Spinosaur taxonomy and evolution of craniodental features: Evidence from Brazil

Marcos A F Sales^{1

2}, Cesar L Schultz^{1

3}

Affiliations

¹ Programa de Pós-Graduação em Geociências, Instituto de Geociências, Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, Rio Grande do Sul, Brazil.
² Instituto Federal de Educação, Ciência e Tecnologia do Ceará (IFCE), Fortaleza, Ceará, Brazil.
³ Departamento de Paleontologia e Estratigrafia, Instituto de Geociências, Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, Rio Grande do Sul, Brazil.

PMID: 29107966
PMCID: PMC5673194
DOI: 10.1371/journal.pone.0187070

Spinosaur taxonomy and evolution of craniodental features: Evidence from Brazil

Marcos A F Sales et al. PLoS One. 2017.

. 2017 Nov 6;12(11):e0187070.

doi: 10.1371/journal.pone.0187070. eCollection 2017.

Authors

Marcos A F Sales^{1

2}, Cesar L Schultz^{1

3}

Affiliations

¹ Programa de Pós-Graduação em Geociências, Instituto de Geociências, Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, Rio Grande do Sul, Brazil.
² Instituto Federal de Educação, Ciência e Tecnologia do Ceará (IFCE), Fortaleza, Ceará, Brazil.
³ Departamento de Paleontologia e Estratigrafia, Instituto de Geociências, Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, Rio Grande do Sul, Brazil.

PMID: 29107966
PMCID: PMC5673194
DOI: 10.1371/journal.pone.0187070

Abstract

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.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

**Fig 1. Map of northeastern Brazil showing the location of the Araripe and São Luís-Grajaú basins.**
The (likely) provenance of the holotypes of local spinosaurid taxa is indicated. Modified from Bittencourt and Langer [51].

**Fig 2. Specimen SMNS 58022, holotype of *Irritator challengeri*.**
A, Left lateral view. B, Right lateral view. The abbreviation for the third tooth of the left maxilla follows Hendrickx et al. [58]. Additional abbreviations: ao.f, antorbital fenestra; c.c, crista cranii; e.n, external naris; m, maxilla; m.r, mandibular ramus; n, nasal; n.c, nasal sagittal crest; n.p, nasal process; o, orbit; pm, premaxilla; s, stapes.

**Fig 3. Dentition of *Irritator challengeri*.**
A, Detail of the left maxillary tooth row. B, Detail of the first tooth crown preserved in situ of the left maxilla. C, Detail of the artificially detached fragment of the right maxilla bearing the right maxillary tooth row. D, Detail of the sixth tooth crown preserved in situ of the right maxilla in mesial view. Abbreviations for teeth follow Hendrickx et al. [58]. Additional abbreviations: e.n, external naris; m, maxilla; m.r, mandibular ramus; m.u, marginal undulations; n, nasal; pm, premaxilla; r.m, rock matrix.

**Fig 4. Schematic illustration of spinosaurid cranial remains.**
A, Premaxillae and maxillae of *Baryonyx walkeri*. B, Partial rostrum (MNN GDF501) referred to *Suchomimus tenerensis*. C, Specimen MSNM V4047. D, Reconstructed skull of *Irritator challengeri*. All specimens are aligned based on the position of the fourth maxillary tooth, whereas the last maxillary tooth (or alveolus) in each is indicated by a black star. Abbreviations for teeth follow Hendrickx et al. [58]. Additional abbreviations: n.c, nasal contact; ao.f, antorbital fenestra; e.n, external naris. A, B, C, and D are modified from Charig and Milner [3], Sereno et al. [4], Dal Sasso et al. [5], and Sues et al. [15], respectively.

**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.

**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.

**Fig 7. Strict consensus cladogram (1069 steps; CI = 0.409; RI = 0.666) of 145 MPTs obtained from the current cladistic analysis.**
Spinosaurid taxa are in bold. The spinosaurid silhouette is from Sales et al. [71].

**Fig 8. Strict consensus cladogram (1051 steps; CI = 0.415; RI = 0.670) of 150 MPTs obtained from the current cladistic analysis excluding *Irritator*.**
Spinosaurid taxa are in bold. The spinosaurid silhouette is from Sales et al. [71].

**Fig 9. Strict consensus cladogram (1056 steps; CI = 0.413; RI = 0.664) of 148 MPTs obtained from the current cladistic analysis excluding *Angaturama and Oxalaia*.**
Spinosaurid taxa are in bold. The spinosaurid silhouette is from Sales et al. [71].

**Fig 10. Synapomorphies of Spinosauridae recovered by the current analyses.**
A, Ingroup relationships after the cladistic analysis which excludes *Irritator*. B, Ingroup relationships after the cladistic analysis which excludes *Cristatusaurus*, *Angaturama* and *Oxalaia*. Silhouettes modified from Sales et al. [37,71].

**Fig 11. Spinosaurid cranial remains from Brazil.**
A, Reconstruction of specimen SMNS 58022, the holotype of *Irritator challengeri*. B, Specimen USP GP/2T-5, the holotype of *Angaturama limai*. C, Specimen MN 6117-V, the holotype of *Oxalaia quilombensis*. The fragmentary maxilla (MN 6119-V) tentatively referred to O. *quilombensis* was not included. A is modified from Sues et al. [15].

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References

1. Hone DWE, Holtz TR. A century of spinosaurs—A review and revision of the Spinosauridae with comments on their ecology. Acta Geol Sin-Engl. 2017;91: 1120–1132.
1. Charig AJ, Milner AC. Baryonyx, a remarkable new theropod dinosaur. Nature. 1986;374: 359–361. - PubMed
1. Charig AJ, Milner AC. Baryonyx walkeri, a fish-eating dinosaur from the Wealden of Surrey. Bull Nat Hist Mus Lond Geol. 1997;53: 11–70.
1. Sereno PC, Beck AL, Dutheil DB, Gado B, Larsson HCE, Lyon GH, et al. A long-snouted predatory dinosaur from Africa and the evolution of spinosaurids. Science. 1998;282: 1298–1302. - PubMed
1. Dal Sasso C, Maganuco S, Buffetaut E, Mendez MA. New information on the skull of the enigmatic theropod Spinosaurus, with remarks on its size and affinities. J Vertebr Paleontol. 2005;25: 888–896.

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Spinosaur taxonomy and evolution of craniodental features: Evidence from Brazil

Affiliations

Spinosaur taxonomy and evolution of craniodental features: Evidence from Brazil

Authors

Affiliations

Abstract

Conflict of interest statement

Figures

References

MeSH terms

LinkOut - more resources

Full Text Sources

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