Tournaisian

The Tournaisian saw a new diversification of arborescent (tree-sized) lycophytes and giant sphenophytes (horsetails). They coexisted alongside ferns and lignophytes (wood-bearing plants), including early seed plants such as lyginopteridalean pteridosperms ("seed ferns").[12] The Tournaisian was a transitional stage for lignophyte evolution: Devonian progymnosperm taxa such as Archaeopteris had gone extinct, but new types of woody trees such as Pitus and Protopitys set the stage for even greater morphological diversity. There is still much debate over the proportion of spore-bearing (progymnosperm) to seed-bearing (spermatophyte) woody plants, but both were evidently major parts of Tournaisian ecosystems.[13]

Tropical and subtropical swamps, in what is now Europe, North America, and China, represent a low-latitude paleobiogeographical realm known as the Amerosinian realm.[12] Divaricating (widely branching) trunks of Lepidodendropsis lycophytes are by far the most abundant and widespread plant fossils of the Tournaisian, yet there was some minor variation in other flora through time and space. In eastern North America, lyginopterids and probable progymnosperms were also common, as indicated by leaf form genera such as Adiantites, Rhodeopteridium, and Genselia.[12] The progymnosperm leaf Triphyllopteris may be more common in Europe while the lycophyte Sublepidodendron characterizes Tournaisian China. Late Devonian seed plants like Rhacopteris also persisted into the Tournaisian tropics. Lepidodendron, a massive arborescent lycophyte which would dominate coal forests through the rest of the Carboniferous, first appeared near the Tournaisian-Viséan boundary.[12]

Northern Asia (Kazakhstan and Siberia) was positioned within subtropical or temperate northern latitudes, and developed its own endemic floras, the Angaran realm. The most common plant fossils in this region were shrub-sized lycophytes such as Ursodendron and Tomiodendron, shorter than their arborescent tropical relatives.[12]

Gondwanan plant fossils are uncommon: southernmost Gondwana was covered by dwarf lycophytes, even smaller than those of the Angaran realm.[14] Subtropical and temperate lycophytes such as Lepidodendropsis, Archaeosigillaria, and Frenguellia could be found in some parts of the supercontinent, such as Argentina and Australia.[12] In the middle Tournaisian glaciation, species-poor frigid tundra developed in western Argentina.[14] These south polar tundras hosted the oldest known seed plants in Gondwanan territories, which likely spread south across a land bridge once the Rheic Ocean closed between Laurussia and Gondwana.[15] Tournaisian terrestrial sediments in South America are additionally characterized by the miospore index fossil Waltzispora lanzonii. The floral diversity of Tournaisian southern tundra consists almost entirely of relict Devonian genera; this suggests that Late Devonian land plant extinctions in lower latitudes were mostly driven by competition from new tropical species, rather than global environmental pressures.[15]

Trilobites experienced their final substantial diversification event in the mid-late Tournaisian, briefly regaining a level of diversity not seen since the Middle Devonian. Almost all new species belonged to the recently-evolved family Phillipsiidae, while the few surviving Devonian-type trilobites declined.[16] Most early Tournaisian trilobites were widespread deep-water species. By the late Tournaisian, they had recolonized shallower environments and divided into three different biogeographic zones corresponding to North America, Europe, and East Asia.[17]

• Dumont, A.H.; 1832: Mémoire sur la constitution géologique de la province de Liège, Mémoires couronnés par l'Académie Royale des Sciences et Belles-Lettres de Bruxelles 8 (3), VII. (in French)
• Gradstein, F.M.; Ogg, J.G. & Smith, A.G.; 2004: A Geologic Time Scale 2004, Cambridge University Press
• Heckel, P.H. & Clayton, G.; 2006: The Carboniferous system, use of the new official names for the subsystems, series and stages, Geologica Acta 4(3), pp 403–407
• Kaiser, Sandra (1 April 2009). "The Devonian/Carboniferous boundary stratotype section (La Serre, France) revisited". Newsletters on Stratigraphy. 43 (2): 195–205. doi:10.1127/0078-0421/2009/0043-0195. Retrieved 7 December 2020.
• Menning, M.; Alekseev, A.S.; Chuvashov, B.I.; Davydov, V.I.; Devuyst, F.-X.; Forke, H.C.; Grunt, T.A.; Hance, L.; Heckel, P.H.; Izokh, N.G.; Jin, Y.-G.; Jones, P.J.; Kotlyar, G.V.; Kozur, H.W.; Nemyrovska, T.I.; Schneider, J.W.; Wang, X.-D.; Weddige, K.; Weyer, D. & Work, D.M.; 2006: Global time scale and regional stratigraphic reference scales of Central and West Europe, East Europe, Tethys, South China, and North America as used in the Devonian–Carboniferous–Permian Correlation Chart 2003 (DCP 2003), Palaeogeography, Palaeoclimatology, Palaeoecology 240 (1-2): pp 318–372
• Paeckelmann, W. & Schindewolf, O.H.; 1937: Die Devon-Karbon-Grenze, Comptes Rendus (2) du Cinquième Congrès International de Stratigraphie et Géologie du Carbonifère, Heerlen 1935 (2), pp 703–714 (in German)
• Paproth, Eva; Feist, Raimund; Flajs, Gerd (December 1991). "Decision on the Devonian-Carboniferous boundary stratotype" (PDF). Episodes. 14 (4): 331–336. doi:10.18814/epiiugs/1991/v14i4/004. Archived (PDF) from the original on 2022-10-09.