First report of silicified wood from a late Pennsylvanian intramontane basin in the Pyrenees: systematic affinities and palaeoecological implications

The first anatomically preserved wood specimens of an upland Carboniferous flora from the Iberian Peninsula are reported from the Erillcastell Basin (Eastern Pyrenees, Catalonia, Spain). Two taxa are described, a calamitacean Equisetales (Arthropitys sp.) and a Cordaitales (Dadoxylon sp.). The Arthropitys specimen has fusiform multiseriate rays composed of square parenchyma cells with conspicuous uniseriate or multiseriate simple pits. These pits are located near the transverse walls and occasionally in the tangential walls. The tracheids vary in lumen size, with scalariform‐bordered pits on their radial walls and multiseriate pits in their cross‐field areas. The Dadoxylon specimen commonly has uniseriate fusiform rays. The tracheids are long, with a square shape in transverse section. Their radial walls bear araucarian pitting with a uniseriate to triseriate arrangement. The pits are circular with a spindle‐shaped aperture. Comparison of the Erillcastell specimens with coeval species from Europe indicates that they could belong to new species. The good preservation of the new fossil wood yields significant palaeoenvironmental information. The lack of marked growth rings in both specimens and the presence of tyloses in Dadoxylon suggest that the climate in the intramontane basins of the Pyrenees was slightly seasonal towards the end of the Carboniferous. This contrasts with the marked seasonality of coeval lowland basins. Such upland habitats may have enhanced the survival of plants adapted to humid conditions in a global context of increasing aridity.

circular with a spindle-shaped aperture.Comparison of the Erillcastell specimens with coeval species from Europe indicates that they could belong to new species.The good preservation of the new fossil wood yields significant palaeoenvironmental information.The lack of marked growth rings in both specimens and the presence of tyloses in Dadoxylon suggest that the climate in the intramontane basins of the Pyrenees was slightly seasonal towards the end of the Carboniferous.This contrasts with the marked seasonality of coeval lowland basins.Such upland habitats may have enhanced the survival of plants adapted to humid conditions in a global context of increasing aridity.
T H E vegetation of the Pennsylvanian palaeotropical wetlands of Euramerica is among the most iconic and wellknown in the fossil record.Studies conducted for over two centuries have exhaustively explored the vegetation framework, from the characteristics of individual plant organs to the organization of communities and their dynamics in response to the climate changes of the Late Palaeozoic Ice Age (e.g.DiMichele et al. 2009;Bashforth et al. 2016;Richey et al. 2021).This considerable amount of knowledge about Pennsylvanian floras is based on palynological data and the abundant macro-remains from paralic basins, including both adpressions and anatomically preserved plants.The latter commonly occur in coal balls, carbonate concretions that formed in marineinfluenced coal swamps (Scott & Rex 1985).The permineralized plant remains inside coal balls have enabled the study of the fine anatomical features of lowland Pennsylvanian plants, providing detailed information on their development (e.g.Eggert 1961) and physiology (e.g.Cichan 1986;Baker & DiMichele 1997), as well as their interactions with arthropods (e.g.Scott & Taylor 1983) and microorganisms (e.g.Baxter 1975;Stubblefield et al. 1984).
There is significantly less information about the vegetation of intramontane basins such as those that developed in Southern Europe during the late Pennsylvanian (Kasimovian and Gzhelian, 307-299 Ma), here considered equivalent to the Stephanian European regional stage (Heckel & Clayton 2006;Aretz et al. 2020).There is general agreement that the elevation of these basins was above 1000 m and their fossil floras represent the upland vegetation of the late Pennsylvanian tropics (Thomas & Cleal 2017).In Southern Europe, data on the floras of these basins come mostly from palynomorphs (e.g.Juncal et al. 2019) and adpressions (e.g.Mart ın-Closas & Galtier 2005).In the absence of a marine influence, coal balls did not form in intramontane wetlands and, therefore, anatomically preserved plant assemblages are overall rare (Tr€ umper et al. 2022).The Stephanian A (Kasimovian) silicified plant assemblage of Grand-Croix from the St Etienne Basin (Central France; Fig. 1) is the richest to date, containing 54 plant genera (Doubinger et al. 1995;Galtier 2008) and well-preserved associated microorganisms (e.g.Renault 1900;Krings et al. 2009;Taylor et al. 2012).The assemblage is dominated by Cordaitales and differs from the contemporaneous adpression flora of the same basin, which is dominated by ferns and pteridosperms (Galtier & Phillips 1985;Doubinger et al. 1995).In the Graissessac-Lod eve Basin, one of the best-known examples of late Pennsylvanian intramontane wetlands in Southern Europe, a few silicified trunks that are up to 50 cm in diameter and 2 m in length have been recovered from Stephanian C fluvial channels (Galtier et al. 1997).They correspond to Cordaitales (Dadoxylon cf.brandlingii and Dadoxylon sp.) and a calamitacean Equisetales (Arthropitys sp.).The palaeoecology of these plants is known from adpressions.According to Mart ın- Closas & Galtier (2005), the Cordaitales would have inhabited the proximal areas of the basin such as the alluvial fans and the banks of braided rivers, while the Calamitaceae would have grown in the floodplains and along the riverbanks.Interestingly, the Arthropitys trunks found in the Graissessac-Lod eve Basin have a significant amount of wood (at least 10 cm thick), in contrast to the poorly lignified contemporaneous Equisetales from the basin preserved as adpressions and moulds (Galtier et al. 1997;Mart ın-Closas & Galtier 2005).This suggests different growth patterns and/or ecology (Galtier et al. 1997;Martin-Closas & Galtier 2005).
In  Schneider (2006).(C esari et al. 2015 and references therein).Here, we describe permineralized wood specimens recently collected in the Erillcastell Basin (Central Pyrenees, Catalonia, Spain).They represent the first evidence of anatomically preserved plants from a late Pennsylvanian intramontane basin of the Iberian Peninsula.The excellent preservation of the specimens enabled us to assign them to two genera.They provide additional information on the late Pennsylvanian upland vegetation in Europe and highlight the potential for new palaeobotanical discoveries in the region.

GEOLOGICAL SETTING
The study area is located 12 km northeast of the town of Pont de Suert, in the Pyrenean Axial Zone (northwest Catalonia, Spain), near the abandoned village of Erillcastell.From a geological viewpoint, the palaeobotanical locality studied here belongs to the Erillcastell Basin, which is Carboniferous-Permian in age (Mart ı 1983(Mart ı , 1995;;Soriano et al. 1996).The origin of the basin is related to a transtensional tectonic regime occurring before the end of the Hercynian orogeny, during the Pennsylvanian (Moscovian-Gzhelian) and Permian (M enard & Molnar 1988).The thinning of the continental crust produced intense volcanism and the subsidence of the Carboniferous-Permian Variscan intramontane basins (Mart ı & Mitjavila 1988).In the Catalan Pyrenees (northeast Spain), four such late Hercynian pull-apart basins were shaped from west to east: Erillcastell (Fig. 2), Estac, Cad ı and Castellar de N'Hug-Camprodon (Mart ı 1995;Soriano et al. 1996).
The Erillcastell Basin is a narrow basin (c. 15 km long and 3 km wide), oriented east to west, limited to the north by strike-slip faults, and internally compartmentalised by normal faults according to Gisbert (1981), Mart ı & Mitjavila (1987, 1988) and Mart ı (1995).During the Westphalian, high tectonic subsidence caused intense volcanic activity, leading to the accumulation of thick volcanic and volcano-sedimentary sequences rich in silica (Mart ı 1981(Mart ı , 1983;;Mart ı & Mitjavila 1988).The magmatic activity decreased during the Stephanian, enabling the development of fluvio-lacustrine deposits.This trend continued during the Permian, which is mainly represented by red beds of Saxonian facies.However, Permian deposits are locally missing in Erillcastell, where the lower Triassic Buntsandstein facies unconformably overlies the latest Carboniferous deposits.This unconformity is associated with the tilting and erosion of some of the underlying deposits (Mateu-Ibars & Marzo 1985, pp. 1-49) before the beginning of the Mesozoic Iberian rift (Salas & Casas 1993).
Stratigraphic studies in the Erillcastell Basin were undertaken by Mey et al. (1968) andNagtegaal (1969).These authors proposed a subdivision of these deposits based on the lithostratigraphy.Later, Gisbert (1981) proposed a new subdivision based on allostratigraphic units.These units were termed the Grey Unit, the Transition Unit, the Lower Red Unit and the Upper Red Unit.The specimens studied here were found in the lowermost part of the Transition Unit.
The Transition Unit was first described by Gisbert (1981Gisbert ( , 1983)).Since then, it has generally been accepted that it is Gzhelian in age based on biostratigraphic studies of macroscopic plant remains (Tosal et al. 2022 and references therein).In Erillcastell, the Transition Unit is 142 m thick (Fig. 3), rests unconformably on the Grey Unit, and is cut off by the basal Mesozoic unconformity (Gisbert 1981(Gisbert , 1983;;Tosal et al. 2022).It consists of lenticular conglomerates, sandstones with epsilon stratification and trough cross-bedding, black shales and bituminous coal rich in fossil plant adpressions.The silicified specimens come from a fining-upward sequence composed of conglomerates and coarse-grained sandstones with an erosive base, followed by sandstones with cross-beddings that are covered at the top of the sequence by siltstones (Fig. 3).This sequence is interpreted as an infill of a braided-river channel and the associated floodplain facies (Tosal et al. 2022).The silicified wood specimens studied here were found at the top of sandstone bodies, being commonly associated with Cardiocarpus seeds and being interpreted as parautochthonous (Tosal et al. 2022).

MATERIAL AND METHOD
Two specimens preserved in silica from the late Pennsylvanian were found in Erillcastell.Ten thin sections c. 30 lm thick were prepared in transverse, radial and tangential planes.They are stored at the Museu de Ci encies Naturals de Barcelona with the collection numbers MGB 90407 LP1-MGB 90407 LP3; MGB 90408 LP1-MGB 90408 LP7.Cellulose acetate peels using HF (Galtier & Phillips 1999) were also prepared at UMR AMAP, Montpellier, to provide complementary information, and are deposited at the Museu de Ci encies Naturals de Barcelona under the numbers MGB 90407 P1 and MGB 90408 P1-3.The slides and peels were studied and photographed with a Keyence VHX-7000 digital microscope.For comparative purposes, additional silicified wood specimens from the French limnic basins of Graissessac (Gzhelian) and Autun (early Permian) were studied.These specimens are part of the palaeobotanical collections of the Universit e de Montpellier; the specimen from Graissessac has accession number G2283; those from Autun have numbers ARX1, ARX2 and ARX3.
At least 50 measurements were taken for each wood character using the free software ImageJ (https://imagej.net/Welcome).These data are archived in the Dryad repository (Tosal et al. 2023).The measurements indicated in the text were made on the thin sections.A comparison of the tracheid diameter between the thin sections and the peels showed that although the range was similar, the average size could be slightly different.Such differences were taken into account when comparing the material studied with previous taxonomic descriptions.
Throughout the text, equivalences between global and European regional chronostratigraphic units follow that of Heckel & Clayton (2006)

SYSTEMATIC PALAEONTOLOGY
Two well-preserved silicified wood specimens from Stephanian C (Gzhelian) deposits from Erillcastell are described here.One is 10 cm long and 5 cm wide (Fig. 4A) and corresponds to a secondary xylem portion of a calamite (Fig. 4B-D).The other specimen is 20 cm long and 30 cm wide (Fig. 5A) and corresponds to a secondary xylem portion of a Cordaitales (Fig. 5B-D).Locally, small fissures without preferential orientation infilled by minerals rich in silica (mainly quartz) cross the thin sections.Each specimen is described below in the different planes.Material.MGB 90407.
Description.In transverse section, the tracheids are rounded, rarely polygonal, with walls 17 lm thick (Fig. 6A).The mean diameter of the tracheid lumen is 49 lm tangentially and 62 lm radially (n = 33).In some localized areas of the wood, the average radial diameter of the lumen is reduced to 25 lm (Fig. 6A, B).However, this reduction in size is not associated with the substantial increase in tracheid wall thickness that characterizes latewood.
Here, the wall thickness of the tracheids remains constant throughout the wood, and we infer that the specimen lacks true growth rings.Apart from the changes just mentioned, the sample does not show a substantial variation in the radial and tangential diameters of the tracheids outward.The wood is characterized by two types of rays: large ones that are up to 11 cells wide and narrow ones that are 1-4 (mainly 2) cells wide (Fig. 6C).Both types are separated by  1-4 rows of tracheids and are composed of parenchyma cells that are square or rectangular and measure 24-51 lm tangentially (mean, 37.5 lm; n = 50) and 49-121 lm radially (mean, 84 lm).Their wall is thin (mean, 6 lm).The ray cells show conspicuous uniseriate or multiseriate (2-10; mean, 4) simple pits.They are spaced and located in the transverse walls and occasionally the tangential walls (Fig. 6C).These pits are rounded or elongated in shape.The diameter of the rounded pits is 5-13 lm (mean, 9 lm; n = 50), while that of the elongated pits is 13-26 lm tangentially and 5-10 lm radially (n = 50).
In tangential section, the tracheids measure more than 2.6 cm long (the size of the thin section) and are devoid of pits in the tangential walls.The rays are fusiform (Fig. 6D).The large rays are 2-4.2mm high, 0.3-0.7 mm wide, and composed of 40-100 parenchyma cells in height.Most cells are polygonal in shape, except those located at the extremities of the rays, which have a rectangular shape.The size of the cells ranges from 24 to 91 lm.The narrow rays are 0.6-1.7 mm high and 52-151 lm wide.They are 14-30 polygonal cells in height, with the width varying from 29 to 78 lm.Pitting is not observed in the wall of the ray cells in the available tangential section.Occasionally, two narrow rays are connected by a thin row of rectangular parenchyma cells (Fig. 6E).
The radial section shows long tracheids with uniseriate to rarely biseriate pits.The pits are scalariform-bordered and the pit aperture is 3-6 lm long (Fig. 6F).Ray cells are rectangular (33-69 lm 9 31-48 lm) with a thin wall (3-7 lm).They bear simple pits distributed sparsely in the cell wall (Fig. 6G).The pits are rounded or elongated in shape and located close to the transverse walls.Cross-field areas show crowded multiseriate pits with an elongated and sub-rounded irregular shape.They measure 12-22 9 7-13 lm.Often, brownish rounded organic structures are observed in the ray cells.They measure 14 lm in diameter and presumably correspond to fungal spores (Fig. 6H).
Affinities.The most conspicuous character of the specimen is the presence of both small rays and large rays, the latter being interpreted as interfascicular rays.It also shows rectangular or square ray cells in the transverse and radial sections, and a uniform diameter of the tracheids tangentially and radially.These characteristics are consistent with Arthropitys (Wang et al. 2003;R€ obler & Noll 2010;R€ obler et al. 2012), a genus of the family Calamitaceae that existed from the Pennsylvanian to the Permian.For the specific attribution of the specimen, the anatomical features of the rays and the pitting of the primary and secondary xylem tracheids are considered in more detail hereafter.
Arthropitys  1).Arthropitys bistriata differs from the Arthropitys from Erillcastell by shorter and wider ray cells (Table 1).By contrast, A. barthelii and A. tocatinensis have ray cells of comparable size, which also show circular pits on the horizontal walls.However, unlike the Erillcastell Arthropitys, both species lack pits on the radial walls of the ray cells.Furthermore, A. deltoides has larger and rounded or sub-rounded ray cells tangentially (Cichan & Taylor 1983), which is in contrast to the polygonal (angular) shape seen in the Arthropitys specimen studied here.
The two species with the most similarities to the Arthropitys specimen from Erillcastell are A. medullata and A. ezonata (Table 1).Arthropitys medullata is a common species in the lower Permian limnic basin of Autun (France) that Marguerier (1967) described in detail.Although there is a strong resemblance, a slight difference in the wall thickness of the different cell types is observed.While the tracheid wall of the specimen from Erillcastell is thick, that of the specimens from Autun is thin according to Marguerier (1967).Similar differences are observed in the ray cell walls, which are thicker in the specimen from Erillcastell than in those from Autun.The secondary xylem of A. ezonata also has similar anatomical features to those of the Arthropitys specimen from Erillcastell.However, the tracheid cells are slightly narrower in A. ezonata (Table 1).These quantitative differences may be caused by environmental differences during plant growth, as observed by Andrews (1952) in some silicified calamitacean Equisetales specimens from North America, or by abiotic factors, such as the diagenetic processes described by R€ oßler et al. (2021).Therefore, they should not be considered for taxonomic purposes.To further specify the taxonomic attribution of the Arthropitys specimen from Erillcastell, it would be necessary to characterize the anatomy of its primary xylem.However, this tissue is missing from the specimen.For this reason, it will be referred to as Arthropitys sp.here.Material.MGB 90408.
Description.In transverse section, the tracheids are rectangular or square in shape and their lumen size is relatively uniform.They measure 20-46 lm tangentially (mean, 30 lm; n = 101) and 11-41 lm radially (mean, 28 lm; n = 101).The tracheid walls are 6 lm thick (n = 70).The regular lumen diameter and the wall thickness indicate the absence of growth rings.1-7 rows of tracheids separate the uniseriate to rarely biseriate rays (Fig. 7A).The ray cells are 81-160 lm long (mean, 95 lm) and 10-22 lm wide (mean, 14 lm; n = 7) and their tangential walls are oblique.Occasionally, pale brown spherical structures (10 lm in diameter) occur in the ray cells and may correspond to fungal spores (Fig. 7B).
Affinities.The specimen described above has uni-to biseriate rays that separate one to several rows of square to rectangular tracheids with araucarian radial pitting.Based on the work of Marguerier (1971), these features are consistent with the secondary xylem of both the Cordaitales and Coniferales.To date, only the remains of Cordaitales (i.e.Artisia pith casts, Cordaites leaves and Cardiocarpus seeds) have been found in the Erillcastell Basin, while coniferalean specimens are absent (Tosal et al. 2022).We assume, therefore, that the permineralized wood remains studied here are likely to correspond to Cordaitales.At present, three morphogenera are informally accepted as woody axes of F I G .6 .Thin sections of Arthropitys sp. from Erillcastell.A, transverse section showing the rounded shape and thick walls of the tracheids; discontinuous lines mark a tangential zone of the tracheids with a smaller lumen diameter (MGB 90407 LP2).B, transverse section showing variations in the tracheid lumen diameter suggesting changes in growth patterns (arrows) (MGB 90407 LP2).C, transverse section showing large rays with simple pits located in the transverse walls and occasionally at the border of the tangential walls (MGB 90407 LP2).D, tangential section showing fusiform-shaped rays (MGB 90407 LP3).E, tangential section showing a large ray and two narrow rays connected by a thin row of rectangular parenchyma cells (arrow) (MGB 90407 LP3).F, radial section showing the tracheids with scalariform-bordered pits and the cross-fields with characteristic multiseriate pits showing an elongated and subrounded irregular shape (MGB 90407 LP1).G, radial section with square-shaped ray cells bearing simple pits (MGB 90407 LP1).H, radial section showing ray cells with brown rounded structures that may correspond to fungal spores (MGB90407 LP1).Scale bars represent: 100 lm (A, C, E-H); 500 lm (B, D).Marguerier (1977), is provided below and summarized in Table 2.
Dadoxylon rollei and the specimen from Erillcastell show small uni-to partly biseriate rays that separate one to several rows of tracheids.Their tracheids are square to rectangular in the transverse section and have thick walls with circular pits radially (Fig. 8A, B).However, three main differences are observed: (1) the Dadoxylon specimen from Erillcastell has a multiseriate pitting arrangement in the tracheid walls, unlike the uniseriate (Fig. 8C) or rarely biseriate pitting of D. rollei (Fig. 8D); (2) the pit apertures of the Dadoxylon specimen from Erillcastell are spindle shaped, which contrasts with the circular pit apertures of D. rollei (Fig. 8C, D); and (3) the rays of the Dadoxylon specimen from Erillcastell are narrower and have a lower density than those of D. rollei (Table 2).
Dadoxylon cf.brandlingii as described by Galtier et al. (1997), is relatively poorly preserved and some delicate characters, such as the type of the pit aperture, are missing.Like the Dadoxylon sp. from Erillcastell, D. cf.brandlingii also has square-shaped tracheids in the transverse section (Fig. 9A).The tracheids are long and show multiseriate pitting radially (Fig. 9C).The rays are uniseriate to locally biseriate (Fig. 9B) and the cross-field pits are circular in shape (Fig. 9C, D).However, the Dadoxylon sp. from Erillcastell has smaller tracheid lumens and smaller rays than D. cf.brandlingii from Graissessac (Table 2).
The well-preserved wood of Cordaixylon andresii described by C esari et al. ( 2015) is characterized by tracheids with uniseriate or alternate biseriate and triseriate pitting of the araucarian type.These features are also observed in the Dadoxylon sp. from Erillcastell.However, two remarkable differences in the pitting features are observed between them that are significant for taxonomy: (1) the radial pits of the Dadoxylon sp. from Erillcastell are circular in shape, while those of C. andresii are hexagonal (C esari et al. 2015); and (2) the cross-field pits of the Dadoxylon sp. from Erillcastell are numerous, small and circular, with spindle-shaped apertures, which contrasts with the 1-2 large pits of C. andresii.
Dadoxylon subrhodeanum as briefly described by Grand'Eury (1877) differs from the Erillcastell specimen by the uniseriate pitting of the tracheid radial walls and by its higher rays (10-30 cells high).The specimen resembling Dadoxylon subrhodeanum according to Lemoigne (1965) possesses tracheids with uniseriate to triseriate pits of the araucarian type on their radial walls.It differs from the Erillcastell specimen by tracheids that are larger (up to 90 lm in diameter) and mostly hexagonal in transverse section.Its rays are uniseriate but occasionally bi-or even triseriate and higher, with 20 cells in height on average.
To summarize, the wood from Erillcastell is consistent with the morphogenus Dadoxylon.However, its anatomical features do not correspond exactly to those of previously reported wood specimens from southwestern Europe from that time.As with Arthropitys, finding new specimens with a preserved primary xylem will be crucial in further specifying the affinities of Dadoxylon from Erillcastell.

Anatomically preserved plants from the Pennsylvanian and lower Permian of Spain
The silicified wood specimens from Erillcastell add data to the sparse record of anatomically preserved plants from the Pennsylvanian to lower Permian deposits of the Iberian Peninsula.The oldest Pennsylvanian record is from the province of Le on (northern Spain).It consists of coal balls containing marine fauna and terrestrial plants that are late Namurian (= Bashkirian) in age (G omez de Llarena & Arango 1946;Beckary 1987;Vachard & Beckary 1989).These coal balls have yielded a taxonomically diverse floral assemblage containing 54 species, most of them corresponding to pteridosperms (Beckary 1987;Galtier 1997).In the province of Asturias, Renier (1926) reported a Westphalian coal ball found in a building of the Lieres coal mine company (p.1291).The coal ball contains Stigmaria (Lepidodendrales), Sphenophyllum (Equisetales), Myeloxylon (Medullosales) and some gymnosperm wood.More recently, C esari et al. (2015) described well-preserved silicified trunks of Cordaixylon as well as roots of Psaronius (Marattiales) from Stephanian C deposits in Asturias (Cantabrian Mountains; northern Spain).To date, these are the only known anatomically preserved plants from the Carboniferous in Spain.However, they represent plants from a lowland (paralic) setting that would have grown in transitional environments, which makes it difficult to compare them with the upland (limnic) floras from Erillcastell.

Palaeodiversity and palaeoecology of the upland flora from the Erillcastell Basin
Calamitacean trees are one of the iconic components of Pennsylvanian and Permian floras.The good preservation of the wood found at Erillcastell enables the determination of the occurrence of pits in the transverse walls of ray cells (Fig. 6A).A similar feature has been reported in the rays of some Palaeozoic Calamitaceae such as Archaeocalamites, Arthropitys and Calamitea (= Calamodendron) (Marguerier 1970), but has not been documented for all calamitacean taxa.This character may have been advantageous for fluid circulation in these genera (Marguerier 1970).
Late Palaeozoic Calamitaceae have been reported from various habitats, indicating their adaptation to diverse ecological conditions.For instance, some species with little wood would have inhabited permanently flooded environments, similar to those of present-day Equisetum.Some other taxa have succulent stems and/or deep root systems that would be adapted to reach the phreatic water during seasonally dry conditions (e.g.Barthel & R€ oßler 1994;Naugolnykh 2005).Finally, others have abundant wood and a well-developed root system (Taylor et al. 2009), which have been linked to growth in disturbed settings (Gastaldo 1992).The Arthropitys specimen from Erillcastell has a well-developed secondary xylem, suggesting that this plant inhabited an environment with significant clastic inputs close to watercourses.This result fits with the palaeoenvironmental interpretation proposed by Tosal et al. (2022) based on a taphonomic study of the early Gzhelian flora from Erillcastell.The authors concluded that Calamites was a riparian element there and grew in point bars and river margins.
The proportions of parenchyma in the Calamitaceae can also be used to infer the climatic conditions in which the plants grew.In extant Equisetum species, water stored in the wood parenchyma can indeed sustain the functioning of the vascular system under dry conditions, notably by preventing embolism or by facilitating the refilling of the xylem conducts (Morris et al. 2016 and references therein).The Arthropitys specimen from Erillcastell is characterized by abundant parenchyma (46%; Fig. 6A).Such high proportions of parenchyma (up to 50% of the total silicified tissue) have also been documented in calamitacean wood specimens from other intramontane basins in Europe (e.g.R€ oßler et al. 2012;Mencl et al. 2013), which have been interpreted as an adaptation to dry conditions (Barthel & R€ oßler 1994;R€ oßler et al. 2012).Indeed, seasonal precipitation has been recently proposed for the early Gzhelian in Erillcastell Basin by Tosal et al. (2022), based on the frequent alternation between oxidized and reduced horizons in the floodplain deposits.
Calamitaceae were also capable of adapting their secondary growth to environmental factors, resulting in the development of growth rings.The analysis by Luthardt et al. (2017) of an in situ early Permian plant community growing around a wet spot under a generally semi-arid climate showed that the Calamitaceae had a higher sensitivity to environmental stress than seed plants.The specimen from Erillcastell shows small changes in the tracheid diameter (Figs 4B; 6A, C), similar to those of the indistinct type 2 rings interpreted by Luthardt et al. (2017) as drought-induced false rings.This feature suggests that the plant was growing in relatively favourable conditions, but with variations in the precipitation and/or the water table depth.
The second group of plants represented in the silicified wood specimens from Erillcastell is the Cordaitales, which is regarded as the sister group of the conifers and is also an important component of Pennsylvanian-Permian tropical floras (Anderson et al. 2007).Like the Equisetales, the Cordaitales were morphologically diverse and occurred in various habitats.Some Cordaitales, mainly from limnic basins (lowland vegetation), grew in peat swamps and clastic wetlands, where they were represented by shrubs and trees of relatively small stature (<10 m high) (Rothwell & Warner 1984;Costanza 1985;Trivett & Rothwell 1985;Raymond 1988).Other taxa produced large trunks and have been reconstructed as trees up to 30-40 m high.These larger Cordaitales are typically reported to have grown in welldrained substrates at higher altitudes ('uplands', Falcon-Lang & Bashforth 2005) and/or during drier, sub-humid to semi-arid climatic episodes ('drylands', e.g. Bashforth et al. 2016).However, some may also have grown in more humid conditions (Wan et al. 2020).
The silicified cordaitalean trunk described in this study is relatively large (more than 30 cm across; Fig. 5A), suggesting a height of at least 20 m based on the approach of Niklas (1994).Its wood anatomy is different from that of Arthropitys, with a much lower proportion of parenchyma and smaller tracheids.However, like Arthropitys, it does not show any evidence of growth rings in the part studied (Fig. 5B).This suggests that the Dadoxylon tree grew under relatively equal environmental conditions, as Arthropitys.Cordaitalean adpressions are frequently found in the lower Gzhelian fluvial deposits from Erillcastell.They are represented by different plant organs, such as foliage and pith casts (Artisia) or seeds (Cardiocarpus) (Tosal et al. 2022).These remains have been found in association with Calamites (mainly C. suckowii) and have been interpreted as growing alongside braided rivers (Tosal et al. 2022), supporting the hypothesis that both plants grew under similar environmental conditions.
The presence of tyloses in the Dadoxylon wood from Erillcastell could be linked to normal heartwood formation.It could also represent a response to an environmental stimulus such as fungal infections or injury-induced or drought-related embolism of the conducting cells (De Micco et al. 2016;Decombeix et al. 2022).Interestingly, tyloses have also been reported in the late Pennsylvanian C. andresii from Asturias, where they may have formed as a response to a fungal infection or wounding (C esari et al. 2015).Unlike the specimen from Asturias that shows early stages of tylose formation in the form of isolated bubble-like structures in the tracheid lumina, the Dadoxylon sp.wood from Erillcastell shows only the late stages in which the tracheid lumen appears completely filled with tylose walls (Fig. 7E).

Intramontane vegetation and environmental changes in the late Palaeozoic palaeotropics
The late Pennsylvanian and early Permian was an important time for plant evolution in the palaeotropics of Euramerica.A general aridification trend caused a change in the composition of lowland vegetation, with a switch to a dominance by plants adapted to more arid environments (DiMichele 2014).By the end of the Stephanian C (Gzhelian), the coal swamp vegetation is considered to have been restricted geographically to isolated wetter spots (DiMichele et al. 2007).This period, sometimes called the 'Carboniferous rainforest collapse' (e.g.Sahney et al. 2010), corresponds to one of the main extinction events in the plant fossil record (Cascales-Miñana & Cleal 2014).In this context, intramontane basins are likely to have formed refugia, where the effect of the global climate change towards aridity was less marked due to more favourable temperatures and/or higher precipitation.While DiMichele & Phillips (1996) showed that there was a shift to mires dominated by tree ferns and pteridosperms in the late Pennsylvanian in North America, coeval mires of European intramontane basins typically remained dominated by arborescent lycopsids (Wagner 1989;Martin-Closas & Galtier 2005;Mart ın-Closas & Mart ınez-Roig 2007).This is also the case for the Erillcastell Basin, where Sigillaria brardii prevailed in peat-mires, while medullosacean pteridosperms and marattialean tree ferns grew in the distal areas of the floodplain (Tosal et al. 2022).The silicified specimens described in this study indicate the presence of large woody calamitacean Equisetales and Cordaitales in the basin.Despite their different systematic affinities, wood anatomy and putative physiology, both apparently grew under fairly favourable local conditions.The results obtained here indicate a weakly marked seasonal climate in Erillcastell, which did not vary widely enough to deeply influence the ecology of plant groups such as the Calamitaceae and Cordaitales.However, this seasonality would have been strong enough to influence the palaeoecology of the lycopsids, with S. brardii from Erillcastell growing in fluvial environments, as noted by Tosal et al. (2022).

CONCLUSION
Silicified wood specimens from Erillcastell represent the first occurrence of anatomically preserved plants from a late Pennsylvanian (Gzhelian) intramontane wetland of the Iberian Peninsula.The specimens correspond to two types of arborescent plants, a calamitacean Equisetales (Arthropitys sp.) and a Cordaitales (Dadoxylon sp.).They provide information not available from the adpression flora found in this locality, such as growth patterns, interactions with fungi, and the presence of tyloses, which enables us to better understand the plants and their environments.The lack of marked growth rings in the wood of both specimens suggests that they grew under stable local conditions, with possible drier episodes reflected in the reduction of the tracheid lumen size in the Arthropitys wood.The data provided here indicate a slightly seasonal climate, at least in terms of precipitation in the intramontane basins of the Pyrenees close to the Carboniferous-Permian boundary.These conditions would have been favourable for most palaeotropical plants, such as sphenopsids, ferns, pteridosperms and cordaitaleans.However, the seasonality in Erillcastell would have been strong enough for lycopsids such as S. brardii, which would have spread into fluvial environments during this time span.Future exploration of the area to recover new silicified plants is expected to lead to a better understanding of the palaeotropical upland floras of Euramerica and their response to the late Pennsylvanian and early Permian aridification and floral turnover.
Spain there are well-documented late Pennsylvanian intramontane floras preserved as adpressions (e.g.Wagner 1989 in the Iberian Massif; and G omez-Alba 2007, Mart ın-Closas & Mart ınez-Roig 2007 and Tosal et al. 2022 in the Pyrenees), but there has been no report of silicified plants in this type of basin to date.The only other Stephanian silicified plants from Spain belong to the coastal marine (deltaic) facies of the Arnao coalfield (Asturias), with the older records also corresponding to lowland paralic floras such as those found in the coal balls from the Namurian of Le on and the Westphalian of Asturias F I G . 1 .Geological map of Europe during the Carboniferous-Permian transition.Red pentagons correspond to the upland basins with silicified wood, while the blue pentagon corresponds to a lowland basin with silicified wood.Modified from Roscher &

F I G . 7 .
Thin sections of Dadoxylon sp. from Erillcastell.A, transverse section showing rectangular to square tracheids and narrow rays with radially elongated cells (MGB 90408 LP2).B, transverse section showing a brown spherical structure, possibly a fungal spore, in a ray cell (MGB 90408 LP3).C, tangential section showing fusiform uniseriate, rarely occasionally biseriate rays (see inset) (MGB 90408 LP7).D, radial section showing triseriate pits in the tracheid walls; inset: detail of the circular pits with a spindle-shaped aperture (MGB 90408 LP4).E, radial section showing ochre-orange contents with polygonal shapes, possibly tyloses, filling the tracheids (MGB 90408 LP4).F, cross-field pitting with biseriate circular pits (cfp) that are significantly smaller than the tracheid pits (P) (MGB 90408 LP1).Scale bars represent: 100 lm (A, C); 10 lm (B); 50 lm (D-F); 10 lm (C inset, D inset).traditionally for isolated wood specimens with araucarian pitting: Agathoxylon Hartig, Dadoxylon and Dammaroxylon Schultze-Motel.However, a discussion on the taxonomy of this morphological complex is beyond the scope of this study and we refer interested readers to the work of Philippe (2011) and R€ oßler et al. (2014).Here, we provide a comparison of the new specimen

F I G . 8 .
Thin sections of early Permian Dadoxylon rollei from Autun.A, transverse section showing rays separating 2-7 rows of tracheids (ARX1).B, tangential section showing uniseriate and occasionally biseriate rays; inset: detail of a triseriate ray (ARX2).C, radial section showing uniseriate circular pits in the tracheid walls; inset: detail of pitting (ARX2).D, radial section showing rare biseriate pitting in the tracheid walls; inset: detail of pitting (ARX2).Scale bars represent: 500 lm (A, B inset), 200 lm (B), 100 lm (C, D); 50 lm (C inset, D inset).T O S A L E T A L .: P E N N S Y L V A N I A N W O O D F R O M T H E P Y R E N E E S 1 1 from Erillcastell with other late Palaeozoic silicified wood specimens of Cordaitales from southwest Europe (i.e. from the Graissessac-Lod eve, St Etienne and Autun basins in France, as well as Arnao in the northwest Iberian Peninsula).Several Cordaitales have been described from these localities: Dadoxylon rollei Unger from the lower Permian deposits of Autun (Massif Central, France; Marguerier 1971), Dadoxylon cf.brandlingii from the Stephanian C deposits of Graissessac-Lod eve Basin (Massif Central, France; Galtier et al. 1997) and Cordaixylon andresii C esari, Alvarez-V azquez, M endez-Bedia, Alvarez-La o, Turrero & Arbizu from the Stephanian C deposits of Arnao Basin (Cantabrian Mountains, northwest Iberian Peninsula, C esari et al. 2015), and a specimen from Stephanian C deposits near Saint Etienne that resembles Dadoxylon subrhodeanum Grand'Eury.Comparison with the Dadoxylon sp. from Erillcastell, using six anatomical characters of wood that are considered diagnostic by imbricata"? Abhandlungen Naturhistorisches Museums Schleusingen, 9, 69-80.B A S H F O R T H , A., D I M I C H E L E , W., E B L E , C. and N E L -S O N , W. 2016.Dryland vegetation from the Middle Pennsylvanian of Indiana (Illinois Basin): the dryland biome in glacioeustatic, paleobiogeographic, and paleoecologic context.Journal of Paleontology, 90, 785-814.B A X T E R , R. W. 1975.Fossil fungi from American Pennsylvanian coal balls.Aretz, 77, 1-6.B E C K A R Y , S. 1987.Association floristique et faunique rencontr ee dans les coal balls de la mine Rosario (NW de l'Espagne, Namurien C-Westphalien A).Interpr etation pal eo ecologique.Annales de la Soci et e G eologique du Nord, 106, 111-116.v o n B E R C H T O L D , F. G. and P R E S L , J. S. 1820.O Prirozenosti Rostlin.Krala Wiljma Endersa, Prague, 322 p. C A S C A L E S -M I ÑA N A , B. and C L E A L , C. J. 2014.The plant fossil record reflects just two great extinction events.Terra Nova, 26, 195-200.C I C H A N , M. A. 1986.Conductance in the wood of selected Carboniferous plants.Paleobiology, 12, 302-310.C I C H A N , M. A. and T A Y L O R , T. N. 1983.A systematic and developmental analysis of Arthropitys deltoides sp.nov.Botanical Gazette, 144, 285-294.
O , P. and A R B I Z U , M. 2015.First report of permineralised plants in the Stephanian of Arnao (Asturias, northwestern Spain).Palaeogeography, Palaeoclimatology, Palaeoecology, 440, 475-486.C O S T A N Z A , S. H. 1985.Pennsylvanioxylon of Middle and Upper Pennsylvanian coals from the Illinois Basin and its comparison with Mesoxylon.Palaeontographica Abteilung B, 197, 81-121.D E C O M B E I X , A.-L., H A R P E R , C. J., G A L T I E R , J., M E Y E R -B E R T H A U D , B. and K R I N G S , M. 2022.Tyloses in fossil plants: new data from Mississippian tree, with a review of previous records.Botany Letters, 169, 510-526.D E M I C C O , V., B A L Z A N O , A., W H E E L E R , E. A. and B A A S , P. 2016.Tyloses and gums: a review of structure, function and occurrence of vessel occlusions.IAWA Journal, 37, 186-205.D I M I C H E L E , W. A. 2014.Wetland-dryland vegetational dynamics in the Pennsylvanian ice age tropics.International Journal of Plant Sciences, 175, 123-164.D I M I C H E L E , W. A. and P H I L L I P S , T. L. 1996.Climate change, plant extinctions and vegetational recovery during the Middle-Late Pennsylvanian Transition: the case of tropical peat-forming environments in North America.201-221.In H A R T , M. B. (ed.) Biotic recovery after mass extinction events.Geological Society, London, Special Publications, 102.D I M I C H E L E , W. A., F A L C O N -L A N G , H. J., N E L S O N , W. J., E L R I C K , S. D. and A M E S , P. R. 2007.Ecological gradients within a Pennsylvanian mire forest.Geology, 35, 415-418.D I M I C H E L E , W. A., M O N T A ÑE Z , I. P., P O U L S E N , C. J. and T A B O R , N. J. 2009.Climate and vegetational regime shifts in the late Paleozoic ice age earth.Geobiology, 7, 200-226.D O U B I N G E R , J., V E T T E R , P., L A N G I A U X , J., G A L -T I E R , J. and B R O U T I N , J. 1995.La flore fossile du bassin houiller de Saint-Etienne.M emoires du Museum National d'Histoire Naturelle, Paris, 164, 1-357.E N D L I C H E R , S. 1847.Synopsis coniferarum.Scheitlin & Zollikofer, St Gallen, Switzerland, 368 p. E G G E R T , D. A. 1961.The ontogeny of Carboniferous arborescent Lycopsida.Palaeontographica Abteilung B, 108, 43-92.F A L C O N -L A N G , H. J. and B A S H F O R T H , A. R. 2005.Morphology, anatomy, and upland ecology of large cordaitalean trees from the Middle Pennsylvanian of Newfoundland.Review of Palaeobotany & Palynology, 135, 223-243.G A L T I E R , J. 1997.Coal-ball floras of the Namurian-Westphalian of Europe.Review of Palaeobotany & Palynology, 95, 51-72.G A L T I E R , J. 2008.A new look at the permineralized flora of Grand-Croix (Late Pennsylvanian, Saint-Etienne Basin, France).Review of Palaeobotany & Palynology, 152, 129-140.G A L T I E R , J. and P H I L L I P S , T. L. 1985.Swamp vegetation from Grand-Croix (Stephanian) and Autun (Autunian), France and comparison with Coal Ball Peats of Illinois Basin.Comptes Rendus du 9 eme Congr es International de Stratigraphie et G eologie du Carbonif ere, Urbana, USA, 5, 13-24.G A L T I E R , J. and P H I L L I P S , T. L. 1999.The acetate peel technique.67-70.In J O N E S , T. P. and R O W E , N. P. (eds) Fossil plants and spores: Modern techniques.The Geological Society, London.G A L T I E R , J., D A V I E R O , V. and M E Y E R -B E R T H A U D , B. 1997.D ecouverte de fragments de troncs d'arbres permin eralis es dans le bassin St ephanien de Graissessac (Sud du Massif Central, France).Geobios, 20, 243-247.G A S T A L D O , R. A. 1992.Regenerative growth in fossil horsetails (Calamites) following burial by alluvium.Historical Biology, 6, 203-220.G I S B E R T , J. 1981.Estudio geol ogico-petrol ogico del Estefaniense-P ermico de la sierra del Cad ı (Pirineo de L erida).Diag enesis y sedimentolog ıa.PhD thesis, University of Zaragoza, 314 pp.G I S B E R T , J. 1983.El P ermico de los Pirineos Españoles.405-420.In M A R T IN E Z -D IA Z , C. (ed.) Carbon ıfero y P ermico de España.Publicaciones del Instituto Geol ogico y Minero de España.G OM E Z -A L B A , J. 2007.La Cuenca carbon ıfera de Surroca-Ogassa (Ripoll es, Catalunya, España).Monografies el Museu de Ci encies Naturals de Barcelona, 4, 263 pp.G OM E Z D E L L A R E N A , G. and A R A N G O , C. R. 1946.Las "tacañas" (coal balls) de la mina "Rosario" de Tru ebano (Le on).Notas y communicaciones del I.G.M.E., Madrid, 16, 215-236.G € OP P E R T , H. R. 1864.Die fossile Flora der Permischen Formation.Palaeontographica, 12, 1-124.G R A N D ' E U R Y , F.-C. 1877.Flore carbonif ere du d epartement de la Loire et du centre de la France.1e partie, Botanique.M emoires Acad emie des Sciences de l'Institut de France, 24, Imprimerie nationale, Paris, 348 pp.H E C K E L , P. H. and C L A Y T O N , G. 2006.The Carboniferous System.Use of the new official names for the subsystems, series and stages.Geologica Acta, 4, 403-407.
T A B L E 2 .