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A Reappraisal of the Morphology and Systematic Position of the Theropod Dinosaur Sigilmassasaurus From the "Middle" Cretaceous of Morocco

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A Reappraisal of the Morphology and Systematic Position of the Theropod Dinosaur Sigilmassasaurus From the "Middle" Cretaceous of Morocco

Serjoscha W Evers et al. PeerJ.

Abstract

Sigilmassasaurus brevicollis is an enigmatic theropod dinosaur from the early Late Cretaceous (Cenomanian) of Morocco, originally based on a few isolated cervical vertebrae. Ever since its original description, both its taxonomic validity and systematic affinities were contentious. Originally considered to represent its own family, Sigilmassasauridae, the genus has variously been suggested to represent a carcharodontosaurid, an ornithischian, and, more recently, a spinosaurid. Here we describe new remains referrable to this taxon and re-evaluate its taxonomic status and systematic affinities. Based on the new remains, a re-evaluation of the original materials, and comparisons with other spinosaurids, the holotype of Sigilmassasaurus brevicollis is identified as an anterior dorsal, rather than a cervical vertebra, and differences between elements referred to this taxon can be explained by different positions of the elements in question within the vertebral column. Many characters used previously to diagnose the genus and species are found to be more widespread among basal tetanurans, and specifically spinosaurids. However, the taxon shows several autapomorphies that support its validity, including the presence of a strongly rugose, ventrally offset triangular platform that is confluent with a ventral keel anteriorly in the mid-cervical vertebral centra and a strongly reduced lateral neural arch lamination, with no or an incomplete distinction between anterior and posterior centrodiapophyseal laminae in the posterior cervical and anterior dorsal vertebrae. We argue furthermore that Spinosaurus maroccanus, also described on the basis of isolated cervical vertebrae from the same stratigraphic unit and in the same paper as Sigilmassasaurus brevicollis, is a subjective synonym of the latter. Both a detailed comparison of this taxon with other theropods and a formal phylogenetic analysis support spinosaurid affintities for Sigilmassasaurus. However, we reject the recently proposed synonymy of both Spinosaurus maroccanus and Sigilmassasurus brevicollis with Spinosaurus aegyptiacus from the Cenomanian of Egypt, as there are clear differences between the vertebrae of these taxa, and they do not share any derived character that is not found in other spinosaurids. Together with a comparison with other spinosaurid vertebral material from the Kem Kem, this suggests that more than one taxon of spinosaurid was present in the Kem Kem assemblage of Morocco, so the referral of non-overlapping material from this unit to a single taxon should be regarded with caution.

Keywords: Africa; Kem Kem; Spinosauridae; Vertebral morphology.

Conflict of interest statement

The authors declare there are no competing interests.

Figures

Figure 1
Figure 1. CMN 50791, mid-cervical vertebra (C6) of Sigilmassasaurus brevicollis.
(A) posterior view; (B) anterior view; (C) ventral view; (D) dorsal view; (E) right lateral view; (F) left lateral view. Abbreviations: cpf, central pneumatic foramen; epi, epipophyses; iprl, interprezygapophyseal lamina; ns, neural spine; poz, postzygapophysis; pp, parapophysis; prz, prezygapophysis; tp, transverse process; vtp, ventral triangular plateau. Scale bar equals 10 cm.
Figure 2
Figure 2. BSPG 2011 I 118, mid-cervical vertebra (C5) of Sigilmassasaurus brevicollis.
(A) posterior view; (B) anterior view; (C) ventral view; (D) dorsal view; (E) right lateral view; (F) left lateral view. Abbreviations: cpf, central pneumatic foramen; k, keel; pp, parapophysis; vtp, ventral triangular plateau. Scale bar equals 5 cm.
Figure 3
Figure 3. BSPG 2011 I 117, mid-cervical vertebra (C6) 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 median tuberosity; cpf, central pneumatic foramen; k, keel; pp, parapophysis; vtp, ventral triangular plateau. Scale bar equals 5 cm.
Figure 4
Figure 4. NHMUK PV R 16427, mid-cervical neural arch (C4) of Sigilmassasaurus brevicollis.
(A) posterior view; (B) anterior view; (C) ventral view; (D) dorsal view; (E) right lateral view; (F) left lateral view. Abbreviations: epi, epipophyses; ns, neural spine; poz, postzygapophysis; prz, prezygapophysis. Scale bar equals 5 cm.
Figure 5
Figure 5. BSPG 2006 I 56, posterior cervical vertebra (C8) of Sigilmassasaurus brevicollis.
(A) posterior view; (B) anterior view; (C) ventral view; (D) dorsal view; (E) right lateral view; (F) left lateral view. Abbreviations: apc, anterior pneumatic chamber of the transverse process; apf, anterior pneumatic foramen of the prezygodiapophyseal fossa; at, anterior medial tuberosity; cpf, central pneumatic foramen; k, keel; ns, neural spine; poz, postzygapophysis; pp, parapophysis; ppc, posterior pneumatic chamber of the transverse process; ppf, posterior pneumatic foramen of the postzygodiapophyseal fossa; prz, prezygapophysis; tp, transverse process; vtp, ventral triangular plateau. Scale bar equals 5 cm.
Figure 6
Figure 6. BSPG 2011 I 115, posterior cervical vertebra (C9) 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; dp, diapophysis; k, keel; ns, neural spine; poz, postzygapophysis; pp, parapophysis; ppf, posterior pneumatic foramen of the postzygodiapophyseal fossa; prz, prezygapophysis; prz-p, prezygapophysis of posteriorly adjacent vertebra; tp, transverse process. Scale bar equals 5 cm.
Figure 7
Figure 7. BSPG 2006 I 53, 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: apc, anterior pneumatic chamber of the transverse process; at, anterior medial tuberosity; cpf, central pneumatic foramen; hyp, hypapophysis; k, keel; pp, parapophysis; ppc, posterior pneumatic chamber of the transverse process; prz, prezygapophysis; tp, transverse process. Scale bar equals 5 cm.
Figure 8
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
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
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
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.
Figure 12
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.
Figure 13
Figure 13. NHMUK PV R 16435, anterior dorsal vertebra (D3) 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; cdpf, centrodiapophyseal fossa; cpf, central pneumatic foramen; dp, diapophysis; k, keel; ns, neural spine; poz, postzygapophysis; pp, parapophysis; ppf, posterior pneumatic foramen of the postzygodiapophyseal fossa; prz, prezygapophysis; spof, spinopostzygapophyseal fossa; tp, transverse process. Scale bar equals 5 cm.
Figure 14
Figure 14. BSPG 2013 I 95, anterior dorsal vertebra tentatively referred to Sigilmassasaurus.
(A) posterior view; (B) anterior view; (C) ventral view; (D) dorsal view; (E) right lateral view; (F) left lateral view. Abbreviations: cdpf, centrodiapophyseal fossa; cpof, centropostzygapophyseal fossa; cprf, centroprezygapophyseal fossa; hyp, hypapophysis; ipol, interpostzygapophyseal lamina; k, keel; ns, neural spine; poz, postzygapophysis; pp, parapophysis; prz, prezygapophysis. Scale bar equals 5 cm.
Figure 15
Figure 15. CT images of BSPG 2006 I 54.
(A) slice through anterior part of the vertebra in popsterior view. (B) slice through centrum in dorsal view. Pink arrows indicate course of bony septum separating two large camerate chambers. The yellow arrow indicates hollow structure in prezygapophysis. The blue arrow indicates accessory foramen underneath transverse ridge. Scale bars equal 10 cm.
Figure 16
Figure 16. Multi planar reformat (MPR) image of BSPG 2011 I 115.
(A) slice through right lateral aspect of vertebra; (B) transversal slice through vertebra in posterior view, (C) horizontal slice through centrum. All sections are orthogonal to one another, with colors indicating relations between the images. The yellow arrow shows connection of posterior and anterior pneumatic cavities of transverse process; The pink arrow shows thin lamina separating cavities laterally. Scale bars equal 10 cm.
Figure 17
Figure 17. BSPG 2006 I 57, mid-cervical vertebra (C6) of an indeterminate spinosaur.
(A) posterior view; (B) anterior view; (C) right lateral view; (D) left lateral view. Abbreviations: cam, camerate pneumatic chamber; cprf, centroprezygapophyseal fossa; epi, epipophysis; ipol, interpostzygapophyseal lamina; ns, neural spine; poz, postzygapophysis; pp, parapophysis; prz, prezygapophysis; spof, spinopostzygapophyseal fossa; tp, transverse process. Scale bar equals 5 cm.
Figure 18
Figure 18. NHMUK PV R 16429, anterior cervical vertebra of an indeterminate spinosaur.
(A) right lateral view; (B) anterior view; (C) ventral view. Abbreviations: cpf, central pneumatic foramen; dep, depression; ltub, lateral tubercle; pp, parapophysis; prz, prezygapophysis; tp, transverse process. Scale bar equals 5 cm.
Figure 19
Figure 19. Comparisons of different spinosaurid mid-cervical vertebrae from the Kem Kem compound assemblage.
(A) & (C) BSPG 2006 I 57, C6 of an indeterminate Spinosauridae; (B) & (D) CMN 50791, C6 vertebra of Sigilmassasaurus brevicollis. (A) & (B) anterior view; (C) right lateral view, (D) left lateral view. Labels (i–iv) indicate state of osteological features in the indeterminate spinosaur (−1) and Sigilmassasaurus (−2); (i) state of centroprezygapophyseal fossa (i-1: present; i-2: absent); (ii) state of epipophyses (ii-1: strongly developed; ii-2: weakly developed); (iii) state of neural spine (iii-1: anteroposteriorly long and dorsally high; iii-3: short and relatively low); (iv) state of ventral triangular plateau (iv-1: absent; iv: present). Left scale bar equals 5 cm, right scale bar equals 10 cm.
Figure 20
Figure 20. Stereographic comparisons of spinosaur cervical vertebrae from the Kem Kem compound assemblage.
(A) stereopair showing ventral view of BSPG 2011 I 117, Sigilmassasaurus brevicollis; (B) right lateral view of BSPG 2011 I 117; (C) right lateral view of BSPG 2013 I 97; (D) stereopair showing ventral view of BSPG 2013 I 97, Spinosauridae indet.; (E) stereopair showing ventral view of BSPG 2006 I 56, Sigilmassasaurus brevicollis. Note triangular plateau in Sigilmassasaurus and prominent step in lateral outline in mid-cervicals, and ventral lateral tubercula with central depression and weak lateral step in BSPG 2013 I 97. Scale bars equal 5 cm.
Figure 21
Figure 21. BSPG 2012 I 97, mid-cervical of an indeterminate spinosaur.
(A) anterior view; (B) left lateral view. Abbreviations: cpf, central pneumatic foramen; cprf, centroprezygapophyseal fossa; epi, epipophysis; ns, neural spine; pp, parapophysis; poz, postzygapophysis; tp, transverse process. Scale bar equals 5 cm.
Figure 22
Figure 22. NHMUK PV R 36637, posterior mid-cervical vertebra of an indeterminate spinosaur.
(A) posterior view; (B) anterior view; (C) ventral view; (D) dorsal view; (E) right lateral view; (F) left lateral view. Abbreviations: apc, anterior pneumatic chamber of the transverse process; cdpf, centrodiapophyseal fossa; cpf, central pneumatic foramen; k, keel, pp, parapophysis, ppc, posterior pneumatic chamber of the transverse process. Note that specimen is slightly dorsoventrally compressed. Scale bar equals 10 cm.
Figure 23
Figure 23. Drawings comparing “Spinosaurus B” and Sigilmassasaurus.
(A) “Spinosaurus B” in anterior view; (B) holotype of Sigilmassasaurus brevicollis in anterior view; (C) BSPG 2006 I 54 in anterior view; (D) “Spinosaurus B” in left lateral view; (E) holotype of Sigilmassasaurus brevicollis in left lateral view; (F) BSPG 2006 I 54 in left lateral view. (A, C) modified from Stromer 1934. (B) E re-drawn from Russell (1996). Cross-hatching in (C) represents breakage. Scale bars equal 10 cm.
Figure 24
Figure 24. CMN 50792, posterior cervical vertebra of an indeterminate carcharodontosaurid.
(A) right lateral view; (B) anterior view; (C) left lateral view. Abbreviations: cal, camellate pneumatic structure; cpf, central pneumatic foramen; cprf, centroprezygapophyseal fossa; pp, parapophysis; prz, prezygapophysis. Scale bar equals 10 cm.
Figure 25
Figure 25. Neck reconstructions of Sigilmassasaurus and Baryonyx.
(A) Sigilmassasaurus; (B) Baryonyx. Scale bar equals 10 cm. Scale bar only applies to Baryonyx, for which associated material is preserved. Reconstructions are based on the holotype material for Baryonyx, and material discussed in this paper for Sigilmassasaurus. Note that the first vertebra depicted is the C2 (axis), and that reconstruction includes anterior dorsal vertebrae.
Figure 26
Figure 26. Morphological changes along the cervical vertebral column of Sigilmassasaurus andBaryonyx.
(A) CMN 50791, holotype mid-cervical vertebra (C6) of Sigilmassasaurus brevicollis in left lateral view; (B) BSPG 2005 I 56, posterior cervical vertebra (C8) of Sigilmassasaurus brevicollis in left lateral view; (C) NHMUK PV R 9951, C6 of Baryonyx walkeri in left lateral view; (D) NHMUK PV R 9951, C9 of Baryonyx walkeri in left lateral view. Note the extreme morphological changes in centrum length, orientation of prezygapophzses, and shape of the neural spine in both taxa. For discussion of axial placement of Baryonyx vertebrae see main text. Scale bars equal 10 cm.
Figure 27
Figure 27. Comparison between mid-cervical vertebrae of Baryonyx and Sigilmassasaurus.
(A) Ce4 of Baryonyx in anterior view; (B) CMN 50791, Sigilmassasaurus mid-cervical vertebra (Ce6-7); (C) NHMUK PV 16427 Sigilmassasaurus mid-cervical (?Ce4) in anterior view; (D) Ce4 of Baryonyx in left lateral view; (E) NHMUK PV 17427 Sigilmassasaurus in left lateral view. Abbreviations: cprl, centroprezygapophyseal lamina; ifpl, infraprezygapophyseal lamina; prdl, prezygodiapophyseal lamina; sns, stepped neural spine. Scale bars equal 5 cm.
Figure 28
Figure 28. Reduced consensus tree from our phylogenetic analysis after pruning Xuanhanosaurus using 3,070 most parsimonious trees.
Capitalised terminal clades have been summarised, but are fully shown in a version of this tree in Fig. S6. Note that Sigilmassasaurus is found in a monophyletic Spinosauridae, highlighted by a turquoise box.

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