A new spinosaurid dinosaur species from the Early Cretaceous of Cinctorres (Spain)

Geographical and geological setting

The materials studied herein were recovered at the ANA fossiliferous site. This site is located near the village of Cinctorres (Fig. 1). Cinctorres is approximately 100 km northwest of Castellón de la Plana (Castellón province, eastern Spain) and 12 km WSW of the city of Morella. Geologically, they are located in the tectonosedimentary domain of the Linking Zone of the Iberian Range. The ANA fossil site is found in the materials of the Arcillas de Morella Formation. This formation is a stratigraphic unit from the Lower Cretaceous (upper Barremian) that was deposited in the Maestrat Basin, specifically in the Morella subbasin³⁰.

This formation, with a maximum thickness of 96 m, is composed of red clay, yellowish-white sandstone, grey marl, limestone and locally conglomerate. These lithofacies are arranged vertically and laterally, forming a set of depositional sequences limited by erosion surfaces. These sequences have a transgressive–regressive character and are composed of minor cycles of the parasequence type, which may present flood limits, subaerial exposure or erosion. The Morella Formation in the ANA fossil site has an average thickness of approximately 80 m, and a maximum of six depositional sequences have been identified in it. Following Bover-Arnal et al.³¹, the Arcillas de Morella Formation has an age of 0.745 M.a., although each of the six depositional sequences has an average age of 0.124 M.a. This is consistent with Milankovitch cycles of short orbital eccentricity of the Early Cretaceous astronomical periodicities³². Further analysis of the influence of astronomical parameters on sedimentology is in progress. All lithologies were deposited in flood plains, estuaries and beaches of a delta. The palaeocurrents come from the north and north‒west from an emerged massif located at the centre of the Iberian Trough. This relief separates the Maestrat Basin from the Iberian–Levantine Basin. In the surroundings of Cinctorres where the fossil site is located, the thickness of the Arcillas de Morella Formation is 57 m.

The ANA site was discovered in 1998 by the geologist Ramón Ortí, but it remained unexcavated until 2002, when a palaeontological team formed by members of the Institut de Paleontologia Miquel Crusafont from Sabadell (Barcelona) and the Grup Guix from Vila-real (Castellón) unearthed the first fossil from the locality. The ANA site is located 37 m from the base of the Arcillas de Morella Formation and consists of approximately 2 m of grey‒yellow sandy mudstones containing limonite and goethite crusts and nodules.

Systematic palaeontology

DINOSAURIA Owen, 1842.

THEROPODA Marsh, 1881.

TETANURAE Gauthier, 1986.

SPINOSAURIDAE Stromer, 1915.

BARYONYCHINAE Charig and Milner, 1986, sensu Sereno et al., 1998.

Genus Protathlitis nov.

LSID urn:lsid:zoobank.org:act:58246771-3887-4E7B-BC7F-695CF08FD97F.

Etymology: Protathlitís (Greek, Πρωταθλητής)—“champion”, in reference to the UEFA Europa League title won by Villarreal C.F. in 2021 and as a tribute to the club centenary celebrated in 2023.

Type species: Protathlitis cinctorrensis.

Protathlitis cinctorrensis sp. nov.

LSID urn:lsid:zoobank.org:act:FDC6CE8E-D932-4A72-9C3A-DF797E32B539.

Etymology: The specific name is taken from the town in which the fossil was discovered, “Cinctorres”.

Holotype: fragment of a right maxilla (8ANA-109) (Figs. 2, 3, 4) and five caudal vertebrae (3ANA83, 4ANA43, 4ANA69, 4ANA76, 5ANA78) (Figs. 2, 5, 6).

Referred material: 4ANA-11, a left mandibular tooth or a right maxillary tooth, published by Suñer and Santos-Cubedo³⁴.

Diagnosis: Baryonychine distinguished by the presence of the following unique autapomorphic feature: subcircular depression in the anterior corner of the antorbital fossa in the maxilla. In addition, Protathlitis cinctorrensis gen. et sp. nov. can be distinguished from other baryonychines on the basis of a unique combination of characters: in caudal vertebrae, the transverse process has only two fossae and one buttress, and they are posteriorly oriented; centra with a narrow ventral groove; circular outlines of the articular facets are clearly oval; prezygapophyses and postzygapophysis projected beyond the anterior and posterior rims of the centrum; and no type of element such as hyposphene below the postzygapophysis.

Type locality and type horizon: The ANA site is near Cinctorres (approximately 2 km), Castellón (Spain). The exposed beds belong to the Arcillas de Morella Formation, which is late Barremian (~ 127–126 Ma)^30,31. Fossils were recovered in grey‒yellow sandy mudstones containing limonite and goethite crusts and nodules that were deposited in a shallow low-energy estuarine environment (Figs. 1, 5). The universal transverse Mercator (UTM) coordinates of the ANA site are 30T YK 734714 4497540.

Description

Maxilla

8ANA-109 is a nearly complete right maxilla (Figs. 2, 3, 4). It is broken into three separate pieces that fit together. It lacks the anterior part of the maxilla. The maxilla is anteroposteriorly elongate with a length of 430 mm preserved. The maximum width is 71 mm from the medial side of the medial shelf to the lateral wall and is 94 mm in height at its highest point. There are 16 alveoli separated by interdental plates. The maxilla lacks the anterior part, the zone of contact with the premaxilla. Part of the anteromedial process, the ascending ramus and the jugal ramus are preserved. Fragments of four teeth can be distinguished in the most posterior alveolus (Fig. 3). Additionally, some dentine laminae can be observed in other alveoli that form the lower part of the root of some teeth. The medial shelf is broken.

The ventral margin is straight and tapers anteriorly with respect to the distal part in ventral view. The dorsal margin has two subcircular depressions, one situated in the anterior corner of the antorbital fossa (Fig. 3).

The lateral surface of the maxilla is clearly dorsoventrally convex. The lateral wall is pierced by numerous neurovascular foramina arranged in two rows. The lower one is very deep and bears three foramina with an elliptical outline. From each foramen, a groove runs anteroventrally. These grooves are straight or slightly parabolic and become deeper near the foramina. They penetrate the lateral wall of the ramus posterodorsally (Fig. 4). Among these foramina, a dorsally positioned row of two neurovascular foramina running anteroposteriorly can be distinguished. These holes are smaller. Additionally, they are elliptical in outline, a groove runs anteroventrally, becomes deeper near the foramina and penetrates the lateral wall of the ramus posteriorly. Both rows of foramina connect internally into a wide, oval-shaped canal (Figs. 3, 4). This canal runs anteroposteriorly and laterally to the length of the ramus and is parallel to the row of teeth. It originates on a lateral groove from the anterior medial wall of the antorbital fenestra. This canal is the promaxillary sinus³⁵.

The maxillary alveoli extend far dorsally, but they are not totally vertical. They are oriented slightly lateral to the external wall of the maxilla. These alveoli are narrower anteriorly, and they become subquadrangular posteriorly. The interdental plates with the continuous interdental bone (sensu Currie³⁶) have an hourglass shape in ventral view. Four of the most posterior alveoli retain part of the root of the teeth, decreasing in size. The cross-section of these roots is elliptical. The last of the roots shows the lingual margin not preserved. It has been resorbed to let the replacement tooth migrate labially (Fig. 3), as is observed in other baryonychines²⁹.

Vertebrae

The identification of the position of the isolated vertebrae in the vertebral column is difficult. In the following description, it is assumed that the vertebral column included forty-one caudal vertebrae or more. This is the general condition in basal tetanurans³⁷. The centra of the vertebrae are fused to the neural arch, suggesting that the material belongs to a subadult or an adult form.

The centra of the five anterior vertebrae are well preserved. They are spool-shaped with the side faces lightly compressed. They are amphicoelous, with the proximal face slightly more concave than the distal face. All of the recovered vertebrae are anterior to the “transition point”, defined by the last caudal vertebra with transverse processes¹ and the first vertebra with elongated prezygapophysis³⁸ (usually occurring between Ca17-Ca19). The shape of the centra and the arrangement of the transverse processes suggest that the vertebrae recovered in the ANA site are between positions Ca3 and Ca10.

In the most proximal vertebrae (4ANA43, 4ANA76) (Fig. 5; Table 1), the total height of the centrum is slightly smaller than its length, and the centrum is longer than it is high. The shape of the articular faces is oval with the major axis in the dorsoventral direction. 4ANA43 shows a protuberance in the central part of the two articular faces of the centrum.

In lateral view, the distal ventral edge of the centrum is located below the proximal ventral edge, while the distal dorsal edge is rounded forwards to the junction with the neural arch. In the dorsal region of the centrum, just below the lateral processes, is the neurocentral suture, with a marked depression in 4ANA43 (Fig. 5). The more proximal vertebra has a deeper depression dorso-distally in both side faces, just below the neurocentral suture. This depression corresponds to the posterior region of a dorsal protrusion that is observed within the neural canal.

The distal articulation facets of the chevrons are more developed anteriorly than distal facets. There is a groove that divides both of them and continues anteriorly. The anterior facets are not as marked or differentiated as the distal facets. The ventral groove is shallower and narrower anteriorly. In the proximal region, there is a rounded and less developed crest that is located in the midline of the groove, which extends distally to approximately half the centrum.

The transverse processes are not completely preserved, except in 4ANA76 (Fig. 5), which maintains the left process, although it is deformed. The base of the processes is located slightly behind the midpoint of the vertebral centrum and is quite robust in section but flat and wide distally. The branch of the transverse process is directed slightly posterior and dorsally. Ventrally, the processes present a support ridge that is broad and slightly pronounced, which extends to half of their length.

The prezygapophysis of the anterior vertebrae is eroded. In 4ANA76, the facet joint of the right prezygapophysis is directed dorso-medially. In the prezygapophysis, there are well-developed spinoprezygapophyseal laminae. These laminae bind medially near the midpoint of the centrum, where the base of the neural spine arises. Among these laminae, there is a deep and narrow fossa. From the prezygapophysis, there are laterally prezygadiapophyseal laminae. They are bound to the proximal region of the transverse processes. The binding area of the process is located ahead of the union zone between the spinoprezygapophyseal laminae, forming a slightly concave lateral surface. This area is medially deeper near the laminae.

The postzygapophyses of both vertebrae are eroded, and they do not allow observation of the facet joint. The basis of these is located in front of the distal edge of the centrum, and the angle between them is less than that between the prezygapophyses. At the centre of the postzygapophysis, a deep and narrow depression that extends dorsally is observed.

The neural spine is not complete in any of the vertebrae recovered. The base of the spine arises proximally at the junction of the spinoprezygapophyseal laminae, and caudally, it does not exceed the distal edge of the centrum.

The centra of the middle caudal vertebrae (3ANA83, 4ANA69, 5ANA78) (Fig. 6; Table 1) have the same shape as the proximal caudal ones. The length of these vertebrae is greater than their height, as in the case of the proximal caudal ones, they are also amphicoelous, and the articular faces are oval with the dorso-ventral axis greater than the medial–lateral axis.

In lateral view, the distal ventral edge is not as low as in the proximal caudal vertebrae, and the depression of the neurocentral suture is not as marked. In these vertebrae, a deep depression was not observed in the 4ANA43 vertebra.

The articulation facets with the chevrons are more pronounced in the distal region of the vertebrae, and as in the case of the anterior vertebrae, and the facets are less marked in the proximal face. Ventrally, there is a slightly marked groove, but there is not a medial crest.

None of these vertebrae maintain complete transverse processes. The basis of the processes is long antero-posteriorly. The proximal edge arises near the anterior end of the centrum. The lamina of the process is thin in the dorsoventral direction, but in the 5ANA78 specimen, a less developed support crest is observed. The processes are directed posteriorly, and they are slightly dorsal.

The prezygapophysis is badly eroded, and the articular facet is not perceived. As in the case of the proximal vertebrae, the spinoprezygapophyseal laminae are highly developed, and they are joined together near the base of the prezygapophysis, forming a narrow but deep fossa anteriorly. In the 5ANA78 vertebra, the right prezygadiapophyseal lamina forms a thin ridge on the anterior edge of the process, as in the case of the anterior vertebrae forming a large lateral concave surface to the spinoprezygapophyseal lamina.

The postzygapophyses are long and protrude slightly behind the distal edge of the centrum. The articulation facets are large, and they are lateroventrally oriented at an angle similar to that of the anterior vertebra. Dorsally to the postzygapophysis, a deep and elongated depression is observed that is directed towards the neural spine.

The neural spine is not complete in any of the medial vertebrae. The base is slightly shorter in the anterior–posterior direction than in the case of the anterior vertebrae, and it originates from the joining of the spinoprezygapophyseal lamina, which is anterior to the midline of the centrum.

Phylogenetic results

Using the phylogenetic analysis program TNT³⁹, we performed a “traditional search” with tree bisection reconnection. Wagner trees with a random seed of 1 and 9,999 replicates with 10 trees saved per replication were used. All characters were equally weighted and treated as unordered. TNT revealed 9,386,515 rearrangements. As a result, one most parsimonious tree (MPT) was recovered (Fig. 7) with a length of 157 steps, a consistency index (CI) of 0.8089, a homoplasy index (HI) of 0.1911, and a retention index (RI) of 0.8598 (the ‘describetree’ command in PAUP 4.0a build 167⁴⁰).

In the resulting tree, Protathlitis cinctorrensis is tentatively positioned as the most basal baryonychine. Our phylogenetic analysis is consistent with the definition of Spinosauridae (with Camarillasaurus), Ceratosuchopsini (Suchomimus + Ceratosuchops), Spinosaurinae, Vallibonavenatrix (Spinosaurus + Irritator) and Spinosaurus + Irritator. However, in our analysis, Baryonychinae is supported only by one apomorphic character: Ch. 57 (0 → 1) 30 dentary teeth (unambiguous).

Protathlitis cinctorrensis is recovered as a basal baryonychine (Fig. 7). Unambiguous synapomorphies include character 14, which corresponds to a: (14) Maxilla, subcircular depression in the anterior corner of the antorbital fossa present.

Mateus and Estraviz-López¹ described a new Spinosauridae dinosaur, Iberospinus natarioi. They pointed out that the fossil shows some characteristics of baryonychines, suggesting a closer relation to the group but placing it outside of both the Baryonychinae and the Spinosaurinae. This suggests that Iberospinus would be a sister taxon to Camarillasaurus (outside both subfamilies), or perhaps both taxa are the same (synonymy). Future research should focus on this topic.