colonisation in different ways, depending on the fungus. The rhizoids of ''[[Nothia]]'' displayed three responses to fungal infestation: the hyphae of some (mutualistic) colonists were encased by plant cell walls; other (parasitic) fungi were met with typical host responses of increased rhizome cell size; while yet other fungi solicited an increase in thickness and pigmentation of cell walls.<ref name=Berbee2007>{{cite journal|doi=10.1111/j.1469-8137.2007.02080.x|title=Rhynie chert: a window into a lost world of complex plant?fungus interactions|year=2007|author=Berbee, Mary L.|journal=New Phytologist|volume=174|pages=475}}</ref> Once inside a plant cell, fungi produced spores, which are found in decaying plant cells;<ref name=Berbee2007/> the cells may have decayed as a defence mechanism to prevent the fungi from spreading.<ref name=Kriggs2007/>
Fungal interactions are known to promote speciation in modern plants, and presumably also affected Devonian diversity by providing a selection pressure.<ref name=Kriggs2007/>
{{incomplete}}
{{main|mycorrhiza}}
[[Mycorrhizae]] are also found in the Rhynie chert.<ref name="Remy1994">{{cite journal|author=Remy W, Taylor TN, Hass H, Kerp H |year=1994|title= 4 hundred million year old vesicular-arbuscular mycorrhizae|journal= Proc. National Academy of Sciences|volume=91|pages=11841–11843|doi= 10.1073/pnas.91.25.11841|pmid= 11607500}}</ref>
==Location==
The bed lies under at least 1 [[metre]] of [[overburden]], in a single small field near the village of [[Rhynie]], so is effectively inaccessible to collectors; besides which, the site is an [[SSSI]]. A second unit, the Windyfield chert, is located some 700m from the Rhynie. The Rhynie chert extends for at least 80m along strike and 90m down-dip.<ref name=Trewin2004/>
==History of research==
The chert was discovered by Dr William Mackie while mapping the western margin of the Rhynie basin in 1910–1913.<ref name=Trewin2003h/> Trenches were cut into the chert at the end of this period, and Kidston & Lang worked furiously to describe the plant fossils between 1917 and 1921.<ref name=Trewin2003h/> The arthropods were examined soon afterwards by different workers.<ref name=Trewin2003h/> Interest in the chert then waned until the field was reinvigorated by Lyon in the late 1950s, and new material was collected by further trenching from 1963-71.<ref name=Trewin2003h/> Since 1980, the chert has been examined by the Münster school, and from 1987 Aberdeen University, who confirmed that the chert was indeed produced by a hot spring setting.<ref name=Trewin2003h/>
Cores, allowing an insight into the evolution of the chert over time, were drilled in 1988 and 1997, accompanied by further trenching efforts, which unearthed the Windyfield chert.<ref name=Trewin2003h>{{cite journal | author = Trewin | year = 2003 | doi = 10.1017/S0263593300000699 | title = History of research on the geology and palaeontology of the Rhynie area, Aberdeenshire, Scotland | journal = Transactions of the Royal Society of Edinburgh Earth Sciences | volume = 94 }}</ref>
Until recently, the Rhynie chert was the only such deposit known from the geological record, although recent work has turned up other localities from different time periods and continents.<ref name=Channing2007>{{cite journal | author = Channing | year = 2007 | doi = 10.1017/S0016756807003263 | title = A new Middle – Late Jurassic flora and hot spring chert deposit from the Deseado Massif, Santa Cruz province, Argentina | journal = Geological Magazine | volume = 144 | pages = 401 }}</ref>
==See also==
* [[Geology of Scotland]]
* [[Evolutionary history of plants]]
==External links==
* {{cite web|url=http://www.abdn.ac.uk/rhynie/intro.htm|title= Rhynie Chert Learning Resource|publisher = University of Aberdeen}}
==Further reading==
* {{cite book
| author = Taylor, T.N.
| coauthors = Taylor, E.L.
| year = 2000
| title = The Rhynie chert ecosystem: a model for understanding fungal interactions
| journal = Microbial Endophytes
| url = http://books.google.com/books?hl=en&lr=&ie=UTF-8&id=c_kuo5WD6GUC&oi=fnd&pg=PA31&dq=rhynie+chert+herbivory&ots=0K4HgbKoch&sig=J13ZbOTUCUQIZOuw8IyIeqCjr00
| format = Free access @ Google books
| accessdate = 2008-05-16
}}
==References==
{{reflist|2}}
{{early plants}}
[[Category:Paleontological sites]]
[[Category:Sedimentary rocks]]
[[Category:Devonian]]
[[de:Rhynie Chert]]