Arborescent Gymnosperms from the Permian of the Parnaíba Basin

In the Parnaíba Basin in central-north Brazil, the Pedra de Fogo and Motuca formations were deposited during the Permian. In this period, the paleoclimate was probably arid to semiarid but with phases of more humid influence, which allowed for the growth of a lush forest. Today, the fossil woods of this forest are scattered in outcrops in the Maranhão, Piauí, and Tocantins states. The forests in the central part of the basin (Pedra de Fogo Formation), such as the Poti River Petrified Forest, the Petrified ForestPetrified forest of the Garapenses Hills, and the Altos Petrified Forest, encompass gymnosperm woods as their main component, and these forests provide a rare record of autochthonous (in growing position) stems. In contrast, the fossil forest located on the southwestern border of this basin in deposits of the Motuca Formation (Tocantins Fossil Trees Natural Monument) lacks autochthonousAutochthonous stems and is dominated by spore-producing vascular plants. Since the beginning of this century, several taxonomic works about the fossil trees from Permian deposits from the Parnaíba Basin have been published. Concerning the gymnosperms, 23 fossil-species of 18 fossil-genera were described. Seven genera, Amyelon, Cycadoxylon, Damudoxylon, Kaokoxylon, Cordaixylon, Europoxylon, and Taeniopitys, have already been described in other parts of the world, including the Gondwanan and Euramerican realms. On the other hand, these 21 fossil-species are endemic to Parnaíba Basin. The anatomical characteristics of these woods show a significant variability, probably corresponding to a high taxonomic diversity, i.e., “biological” species diversity. Because of this high degree of endemism, the paleoflora was considered transitional between the classical phytopaleogeographic regions, but more likely, it represents a distinct new phytopaleogeographic province. The forest grew near large lakes associated with river systems crossing the basin. From time to time, high energy, non-channelized flood flows, carrying large amounts of sediment load, buried either fallen trees or bases of upright stems. During the deposition of the Pedra de Fogo Formation, gymnosperms grew close to the lake shores, but during the deposition of the Motuca Formation, they migrated away from the lake shores to upland habitats concluded from their decreasing abundance. In the Pedra de Fogo Formation sediments, these gymnosperm trees are sometimes preserved in growth position.