1 Introduction

Nowadays, the recurrent discoveries of fossils in the Lower Cretaceous sediments of the Province of Teruel have evidenced that dinosaurs were highly diverse (Alcalá et al., 2018; Pereda-Suberbiola et al., 2012; Verdú et al., 2019; references therein). In fact, several new genera and species have been erected in the last two decades in the Province of Teruel (e.g., Canudo et al., 2008; Kirkland et al., 2013; McDonald et al., 2012; Ruiz-Omeñaca et al., 2012; Sánchez-Hernández & Benton, 2014; Verdú et al., 2015). The upper Hauterivian–lower Barremian El Castellar Formation (Salas, 1987), in the southwest of the Maestrazgo Basin (Teruel, Spain) (Salas & Guimerà, 1996), has provided a considerable number of osteological fossils of diverse groups of dinosaurs (e.g., García-Cobeña et al., 2022, 2023; Gasca et al., 2009b; Ruiz-Omeñaca, 2006; Verdú et al., 2019). In contrast, dinosaur track findings at present are scarcer and less diverse than direct remains, and all of them are preserved as casts with different degrees of anatomical detail (e.g., Castanera et al., 2022; García-Cobeña et al., 2022, 2023).

Here, we report on several new isolated vertebral centra of a large-sized ornithopod from the site CT-7 (Fon Santi site), in facies of the El Castellar Formation in the municipality of El Castellar (Teruel, Spain). We conduct a systematic study of this material to determine the taxonomic affinities with other Early Cretaceous large ornithopods from Europe. In addition, we review the most relevant dinosaur fossil discoveries from the El Castellar Formation in the Province of Teruel, in order to describe their diversity in this region (Maestrazgo Basin, eastern Iberian Basin).

Institutional abbreviations: CPT- Conjunto Paleontológico de Teruel, Teruel, Spain; MAP, Museo Aragonés de Paleontología, Teruel, Spain.

Other abbreviations: CT, El Castellar sites, El Castellar, Teruel, Spain.

2 Geographical and geological settings

In 1987, Salas formally defined a siliciclastic-carbonatic unit, which he named the El Castellar Formation and whose stratotype is located in the municipality of El Castellar, in the Province of Teruel (Aragón, north–eastern Spain) (Fig. 1a, b).

Fig. 1
figure 1

Geographical and geological settings. a, b Geographical situation of the study area (Province of Teruel). c Map of the Iberian Peninsula with the location of the Maestrazgo Basin (redrawn from Salas et al., 2001). d Map of the Maestrazgo Basin (redrawn from Liesa et al., 2019). e Simplified stratigraphic section of the Lower Cretaceous (pre-Aptian) of the southwest Maestrazgo Basin (modified from García-Cobeña et al., 2022). Abbreviations: H.F., Herbers Fault; Haut., Hauterivian; Kimm., Kimmeridgian; L.F., La Llaberia Fault; M.F., Miravete Fault; S. F. Segre Fault; Sb., Sub-basin; Tithon., Tithonian; T.F., Turmell Fault

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Geologically, this formation outcrops extensively in the southwest of the Maestrazgo Basin (eastern Iberian Basin) (Fig. 1c), mainly in the Peñagolosa (or Cedramán sensu Salas et a., 2019) and Galve sub-basins (Fig. 1d). Both areas, together with those known as La Saledella, Morella, El Perelló, Aliaga (or Las Parras sensu Soria, 1997) and Oliete, constitute this basin. The Galve and Peñagolosa sub-basins are separated by the Cedrillas normal fault (Salas & Guimerà, 1996) (Fig. 1d).

The El Castellar Formation is, in essence, divided into two stages: a detrital lower one with shales, evaporites and sandstones, and a carbonatic upper one with marlstones and limestones (e.g., Cobos et al., 2012) (Fig. 1e). Fernández-Labrador (2016, unpublished data) interprets the sedimentary system as a coastal wetland system, composed of fluvial, lacustrine and palustrine facies that represent several sedimentary environments. Moreover, Fernández-Labrador (2016, unpublished data) pointed out that it was easily flooded and with a continental contribution. This unit uncomfortably rests on the Villar del Arzobispo Formation (Kimmeridgian-Tithonian sensu Campos-Soto et al., 2017) in both sub-basins, and overlies the Mora de Rubielos Formation (late Berriasian-early Valanginian in age according to Mas et al., 2004; Salas et al., 2001) locally, in the south–southeast of the Peñagolosa sub-basin (Caja-Rodríguez, 2004; Campos-Soto et al., 2017, 2019). Finally, the El Castellar Formation is dated as upper Hauterivian–lower Barremian based on its charophyte content (Martín-Closas, 1989).

3 Material and methods

The material of the large ornithopod from the CT-7 site is constituted by one cervical, one potential dorsal and five caudal vertebrae (Table 1). These bone remains are systematically studied using the phylogenetic hypothesis of Iguanodontia by Verdú et al. (2018) as a framework and compared with other Early Cretaceous styracosternans. Measurements of these fossils were taken for the length (L), the anterior (Ha) and posterior height (Hp) and the anterior (Wa) and posterior width (Wp) (Table 1). Assignations in open nomenclature are made following Sigovini et al. (2016).

Table 1 Measurements (in mm) of the osteological fossils from the CT-7 site
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In addition, our revision of the most significant dinosaur findings from the El Castellar Formation of the southwest Maestrazgo Basin is based mainly on the works of Ruiz-Omeñaca (2006), Gasca et al. (2009b) and Cobos (2011, unpublished). However, we update the general dinosaur record of this lithostratigraphic unit and geological area with the most recent works. Moreover, we figure some relevant fossils of dinosaurs previously described in this formation.

4 Results

4.1 Systematic palaeontology

Dinosauria Owen, 1842

Ornithischia Seeley, 1887 (sensu Madzia et al., 2021).

Ornithopoda Marsh, 1881 (sensu Madzia et al., 2021).

Iguanodontia Dollo, 1888 (sensu Madzia et al., 2021).

Dryomorpha Sereno, 1986 (sensu Madzia et al., 2021).

Ankylopollexia Sereno, 1986 (sensu Madzia et al., 2021).

Styracosterna Sereno, 1986 (sensu Madzia et al., 2021).

4.2 Styracosterna indet

4.2.1 Referred material

A centrum of a cervical vertebra (MAP-8343; Fig. 2a–e), a fragment of a possible centrum of a middle-to-posterior dorsal vertebra (MAP-8345; Fig. 2f, g), a centrum of an anterior caudal vertebra (CPT-3901; Fig. 2h, i), three centra of middle caudal vertebrae (MAP-8344, CPT-727 and CPT-726; Fig. 2j–o), and a centrum of a posterior caudal vertebra (CPT-3904; Fig. 2p, q).

Fig. 2
figure 2

Styracosterna indet. fossils from CT-7 site. a–e Cervical centrum MAP-8343 in anterior (a), posterior (b), lateral (c), ventral (d) and dorsal (e) views. F, g Centrum of a possible middle-to-posterior dorsal MAP-8345 in anterior (f) and ventral (g) views. h, i Anterior caudal centrum CPT-3901 in anterior (h) and lateral (i) views. j, k Middle caudal centrum MAP-8344 in anterior (j) and lateral (k) views. l, m Middle caudal centrum CPT-727 in anterior (l) and lateral (m) views. n, o Middle caudal centrum CPT-726 in anterior (n) and lateral (o) views. p, q Posterior caudal centrum CPT-3904 in anterior (p) and lateral (q) views. Abbreviations: g, ventral groove; k, keel; nc, neural canal; ns, neurocentral suture; p, parapophyses; svs, smooth ventral surface; tp, transverse processes

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4.2.2 Site, Horizon, and Age.

The CT-7 (Fon Santi) site, in the El Castellar Village (Teruel, Spain) (Fig. 1a, b). Peñagolosa sub-basin, Maestrazgo Basin (Fig. 1c, d). The El Castellar Formation, upper Hauterivian–lower Barremian (Lower Cretaceous) (Fig. 1e).

4.2.3 Descriptions

MAP-8343 is a centrum of a cervical vertebra. The cranial articular facet is heart-shaped (higher than wide) (Fig. 2a) and the caudal articular facet is subelliptical (wider than high) (Fig. 2b). It is rather larger than high and wide and is highly opisthocoelous (Fig. 2c). The lateral surfaces are craniocaudally concave and preserve the base of the parapophyses, which are almost eroded (Fig. 2c). The ventral surface displays a protuberance similar to a non-developed keel in the anterior region (Fig. 2d). In dorsal view, the neural canal becomes wider towards the caudal region. The neurocentral suture is closed (Fig. 2e).

The centrum of a possible middle-to-posterior dorsal vertebra MAP-8345 is highly fractured and eroded. It only preserves its half anterior articular facet, the right lateral and the ventral surface. This centrum is apparently amphiplatyan and higher rather than long (Fig. 2f). In lateral view, it is moderately compressed and preserves a region with a closed neurocentral suture. Moreover, the ventral surface is flat, without a ventral keel (Fig. 2g).

The anterior caudal region is represented only by a platycoelous centrum CPT-3901. The articular facets are subrectangular, and higher than wide (Fig. 2h). In lateral view, it has a rectangular shape, and it is higher than long (Fig. 2i). The neural canal is narrow.

The middle and posterior regions of the tail are represented by MAP-8344, CPT-727, CPT-726, and CPT-3904 centra (Fig. 2j–o). All of them are amphiplatyan (slightly platycoelous) and with hexagonal or subhexagonal articular facets (Fig. 2j, l, n, p). Due to their preservation, they do not show chevron facets. The neural canal, which is already narrow in the case of MAP-8344, becomes even narrower towards the more posterior caudals, as in the case of CTP-3904. A ventral sulcus is only present in MAP-8344 and CPT-726 (Fig. 2k, o). The other centra have an eroded ventral surface.

5 Discussion

5.1 Comparisons of the skeletal remains with other Lower Cretaceous styracosternans

The lack of repetition of osteological remains from the CT-7 site, their considerable size and the concordance in the size of these fossils, reflect that they may belong to a single specimen. Moreover, the presence of a closed neurocentral suture in the centrum of the cervical vertebra MAP-8343 (Fig. 2c), and that of the possible middle-to-posterior dorsal vertebra MAP-8345 (Fig. 2f), evidence that these fossils potentially belonged to a subadult or adult individual (e.g., Hübner, 2018; Verdú, 2017). Moreover, they are identified as belonging to an iguanodontian ornithopod based on the presence of a sinuous neurocentral suture in the vertebral centra and these without pleurocoeli, and middle caudal vertebrae with hexagonal articular facets (Knoll, 2009; Norman, 2004; Pereda-Suberbiola et al., 2011; Verdú et al., 2019, 2020). In particular, they belong to Styracosterna indet. because of the strongly opisthocoely in the cervical centrum MAP-8343 (Fig. 2c), a diagnostic feature of the clade (sensu Norman, 2015). This element resembles those highly opisthocoelous and ventrally keeled (not markedly pronounced in MAP-8343 and more similar to a protuberance, Fig. 2c) cervical vertebrae of other European Early Cretaceous styracosternans—for instance, Barilium (Norman, 2011), Hypselospinus (Norman, 2015), Iguanodon cf. galvensis (García-Cobeña et al., 2022; Verdú et al., 2020), I. bernissartensis (Norman, 1980), Mantellisaurus (Norman, 1986) and Proa (unpublished specimen AR-1/103).

The possible centrum of a middle-to-posterior dorsal centrum MAP-8345 (Fig. 2f, g) resembles those higher than long of Barilium (Norman, 2011), Magnamanus (Fuentes-Vidarte et al., 2016), I. cf. galvensis (Verdú et al., 2020; García-Cobeña et al., 2022), Brighstoneus (Lockwood et al., 2021) and I. bernissartensis (Norman, 1980), unlike those longer than high of Mantellisaurus (Norman, 1986) and Morelladon (Gasulla et al., 2015). Moreover, it apparently lacks a ventral keel, such as the middle and posterior dorsal vertebrae of I. cf. galvensis (García-Cobeña et al., 2022; Verdú et al., 2020) and Magnamanus (Fuentes-Vidarte et al., 2016). In contrast, those of Barilium (Norman, 2011), Hypselospinus (Norman, 2015), I. bernissartensis (Norman, 1980), Mantellisaurus (Norman, 1986), Brighstoneus (Lockwood et al., 2021), and Morelladon (Gasulla et al., 2015) exhibit a ventral keel. Moreover, this centrum is moderately compressed between the articular facets, as in I. cf. galvensis (García-Cobeña et al., 2022; Verdú et al., 2020) and Magnamanus (Fuentes-Vidarte et al., 2016).

For its part, the anterior caudal centrum CPT-3901 is platycoelous with subquadrangular articular facets and a smooth ventral surface (Fig. 2h, i), as in Hypselospinus (Norman, 2015), Magnamanus (Fuentes-Vidarte et al., 2016), I. cf. galvensis (García-Cobeña et al., 2022), I. bernissartensis (1980) and, apparently, Brighstoneus (Lockwood et al., 2021). In contrast, it differs from the amphiplatyan caudal vertebrae of Barilium (Norman, 2011), perinates of I. galvensis (Verdú, 2017), and Mantellisaurus (Norman, 1986).

Therefore, the material of the CT-7 site is assigned to Styracosterna indet. based on the highly opisthocoely of the centrum of a cervical vertebra. Besides, the middle-to-posterior dorsal vertebra with higher than long and moderately compressed centrum with a smooth ventral surface, and the anterior caudal vertebra with platycoelous centrum and subquadrangular articular facets, resemble those vertebrae of some indeterminate styracosternans from the Barremian of the Province of Teruel (García-Cobeña et al., 2023; Medrano et al., 2023; Verdú et al., 2019) and from the Cape Espichel of Portugal (e.g. Figueiredo et al., 2022), and others related to I. galvensis (García-Cobeña et al., 2022; Verdú et al., 2020). This osteological material is clearly different from that of other Early Cretaceous styracosternans of Europe, except for Magnamanus, whose relation with Iguanodon should be re-assessed (Verdú et al., 2020). Despite this similarity, the fragmentary preservation of these fossils does not allow us to confidently assign them to Iguanodon galvensis.

5.2 Dinosaur diversity of the El Castellar Formation in the southwest of the Maestrazgo Basin

Although osteological fossils are abundant in the facies of the El Castellar Formation, they are usually fragmentary (e.g., Gasca et al., 2009b), being vertebral centra, teeth and bone fragments the most common skeletal elements found (García-Cobeña et al., 2022). However, a great variety of direct remains of saurischian and ornithischian dinosaurs have been described in the last few years in the Galve and Peñagolosa sub-basins (e.g. Castanera et al., 2022; Cobos, 2012; Cobos et al., 2012; García-Cobeña et al., 2022, 2023; Gasca, 2011; Gasca et al., 2008, 2009a, b; Ruiz-Omeñaca, 2006; Verdú et al., 2019).

Firstly, several taxa have been described among saurischians: (1) indeterminate theropods (e.g., Guerrero & Cobos, 2017; Fig. 3a, b); (2) basal tetanurans, for instance Allosauroidea? indet. (Ruiz-Omeñaca, 2006), Spinosauridae indet. (Gasca et al., 2018), Baryonychinae indet. (Gasca et al., 2008, 2009a, b) and aff. Baryonyx sp. (Gasca et al., 2018); (3) small coelurosaurs, such as Maniraptoriformes indet. (Gasca et al., 2009a, b; Ruiz-Omeñaca, 2006), Maniraptora indet., Velociraptorinae indet. and ‘Prodeinodon’ sp. (Ruiz-Omeñaca, 2006); (4) and huge sauropods, such as Camarasauridae? indet., Euhelopodidae indet. (Ruiz-Omeñaca, 2006), ‘Pleurocoelus valdensis’ (Ruiz-Omeñaca, 2006; Ruiz-Omeñaca & Canudo, 2005) and Oplosaurus armatus (Royo-Torres & Cobos, 2007; Fig. 3c–e).

Fig. 3
figure 3

Some relevant dinosaur fossils from the El Castellar Formation of the Peñagolosa sub-basin. a, b Tooth of Theropoda indet. (MAP-7555) in lingual (a) and labial (b) views. c–e Tooth of Oplosaurus armatus (CPT-678) in labial (c), distal (d) and lingual (e) views. f, g Tooth of Styracosterna indet. (MAP-7566) in lingual (f) and labial (g) views. h–m Vertebral centra of the medium-sized styracosternan related to Morelladon (sensu Verdú et al., 2019): middle-to-posterior dorsal centrum MAP-816 in anterior (h), lateral (i) and ventral (j) views; middle-to-posterior dorsal centrum MAP-814 in anterior (k), lateral (l) and ventral (m) views. n–v Vertebral centra of the large-sized Iguanodon cf. galvensis (sensu García-Cobeña et al., 2022): anterior dorsal centrum MAP-8038 in anterior (n), lateral (o) and ventral (p) views; middle dorsal centrum MAP-8037 in anterior (q), lateral (r) and ventral (s) views; anterior caudal centrum MAP-8043 in posterior (t), lateral (u) and ventral (v) views. Abbreviations: cfw, carina wear facet; k, keel; lag, labial groove; svs, smooth ventral surface

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On the other hand, ornithischians are represented by: (1) basal forms such as Heterodontosauridae indet. (Ruiz-Omeñaca, 2006); (2) thyreophorans such as Ankylosauria indet. (Gasca et al., 2009b); (3) small basal ornithopods, for instance Hypsilophodontidae indet. (Gasca et al., 2009a, b; Ruiz-Omeñaca, 2001, 2006;); and (4) styracosternan ornithopods, such as Styracosterna indet. (e.g., Guerrero & Cobos, 2017; Fig. 2f, g; large-sized and medium-sized morphotypes in Verdú et al., 2019; Fig. 3h–m), Iguanodontoidea indet. (Gasca et al., 2009a, b; Luque et al., 2006), cf. Iguanodon sp. (García-Cobeña et al., 2023; Ruiz-Omeñaca, 2006) and Iguanodon cf. galvensis (García-Cobeña et al., 2022; Fig. 3n–v). Besides, Pereda-Suberbiola et al. (2005) assigned two dermal armour remains from the El Castellar Formation of Galve to Stegosauria indet. However, other authors consider that these fossils come from the underlying Villar del Arzobispo Formation (Cobos et al., 2012; Luque et al., 2006; Royo-Torres et al., 2009).

This faunal composition is strongly similar to that of other Lower Cretaceous regions of the Iberian Peninsula, such as those registered in the facies of the Golmayo Formation of Soria Province (Fuentes-Vidarte et al., 2005, 2016; Pereda-Suberbiola et al., 2007; Royo-Torres et al., 2017), and Europe such as the Isle of Wight (e.g., Barker et al., 2021; Lockwood et al., 2021; Longrich et al., 2021; Martill & Hutt, 1996; Pond et al., 2014).

In contrast to skeletal fossils, tracks are less common in the El Castellar Formation. Despite this, there are some limestones, sandy limestones or sandstone levels that outcrop in the Peñagolosa sub-basin, which show a high number of load-bearing structures that can be attributed to a dinosaurian trackmakers. This phenomenon repeats laterally in other outcrops where the middle-upper stage of the El Castellar Formation appears, at least in this sub-basin (Fig. 4a–d). To date, all these tracks are preserved as casts and related to large-sized ornithopod styracosternan trackmakers (Castanera et al., 2022; García-Cobeña et al., 2022), some of which may be attributed to the genus Iguanodon (García-Cobeña et al., 2023). Systematically, García-Cobeña et al. (2022) identified several of these casts as Iguanodontipodidae indet. and others to Caririchnium-like morphologies. Posteriorly, García-Cobeña et al. (2023) assigned several tracks to Caririchnium isp, including an unusual association of a large manus and pes casts. In addition, Castanera et al. (2022) assigned some highly preserved tracks to the ichnospecies C. magnificum in the Galve sub-basin.

Fig. 4
figure 4

Levels with load-bearing structures (dinosaur tracks) from the middle to upper part of the El Castellar Formation: several tracks in the same level (a), others isolated (b), some with a great size and thickness (c) and others less thick (d)

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6 Conclusions

The El Castellar Formation (upper Hauterivian–lower Barremian) of the southwest of the Maestrazgo Basin represents a clear example of the wide presence of large ornithopods in the Lower Cretaceous of the Iberian Peninsula. The majority of the fossils of these dinosaurs were assigned to styracosternans. Indeed, those from the CT-7 site are here classified as belonging to a large specimen of Styracosterna indet. based on the highly opisthocoely of the cervical centrum. Although these fossils share some features in common with the early Barremian styracosternan I. galvensis, their degree of preservation does not allow us to classify them more inclusively.

The presence of these kinds of fossils provides increasing evidence that these dinosaurs, particularly those that may be potentially related to the large-sized I. galvensis, were frequent inhabitants of the ancient ecosystems developed in coastal wetland systems during the late Hauterivian–early Barremian, and they shared them with other contemporaneous dinosaurs, such as huge sauropods, spinosaurids, small coelurosaurs, small basal ornithopods and ankylosaurs.

Finally, the faunal composition registered in the El Castellar Formation is similar to other synchronic areas of the Iberian Peninsula and Europe, which reflects the great similarity among dinosaur faunas during the Early Cretaceous (Medrano-Aguado et al. 2023).