Carcharodontosauridae, Stromer, 1931

Carcharodontosauridae gen. et sp. indet.

( Fig. 14 View Figure 14 )

Referred specimen

A partial left ischium (NHMUK PV R 16437).

Morphological description

The left ischium NHMUK PV R 16437 has its proximal portion preserved, missing the distalmost portion of the shaft and the ventralmost portion of the obturator process (Fig. 14). The iliac and pubic peduncles are separated by a concave acetabular rim that is shallow, wide in anterior view with a middle constriction, giving it an 'hourglass-shape' in proximal view (Fig. 14). The peduncles are subequal in size. In the proximal region, the iliac articular surface is triangular and deeply concave suggesting a peg-and-socket articulation (Fig. 14). In the anteriormost region of the iliac peduncle, anterior to the articular surface with the ilium, the ischium is thick mediolaterally, forming the ischial antitrochanter, which is parallelogram-shaped in anterior view. Although the antitrochanter is thick, it is not well projected, being a reduced ridge. In the posterior part of the iliac joint, there is a posterior flange that rises, and it is broken in the dorsalmost portion. The pubic peduncle is subtriangular and medially concave with the articular surface being laterally oriented.

The lateral and medial surfaces of the ischium are concave between the peduncles, with the concavity displaced dorsally in the lateral side and ventrally in the medial side. Posteroventral to the flange in the iliac peduncle, a deep and rugose sulcus, homologous to the ischial tuberosity (e.g. Hutchinson 2001b, Brusatte et al. 2008, Cuesta et al. 2018), runs in the lateral surface becoming shallower posteriorly (Fig. 14). The most proximal part of this sulcus, somewhat elliptical in shape, represents the osteological correlate of the origin of the muscle flexor tibialis internus 3 (FTI3), which is delimited slightly more distally. The most distal part of the sulcus in the posterodorsal region of the ischial shaft, which is more linear, less elliptical than the proximal part, becomes shallower distally, and represents the osteological correlate of the origin of the muscle adductor femoris 2 (ADD2) (Fig. 14A, B). Both of these muscle origins are level II inferences by Witmer's (1995) systematization and are topologically compatible with other theropods (e.g. ceratosaurs— Cerroni et al. 2024, early tetanurans— Lacerda et al. 2024, and derived coelurosaurs— Carrano and Hutchinson 2002).

In the preserved portion of the ischium, the shaft is dorsoventrally flattened, giving it a subrectangular shape, lacking the distalmost part (Fig. 14). Ventral to the shaft and posterior to the pubic peduncle, the obturator process is separated from the pubic peduncle by a shallow and anteroposteriorly notch. Posterior to this notch, the obturator process is twisted medially from the pubic peduncle and broken in its ventralmost portion (however, a notch ventral to obturator process can be noted) and seems to be confluent with the shaft (Fig. 14). Although the ischial shaft is not completely preserved, the preserved part is straight, suggesting that the orientation of the main axis of the ischium was straight in NHMUK PV R 16437.

Morphological comparisons

The overall shape of the NHMUK PV R 16437 partial ischium resembles that of carcharodontosaurid theropods rather than of other dinosaurs. The acetabular rim is shallow in lateral view with a weak 'U-shape' due to the ventral position of the pubic peduncle, as seen in allosauroids (sensu Rauhut and Pol 2019), including the carcharodontosaurids Acrocanthosaurus , Concavenator , Giganotosaurus , Mapusaurus , and Neovenator . In some neovenatorids, such as Siats , the acetabular rim is shallow, not forming a 'U-shaped' border, being straighter than in other allosauroids ( Zanno and Makovicky 2013). The 'U-shape' of the acetabular rim is more pronounced in megalosauroids such as Piatnitzkysaurus and also in the spinosaurids Baryonyx , Ichthyovenator , Vallibonavenatrix, FSAC-KK 11888, and possibly in Suchomimus due to a dorsal projection of the pubic peduncle ( Allain et al. 2012, Malafaia et al. 2020, Sereno et al. 2022, Lacerda et al. 2024). This condition differs from that observed in NHMUK PV R 16437.

The ilioischiatic articulation of NHMUK PV R 16437 has a deep peg-and-socket (or ball-and-socket) configuration, as seen in Acrocanthosaurus , Concavenator , Giganotosaurus , Mapusaurus , and Siats ( Stovall and Langston 1950, Coria and Currie 2006, Carrano et al. 2012, Zanno and Makovicky 2013, Cuesta et al. 2018, Rauhut and Pol 2019, Lacerda et al. 2023). In other theropods, this articulation has a concave plane configuration (e.g. Carrano et al. 2012, Lacerda et al. 2023, Isasmendi et al. 2024).

The ischial antitrochanter is a well-developed, notch-shaped structure in coelophysoids, some ceratosaurs, the early tetanuran Sinosaurus , the spinosaurid Ichthyovenator , and the neovenatorid Siats ; it is a reduced notch in the ischium of other theropods (e.g. Allain et al. 2012, Carrano et al. 2012, Zanno and Makovicky 2013, Cuesta et al. 2018, Lacerda et al. 2023). In NHMUK PV R 16437, although the ischial antitrochanter is a reduced ridge, it represents a thick structure at its base, and this is more comparable with forms such as Acrocanthosaurus , Giganotosaurus , and Sinraptor , than Siats and other contemporary theropods such as spinosaurids.

The presence of the sulcus in the dorsolateral shaft of the ischium, which is posterior to the flange, is similar in NHMUK PV R 16437 and other theropods (e.g. Zanno and Makovicky 2013, Cuesta et al. 2018); however, in the ischium described here it is deeper, similar to carcharodontosaurids and neovenatorids rather than spinosaurids. Consequently, the osteological correlates of the origins of the muscles FTI3 (proximal) and ADD2 (distal) in NHMUK PV R 16437 are deeper than those noted in other non-carcharodontosaurid theropods (e.g. Carrano and Hutchinson 2002, Cerroni et al. 2024, Lacerda et al. 2024).

The obturator process of NHMUK PV R 16437 presents a notch that is shared with other theropods such as the ceratosaur Ceratosaurus , piatnitzkysaurids, spinosaurids (except Ichthyovenator ), and allosauroids such as Acrocanthosaurus, Allosaurus , Giganotosaurus , and Sinraptor ( Stovall and Langston 1950, Carrano et al. 2012, Lacerda et al. 2023). However, NHMUK PV R 16437 has a lamina, part of the dorsalmost portion of the obturator process, which is immediately ventral to the pubic peduncle. This feature is also shared with the metriacanthosaurid Sinraptor and the carcharodontosaurid Giganotosaurus .

Furthermore, if the ischial shaft in NHMUK PV R 16437 is indeed straight, as the preserved portion suggests, this would be another feature shared between this individual and carcharodontosaurids (also seem in some allosauroids— Madsen 1976), but not with some early diverging tetanurans and also metriacanthosaurids. Thus, based on the set of characteristics shared between NHMUK PV R 16437 and carcharodontosaurid theropods, as well as the differences between this ischium and those of spinosaurids, we assign this material to an indeterminate Carcharodontosauridae .

Brief survey of theropod dinosaurs from the Kem Kem Group

Several records of theropod dinosaurs are known from the North Africa, especially those that derive from Middle Cretaceous rocks from the Kem Kem Group region, therefore, suggesting a high theropod diversity. However, much of the diversity known for the region is represented by shed teeth, which are more likely to be fossilized as they are more resistant to weathering and taphonomic alterations ( Benyoucef et al. 2015, Hendrickx et al. 2024). There is also a good and broad ichnological record that helps confirm faunal occurrences and serves as a proxy for more reliable palaeoenvironmental reconstructions ( Belvedere et al. 2013, Ibrahim et al. 2014b). Regarding skeletal remains, records are scarcer ( Hendrickx et al. 2024); however, they are still of broad relevance for understanding both biogeographical and evolutionary issues in different clades. Below, a brief nonexhaustive survey of the body fossil occurrences is presented, as well as integration with our findings and their relevance to current knowledge.

Abelisauridae

The fossil record of abelisaurids is one of the most abundant in the Kem Kem Group, being less abundant only than spinosaurids. Russell (1996) described several bone fragments, including two partial right dentaries, in addition to two partial cervical vertebrae that were attributed to an undetermined theropod, but recently were assigned to abelisaurids ( Souza-Júnior et al. 2023). Although the locality from which these materials were derived is unknown, they were probably recovered from the Cenomanian of southern Morocco ( Souza-Júnior et al. 2023). A partially preserved maxilla that probably comes from Erfoud was described by Mahler (2005). Novas et al. (2005) related a ungual pedal to Abelisauroidea from the Tafilalt region. A partially preserved left maxilla that derives from a region near Taouz was described by Porchetti et al. (2011). The proximal part of a femur was described by Chiarenza and Cau (2016). In addition to these, an axis vertebra described by Smyth et al. (2020a) was also attributed to Abelisauridae .

Noasauridae

A postcranial skeleton that is relatively well preserved, including hindlimbs and partial forelimbs as well as part of the tail, was erected as Deltradomeus agilis by Sereno et al. (1996). However, the assignment of this taxon to noasaurid theropods occurred only in later phylogenetic analyses (e.g. Sereno et al. 2004) and the phylogenetic position of this taxon remains under debate. Evans et al. (2015) described a well-preserved femur from south-east Taouz, which could possibly belong to Deltradomeus. Another noasaurid occurrence was presented by Smyth et al. (2020a), based on an isolated cervical vertebra.

Spinosauridae

This group is one of the most representative in the Kem Kem Group fossil record; however, the nature of the material is isolated or semi-articulated fossils. Two partial dentaries from south-eastern Morocco were described by Buffetaut (1989), being both referred to Spinosaurus cf. Sp. aegyptiacus . Based on a set of isolated bones, including cervical vertebrae, dorsal neural arch, and a fragmentary dentary recovered from Morocco, Russell (1996) erected the name Spinosaurus maroccanus ; later on, Taquet and Russell (1998) referred a rostrum and some axial elements recovered from the Algerian portion of the Sahara Desert to this species. However, this species is frequently regarded as a nomen dubium (e.g. Carrano et al. 2012), a junior synonym of Spinosaurus aegyptiacus (e.g. Ibrahim et al. 2014a), or Spinosaurinae indet. (e.g. Lacerda et al. 2022). Milner (2003) presented a rostrum and a relatively well-preserved dentary from Morocco in a brief note; both of them were referred to Sp. aegyptiacus . This rostrum is redescribed in detail in this work (NHMUK PV R 16420) and considered as an indeterminate Spinosaurinae , agreeing with the current debate (e.g. Sales and Schultz 2017, Lacerda et al. 2022). Another rostrum, which represents the most complete and well-preserved known to date, and a pair of nasals from Morocco were described by Dal Sasso et al. (2005), with both referred to Spinosauru s cf. Sp. aegyptiacus . Lately, some studies (e.g. Sales and Schultz 2017, Lakin and Longrich 2019, Lacerda et al. 2022) have argued that the most reliable identification of that rostrum is Spinosaurinae indet. due to a lack of overlap between these specimens and the Sp. aegyptiacus holotype. Based on several skeletal elements of a subadult individual, Ibrahim et al. (2014a) proposed a neotype to Sp. aegyptiacus , and later on, new skeletal remains possibly of the same individual represented by a robust tail were also recovered from Morocco ( Ibrahim et al. 2020a). Two morphotypes of spinosaurids, Sp. aegyptiacus and cf. Sigilmassasaurus brevicollis , were identified by Hendrickx et al. (2016) based on six quadrates that probably derived from Morocco. A tiny pedal ungual recovered from between the villages of Taouz and Begaa was presented by Maganuco and Dal Sasso (2018). Arden et al. (2019) also described two morphotypes of spinosaurids from the Kem Kem Group: one referred to Sp. cf. Sp. aegyptiacus based on frontals and a frontoparietal, and a skull roof referred to Sigilmassasaurus cf. Si. brevicollis . Based on cranial remains and isolated axial elements, Lakin and Longrich (2019) also described fossils referred to Si. brevicollis and Sp. cf. Sp. aegyptiacus . Besides the previous mentions, other studies also described axial elements of Sigilmassasaurus brevicollis recovered from the same region (e.g. Russell 1996, McFeeters et al. 2013, Evers et al. 2015).

In this contribution we have described several specimens that expand the knowledge of occurrences of spinosaurids in the Kem Kem Group. Among these, we have presented a cervical vertebra referred to Si. brevicollis (NHMUK PV R 38358), in addition to nine specimens (NHMUK PV R 16391, 16422, 16423, 16424, 16426, 16430, 16431, 16433, 16438) that we conservatively classified as indeterminate Spinosaurinae . Our findings, combined with materials mentioned above, contribute to general aspects of the occurrence of spinosaurids in the region, making them one of the most abundant groups of theropod dinosaurs in the Kem Kem Group.

Carcharodontosauridae

At least two species are known from the Kem Kem Group (although some studies consider only one species— Ibrahim et al. 2020a). A nearly complete skull and some vertebral elements of Carcharodontosaurus saharicus were described by Sereno et al. (1996), in which a neotype was designated, recovered from the Douira Formation, south-eastern Morocco ( Sereno et al. 1996, Ibrahim et al. 2020a). An isolated and fragmentary portion of a dentary [originally referred to an abelisaurid by Russell (1996) —see Ibrahim et al. (2020a)] can also be assigned to C. saharicus . A second carcharodontosaurid species, Sauroniops pachytholus , was erected by Cau et al. (2013) based on an almost complete frontal. Later on, Paterna and Cau (2023) also referred additional materials (a partial maxilla and a jugal) to Carcharodontosauridae , discussing the status of both— Carcharodontosaurus and Sauroniops . A probably indeterminate carcharodontosaurids manual ungual [ Ibrahim et al. (2020a), originally described as Theropoda indet. by Russell (1996)] adds to the fossil record of this clade.

Here we also provided the description of an isolated ischium we identify as an indeterminate carcharodontosaurid (NHMUK PV R 16437), adding to the fossil record of this clade from the Kem Kem Group.

Taxonomic attributions of NHMUK PV R 16420 and MSNM V4047 snouts

There is a consensus in the literature considering both well-preserved rostra from the Kem Kem Group—NHMUK PV R 16420 and MSNM V4047—as Spinosaurinae theropods (e.g. Milner 2003, Dal Sasso et al. 2005, Lakin and Longrich 2019, Lacerda et al. 2022). However, the referral of both to Spinosaurus aegyptiacus (e.g. Milner 2003, Dal Sasso et al. 2005, Ibrahim et al. 2014a) is not possible to corroborate, at least yet, due to the lack of overlap among these and the Sp. aegyptiacus holotype ( Evers et al. 2015, Sales and Schultz 2017, Lakin and Longrich 2019, Lacerda et al. 2022).

Some studies ( Lakin and Longrich 2019, Lacerda et al. 2022) noted some differences between both specimens. Lakin and Longrich (2019) considered NHMUK PV R 16420 as having a deeply concave dorsal profile and a curved premaxillary ventral profile, a straighter maxillary tooth row, larger external nares, and distinct outline of the premaxilla when compared with MSNM V4047. Although Lakin and Longrich (2019) did not consider these, necessarily, as two distinct taxa, they considered this set of features enough to designate two distinct morphotypes. However, Lacerda et al. (2022) quantitatively showed a high degree of compression/erosion in NHMUK PV R 16420, preventing any morphological differentiation from MSNM V4047.

As previous noted, the only major differences between the two rostra are the number of premaxillary teeth and the pattern of the intramaxillary suture anteriorly. However, these features seem to have no systematic significance. Based on our detailed redescription, we reject the possibility of two distinct taxa based on the NHMUK PV R 16420 and MSNM V4047 rostra. Excluding some features that are taphonomic artefacts, both snouts have virtually the same shape and probably represent the same taxon.

One or two Spinosaurinae taxa in the Kem Kem Group?

There is a prolific debate regarding the presence of one or more spinosaurid species in the Cenomanian of the Kem Kem Group. Several studies consider that Spinosaurus aegyptiacus is the only well-established species from this region and Sigilmassasaurus brevicollis is not supported due to the lack of autapomorphies (e.g. Ibrahim et al. 2014a, 2020a, b, Maganuco and Dal Sasso 2018, Smyth et al. 2020b). Meanwhile, other studies have argued the plausibility of two (contemporary?) species, considering Si. brevicollis a valid taxon ( McFeeters et al. 2013, Evers et al. 2015, Hendrickx et al. 2016, Hone and Holtz 2017, Arden et al. 2019). However, there is a degree of plausibility to both propositions, as we explain here. On one hand, those studies that consider Sp. aegyptiacus the only species argue that any morphological variation noted in multiple specimens is due to ontogeny, individual variations or sexual dimorphism (e.g. Ibrahim et al. 2014b, Smyth et al. 2020b). Nevertheless, there are no studies showing the main ontogenetic stages of Sp. aegyptiacus , for example, leaving these propositions as speculative. On the other hand, several 'diagnostic' or 'autapomorphic' features are described in the literature, and several studies discuss distinct morphotypes of spinosaurids from the Kem Kem Group (e.g. Chiarenza and Cau 2016, Hendrickx et al. 2016, Arden et al. 2019; McFeeters 2021).

This study also supports different morphotypes from this geological unit, for example, based on the proximal portion of the femur described here (NHMUK PV R 16433) when compared with the proximal femur attributed to Sp. aegyptiacus (FSAC-KK 11888; Ibrahim et al. 2014 a, Sereno et al. 2022). Besides that, several fossil specimens that have been synonymized with, and referred to, Sp. aegyptiacus do not even overlap with the lost holotype specimen ( Evers et al. 2015, Sales and Schultz 2017, Lakin and Longrich 2019, Lacerda et al. 2022), and thus remain difficult to corroborate. Although this study does not intend to resolve these issues, we considered the extended diagnosis provided by Evers et al. (2015), and thus the potential validity of Si. brevicollis . Meanwhile, we did not relate other materials to Sp. aegyptiacus due to lack of overlap and the possibility of a proper morphological comparison. Our study highlights the complexity of the analysis of spinosaurid diversity from the Kem Kem Group, and describes some fossil remains in detail, instead of only mentioning the occurrences of fossils, lacking proper descriptions and anatomical comparisons. We urge a detailed review of all spinosaurid materials from the Kem Kem Group, and also suggest caution in considering either a single taxon of spinosaurine with a large amount of morphological variation, or two taxa lacking proper diagnosis; thus, encouraging more detailed/rigorous studies. Resolution of this issue probably depends upon new discoveries of specimens.