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Article

Morphological Diversity of Desmiophyllum Lesquereux Fossil Leaves and Related Palaeoenvironmental Implications from the Early Cretaceous of Northeastern Spain

by
Luis M. Sender
1,*,
Josué García-Cobeña
1,
José B. Diez
2,3 and
Alberto Cobos
1
1
Fundación Conjunto Paleontológico de Teruel-Dinópolis/Museo Aragonés de Paleontología, 44002 Teruel, Spain
2
Departamento de Xeociencias Mariñas e Ordenación do Territorio, Facultade de Ciencias do Mar, Universidade de Vigo, 36310 Vigo, Spain
3
Centro de Investigación Mariña, Universidade de Vigo (CIM-UVIGO), 36310 Vigo, Spain
*
Author to whom correspondence should be addressed.
Diversity 2024, 16(12), 730; https://doi.org/10.3390/d16120730
Submission received: 9 September 2024 / Revised: 7 November 2024 / Accepted: 19 November 2024 / Published: 28 November 2024
(This article belongs to the Section Plant Diversity)

Abstract

:
A variety of leaves of different morphological sizes and venation types corresponding to the gymnosperm genus Desmiophyllum have been found in five fossil sites originating from the Barremian to the Cenomanian periods in northeastern Spain over an interval comprising 25 million years that encompasses the Early Cretaceous–Late Cretaceous boundary. These leaves are preserved in various lithologies corresponding to different depositional environments such as lagoonal systems, coastal swamps, deltaic plains, lacustrine environments and fluvial-related deposits. These new data shed light on the morphological and paleoenvironmental variability of Desmiophyllum recorded in the Cretaceous deposits from southwestern Eurasia.

1. Introduction

Desmiophyllum Lesquereux emend. Miller et Hickey is a widespread genus established to classify elongate to lanceolate and linear to curvilinear strap-shaped leaves of late Paleozoic and Mesozoic gymnosperms with parallel or subparallel veins, forking or without forking near the base, but lacking taxonomic characters to be included in a specific order and family [1,2,3].
This genus was initially used to classify a specific type of leaf from the Carboniferous period of Pennsylvania (United States) showing a lanceolate to strap-shaped morphology and parallel venation but without connection between them [4], and are very similar to the leaves of the Carboniferous gymnosperms genus Cordaites Unger. Later, Ref. [5] generalized this denomination, extending it to the leaves with parallel venation similar to those of the czekanowskialean genus Phoenicopsis Heer. Ref. [6] described the cuticles of several Mesozoic species assigned to the genus Desmiophyllum, showing their relationship to the group of gymnosperms based on the characteristics of their stomata. Since then, most authors have used this name to classify the leaves of Paleozoic and Mesozoic gymnosperms with the characteristics mentioned above but which do not present defined taxonomic characters to include them in a specific order and family (except if they are associated with reproductive structures). This type of strap-like leaf could correspond to Cordaitales, Cycadales, Bennettitales, Coniferales, Czekanowskiales, Ginkgoales, or Gnetales [3,7,8,9,10,11,12,13,14].
Records of leaves with well-preserved cuticles indicate that some types presenting the mentioned characteristics are related to conifers of the family Podocarpaceae [8]. Likewise, in [2], their amendment of the genus points out the possibility that the Mesozoic leaves assigned to Desmiophyllum could belong to conifers of the families Podocarpaceae or Araucariaceae. Ref. [2] maintains the name Desmiophyllum instead of replacing it with Harrisiophyllum Pant as proposed by [9] based on the study of leaves from the Lower Cretaceous period of India that present a better preservation. Ref. [9] pointed out the apparent illegitimacy of the name Desmiophyllum for Mesozoic records and proposed its application only to Paleozoic leaves of the cordaitalean type. However, according to [15], the application of the taxonomical categories supports maintaining the name Desmiophyllum as a gymnosperm morphogenus as it is also applicable to Mesozoic leaves, which is a fact that is endorsed by the amendment of the genus carried out by [2] and which follows the rules of the International Code of Nomenclature for algae, fungi, and plants (the Melbourne Code) [16], as well as the general use of this name by the vast majority of authors. More recently, Ref. [3] made a new amendment of one species of the genus based on new findings of this type of leaves with cuticle and anatomical connections from the Upper Triassic of Germany. These authors designated the name Desmiophyllum to be used specifically as a fossil genus for fragmentary leaf records, assuming that they correspond to more than one botanical affinity. Leaves assigned to the genus Desmiophyllum occur in Mesozoic deposits around the world. In the Cretaceous period, it has been found in continental and coastal deposits in the Early Cretaceous of India [13], Ecuador [17] and Argentina [14], Wealdian of Germany [18], Aptian of Colombia [19], Aptian–Albian of Portugal [20] and Canada [21], Albian of the United States [2,22,23,24,25,26,27], Albian and Cenomanian of Russia [28] and Alaska [1,29,30] and Cenomanian of Lebanon [31,32]. In Spain, this genus has also been recorded in the uppermost Albian of Plou [33] and Estercuel [34], and the Albian–Cenomanian deposits of Mosqueruela [35] both in the province of Teruel. However, despite the extensive record assigned to this genus in Cretaceous materials, little is known regarding the diversity and the environments in which this plant producer of strap-shaped leaves lived.
In this work, we show evidence of leaves of different types assigned to the genus Desmiophyllum in rocks of different ages within the Cretaceous period of northeastern Spain and their related depositional environments.

2. Materials and Methods

The fossils come from several localities placed in the province of Teruel, Aragon region, northeastern Spain. These localities are situated in the surroundings of the villages of Galve, Utrillas, Estercuel, Mosqueruela, and Plou (Figure 1A). The related sediments bearing the fossils from these localities were deposited into several sub-basins of the Maestrazgo Basin in northeastern Iberia during Early Cretaceous and Late Cretaceous times as follows: the Galve Sub-Basin (Galve locality), Las Parras Sub-Basin (Utrillas locality), Oliete Sub-Basin (Estercuel and Plou localities), and Peñagolosa Sub-Basin (Mosqueruela locality) (Figure 1B). The distribution of these sub-basins of the Maestrazgo Basin is the result of the latest phase of the Jurassic–Early Cretaceous period rifting and the corresponding differential tectonic subsidence in this part of eastern Iberia, which led to the development of a variety of coastal sedimentary systems with several geological formations involved [36,37,38]. The studied plants were found in different geological formations from the Early–Middle Barremian, the Albian, and the Albian–Cenomanian boundary in the province of Teruel (Figure 2).
The Galve locality called Mina Galve 7 (MGA-7) is 56 km north of Teruel city inside PAMESA CerámicaCompacto S.L.U. (formerly SIBELCO Minerales Cerámicos S.A.) a clay mine located nearby the village of Galve. The fossils were found in a layer composed of white to light-orange-coloured medium-grained sandstones, including some intercalations of light-grey-coloured breccias with blocks mainly1 cm to 2 cm in length. These materials belong to the Camarillas Formation (Figure 2), which is Early–Middle Barremian in age in this area based on ostracods and palynomorphs [41]. This geological formation is composed of fluvial deposits in the Galve area related to a tide-dominated estuary and a barrier island-tidal inlet that developed in the Galve Sub-Basin (e.g., [36,42]).
The Utrillas locality called the El Vinagre coal mine (UT—VIN) is 70 km north of Teruel city. The fossils were found in the middle member of the Escucha Formation (Figure 2), composed of highly cemented lenses of dark grey claystones and finely laminated poorly unconsolidated grey claystones. This formation is early to middle Albian in age by palynological studies [43], and it is composed of freshwater swamp plain deposits in the Utrillas area corresponding to a deltaic–estuarine tidally influenced system developed in this part of Iberia [44].
The Estecuel locality called the La Dehesa clay pit, is 98 km northeast of Teruel City. The layers containing the studied fossils (ET2-1 and ET2-2) consist of light grey claystones intercalated with fine–to coarse-grained yellow sandstones and dark grey claystones located in the uppermost Albian Boundary Marls Unit [45] at the top of the coastal fluvial sands of the Utrillas Formation (Figure 2). These materials from Estercuel were deposited in a tidally influenced fluvial sedimentary environment composed of mainly freshwater rivers, coastal marshes, and ponds in this zone [34].
The Plou locality, called the Plou clay pit, is 96 km north of Teruel city. The beds bearing the fossil leaves are composed of alternate thin laminated light brown sandy claystones and sandstones of coastal freshwater lacustrine origin in Plou, which are placed in the uppermost Albian Boundary Marls Unit [45] at the top of the coastal fluvial sands of the Utrillas Formation (Figure 2).
The Mosqueruela locality called the Mosqueruela 1 is 103 km east of Teruel city. This locality has provided a single but large specimen preserved in laminated sandy claystones deposited in tidal flats and lagoonal environments related to an extensive coastal and shallow marine area, which belongs to the upper Albian–lower Cenomanian deposits of the lower part of the Mosqueruela Formation—Aras de Alpuente Limestones Formation in the Maestrazgo Basin (Figure 2) [35,38,46,47].
A total of 59 leaves of the genus Desmiophyllum have been studied. The leaves are preserved as impressions and compressions with a carbonaceous layer but lack the cuticle. The specimens were prepared using a micro-pneumatic hammer under a stereomicroscope, and photographs were taken using a Canon EOS R8 Full Frame camera with an RF Canon 85 mm macro lens. The material wasdeposited in the Museo Aragonés de Paleontología (MAP) located in the Fundación Conjunto Paleontológico de Teruel–Dinópolis in the city of Teruel (Spain) under the acronyms MAP-9031 to MAP-9098.
Figure 2. Synthetic stratigraphical section corresponding to the different geological formations in the western part of the Maestrazgo Basin from the late Early Cretaceous to Early–Late Cretaceous period with the indication of ages, lithostratigraphic units, related sedimentary environments, and situation of levels with fossil localities bearing leaves of the genus Desmiophyllum (modified from [48]). Abbreviations: U. Cretac.: upper cretaceous; Cenom.: Cenomanian; Turon.: Turonian; Cas. Fm.: El Castellar Formation; B.M.U.: Boundary Marls Unit; Mosquer. Fm.: Mosqueruela Formation; Bco. Degoll. Fm.: Barranco de losDegollados Formation; Lac. pal.: Lacustrine—palustrine; Ga: Galve locality; Ut: Utrillas locality; Pl: Plou locality; Et: Estercuel locality; Mq: Mosqueruela locality.
Figure 2. Synthetic stratigraphical section corresponding to the different geological formations in the western part of the Maestrazgo Basin from the late Early Cretaceous to Early–Late Cretaceous period with the indication of ages, lithostratigraphic units, related sedimentary environments, and situation of levels with fossil localities bearing leaves of the genus Desmiophyllum (modified from [48]). Abbreviations: U. Cretac.: upper cretaceous; Cenom.: Cenomanian; Turon.: Turonian; Cas. Fm.: El Castellar Formation; B.M.U.: Boundary Marls Unit; Mosquer. Fm.: Mosqueruela Formation; Bco. Degoll. Fm.: Barranco de losDegollados Formation; Lac. pal.: Lacustrine—palustrine; Ga: Galve locality; Ut: Utrillas locality; Pl: Plou locality; Et: Estercuel locality; Mq: Mosqueruela locality.
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3. Results

All the specimens studied correspond to isolated and detached leaves preserved as impressions and compressions with carbonaceous or limonitic patina presenting strap-shaped morphology and leathery appearance, parallel-veined, and with entire margins throughout the lamina. However, the particular characteristics regarding the presence or absence of intermediate veins, the total number of veins/cm and the morphology of the base and the apex in the studied specimens have allowed us to identify five different types of leaves belonging to the fossil genus Desmiophyllum in northeastern Spain (Table S1). Two kinds of leaves of different sizes have been grouped into Desmiophyllum type 2, and leaves from two different sites presenting the same characteristics comprise Desmiophyllum type 5. It has not been possible to establish specific assignments for the studied fossil leaves due to the absence of cuticular characters in all the specimens.
 
Gymnospermae incertae sedis
Order incertae sedis.
Family incertae sedis.
Genus Desmiophyllum (Lesquereux) 1878 emend. Miller et Hickey, 2010.
Desmiophyllum type 1
Locality: Mina Galve 7 (MGA-7) (Galve village).
Lithostratigraphic unit: lower–middle part of the Camarillas Formation.
Age: Early–Middle Barremian.
Number of studied leaves: 12.
Samples: MAP-9031 to MAP-9042.
Description: Fragments of large, strap-shaped leaves, up to 12.5 cm long and 4.5 cm wide, with a leathery appearance (Figure 3A–D), and lamina sometimes slightly frayed and bent (Figure 3B,C). The margins are entire and parallel. The base and apex of the leaves are not preserved. The venation consists of a set of parallel thick veins, with circa 180 veins in the leaf running parallel (Figure 3A,B) with a density of veins 40 veins/cm on average. The distance between the veins is 0.3 mm. The intermediate veins are not present.
Figure 3. Leaves of Desmiophyllum type 1 from Galve locality. (A) Strap-shaped leaf showing parallel veins (MAP-9038); (B) leaf with partially frayed lamina (MAP-9032); (C) accumulation of several leaves, some of them preserved as bend laminae (arrows) in sandstones with patches of breccias (MAP-9038 to MAP-9042); and (D) three leaves disposed in an imbricate pattern (MAP-9033 to MAP-9035). Scale bars: 2 cm (A,B), 4 cm (C,D).
Figure 3. Leaves of Desmiophyllum type 1 from Galve locality. (A) Strap-shaped leaf showing parallel veins (MAP-9038); (B) leaf with partially frayed lamina (MAP-9032); (C) accumulation of several leaves, some of them preserved as bend laminae (arrows) in sandstones with patches of breccias (MAP-9038 to MAP-9042); and (D) three leaves disposed in an imbricate pattern (MAP-9033 to MAP-9035). Scale bars: 2 cm (A,B), 4 cm (C,D).
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Desmiophyllum type 2
Locality: El Vinagre coal mine (UT-VIN) (Utrillas village).
Lithostratigraphic unit: middle member of the Escucha Formation.
Age: Early–Middle Albian.
Number of studied leaves: 42
Samples: MAP-9043 to MAP-9084.
Description: fragments of isolated and detached leaves of different sizes, some large specimens, with two types of leaves defined depending on the sizes and types of veins: “wide subtype” leaves and “narrow subtype” leaves.
The “wide subtype” leaves (Figure 4A–D and Figure 5) have a typically ribbon-like morphology narrowing towards the apex (Figure 4B). The leaves have a coriaceous appearance (Figure 4A–D and Figure 5), some of them showing corrugations both longitudinally and transversely (Figure 4B,D).The sizes of leaves are up to 27 cm long and 7.5 cm wide, with margins intact and very well marked, which remain parallel to–subparallel along the blade. Leaves frayed in the favour of the veins (Figure 4A,C and Figure 5E). The base is straight truncated, presenting a protuberance or abscission callosity that extends across the complete width of the leaf (Figure 5C,D). The apex is not preserved. Venation consists of up to 65 thick, well-marked veins parallel to each other and to the margins with about 10 thick veins/cm (Figure 4B,D and Figure 5A,B). The separation between the thick veins is 1 mm, and there are three to four intermediate thinner parallel veins (Figure 4B). All veins develop independently, directly from the leaf insertion, with thickening present at the base. The total vein density is 50 veins/cm.
The “narrow subtype” leaves (Figure 4A,D–G) are up to 12 cm long and 1.3 cm wide, having entire very well-marked margins, which remain parallel along the lamina (Figure 4D–G) but converge towards the apical zone (Figure 4A,E,F). The base is not preserved, but the apex is acute and very pointed (Figure 4E,F). The venation comprises about 12 thick and well-marked veins, arranged parallel to each other and with respect to the margins but converging towards the apex (Figure 4E,F). The separation between the thick veins is 1 mm, and there are three to four thinner parallel intermediate veins (Figure 4D,F,G). The density of veins in the leaves is 12 thick veins/cm, and alongside the thin intermediate veins, the density rises to 60 veins/cm. The characteristics of these “narrow subtype” leaves indicate that they could correspond to younger specimens of the “wide subtype” leaves.
Figure 4. Leaves of Desmiophyllum type 2 from the Utrillas locality. (A) accumulation of leaves of both “wide” and “narrow” subtypes of Desmiophyllum type 2 and branched axis of the conifer genus Cyparissidium (MAP-9051 to MAP-9060); (B) large medial–apical fragment of the leaf of the “wide subtype” (MAP-9082); (C) two large fragments of leaves of the “wide subtype” and axis of the conifer genus Pagiophyllum (MAP-9068 and MAP-9069); (D) leaf of the “wide subtype” (central leaf MAP-9083), a leaf of the “narrow subtype” (right leaf MAP-9084) and a thin leaf of an undetermined gymnosperm (left leaf); (E) a detail of the central area of (A) showing several leaves of the “narrow subtype”, some of them preserving the apex (MAP-9055 to MAP-9060); (F) detail of two leaves of the “narrow subtype” showing parallel veins converging to the apex (MAP-9061 and MAP-9062); and (G) detail of the medial part of a leaf of the “narrow subtype” showing entire margins and parallel venation pattern (MAP-9063). Scale bars: 4 cm (A,B), 2 cm (CE), 1 cm (F,G).
Figure 4. Leaves of Desmiophyllum type 2 from the Utrillas locality. (A) accumulation of leaves of both “wide” and “narrow” subtypes of Desmiophyllum type 2 and branched axis of the conifer genus Cyparissidium (MAP-9051 to MAP-9060); (B) large medial–apical fragment of the leaf of the “wide subtype” (MAP-9082); (C) two large fragments of leaves of the “wide subtype” and axis of the conifer genus Pagiophyllum (MAP-9068 and MAP-9069); (D) leaf of the “wide subtype” (central leaf MAP-9083), a leaf of the “narrow subtype” (right leaf MAP-9084) and a thin leaf of an undetermined gymnosperm (left leaf); (E) a detail of the central area of (A) showing several leaves of the “narrow subtype”, some of them preserving the apex (MAP-9055 to MAP-9060); (F) detail of two leaves of the “narrow subtype” showing parallel veins converging to the apex (MAP-9061 and MAP-9062); and (G) detail of the medial part of a leaf of the “narrow subtype” showing entire margins and parallel venation pattern (MAP-9063). Scale bars: 4 cm (A,B), 2 cm (CE), 1 cm (F,G).
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Figure 5. Leaves of the Desmiophyllum type 2 “wide subtype” from the Utrillas locality. (A) fragment of a large strap-shaped leaf with profuse parallel venation (MAP-9070); (B) detail of the central area in (A) showing main gross veins and several intermediate thinner veins between them; (C,D) part and counterpart of a strap-shaped leaf with parallel venation preserving the base that is composed of a callus with parallel ridges and furrows (arrows) (MAP-9072); and (E) fragment of a leaf with extensively frayed lamina (MAP-9080). Scale bars: 2 cm (A,CE), 1 cm (B).
Figure 5. Leaves of the Desmiophyllum type 2 “wide subtype” from the Utrillas locality. (A) fragment of a large strap-shaped leaf with profuse parallel venation (MAP-9070); (B) detail of the central area in (A) showing main gross veins and several intermediate thinner veins between them; (C,D) part and counterpart of a strap-shaped leaf with parallel venation preserving the base that is composed of a callus with parallel ridges and furrows (arrows) (MAP-9072); and (E) fragment of a leaf with extensively frayed lamina (MAP-9080). Scale bars: 2 cm (A,CE), 1 cm (B).
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Desmiophyllum type 3 (“wide subtype” leaves from Estercuel locality).
Locality: La Dehesa clay pit (Estercuel village).
Lithostratigraphic unit: Boundary Marls Unit at the top of the Utrillas Formation.
Age: uppermost late Albian.
Number of studied leaves: 2.
Samples: MAP-9085 and MAP-9086.
Figure 6A–C.
Description: Fragments of elongate strap-like leaves up to 6 cm long and 4.6 cm wide. Margins are straight but poorly preserved and sometimes frayed (Figure 6A–C). The base and apex are not preserved. Venation consists of circa 120 gross veins, with a density of 25 veins/cm, separated by 0.3 mm and parallel to the leaf margins (Figure 6A,C). Up to four veins extend between each gross vein with a total density of 125 veins/cm.
 
Desmiophyllum type 4.
Locality: Mosqueruela (Mosqueruela village).
Lithostratigraphic unit: basal part of the Mosqueruela Formation.
Age: Late Albian–Early Cenomanian.
Number of studied leaves: 1.
Samples: MAP-8827.
Description: Fragment of a large, strap-shaped and parallel-veined leaf with a leathery appearance. The leaf fragment is 34 cm long and 5.5 cm wide in its widest zone and 1 cm at the apex (fractured in its most distal part). The margins are entire, very well-marked, and parallel throughout the lamina but converging at the apex. The base of the leaf is not preserved, and the apex is acute. Venation consists of thick veins running in parallel from the basal zone to converge at the apex and separated by 0.2 mm, with circa 275 veins and a density of 50 veins/cm in its widest part. Intermediate veins are not present.
 
Desmiophyllum type 5 (“narrow subtype” leaves from Estercuel and leaves from Plou localities).
Locality: La Dehesa clay pit (Estercuel village) and Plou clay pit (Plou locality).
Lithostratigraphic unit: Boundary Marls Unit at the top of the Utrillas Formation.
Age: uppermost late Albian.
Number of studied leaves: 12 (3 from Estercuel and 9 from Plou).
Samples: MAP-9087 to MAP-9098.
Description: Leaf fragments with ribbon-shaped morphology, some leaves very long (Figure 6E), with a coriaceous appearance, up to 14.6 cm long and 2.5 cm wide. Margins are complete and well marked, running parallel along the lamina (Figure 6E and Figure 7A,B,D,E). The leaf narrows towards the base (Figure 7A,B), which has a concave truncate abscission pad (Figure 7B,C). The apex is acute (Figure 6E). Venation is composed of 50 to 60 thick veins, 25 to 30 veins/cm, running parallel to the leaf margins (Figure 6E and Figure 7A,B,D,E) from the base and converging to the apex (Figure 6E). The distance between the veins is 0.3 mm. There are three to four intermediate thinner parallel veins between each of the gross veins (Figure 7F,G) with a total vein density of 125 to 150 veins/cm.
Figure 6. Leaves of Desmiophyllum type 3 from the Estercuel locality (AC), type 4 from the Mosqueruela locality (D) and type 5 also from the Estercuel locality (E). (A) fragment of a Desmiophyllum type 3 leaf showing a venation pattern (MAP-9085); (B) fragment of the Desmiophyllum type 3 leaf with frayed lamina MAP-9086); (C) detail of (B) showing multiple parallel veins; (D) large leaf of Desmiophyllum type 4 with acute apex and profuse parallel venation pattern (MAP-8827); (E) long leaf of Desmiophyllum type 5 from the Estercuel locality, preserving the apex and venation pattern with veins running along the lamina(MAP-9087). Scale bars: 2 cm (A), 1 cm (B), 5 mm (C), with each rectangle representing 1 cm (D) and 5 cm (E).
Figure 6. Leaves of Desmiophyllum type 3 from the Estercuel locality (AC), type 4 from the Mosqueruela locality (D) and type 5 also from the Estercuel locality (E). (A) fragment of a Desmiophyllum type 3 leaf showing a venation pattern (MAP-9085); (B) fragment of the Desmiophyllum type 3 leaf with frayed lamina MAP-9086); (C) detail of (B) showing multiple parallel veins; (D) large leaf of Desmiophyllum type 4 with acute apex and profuse parallel venation pattern (MAP-8827); (E) long leaf of Desmiophyllum type 5 from the Estercuel locality, preserving the apex and venation pattern with veins running along the lamina(MAP-9087). Scale bars: 2 cm (A), 1 cm (B), 5 mm (C), with each rectangle representing 1 cm (D) and 5 cm (E).
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Figure 7. Leaves of Desmiophyllum type 5 from the Estercuel locality (AC) and Plou locality (DG). (A) thin strap-shaped leaf with parallel venation and lamina narrowing at the base and axis of conifer Frenelopsis (MAP-9088); (B) large fragment of the leaf preserving a parallel venation pattern and complete base (MAP-9089); (C) detail of the lower part of (A) showing truncate concave-shaped morphology at the insertion point of the leaf base; (D,E) central part of narrow strap-shaped leaves preserving the venation pattern (MAP-9098 and MAP-9095); and (F,G) details of (D,E), respectively, showing main parallel gross veins and intermediate thinner veins. Scale bars: 2 cm (A,B,D), 5 mm (C), 1 cm (E), 3 mm (F), and 2 mm (G).
Figure 7. Leaves of Desmiophyllum type 5 from the Estercuel locality (AC) and Plou locality (DG). (A) thin strap-shaped leaf with parallel venation and lamina narrowing at the base and axis of conifer Frenelopsis (MAP-9088); (B) large fragment of the leaf preserving a parallel venation pattern and complete base (MAP-9089); (C) detail of the lower part of (A) showing truncate concave-shaped morphology at the insertion point of the leaf base; (D,E) central part of narrow strap-shaped leaves preserving the venation pattern (MAP-9098 and MAP-9095); and (F,G) details of (D,E), respectively, showing main parallel gross veins and intermediate thinner veins. Scale bars: 2 cm (A,B,D), 5 mm (C), 1 cm (E), 3 mm (F), and 2 mm (G).
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4. Discussion

4.1. Systematic Discussion

The studied leaves show many similarities with the typical morphology and venation of the leaves of the genus Cordaites Unger. However, the leaves of this group of typically Paleozoic gymnosperms are dichotomously divided [2], and the similar characteristics of our specimens correspond to a morphological convergence developed by another type of gymnosperms, in this case, Mesozoic. The Spanish leaves are also very similar in their shape, venation type, and morphology from the base to the leaves of genus Pelourdea Seward, which is a gymnosperm of uncertain affinity found in Triassic deposits from the northern hemisphere [49,50]. However, unlike the leaves of the genus Desmiophyllum, which have a density of 50 to 60 veins/cm, the density of veins in the leaves of the genus Pelourdea is 10 to 13 veins/cm. Our leaves also resemble the central parts of the leaves of some Mesozoic Ginkgoales, such as the genus Eretmophyllum Thomas emend. Harris [51]. Nevertheless, the venation pattern of the leaves, in this case, is very different from that in the studied specimens with parallel venation throughout their length since Eretmophyllum has a scarce number of veins that divide dichotomously at the base of the leaf and then become parallel or curve to converge towards the apex [52].
The leaves of Desmiophyllum type 1 from the Galve locality occur occasionally in parallel and imbricate (Figure 3D) in the same pattern as those of Desmiophyllum sp. B in Figure 41E [2] from the Albian deposits of the Winthrop Formation in Washington State, USA. Nevertheless, these leaves have 3 veins/cm, and the leaves from the Galve locality have 40 veins/cm.
The leaves of Desmiophyllum types 1, 2, 3 and 4 closely resemble those leaves of the genus Welwitschiophyllum Dilcher et al. assigned to the Order Gnetales [53], which has been found in the upper Aptian deposits of Crato Formation in Brazil [53,54] and uppermost Cenomanian deposits of the Akrabou Formation in Morocco [55]. These leaves have lengths of up to 85 cm and lanceolate morphologies when they retain the acute apex, a truncated curved base and parallel and very profuse venation, also showing intermediate veins between main ones Sup. data Figure S2B [56], 40 to 50 veins, and density of 9 to 15 veins/cm [53]. This distribution and the number of veins are similar to those in the leaves of Desmiophyllum type 2 “wide subtype” from the Utrillas locality (Figure 4A–C and Figure 5). It is also noticeable that the largest specimens from the Desmiophyllum type 2 “wide subtype” (Figure 4 and Figure 5) and Desmiophyllum type 4 (Figure 6E) described in the present work also show very similar morphology to the long leaves from the Crato Formation in Brazil, which were figured by [11,57]. These authors assigned these leaves to the genus Desmiophyllum, comparing their characteristics with those in the extant gnetalean Welwithschia Hooker. Nevertheless, leaves of this taxon have cross veins between the parallel main ones [58] and leaves of Welwitschiophyllum also have ghost chevrons between the main veins in the young specimens [53], which is a character not preserved in the leaves of Desmiophyllum from the province of Teruel in Spain. Furthermore, the leaves of Welwitschiophyllum have a concave base, while the leaves of the Utrillas locality have a straight base with calluses or thickening (Figure 5C,D).
The leaves of Desmiophyllum types 1, 2, 3 and 4 resemble the leaves of the taxon Desmiophyllum truncatum Miller et Hickey, from the Albian of the Winthrop Formation in Washington (USA) [2] concerning their morphology and vein distribution. However, the specimens from the province of Teruel have two orders of simple, parallel veins throughout their length, unlike the veins in D. truncatum, which show a dichotomous venation pattern at the base of the leaf. In addition, the leaves of the Spanish specimens have a vein density of 40 to 150 veins/cm, which is much higher than the 12 veins/cm present in the D. truncatum specimens. However, these leaves of Desmiophyllum type 2 are very similar to the leaves of Desmiophyllum magnum Samylina from the Albian of Russia [59] and Alaska [60], regarding their morphology and the number of veins present, which, in both cases, are circa 12 veins/cm. However, it is impossible to establish a direct taxonomic assignment with this taxon since the specimens studied lack the cuticle preserved. The leaf of Desmiophyllum type 4 (Figure 6D) also resembles the leaf of Phragmites Adams from the Cenomanian of Nammoura in Lebanon, which [31] assigned with reservations to monocotyledonous angiosperms. However, the Lebanese leaf is traversed by a few dozen primary veins [31], while the leaf of Desmiophyllum type 4 is more than twice as long and wide and has about 275 veins.
The leaves of Desmiophyllum type 5 studied in this work also present many similarities to the leaves of the broad-leaved conifer genus Dammarites C. Presl, which has also been recorded in Albian deposits from eastern Spain [61].Ref. [62], in their revision of the genus, indicated that Dammarites have lanceolate to ribbon-shaped leaves of up to 40 cm long (and probably more due to the fragmentary remains), 1–5 cm wide, a bluntly pointed apex, truncate base, profuse venation, parallel veins, and the possibility of interstitial veins, which are characters also occurring in the records of Desmiophyllum type 5. Although [62,63] indicated that the name Dammarites should have priority, we classified the specimens from Spain as Desmiophyllum sensu [2] because almost all the studied leaves lack a preserved base, basal venation, and cuticle. Only one specimen from Estercuel has a truncated concave base preserved (Figure 7B,C), which is similar to that in the leaves of Dammarites albens Presl in Sternberg from the Cenomanian of the Czech Republic ([64], Figure 5I), but the apex is not preserved in the specimen from Spain. The leaves of Desmiophyllum type 5 also resemble those of Heidiphyllum Retallack, which is a genus possibly related to conifers of the Family Podocarpaceae from the Triassic period in the southern hemisphere [65,66]. However, the leaves of Heidiphyllum have 8 to 12 parallel veins that come from the dichotomy of between 2 and 4 basal veins [65], but leaves of Desmiophyllum type 5 have 50 to 60 exclusively parallel non-dichotomous veins.
The leaves of Desmiophyllum type 5 also present similarities with the Mesozoic genus Phyllotaenia Saporta and Phyllites Brongniart, which were assigned to fragments of leaves related tentatively to cycadales, bennettitales, ginkgoales or even to monocotyledonous angiosperms with strap-shaped leaves and a parallel-like venation [7,12,13,14,20]. However, ref. [67] included Phyllites latifolia within the genus Desmiophyllum, and [20] put both genera Phyllotaenia and Desmiophyllum in synonymy in his study about the Portuguese Mesozoic floras. On this matter, leaves assigned to Phyllotaenia sp. were recorded previously in several Cretaceous localities from the Iberian Peninsula, as they are the fluvial claystones of the upper Albian of Pola de Siero in the region of Asturias [68], fluvial sandstones of the La Cierva in the province of Cuenca [69], coastal deposits from the Albian to the Campanian of Soto del Real and Guadalix de la Sierra [70,71] and El Vellón in the region of Madrid [72], coastal environments of the middle Cenomanian of Algora in the province of Guadalajara [73] and in some Albian and Cenomanian fossil sites from Portugal [20]. Nevertheless, the corresponding Cenomanian Portuguese leaves represent monocot angiosperms due to the cuticular evidence [74].
In addition, some other large, isolated lanceolate leaves of uncertain affinity found in Cretaceous deposits also resemble the leaves of Desmiophyllum type 5, as it is the leaf of Phragmites sp. from the Cenomanian of Lebanon [31]. This leaf has a very similar morphology at its basal part to the leaf of Figure 7B from Estercuel. However, this specimen has twice the number of main veins as the Lebanese leaf.

4.2. Sedimentological, Taphonomical, and Paleoenvironmental Discussion

Most records of Desmiophyllum leaves from fossil sites worldwide usually consist of leaf fragments of different lengths lacking a base and/or apex and corresponding to a single morphological type, which have undergone some transport from the area where they developed. However, the new evidence from Spain represents a variety of types from several sedimentary environments.
The leaves of Desmiophyllum type 1 recorded from Galve were found in fine to very coarse-grained sandstones, alternating with layers of small-sized breccias and mudstones corresponding to the Camarillas Formation. The materials of this geological unit in the Galve area were interpreted as deposited in a wide tide-dominated estuary and a barrier island–tidal inlet sedimentary environment [36]. The studied leaves are part of a macrofloral assemblage that is composed of both simple and branched axes of the conifer Pagiophyllum Heer and huge accumulations of heterometric and heteromorphic branches and trunks of conifers, which are disposed of randomly in a chaotic pattern into the strata. However, the fragments of leaves of Desmiophyllum at this site are large, maintaining the margins intact, although some of them are slightly frayed (Figure 3A,B), bent (Figure 3C) or even imbricate in a parallel arrangement (Figure 3D), which suggest a short transportation from the place they grew to the burial area. The lithological, sedimentological, and taphonomical characteristics of these materials indicate that they were deposited by a high-energy turbulent flow of a crevasse splay into a supra- and intertidal mudflat subenvironment with ponds (Facies 2.3 of the second stage of the mixed energy estuary of [36]).
Regarding this matter, the presence of osteological fossils of multiple specimens of Iguanodon galvensis Verdú et al. from embryos to adults in lateral facies related to the strata where the leaves of Desmiophyllum type 1 occur in Galve [75,76,77,78] and tracks of large ornithopods in the same (or closely located) area [79,80], is considered by [42] as an indicator of the habitat preference of this taxon. In addition, [81] interpreted that Iguanodon galvensis from Galve could feed on a wide variety of plants, such as the macroremains of the Cheirolepidicaceae conifer Pseudofrenelopsis Nathorst and those represented by a registered palynological assemblage of schizaeacean fern spores and pollen grains of both gymnosperms and angiosperms, found in closely similar facies in the same locality [41,81]). In this paleogeographycal and lithosstratigraphical context, the sediments containing the bones of the dinosaur Iguanodon bernissartensis from the Barremian–Aptian of Morella in the province of Castellón (eastern Spain) showed a diverse palynological assemblage that was also dominated by Cheirolepidiaceae conifer pollen grains and Schizaeales fern spores [82].On this matter, the well-preserved strap-shaped leaves of Desmiophyllum type 1 point to them being potential food sources for these large phytophagous styracosternans dinosaurs, at least in the Galve area from northeastern Spain.
The leaves of Desmiophyllum type 2 occur in highly cemented claystones of the middle member of the Escucha Formation. This part of the geological unit was interpreted as corresponding to an upper deltaic coastal plain integrated with a wide, tidally influenced deltaic–estuarine sedimentary environment. A diversity of sedimentary sub-environments was identified in this geological unit, such as tidal plains with tidal channels, flood plains with paleosol development, freshwater swamps and marsh with marine influence and vegetation development, as well as freshwater lacustrine–palustrine and intertidal plains [44,83,84,85,86,87]. The leaves of Desmiophyllum type 2 constitute the dominant taxon, followed, in order of greater to lesser abundance, by simple or sporadically branched fragments of the conifer axes of genera Pagiophyllum and Cyparissidium Heer, as well as the leaves of Podozamites Braun, and small-sized female cones < 1 cm in diameter of indeterminate conifers [88]. Records of Desmiophyllum type 2 from Utrillas are arranged randomly in the highly cemented clayey matrix and disposed of in a chaotic pattern. Most Desmiophyllum type 2 “wide subtype” leaves consist of large fragments of laminae that are occasionally frayed (Figure 4), with only some Desmiophyllum type 2 “narrow subtype” leaves preserving the apex. These data indicate that the plant remains could have suffered a prolonged transport by a turbulent water current from the area where the plants grew up, and later, they were deposited quickly in a stagnant water body before being buried [88]. Notably, the fraying of the leaves in favour of the veins also occurred in records of the genus Welwitschiophyllum from the Aptian Crato Formation of Brazil, which were deposited in a lagoon environment [55,56]. In this respect, taphonomical studies in extant strap-shaped leaves with parallel veins show that the foliar lamina of this kind of leaf is usually shredded when they are transported in an aqueous environment with moderate energy [89].
The leaves of Desmiophyllum type 3 are preserved in intercalated sandy claystones and fine to medium-sized sandstones at the top of the Utrillas Formation corresponding to the Boundary Marls Unit. This geological unit has been interpreted as deposited in freshwater swamps, marshes, beaches, and lagoons within a wide coastal plain with marked tidal influence [84]. The floral assemblage containing the leaves of Desmiophyllum type 3 consists of, in order of greater to lesser abundance, ramified shoots and female cones of the conifer Pagiophyllum, the leaves of three types of dicotyledonous angiosperms, accumulations of leaves of the putaitive ranunculacean angiosperm Klitzschophyllites choffatti Saporta sensu Teixeira emend Gomez et al., leaves of the nyphaealean Aquatifolia cf. fluitans Wang et Dilcher, floral receptacles of Nelumbonales, detached leaves of the conifer Podozamites, megasporophylls of the lycopsid Isoetites Münster, occasional pinnae of the fern genus Onychiopsis Yokoyama, massive concentrations of irregular-shaped fragments of plants, as well as comminuted plant debris [34]. The leaves of Desmipophyllum type 3 from Estercuel are fragmentary and have frayed margins, which would indicate that energetic water currents transported them before their deposit in a nearshore area of a pond in a coastal fluvial subenvironment [34].
The leaves of Desmiophyllum type 4 are preserved in finely laminated sandy limestones of marine origin corresponding to the lower part of the Mosqueruela Formation. This part of the geological formation is interpreted as deposited in a subtidal flat or the shore of a lagoon environment integrated into an extensive coastal shallow area [83,90,91,92]. This large fragment of the leaf of Desmiophyllum and multi-branched axis of frenelopsid conifers is part of the newly described floral elements discovered in the upper Albian–Cenomanian materials of the Mosqueruela Formation in the eastern province of Teruel, Spain [35]. The fossil from Mosqueruela preserves both the margins and apex unaltered, indicating relatively quiet transportation before burial in a near-shore carbonated coastal-to-shallow marine environment [35].
The leaves of Desmiophyllum type 5 from Estercuel occur in dark grey laminated claystone corresponding to the Boundary Marls Unit, which overlies the layers of sandy claystones and fine-to-medium-sized sandstones where Desmiophyllum type 3 leaves occur in the same fossil site. The leaves of Desmiophyllum type 5 are part of a floral assemblage that consists of dominant ramified shoots of conifers of the cheirolepidiaceous genus Frenelopsis Schenj, branches of the conifer Pagiophyllm, fragments of leaves of large dicotiledoneous angiosperms, and scarce pinnae of the fern Cladophlebis Brongniart [34]. The larger fragments of leaves of Desmiophyllum type 5 from Estercuel maintain both the margins and the base, or the apex in some of the fossils, and the leaves are disposed of in laminated dark grey colored claystones. These characters could indicate a short and not very energetic transport from where they grew to a palustrine area or a small pond in the coastal system where they were buried [34].
The leaves of Desmiophyllum type 5 from Plou were found in finely laminated sandy claystones that alternate with fine to very coarse-grained sandstones corresponding to the basal part of the Boundary Marls Unit. The floral assemblage containing the leaves of Desmiophyllum type 5 is dominated by small-sized leaves of the aquatic nymphaealean genus Ploufolia Sender et al., occasional remains of leaves of dicotyledoneous angiosperms with wide ovate-shaped blades and entire margins, sporadic small fragments of simple branches of conifers of the genus Pagiophyllum and small fragments of fern pinnae of the genus Cladophlebis, as well as a considerable amount of comminuted plant debris [33,88]. The heterolithic nature of the layers where the leaves of Desmiophyllum type 5 occur would indicate a low moderate energy in the sedimentary environment and possibly a distal area of a small freshwater lacustrine sub-environment, which would receive rhythmic detrital contributions from high-energy aqueous flows in a coastal plain environment [33]. In this sense, the fragmentary nature of most of the plant remains and the high percentage of very tiny plant fragments in these layers could indicate that the leaves of Desmiophyllum type 5 from Plou suffered moderate transport before their burial in this freshwater coastal lacustrine sub-environment [33].

5. Conclusions

The study of the records of the leaves of the genus Desmiophyllum found in several fossil sites spanning from the Barremian to the Cenomanian in the province of Teruel in the northeastern Iberian Peninsula has provided five types of leaves of this genus, which differentiate according to the morphology of their blades and their characteristic venation pattern. Some of these leaves show remarkable similarities with the leaves of the fossil genus Welwistchyophyllum assigned to the Gnetales, while others resemble the leaves of the broad-leaved conifer genus Dammarites. Furthermore, the sedimentological and taphonomical study of the different records has related the different types of leaves with various depositional environments and sub-environments. The different types belonging to this genus would have grown in the vicinity of river channels, ponds, coastal freshwater swamps, and tidal flats integrated into the sedimentary environments corresponding to wide deltas and also in estuaries with tidal influence and coastal plains or restricted bays with lagoons developed during the Early Cretaceous period and the beginning of the Late Cretaceous in northeastern Spain. Co-occurrences with the leaves of the genus Desmiophyllum in the same (or laterally closed) layers includedabundant osteological remains of large phytophagous styracosternans dinosaurs from different ontogenetic states, which could lead to the possibility of this taxon as a potential food for these large ornithopods during the Early Cretaceous period in this area of southwestern Eurasia.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/d16120730/s1, Table S1: five different types of leaves belonging to the fossil genus Desmiophyllum in northeastern Spain.

Author Contributions

Conceptualization, L.M.S. and J.G.-C.; methodology, L.M.S. and A.C.; software, L.M.S.; validation, L.M.S., J.G.-C., J.B.D. and A.C.; formal analysis, L.M.S. and J.G.-C.; investigation, L.M.S., J.B.D. and J.G.-C.; resources, A.C.; data curation, L.M.S. and A.C.; writing—original draft preparation, L.M.S. and J.G.-C. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Gobierno de Aragón (Spain) through the Research Group E04_23R FOCONTUR, the Instituto Aragonés de Fomento, Asociación de Desarrollo Gúdar—Javalambre y Maestrazgo (AGUJAMA), and Unidad de Paleontología de Teruel (Ministerio de Ciencia, Innovación y Universidades, Gobierno de España).

Institutional Review Board Statement

Not applicable.

Data Availability Statement

The specimens studied inthe current study are available in the fossil collection of Museo Aragonés de Paleontología located at the Fundación Conjunto Paleontológico de Teruel-Dinópolis in Teruel City, Spain, and they are accessible to researchers.

Acknowledgments

This article is a contribution to the Research Group E04_23R FOCONTUR of the Gobierno de Aragón (Spain). We thank SAMCA mining company from Estercuel and PAMESA CerámicaCompacto S.L.U. (previously SIBELCO Minerales Cerámicos S.A.) from Galve villages for their disposition in the extraction of the fossils and Ana González for her help in recovering the samples from the Galve locality. We also appreciate useful comments and suggestions made by the Assistant Editor and the of two anonymous reviewers that have helped to improve this manuscript.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Figure 1. Geographical and geological setting of the localities bearing the studied leaves of Desmiophyllum. (A) Geographical situation of the Maestrazgo Basin in the Iberian Peninsula. (B) Detailed paleogeographical reconstruction of the Maestrazgo Basin and corresponding sub-basins during the Early Cretaceous period, with localities bearing the leaves of the genus Desmiophyllum indicated with red stars (modified from [39,40]). Abbreviations: Pl: Plou locality; Et: Estercuel locality; Ut: Utrillas locality; Ga: Galve locality; Mq: Mosqueruela locality.
Figure 1. Geographical and geological setting of the localities bearing the studied leaves of Desmiophyllum. (A) Geographical situation of the Maestrazgo Basin in the Iberian Peninsula. (B) Detailed paleogeographical reconstruction of the Maestrazgo Basin and corresponding sub-basins during the Early Cretaceous period, with localities bearing the leaves of the genus Desmiophyllum indicated with red stars (modified from [39,40]). Abbreviations: Pl: Plou locality; Et: Estercuel locality; Ut: Utrillas locality; Ga: Galve locality; Mq: Mosqueruela locality.
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Sender, L.M.; García-Cobeña, J.; Diez, J.B.; Cobos, A. Morphological Diversity of Desmiophyllum Lesquereux Fossil Leaves and Related Palaeoenvironmental Implications from the Early Cretaceous of Northeastern Spain. Diversity 2024, 16, 730. https://doi.org/10.3390/d16120730

AMA Style

Sender LM, García-Cobeña J, Diez JB, Cobos A. Morphological Diversity of Desmiophyllum Lesquereux Fossil Leaves and Related Palaeoenvironmental Implications from the Early Cretaceous of Northeastern Spain. Diversity. 2024; 16(12):730. https://doi.org/10.3390/d16120730

Chicago/Turabian Style

Sender, Luis M., Josué García-Cobeña, José B. Diez, and Alberto Cobos. 2024. "Morphological Diversity of Desmiophyllum Lesquereux Fossil Leaves and Related Palaeoenvironmental Implications from the Early Cretaceous of Northeastern Spain" Diversity 16, no. 12: 730. https://doi.org/10.3390/d16120730

APA Style

Sender, L. M., García-Cobeña, J., Diez, J. B., & Cobos, A. (2024). Morphological Diversity of Desmiophyllum Lesquereux Fossil Leaves and Related Palaeoenvironmental Implications from the Early Cretaceous of Northeastern Spain. Diversity, 16(12), 730. https://doi.org/10.3390/d16120730

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