event, of a slightly lesser extent than the glaciations which swept over Gondwana in the later Carboniverous and the very end of the Devonian. During the Tournaisian, South America was located at south polar latitudes and formed the westernmost part of the supercontinent Gondwana. The southwestern coastline of Gondwana was bustling with distinctive cold-water brachiopod and bivalve faunas. Coal is less common in the Tournaisian than in the rest of the Carboniferous, and forests and swamps were at low-density despite some trees reaching heights of up to 40 meters (131 feet). Anabranching channels and anastomosing rivers (with permanent channels splitting around large vegetated islands) would not develop until the Viséan, and river systems of the Tournaisian were more similar to those of the Late Devonian. Flora 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"). 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. Tropical and subtropical swamps, in what is now Europe, North America, and China, represent a low-latitude paleobiogeographical realm known as the Amerosinian realm. 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. 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. 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. Gondwanan plant fossils are uncommon: southernmost