Fossil sites from Brazil have yielded specimens of spinosaurid theropods, among which the most informative include the cranial remains of Irritator, Angaturama, and Oxalaia. In this work some of their craniodental features are reinterpreted, providing new data for taxonomic and evolutionary issues concerning this particular clade of dinosaurs. The mesial-most tooth of the left maxilla of the holotype of Irritator is regarded as representing the third tooth position, which is also preserved in the holotype of Angaturama. Thus, both specimens cannot belong to the same individual, contrary to previous assumptions, although they could have been the same taxon. In addition, the position of the external nares of Irritator is more comparable to those of Baryonyx and Suchomimus instead of other spinosaurine spinosaurids. In fact, with regards to some craniodental features, Brazilian taxa represent intermediate conditions between Baryonychinae and Spinosaurinae. Such a scenario is corroborated by our cladistic results, which also leave open the possibility of the former subfamily being non-monophyletic. Furthermore, the differences between spinosaurids regarding the position and size of the external nares might be related to distinct feeding habits and degrees of reliance on olfaction. Other issues concerning the evolution and taxonomy of Spinosauridae require descriptions of additional material for their clarification.

Copyright: © 2017 Sales, Schultz. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Current research on spinosaurids is largely focused on African material, whereas most Brazilian specimens have already been described and redescribed. However, the re-examination of the latter revealed the need for further considerations on a set of their traits. This is particularly true for cranial remains, which overlap other relevant specimens from overseas fossil sites with respect to the known portions of the skull. Moreover, many diagnostic features both at or below family rank for spinosaurids reside in the skull [ 1 , 4 , 5 , 29 ]. Here, we provide a reappraisal of spinosaurid skull materials from Brazil, focusing mainly on attributes that were either overlooked or previously interpreted. The new data also provide taxonomic and evolutionary implications for Spinosauridae as a whole, regarding craniodental features and phylogenetic ingroup relationships.

Spinosaurid remains from Brazil have played an important role in discussions regarding this clade. Firstly, they comprised the first unequivocal record out of Africa and Europe [ 19 , 26 ], despite putative reports from Asia by that time [ 27 ]. Secondly, the holotype of Irritator challengeri Martill et al., 1996, from the Romualdo Formation (Albian, Araripe Basin), is the spinosaurid specimen with the most complete preserved skull [ 15 ]. On the other hand, the holotype of Oxalaia quilombensis Kellner et al., 2011, from the Alcântara Formation (Cenomanian, São Luís-Grajaú Basin), represents the largest theropod hitherto known from Brazil, likely reaching c. 12–14 m in length [ 28 ]. Despite being smaller than the largest spinosaurid skull reported [ 5 ], it provides additional evidence for the wide distribution of large-bodied spinosaurs during the mid-Cretaceous [ 1 , 29 ]. Finally, the Brazilian spinosaurid record also includes isolated teeth and postcranial remains [ 30 – 37 ]. Among them, the most outstanding specimen is a partial postcranial skeleton firstly mentioned in scientific meeting abstracts [ 38 – 40 ] and later described in an unpublished Master’s thesis [ 41 ].

Consequently, for a long time spinosaurid material was restricted to isolated bones and teeth, although many records were probably misinterpreted as crocodylomorph remains (even prior to the discovery of Spinosaurus) [ 12 – 14 ]. However, since the 1980s, new remains have been reported from various parts of the world, providing insights on the anatomy of these theropods (e.g., [ 1 , 2 , 4 , 5 , 7 , 11 , 15 – 18 ]). These records extended the geographic range of Spinosauridae to Europe, Asia, and Gondwanan regions other than Africa, such as South America and perhaps Australia, and its temporal distribution back into the Jurassic [ 2 , 16 , 19 – 23 ]. Some authors have also suggested their possible presence in the Late Jurassic of North America [ 16 , 24 , 25 ].

Spinosauridae are among the most iconic dinosaur groups of all time [ 1 ]. This status is strengthened every time a new study on them is published (e.g., [ 2 – 7 ]). The history of the knowledge on spinosaurids began in 1912, when the fossil collector Richard Markgraf unearthed a partial skeleton with neural spines up to 165 cm in height from the Bahariya Oasis, western Egypt [ 8 , 9 ]. These remains, which represented the holotype of Spinosaurus aegyptiacus Stromer, 1915 and were housed at the Paläontologische Staatssammlung München, were destroyed by a British air raid on Munich during World War II, along with other specimens also referred to that genus [ 1 , 8 – 11 ].

On the other hand, the holotypic premaxillae of Oxalaia, along with a fragmentary left maxilla referred to the same taxon, came from a fossil site called Laje do Coringa, in Cajual Island, Alcântara Municipality, Maranhão State ( Fig 1 ) [ 28 ]. This locality corresponds to the most important fossiliferous outcrop of the Alcântara Formation, which is characterized by sandstones and mudstones intercalated with conglomeratic beds where most fossil remains are found. The majority of these fossils are released from the matrix by the continuous action of tides and waves. Due to its macrofossil and palynological content, the Alcântara Formation is usually regarded as the Cenomanian strata of the São Luís-Grajaú Basin, deposited in a transitional setting related to the opening of the equatorial portion of the South Atlantic Ocean [ 52 – 54 ]. Fossil remains are frequently fragmentary and show evidence of reworking; therefore, some degree of time-averaging is expected for the Alcântara fossil assemblage, which is composed of continental, coastal, and marine taxa. Despite the time-averaging, most of the identified taxa might have been coeval throughout part of the Cenomanian and ecologically related to each other [ 30 , 31 , 54 , 55 ]. The holotype of Oxalaia was reportedly found in situ, while the referred maxilla was collected as “surface float” [ 28 ].

Brazilian spinosaurids are Cretaceous in age and were found in the northeastern region of Brazil ( Fig 1 ). Cranial remains correspond mainly to the holotypes of all formally described species, namely Irritator challengeri, Angaturama limai, and Oxalaia quilombensis. The first two taxa are from the concretion-bearing beds of the Araripe Basin, one of the most famous Fossil Lagerstätten in the world [ 42 , 43 ]. For nomenclatural purposes, we will follow here Valença et al. [ 44 ], referring to the lithostratigraphic unit of the concretion-bearing beds as the Romualdo Formation. Besides its remarkable and abundant carbonate concretions, usually containing exquisitely preserved fossils, this formation is also characterized by the presence of shales, marls, and limestones. Along with its fossil content, geological data indicate a transitional depositional setting for the majority of the stratigraphic sequence of the Romualdo Formation and a late Early Cretaceous (Albian) age. However, in the western portion of the formation and above the concretion-bearing beds, there are strata containing echinoids and mollusks, thereby evidencing local marine conditions [ 44 – 47 ]. In fact, the holotypes of Irritator and Angaturama have been found inside concretions, which is common for most Romualdo Formation fossils. Again, as many Romualdo fossils, both spinosaurs lack accurate geographic and stratigraphic information [ 43 , 48 ]. The concretion containing Irritator was briefly described as including the ostracod Pattersoncypris and scales of the ichthyodectiform fish Cladocyclus. It may have come from Buxexé, a locality near Santana do Cariri Municipality, Ceará State [ 15 , 49 ]. On the other hand, the concretion enclosing Angaturama was considered as typically resembling those from the Romualdo Formation (Romualdo Member of the Santana Formation in Kellner and Campos [ 19 ]). Both cranial remains are distinct yet complementary to each other. Due to coming from the same stratigraphic unit, some authors suggested that they could have pertained to the same specimen (e.g., [ 4 , 50 ]).

We also performed one analysis excluding only Irritator and another removing only the other Brazilian taxa. We did so because, due to the large amount of missing data, each OTU from Brazil acted as a wild card within Spinosauridae. This procedure recovered more refined hypothetical phylogenetic relationships for Irritator and both Angaturama and Oxalaia in each analysis, which contributed to the discussions regarding the evolution of the craniodental features considered in this work.

Another taxonomic issue pervading the choice of spinosaurid OTUs is the possible synonymy between Cristatusaurus and Suchomimus, both from the Elrhaz Formation (horizon GAD 5; Aptian-Albian?) of the Tegama Group of Niger [ 4 , 28 , 29 , 62 ]. The former taxon was the first described, but its remains and proposed diagnosis are thought to be too general to differentiate it from other serrated-toothed spinosaurids [ 3 , 4 , 29 ]. Shortly after the description of Cristatusaurus, Suchomimus was described and the provided diagnosis for this taxon is enough to set it apart from Baryonyx [ 2 – 4 , 29 ]. Despite claims of Cristatusaurus as a nomen dubium, as well as some similarities between it and Suchomimus or even Baryonyx, we recognize some differences between them with possible taxonomic significance (see Discussion ). However, as specifically addressing this issue is not the main goal of this work, for practical purposes we regard Cristatusaurus and Suchomomimus as distinct OTUs also coded for this analysis.

With respect to operational taxonomic units (OTUs), we also performed additional modifications. For example, we added Oxalaia as a new OTU in order to investigate the phylogenetic relationships of all Brazilian taxa. In addition, we excluded the OTUs previously regarded by Carrano et al. [ 29 ] as wild cards, Megaraptor (whose coding did not include recent data [ 59 ]), and the spinosaurids whose holotypes correspond solely to non-cranial remains (i.e., Ichthyovenator and Sigilmassasaurus [ 16 , 17 , 60 , 61 ]). Spinosaurus is another spinosaurid whose holotype comprises mainly postcranial bones, but normally this taxon has been coded (e.g., [ 4 , 29 ]) considering also cranial remains later assigned to it [ 5 , 60 , 62 ]. Nevertheless, we consider their attribution as tentative because some of those remains were found either isolated or lacking accurate field data and they only just overlap the holotypic remains described by Stromer [ 8 ]. Furthermore, keeping in mind that many mid-Cretaceous African sites are only roughly coeval and the possible evidence indicating the presence of more than one spinosaurid morphotype (and taxon?) therein [ 17 , 18 , 63 ], it is difficult to accurately attribute isolated skulls to any of the taxa recognized locally. This is the case of the Kem Kem Beds of Morocco, from which comes material also assigned to Sigilmassasaurus [ 17 , 60 , 61 ]. As Spinosaurus and Sigilmassasaurus may not be synonymous (see Ibrahim et al. [ 7 , 64 ] for a different opinion), it is not possible yet to assign a huge Moroccan partial skull (MSNM V4047, Museo Civico di Storia Naturale di Milano, Milan, Italy) [ 5 ] to any of them. The same is true for another skull found in Algeria and tentatively attributed to S. maroccanus (MNHN SAM 124, Muséum National d’Histoire Naturelle, Paris, France) [ 62 ], which is a nomen dubium according to Sereno et al. [ 4 ] and Carrano et al. [ 29 ]. Thus, we prefer not to refer these two non-Egyptian skulls to S. aegyptiacus. Recently, a partial skeleton, including cranial bones, was proposed as the neotype of S. aegyptiacus [ 7 ]. However, some authors [ 17 ] have challenged its attribution specifically to that species. Considering that we could not handle the proposed neotype, which awaits a thorough description, we opted for not including Spinosaurus in our analyses. Instead, we coded MSNM V4047 as a distinct OTU in place of the latter.

The cladistic analyses presented here are based on the data matrix of Carrano et al. [ 29 ], which was designed for evaluating ingroup relationships of Tetanurae. However, some significant changes were performed. First of all, we incorporated all the changes made by Evers et al. [ 17 ], regarding the vertebral character coding of Carcharodontosaurus. We then added three character statements and modified others as the result of our new perspective on relative spinosaurid cranial features (see S1 File ).

Below, we provide a revised diagnosis for each Brazilian taxon in light of the current knowledge on spinosaurids. The revised diagnoses are differential in essence and do not focus solely on autapomorphies, given that distinct features are, in general, independently distributed among all spinosaurids. Therefore, they constitute a unique set of characters for each taxon. However, wherever possible, autapomorphies are temporarily recognized with the caution of each of them being possibly later figured out to be an intraspecific or ontogenetic variation, or even a pathologic condition. This possibility is real as most taxa are represented only by a single individual with the skull preserved, considering formally published specimens [ 1 ].

As already stated, this work focuses on craniodental features either overlooked or interpreted previously in a different manner. We follow Carrano et al. [ 29 ] and Hendrickx and Mateus [ 56 ] wherever possible when referring to cranial structures. Regarding teeth and alveoli, we adopt the terminology proposed by Smith and Dodson [ 57 ], which was further developed by Hendrickx et al. [ 58 ].

Results

Systematic paleontology Dinosauria Owen, 1842 [66] Theropoda Marsh, 1881 [67] Tetanurae Gauthier, 1986 [68] Spinosauridae Stromer, 1915 [8] Angaturama limai Kellner and Campos, 1996 [19] Holotype and only known specimen. USP GP/2T-5, the tip of a rostrum, comprising both premaxillae and the anteriormost portions of both maxillae (Fig 5). PPT PowerPoint slide

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larger image TIFF original image Download: Fig 5. Specimen USP GP/2T-5, holotype of Angaturama limai. A, Left lateral view. B, Right lateral view. C, Dorsal view. D, Detail of the secondary palate. E, Anterior view. Abbreviations for teeth follow Hendrickx et al. [58]. Additional abbreviations: am.p, anteromedial process of maxilla; i.su, intermaxillary suture; m, maxilla; pm, premaxilla; pm.c, premaxillary sagittal crest; pm.p, anterior premaxillary projection; r.t, replacement tooth; su, suture between premaxilla and maxilla. https://doi.org/10.1371/journal.pone.0187070.g005 Revised diagnosis. Spinosaurid that differs from Baryonyx, Suchomimus, and Cristatusaurus by both the possession of unserrated teeth and the comparatively smaller first premaxillary tooth. It also differs from all other spinosaurid skulls by the presence of a dorsal sagittal premaxillary crest that nearly reaches the anterior end of the snout, beginning much more anteriorly than in Baryonyx, Suchomimus, and Cristatusaurus. Another autapomorphy of Angaturama is the rounded and knob-like anterodorsal projection of the conjoined premaxillae. Occurrence. Unspecified locality in the Araripe Basin, northeastern Brazil. Romualdo Formation; Albian, Lower Cretaceous.

Remarks and comparisons Angaturama was described shortly after Irritator, but it was the first theropod from the Araripe Basin to be considered as a spinosaurid [19,26,34,49]. Given that those taxa were proposed based on supposedly non-overlapping cranial materials (Figs 2 and 5), they could not be compared to each other [15]. Also, for the same reason, Angaturama cannot be fully compared to the holotype of Spinosaurus [8]. The premaxillae of Angaturama were firstly distinguished from other spinosaurids based on the following features: 1) the degree of lateral compression of the rostrum, which is narrowest at the level of teeth pm6; 2) less broad mediolateral width; and, 3) a well-developed dorsal sagittal crest (Fig 5). Among these, only the last feature is still held as an autapomorphy of that genus, but in a modified version [29]. Given that Baryonyx, Cristatusaurus, and Suchomimus also exhibit a dorsal sagittal rim on their premaxillae [3,4,62], this sort of structure is not exclusive of the Brazilian taxon, although it is indeed more conspicuous and, more importantly, extends more anteriorly than in baryonychine spinosaurids [29]. Regarding the mediolateral compression of the rostrum of Angaturama, it was initially considered as a natural feature instead of the result of postmortem compression [19]. The expanded condition of the premaxillae, which are often referred together as a “terminal rosette”, appears less broad than in other spinosaurids [15,19]. This might be a consequence of the less pronounced constriction caudal to the rosette, i.e., at the level of the last two premaxillary teeth in Angaturama [5]. However, the degree of compression of the holotype might not reflect the original condition, although it may be still regarded as less broad in overall shape. For instance, the ventral borders of both premaxillae are not preserved and some in situ partial teeth are longitudinally sectioned, which consequently reduce the total width of the preserved rosette (Fig 5A and 5B). Additional evidence of postmortem compression is in the palate. As other spinosaurids, Angaturama presents a secondary palate formed by the palatal portions of the premaxillae along with the anteromedial processes of the maxillae [4,5,62]. These processes in spinosaurids are positioned between the palatal portions of the premaxillae and were firstly misidentified as belonging to the vomers [3,19]. Thus, the sagittal plane of the spinosaurid rostrum should pass through the medial sutures between the premaxillae and maxillae and equally divide the palate. Nevertheless, contrary to this reasoning, the left half of the palate of Angaturama is slightly narrower than the right (Fig 5D) and this might be an indication that the left side underwent some degree of postmortem compression. Along with the condition of the dorsal sagittal crest, Angaturama bears another remarkable feature that differs from all other spinosaurids with the tip of the rostrum preserved. The premaxillae form a protuberance on their anterior outlines close to their dorsal surfaces (Fig 5). This feature implies that the dorsal outline of the premaxillae ends more anteriorly than the ventral one, whereas in other spinosaurid skulls the condition is opposite—the dorsal outline more gradually slopes anteroventrally (Fig 4) [3–5,62]. It is possible that the sagittal crest extended anteriorly and partially over that projection, as the latter is covered by a break indicating that it misses some dorsal portion of the bone (Fig 5C). One could argue that, as the premaxillae of the holotype lack their ventral portions in lateral view, part of the anterior margin of the premaxillae of Angaturama is also missing just below the protuberance. Accordingly, the alveoli of pm1 are incompletely preserved. In this sense, this structure would not be natural. However, in spinosaurid theropods, the first premaxillary alveoli are usually separated from the anterior margins of the premaxillae by a distance smaller than half their diameters. A hypothetical reconstruction of the missed anterior borders of the premaxillae of Angaturama would not significantly extend them anteriorly in relation to what is currently preserved. Furthermore, the bone surface of the protuberance and the surrounding region does not present any sign of having been severely damaged, as it would be after losing a significant portion of the bone by taphonomic causes or preparation techniques. Thus, the anterior outline of the premaxillae of Angaturama must have been relatively straight or at least concave just below the anterior salience seen in the holotype, which does seem to be a natural feature. The premaxillae of Angaturama present the typical condition of seven premaxillary teeth of spinosaurids. Regarding the size variation within the preserved tooth row, it was described as increasing from pm1 to pm3, gradually decreasing from pm3 to pm6, increasing again from pm6 to m3, and finally decreasing from m3 to at least m4 [19]. Kellner and Campos [19] only figured the right side of Angaturama, in which there is no indication of m4, but in the left side there is indeed one partially preserved alveolus after m3. However, considering its smaller size and distolingual position in relation to Lm3, this alveolus must correspond to a replacement tooth (Fig 5A). This inference is in accordance with the aforementioned pattern of tooth size variation of spinosaurids. Besides this replacement tooth and the one associated to Lm2 previously reported by Kellner and Campos [19], there are others incompletely preserved. They can be noticed more clearly in association with Lpm4, Lm1, and Rpm1. The replacement tooth associated to Lpm1 is likely indicated by the empty alveolus between the alveoli of Lpm1 and Lpm2. Finally, with respect to the tooth ornamentation, enamel flutes are seen in the lingual side of Rpm6 [19].

Systematic paleontology Dinosauria Owen, 1842 [66] Theropoda Marsh, 1881 [67] Tetanurae Gauthier, 1986 [68] Spinosauridae Stromer, 1915 [8] Oxalaia quilombensis Kellner et al., 2011 [28] Holotype. MN 6117-V, fused premaxillae (Fig 6). PPT PowerPoint slide

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larger image TIFF original image Download: Fig 6. Specimen MN 6117-V, holotype of Oxalaia quilombensis. A, Left lateral view. B, Right lateral view. C, Dorsal view. D, Slightly oblique ventral view, emphasizing the sculptured condition of the palatal portion of the left premaxilla. Abbreviations for teeth follow Hendrickx et al. [58]. Additional abbreviations: am.p, anteromedial process of maxilla; pm, premaxilla; r.t, replacement tooth; s.p, secondary palate. https://doi.org/10.1371/journal.pone.0187070.g006 Referred specimen. MN 6119-V, an isolated fragment of a left maxilla. Revised diagnosis. Spinosaurid that differs from Baryonyx, Suchomimus, and Cristatusaurus by both the possession of unserrated teeth and the relatively much smaller first premaxillary tooth. The lack of a dorsal sagittal premaxillary crest or rim also differs in relation to those taxa and Angaturama. It differs from MNHN SAM 124 and MSNM V4047 by oval-shaped conjoined premaxillae in dorsal view due to a weaker lateral compression of the rostrum just posterior to m3, whereas in both African specimens the fused premaxillae are mushroom-shaped. Finally, autapomorphies of Oxalaia include the possession of two replacement teeth associated with functional pm3 and the sculptured condition of the palatal portion of the premaxillae. Occurrence. Laje do Coringa locality, Cajual Island, Alcântara Municipality, Maranhão State, São Luís-Grajaú Basin, northeastern Brazil. Alcântara Formation; Cenomanian, Upper Cretaceous.