Review of Palaeobotany and Palynology 318 (2023) 104971 Available online 17 August 2023 0034-6667/© 2023 Published by Elsevier B.V. Taxonomy of Early Mississippian gulate megaspore assemblage from northern Bolivia Marcela A. Quetglas a, * , Mercedes Di Pasquo b , C. Cecilia Macluf a a C´ atedra de Palinología, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, Calle 64, 3, B1904DZA La Plata, Buenos Aires, Argentina b Laboratorio de Palinoestratigrafía y Paleobot´ anica, Centro de Investigaciones Científcas y Transferencia de Tecnología a la Producci´ on (CONICET-Entre Ríos-UADER), Matteri y Espa˜ na s/n, E3105BWA Diamante, Entre Ríos, Argentina A R T I C L E INFO Keywords: Bolivia Carboniferous Lycopsids Megaspores Tournaisian ABSTRACT A taxonomic study of gulate megaspores, characterised by having an apical prominence associated with the trilete mark, from the Toregua Formation, Retama Group, Early Carboniferous (mid-upper Tournaisian) of northern Bolivia was performed. To achieve this, the general morphology and wall structure of around a hundred of specimens of megaspores isolated from palynologic residues of the Pando X-1 and Manuripi X-1 boreholes were studied in detail and thoroughly described and illustrated using light, fuorescence and scanning electron microscopy. From this analysis, nine morphospecies of the genus Lagenicula were identifed, including a new species (L. morbelliae sp. nov.), of which some were considered Mississippian in age (L. brasiliensis, L. microechinata, cf. L. crassiaculeata, cf. L. hirsutoida) and others (L. devonica, L. illizii, L.magna, L. media) were interpreted as likely reworked forms from Devonian deposits. The sporoderm morphological features of the studied megaspores confrm the botanical affnity assigned to heterosporous arborescent lycopsids (Lep- idocarpaceae/Lepidodendraceae), which would have formed dense forests, not only of great dimensions and variability but also with ecological complexity, during the Early Carboniferous in Bolivia. 1. Introduction Megaspores are found in the fossil record from sediments as old as Early Devonian (early Emsian; Bonacorsi et al., 2020). From that period, the size differentiation between microspores and megaspores became more pronounced (Chaloner, 1967; Richardson, 1967) and the diversity of megaspores increased (Scott and Hemsley, 1996), reaching its maximum importance during the Carboniferous, in which heterosporous lycopsids had a rapid diversifcation (Bateman et al., 1992) and domi- nated major portions of the landscape (Phillips, 1978). Currently, there are heterosporous plants that produce megaspores (e.g. Selaginella, Isoetes, Marsilea and Azolla) however, the study of ancient megaspores such as those from the Devonian and Carboniferous is especially relevant to ascertain the origin and evolution of heterospory and the groups of plants involved in this event (Traverse, 2007). Comparing with the Pennsylvanian epoch, the knowledge on Missis- sippian dispersed megaspores is still limited due to the scarcity of described assemblages (Arioli et al., 2007; Wellman et al., 2009), and especially from the Tournaisian, where megaspores assemblages revealed a low diversity of morphospecies in relation to those from Late Devonian and Visean age (Scott and Hemsley, 1996). Within Early Carboniferous assemblages, specifcally of Tournaisian age, there are megaspores characterised by having a gula, i.e., a particular form of development of the trilete mark, which is more or less raised, apparently formed also by the contact areas in laterally com- pressed specimens (Dybov´ a-Jachowicz et al., 1979). These gulate megaspores are assigned to heterosporous arborescent lycopsids of the Lepidocarpaceae or Lepidodendraceae family (Balme, 1995). Previous studies on megaspores with gula suggest they could derive almost exclusively from that family (Arioli et al., 2007), which is generally considered to form dense and diverse forests (Wellman et al., 2009). This is primarily evidenced not only by the preservation of deposits bearing abundant plant material of different parts of lycopsids documented in the Pennsylvanian (DiMichele et al., 2007) and Mississippian (Bell, 1960) but also by the morphological diversity found in gulate mega- spore assemblages (Glasspool and Scott, 2005; Arioli et al., 2007; Wellman et al., 2009). Gulate megaspores have been described within assemblages found in North America (e.g., Chaloner, 1954; Winslow, 1962; Glasspool et al., 2000) and Europe (Mortimer et al., 1970; Hemsley et al., 1994), while in * Corresponding author. E-mail address: quetglasm@fcnym.unlp.edu.ar (M.A. Quetglas). Contents lists available at ScienceDirect Review of Palaeobotany and Palynology journal homepage: www.elsevier.com/locate/revpalbo https://doi.org/10.1016/j.revpalbo.2023.104971 Received 23 January 2023; Received in revised form 3 August 2023; Accepted 11 August 2023