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

CA are mainly plotted against the negative side of the axis, levels from SJ are mainly restricted to the positive quadrant. Mega- and mesoremains were collected in the three studied sections. Generally, they exhibit good preservation and occur more abundantly in levels with marine influence (i.e., associated with palynological samples containing dinocysts) and without amber (e.g., SJ-2.1, CA-2, AP- 4.2; Figs 3–5). In sharp contrast with the palynofloras, the megafloral assemblages are poorly diverse and dominated by conifers, being Frenelopsis particularly abundant. Angiosperms rep- resent only a minor part of the mesofossil assemblages. The megaremain assemblage of AP has been interpreted as mostly allochthonous due to the range of disarticulation and fragmenta- tion of specimens of Frenelopsis turolensis [106]. The preservation of most of the fossil plants as compressions including well-preserved cuticles and the occurrence of ramified and articu- lated branches of Frenelopsis (Fig 11D), some of them presenting cones attached to their axes, would indicate, however, a parautochthonous production sensu [107]. One of the most abundant taxon is Frenelopsis, which presents in the Maestrazgo Basin a vegetative morphology markedly xeromorphic with highly reduced leaves, thick cuticles and deeply sunken stomatas [37, 106]. Leaves of Eretmophyllum, Mirovia and Dammarites, as well as twigs of Brachyphyllum and Widdringtonites, have been commonly found. San Just section (SJ). The lower palynological interval of this section (SJ-2.1–SJ-3.4; Fig

12 clusters I–II) is characterised by marine palynomorphs and high percentages of Inaperturo- pollenites dubius (Fig 7K) and Classopollis spp. (Fig 7Q). Its upper part (SJ-3.5–SJ-5.3; Fig 12 clusters III–V), corresponding with the amber outcrop, is devoid of dinocysts and reveals increasing abundances of fern spores (Cyathidites/Deltoidospora and Gleicheniaceae) and angiosperms (mainly Pennipollis). A renewed increase of I. dubius and Classopollis, this time accompanied by numerous Anemiaceae and spores of uncertain botanical affinities (Patellas- porites tavaredensis, Fig 8T), is characterising the uppermost interval of the succession (Fig 12, cluster V). The megaflora collected in SJ (Fig 3) is the most diversified among the studied outcrops from the Maestrazgo Basin. Frenelopsis justae is numerically prevailing (Fig 11E). This species shows robust axes consisting of nodes and internodes formed by three unified leaves [37]. In addition, scarce remains of Brachyphyllum cf. obesum (Fig 11I), Eretmophyllum sp., Dammar- ites sp. and Widdringtonites sp. (Fig 11J) have been found. Several small fruits of angiosperms were found as mesofossils. They mainly include fruits of Montsechia-type (Fig 11F) and seg- mented fruitlets of cf. Serialis sp. (Fig 11H). Cortes de Arenoso section (CA). The lower palynological interval of CA (CA-1–CA- 14.01; Fig 13, clusters I–IV) is characterised by fluctuating abundances of Classopollis and Ina- perturopollenites dubius. The levels with the highest numbers of Classopollis usually include

more dinocysts (Cyclonephelium vannophorum and Kiokansium unituberculatum) and other marine palynomorphs. In this interval, two levels with significantly high percentages of angio- sperms (>40% of the total miospores) are noteworthy. The lower (CA-3.2) is characterised by the dominance of Tucanopollis spp. (Fig 9N), while the upper (CA-14.01; Fig 13, cluster IV) is characterised by a spike of “Liliacidites” minutus, and the near-complete absence of conifers. The overlying interval (CA-21.01–CA-35.03; Fig 13) includes high percentages of Classopollis (cluster V) and Inaperturopollenites (cluster VI), accompanied by moderate amounts of bisac- cate grains and lower proportions of spores. The amber-bearing stratum (La Hoya amber out- crop) is restricted to the uppermost part of the succession (cluster VI). Over 90% of the plant megaremains of this section are attributed to Frenelopsis cf. turolensis (Fig 11D). Particularly, this assemblage occurs in its lower part (levels CA-2, CA-3, CA-4, CA- 10; Fig 5). Leaves of Mirovia gothanii and Nehvizdya (= Eretmophyllum) penalveri and elon- gated seeds of the Spermatites-type constitute the remains of the assemblage. PLOS ONE Late Albian desert biota from Iberia PLOS ONE | https://doi.org/10.1371/journal.pone.0282178 March 2, 2023 26 / 51