The main objective of this study is to provide a revised overview of the anatomy and systematics of Sigilmassasaurus , based on vertebral material directly comparable with the holotype. Previously unpublished Sigilmassasaurus material housed in the Bayerische Staatssammlung für Paläontologie und Geologie in Munich, Germany, and the Natural History Museum, London, United Kingdom, is described in detail. The material includes vertebrae from middle neck positions, and well-preserved specimens from posterior cervical and anterior dorsal positions. Other Sigilmassasaurus vertebrae have been recently described in detail ( McFeeters et al., 2013 ) and are here compared with the new material. Finally, we describe and discuss material referred to Spinosaurus maroccanus , as far as it is relevant to give a comprehensive overview of Sigilmassasaurus .

Ibrahim et al. (2014a) recently described an allegedly associated partial skeleton of a spinosaurid from the Kem Kem beds and argued that both Sigilmassasaurus brevicollis and Spinosaurus maroccanus represent junior synonyms of Spinosaurus aegyptiacus , although no detailed justifications for these referrals were given. This conclusion has been challenged even more recently on the basis of the report of the complete cervical series of the spinosaurid Ichthyovenator Allain et al., 2012 from the Savannakhet Basin ( Allain, 2014 ), based on a phylogenetic analysis that retained Sigilmassasaurus as belonging to Spinosauridae ( Allain, 2014 ).

The first opposing views were published shortly after the establishment of the genus Sigilmassasaurus . Sereno et al. (1996) proposed an ‘overlap’ of Stromer’s “ Spinosaurus B” with Carcharodontosaurus material. In the same study, and also in a later paper ( Brusatte & Sereno, 2007 ), the authors illustrate vertebral material very similar to Sigilmassasaurus vertebrae as belonging to different species of Carcharodontosaurus , although the association with Carcharodontosaurus skull material is questionable in each case. In 1998, Sereno and colleagues ( 1998 ) formally argued that Sigilmassasaurus brevicollis is a junior synonym of Carcharodontosaurus saharicus . Consequently, they treated the Sigilmassasaurus cervicals as Carcharodontosaurus material.

Russell (1996) also noted that the “ Spinosaurus B” material was different from that referred to Carcharodontosaurus saharicus by Stromer (1934) , thus precluding the possibility that Sigilmassasaurus material belonged to Carcharodontosaurus. Because the material described by Stromer (1934) was destroyed during World War II ( Rauhut, 2005 ), Stromer’s plates and texts remain the only source for comparison of Sigilmassasaurus with “ Spinosaurus B.”

The Kem Kem compound assemblage has traditionally been considered “Infracénomanien” in age (i.e., at the base of the Cenomanian). Cavin et al. (2010) noted that there is indeed no evidence for pre-Cenomanian fossils at the base of the Cretaceous series. Also they pointed out that the Kem Kem compound assemblage is very similar to other North-African assemblages: The shark assemblage resembles that of the Bahariya Formation of Egypt ( Sereno et al., 1996 ), which is dated safely to be Early Cenomanian ( Catuneanu, Khalifa & Wanas, 2006 ), and the same is true for the dinosaur assemblage (though see below).

Following this stratigraphic scheme, the informal ‘Kem Kem beds’ are equivalent to the bottom formations, i.e., the Ifezouane and Aoufous Formations. The term “Kem Kem compound assemblage” is useful to describe the vertebrate assemblage as such ( Cavin et al., 2010 ), because until now only the Ifezouane and Aoufous Formations have produced such material, and in most of the cases material cannot be demonstrated to be derived from either formation with certainty.

Yet another factor regarding the unsatisfactory geological context of Moroccan vertebrate remains is that the stratigraphy of the region has been subject to different approaches of systematization. In a recent paper, Cavin et al. (2010) tried to synthesize a stratigraphic concept for the area with information from earlier attempts and first hand field data. Several authors have recognized a succession of three sedimentologically distinct units in Cretaceous rocks of Southern Morocco (e.g., “trilogie mésocrétacée” of Choubert (1948) ; Sereno et al. (1996) , who unite the bottom two units of Choubert’s systemization to the informal ‘Kem Kem beds’ but distinguish between a lower unit and an upper unit; and Dubar (1949) , who formally erected three formations, which are (from bottom to top) the Ifezouane Formation, the Aoufous Formation, and the Akrabou Formation). It has been proposed that the Cretaceous of southern Morocco was deposited in two different, though maybe sporadically communicating basins (e.g., Choubert, 1948 ). Cavin et al. (2010) , however, advocated that the deposition took place in a single sedimentary basin, and that the series displays a continuous time interval between the Early Cenomanian and the Middle Turonian. Accordingly, Cavin et al. (2010) use the formerly named formations by Dubar (1949) as a reference sequence for the entire southern Moroccan Cretaceous deposits.

Unfortunately, most material from this region lacks detailed locality information. This is in part because descriptions of localities of expeditions to remote areas before the late 20th century often lack precise locality data. Another, and even more important factor contributing to the lack of data, is the establishment of a market for vertebrate fossils coming from Morocco. Moroccan locals collect and excavate material without recording scientifically relevant data. These fossils are usually purchased and then resold by fossil dealers who operate on a global scale.

In recent times, the Cretaceous Moroccan vertebrate assemblage has been informally referred to as the ‘Kem Kem compound assemblage’ ( Cavin et al., 2010 ), since many Moroccan vertebrate fossils, including the holotype vertebra of Sigilmassasaurus brevicollis , have been found in the Kem Kem region of Morocco ( Russell, 1996 ). However, the Cretaceous outcrops in Southeastern Morocco producing material referred to this assemblage extend beyond the Kem Kem area, and extend into the alluvial plain north of the Kem Kem area, which was called the ‘Tafilalt’ in Russell (1996) . The outcrop area thus spans over parts of both of these regions of southeastern Morocco, and are geographically located in the eastern part of the Anti-Atlas area, south to the High Atlas and west to the Guir Hamada ( Cavin et al., 2010 ).

The analysis was performed using TNT 1.1 ( Goloboff, Farris & Nixon, 2008 ). Eoraptor Sereno et al., 1993 was chosen as the outgroup taxon. A heuristic search was carried out using 0 random seed for starting Wagner trees, and 10.000 replicates. The tree bisection reconnection (TBR) algorithm was applied, with 10 trees saved per replication. The collapse trees after search option was chosen. Minimum tree length was 1.041, and a strict consensus tree was calculated from 3.070 most parsimonious trees (see discussion).

We used a modified version of the Carrano, Benson & Sampson (2012) data matrix ( Data S2 ) to evaluate the phylogenetic relationships of Sigilmassasaurus . Cervical and dorsal characters were re-coded for all operational taxonomic units (OTUs), and several character definitions were modified. We also deleted a few of the original characters and added a number of new characters. Sigilmassasaurus was added to the list of OTUs, and material herein referred to Sigilmassasaurus was removed from the hypodigm of Carcharodontosaurus . Vertebral characters for Carcharodontosaurus are based on 1922 X 46 instead ( Stromer, 1931 ). For Baryonyx , scorings are based on our new interpretation for the axial placement of preserved vertebral elements. Additionally, Ichthyovenator was added to the matrix, and the codings for Spinosaurus aegyptiacus were modified to be based on the holotype material only, and scored an additional OTU for the partial snout MSNM V4047, which was previously referred to Spinosaurus cf. aegyptiacus by Dal Sasso et al. (2005) . For a full character description and a list of character codings for all taxa, see ( Data S1 ).

Material housed in the BSPG was examined first hand by two of us (SWE, OWMR); material at the NHMUK (including Baryonyx Charig & Milner, 1986 ) was examined first hand by four of us (SWE, OWMR, ACM, RA); material housed at the University of Chicago (including the holotype and referred material of Suchomimus Sereno et al., 1998 , vertebrae originally referred to Carcharodontosaurus iguidensis Brusatte & Sereno, 2007 , and casts of the ‘neotype’ of Spinosaurus aegyptiacus ) were examined first hand by two of us (SWE, OWMR); material from the Canadian Museum of Nature was examined first hand by two of us (BMF, ACM). Comparative material of Ichthyovenator has been collected in 2012 by one of us (RA) from the type locality of the taxon and will be described in detail in a forthcoming publication. Other comparative material was either examined first hand, or based on the published literature. Anatomical nomenclature follows Wilson (1999) for vertebral laminae and Wilson et al. (2011) for vertebral fossae.

We primarily describe new and previously undescribed specimens housed in the collections of the Bayerische Staatssammlung für Paläontologie und Geologie (BSPG) in Munich and the Natural History Museum (NHMUK) in London. Material referable to Sigilmassasaurus includes two mid-cervical vertebral centra (BSPG 2011 I 117 & 118), four posterior cervical (BSPG 2006 I 53 & 56, BSPG 2011 I 115 & 116) and two anterior dorsal (BSPG 2006 I 54 & 55) and, tentatively, one anterior mid-dorsal vertebra (BSPG 2013 I 95) and a mid-cervical vertebral neural arch (NHMUK PV R 16427) and three anterior dorsal vertebrae (NHMUK PV R 16434, 16435 & 16436). We frequently refer to the material, originally described by Russell (1996) , which is housed in the Canadian Museum of Nature (CMN). All of this material was purchased by the respective institutions from fossil dealers, mainly from Moussa Minerals and Fossils, Cambridge. Thus, unfortunately, there is no detailed information on localities or association of individual specimens, but all certainly come from the Kem Kem beds in south–eastern Morocco (see Cavin et al., 2010 ).

Both Spinosaurus maroccanus and Sigilmassasaurus brevicollis were described in the same paper ( Russell, 1996 ). Although the former was mentioned first in the respective paper, both names are available, as the ICZN does not formally recognize page priority. As our analysis indicates that the species comprising Sigilmassasaurus brevicollis and Spinosaurus maroccanus is not referable to the genus Spinosaurus , we used the other available generic name, which is Sigilmassasaurus . Without page priority, the species epithet maroccanus has no priority over the species epithet brevicollis , and in spite of the latter being unfortunate because descriptively inadequate according to our neck reconstruction, we decided to keep the name Sigilmassasaurus brevicollis for taxonomic simplicity.

Comments : The elongate shape of the holotype vertebra of Spinosaurus maroccanus is very unlike the ‘typical’ Sigilmassasaurus morphology of a cervical or anterior dorsal vertebra with extraordinarily broad intercentral articulations and relatively short centrum. However, we present evidence that there is a continuum between the morphology of the holotypes of Sp. maroccanus and S. brevicollis (see discussion below) as seen in Ichthyovenator ( Allain, 2014 ; R Allain, 2015, unpublished data). General trends in the axial sequence of theropod dinosaurs show a reduction in length–width relations, among other features, which explain the observed differences between Sp. maroccanus and Sigilmassasaurus morphotypes. Furthermore, the vertebrae share a number of characters that are unique or otherwise unusual in theropod dinosaurs, supporting the synonymy of the two taxa. However, we do not accept the recent synonymization of both of these names with Spinosaurus aegyptiacus ( Ibrahim et al., 2014a ; see discussion below).

Emended diagnosis : Very large spinosaurid theropod dinosaur. The taxon can be diagnosed on the basis of the following autapomorphies: mid-cervical vertebrae with offset, transversely convex, strongly rugose triangular platform at the posterior end of the ventral side that is confluent with a ventral keel anteriorly; anteriorly broad centroprezygapophyseal lamina with no or strongly reduced centroprezygapophyseal fossa already in anterior mid-cervical vertebrae; reduced neural arch lamination with no or incomplete distinction between anterior and posterior centrodiapophyseal laminae in posterior cervicals and first dorsal; small elongate fossa on either side of the base of the neural spine in last cervical and first dorsal vertebrae. Furthermore, Sigilmassasaurus brevicollis differs from most other theropods in the combination of the following characters: anterior articular surface of posterior cervical and anterior dorsal vertebrae more than 1.5 times wider than high and wider than length of centrum (also in Ichthyovenator ); well-developed anterior tubercle present on the anterior articular surface in posterior cervical and anterior dorsal vertebrae; interzygapophyseal laminae absent in posterior cervicals and anteriormost dorsals, resulting in ventrally open spinopre- and spinopostzygapophyseal fossae (also in Ichthyovenator ); posterior cervical and anterior dorsal vertebrae with massive transverse processes with deeply penetrating pneumatic openings at the base anteriorly and posteriorly (also in D1 in Ichthyovenator ); epipophyses weakly developed in mid-cervicals and absent in posterior cervicals; posterior cervical and anteriormost dorsal vertebrae with anteroposteriorly short, posteriorly inclined, low and spike-like neural spines (modified from Russell, 1996 ; McFeeters, 2011 ; Evers, 2012 ; McFeeters et al., 2013 ).

Occurrences : ‘Kem Kem beds,’ Ifezouane and/or Aoufous Formation, Cenomanian, south–eastern Morocco. We only refer material from these units to Sigilmassasaurus maroccanus , as there is insufficient data to exclude with certainty that similar material from other areas and geological untis might represent different species. However, very similar material, such as at least parts of the specimen described as “ Spinosaurus B” by Stromer (1934) from the Cenomanian of Egypt or a vertebra referred to Carcharodontosaurus by Brusatte & Sereno (2007) from the Cenomanian of Niger can be referred to a spinosaurid close to Sigilmassasaurus .

Description

Mid-cervical vertebrae Vertebrae identified as mid-cervicals are BSPG 2011 I 117, BSPG 2011 I 118, CMN 50791 (type of S. maroccanus; Fig. 1), and NHMUK PV R 16427. BSPG 2011 I 117 and BSPG 2011 I 118 are centra isolated from their neural arches. In both vertebrae, the ornamentation of the areas for neural arch articulations is largely intact, suggesting the neural arches and centra had not yet fused at time of death. Accordingly, the animals probably died before somatic adulthood. This is quite remarkable, because BSPG 2001 I 118 is a particularly large specimen reaching 160 mm in length, excluding the anterior condyle. NHMUK PV R 16427 is an isolated neural arch. The isolated centra, as well as the isolated neural arch all share important features with CMN 50791. Centra of mid-cervical vertebrae of Sigilmassasaurus are longer than wide, and only slightly wider than high. The anterior articular condyles face slightly anteroventrally in respect to the long axis of the vertebra. Transverse processes are strongly ventrally inclined, epipophyses and ventral keels on the centrum are weakly developed but present, while hypapophyses are completely absent. Both centra BSPG 2011 I 117 and 118 (Figs. 2 and 3), as well as CMN 50791 display a different centrum morphology than the ‘typical’ vertebrae referred to Sigilmassasaurus brevicollis (e.g., holotype CMN 41857). The centra are elongate, and the length (without anterior condyle) corresponds to 167% of the width of the anterior facet in BSPG 2011 I 117, and equals 162% of the width in BSPG 2011 I 118. Also the width–height ratios are low with 1.15 (anterior facet) and 1.21 (posterior facet) in BSPG 2011 I 117, and 1.33 (anterior facet) and 1.26 (posterior facet) in BSPG 2011 I 118. These measurements compare well to those of the holotype of S. maroccanus (CMN 50791), in which the length corresponds to c. 175% of the anterior width and the width–height ratio of the anterior face is approximately 1.16. BSPG 2011 I 117 and 118, and CMN 50791 are strongly opisthocoelous and share anterior articular facets that are ventrally inclined at about an angle of 17–20° from the perpendicular to the long axis of the centra, and are slightly displaced dorsally from the level of the posterior surface. This displacement is more marked in BSPG 2011 I 118 than in the other two elements. The posterior facets lack the distinct, notably reniform outlines of the holotype of Sigilmassasaurus brevicollis, but the dorsal edge of the posterior articular facet is slightly concave, contributing to a weakly reniform outline. In BSPG 2011 I 118 the dorsal part of the posterior articular facet is eroded so that the shape cannot be reconstructed with certainty. Both isolated centra display a low median tuberosity on the condyle of the anterior side of the vertebrae, which is better developed in BSPG 2011 I 117 than in BSPG 2011 I 118. In the latter specimen, the median tuberosity has a vertically oriented depression, which is not evident in other specimens. No median tuberosity could be confirmed for CMN 50791. An elongate but narrow groove is incised into the surface on the left side of the anterior condyle of BSPG 2011 I 118. It is 3–4 mm deep and 40 mm long. The surface of the groove is rough, and the edges seem to have experienced some erosion. A sandgrain is tightly embedded in one edge of the mark, indicating that this structure was present prior to fossilisation. This groove differs from the definite chisel marks seen in another specimen (BSPG 2006 I 56, see below), which show quadratic outlines, smooth surfaces, and sharp, uneroded edges. An alternative interpretation supported here is that the feature represents a post-mortem bite mark. Ventral keels are present in the anterior half of the ventral sides of BSPG 2011 I 117 and 118, but developed only as a shallow ridge. A prominent feature of the ventral side is an elevated triangular platform of bone in its posterior half, which anteriorly merges into the keel, and posteriorly connects to the rim of the posterior articular facet. The ventral keel is better developed in BSPG 2011 I 117, where it continues anteriorly from the platform as a broad, rounded ridge to a pronounced rugose area at the anterior end of the centrum, whereas it is only marked as a slightly raised, broad ventral area in BSPG 2011 I 118, where it fades anteriorly just posterior to a similar rugose patch. Both the triangular ventral platform and a broad, weakly developed ventral keel are also evident in CMN 50791. This condition is very different from that seen in posterior cervicals or cervicodorsal vertebrae of Sigilmassasaurus, but an intermediate condition is seen in BSPG 2006 I 56, which also bears a prominent posteroventral triangular plateau, but has a more pronounced keel (see below for detailed description). The triangular elevated plateau is an important feature indicating that the presented specimens are congeneric, since such a well-developed and strongly offset plateau that merges with a low keel anteriorly is unknown in other theropods, and can thus be regarded as an autapomorphy of Sigilmassasaurus. The only other theropod with a similar feature is Ichthyovenator, in which a ventral platform, which is, however, not continuous anteriorly with a keel, is present in the Ce7 and Ce8 (BK10 21; BK10-22). Usually, the ventral surface of mid-cervical theropod vertebrae is either concave, as in Sinraptor (Currie & Zhao, 1993), or a narrow keel runs along the entire ventral side of the centrum, as in keeled vertebrae of Neovenator (Brusatte, Benson & Hutt, 2008). Importantly, the triangular plateau is neither found in Spinosaurus aegyptiacus (Stromer, 1915), Baryonyx (Charig & Milner, 1997), Suchomimus (S Evers & O Rauhut, pers. obs., 2015), nor in carcharodontosaur vertebrae, e.g., Giganotosaurus (MUCPv–CH–1), Tyrannotitan (Novas et al., 2005) (MPEV–PV 1157), or Acrocanthosaurus (Harris, 1998). A hypapophysis is absent in BSPG 2011 I 117, BSPG 2011 I 118, and CMN 50791. Anteriorly, the keel fades towards a slightly elevated transverse connection of the parapophyses that occupies the anterior margin of the centrum. Both this transverse area and the triangular plateaus in BSPG 2011 I 117 and 118, as well as in CMN 50791, bear an intensely rugose surface structure. The rugosity is composed of numerous small ridges and furrows, which align in a longitudinal pattern. Although this texture is developed most prominently in BSPG 2011 I 117 and 118, the rugosities can also be observed in specimens BSPG 2006 I 55, BSPG 2011 I 115, and BSPG 2011 I 116, NHMUK PV R 16435 (other specimens either show only weak rugosities, or respective areas on the centrum are too damaged to determine the character). The rugosities are furthermore evident in the holotype of Sigilmassasaurus brevicollis (see Russell, 1996; McFeeters et al., 2013), although the structures have not been mentioned in previous works. A vertebra referred to as Carcharodontosaurus iguidensis, which we consider to represent Sigilmassasaurus or a closely related form, also shows the same pattern (Brusatte & Sereno, 2007). These rugosities are more strongly developed than in other theropod dinosaurs, and are thought to be related to hypaxial muscle attachment (Snively & Russell, 2007). The parapophyses of BSPG 2011 I 117 and CMN 50791 seem to be mainly laterally directed, while the orientation has a more ventral component in BSPG 2011 I 118. The latter is hard to constrain, however, because the parapophyses are heavily eroded in this vertebra. In all vertebrae, the parapophyses are placed at the anterior rim and positioned ventrally on the centrum. Because of the ventral tilt of the anterior facet, the parapophyses appear to be placed somewhat more posteriorly on the centrum, but their position is actually consistent with that of the parapophyses observed in other cervical and the anteriormost dorsal vertebrae of Sigilmassasaurus. The articular facets of the parapophyses are large and semioval in outline, tapering posteriorly. Posteriorly, the parapophyses are connected to the lateral side of the centrum by a short but stout ridge. This ridge is best developed in BSPG 2011 I 117, but is shared among all three vertebrae. In continuation to this posterior parapophyseal ridge a notable edge marks the sharp transition from lateral surface and ventral surface of the centrum. This edge extends from the ridge posteriorly and slightly dorsally, so that it meets the posterior end at about the mid-height of the centrum. About halfway between the parapophysis and the posterior end of the centrum there is a low, rounded tubercle on this edge; this tubercle is also present in all three vertebrae. The lateral pneumatic foramina are located posterodorsal to the parapophyses. They are symmetrically developed and are anteroposteriorly elongate. In BSPG 2011 I 117, the better preserved foramen on the left side is 25 mm long and maximally 10 mm high; these measurements are 28 mm and 10 mm, respectively, in BSPG 2011 I 118. In BSPG 2011 I 117 and 118, both the anterior and the posterior rim of the foramen taper to a sharply angled point; in CMN 50791 this is only the case in the anterior margin, whereas the posterior margin is narrow, but rounded. A very shallow, triangular depression is present posterior to these pneumatic foramina. Anteriorly, the pneumatic foramen also incises into the dorsal surface of the base of the parapophysis. In both BSPG 2011 I 117 and 118, the pneumatic foramina lead into large internal cavities, with a smaller, anteroposteriorly elongate ventral depression just adjacent to the foramen being separated from a larger medial cavity by a low, rounded ridge. The surface directly above the pneumatic foramina is slightly swollen. This feature was also observed by McFeeters et al. (2013) in the holotype material of Sigilmassasaurus, and has been described as a lateral bulge. Between this bulge and the neurocentral suture the lateral surface is very gently concave dorsoventrally. In dorsal view, the centra are medially constricted. The narrowest part of the centrum is at about two thirds of centrum length as measured from the posterior end in BSPG 2011 I 117; in BSPG 2011 I 118, the neurocentral suture bulges slightly laterally in this area, so that the narrowest part in dorsal view is just behind mid-length of the centrum. The articular surfaces for the neural arch pedicles meet in the center of the vertebrae in BSPG 2011 I 117 and 118. In CMN 50791, which preserves the neural arch, both neural arch pedicles also meet on the floor of the neural canal, resulting in a ventrally narrow neural canal. In BSPG 2011 I 117, the posterior part of the neural canal floor is a trench-like depression in the centrum due to the dorsally elevated articular surfaces for the neural arch, with steep lateral boundaries that progressively open posteriorly and result in a “V”-shaped pattern. One neurovascular foramen penetrates the surface of the bone. In BSPG 2011 I 118, the dorsal surface posterior to where the articular surfaces of the neural arch meet is eroded, and neurovascular foramina are not evident. Anteriorly, the floor of the neural arch also widens in a V-shaped fashion, but its margins are less notably raised. The neural arch of CMN 50971 shares many features with the isolated neural arch NHMUK PV R 16427 (Fig. 4). The neural canal opening widens dorsally in both specimens. This is also to be expected for BSPG 2011 I 117 and 118, based on the narrowing floor of the neural canal. The bases of the transverse processes are preserved in both specimens. The processes are more ventrally than laterally directed, so that they overhang the lateral side of the neural arch in lateral view. Their anterior margin is placed far anteriorly on the neural arch, as it is ‘typical’ for anterior to mid-cervical vertebrae. Whereas the transverse process is anteroposteriorly narrow at its base in NHMUK PV R 16427, with the posterior margin being placed at about the mid-length of the neural arch, it is anteroposteriorly longer in CMN 50791, ending at approximately two-thirds of the length of the neural arch. The best-developed lateral lamina is the prezygodiapophyseal lamina (prdl) in both elements, which expands from the ventromedial edge of the prezygapophysis in slightly concave arch posteroventrally towards the anterior margin of the transverse process. Anteriorly, the short, but stout centroprezygapophyseal lamina (cprl) and the prezygodiapophyseal lamina border a transversely narrow, triangular prezygapophyseal centrodiapophyseal fossa of the transverse processes. On the posterior side of the transverse processes, a short posterior centrodiapophyseal lamina (pcdl) is present. In NHMUK PV R 16427, this lamina is developed only as a sharply defined ridge that extends from the posterior border of the transverse process in a gently concave arch first posterodorsally and then posteroventrally and ends on the lateral side of the neural arch pedicle some one-fourth of the length of the latter anterior to its posterior margin. In CMN 50791, the lamina is slightly better developed and extends from the transverse process traight posteriorly to end on the base of the neural arch pedicle a short way anterior to the posterior margin of the latter. In both cases, this lamina defines a deep posterior fossa underneath the transverse process. A true postzygodiapophyseal lamina (podl) is absent in both neural arches, but there is a low, broad ridge that curves anteroventrally from the lateral margin of the postzygapophysis that corresponds to this lamina. This ridge fades approximately halfway to the transverse process into the lateral side of the neural arch in NHMUK PV R 16427, whereas it reaches the posterior margin of the process as a slight lateral swelling in CMN 50791, thus defining a broad, triangular, but very shallow postzygapophyseal–centrodiapophyseal fossa (pocdf). The prezygapophyses project far anteriorly in both specimens, with their articular surfaces completely extending beyond the anterior end of the centrum in CMN 50791. In both neural arches, the prezygapophyses are placed well lateral to the neural canal, but their angle of divergence is quite different. In NHMUK PV R 16427, both prezygapophyses diverge in an angle of approximately 90°, whereas the divergence is considerably narrower, at c. 65° in CMN 50791. The articular surfaces of the prezygapophyses are oval in outline, being longer than wide. They are slightly wider posteriorly in CMN 50791 and wider anteriorly in NHMUK PV R 16427. The facets face dorsomedially, and stand at an angle of approximately 130° towards each other in both specimens in anterior view. NHMUK PV R 16427 lacks a well-defined interprezygapophyseal laminae; the prezygapophyses are connected to each other anterior to the neural spine by a broad ridge, rather than a lamina. CMN 50791 bears two small flanges in front of the neural spine that project from the medial surface of each prezygapophysis over the opening of the neural canal and meet in an open suture. Centroprezygapophyseal fossae are poorly developed in both neural arches; the space between the centroprezygapophyseal lamina, the medial rim of the prezygapophysis and the rim of the neural canal is only very slightly concave, quite unlike the deep and well-defined fossae seen in many theropods in this area, including several specimens of indeterminate spinosaurids (see below). The postzygapophyses are long and narrow in both CMN 50791 and NHMUK PV R 16427. In the former, they overhang the centrum posteriorly for about half the length of their articular surfaces. As the centrum is not preserved, nothing can be said about a possible overhang of the postzygapophyses in NHMUK PV R 16427, but the end of the postzygapophyses are only slightly posterior to the posterior tip of the neural spine, whereas they protrude far posterior from the spine in CMN 50791. The articular facets are oval in outline, being longer than wide, and stand at an angle of slightly more than 110° towards each other. Epipophyses are present on the dorsal surfaces of the postzygapophyses and are situated at the medial side of the latter. They are developed as robust, laterally inclined ridges with bluntly rounded posterior ends that slightly overhang the postzygapophysis posteriorly in NHMUK PV R 16427. In CMN 50791 the epipophyseal ridges are lower, more erect and stand in continuation of the spinopostzygapophyseal laminae. They taper posteriorly and end just above the posterior end of the zygapophyses. The epipophyses in these vertebrae are generally not as strongly developed as in Spinosaurus aegyptiacus (Stromer, 1915) and material we consider to represent a spinosaurid from Morocco, for which a generic classification cannot currently be made (BSPG 2006 I 57, CMN 41768, CMN 50790). A weakly developed laterodorsal edge extends anteriorly from the epipophyses over the lateral surface of the neural canal. This edge, which corresponds in position to the prezygoepipophyseal lamina in other theropods, is better developed in NHMUK PV R 16427, but does not reach the prezygapophysis anteriorly. In NHMUK PV R 16427, the neural spine has a weak posterodorsal inclination. The neural spine is low in NHMUK PV R 16427, and only minor portions in the posterior part seem to be missing due to breakage. The neural spine is anterodorsally elongate, and its edge is thinnest in its mid-part. It has an unusual shape, its anterior half being especially low (only about half as high as the neural arch excluding the spine), with a straight dorsal margin, whereas the posterior half raises posterodorsally. The anterior margin of the neural spine is slightly thickened and has a slightly depressed anterior facing surface that seems to be a ligament groove. In this groove, parts of an ossified ligament attachment remain as a low, longitudinal ridge. Posteriorly, the spine broadens transversely, and there seems to have been a robust dorsal projection, which is broken off. CMN 50791 also shows an anterior facing groove in the lower part of the neural spine, which is laterally bound by spinoprezygapophyseal laminae (sprl) and also represents a ligament groove. CMN 50791 has an upright, rather elongate, transversely narrow and thus blade like neural spine, the dorsal end of which is broken off. The posterior margin of the neural spine is flanked by right and left spinopostzygapophyseal laminae (spol). Between the laminae, a spinopostzygapophyseal fossa (spof) covers the posterior aspect of the spine. The fossa is narrow over its entire length in CMN 50791, but expands transversely between the postzygapophyses in NHMUK PV R 16427, and is also deepest in this area. The ventromedial aspects of the postzygapophyses have flange like medial laminae, which in some Sigilmassasaurus specimens partly close the neural canal dorsally (or the spof ventrally). In NHMUK PV R 16427, these flanges meet and appear to form an interpostzygapophyseal lamina. However, although the flanges meet in the midline, they are not fused; there is a clear suture between right and left flange. CMN 50791 also exhibits the interpostzygapophyseal lamina, but the flanges are fused. The absolute positioning of these four elements is problematic, especially since only the type vertebra retains both centrum and neural arch. The most anterior element of these specimens is NHMUK PV R 16427. Several lines of evidence indicate that it is more anteriorly positioned than CMN 50791, including the better developed epipophyses, the more strongly diverging prezygapophyses, the shorter postzygapophyses, the anteroposteriorly shorter base of the transverse processes, and the weakly developed lateral lamination (see e.g., Charig & Milner, 1997). Furthermore, the neural spine shows a conspicuous step, with a rectangular anterior portion and a further dorsally expanded posterior part. This morphology is also found in an anterior mid-cervical (probably C4) of Baryonyx (Charig & Milner, 1997): Fig. 20C; though these authors identified the element as C5) and in C4–C6 of Ichthyovenator (BK10-18 to BK10-20). Thus, we tentatively identify this neural arch as C4. Nevertheless, the general similarity between NHMUK PV R 16427 and CMN 50791 indicate that they represent the same taxon. Characters supporting this hypothesis are the weakly developed epipophyses in both elements and an unusual arrangement of the laminae on the anterior end of the neural arch. In Baryonyx (NHMUK PV R 9951; Charig & Milner, 1997) and Ichthyovenator (BK 10-18, BK 10-21), the centroprezygapophyseal lamina is short and laterodorsally directed and meets the prezygodiapophyseal lamina from ventral in an almost right angle; together with the intraprezygapophyseal lamina these two laminae thus define the lateroventral, lateral, and dorsal borders of the centroprezygapophyseal fossa. In NHMUK PV R 16427 and CMN 50791, the centroprezygapophyseal lamina is less laterally directed and joins the prezygodiapophyseal lamina in a sharp angle to form a robust joint lamina that meets the prezygapophysis from ventral. Since the intraprezygapophyseal lamina is furthermore reduced to stout, low ridges, this very robust prezygapophyseal stalk lacks a clearly defined centroprezygapophyseal fossa. Some features, such as the unfused postzygapophyseal flanges, suggest that the specimen NHMUK PV R 16427 represents a younger individual than CMN 50791. This is also supported by the fact that the neural arch is isolated from its centrum, because separation of arch and centrum does not seem to be due to breakage. CMN 50791 probably represents C6 (though an identification as C7 cannot be completely excluded). This interpretation is supported by the relative elongation of the vertebral centrum, with the ventral length-posterior height ratio (length measurements excluding anterior condyles) being approximately 1.45, which is very similar to C6 of Ichthyovenator. In contrast, the fifth cervical is considerably shorter (ratio of c. 1.05) and the seventh cervical relatively longer (c. 1.75) in the latter taxon. Further support comes from the lateral neural arch lamination. In Ichthyovenator, C6 lacks a postzygodiapophyseal lamina, and there is only a slight lateral swelling that extends from the anterior rim of the postzygapophysis anteroventrally and ends on the neural arch above the posterior half of the transverse process. In contrast, the swelling is more strongly developed in C7 and extends to the posterior end of the transverse process. CMN 50791 corresponds to the situation in C6. As for the isolated centra BSPG 2011 I 117 and 118, the former corresponds very well to the morphology seen in the centrum of CMN 50791 and might thus represent the same vertebral position. The less pronounced ventral keel and the stronger offset of the articular facets in BSPG 2011 I 118 indicate that this centrum, although larger in overall size than BSPG 2011 I 117, represents a more anterior element. Thus, a positon as C5 seems likely.

Posterior cervical vertebrae In most posterior cervical vertebrae, with the exception of BSPG 2006 I 56 (see below), the width of the articular facets exceeds both the height and length of the centra, and transverse processes are elongate, stout and ventrally inclined. They become elevated progressively in more posterior positions, but without reaching a horizontal orientation, as it is the case in dorsal vertebrae. Posterior cervical vertebrae are very similar to the ‘typical’ Sigilmassasaurus morphology, although the holotype of S. brevicollis is most probably a first dorsal vertebra (see below). Here, we recognize seven vertebrae as posterior cervicals: BSPG 2006 I 53, BSPG 2006 I 56, BSPG 2011 I 115, BSPG 2011 I 116, CMN 41774, CMN 41790, and CMN 41856. As noted above, the following descriptions will mainly be based on the new specimens from the collections of the BSPG; for detailed descriptions of the CMN specimens see McFeeters et al. (2013). BSPG 2006 I 53 is a large partial vertebra, which preserves most of the centrum but the distal part of its left parapophysis. Parts of the neural arch are preserved, such as the left prezygapophysis, and the medial part of its transverse process. BSPG 2006 I 56 preserves the right pre- and postzygapophyses and the base of the right transverse process. The neural spine is broken but partly preserved, but all processes of the left side of the neural arch are broken away. There is a large piece of bone missing on the right side of the dorsal part of the anterior condyle. A mark with a smooth surface and squared outline penetrates the bone in this area. The area of broken bone is lighter in color than other broken parts, which suggest the damage is relatively fresh. Overall, the morphology of the mark is consistent with the size and shape of a small chisel or hammer, and we propose the damage occurred during excavation of the specimen. This condition is unlike the mark on the anterior condyle of BSPG 2011 I 118 (see above), which seems to be bite mark. Another chisel-mark can be seen in the floor of the pneumatic invasion connected with the left central pneumatic foramen of the same specimen. Here, a squared, smooth-walled mark with decreasing depth is evident. BSPG 2011 I 115 is virtually complete, with only half of the right prezygapophysis and the tip of the right postzygapophysis being missing. However, this specimen also shows a chisel mark; it has a squared hole virtually identical in appearance to the one described for BSPG 2006 I 56. The abundance of anthropogenic damage to the specimens described in this study shows that specimens often seem to be excavated without appropriate caution. In BSPG 2011 I 116, the right prezygapophysis is eroded and most of the left transverse process is missing. CMN 41774 lacks its left postzygapophysis; CMN 41790 preserves only parts of the left transverse process, left prezygapophysis and neural spine. CMN 41856 lacks both postzygapophyses and most of its spine. We can tentatively identifiy the positions of these vertebrae mainly on the morphology of the centrum (especially the development of the ventral keel) and the orientation of the transverse processes, and in comparison with the complete cervical vertebral column of Ichthyovenator (BK10-16–BK10-24). BSPG 2006 I 56 is the most anterior of these posterior cervicals, and would thus correspond to C8, followed by BSPG 2011 I 115, CMN 41774 and CMN 41856, which represent C9. BSPG 2006 I 53 and BSPG 2011 I 116 are ultimate cervicals (C10). CMN 41790 can clearly also be referred to Sigilmassasurus (McFeeters et al., 2013), but its morphology does not correspond exactly to any of these other vertebrae, possibly due to restorations of this element carried out prior to its purchase by the CMN (B McFeeters, pers. obs., 2013). This element is most similar to BSPG 2006 I 56 and BSPG 2011 I 115 and might thus also represent a vertebra from the transition between the mid-cervicals to the posterior cervicals. BSPG 2006 I 56 is an important specimen, as it shows transitional features between the mid-cervical vertebrae described above, and the ‘typical’ Sigilmassasaurus brevicollis morphology observed in the holotype (CMN 41857) and referred material (Fig. 5). The specimen is strongly opisthocoelous, with the anterior articular facet exhibiting a rimmed edge, as it is found in many megalosauroids (Carrano, Benson & Sampson, 2012). The posterior articular facet is reniform. As in other ‘typical’ Sigilmassasaurus vertebrae, the anterior condyle bears a median tuberosity and intercentral articulations are wider than high (the width–height ratio of the anterior facet is 1.67, the one of the posterior facet is 1.52), but in contrast to these the centrum is longer than it is wide. The width–height ratio is intermediate between proposed mid-cervical vertebrae like BSPG 2011 I 118 with a posterior width–height ratio of 1.26, and ‘typical’ Sigilmassasaurus vertebrae like BSPG 2006 I 54 with a posterior width–height ratio of 1.71. The length–width ratio is also intermediate (BSPG 2011 I 118: 1.83; BSPG 2006 I 56: 1.14; BSPG 2011 I 116: 0.8; ratios based on dorsal central length including the anterior condyle and width of the posterior articular facets). The posterior articular end is set at an angle of slightly less than 90° towards the long axis of the centrum, so that the latter slopes anterodorsally when the posterior end is oriented vertically. Furthermore, the dorsal side of the centrum is slightly shorter than the ventral side, so that the anterior articular surface is angled slightly dorsally in comparison to the posterior end. The parapophyses are massive processes as in both the holotypes of Sp. maroccanus and S. brevicollis, but more lateroventrally directed than in the former. The ventral keel is more pronounced than in mid-cervical vertebrae, but less prominent than in ‘typical’ Sigilmassasaurus vertebrae. The keel is similar in shape and extent to the structure found in BSPG 2011 I 117, but more sharply defined. Importantly, the keel fades posteriorly into a transversely broad and ventrally elevated triangular platform, as in the proposed mid-cervical vertebrae, including the holotype of Sp. maroccanus (CMN 50791). The triangular platform is less prominent, and intermediate in size between mid-cervical vertebrae and posterior cervicals, as for instance BSPG 2011 I 116. In contrast to the mid-cervicals and many of the other posterior cervicals, this vertebra lacks the intense rugose pattering on the platform and along the anterior rim; since this vertebra is rather small in comparison with most of the elements dealt with here, this is probably due to immaturity. The ventral side lateral to the keel faces mainly ventrally, in contrast to the gently dorsolaterally sloping ventral side in the mid-cervical vertebrae. In lateral view, the ventral side is straight, which also contrasts with the mid-cervicals, in which the ventral margin is anteroposteriorly concave anterior to the posterior platform. Due to the shortening of the centrum and the resulting relative elongation of the parapophysis, the lateral pneumatic foramen is placed dorsal to the latter, rather than posterodorsal, as in the mid-cervicals. The pneumatic foramina are large and anteroposteriorly elongate, less so than in the mid-cervicals, yet more elongate than in more posteriorly positioned specimens. The foramina are oval in outline, with less angled anterior end posterior margins, and lead into large internal cavities, as in the mid-cervicals. Posteroventrally, the pneumatic foramen is bordered by a stout, rounded ridge extending from the parapophysis posterodorsally. This ridge continues on the lateroventral side of the centrum as a rounded edge that separates the lateral from the ventral side, very similar in position and orientation to that seen in mid-cervicals, but less marked. The lateral bulge above the pneumatic foramen and the corresponding dorsal depression between this bulge and the neurocentral suture are also present, but relatively smaller than in the mid-cervicals. Although the neural arch of this vertebra is preserved in articulation with the centrum, the neurocentral suture is open and clearly visible. The attachment of the neural arch is extensive and reaches down to almost half the height of the lateral side of the centrum. As in the mid-cervical vertebrae, the left and right pedicles meet in the midline at the floor of the neural canal, though the contact is relatively more anterior than in the former. Posteriorly, there is a large, posteriorly opening triangular area between the pedicles that houses three larger foramina in its anterior part, similar to the situation in BSPG 2011 I 117. The neural canal is very large, being slightly wider than high. The relatively steeply ventrally inclined remains of the broken transverse processes are consistent with the interpretation that BSPG 2006 I 56 occupies the anterior-most position of all vertebrae considered in this section and further confirm its intermediate position between the mid-cervical vertebra that represents the holotype of Sp. maroccanus and the unambiguously posterior cervical position of the other vertebrae. The broken bases of the transverse processes show that a single, very robust centrodiapophyseal lamina was present on each side, as in other Sigilmassasaurus specimens. This lamina extends ventrolaterally from the base of the neural arch to the ventral side of the transverse process and is broad and anteroposteriorly convex ventrally, without any indication of a separation of an anterior and posterior centrodiapophyseal lamina and thus without any centrodiapophyseal fossa. The prezygapophyses are widely spaced, strongly divergent, and not interconnected by an interprezygapophyseal lamina. They sit on anterodorsally expanded stalks and are elongate oval in outline, their anterior end being approximately flush with the anterior margin of the anterior convexity of the centrum. The articular surface is very slightly convex anteroposteriorly. Due to the shortness of the neural arch, the posterolateral rim of the prezygapophyses is placed at the level of the anterior end of the neural spine and overhangs the anterior margin of the transverse process; it forms a posterolaterally expanded lip on the neural arch. Prezygapophyseal stalks are anteriorly broad, have a laterally positioned cprl and lack centroprezygapophyseal fossae, as in both the holotypes of Sp. maroccanus and S. brevicollis. The centroprezygapophyseal lamina meets the robust prezygodiapophyseal lamina approximately half way between the centrum and the prezygapophysis, and together the two laminae form the robust stalk, which meets the prezygapophysis from lateroventral. A small, but deep, cone-shaped recess is present between the two laminae underneath the anterior side of the transverse process and opens anterolateroventrally. Posteriorly, the transverse process has a sharp posterior margin that corresponds to the lower part of the postzygodiapophyseal lamina, which is otherwise interrupted between the lateral margin of the postzygapophysis and this margin. Together with the centrodiapophyseal lamina and the short and laterally oriented centropostzygapophyseal lamina, this margin defines an oval, very deep recess below the posterior base of the transverse process, which opens posterolaterally. The postzygapophyses are large and anteroposteriorly elongate. The articular facet is slightly concave anteroposteriorly and overhangs the centrum posteriorly for approximately half its length. The facet has a straight to slightly concave medial margin, a strongly convex anterolateral margin, and an angular posterior margin, being pointed posteriorly in its medial third. Epipophyses are missing, as in the holotype of S. brevicollis, but the base of the spinopostzygapophyseal lamina on the dorsal surface of the postzygapophysis has a slightly swollen appearance, which is interpreted as the remnant of reduced epipophyses. The postzygapophyses lack an interpostzygapophyseal lamina, but small, medially projecting flanges are present at the base of their stalks, as observed also in posterior cervical and cervicodorsal vertebrae. A prezygoepipophyseal lamina or ridge is not present, but the area between the lateral margins of the pre- and postzygapophyses is dorsoventrally convex, whereas there is a very shallow depression on the dorsolateral surface of the base of the transverse process and a smaller, more marked depression dosally between the neural spine, the spinopostzygapophyseal lamina and the roof of the neural arch. The neural spine is anteroposteriorly very short and spike-like, as seen in many Sigilmassasaurus specimens. However, the spine generally seems to be subject to relatively great positional variance (see neural spine descriptions across axial positions). No spinoprezygapophyseal laminae are present, but the anterolateral margin of the spine is connected to the medial side of the prezygapophyses by a stout, diverging edge, resulting in a broad, anteriorly facing, triangular surface at the base of the spine. No medial ridge for the attachment of the interspinal ligament is present in this area, though this might be due to poor preservation. Posteriorly, the spinopostzygapophyseal laminae are well-developed and stout, but low, extending almost horizontally from the dorsal surface of the postzygapophysis anteromedially to the posterolateral margin of the neural spine. Between the laminae, a low ridge extends over the posterior surface of the spine, but there is no deep spinopostzygapophyseal fossa, which is at least partially be due to the lack of an interpostzygapophyseal lamina. In summary, there is substantial anatomical evidence that BSPG 2006 I 56 is a specimen in transition between the elongate morphology of proposed mid-cervicals of Sigilmassasaurus brevicollis, and the extreme broad appearance of posterior cervicals. The trends described and the transitional morphology of BSPG 2006 I 56 are not particularly unusual for theropod vertebrae. Several other taxa go through major morphological transitions throughout the axial and especially the cervical series, as for example Baryonyx and Ichthyovenator (see discussion). Posterior cervical vertebrae of Sigilmassasaurus are strongly opisthocoelous, and a conspicuous rim surrounds the articular facets in these vertebrae. The anterior articular facet has a distinct centrally placed, bump-like elevation, the anterior median tuberosity. The median tuberosity is expressed to a different degree in the specimens; in BSPG 2006 I 53 and BSPG 2006 I 56 it is very pronounced, while it is more subtle in BSPG 2011 I 115, where it is best seen in ventral view. All of these vertebrae show very broad intercentral articulations, with width–height ratios of the anterior articular facets exceeding 1.7. The vertebrae are also wider than they are long. In BSPG 2006 I 53, the width of the anterior articular facet exceeds the length of the centrum (without the anterior condyle) by 72.5%. The centrum is slightly anterodorsally angled if the posterior articular end is held vertically in C9 (e.g., BSPG 2011 I 115, Fig. 6), but only very slightly so in the last cervical vertebra. In all vertebrae, the dorsal side of the vertebral centrum is slightly shorter than the ventral side, so that the anterior facet is inclined anterodorsally to similar, but slightly variable extent across the specimens, which we account to different axial positions within the posterior cervical series and individual variation. The posterior articular facets of the centra are strongly concave and reniform in outline. The edge of the posterior articular facet is straight in ventral view, but dorsally the rim slightly curves towards the opening of the neural canal. This, again, is variable in its extent across specimens. Well-developed ventral keels are present in all posterior cervical vertebrae and expand posteriorly into a small triangular platform. There is a progressive change from less prominent keels in more anterior specimens (such as BSPG 2006 I 56) to very pronounced structures in more posterior elements, although there also seems to be some individual variation in the development of this structure. BSPG 2011 I 115, CMN 41774 and CMN 41856 have low but distinct keels with a straight ventral edge. In BSPG 2006 I 115, the keel is positioned slightly off the midline and placed more on the right side of the specimen. Anteriorly, the keel becomes progressively lower and merges into the broad, rugose area between the parapophyses, which are notably ventrolaterally directed in these vertebrae. In anterior view, the keels might be visible as small, triangular ventral prominences. The probable last cervical vertebrae BSPG 2006 I 53 (Fig. 7) and 2011 I 116 (Fig. 8) have relatively high keels that become deeper anteriorly, but lack a distinct hypapophysis. Instead, the keel lowers more or less abruptly between the parapophyses, which, in these vertebrae are connected by a thick, rounded transverse ridge anteriorly. In these specimens, the keel is visible in anterior view and extends ventrally to or even beyond the level of the ventral margin of the parapophyses. There is some variation in the development of the ventral keel in these vertebrae: whereas it is deeper in BSPG 2011 I 116, it is more robust and becomes especially robust anteriorly in the slightly larger BSPG 2006 I 53. Likewise, the ventral edge of the keel is straight in lateral view in BSPG 2006 I 53, but slightly convex in BSPG 2011 I 116. Figure 8: BSPG 2011 I 116, posterior cervical vertebra (C10) of Sigilmassasaurus brevicollis. (A) posterior view; (B) anterior view; (C) ventral view; (D) dorsal view; (E) right lateral view; (F) left lateral view. Abbreviations: apf, anterior pneumatic foramen of the prezygodiapophyseal fossa; at, anterior medial tuberosity; cpf, central pneumatic foramen; dp, diapophysis; hyp, hypapophysis; k, keel; ns, neural spine; poz, postzygapophysis; pp, parapophysis; ppf, posterior pneumatic foramen of the postzygodiapophyseal fossa; prz, prezygapophysis; tp, transverse process. Scale bar equals 5 cm. Figure 9: BSPG 2006 I 54, anterior dorsal vertebra (D1) of Sigilmassasaurus brevicollis. (A) posterior view; (B) anterior view; (C) ventral view; (D) dorsal view; (E) right lateral view; (F) left lateral view. Abbreviations: at, anterior medial tuberosity; cpf, central pneumatic foramen; dp, diapophysis; hyp, hypapophysis; k, keel; ns, neural spine; poz, postzygapophysis; pp, parapophysis; ppf, posterior pneumatic foramen of the postzygodiapophyseal fossa; prz, prezygapophysis; tp, transverse process. Scale bar equals 5 cm. Figure 10: BSPG 2006 I 55, anterior dorsal vertebra (D1) of Sigilmassasaurus brevicollis. (A) posterior view; (B) anterior view; (C) ventral view; (D) dorsal view; (E) right lateral view; (F) left lateral view. Abbreviations: apf, anterior pneumatic foramen of the prezygodiapophyseal fossa; at, anterior medial tuberosity; cpf, central pneumatic foramen; dp, diapophysis; hyp, hypapophysis; k, keel; ns, neural spine; poz, postzygapophysis; pp, parapophysis; ppf, posterior pneumatic foramen of the postzygodiapophyseal fossa; prz, prezygapophysis; tp, transverse process. Scale bar equals 5 cm. Figure 11: NHMUK PV R 16434, anterior dorsal vertebra (D1) of Sigilmassasaurus brevicollis. (A) posterior view; (B) anterior view; (C) ventral view; (D) dorsal view; (E) right lateral view; (F) left lateral view. Abbreviations: at, anterior medial tuberosity; dp, diapophysis; k, keel; ns, neural spine; poz, postzygapophysis; pp, parapophysis; ppf, posterior pneumatic foramen of the postzygodiapophyseal fossa; prz, prezygapophysis; tp, transverse process. Scale bar equals 5 cm. A broad but shallow fossa is found on the ventral side of the centrum, and expands between the ventral keel medially, the parapophysis and transverse ridge anterolaterally, and the posterior connection of the parapophysis posterolaterally. The fossa is deeply excavated in more posterior positioned vertebrae, and this is emphasized by the high ventral keel. The depth decreases with lower keels in anterior-more posterior cervicals. The parapophyses are robust processes that are situated on the anteroventral part of lateral side of the centrum and project ventrolaterally. Their anterior surface is confluent with the rim around the anterior facet. The extent to which the parapophyses point ventrolaterally differs with the different vertebral positions. The strongest ventrolateral orientation is found in the possible C9, such as BSPG 2011 I 115, in which the divergence of the parapophyses is slightly less than 90°, but also in the CMN specimens (McFeeters et al., 2013). In the probably ultimate cervical BSPG 2011 I 116, the angle of divergence between the parapophyses is slightly wider at 95–100°. The parapophyses are relatively long and project further than for example in Baryonyx (Charig & Milner, 1997), but not further than in Allosaurus (e.g., UMNH VP 8358, 8365, 8488, 8489, 10192; all posterior cervical vertebrae). Parapophyseal articular facets are generally concave, both anteroposteriorly and dorsoventrally. The concavity is more pronounced in C9 than in C10. The outline of the parapophyseal facets is oval to triangular in the presumed C9. One edge of the triangle points posteriorly and continues onto the centrum as a thick ridge that borders the lateral pneumatic foramen ventrally. In these vertebrae, the articular facets of the parapophyses are longer anteroposteriorly than high dorsoventrally. BSPG 2011 I 116 shows an intermediate state in the outline of the facet between the more triangular shape seen in BSPG 2011 I 115 and the high oval shape in the first dorsal vertebra, in that the facet is generally oval, but has a slightly posterodorsally expanded corner. As in the more anterior vertebrae, the posterior end of the parapophysis is connected to the centrum by a broad ridge, from which a rounded edge separating the lateral from the ventral side extends posteriorly. This edge becomes broader and more rounded and thus less marked in more posterior elements. A single, undivided lateral pneumatic foramen opens directly above the parapophysis in all specimens. Foramina can be symmetrically developed, as in BSPG 2011 I 116, or asymmetrically as in BSPG 2011 I 115, in which the right foramen is much smaller in size. In most vertebrae, the pneumatic foramina are large and oval to triangular (pointed posteriorly) in outline, but BSPG 2006 I 53 has only a small, slit-like foramen on the right side and a foramen that is no larger than a neurovascular foramen on the left side. Features related to skeletal pneumaticity seem to be highly variable on an intraspecific level. The number of foramina is for example known to vary between individuals of Acrocanthosaurus (Harris, 1998) and within the cervical vertebral column in Aerosteon Sereno et al., 2008. The transition from an anteroposteriorly elongate, oval shape to a more oval to subcircular shape can be observed in other megalosauroid theropods, such as Eustreptospondylus (Sadleir, Barrett & Powell, 2008), as well. A lateral bulge that runs parallel and ventral to the neurocentral suture is only present in BSPG 2006 I 53 among the posterior cervical vertebrae. This bulge divides the lateral depression on the centrum into a dorsal part on or above the neurocentral suture, and a ventral part that is more or less entirely occupied by the lateral pneumatic foramen. McFeeters et al. (2013) noticed the same feature on the holotype of Sigilmassasaurus brevicollis and termed it lateral bulge of the centrum. It is well-developed and marked by an especially deep dorsal depression on the neurocentral suture in BSPG 2006 I 53. In the other vertebra that probably occupies the same vertebral position, BSPG 2011 I 116, this bulge is only hinted at, and no dorsal depression is present. The neurocentral suture is well visible and not fully closed in even the largest specimens; none of the specimens shows even partial fusion and obliteration of the suture. In all specimens, the neurocentral suture reaches far onto the lateral side of the centrum to about half of its height (excluding the ventral keel). The neural arch has two pedicels that enclose the neural canal. As in the more anterior vertebrae, the pedicles meet each other in the midline of the neural canal anteriorly, thus forming most of the anterior part of the floor of the neural canal. The posterior part of the floor of the neural canal between the ventromedial borders of the neural arch pedicles is penetrated by several basivertebral foramina, which are mostly aligned in a small, elongate, trench-like depression. The neural canal is large and wider than high in all specimens. The shape of the neural canal is oval in most specimens, though its dorsal margin is convex in some vertebrae, most notably 2011 I 116, resulting in a heart-shaped outline in anterior view. The transverse processes merge to the lateral sides of the neural arch directly above the centrum. They are directed ventrolaterally at an angle of approximate 40–55° in the more anterior posterior cervicals BSPG 2006 I 56, BSPG 2011 I 115, CMN 41774, CMN 41790, and CMN 41856. This tilt decreases to an angle of c. 30° in the ultimate cervical BSPG 2011 I 116. Toward their distal ends, the transverse processes are gently ventrally curved, and their dorsal surface is slightly tilted anteriorly. Distally they expand anteroposteriorly, best seen in dorsal or ventral view. Whereas the posterior margin of the transverse process is straight, but slightly posterolaterally directed, this expansion is mainly defined by a rounded expansion of the anterior margin. This rounded anterior expansion is most marked in the more anterior vertebrae (e.g., BSPG 2011 I 115), but becomes less notable in the probable C10 BSPG 2011 I 116. The dorsal length of the transverse process is longer than the ventral length, resulting in a ventral to ventrolateral orientation of the diapophyses. In specimens that preserve the diapophyses, the facets show a roughly triangular outline and are flat. The transverse processes are massive, and neural arch lamination seems to be largely reduced in Sigilmassasaurus. The prezygodiapophyseal laminae (prdl) and postzygodiapophyseal laminae (podl) are developed as robust, transversely oriented ridges, which form the anterodorsal and posterodorsal margin of the transverse process. They thus delimit the dorsal surface of the transverse processes, which is flat and table-like. The prezygodiapophyseal lamina joins the stout centroprezygapophyseal lamina at the anterior base of the transverse process in all vertebrae, and the joint laminae meet the central part of the ventral surface of the prezygapophysis from ventrolateral. The postzygodiapophyseal lamina shows somewhat more variation. In the anteriormost of these vertebrae, such as BSPG 2006 I 56 and BSPG 2011 I 115, there is only a small swelling on the lateral side of the neural arch anteroventral to the postzygapophysis, which is discontinuous with the ridge that forms the posterodorsal margin of the transverse process. In the probable ultimate cervical BSPG 2011 I 116, this swelling is expanded into a lateral ridge that connects the postzygapophysis with the posterodorsal margin of the transverse process. Both the lateral extensions of the prezygodiapophyseal and postzygodiapophyseal lamiane become lower distally, where they merge into the massive articular end of the diapophysis. A cross-section of the middle part of the transverse process would thus result in a “T”-shape, due to the medially narrow ventral ridge and the wide dorsal surface of the transverse process. A prominent ridge extends from the ventral side of the transverse processes to the lateral side of the vertebrae, and connects to the centrum directly above the neurocentral suture. This ridge represents the joint centrodiapophyseal laminae. In the posterior cervicals, the ventral ridge remains unbifurcated as a single “centrodiapophyseal lamina,” which we consider to be an autapomorphy of Sigilmassasaurus, as it is not present in other spinosaurids, such as Baryonyx (Charig & Milner, 1997) and Ichthyovenator. In the more anterior vertebrae, such as BSPG 2011 I 115, the ventral side of this ridge is convex, but in BSPG 2011 I 116, it is almost flat ventrally. There is a stout posterior ridge that extends from the proximal part of the central ventral side of the transverse process posteriorly to join the pedicle of the neural arch at the level of the dorsal margin of the centrum; this ridge probably corresponds to the posterior centrodiapophyseal lamina. In all specimens, the anterior sides of the transverse processes display prezygapophyseal centrodiapophyseal fossae (prcdf), which are open ventrally in their lateral part, being bound posteriorly by the joint centrodiapophyseal laminae, dorsally by the prdl, and anteriorly by the centroprezygapophyseal lamina (cprl). The centroprezygapophyseal lamina, which usually connects the prezygapophysis with the rim of the anterior articular facet (Wilson, 1999), is more laterally than anteriorly directed in Sigilmassasaurus, as already seen in mid-cervicals like CMN 50791. The centroprezygapophyseal lamina is placed slightly posterior to the anterior rim of the centrum and extends on the lateral aspect of the pedicle of the prezygapophysis and eventually curves onto the transverse process, where it meets the prezygodiapophyseal lamina. The prcdf extends over most of the anterior side of the transverse process below the lateral extension of the prezygodiapophyseal lamina and becomes more distinct medially. At the base of the transverse process, it leads into a depression that penetrates the lateral side of the prezygapophyseal pedicle, and which is developed as a deep foramen in several specimens. The foramina are slit-like in most specimens and of various sizes. There is considerable variation both in the size and depth of these foramina, sometimes from one side of the vertebra to the other. This variation is apparently not ontogenetic, as in BSPG 2006 I 56, interestingly one of the smallest vertebrae, the foramina are largest. The foramina are hidden by the centroprezygapophyseal lamina in anterior view. On the posterior side of the transverse processes, postzygapophyseal centrodiapophyseal fossae (pocdf) are present. The pocdf expands over the medial three-fourth of the posterior side of the transverse processes. A medial part, on the neural arch, and a lateral part, on the transverse process, can be distinguished and is separated by the posterior pneumatic foramen of the transverse process. The medial part is a gentle and shallow depression anterolateral to the base of the postzygapophysis. It is variably developed in the posterior cervicals: it is clearly distinct as a depression in BSPG 2006 I 116, CMN 41774, and CMN 41856, but in BSPG 2007 I 56, the area between the posterior foramen and the base of the postzygapophysis is flat and not or only very slightly depressed. In BSPG 2011 I 115, a narrow and very shallow depression is present on the right side, but the left side is flat. Whereas the fossa, or the flat area anterolateral to the postzygapophysis faces posterolaterally in the more anterior vertebrae, it faces posteriorly and is largest and deepest in the last cervical, BSPG 2011 I 116. The depression on the posterior side of the transverse process is generally better developed and becomes more marked medially towards the opening of the pneumatic foramen. In Sigilmassasaurus, the pneumatic invasions of the transverse processes seem to be generally larger on the posterior side than anteriorly. The foramen is bordered dorsally by the continuation of the postzygadiapophyseal lamina. Medially, a ventrally flexing branch of the postzygodiapophyseal lamina curves around back onto the transverse process to border the medially penetrating posterior foramen from all but the lateral side. The foramina are usually large and deep, penetrating the posterior base of the transverse process from posterolateral. In BSPG 2006 I 53, the partial breakage of the transverse processes allows detailed study of the pneumatic features of the transverse processes. On the right side, anterior and posterior foramina of the transverse processes lead into a medial chamber that invades the ventral part of the right neural arch pedicle. The right and left cavities connect internally to a single large chamber. On the left side, however, both cavities remain separated by a thin septum. Such a septum is clearly not developed on the right side, as the medial floor of the connected pneumatic cavity has a smooth texture. On the left side of BSPG 2006 I 53, the prezygapophyses is preserved, and no connection in the top of the chamber indicates any pneumatization of the prezygapophyses. Also, no channel opens toward the (missing) postzygapophysis, indicating that the latter was not pneumatized. A similar situation seems to be present in BSPG 2011 I 116, in which the anterior and posterior pneumatic recesses of the transverse process are confluent on the left, but apparently not on the right side. In all specimens, the prezygapophyses are widely spaced, being placed far lateral to the neural canal. They are generally developed as anterodorsally projecting processes. They are placed anterodorsal to the transverse process, overhanging the latter only with their anterior third. In all posterior cervicals with the exception of the most anterior element BSPG 2006 I 56, the anterior margin of the prezygapophysis is placed above the anterior end of the centrum, posterior to the anterior convexity of the centrum. In the other specimens, the prezygapophyses are either anteroposteriorly oval or roughly spade shaped, being wider posteriorly. More anterior vertebrae, such as BSPG 2006 I 56, BSPG 2011 I 115 and CMN 41774 have anteroposteriorly elongate, prezygapophyses that are considerably longer than wide. In the ultimate cervicals BSPG 2006 I 53 and BSPG 2011 I 116, the articular facets are relatively broader, and their posterior margin is straight. Exceptions are CMN 41856, a probably 9th cervical, in which the prezygapophyses are broad. All prezygapophyseal facets are dorsomedially exposed. The angle between the prezygapophyseal facets is approximately 115°–130°. The articular facets are very slightly flexed anteroposteriorly, and somewhat tilted posteriorly, obviously reflecting a notable upward bent of the neck at its base. Therefore, the posterior connections of the prezygapophyses to the table of the transverse processes are very short. There is no epipophyseal prezygapophyseal lamina (eprl). The prdl start anteriorly at the apex of the prezygapophyses, and run ventrolaterally towards the diapophyses. The prezygapophyseal pedicles display a large anteromedial surface, which is not excavated by prezygodiapophyseal fossae. The prezygapophyses lack interprezygapophyseal laminae, which McFeeters et al. (2013) considered an autapomorphic feature of Sigilmassasaurus, but which is also the case in Ichthyovenator (BK10-17–BK10-25). The postzygapophyses have a spoon-like shape, are slightly less widely spaced than the prezygapophyses, and project posteriorly beyond the level of the posterior articular facet, overhanging the latter for approximately half the length of their articular facets. They have a slightly concave facet with a posteroventral and lateral orientation. The postzygapophyses are anteromedially connected to the neural spine by robust spinopostzygapophyseal laminae. These laminae border a dorsoventrally high, trough-like spinopostzygapophyseal fossa laterally. The fossa is ventrally open, since an interpostzygapophyseal lamina is missing. However, the medial sides of the postzygapophyseal pedicles show thin, flange-like laminae that project into the interpostzygapophyseal space. These flanges are lost or at least partially broken in most specimens, although their bases are usually recognizable. BSPG 2011 I 115 is the only specimen that preserves what seems to be an entirely intact right flange. The flange is triangular, with straight medial and posterior margins that meet at an angle of 90°. As mid-cervical vertebrae seem to close the flanges to a continuous interpostzygapophyseal lamina (NHMUK PV R 16427 has closed flanges with a suture, CMN 50791 has a continuous interpostzygapophyseal lamina), this feature seems to be of positional relevance. None of the posterior cervicals bear epipophyses. However, the penultimate elements BSPG 2011 I 115 and CMN 41774 have a marked kink in the course of their spinopostzygapophyseal laminae. In dorsal view, the angle of divergence of the postzygapophyses notably increases posterior to the kink. Furthermore, the bone surface at the kink is slightly rugose, indicating the attachment of muscles or tendons. Therefore, the kinks might be the remnant of the epipophyses found in the mid-cervicals. In BSPG 2011 I 116, there is a notable depression on either side of the base of the neural spine, which has a rugose texture and might have served for as a ligament attachment site. This depression reaches anteriorly to approximately two thirds of the anteroposterior length of the base of the neural spine; its anterior border is especially well-defined. The neural spine is damaged or completely broken in all specimens. The preserved bases or partial spines show that the neural spine was an anteroposteriorly short, spiky process. The base of the spine is anteroposteriorly especially short, being approximately as long anteroposteriorly as wide transversely, in the more anterior posterior cervicals, such as BSPG 2006 I 56 and BSPG 2011 I 115. In the former, the spine seems to have been rather straight, whereas the base indicates a very slight posterodorsal inclination in the latter. In the last cervical BSPG 2011 I 116 the base of the neural spine is slightly longer anteroposteriorly, being 1.5 to two times as long as wide. Two spinoprezygapophyseal laminae (sprl) connect the neural spine to the medial aspect of the prezygapophyses. The laminae are generally poorly developed, and mainly marked as the edge separating the anterior from the lateral surface of the neural spine. The edges are least marked in the probable C9 (e.g., BSPG 2011 I 115). Because the prezygapophyses are situated far laterally in respect to the neural spine, the spinoprezygapophyseal laminae diverge from the apex ventrally and form a reverted “V.” The resulting anteriorly exposed, triangular area is medially parted by a prespinal lamina (prsl). The prespinal lamina is a low, but stout ridge that extends probably from the apex of the neural spine to its base above the opening of the neural canal. In some specimens, for example BSPG 2011 I 116, the prsl projects slightly ventrally beyond the dorsal margin of the neural canal and forms an overhanging tip, which results in a heart-shaped outline of the neural canal opening. To either side of the prsl, a shallow, longitudinal depression is present in the last cervical vertebrae.

Dorsal vertebrae The first dorsal vertebra of Sigilmassasaurus, represented by a total of four vertebrae in our sample (BSPG 2006 I 54, BSPG 2006 I 55, CMN 41857, NHMUK PV R 16434; Figs. 9–11), including the holotype of S. brevicollis, is notably similar to the posterior cervical vertebrae, up to a parapophysis that is placed on the anteroventral end of the centrum. This is in contrast to the vast majority of theropods, in which this process shows a marked dorsal shift in the first dorsal. Indeed, but for the comparison with the complete cervical column and first dorsal vertebra of Ichthyovenator (BK10-25), one could take these vertebrae for posterior cervicals. More posteriorly placed dorsal vertebrae of Sigilmassasaurus can be identified on the basis of progressively elevated parapophyseal positions, a regressed expression of the hypapophyses, sharp but low ventral keels, absence of lateral pneumatic foramina of the centrum in all but he most anterior elements, horizontal to slightly dorsally elevated and slightly posteriorly directed transverse processes, elongation of transverse processes, more elaborate transverse process lamination, anteroposteriorly elongate bases of the neural spine, and progressively more narrowly spaced pre- and postzygpophyses. We thus identify CMN 41858, NHMUK PV R 16435 and NHMUK PV R 16436 (Figs. 12 and 13; note that the holotype vertebra is adequately figured in McFeeters et al., 2013) as dorsal vertebrae posterior to D1, and BSPG 2013 I 95 (Fig. 14) and CMN 41850 as anterior dorsal vertebrae possibly belonging to Sigilmassasaurus (see below). While their dorsal positioning in the axial series can be determined following the above trends, several features support their referral to Sigilmassasaurus. NHMUK PV R 16436, NHMUK PV R 16435 especially, and the poorly preserved CMN 41858 closely resemble the posterior cervical and first dorsal vertebrae of Sigilmassaurus, so that there can be little doubt that they represent the same taxon. The latter specimen resembles the first dorsal vertebra slightly more in the morphology of its transverse process and neural spine and NHMUK PV R 16436 is very similar to this vertebra in all comparable characters, so that these elements might represent the second dorsal, whereas NHMUK PV R 16435 might be a third dorsal. BSPG 2013 I 95 and CMN 41850 are very similar to each other in their morphology, but differ markedly from the posterior cervicals or anteriormost dorsals of Sigilmassasaurus. These vertebrae lack autapomorphies of Sigilmassasaurus, which are all based on more anterior vertebral material. However, a tentative referral of these specimens to Sigilmassasaurus is supported by a suite of features shared between BSPG 2013 I 95 and CMN 41850 with Sigilmassasaurus, some of which are unusual for theropods but not exclusively present in Sigilmassasaurus. These include their notably wide and opisthocoelous anterior articular surface (while Allosaurus [SMA 0005, MOR 693], for instance, has greatly reduced anterior condyles in the anterior dorsal vertebrae and loses the opisthocoelous state completetly by the third dorsal vertebra,) the presence of a marked, concave ventral keel with a small anterior hypapophysis, and the presence of a subtle median tuberosity on the anterior condyle in BSPG 2013 I 95. Also, the neural spines of both vertebrae are not expanded at their base, as in “Spinosaurus B” but unlike in Spinosaurus aegyptiacus or Ichthyovenator (Stromer, 1931; Allain et al., 2012). The two vertebrae can be clearly assigned to an anterior dorsal position within the axial series of a large theropod, as they show several features indicative of such a position (see below). Notably, many features of their morphology fit well with expectations of anterior dorsal vertebrae of Sigilmassasaurus following vertebrae such as NHMUK PV R 16435. For example, the parapophyses of BSPG 2013 I 95 and CMN 41850 are slightly more dorsally positioned than in NHMUK PV R 16435, or the central pneumaticity is further reduced to a fossaeous depression on the lateral side of the centrum (see below). We therefore identify these vertebrae as more posterior anterior dorsal vertebrae likely pertaining to Sigilmassasaurus, with their difference from the anteriormost dorsals being due to differences in position within the vertebral column, and include them in this description for comparative reasons. We acknowledge that this referral is tentative at this stage, but feel that the differences to other spinosaurid dorsal vertebrae such as Spinosaurus (Stromer, 1915) and the features indicative of spinosaurid affinities and compatible with Sigilmassasaurus justify this referral, pending associated discoveries. Parts of the right postzygapophysis and the distal part of the right transverse process is missing in BSPG 2006 I 54. CMN 41857 has a fairly complete neural arch, with parts of the right transverse process and the tip of the spine missing. BSPG 2006 I 55 and NHMUK PV R 16434 are fairly complete specimens. Both lack parts of their right transverse processes, BSPG 2006 I 55 lacks the distal part of its left postzygapophysis, neural spine and right parapophysis, and NHMUK PV R 16434 has a broken right postzygapophysis and partly eroded rim of the posterior articular facet. NHMUK PV R 16436 lacks the right prezygapophysis and postzygapophysis, the distal part of both transverse processes, and has a strongly eroded posterior articular facet. NHMUK PV R 16435 is one of the most complete dorsal vertebrae described, only missing its right transverse process. In CMN 41858, most of the transverse processes, the tip of the neural spine, and the anterior part of the centrum is broken off. BSPG 2013 I 95 is a large specimen that lacks most of its transverse processes, both prezygapophyses, and the dorsal part of the neural spine. CMN 41850 lacks the pre- and postzygapophyses and the distal parts of the transverse processes are broken. The centrum of the first dorsal vertebra corresponds closely to those of the posteriormost cervicals in most characters. The anterior articular surface is strongly opisthocoelous and very wide, being more than 1.7 times wider than high and wider than the centrum is long. A strongly developed median tuberosity is present on the anterior condyle. The posterior articular surface is higher than the anterior surface, but the dorsal rim of both surfaces is approximately level. However, the anterior articular surface is slightly angled dorsally so that the centrum is slightly shorter dorsally than ventrally. Thus, the neck curved upwards from the base of the dorsal vertebral column. The posterior articular surface is deeply concave and reniform in outline. A very deep ventral keel is present and becomes deeper anteriorly, where it ends in a prominent hypapophysis just beneath a transverse ridge connecting the parapophyses. The hypapophysis is transversely expanded in comparison to the ventral side of the keel and overhangs the latter anteriorly with its tip, being offset from the ventral end of the anterior articular surface by a well-developed, anteriorly facing transverse groove. In anterior view, the hypapophysis displays a transversely broad base. The keel is slightly convex along its course in lateral outline, and the edge tends to be thicker than its sheet. Both the relative depth and the ventral convexity of the ventral keel seem to increase during ontogeny: whereas this structure is still rather low and almost straight ventrally in the smallest specimen (BSPG 2006 I 55), it is especially deep and strongly convex in large specimens, such as BSPG 2006 I 54 and NHMUK PV R 16434. Posteriorly, the keel merges into the rim of the posterior articular facet, thereby broadening into a small triangular platform. The surface of this platform is faintly striated by longitudinal rugosities. The rugosities are also apparent on the holotype of Sigilmassasaurus (CMN 41857), although previous authors have not mentioned this feature (Russell, 1996; McFeeters et al., 2013). As in the posterior cervicaly, the area between the keel and the marked lateroventral edges is depressed into a very shallow fossa. In BSPG 2006 I 54, there are two small foramina visible on the anterior rim of the fossa in posterior view. They are positioned at the base of the hypapophysis, somewhat medially on the posterior side of the transverse ridge connecting the parapophyses. In the right fossa, there are two small foramina, both of approximate circular shape. On the left side, the rim of the fossa is penetrated by only one foramen. This left foramen is bigger and more oval in outline than those on the other side, and it may be speculated that this foramen results from the confluence of the two on the right side. BSPG 2006 I 54 is the only specimen in which those foramina could be observed. These foramina do not seem to lead into an internal chamber, and are thus apneumatic (see ‘CT’ below). Instead, the foramina might be associated with the vascular system of the animal. The anterior ventral ridge connecting the parapophyses transversely is somewhat expanded ventrally, resulting in an almost straight ventral margin between these processes in anterior view. Nevertheless, the articular surfaces of the parapophyses are still ventrolaterally directed, as in the posterior cervical vertebrae, though less strongly than in the latter elements. The articular surface of the parapophysis is oval in utline, being longer than high. It is large, accounting for one third to almost one half of the length of the centrum (excluding the anterior convexity). Large pneumatic foramina are present in the first dorsal vertebra on the lateral side, above the parapophysis. The foramina are oval in outline, being longer than high. The smallest specimen, BSPG 2006 I 55, is unusual in that the foramen cuts a deep transverse trough in the dorsal margin of the parapophysis, resulting in a triangular outline of this opening. A lateral bulge and associated dorsal fossa is well-developed in the first dorsal vertebra. In CMN 41857 (holotype of S. brevicollis), the lateral bulge crosses the neurocentral suture and is therefore slightly different from the one described above for BSPG 2006 I 53. However, in other first dorsals, including BSPG 2006 I 54, BSPG 2006 I 55, and NHMUK PV R 16434 the lateral bulge is similar to the one of BSPG 2006 I 53. As in the posterior cervicals, the neurocentral sutures are clearly visible in all first dorsals. Interestingly, the smallest specimen, BSPG 2006 I 55, shows rather tight suturing of the neural arch to the centrum, despite being only almost half the size of the largest vertebra. Thus, it seems unlikely that the degree of suture fusion is a reliable indicator of skeletal maturity in Sigilmassasaurus. As in the cervical vertebrae, the neural arch pedicles meet in the midline below the neural canal in the anterior half of the centrum. In large specimens, the entire anterior floor of the neural canal is thus formed by the medial expansions of the pedicles. In contrast, in the smallest specimen, BSPG 2006 I 55, the medial contact between the pedicles is small, indicating that this suture expands during ontogeny. The neural canal is large and slightly wider dorsally than ventrally, as in the cervical vertebrae, including the type of Spinosaurus maroccanus. In several vertebrae, the dorsal margin of the canal is slightly expanded ventrally in its central part, resulting in a heart-shaped outline of the canal. There seems to be a negative allometry in the size of the neural canal, as the smallest specimen BSPG 2006 I 55 has the relatively largest opening. The neural arch, transverse processes and zygapophyses of the first dorsal vertebra are very similar to those of the last cervical. The transverse process is very slightly ventrolaterally directed, at an angle of approximately 15–20° from the horizontal in BSPG 2006 I 54, BSPG 2006 I 55, NHMUK PV R 16434, and CMN 41857. In contrast to the posterior cervicals, the distal end of the processes is not or only very slightly flexed ventrally, but the diapophysis remais ventrolaterally directed. In dorsal view, the processes expand slightly distally. The anterior margin is almost straight to slightly concave, so that the moderate distal expansion in these elements mainly stems from a funnel-like divergence of the anterior and posterior margins. The dorsal surface of the process twists slightly towards the distal end, so that it faces slightly anterodorsally. Lateral lamination of the neural arch is very similar to that seen in posterior cervicals. Only in BSPG 2006 I 54, the ridge ventral to the transverse process branches into rudimentary posteriorly and anteriorly oriented laminae in its proximal part. These are the posterior centrodiapophyseal laminae (pcdl) and anterior centrodiapophyseal laminae (acdl), respectively. The pcdl is disproportionally stronger developed than the acpl. It is also longer and extends to a more ventral point on the lateral side of the vertebra than the acpl. The bifurcation of the centrodiapophyseal lamina into acdl and pcdl serves as the dorsal roof of a fossa on the ventrolateral part of the neural arch, which is confluent with the depression above the dorsal bulge dorsal to the pneumatic foramen on the anteroventral part of the centrum described above. However, both the distinction of the laminae and the fossa are much less developed than in Baryonyx (NHMUK PV R 9951) and Ichthyovenator (BK10-25). As in the posterior cervical vertebrae, stout prezygodiapophyseal and postzygodiapophyseal laminae are present and extend far laterally onto the anterior and posterior edge, respectively, of the transverse process. In contrast to the former, however, the prezygadiapophyseal lamina rapidly becomes more robust and flexes ventrally distally, thus contributing to the distal twist of the transverse process. Furthermore, the postzygapophysis is somewhat more offset from the transverse process than in posterior cervicals, so that the ridge representing the postzygodiapophyseal lamina is lower and slightly more dorsolaterally directed. Large pneumatic foramina leading into the base of the transverse process are present on the anterior and posterior side, very similar to the situation in the posterior cervicals. These foramina can be developed quite asymmetrically, as for example in BSPG 2006 I 54, in which the right foramen is much larger than the one on the left side (Fig. 9). The pneumatic organization of the transverse processes in BSPG 2006 I 55 is similarly asymmetric (Fig. 10). While the left posterior pneumatic foramen of the transverse process is developed as a regular, transversely elongate opening, the right foramen is developed as a very small, round opening which leads into a channel-like diverticulum. Simultaneously, the anterior pneumatic opening on the right transverse process is unusually large. On both transverse processes, the anterior and posterior pneumatic cavities are not interconnected. In this specimen, the left postzygapophysis is broken, and the exposed base is hollow. This internal cavity does not seem to be connected with the pneumatic foramina in the transverse process, and it might have served as a chamber for fatty tissue or marrow, but a taphonomic origin of the feature can also not be ruled out completely. The prezygapophyses of D1 do not overhang the anterior end of the centrum and their posterior half is placed over the base of the transverse process. They stand on rather high, dorsally projecting stalks and are connected to the anterior margin of the transverse process by a stout lamina that extends laterally to approximately half the length of the process. The articular surface of the prezygapophysis is anteroposteriorly expanded and overhangs the stalk anteriorly and posteriorly. The articular surfaces stand at an angle of 100°–110° to each other and are elongate oval in outline. However, there seems to be some variation in this character, as the holotype of S. brevicollis (CMN 41857) has differently shaped left and right prezygapophyses (see McFeeters et al., 2013). The postzygapophysis projects posterodorsally and overhangs the centrum posteriorly for one third to half of its length. The articular surface is elongate oval in outline, placed approximately at the same level as the prezygapophysis and faces ventrolaterally and slightly posteriorly. As in the posterior cervicals there is neither an interpostzygapophyseal lamina, nor an epipophysis. As in the ultimate cervical BSPG 2011 I 116, there is a well-developed, but more shallow and less rugose longitudinal depression on either side of the neural spine in BSPG 2006 I 54, BSPG 2006 I 55, and CMN 41857. In these specimens, the depression is less marked and reaches anteriorly to the anterior end of the spine. Such a depression flanking the neural spine in the ultimate cervicals has not been described in any other theropod and might thus represent an autapomorphy of Sigilmassasaurus, although there seems to be some variation in the development of this feature. The only specimen that has a complete spine preserved, NHMUK PV R 16434, shows that this structure was anteroposteriorly short and low, being approximately as high as the neural arch between the centrum and the prezygapophyses (Fig. 11). In this element, the spine is anteroposteriorly elongate at its base, but continuously tapers dorsally. It is also slightly inclined posteriorly, being curved, with a notably convex anterior and a slightly concave posterior margin. A stout prespinal lamina is present in the apical part of the neural spine, but becomes less marked ventrally. The development of spinopre- and spinopostzygapophyseal laminae corresponds to the situation in the last cervical (BSPG 2011 I 116). In the more posterior anterior dorsal vertebrae, intercentral articulations are also broader than high, with width–height ratios ranging from approximately 1.7 in NHMUK PV R 16436 to c. 1.3 in BSPG 2013 I 95 and CMN 41850. The vertebrae are strongly opisthocoelous, with the more posterior elements being only insignificantly less convex anteriorly. A medial tuberosity is very prominent in NHMUK PV R 16436 (Fig. 12), clearly present in NHMUK PV R 16435 and developed as a very subtle bump in BSPG 2013 I 95, but could not be identified in CMN 41850. As in other Sigilmassasaurus specimens, both the anterior and the posterior articular facets have a reniform outline. The posterior articular surface is deeply concave in all specimens, indicating that even the dorsal vertebrae following BSPG 2013 I 95 and CMN 41850 in position had convex anterior articulations. Anterior and posterior articulations do not show an offset to one another in NHMUK PV R 16436 and NHMUK PV R 16435, but in BSPG 2013 I 95 and CMN 41850, the anterior articular end is slightly displaced ventrally in relation to the posterior face, indicating that the anterior part of the dorsal vertebral column was flexed anteroventrally. A marked rim around the anterior articular facet, as it is also present in the cervical vertebrae, is present in NHMUK PV R 16436 and NHMUK PV R 16435, but only poorly marked in the more posterior elements. Figure 12: NHMUK PV R 16436, anterior dorsal vertebra (D2) of Sigilmassasaurus brevicollis. (A) posterior view; (B) anterior view; (C) ventral view; (D) dorsal view; (E) right lateral view; (F) left lateral view. Abbreviations: at, anterior medial tuberosity; cdpf, centrodiapophyseal fossa; cpf, central pneumatic foramen; hyp, hypapophysis; k, keel; poz, postzygapophysis; pp, parapophysis; ppc, posterior pneumatic chamber of the postzygodiapophyseal fossa; prdf, prezygodiapophyseal fossa; prz, prezygapophysis; spof, spinopostzygapophyseal fossa; tp, transverse process. Scale bar equals 5 cm. BSPG 2013 I 95 and CMN 41850 both have a low but sharp keel, which follows the constricted outline of the centrum in lateral view, and is accordingly concave ventrally in lateral view. Anteriorly, the keel develops into a small, rounded and slightly thickened hypapophysis, which projects slightly further ventrally than the keel itself. Posteriorly, the keel becomes less conspicuous and merges into a low triangular expansion at the posterior end of the centrum. CMN 41858 does not preserve a keel, as the ventral and anterior parts of the centrum are broken off, but a strongly developed ventral keel is present in NHMUK PV R 16436. The keel in the latter vertebra and NHMUK PV R 16435 differs from those in the more posterior dorsal vertebrae in that it is more notably transversely broadened anteriorly and strongly convex ventrally in lateral view, but a strongly developed hypapophysis, as it is present in D1, is absent. Although the posterior end of the keel is eroded in both specimens, the preserved parts in NHMUK PV R 16435 indicate that it terminated in a posteriorly broadening triangular expansion towards the rim of the posterior central articulation facet, as in the cervicals and more posterior dorsals. The position of NHMUK PV R 16436 and NHMUK PV R 16435 as among the anteriormost dorsals is supported by the parapophyseal position. The parapophyses in the former specimen are still very low on the centrum and only very slightly elevated over its ventral rim. In NHMUK PV R 16435, they are slightly higher positioned on the centrum, so that the ventralmost part of the rim of the anterior articular facet can be seen below them in lateral view (Fig. 13). However, the parapophyses remain on the ventral half of the centrum in this specimen. They project only slightly lateral from the lateral rim of the anterior articular facet and are large, being only slightly lower than half the height of the centrum. The articular surface of the parapophysis is oval in outline, being higher than long and becoming wider ventrally, and is laterally directed. The parapophyses attain a substantially higer position in BSPG 2013 I 95 and CMN 41850, in which they are situated at or just above the mid-height of the centrum, below the anterior part of the neurocentral suture. In these specimens, the parapophyses barely project laterally from the rim of the anterior articular end of the centrum, and are confluent anteriorly with the anterior condyle. The parapophyses in these specimens are relatively smaller than in NHMUK PV R 16436 and NHMUK PV R 16435. Their articular surface is rounded triangular in outline, being wider ventrally. In CMN 41858, the parapophyses are not preserved. In all dorsals a stout ridge connects the posterior margin of the parapophysis with the lateral side of the centrum. From this ridge, a rounded edge extends posteriorly, and partitions the sid