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

succession was deposited during the transition from the Late Jurassic–Early Cretaceous syn- rift stage to the Late Cretaceous post-rift stage, associated with the gradual opening of the Western Tethys and the North Atlantic Ocean [45, 48, 49]. The Maestrazgo Basin forms a NW-SE-oriented depositional trough (Fig 1A), where the sedimentary succession generally becomes thicker towards the SE (Tethyan margin). During the Early Cretaceous the syn-rift sedimentary succession was dominated by thick, continental to coastal siliciclastic-dominated deposits (previously referred to as ‘Weald facies’) and marine carbonates (‘Urgonian facies’) [50–55] (Fig 2). Towards the end of the syn-rift stage (uppermost Aptian to early Albian), the sedimentary succession became more homogeneous across the basin, and coal-bearing strata attributed to the Escucha Formation were deposited [56–59]. The Escucha Formation has been interpreted as lagoons and marshes [59, 60]. The Escucha Formation is overlain by strata forming the Utrillas Group, a highly diachro- nous unit widespread along the IBRS, which has been traditionally interpreted as the transition into the post-rift stage [57, 59, 61]. In the Maestrazgo Basin, the Utrillas Group spanned the middle Albian–earliest Cenomanian [59]. In the Maestrazgo Basin, this Group includes facies originally interpreted as tidally-influenced fluvial deposits [57, 62] and later reinterpreted as part of an erg system (aeolian dune desert), covering more than 16,000 km2 on the eastern side of the Iberian Peninsula [18, 59].

According to [18, 59], this erg system (Fig 2B) displayed a threefold zonation developed along a NW–SE direction characterised by: (i) a back-erg area close to the main source area of siliciclastics (Iberian Massif), dominated by coarser-grained wadi sediments and minor aeolian accumulations; (ii) a central-erg area corresponding to the main locus of aeolian dune accu- mulation; and (iii) a fore-erg area characterised by the interplay between aeolian dunes and shallow marine deposits from the Western Tethys, giving rise to a complex interaction of tid- ally-reworked aeolian dune and subtidal facies associations. In the Maestrazgo Basin, the Utrillas Group is overlain by the Mosqueruela Formation [50, 57, 59, 63] (Fig 2B), a marine carbonate unit, that represents the onset of carbonate sedimenta- tion (Southern Iberian Ramp), which will prevail during most of the Late Cretaceous [48, 64]. The Maestrazgo Basin is divided into several sub-basins (Fig 1) that include: the Galve, Oliete, Las Parras, Morella, El Perello´, La Salzedella, and Peñagolosa sub-basins [49]. In this paper, three stratigraphic sections have been measured in three outcrops in the Maestrazgo Basin, namely: San Just (according to [31]: “left slope of San Just”), Arroyo de la Pascueta and Cortes de Arenoso (according to [40]: “La Hoya outcrop”) sections. The San Just section is located in the Las Parras Sub-basin, about 70 km to the NNW from the other studied sections which crop out in the NNW sector of the Penyagolosa Sub-basin (Fig 1). The studied

sedimentary succession is located in the distal part of the mid-Cretaceous desert system, which is characterised by a fore-erg setting where aeolian strata interacted with shallow marine deposits in the coastal fringe of the Western Tethys. San Just section (SJ). The 22 m-thick section is located on a roadside (N-420 road), approximately 3 km to the south of Utrillas village (Teruel Province) and overlain by the marine carbonates of the Mosqueruela Formation, dated as Cenomanian [46]. The succession can be divided into a lower part mainly consisting of dark siltstones and mudstones inter- spersed with cm- to dm-thick fine-grained sandstone layers with wavy to flaser heterolithic laminations (Fig 3), and an upper part dominated by fine-grained, cross-bedded, sandstones with thin (dm-thick) interbedded mudstones, which may include water deformation struc- tures and slumps. The amber-bearing bed is located in the lower part of the section and is over- lain by (large-scale) planar cross-bedded fine-grained sandstones exhibiting sharp basal contacts. Kindney-shaped amber pieces together with “stalactitic aerial” amber pieces, the lat- ter with bioinclusions, are abundant in this bed [43] (Fig 4A and 4B). PLOS ONE Late Albian desert biota from Iberia PLOS ONE | https://doi.org/10.1371/journal.pone.0282178 March 2, 2023 4 / 51