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Devonian Period


Abstract

This page describes the Devonian Period, including stratigraphy, paleogeography, and famous lagerstätten, followed by a sketched outline of some of the major evolutionary events.

Keywords: stratigraphy, Devonian Period, Devonian biota, fossil record, evolution, extinction, Rhynie Chert, Hunsruck Shale, Achanarras, Cleveland Shale, Canowindra, Escuminac Bay

Introduction

Fishes are the dominent animals; scale tree forests appear on land, inhabited by the first wingless insects; blastoids are at their peak; the first ammonites and amphibians evolve.

 
 

Related Topics


Further Reading

  • The Concise Geologic Time Scale (Ogg et al. 2008)
       
       

      Stratigraphy

      Type Section/Sections

      The Devonian was proposed by Adam Sedgwick and Roderick I. Murchison in 1839 (Sedgwick & Murchison 1839). The type section is in Devonshire; its boundaries are based mainly on fossils.

      Lower (Silurian-Devonian) Boundary

      The base of the Devonian is defined immediately at the first appearance of the graptolite species Monograptus uniformis in the rhythmically alterating limestones and calcareous shales of ‘Bed 20’ in the Klonk Section, which is located near the village of Suchomasty, about 35km southwest of Prague in the Czech Republic. The age is established at 419 ± 3.2 Ma.

      Upper (Devonian-Carboniferous) Boundary

      The GSSP defining the the base of the Carboniferous (i.e., the Devonian-Carboniferous Boundary) was established in 1991 (Paproth et al. 1991) at La Serre, France, where it is set at the first appearance datum (FAD) of the conodont Siphonodella sulcata. Subsequent research, however, has revealed stratigraphic problems with this datum, and it is now relised that this horizon cannot be correlated with precision at present.

      The GSSP is at the base of Bed 89 in Trench E at La Serre. The La Serre section is located in the southeastern Montagne Noire, Departement Hérault, District of Cabrières, in southern France. Artificial trench E, which averages 80cm in depth on the southern slope of La Serre Hill, is about 125m south of the hilltop (252m), about 525m east of La Roquette farmhouse, 2.5km northeast of the village of Fontès (sheet 1:25,000 Pézenas XXVI/44, 1-2, x = 682.55, y = 140.12).

      Sedimentology: The rocks in trench E’ are part of a geologic unit named “Klippen of Cabrières”. The youngest Devonian and earliest Carboniferous beds are characterized by a sequence of predominantly biodetrital oolitic limestone within a pelagic matrix of shale and cephalopod bearing calcilutites.

      Primary Markers: First appearance of the conodont Siphonodella sulcata within the evolutionary lineage from Siphonodella praesulcata to Siphonodella sulcata at the base of Bed 89 in trench E’.

      Secondary Markers: The trilobites Belgibole abruptirhachis, Archegonus (Phillibole) and Carbonocoryphe also occur in Bed 89. Some of these other taxa are especially important at other Locations around the world. For example, Belgibole abruptirhachis occurs immediately above the Hangenberg Schiefer interval in various cephalopod-bearing sections from the Renish Slate Mountains (Germany), the Holy Cross Mountains (Poland) and the Carnic Alps (Austria). See Paproth et al. 1991.

      Chronology

      ICS (Cohen et al. 2015) from 419.2 ± 3.2 to 358.9 ± 0.4 Ma.

      Paleogeography

      Major Tectonic Events

      Land and Sea

      During the Devonian, there were three major continental masses: North America and Europe sat together near the equator, much of their current land underneath seas. To the north lay a portion of modern Siberia. A composite continent of South America, Africa, Antarctica, India, and Australia dominated the southern hemisphere.

      Ron Blakey (Northern Arizona University) paleogeographic reconstruction

      Climate

      Paleontology

      General Characteristics

      Early terrestrial arthropods, including wingless insects and the earliest arachnids. In the oceans, brachiopods flourished; crinoids and other echinoderms, tabulate and rugose corals, and ammonites were also common. Fishes are the dominent animals; scale tree forests appear on land, inhabited by the first wingless insects; blastoids are at their peak; the first ammonites and amphibians evolve.

      However, the Devonian is probably most noted for the diversification of rise to prominence of various groups of fishes; indeed this period is occasionally referred to as the "age of fishes."

      Tetrapods appear.

      The vegetation of the early Devonian consisted primarily of small plants, the tallest being only a meter tall. By the end of the Devonian, ferns, horsetails and seed plants had also appeared, producing the first trees and the first forests. Archaeopteris is one of these first trees.

      Major Taxa

      Fishes are the dominent animals; scale tree forests appear on land, inhabited by the first wingless insects; blastoids are at their peak; the first ammonites and amphibians evolve.

      Mollusca

      Annelida

      Arthropoda

      terrestrial arthropoda

      Brachiopoda

      Echinodermata

      graptolites

      The oldest lobe-fin fossil fish are Early Devonian, though the group likely appeared earlier.

      tetrapods – see Clack 2002a

      Bryophyta

      higher plants

      Major Evolutionary Events

      The first major diversification of land plant life, such as rhyniophytes, zosterophylls, drepanophycaleans, lycophytes, trimerophytes, and (in the southern hemisphere) Baragwanathia, began as early as Late Ludlow (Late Silurian) in Australia through Gedinnian (Early Devonian) on Laurentia.

      In contrast to megascopic plants, which appear to have colonized the land only once, many animal groups made the transition to terrestrial existence independently and overcame the problems of water relations in different ways. Early evidence for terrestrial animals is sparse, but by the Early Devonian exquisitely preserved arthropod faunas are known from several localities in North America, Germany and the United kingdom. These faunas document the appearance of diverse arthropod communities including centipedes, millipedes, trigonotarbids and their living relatives spiders, pseudoscorpians, mites (orbatids and endeostigmatids), arthropleurids (extinct arthropods), archaeognathans (primitive wingless insects), collembolans and possibly bristletails. Available evidence indicates that these animals were mainly predators and detritivores and, until the appearance of vertebrate herbivores in the latest Palaeozoic, most energy flow into animal components of early terrestrial ecosystems was probably through the decomposer pathway rather than direct herbivory. Indirect evidence for herbivory comes from wound responses in the tissues of some fossil plants, and perhaps also from fossil faecal pellets containing abundant spores (abridged from Kenrick & Crane 1997, p. 38).

      Lagerstätten

      Some of the several famous lagerstätten of Devonian age are briefly described below.

      Rhynie Chert: The Rhynie Chert in Scotland is an Early Devonian age deposit containing fossils of both Zosterophyllophytes and Trimerophytes, the two major lines of vascular plants. This indicates that prior to the start of the Devonian, the first major radiations of the plants had already happened. It has become famous as the oldest known terrestrial ecosystem fossilised in place.

      Hunsrück Schiefer (Hunsrück Slate): The Hunsrück Slate formation, originally and still mined for roofing slates, is one of the most important Devonian fossil localities known. Although the fossils are generally not spectacular in a manner which appeals to amateurs, the unusual preservation of soft tissue by pyritisation makes these rock a unique archive of scientific information. The rock is a marine sediment preserving the usual arthropods and molluscs, but also plants, sponges, vertebrates, and even extremely delicate forms such as ctenophores and chondrophorans.

      Gilboa: M. Dev; New York State; spiders and pseudoscorpions; Shear et al. 1984, Selden et al. 1991

      Achanarras Fauna (Scotland): “The classic Tynet Burn and Gamrie fish localities, in north-east Scotland are of Middle Devonian (Eifelian) age and have, since last century yielded beautifully preserved fossil fish, typical of the Achanarras fauna which occurs in deposits exposed to the south of the Moray Firth and to the far North. The fish are mostly preserved in calcareous concretions and despite the large quantities of specimens that have come from the sites, no special significance has been attributed to the material with respect to unnusual preservation. Current detailed work on newly collected material however, has identified new preservational potential for the fish bearing concretions. A number of rare specimens of acanthodians from both sites consistently exhibit dark traces within the body cavity which are analogous with the sites of internal organs in modern groups. Furthermore, dark ‘spots’ in the heads of acanthodians from Gamrie can be interpreted as the position of the eye. To date, these structures have only been observed in three acanthodian genera, but other groups are present and clearly there is potential for more work. A museum collection survey has been initiated and two more specimens, collected last century, have been located which exhibit internal organ site preservation” (Davidson & Trewin 1999).

      Cleveland Shale: Late Devonian (Fammenian); found near Cleveland, Ohio, USA; a vertebrate lagerstätte containing articulated specimens of the cladodont sharks Cladoselache (several species), Ctenacanthus compressus, and the coronodontid shark Diademodus hydei (the holotype and only specimen of this shark); although some fossils occur in the shale itself, most occur in flattened discoidal dolomitic concretions which preserve soft tissues, such as muscle fibers, outlines of the dermal membrane of the body and fins, and ingested prey. Two Cladoselache specimens, one of C. fyleri and one of C. kepleri, also have preserved kidneys. Two specimens of the arthrodire Dunkleosteus terrelli, an articulated specimen from a concretion and one in cone-in-cone, also have a pectoral fin partially preserved. (Thanks to Douglas Dunn, Cleveland Museum of Natural History, for the detailed information.)

      Canowindra: Late Devonian; famous fish locality

      Escuminac Bay: Late Devonian (Early Frasnian); eastern Canada, near the village of Miguasha; anaspids, placoderms, and other fishes including Eusthenopteron; Schultz & Cloutier 1996, Clack 2002a (p. 87)

      Extinctions

      “The Frasnian-Famennian (F-F) faunal crisis represents one of the ‘Big Five Mass Extinctions’ in Earth History. Studies have been published that favor either a collision with an extraterrestrial bolide ... or changes in the oceanographic and climatic systems .... However, no unequivocal evidence on the origin of the Late Devonian faunal breakdown was reported. E.g. iridium anomalies reported from Australia ... and Southern China ... post-date the F-F boundary by 1.5 to 2 Ma. Microtekites from Belgium boundary sections ... were seen in context with the 368±1 Ma old Siljan Ring impact structure. However, the cosmic origin of these spherules has been questioned ... and the microtektites were found above the F-F boundary and clearly post-date the extinction event. Negative carbon isotope excursions were interpreted as evidence for a sudden biomass crash hat may have been triggered by a bolide impact .... In contrast, two positive δ13C excursions measured in the late Frasnian and at the F-F boundary ... seem not to support the idea of a dramatic decline in primary productivity.

      “The geochemical data base for the Late Devonian extinction event shows no evidence for a bolide impact as potential cause of the mass extinction. Instead, repeated changes in the carbon cycle of the ocean-atmosphere system are indicated by positive carbon excursions. The enhanced organic carbon burial is indicated by the higher δ13C values, deposition of the Kellwasser horizon and a positive excursion in δ34S of sulfides and organically-bound sulfur A decrease in atmospheric and oceanic dissolved CO2 contents is expected and may have culminated in global climatic cooling. A decrease in tropical seasurface temperature of 7°C is indicated by preliminary conodont and fish apatite δ18O data.

      “The paleontological data base seems to support the conclusion that climatic cooling may have represented a potential mechanism for the Late Devonian mass extinction .... Organisms living in the tropical to subtropical pelagic and shallow-water ecosystems were heavily decimated. Organisms thriving in higher latitudes or in deeper waters were only slightly affected. Further, late Frasnian faunal groups that were adapted to cooler temperatures migrated into tropical latitudes during the early Famennian. This pattern suggests that climatic cooling in conjunction with significant oceanographic changes may represent a powerful scenario to account for the Late Devonian mass extinction” (Joachimski & Buggisch 2000; ellipses replace numbered references in the original).

      New Zealand Occurrences

      Devonian rocks are rare in New Zealand. The best known and most accessible are to be found near Reefton, at Lankey Creek and Stoney Creek, where fossil brachiopods are relatively common. Some other animals, such as corals, also occur but they are less common. Very rare trilobites are also known.

      References

      Clack, J.A. 2002: Gaining ground: The Origin and Early Evolution of Tetrapods. Indiana University Press: 1-400.

      Cohen, K.M.; Finney, S.C.; Gibbard, P.L.; Fan, J.X. 2015: The ICS international chronostratigraphic chart v 2015/01. Episodes 36: 199-204.

      Davidson, R.G.; Trewin, N.H. 1999: Unusual Soft Tissue Preservation in Middle Devonian Fish-Bearing Nodule Beds. Palaeontological Association 43rd Annual Meeting, University of Manchester, 19-22 December 1999.

      Kenrick, P.; Crane, P.R. 1997: The origin and early evolution of plants on land. Nature 389: 33-39. Nature.

      Ogg, J.G.; Ogg, G.; Gradstein, F.M. 2008: The Concise Geologic Time Scale. Cambridge: 1-177.

      Paproth, E., Feist, R., and Flaijs, G. 1991: Decision on the Devonian-Carboniferous boundary stratotype. Episodes 14 (4): 331-336.

      Schultze, H.-P.; Cloutier, R. (ed) 1996: Devonian fishes and plants of Miguasha, Quebec, Canada. Verlag Dr. Friedrich Pfeil, Munchen: 1-374.

      Sedgwick, A.; Murchison, R.I. 1839: On the physical structure of Devonshire, and on the subdivisions and geological relations of its older stratified deposits. Transactions of the Geological Society of London, Series 2, no. 5: 633-704.

      Selden, P.A.; Shear, W.A.; Bonamo, P.M. 1991: A spider and other arachnids from the Devonian of New York, and reinterpretations of Devonian Araneae. Paleontology 34 (2): 241-281.

      Shear, W.A.; Bonamo, P.M.; Grierson, J.D.; Rolfe, W.D.I.; Smith, E.L.; Norton, R.A. 1984: Early land animals in North America: evidence from Devonian age arthropods from Gilboa, New York. Science 224 (4648): 492-494.


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