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96-540: The sandstone in the Elgin area was originally quarried for building materials. The quarries were where the first reptile fossils were found, and they have continued to yield fossils to this day. The first Elgin Reptile was discovered in 1844, but because it was only a few scales scientists of the time believed it was an Old Red Sandstone fish fossil, which were relatively well-known from sites across Northern Scotland. In 1851

192-565: A Mid-Devonian cooling of around 5 °C (9 °F). The Late Devonian warmed to levels equivalent to the Early Devonian; while there is no corresponding increase in CO 2 concentrations, continental weathering increases (as predicted by warmer temperatures); further, a range of evidence, such as plant distribution, points to a Late Devonian warming. The climate would have affected the dominant organisms in reefs ; microbes would have been

288-514: A boat trip from Dunglass Burn east along the coast with the geologist Sir James Hall of Dunglass and at Siccar Point found what Hutton called "a beautiful picture of this junction washed bare by the sea", where 345-million-year-old Old Red Sandstone overlies 425-million-year-old Silurian greywacke . In the early 19th century, the paleontology of the formation was studied intensively by Hugh Miller , Henry Thomas De la Beche , Roderick Murchison , and Adam Sedgwick —Sedgwick's interpretation

384-562: A cast of the dicynodont Gordonia . The reptiles of Cutties Hillock , Quarrywood and the Hopeman Sandstones are Late Permian, around 250 million years old, while most other reptile fossils are found in the early Triassic rocks of Lossiemouth , Spynie and Findrassie , and are about 220 million years old. The fossils are “recognised” by the Scottish Government as a Collection of National Significance. Many of

480-464: A county in southwestern England, where a controversial argument in the 1830s over the age and structure of the rocks found throughout the county was resolved by adding the Devonian Period to the geological timescale. The Great Devonian Controversy was a lengthy debate between Roderick Murchison , Adam Sedgwick and Henry De la Beche over the naming of the period. Murchison and Sedgwick won

576-630: A diverse ecosystem of reefs and marine life. Devonian marine deposits are particularly prevalent in the midwestern and northeastern United States. Devonian reefs also extended along the southeast edge of Laurussia, a coastline now corresponding to southern England , Belgium , and other mid-latitude areas of Europe. In the Early and Middle Devonian, the west coast of Laurussia was a passive margin with broad coastal waters, deep silty embayments, river deltas and estuaries, found today in Idaho and Nevada . In

672-763: A low-latitude archipelago to the north of Gondwana. They were separated from the southern continent by an oceanic basin: the Paleo-Tethys . Although the western Paleo-Tethys Ocean had existed since the Cambrian, the eastern part only began to rift apart as late as the Silurian. This process accelerated in the Devonian. The eastern branch of the Paleo-Tethys was fully opened when South China and Annamia (a terrane equivalent to most of Indochina ), together as

768-529: A massive extinction event . ( See Late Devonian extinction ). Primitive arthropods co-evolved with this diversified terrestrial vegetation structure. The evolving co-dependence of insects and seed plants that characterized a recognizably modern world had its genesis in the Late Devonian Epoch. The development of soils and plant root systems probably led to changes in the speed and pattern of erosion and sediment deposition. The rapid evolution of

864-517: A narrow zone from Dulas Bay on Anglesey's northeast coast, southwards to the town of Llangefni . In 1787 James Hutton noted what is now known as Hutton's Unconformity at Inchbonny, Jedburgh , and in early 1788 he set off with John Playfair to the Berwickshire coast and found more examples of this sequence in the valleys of the Tower and Pease Burns near Cockburnspath . They then took

960-594: A number of distinct sedimentary basins throughout Britain has been established. The Orcadian Basin extends over a wide area of North East Scotland and the neighbouring seas. It encompasses the Moray Firth and adjoining land areas, Caithness, Orkney and parts of Shetland . South of the Moray Firth, two distinct sub-basins are recognized at Turriff and at Rhynie . The sequence is more than 4 kilometres (13,000 ft) thick in parts of Shetland. The main basin

1056-601: A second indisputably reptilian fossil was found. Fossils of Gordonia were first found by Scottish naturalist Ramsay Heatley Traquair in 1885 and E.T. Newton described several key fossil specimens. Elgin Museum is Scotland's oldest independent museum. The Elgin Reptiles, footprints, and older fish fossils held by the Elgin Museum are “recognised” by the Scottish Government as a Collection of National Significance due to

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1152-664: A terrestrial ecosystem that contained copious animals opened the way for the first vertebrates to seek terrestrial living. By the end of the Devonian, arthropods were solidly established on the land. The Late Devonian extinction is not a single event, but rather is a series of pulsed extinctions at the Givetian-Frasnian boundary, the Frasnian-Famennian boundary, and the Devonian-Carboniferous boundary. Together, these are considered one of

1248-541: A unified continent, detached from the northeastern sector of Gondwana. Nevertheless, they remained close enough to Gondwana that their Devonian fossils were more closely related to Australian species than to north Asian species. Other Asian terranes remained attached to Gondwana, including Sibumasu (western Indochina), Tibet, and the rest of the Cimmerian blocks. While the South China-Annamia continent

1344-602: A volcanically active region during the Devonian, as it continued to assimilate smaller island arcs. The island arcs of the region, such as the Balkhash-West Junggar Arc, exhibited biological endemism as a consequence of their location. Siberia was located just north of the equator as the largest landmass in the Northern Hemisphere. At the beginning of the Devonian, Siberia was inverted (upside down) relative to its modern orientation. Later in

1440-1005: Is a continuous outcrop along the Highland Boundary Fault from Stonehaven on the North Sea coast to Helensburgh and beyond to Arran . A more disconnected series of outcrops occur along the line of the Southern Uplands Fault from Edinburgh to Girvan . Old Red Sandstone often occurs in conjunction with conglomerate formations, one such noteworthy cliffside exposure being the Fowlsheugh Nature Reserve , Kincardineshire . A series of outcrops occur from East Lothian southwards through Berwickshire . Hutton's famous unconformity at Siccar Point occurs within this basin - see History of study below. This relatively large basin extends across much of South Wales from southern Pembrokeshire in

1536-550: Is an assemblage of rocks in the North Atlantic region largely of Devonian age. It extends in the east across Great Britain, Ireland and Norway, and in the west along the eastern seaboard of North America . It also extends northwards into Greenland and Svalbard . These areas were a part of the paleocontinent of Euramerica (Laurussia). In Britain it is a lithostratigraphic unit (a sequence of rock strata ) to which stratigraphers accord supergroup status and which

1632-738: Is considered to be an intramontane basin resulting from crustal rifting associated with post-Caledonian extension , possibly accompanied by strike-slip faulting along the Great Glen Fault system. There are a scatter of exposures of the Old Red Sandstone around Oban and the Isle of Kerrera on the West Highland coast, this unit is sometimes referred to as the Kerrera Sandstone Formation. The unit

1728-650: Is dominated by terrigenous deposits and conglomerates at its base, and progresses to a combination of dunes , and sediments that may have been laid down in lakes , river , estuaries, and possibly other coastal environments. The Old Red Sandstone was long thought to have been deposited mostly in freshwater, but more recent studies have discovered marine fossils (such as brachiopods ) in some locations, its vertebrate fauna also occurs in typically marine environments, and an isotopic study also found significant marine influence in mineralised tissues of its vertebrates. Thus, at least some strata appear to have been deposited on

1824-695: Is formally broken into Early, Middle and Late subdivisions. The rocks corresponding to those epochs are referred to as belonging to the Lower, Middle and Upper parts of the Devonian System. The Early Devonian lasted from 419.2 to 393.3 Ma. It began with the Lochkovian Stage 419.2 to 410.8 Ma, which was followed by the Pragian from 410.8 to 407.6 Ma and then by the Emsian , which lasted until

1920-578: Is good evidence that Rheic oceanic crust experienced intense subduction and metamorphism under Mexico and Central America. The closure of the eastern part of the Rheic Ocean is associated with the assemblage of central and southern Europe. In the early Paleozoic, much of Europe was still attached to Gondwana, including the terranes of Iberia , Armorica (France), Palaeo-Adria (the western Mediterranean area), Bohemia , Franconia , and Saxothuringia . These continental blocks, collectively known as

2016-431: Is merely an erosional contact incorporating debris of the slate in a basal conglomerate. The ORS deposits around Oban are considered latest Silurian ( Pridoli ) to earliest Devonian in age. They are interpreted as alluvial fans which filled a depositional basin from the east and northeast. Small outliers occur near Taynuilt and either side of Loch Avich . The deposits are especially obvious on Kerrera where they form

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2112-430: Is observed in many of those plants. Some of the early land plants such as Drepanophycus likely spread by vegetative growth and spores. The earliest land plants such as Cooksonia consisted of leafless, dichotomous axes with terminal sporangia and were generally very short-statured, and grew hardly more than a few centimetres tall. Fossils of Armoricaphyton chateaupannense , about 400 million years old, represent

2208-554: Is of considerable importance to early paleontology . The presence of Old in the name is to distinguish the sequence from the younger New Red Sandstone which also occurs widely throughout Britain. The Old Red Sandstone describes a group of sedimentary rocks deposited in a variety of environments in the late Silurian , through the Devonian and into the earliest part of the Carboniferous . The body of rock , or facies ,

2304-707: Is represented by the Gupton and West Angle formations. The Freshwater East Formation, and corresponding Red Cliff Formation of north Pembrokeshire, are both late Silurian in age. A small and separate basin exists here where both alluvial and lacustrine deposits are recorded. Both the middle and upper ORS are missing but the lower ORS is represented, in ascending order, by the Bodafon, Traeth Bach, Porth y Mor and Traeth Lligwy formations. Calcretes are also recorded representing carbonate-rich soils developed between periods of sediment deposition. The present day outcrop occupies

2400-483: Is up to 128m thick in its type area and consists of green and red sandstones and conglomerates, typically containing large (10–30 cm or 4–12 in across) elliptical well rounded clasts, accompanied by siltstones, mudstones and limestones. On Kerrera a conglomerate of andesite boulders rests unconformably on Dalradian black, pyritic slates ( Easdale Slate) of the Easdale Subgroup . At Oban there

2496-669: The Hadley cell and the Ferrel cell . In these near-deserts, the Old Red Sandstone sedimentary beds formed, made red by the oxidised iron ( hematite ) characteristic of drought conditions. The abundance of red sandstone on continental land also lends Laurussia the name "the Old Red Continent". For much of the Devonian, the majority of western Laurussia (North America) was covered by subtropical inland seas which hosted

2592-802: The Moray Firth Basin, south of the Great Glen Fault . The Elgin Reptiles come from the Permian and Triassic rocks. These are called the Hopeman Sandstone Formation and the Burghead Sandstone Formation , both part of the New Red Sandstone Supergroup. Some marine reptiles have been found in a glacial erratic of Jurassic strata. Most of the sandstones are wind-blown desert dune deposits, but there are some river deposits and

2688-525: The Ordovician period. Fishes , especially jawed fish , reached substantial diversity during this time, leading the Devonian to often be dubbed the Age of Fishes . The armored placoderms began dominating almost every known aquatic environment. In the oceans, cartilaginous fishes such as primitive sharks became more numerous than in the Silurian and Late Ordovician . Tetrapodomorphs , which include

2784-481: The Paleo-Tethys Ocean and Rheic Ocean . By the early Devonian, the continent Laurussia (also known as Euramerica ) was fully formed through the collision of the continents Laurentia (modern day North America) and Baltica (modern day northern and eastern Europe). The tectonic effects of this collision continued into the Devonian, producing a string of mountain ranges along the southeastern coast of

2880-751: The Plateau Beds Formation is unconformably overlain by the Grey Grits Formation though further east these divisions are replaced by the Quartz Conglomerate Group which is itself subdivided into a variety of different formations. The sequence in Pembrokeshire differs from that of the main part of the basin and falls into two parts. In North Pembrokeshire to the north of the Ritec Fault , both

2976-475: The cladoxylopsids and progymnosperm Archaeopteris . These tracheophytes were able to grow to large size on dry land because they had evolved the ability to biosynthesize lignin , which gave them physical rigidity and improved the effectiveness of their vascular system while giving them resistance to pathogens and herbivores. In Eifelian age, cladoxylopsid trees formed the first forests in Earth history. By

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3072-463: The science of stratigraphy 's early debates were about the Old Red Sandstone. In older geological works predating theories of plate tectonics , the United States' Catskill Delta formation is sometimes referred to as part of the Old Red Sandstone. In the modern day it is recognized that the two are not stratigraphically continuous but are very similar due to being formed at approximately

3168-452: The " Big Five " mass extinctions in Earth's history. The Devonian extinction crisis primarily affected the marine community, and selectively affected shallow warm-water organisms rather than cool-water organisms. The most important group to be affected by this extinction event were the reef-builders of the great Devonian reef systems. Amongst the severely affected marine groups were the brachiopods, trilobites, ammonites, and acritarchs , and

3264-646: The Armorican Terrane Assemblage, split away from Gondwana in the Silurian and drifted towards Laurussia through the Devonian. Their collision with Laurussia leads to the beginning of the Variscan Orogeny , a major mountain-building event which would escalate further in the Late Paleozoic. Franconia and Saxothuringia collided with Laurussia near the end of the Early Devonian, pinching out the easternmost Rheic Ocean. The rest of

3360-536: The Armorican terranes followed, and by the end of the Devonian they were fully connected with Laurussia. This sequence of rifting and collision events led to the successive creation and destruction of several small seaways, including the Rheno-Hercynian, Saxo-Thuringian, and Galicia-Moldanubian oceans. Their sediments were eventually compressed and completely buried as Gondwana fully collided with Laurussia in

3456-574: The Carboniferous. Sea levels in the Devonian were generally high. Marine faunas continued to be dominated by conodonts, bryozoans , diverse and abundant brachiopods , the enigmatic hederellids , microconchids , and corals . Lily-like crinoids (animals, their resemblance to flowers notwithstanding) were abundant, and trilobites were still fairly common. Bivalves became commonplace in deep water and outer shelf environments. The first ammonites also appeared during or slightly before

3552-612: The Carboniferous. In 19th-century texts the Devonian has been called the "Old Red Age", after the red and brown terrestrial deposits known in the United Kingdom as the Old Red Sandstone in which early fossil discoveries were found. Another common term is "Age of the Fishes", referring to the evolution of several major groups of fish that took place during the period. Older literature on the Anglo-Welsh basin divides it into

3648-408: The Devonian seas. The first abundant genus of cartilaginous fish, Cladoselache , appeared in the oceans during the Devonian Period. The great diversity of fish around at the time has led to the Devonian being given the name "The Age of Fishes" in popular culture. The Devonian saw significant expansion in the diversity of nektonic marine life driven by the abundance of planktonic microorganisms in

3744-650: The Downtonian, Dittonian, Breconian, and Farlovian stages, the latter three of which are placed in the Devonian. The Devonian has also erroneously been characterised as a "greenhouse age", due to sampling bias : most of the early Devonian-age discoveries came from the strata of western Europe and eastern North America , which at the time straddled the Equator as part of the supercontinent of Euramerica where fossil signatures of widespread reefs indicate tropical climates that were warm and moderately humid. In fact

3840-506: The Early Devonian and the existence of fossils such as Protichnites suggest that amphibious arthropods may have appeared as early as the Cambrian ). By far the largest land organism at the beginning of this period was the enigmatic Prototaxites , which was possibly the fruiting body of an enormous fungus, rolled liverwort mat, or another organism of uncertain affinities that stood more than 8 metres (26 ft) tall, and towered over

3936-700: The Late Devonian the tectonic situation had relaxed and much of South America was covered by shallow seas. These south polar seas hosted a distinctive brachiopod fauna, the Malvinokaffric Realm, which extended eastward to marginal areas now equivalent to South Africa and Antarctica. Malvinokaffric faunas even managed to approach the South Pole via a tongue of Panthalassa which extended into the Paraná Basin . The northern rim of Gondwana

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4032-491: The Late Devonian, an approaching volcanic island arc reached the steep slope of the continental shelf and began to uplift deep water deposits. This minor collision sparked the start of a mountain-building episode called the Antler orogeny , which extended into the Carboniferous. Mountain building could also be found in the far northeastern extent of the continent, as minor tropical island arcs and detached Baltic terranes re-join

4128-682: The Late Devonian. The Altai-Sayan region was shaken by volcanism in the Early and Middle Devonian, while Late Devonian magmatism was magnified further to produce the Vilyuy Traps , flood basalts which may have contributed to the Late Devonian Mass Extinction. The last major round of volcanism, the Yakutsk Large Igneous Province, continued into the Carboniferous to produce extensive kimberlite deposits. Similar volcanic activity also affected

4224-782: The Late Permian-Early Triassic, and was moving North. Permian, Triassic and Jurassic rocks are rare in Scotland, but some can be found along the Northern edge of the Moray Firth , and in the Inner Hebrides, particularly on the Isle of Skye . The Hopeman Sandstone Formation quarry at Clashach is designated as a SSSI ( Site of Special Scientific Importance ) for its fossils. Many of the Elgin Reptile fossils contain no actual bone: they are often voids in

4320-497: The Middle Devonian began, 393.3 Ma. During this time, the first ammonoids appeared, descending from bactritoid nautiloids . Ammonoids during this time period were simple and differed little from their nautiloid counterparts. These ammonoids belong to the order Agoniatitida , which in later epochs evolved to new ammonoid orders, for example Goniatitida and Clymeniida . This class of cephalopod molluscs would dominate

4416-743: The Raglan Mudstone is marked by a well-developed calcrete , the Bishop's Frome Limestone . The lowermost Devonian formation is the St Maughans Formation , itself overlain by the Brownstones Formation though with an intervening Senni Formation over much of the area. The Upper Devonian sequence is rather thinner and comprises a series of formations which are more laterally restricted. In the Brecon Beacons ,

4512-416: The Silurian and Devonian, it decreased across the span of the Devonian, particularly during the Pragian, and that the overall diversity of nektonic taxa did not increase significantly during the Devonian compared to during other geologic periods, and was in fact higher during the intervals spanning from the Wenlock to the Lochkovian and from the Carboniferous to the Permian. The study's authors instead attribute

4608-401: The Temeside, Raglan Mudstone and St Maughans formations of the central and eastern part of the basin. In south Pembrokeshire to the south of the Ritec Fault, the lower ORS is represented by, in ascending order, the Freshwater East, Moors Cliff and Freshwater West formations. These are unconformably overlain by the Ridgeway Conglomerate Formation. The middle ORS is missing whilst the Upper ORS

4704-408: The Upper Devonian, the contact between the two being unconformable and representing the complete omission of any Middle Devonian sequence. The lowermost formations are of upper Silurian age, these being the Downton Castle Sandstone Formation and the overlying Raglan Mudstone Formation except in Pembrokeshire where a more complex series of formations is recognized. In the east of the basin, the top of

4800-428: The ancestors of all four- limbed vertebrates (i.e. tetrapods ), began diverging from freshwater lobe-finned fish as their more robust and muscled pectoral and pelvic fins gradually evolved into forelimbs and hindlimbs , though they were not fully established for life on land until the Late Carboniferous . The first ammonites , a subclass of cephalopod molluscs , appeared. Trilobites , brachiopods and

4896-534: The bedrock across half of the island. These are conformably overlain by peperite and the basaltic and andesitic Lorne plateau lavas . The ORS on Kerrera and isolated localities around Oban are known for their fossils, particularly fish. The Midland Valley graben defined by the Highland Boundary Fault in the north and the Southern Uplands Fault in the south harbours not only a considerable amount of Old Red Sandstone sedimentary rocks but also igneous rocks of this age associated with extensive volcanism . There

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4992-406: The beginning and end of which are marked with extinction events. This lasted until the end of the Devonian, 358.9 Ma. The Devonian was a relatively warm period, although significant glaciers may have existed during the Early and Middle Devonian. The temperature gradient from the equator to the poles was not as large as it is today. The weather was also very arid, mostly along the equator where it

5088-466: The climate in the Devonian differed greatly during its epochs and between geographic regions. For example, during the Early Devonian, arid conditions were prevalent through much of the world including Siberia, Australia, North America, and China, but Africa and South America had a warm temperate climate . In the Late Devonian, by contrast, arid conditions were less prevalent across the world and temperate climates were more common. The Devonian Period

5184-409: The coast, probably in marginal marine environments. The familiar red colour of these rocks arises from the presence of iron oxide , but not all the Old Red Sandstone is red or sandstone – the sequence also includes conglomerates, mudstones , siltstones and thin limestones and colours can range from grey and green through to red and purple. These deposits are closely associated with

5280-463: The continent. Deformed remnants of these mountains can still be found on Ellesmere Island and Svalbard . Many of the Devonian collisions in Laurussia produce both mountain chains and foreland basins , which are frequently fossiliferous. Gondwana was by far the largest continent on the planet. It was completely south of the equator, although the northeastern sector (now Australia) did reach tropical latitudes. The southwestern sector (now South America)

5376-409: The continent. In present-day eastern North America, the Acadian Orogeny continued to raise the Appalachian Mountains . Further east, the collision also extended the rise of the Caledonian Mountains of Great Britain and Scandinavia . As the Caledonian Orogeny wound down in the later part of the period, orogenic collapse facilitated a cluster of granite intrusions in Scotland. Most of Laurussia

5472-575: The continents. By the middle of the Devonian, several groups of vascular plants had evolved leaves and true roots , and by the end of the period the first seed -bearing plants ( pteridospermatophytes ) appeared. This rapid evolution and colonization process, which had begun during the Silurian, is known as the Silurian-Devonian Terrestrial Revolution . The earliest land animals , predominantly arthropods such as myriapods , arachnids and hexapods , also became well-established early in this period, after beginning their colonization of land at least from

5568-422: The debate and named it the Devonian System. While the rock beds that define the start and end of the Devonian Period are well identified, the exact dates are uncertain. According to the International Commission on Stratigraphy , the Devonian extends from the end of the Silurian 419.2 Ma, to the beginning of the Carboniferous 358.9 Ma – in North America , at the beginning of the Mississippian subperiod of

5664-405: The early Devonian Period around 400  Ma. Bactritoids make their first appearance in the Early Devonian as well; their radiation, along with that of ammonoids, has been attributed by some authors to increased environmental stress resulting from decreasing oxygen levels in the deeper parts of the water column. Among vertebrates, jawless armored fish ( ostracoderms ) declined in diversity, while

5760-406: The ecosystems and completed the extinction of all calcite sponge reefs and placoderms. Devonian palaeogeography was dominated by the supercontinent Gondwana to the south, the small continent of Siberia to the north, and the medium-sized continent of Laurussia to the east. Major tectonic events include the closure of the Rheic Ocean , the separation of South China from Gondwana, and

5856-401: The end of the Devonian, the first seed-forming plants had appeared. This rapid appearance of many plant groups and growth forms has been referred to as the Devonian Explosion or the Silurian-Devonian Terrestrial Revolution. The 'greening' of the continents acted as a carbon sink , and atmospheric concentrations of carbon dioxide may have dropped. This may have cooled the climate and led to

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5952-420: The environment necessary for certain early fish to develop such essential characteristics as well developed lungs and the ability to crawl out of the water and onto the land for short periods of time. Finally, the Late Devonian started with the Frasnian , 382.7 to 372.2 Ma, during which the first forests took shape on land. The first tetrapods appeared in the fossil record in the ensuing Famennian subdivision,

6048-470: The erosion of the Caledonian Mountain chain which was thrown up by the collision of the former continents of Avalonia , Baltica and Laurentia to form the Old Red Sandstone Continent - an event known as the Caledonian Orogeny . Many fossils are found within the rocks, including early fishes, arthropods and plants. As is typical with terrestrial red beds , the vast majority of the rock is not fossil-bearing; however there are isolated, localized beds within

6144-409: The former Brecknockshire (now south Powys) of south Wales. Devonian The Devonian ( / d ə ˈ v oʊ n i . ən , d ɛ -/ də- VOH -nee-ən, deh- ) is a geologic period and system of the Paleozoic era during the Phanerozoic eon , spanning 60.3 million years from the end of the preceding Silurian period at 419.2 million years ago ( Ma ), to the beginning of

6240-413: The free water column as well as high ecological competition in benthic habitats, which were extremely saturated; this diversification has been labeled the Devonian Nekton Revolution by many researchers. However, other researchers have questioned whether this revolution existed at all; a 2018 study found that although the proportion of biodiversity constituted by nekton increased across the boundary between

6336-418: The great coral reefs were still common during the Devonian. The Late Devonian extinction , which started about 375 Ma, severely affected marine life, killing off most of the reef systems, most of the jawless fish, half of all placoderms, and nearly all trilobites save for a few species of the order Proetida . The subsequent end-Devonian extinction , which occurred at around 359 Ma, further impacted

6432-744: The increased overall diversity of nekton in the Devonian to a broader, gradual trend of nektonic diversification across the entire Palaeozoic. A now-dry barrier reef, located in present-day Kimberley Basin of northwest Australia , once extended 350 km (220 mi), fringing a Devonian continent. Reefs are generally built by various carbonate -secreting organisms that can erect wave-resistant structures near sea level. Although modern reefs are constructed mainly by corals and calcareous algae , Devonian reefs were either microbial reefs built up mostly by autotrophic cyanobacteria or coral-stromatoporoid reefs built up by coral-like stromatoporoids and tabulate and rugose corals . Microbial reefs dominated under

6528-403: The jawed fish (gnathostomes) simultaneously increased in both the sea and fresh water . Armored placoderms were numerous during the early ages of the Devonian Period and became extinct in the Late Devonian, perhaps because of competition for food against the other fish species. Early cartilaginous ( Chondrichthyes ) and bony fishes ( Osteichthyes ) also become diverse and played a large role within

6624-448: The later Jurassic deposits include mudstones. These rocks overly much older Devonian lake deposits from Lake Orcadie . The intervening Carboniferous sediments were eroded before the Permian deposition, leaving a 100 million year gap in the stratigraphy. This unusual sequence of rocks confused 19th century geologists for many years. The Moray Firth Basin has been exploited for offshore oil deposits. Scotland lay at about 20 degrees North in

6720-575: The low, carpet-like vegetation during the early part of the Devonian. Also, the first possible fossils of insects appeared around 416  Ma, in the Early Devonian. Evidence for the earliest tetrapods takes the form of trace fossils in shallow lagoon environments within a marine carbonate platform/shelf during the Middle Devonian, although these traces have been questioned and an interpretation as fish feeding traces ( Piscichnus ) has been advanced. Many Early Devonian plants did not have true roots or leaves like extant plants, although vascular tissue

6816-486: The main reef-forming organisms in warm periods, with corals and stromatoporoid sponges taking the dominant role in cooler times. The warming at the end of the Devonian may even have contributed to the extinction of the stromatoporoids. At the terminus of the Devonian, Earth rapidly cooled into an icehouse , marking the beginning of the Late Paleozoic icehouse . The Devonian world involved many continents and ocean basins of various sizes. The largest continent, Gondwana ,

6912-450: The major part played by the Museum’s founders and associated geologists in helping answer questions about geological succession that challenged 19th century naturalists. The Museum has many original papers, including letters from Hugh Miller , and correspondence with Charles Darwin . The land North of Elgin consists of fragments of Permian , Triassic and Jurassic bedrocks on the edge of

7008-709: The marine fauna until the beginning of the Mesozoic Era. The Middle Devonian comprised two subdivisions: first the Eifelian , which then gave way to the Givetian 387.7 Ma. During this time the jawless agnathan fishes began to decline in diversity in freshwater and marine environments partly due to drastic environmental changes and partly due to the increasing competition, predation, and diversity of jawed fishes . The shallow, warm, oxygen-depleted waters of Devonian inland lakes, surrounded by primitive plants, provided

7104-459: The middle and upper ORS are missing with only the lower ORS present; this is divided into an earlier Milford Haven Group comprising in ascending order, the Red Cliff, Sandy Haven and Gelliswick Bay formations and a later Cosheston Group with, again in ascending order, its constituent Llanstadwell, Burton Cliff, Mill Bay, Lawrenny Cliff and New Shipping formations. These respectively equate with

7200-411: The nearby microcontinent of Amuria (now Manchuria , Mongolia and their vicinities). Though certainly close to Siberia in the Devonian, the precise location of Amuria is uncertain due to contradictory paleomagnetic data. The Rheic Ocean, which separated Laurussia from Gondwana, was wide at the start of the Devonian, having formed after the drift of Avalonia away from Gondwana. It steadily shrunk as

7296-401: The oldest known plants with woody tissue. By the Middle Devonian, shrub-like forests of primitive plants existed: lycophytes , horsetails , ferns , and progymnosperms evolved. Most of these plants had true roots and leaves, and many were quite tall. The earliest-known trees appeared in the Middle Devonian. These included a lineage of lycopods and another arborescent, woody vascular plant,

7392-403: The period continued, as the two major continents approached near the equator in the early stages of the assembly of Pangaea . The closure of the Rheic Ocean began in the Devonian and continued into the Carboniferous. As the ocean narrowed, endemic marine faunas of Gondwana and Laurussia combined into a single tropical fauna. The history of the western Rheic Ocean is a subject of debate, but there

7488-472: The period it moved northwards and began to twist clockwise, though it was not near its modern location. Siberia approached the eastern edge of Laurussia as the Devonian progressed, but it was still separated by a seaway, the Ural Ocean . Although Siberia's margins were generally tectonically stable and ecologically productive, rifting and deep mantle plumes impacted the continent with flood basalts during

7584-587: The resulting expansion of the Paleo-Tethys Ocean . The Devonian experienced several major mountain-building events as Laurussia and Gondwana approached; these include the Acadian Orogeny in North America and the beginning of the Variscan Orogeny in Europe. These early collisions preceded the formation of the single supercontinent Pangaea in the Late Paleozoic. The period is named after Devon ,

7680-498: The rock that do contain fossils. Rocks of this age were also laid down in South West England (hence the name 'Devonian'; from Devon ) though these are of true marine origin and are not included within the Old Red Sandstone. Since the Old Red Sandstone consists predominantly of rocks of terrestrial origin, it does not generally contain marine fossils which would otherwise prove useful in correlating one occurrence of

7776-533: The rock with another, both between and within individual sedimentary basins . Accordingly, local stage names were devised and these remain in use to some extent today though there is an increasing use of international stage names. Thus in the Anglo-Welsh Basin, there are frequent references to the Downtonian , Dittonian , Breconian and Farlovian stages in the literature. The existence of

7872-529: The same time by the same processes. The Old Red Sandstone has been widely used as a building stone across those regions where it outcrops. Notable examples of its use can be found in the area surrounding Stirling , Stonehaven , Perth and Tayside . The inhabitants of Caithness at the northeastern tip of Scotland also used the stone to a considerable extent. Old Red Sandstone has also frequently been used in buildings in Herefordshire, Monmouthshire and

7968-476: The sandstone that used to contain bone, but are now virtually empty. This made them difficult to identify and study. In the 19th century until the late 20th century, the most common method to explore them was to infill the void, then break the surrounding rock. More recently, CT-scanning has been used to see inside the rock and reconstruct the fossils digitally. These can also be printed or cast as models to facilitate study and as museum pieces. Elgin Museum has such

8064-562: The succeeding Carboniferous period at 358.9 Ma. It is the fourth period of both the Paleozoic and the Phanerozoic. It is named after Devon , South West England , where rocks from this period were first studied. The first significant evolutionary radiation of life on land occurred during the Devonian, as free- sporing land plants ( pteridophytes ) began to spread across dry land , forming extensive coal forests which covered

8160-490: The type and significant specimens are on display, with more fossils and archives in the collection at Elgin Museum, available for study and research. More recent fossil discoveries from Elgin have been footprints, with over 200 found prior to 1997. These range in size from 0.5 cm to 24 cm wide, and most belong to therapsids . Numerous taildrags have also been recovered and studied, many from therapsids. Old Red Sandstone Old Red Sandstone , abbreviated ORS ,

8256-521: The warmer conditions of the early and late Devonian, while coral-stromatoporoid reefs dominated during the cooler middle Devonian. By the Devonian Period, life was well underway in its colonization of the land. The moss forests and bacterial and algal mats of the Silurian were joined early in the period by primitive rooted plants that created the first stable soils and harbored arthropods like mites , scorpions , trigonotarbids and myriapods (although arthropods appeared on land much earlier than in

8352-521: The west through Carmarthenshire into Powys and Monmouthshire and through the southern Welsh Marches , notably into Herefordshire , Worcestershire and Gloucestershire . Outliers in Somerset and north Devon complete the extent of this basin. With the exception of south Pembrokeshire, all parts of the basin are represented by a range of lithologies assigned to the Lower Devonian and to

8448-555: The world saw the disappearance of an estimated 96% of vertebrates like conodonts and bony fishes , and all of the ostracoderms and placoderms. Land plants as well as freshwater species, such as our tetrapod ancestors, were relatively unaffected by the Late Devonian extinction event (there is a counterargument that the Devonian extinctions nearly wiped out the tetrapods ). The reasons for the Late Devonian extinctions are still unknown, and all explanations remain speculative. Canadian paleontologist Digby McLaren suggested in 1969 that

8544-480: Was a time of great tectonic activity, as the major continents of Laurussia and Gondwana drew closer together. Sea levels were high worldwide, and much of the land lay under shallow seas, where tropical reef organisms lived. The enormous "world ocean", Panthalassa , occupied much of the Northern Hemisphere as well as wide swathes east of Gondwana and west of Laurussia. Other minor oceans were

8640-594: Was located entirely within the Southern Hemisphere . It corresponds to modern day South America , Africa , Australia , Antarctica , and India , as well as minor components of North America and Asia . The second-largest continent, Laurussia, was northwest of Gondwana, and corresponds to much of modern-day North America and Europe . Various smaller continents, microcontinents , and terranes were present east of Laurussia and north of Gondwana, corresponding to parts of Europe and Asia. The Devonian Period

8736-487: Was located south of the equator, but in the Devonian it moved northwards and began to rotate counterclockwise towards its modern position. While the most northern parts of the continent (such as Greenland and Ellesmere Island ) established tropical conditions, most of the continent was located within the natural dry zone along the Tropic of Capricorn , which (as nowadays) is a result of the convergence of two great air-masses,

8832-469: Was located to the far south, with Brazil situated near the South Pole . The northwestern edge of Gondwana was an active margin for much of the Devonian, and saw the accretion of many smaller land masses and island arcs. These include Chilenia , Cuyania , and Chaitenia , which now form much of Chile and Patagonia . These collisions were associated with volcanic activity and plutons , but by

8928-442: Was mostly a passive margin, hosting extensive marine deposits in areas such as northwest Africa and Tibet . The eastern margin, though warmer than the west, was equally active. Numerous mountain building events and granite and kimberlite intrusions affected areas equivalent to modern day eastern Australia , Tasmania , and Antarctica. Several island microcontinents (which would later coalesce into modern day Asia) stretched over

9024-434: Was the driest. Reconstruction of tropical sea surface temperature from conodont apatite implies an average value of 30 °C (86 °F) in the Early Devonian. Early Devonian mean annual surface temperatures were approximately 16 °C. CO 2 levels dropped steeply throughout the Devonian Period. The newly evolved forests drew carbon out of the atmosphere, which were then buried into sediments. This may be reflected by

9120-577: Was the newest addition to the Asian microcontinents, it was not the first. North China and the Tarim Block (now northwesternmost China) were located westward and continued to drift northwards, powering over older oceanic crust in the process. Further west was a small ocean (the Turkestan Ocean), followed by the larger microcontinents of Kazakhstania , Siberia , and Amuria . Kazakhstania was

9216-617: Was the one that placed it in the Devonian : he coined the name of that period. The term 'Old Red Sandstone' was originally used in 1821 by Scottish naturalist and mineralogist Robert Jameson to refer to the red rocks which underlay the 'Mountain Limestone' i.e. the Carboniferous Limestone. They were thought at that time to be the British version of Germany's Rotliegendes , which is in fact of Permian age. Many of

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