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

could equally represent a range extension down into the late Albian for these taxa, which remain not widely distributed (i.e., rare species). The updated new age for the sections has important implications for the local stratigraphy as it allows us to confidently attribute them to the Utrillas Group [61], while previous studies considered them as part of the Escucha Formation [28, 29, 31, 32, 43]. The new biostrati- graphic inferences are also supported by previous results obtained for the Utrillas Group in the Maestrazgo Basin based on indirect correlations [47, 50], palynological [123, 124] and faunal data (ostracods) [61]. From a palaeoenvironmental perspective, the biostratigraphic markers recorded in the three studied sections suggest that resin production/deposition in the Maestrazgo Basin was either coeval or close in time. In that regard, the amber levels might represent a biostrati- graphic event of regional significance. The marine carbonates of the Mosqueruela Formation [50], immediately overlying the amber-bearing strata at CA and AP, represent the regional expression of the flooding event described elsewhere in uppermost Albian strata (Mortoni- ceras rostratum/M. perinflatum ammonite zones) [125]. In eastern Iberia, this transgressive pulse led to the development of widespread marine platforms across the Mesozoic intraplate basins [48, 49]. Environments and vegetation The record of highly variable fossil remains and amber with biological inclusions suggest the presence of an ecosystem structurally framed by multi-tiered vegetation [14, 28, 34–36] sus-

taining complex arthropod communities (Table 2). Terrestrial ecosystems of such complexity might seem surprising for deposits associated with a desert system. However, there are no rea- sons to believe that arid and semi-arid ecosystems from the Cretaceous were less complex than their modern counterparts, such as the Namib and Kalahari deserts [126, 127]. The presence of palynological assemblages of varying composition in marine-influenced intervals is other- wise expected, given the taphonomic, palynological and palaeobotanical constraints [14, 128– 131], and indicates the existence of mosaic vegetation types in the area with conifer-forests along the Tethyan coasts (Fig 16). The vegetation of this region was strongly conditioned by both the influence of the sea and the desert and other factors such as palaeowildfires, as the abundant charcoal occurrence in the Spanish Cretaceous amber-bearing deposits indicates [40, 132]. A picture of the regional vegetation: Cheirolepidiaceae-Cupressaceae communities The significant representation of Classopollis and Inaperturopollenites dubius in the studied assemblages reflects the importance of the families Cheirolepidiaceae and Cupressaceae in the vegetation. The increased numbers of these two taxa observed in assemblages with marine palynomorphs (Figs 12–14) and the correlation between I. dubius and dinocysts in the PCA (Fig 10), representing the most distal settings indicate that their pollen-producers were wide- spread regionally, probably forming a significant part of the hinterland vegetation.

Cheirolepidiaceae was one of the most widespread conifer families among the Mesozoic vegetation. They colonised a wide range of environments ranging from low to high latitudes in both hemispheres [8, 133–135] and commonly assumed a dominant position in the vegetation from the Early Jurassic to the mid-Cretaceous [134, 136], especially in some low latitude set- tings associated with evaporites [8, 137]. While historically linked to arid environments and/or salty ones [79, 138–140], recent studies suggest broader ecological preferences for, at least, some representatives of the family [134, 141, 142]. PLOS ONE Late Albian desert biota from Iberia PLOS ONE | https://doi.org/10.1371/journal.pone.0282178 March 2, 2023 32 / 51