Spinosaurinae

Spinosaurinae gen. et sp. indet. (Figs 2–12) Referred specimens An almost complete rostrum preserving both premaxillae, maxillae, and the anterior portion of the nasals (NHMUK PV R 16420); a paired premaxillae with a fragment of attached maxilla (NHMUK PV R 16422); and a fragment of an isolated right premaxilla (NHMUK PV R 16424); conjoined nasals (NHMUK PV R 16426); a partial skull roof comprising two fused frontals, left prefrontal, and the posterior portion of the left nasal (NHMUK PV R 16423); a mid-dorsal neural arch (NHMUK PV R 16430); a fragmentary mid-dorsal neural spine (NHMUK PV R 16431); two partial ilia (NHMUK PV R 16391 and NHMUK PV R 16438); and a nearly complete left femur (NHMUK PV R 16433). Morphological description (rostrum) NHMUK PV R 16420 consists of the paired premaxillae, mainly the anterior body of the right and left maxillae, and the anterior portions of the conjoined nasals (Fig. 2). The anterior end of the snout is damaged and seems to be slightly taphonomically deformed (e.g. Fig. 2C). The rostrum is anteroposteriorly long (Milner 2003), being c. 600 mm in length, lateromedially compressed and dorsoventrally rather low (Fig. 2A–C). In lateral view (Fig. 2A–C), the dorsal surface of the rostrum is straight anteriorly, posteriorly becoming concave. The ventral surface is heavily concave anteriorly and straightens posteriorly at the level of the fourth maxillary alveolus [elongate 'S-curve' of Milner (2003)]. The anterior tip of the premaxillae does not project ventral to the maxillary tooth row (Fig. 2A, B). The preserved rostral roof is formed by the premaxillae and the nasals, with the skull roof being narrow mediolaterally. Ventrally the rostrum thickens because the lateral walls of the maxillae are ventrolaterally directed—both the premaxillae and maxillae exhibit a sinusoidal groove (Isasmendi et al. 2023), which separates the lateral dentigerous section from the medial part of the rostral bones and creates a secondary palate visible along the entire lateral view (Fig. 2A, B). The external nares are significantly retracted posteriorly, at about 560 mm from the anterior tip of the snout, and they are proportionately small, being located between the eighth and ninth maxillary alveoli (Fig. 2A, B). The premaxilla does not participate in the external nares. Instead, the latter is delimited anteriorly, ventrally, and posteriorly by the maxillae, and dorsally by the nasals (Fig. 2A, B). Although the entire shape of the external naris cannot be determined, the anterior and dorsal margins are relatively straight and the posteroventral margin seems to be concave in shape (Fig. 2A). Premaxillae The paired premaxillae of the NHMUK PV R 16420 specimen suggest that the dorsal rim was partially fused, potentially indicating that this individual was nearly a somatically mature animal. In the other specimens, NHMUK PV R 16422 (Fig. 3) and NHMUK PV R 16424 (Fig. 4), no bony fusion can be noticed, suggesting that these were somatically immature individuals. The premaxillary body of the NHMUK PV R 16420 rostrum is c. 200 mm in length anteroposteriorly and c. 120 mm in height, with a c. 90 mm broad premaxillary 'rosette' (sensu Charig and Milner 1997). If the posterodorsal process of the premaxilla is considered, this would be c. 570 mm long anteroposteriorly (Fig. 2). The premaxillae of NHMUK PV R 16420 contact the nasals posterodorsally and the maxillae posteroventrally (Fig. 2A, B). The anteriormost portion of all the studied premaxillae is damaged and its shape cannot be determined; however, the anterior premaxillary 'rosette' is present, at least partially, in all of them [see Milner (2003) and this work for NHMUK PV R 16420]. Posterior to the 'rosette', the premaxillary body is constricted both dorsoventrally and mediolaterally (Figs 2–4). In lateral view (Fig. 2A, B, H–K), the anteroventral margin of the NHMUK PV R 16420 premaxillae projects anteroventrally— the anterior surface of the premaxillae is convex, straightening dorsally, while the ventral surface is concave throughout its entire length. The lateral wall of the premaxillae is thoroughly rugose and bears several neurovascular foramina that pierce the premaxilla (e.g. Fig. 3E–H). Generally, the foramina are oval to subcircular in shape and exhibit a ventrally oriented shallow groove, which can be straight or parabolic. The ventral foramina form a row that is parallel to the ventral surface of the lateral wall. The dorsal foramina seem to be scattered. Also in lateral view, the alveolar row can be distinguished (see Figs 2–4). As aforementioned, the external naris is considerably retracted posteriorly (Fig. 2A, B), the typical nasal and subnarial processes of the premaxilla that delimit the external naris dorsally and ventrally, as seen in other theropods, is not present. Nevertheless, two equivalent processes (i.e. the posterodorsal and posteroventral processes of the premaxillae; Fig. 2A, B) are present in the NHMUK PV R 16420 individual, which delimit the subnarial foramen (better preserved on the left lateral side; Fig. 2A). The posterodorsal process of the premaxillae mainly projects posteriorly, being long and forming the skull roof between its base and the nasals, and gradually tapering posteriorly (Fig. 2A, B). This process is straight and anteriorly horizontal; however, it slightly projects posterodorsally, as seen in lateral view (Fig. 2B). The ventral surface of the posterodorsal process contacts the maxilla ventrally from its base to slightly anterior to the external naris; posteriorly it contacts the nasals. The contact between the premaxillae and nasals has a complex morphology. In dorsal view, the premaxillae and nasals contact each other dorsally and interlock via a 'peg-like' process that extends from each premaxillae penetrating the nasals, giving it a 'W-shape' morphology at the contact region. The posteroventral process of the premaxillae is considerably less-developed; however, it is taphonomically damaged (mainly on the right side; Fig. 2B). This tapering process is posteriorly directed and laterally overlaps the maxillae. The bases of the posterodorsal and posteroventral processes are separated by the subnarial foramen (Fig. 2A). In ventral view, each premaxilla (i.e. NHMUK PV R 16420, NHMUK PV R 16422, and NHMUK PV R 16424) exhibits a medially placed robust bone element, forming a convex secondary palate. That secondary palate is also visible in lateral view due to the lateral walls of the premaxillae, which do not project ventrally (Figs 2–4). These elements are divided from the lateral dentigerous portion of the premaxillae by a sinusoidal groove. The robust bone elements meet anteromedially at the level of the second and third premaxillary alveoli (e.g. Fig. 2C, D). This medial contact consists of the interdigitation of both elements, whereas they are posteriorly separated by a gap and, more posteriorly, by the anteromedial processes of the maxillae (Milner 2003). The dentigerous portions of the premaxillae are concave (Figs 2H–J, 3E–H, 4B, C). Each of the NHMUK PV R 16420 premaxillae bear seven alveoli, which are subcircular in shape (Milner 2003, Lacerda et al. 2022). The anteriormost alveolus (premaxillary alveolus 1; pm1) is small, and the second (pm2) and third ones (pm3) are considerably larger, being the largest alveoli of the premaxillary row; towards the rear of the skull, the premaxillary alveoli decrease in size. The fourth (pm4) and fifth alveoli (pm5) are separated from their anterior and posterior ones by a diastema; and the sixth (pm6) and seventh alveoli (pm7) are 'coupled' in the studied premaxillae (Figs 2C, D, 3A, B, 4B, C), similar to other spinosaurines (Lacerda et al. 2022). Between the last premaxillary alveolus (pm6 or pm7) and the first maxillary tooth (mx1), another diastema is present. In NHMUK PV R 16422 and NHMUK PV R 16424, the posterior four alveoli are preserved, which gradually decrease in size posteriorly (Figs 3A, B, 4B, C). If the pattern observed in the spinosaurine specimens, such as NHMUK PV R 16420, MNHN SAM 124, and MSNM V 4047, is considered (Taquet and Russell 1998, Milner 2003, Dal Sasso et al. 2005, Lacerda et al. 2022), the NHMUK PV R 16422 individual would bear six premaxillary teeth and thus the preserved alveoli are interpreted as pertaining to pm3 to pm6 (Fig. 3A–D). On the other hand, the specimen NHMUK PV R 16424 would exhibit seven alveoli on its right premaxilla and the preserved ones would correspond to pm4 to pm7 (Fig. 4). Alveolar metrics are in Table 2. In the left premaxilla of NHMUK PV R 16422, lpm3 is separated from the rest of the premaxillary alveoli by a diastema (Fig. 3A, B). In the right premaxilla of NHMUK PV R 16422 and the right premaxilla NHMUK PV R 16424 (Fig. 4), the two anterior preserved alveoli (pm3–4 of NHMUK PV R 16422 and pm4–5 of NHMUK PV R 16424), as well as the two most posterior alveoli (pm5–6 of NHMUK PV R 16422 and pm6–7 of NHMUK PV R 16420), are paired and separated from each other by a diastema (Figs 2–4). Another diastema is present between the last alveolus of the premaxilla (pm6/7) and the maxilla (m1). In the regions of the premaxillae where the diastemata are located, the lateral walls of the premaxillae have ventrally located concavities (Fig. 2A, B), where the laterocumbent teeth of the dentary would probably have inserted, as indicated by Dal Sasso et al. (2005). The overall outline of the preserved alveoli is subcircular in all three specimens (Figs 2–4). Both NHMUK PV R 16420 and NHMUK PV R 16422 still retain some teeth preserved in situ. In NHMUK PV R 16420, these are present in the lpm1 on the left side, and the rpm 3 in the right premaxilla, and comprise the bases and roots of the teeth (Fig. 2C–H). In the NHMUK PV R 16422 specimen, teeth are preserved in the alveoli lpm4 and lpm6 of the left premaxilla and rpm3 and rpm5 of the right premaxilla (Fig. 3). However, these teeth are not completely erupted, being re