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

prone to significant vegetation shifts when disturbances such as draughts occur [197, 198], and similar disruptions of vegetation could well have happened in similar past environments. A recovery vegetation reduced to pioneer ferns, and conifers and other resilient floral elements remains a plausible ecological scenario. It is interesting to highlight that palynofloras charac- terised by a high proportion of Cyathidites and Deltoidospora (94% of the total miospore con- tent) have already been recorded in other deposits associated with the Iberian Aptian–Albian desert system in SW Spain (Oliete Sub-basin) [2, 199]. If the palaeoenvironmental interpreta- tion presented here is valid, the recurring fern spikes suggest that episodes of accentuated draught were a common feature during the mid-Cretaceous at mid-latitude locations and that the vegetation responded to palaeoenvironmental disturbance in a similar way. The high con- tent in spores of palynofloras reflecting arid and disturbed vegetation may appear counter- intuitive, but a significant number of modern spore-producers can withstand extended periods of drought, present a high tolerance to environmental stress or simply thrive in edaphically low-nutrient habitats [200–202]. This adaptability has also been inferred for several Palaeozoic and Mesozoic spore-producers (e.g. Pennsylvanian sphenophytes, Jurassic Gleicheniaceae, Late Cretaceous Matoniaceae [73, 151]), which are often presented as stress-tolerators. Peri- odic ecological disturbances are also thought to have been favoured by early angiosperms

[155]. Besides Tucanopollis-producers, angiosperms colonising the Iberian Desert System included representatives of the ANITA grade, Chloranthales of diverse affinities (Clavatipolle- nites, Transitoripollis, etc.), probable monocots (Monocolpopollenites, Retimonocolpites) and eudicots (Table 1). These angiosperms were probably well integrated into the landscape, form- ing part of multiple vegetation types, including terrestrial wetlands (wet interdunes, oases sensu [189]) and freshwater aquatic ecosystems as helophytes and/or floating elements [4, 34, 36] (Fig 17). The occurrence of a high abundance of “Liliacidites” minutus in CA (Fig 13 clusters IV) could also reflect advanced stages of ecological succession, involving colonisation of settings dominated by ferns. This pollen type, currently related to Laurales [203], could have been pro- duced by angiosperms of broad ecological tolerances similar to the one exhibited by Eucalypto- laurus deprei, a representative of the family described from the Cenomanian of France [176, 204]. The high number of spores attributed to Anemiaceae (i.e., Cicatricosisporites) in the studied assemblages indicates that ferns were probably still the dominant floral elements in wetlands and maybe in some arid places. Early Cretaceous representatives of the family have been previ- ously associated with swamps, lacustrine, and savanna environments [75, 150, 205], and a sim- ilar environment can be assumed for the Iberian Anemiaceae, along with another spore (Patellasporites tavaredensis) and pollen (Crassipollis chaloneri) producers (Fig 10). The

inferred vegetation should have been of low stature and have surrounded ephemerous or semi-permanent water bodies developed in interdunes, maybe as part of the understory of open woodlands [75, 188, 206]. • Hinterland vegetation The presence of bisaccate grains in assemblages otherwise characterised by marine palyno- morphs suggests that a fourth type of vegetation involving conifers could have constituted a more distant vegetation type. Bisaccate pollen grains present a high dispersal capability, and their higher representation in distal, marine settings is often interpreted to reflect a tapho- nomic (i.e., biostratinomic) bias [207, 208], known as Neves Effect in Palaeozoic floras [209]. In the present context, the higher abundance of bisaccate grains in marine assemblages could represent hinterland vegetation involving Pinaceae and/or Podocarpaceae that would have col- onised topographically higher settings of the Iberian Massif [14]. PLOS ONE Late Albian desert biota from Iberia PLOS ONE | https://doi.org/10.1371/journal.pone.0282178 March 2, 2023 38 / 51