New petrified calamitaleans from the Permian of the Parnaíba Basin, central-north Brazil, part II, and phytogeographic implications for late Paleozoic floras

Abstract

Continuing palaeofloristic studies in the Northern Tocantins Fossil Forest, we describe two new calamitalean species from the Permian of the Parnaíba Basin (central-north Brazil). The fossils comprise axes of various sizes, preserved anatomically as siliceous petrifactions, and found in highly mature sandy fluvial deposits of the Motuca Formation. Based on anatomical and morphological characteristics, Arthropitys tocantinensis sp. nov. and Arthropitys barthelii sp. nov. are described. They share a small central pith cavity (extremely reduced in the latter), scalariform tracheid pitting, and prominent pitting of the ray parenchyma. However, they differ markedly in their branching system: the former having 3-12 branches per node either with or lacking secondary growth, the latter showing 2-17 branches without any secondary growth. However, in A. tocantinensis sp. nov., the presence of large woody branches supports a more complex architecture with at least three successive orders of branches. The extensive secondary tissue in both species is homogeneous; clear segmentation is only visible in the proximal wood of A. tocantinensis sp. nov., but completely absent in A. barthelii sp. nov. The growth architecture of these upright growing, self-supporting trunks are reconstructed based on sizable transverse and longitudinal preparations. Our results confirm that thick woody calamitaleans were elements of disturbed riparian vegetation and much more diverse in terms of anatomy and branching patterns than previously thought. They were well adapted to seasonally dry conditions and formed major plant constituents of Permian low-latitude Southern Hemisphere communities. Additionally, we report the first evidence of colonisation on arborescent calamitaleans by herbaceous sphenophyte axes from the Permian. One of the Arthropitys stems hosts at least 30 Sphenophyllum shoots of various ontogenetic stages, growing inside the destroyed pith, which was previously excavated by arthropod boring. Based on the distribution of key genera within late Paleozoic floras of Euramerica, Gondwana and Cathaysia floral realms cluster analysis and Jaccard Coefficient highlight the distribution of a "Mid-North Brazilian" phytogeographic Region during the early Permian.

The limits of life revealed in a silicified micro-ecosystem: Sphenophyllum stems, leaves, and roots trapped inside an arthropod boring in a Permian calamitalean

“…At least 31 stems, densely interwoven to each other and associated with tiny roots and leaves of this extinct herbaceous sphenopsid, were found in a silica-petrified state. Originally grown upright, they squeezed into in the pith of the arborescent calamite Arthropitys barthelii NEREGATO et al 2017, which was additionally caved by putative xylophagous herbivores. Although restricted within natural limits, the Sphenophyllum organs show different developmental stages that encompass a majority of juvenile stems and a few ones with initial secondary growth.…”

Interrelatedness of Biota Revealed in Fossil Trees from the Permian Fossil Forest of Northern Tocantins, Central-North Brazil

“…Some of the most spectacular ancient forests of the Southern Hemisphere are those from the Permian of the Parnaíba Basin. Here, sizeable tree trunks of adequate anatomical preservation can be found until today (Rößler 2006;Dias-Brito et al 2007;Capretz and Rohn 2013;Conceiḉão et al 2016;Neregato et al 2015Neregato et al , 2017. As we can judge from the published information (e.g., summarized in Iannuzzi et al 2018) and from our fieldwork activities, tall trees, beyond 10 to 15 m in height, may have dominated the Northern Tocantins Fossil Forest.…”

“…Compared to the classical phytogeographic provinces, such as Euramerica, Cathaysia, and higher latitude Gondwana, until now, only scarce paleobotanical investigations have posed floristic assemblages from low-latitude Gondwanan regions (Coimbra and Mussa 1984;Herbst 1985Herbst , 1992Herbst , 1999Mussa and Coimbra 1987;Rößler and Noll 2002;Rößler 2006;Dias-Brito et al 2007;Capretz and Rohn 2013;Kurzawe et al 2013a, b;Tavares et al 2014;Neregato et al 2015Neregato et al , 2017Conceiḉão et al 2016). In the following, we aim to reduce this gap in shedding light on the rich fossil record of a specific Permian phytogeographic province recently termed the Mid-North Brazilian Region (Neregato et al 2017).…”

“…12, 13b). The stem is characterized by segmented wood with continuous interfascicular rays and scalariform pitting, and it resembles A. tocantinensis (Neregato et al 2017). A small amount of extraxylary tissue is recognizable as several roots of the Astromyelon type surrounding the stem (Figs.…”

“…As we can judge from the published information (e.g., summarized in Iannuzzi et al 2018) and from our fieldwork activities, tall trees, beyond 10 to 15 m in height, may have dominated the Northern Tocantins Fossil Forest. The plant fossil record of this most luxuriant and vital late Paleozoic tropical-subtropical biota in the Southern Hemisphere (Dias-Brito et al 2007) was believed significant in recognizing the Mid-North Brazilian phytogeographic region (Neregato et al 2017). The majority of fossil plants consist of trees, particularly tree-like ferns.…”