Biodiversity of ecosystems in an arid setting: The late Albian plant communities and associated biota from eastern Iberia

(known for its tolerance to arid conditions). The presence of these pollen grains, typical for northern Gondwana, associates the Iberian ecosystems with those characterising the men- tioned region. Introduction The Albian vegetation of western Europe has been studied in several works which described micro-, meso- and macroremains [1–7], and highlighting the prevalence of ferns and gymno- sperms–mainly conifers (Araucariaceae-Podocarpaceae-Pinaceae-Cupressaceae-Cheirolepi- diaceae)–, and the increasing representation of angiosperms. The distinctiveness of the western European flora has been recognised for a long time and several biogeographic prov- inces have been named on the basis of the nature of the fossil assemblages (i.e., palynological and megaremains [8, 9]). The increased attention to the time-interval is justified by the rising of the dominance of the flowering plants in many ecosystems [10–13] including arid environ- ments [14]. During the later part of the Early Cretaceous, SW Europe has been described as one of the probable migratory routes of angiosperms originating from a northern Gondwanan centre of radiation [15]. The successive northward migrations of angiosperms, well-character- ised by both pollen and megaremain records, suggest broadly similar climate conditions in low to mid-latitude settings (i.e., low latitudinal climatic gradient) or selective migration of taxa able to tolerate a wide range of climatic conditions [16]. During most of the Albian, Iberia was part of a climatic zone referred to as the Northern Hot Arid (NHA) belt [17], where a desert

system (erg) developed over an extensive area [18]. Arid environments, although less represented in fossil record, existed during the Mesozoic. Semi-arid environments are, e.g., reconstructed for the Early Triassic of northeastern Spain and the Upper Jurassic Morrison Formation based on presence of aeolian sandstones [19, 20]. Arid environments were inferred for Early Cretaceous floras of Quedlinburg (Germany) and Las Hoyas (Central Spain) based on occurrence of dwarf lycopod Nathorstiana and fern Weichselia [21, 22]. Reconstructions of Cretaceous continental ecosystems of Japan based on stable oxygen and carbon isotopes also suggest semi-arid conditions [23]. In addition, aeolian sandtones provide direct evidence of a desert environment during the mid-Cretaceous in mid- to low latitude Asia [24]. In Iberia, the eastern coastal margin consisted of a complex set of depositional environ- ments comprising multifaceted vegetation types including conifer forests [14, 25]. Palaeobota- nical studies of ancient desert successions (see i.e. [26, 27]) report plant remains usually not preserved in sand-sized lithologies, which in turn constitute the bulk of their deposits. Assem- blages belonging to this type of setting usually include remains that have experienced transport over varying, and sometimes considerable, distances to the site of burial. Considering this limi- tation and exploiting the characteristics of sets of fossils with distinct taphonomic histories (i.e., megaremains with limited transport vs. miospores disseminated over wider distances),

the present work focuses on the reconstruction of the mid-Cretaceous plant communities that developed in the distal part of the desert system (or fore-erg) in the Maestrazgo Basin (Eastern Iberian Ranges, E Spain), considering specially the conifer-dominated ones. While the previ- ous studies carried out in Albian deposits from the Maestrazgo Basin considered palaeobotani- cal and palynological data separately [28–37], this study represents the first attempt to integrate both data sets into a unified framework, aiming at the characterisation of the arid palaeoenvironmental and their link with the occurrence of amber. The Cretaceous amber-bearing outcrops from the Maestrazgo Basin have been known for a long time [38] and were traditionally associated with the Escucha Formation [39], an Aptian– PLOS ONE Late Albian desert biota from Iberia PLOS ONE | https://doi.org/10.1371/journal.pone.0282178 March 2, 2023 2 / 51 Funding: This study is a contribution to the project CRE CGL2017-84419 AEI/FEDER, UE from the Ministerio de Ciencia, Innovacio´n y Universidades (Spain) and the “Severo Ochoa” extraordinary grants for excellence IGME-CSIC (AECEX2021). The coauthor S.A´.-P. thanks the support from the Secretaria d’Universitats i Recerca de la Generalitat de Catalonia (Spain) and the European Social Fund (2021FI_B2 0003). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: The authors have declared that no competing interests exist.