A long-snouted predatory dinosaur from Africa and the evolution of spinosaurids

Science

Volumn 282, Issue 5392, 1998, Pages 1298-1302

  Sereno, Paul C ^a   Beck, Allison L ^a   Dutheil, Didier B ^b   Gado, Boubacar ^c   Larsson, Hans C E ^a   Lyon, Gabrielle H ^d   Marcot, Jonathan D ^a   Rauhut, Oliver W M ^e   Sadleir, Rudyard W ^d   Sidor, Christian A ^a   Varricchio, David D ^f   Wilson, Gregory P ^g   Wilson, Jeffrey A ^a  

^a UNIVERSITY OF CHICAGO   (United States)

^b MUSÉUM NATIONAL D'HISTOIRE NATURELLE   (France)

^c Inst pour Rech et Science Humaine   (Nigeria)

^d UNIVERSITY OF ILLINOIS AT CHICAGO   (United States)

^e UNIVERSITY OF BRISTOL   (United Kingdom)

^f Old Trail Museum   (United States)

^g UNIVERSITY OF CALIFORNIA   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

CRETACEOUS; DINOSAUR;

ARTICLE; EVOLUTION; FOSSIL; MANDIBLE; NONHUMAN; PHYSICAL ANTHROPOLOGY; PRIORITY JOURNAL; VERTEBRA;

EID: 0032514871     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.282.5392.1298     Document Type: Article

References (44)

1. E. Stromer, Abh. Kgl. Bayer. Akad. Wiss. Math. Phys. Kl. 28, 1 (1915).
2. S. Bouaziz et al., Bull. Soc. Geol. Fr. 1988, 335 (1988); E. Buffetaut, Neues Jahrb. Geol. Palaeontol. Monh. 1989, 79 (1989).
3. S. Bouaziz et al., Bull. Soc. Geol. Fr. 1988, 335 (1988); E. Buffetaut, Neues Jahrb. Geol. Palaeontol. Monh. 1989, 79 (1989).
4. D. A. Russell, Bull. Mus. Natl. Hist. Nat. Paris Ser. 4 18, 349 (1996).
5. P. Taquet and D. A. Russell, C. R. Acad. Sci. 327, 347 (1998).
6. The holotypic skeleton of Spinosaurus aegyptiacus includes subconical teeth, dentaries with a squared distal end, and high-spined dorsal vertebrae (1); the association of these features is confirmed by additional remains from Morocco (3) and Algeria (4). Although the Moroccan and Algerian materials have been referred to a different species (S. maroccanus), its distinction from S. aegyptiacus (by the proportions of the centrum of an isolated cervical vertebra) and the basis for the referral of additional material are questionable. We regard S. maroccanus as a nomen dubium and provisionally refer all spinosaur material from Albian-and Cenomanian-age rocks in northern Africa to S. aegyptiacus. Stromer (30) described other postcranial remains from the Baharîya oasis as "Spinosaurus B," but these can be shown to overlap with a partial skeleton of the allosauroid Carcharodontosaurus saharicus from the same locality (21). Recently a new genus and species, Sigilmassasaurus brevicollis, was erected on the basis of isolated vertebrae from Cenomanian-age rocks in Morocco (3). We question its distinction from C. saharicus (by proportions of the centrum of an isolated cervical vertebra). We regard Sigilmassasaurus brevicollis as a subjective junior synonym of C. saharicus, to which we provisionally refer all carcharodontosaurid material from Albian-and Cenomanian-age rocks in northern Africa.
7. P. Taquet, Cah. Paleontol. 1976, 1 (1976).
8. _, C. R. Acad. Sci. 299, 217 (1984).
9. A. W. A. Kellner and D. A. Campos, Neues Jarhb. Geol. Palaeontol. Abh. 199, 151 (1996).
10. D. M. Martill et al., J. Geol. Soc. London 153, 5 (1996).
11. Shortly after Irritator challengeri was described (9), the anterior end of a spinosaurid snout was described from the same deposit as Angaturama limai (8), which may well pertain to the same taxon or possibly to the same specimen (73).
12. A. J. Charig and A. C. Milner, Nature 324, 359 (1986).
13. _, in Dinosaur Systematics: Perspectives and Approaches, K. Carpenter and P. J. Currie, Eds. (Cambridge Univ. Press, Cambridge, 1990), pp. 127-140; L. I. Viera and J. A. Torres, Munibe Cienc. Nat. 47, 57 (1995).
14. _, in Dinosaur Systematics: Perspectives and Approaches, K. Carpenter and P. J. Currie, Eds. (Cambridge Univ. Press, Cambridge, 1990), pp. 127-140; L. I. Viera and J. A. Torres, Munibe Cienc. Nat. 47, 57 (1995).
15. A. J. Charig and A. C. Milner, Bull. Nat. Hist. Mus. 53, 11 (1997).
16. The Tegama Group is composed of terrestrial rocks of middle to late Cretaceous age. Three formations (Tazolé, Elrhaz, and Echkar) have been recognized [H. Faure, Mem. B.R.G.M. Paris 47, 1 (1966); J. Greigert and R. Pougnet, ibid. 48, 1 (1967)]. In the region southeast of the Air highlands, the Tegama Group was divided into eight Gadoufaoua (GAD) levels by the Center for Atomic Energy [E. Molinas, Rapp. C.E.A. Marseille 1965, 1 (1965)]. Horizons corresponding to GAD 5 have yielded all of the fossils in the present report and those described previously (6) (Fig. 1). GAD 5 appears to include the upper part of the Elrhaz Formation and the lower part of the Echkar Formation (6).
17. The Tegama Group is composed of terrestrial rocks of middle to late Cretaceous age. Three formations (Tazolé, Elrhaz, and Echkar) have been recognized [H. Faure, Mem. B.R.G.M. Paris 47, 1 (1966); J. Greigert and R. Pougnet, ibid. 48, 1 (1967)]. In the region southeast of the Air highlands, the Tegama Group was divided into eight Gadoufaoua (GAD) levels by the Center for Atomic Energy [E. Molinas, Rapp. C.E.A. Marseille 1965, 1 (1965)]. Horizons corresponding to GAD 5 have yielded all of the fossils in the present report and those described previously (6) (Fig. 1). GAD 5 appears to include the upper part of the Elrhaz Formation and the lower part of the Echkar Formation (6).
18. The Tegama Group is composed of terrestrial rocks of middle to late Cretaceous age. Three formations (Tazolé, Elrhaz, and Echkar) have been recognized [H. Faure, Mem. B.R.G.M. Paris 47, 1 (1966); J. Greigert and R. Pougnet, ibid. 48, 1 (1967)]. In the region southeast of the Air highlands, the Tegama Group was divided into eight Gadoufaoua (GAD) levels by the Center for Atomic Energy [E. Molinas, Rapp. C.E.A. Marseille 1965, 1 (1965)]. Horizons corresponding to GAD 5 have yielded all of the fossils in the present report and those described previously (6) (Fig. 1). GAD 5 appears to include the upper part of the Elrhaz Formation and the lower part of the Echkar Formation (6).
19. Theropods include the spinosaurid described here, an indeterminate tetanuran known primarily from teeth, and a small basal coelurosaur. Currently, there is no evidence to support the previous referral of small theropod remains from Cadoufaoua to Elaphrosaurus iguidensis (6) [A. F. de Lapparent, Mem. Soc. Geol. Fr. 88A, 1 (1960)]. Sauropods include a common, high-spined basal diplodocoid [formerly referred to as a dicraeosaurine (6)] and a rare titanosaur. Ornithopods include the dryosaurid Valdosaurus nigeriensis [P. M. Galton and P. Taquet, Geobios 15, 147 (1982)], the common "Iguanodon trapu" [S. Chablis, thesis, Université de Paris (1988)], and the high-spined Ouranosaurus nigeriensis (6). Nondinosaurian vertebrates that were not previously recorded include a long-snouted basal crocodyloid and an azhdarchid pterosaur.
20. Theropods include the spinosaurid described here, an indeterminate tetanuran known primarily from teeth, and a small basal coelurosaur. Currently, there is no evidence to support the previous referral of small theropod remains from Cadoufaoua to Elaphrosaurus iguidensis (6) [A. F. de Lapparent, Mem. Soc. Geol. Fr. 88A, 1 (1960)]. Sauropods include a common, high-spined basal diplodocoid [formerly referred to as a dicraeosaurine (6)] and a rare titanosaur. Ornithopods include the dryosaurid Valdosaurus nigeriensis [P. M. Galton and P. Taquet, Geobios 15, 147 (1982)], the common "Iguanodon trapu" [S. Chablis, thesis, Université de Paris (1988)], and the high-spined Ouranosaurus nigeriensis (6). Nondinosaurian vertebrates that were not previously recorded include a long-snouted basal crocodyloid and an azhdarchid pterosaur.
21. Theropods include the spinosaurid described here, an indeterminate tetanuran known primarily from teeth, and a small basal coelurosaur. Currently, there is no evidence to support the previous referral of small theropod remains from Cadoufaoua to Elaphrosaurus iguidensis (6) [A. F. de Lapparent, Mem. Soc. Geol. Fr. 88A, 1 (1960)]. Sauropods include a common, high-spined basal diplodocoid [formerly referred to as a dicraeosaurine (6)] and a rare titanosaur. Ornithopods include the dryosaurid Valdosaurus nigeriensis [P. M. Galton and P. Taquet, Geobios 15, 147 (1982)], the common "Iguanodon trapu" [S. Chablis, thesis, Université de Paris (1988)], and the high-spined Ouranosaurus nigeriensis (6). Nondinosaurian vertebrates that were not previously recorded include a long-snouted basal crocodyloid and an azhdarchid pterosaur.
22. Etymology: Souchos, crocodile (Greek); mimos, mimic (Greek); tenere. Ténéré Desert; ensis, from (Latin). Named for the low elongate snout and piscivorous adaptations of the jaws and for the region of the Sahara in which it was discovered. Holotype Partial disarticulated skeleton (MNN GDF500) cataloged in the collections of the Musée National du Niger (MNN), Niamey, Republic of Niger. Referred material: Articulated premaxillae and maxillae (MNN GDF501), right quadrate (MNN GDF502), partial dentaries (MNN GDF503, GDF504, and GDF505), axis (MNN GDF506), posterior cervical vertebra (MNN GDF507), posterior dorsal vertebra (MNN GDF508), two caudal vertebrae (MNN GDF510 and GDF511), and many additional bones and teeth. Diagnosis: Spinosaurid characterized by an elongate posterolateral premaxillary process that nearly excludes the maxilla from the external naris; broadened and heightened posterior dorsal, sacral, and anterior caudal neural spines; robust humeral tuberosities; hypertrophied ulnar olecranon process that is offset from the humeral articulation; and hook-shaped radial ectepicondyle.
23. In contrast to the specimens described here, previously known spinosaurid material from Niger has been limited to fragmentary disarticulated bones that are attributable to an as yet indeterminate spinosaurid (6-8). Recently, however, a new spinosaurid, Cristatusaurus lapparenti, was named on the basis of material from Gadoufaoua (4). The holotypic specimen consists of portions of the premaxillae, maxilla, and dentary, the association of which was not established. The authors state that the material differs from Baryonyx walkeri by the "brevirostrine condition of premaxilla." However, no distinguishing features or proportions are apparent to us or to previous authors (13), who attributed the premaxillae to an indeterminate species of Baryonyx. We therefore regard C. lapparenti as a nomen dubium.
24. We offer alternative identifications for several cranial elements in the holotypic specimen of Baryonyx walkeri. We regard the bones that were identified as the left postorbital, left jugal, right atlantal neural arch, and left angular (13) as the posterior portion of the right surangular, right prearticular, central body of the left pterygoid, and right angular, respectively. These are repositioned accordingly in our cranial reconstruction (Fig. 2, C and D). The plate-shaped anteromedial process of the maxilla was formerly identified as the vomer (13). We regard the deeper proportions of the occiput as reconstructed in B. walkeri (13) as an artifact of unnatural ventral displacement of the quadrate. The cranium in Baryonyx was probably as low, long, and narrow as in Suchomimus. The cervical series in both Baryonyx and Suchomimus shows a dorsal offset of the anterior articular surfaces.
25. E. Buffetaut, Neues Jahrb. Geol. Palaeontol. Monh. 1992, 88 (1992).
26. C. W. Gilmore, Bull. U.S. Natl. Mus. 110, 1 (1920).
27. P. C. Sereno et al., Science 272, 986 (1996).
28. The following 45 synapomorphies (optimized with delayed transformation) correspond with the scored character states [(0) or (1)] (Table 2) that were used in the analysis of the spinosaurid relationships presented in Fig. 4A. Synapomorphies 27 through 34 uniting Baryonyx and Suchomimus cannot be observed in other spinosaurids because of incomplete preservation. Spinosauroidea: 1, anterior ramus of maxilla, length: 70% (0) or 100% or more (1) of maximum depth; 2, lacrimal anterior ramus, length: more (0) or less (1) than 65% of the ventral ramus; 3, humeral deltopectoral crest, length: less (0) or more (1) than 45% of humeral length; 4, radial (forearm) length: more (0) or less (1) than 50% of humeral length; 5, manual digit l-ungual, length: 2.5 (0) or 3 (1) times the depth of the proximal end. Spinosauridae: 6, anterior end of upper and lower jaws, form: convergent (0); expanded into a premaxillary/ dentary rosette (1); 7, snout length: less (0) or more (1) than three times the length of the antorbital fenestra; 8, external nares positioned entirely posterior to the premaxillary tooth row; 9, antorbital fossa, size: larger (0) or smaller (1) than the orbit; 10, interpremaxillary suture, form: open (0); fused (1) at maturity; 11, premaxillary-maxillary articulation, form: scarf or butt joint (0); interlocking (1); 12, maxillary anteromedial process, shape: fluted prong (0); plate (1); 13, maxillary anteromedial process, anterior extension: as far as (0) or far anterior to (1) the anterior margin of the maxilla; 14, paradental laminae: present (0); absent (1); 15, lacrimal anterior and ventral rami, angle of divergence: 75° to 90° (0); 30° to 45° (1); 16, splenial foramen, size: small (0); large (1); 17, midcrown cross section: elliptical (0); circular (1); 18, crown striations: absent (0); present (1); 19, premaxillary tooth count: 3 to 4 (0); 6 to 7 (1); 20, maxillary crowns, spacing: adjacent (0); with intervening space (1); 21, distal root shape: broad (0); strongly tapered (1). Baryonychinae (Suchomimus and Baryonyx): 22, anterior dorsal centra, depth of ventral keel: weak (0); blade-shaped (1); 23, maximum height of dorsal neural spines: less (0) or more (1) than 2.5 times the centrum height; 24, posterior dorsal neural spines, basal webbing: absent (0); present (1); 25, posterior dorsal neural spines, accessory centrodiapophyseal lamina: absent (0); present (1); 26, dentary tooth count: ≃15 (0); ≃30 (1); 27, quadrate head, shape: oval (0); subquadrate (1); 28, quadrate foramen, size: foramen (0); broad fenestra (1); 29, coracoid posterior process, shape: low and rounded (0); crescentic (1); 30, numeral trochanters, size: low and rounded (0); hypertrophied (1); 31, humeral deltopectoral crest, orientation of apex: anterior (0); lateral (1); 32, humeral internal tuberosity, size: low and rounded (0); hypertrophied (1); 33, radial external tuberosity and ulnar internal tuberosity, size: low and rounded (0); hypertrophied (1); 34, pubic foot, size: moderate to large (0); reduced to a small flange (1). Spinosaurinae (Irritator and Spinosaurus): 35, crown recurvature: present (0); very reduced or absent (1); 36, crown serrations: present (0); absent (1). 37, dentary crowns, spacing: adjacent (0); with intervening space (1); 38, premaxiltary tooth 1, size: slightly smaller (0) or much smaller (1) than crowns 2 and 3; 39, diastemata within the premaxillary rosette: narrow (0); broad (1). Torvosauridae: 40, antorbital fossa, width of ventral margin: more (0) or less (1) than 30% of the maximum depth of the posterior (principal) ramus; 41, subcircular depression in the anterior corner of the antorbital fossa: absent (0); present (1); 42, lacrimal foramen, position: near the base (0) or at midheight (1) on the ventral process; 43, jugal posterior ramus, depth: less (0) or more (1) than that of the orbital ramus; 44, postorbital ventral process, cross section of distal half: subcircular (0); U-shaped (1); 45, puboischial fenestra: broadly open (0); closed or nearly closed (1).
29. F. von Huene, Rev. Mus. La Plata 29, 35 (1926);
30. S.-Y. Hu, Vertebr. Palasiat. 8, 42 (1964);
31. P. M. Galton and J. A. Jensen, BYU Geol. Stud. 26, 1 (1979);
32. J. A. Jensen, Great Basin Nat. 45, 710 (1985);
33. B. B. Britt, BYU Geol. Stud. 37, 1 (1991).
34. A previous cladistic analysis placed spinosaurids as the sister taxon to Neotetanurae (13). Notably, synapomorphies linking spinosaurids and torvosaurids were simply ignored in that analysis, and spinosaurids and neotetanurans were joined by one character with an ambiguous optimization (a hook-shaped coracoid).
35. The expanded terminal rosette has a very specific structure in spinosaurids that is probably related to the manner in which its teeth articulate. Seven pre-maxillary teeth are opposed by five dentary teeth. Three diastemata are present in the upper rosette (between teeth 3 and 4, between teeth 5 and 6, and between tooth 7 and the maxillary teeth).
36. Baryonychinae (11) is defined here as all spinosaurids that are more closely related to Baiyonyx than to Spinosaurus; this clade currently includes Baryonyx and Suchomimus. Spinosaurinae (1) is defined here as all spinosaurids that are more closely related to Spinosaurus than to Baryonyx; this clade currently includes Spinosaurus and Irritator (= Angaturama). 27. Revised diagnosis for Baryonyx walkeri: Spinosaurid characterized by fused nasals with a median crest terminating posteriorly in a cruciate process, a solid subrectangular lacrimal horn, a marked transverse constriction of the sacral or anterior caudal centra, a well-formed peg-and-notch articulation between the scapula and coracoid, an everted distal margin of the pubic blade, and a very shallow fibular fossa.
37. Biogeographic hypotheses were optimized with dispersal-vicariance analysis [F. Ronquist, Syst. Biol. 46, 195 (1997)], which counts the minimum number of dispersal or extinction events that is required to account for the observed distributions. There is no cost associated with vicariance. In our example, there is only one hypothesis that requires a single event (dispersal from Europe to Africa during the Early Cretaceous), if one accepts the general pattern of continental breakup as described in the text.
38. E. Buffetaut, Terra Nova 1, 69 (1989); J. Le Loeuff, Cretaceous Res. 12, 93 (1991).
39. E. Buffetaut, Terra Nova 1, 69 (1989); J. Le Loeuff, Cretaceous Res. 12, 93 (1991).
40. E. Stromer, Abh. Bayer. Akad. Wiss. Math. Naturwiss. Abt. N. F. 22, 1 (1934).
41. A. G. Smith, D. C. Smith, B. M. Funnell, Atlas of Mesozoic and Cenozoic Coastlines (Cambridge Univ. Press, Cambridge, 1994), p. 41.
42. D. L. Swofford, PAUP 3.1 (Illinois Natural History Survey, Champaign, IL, 1993).
43. W. B. Harland et al., A Geologic Time Scale (Cambridge Univ. Press, Cambridge, 1989).
44. Supported by the David and Lucile Packard Foundation, National Geographic Society, Pritzker Foundation, and the Women's Board of the University of Chicago. We thank K. Bainbridge, A. Boldizar, J. Bradshaw, J.-P. Cavigelli, J. Ogradnick, and F. Stroik for participation in field excavation; C. Abraczinskas for drawing from the original specimens and executing the final drafts of Figs. 1A and 2 through 4; B. Strack (Field Museum) for assistance with microphotography; Q. Cao and E. Dong for directing fossil preparation and casting; and J. Hopson, F. Lando, R. Molnar, and H.-D. Sues for reviewing an earlier draft of the paper. We gratefully acknowledge the assistance of I. Kouada of the Ministère de L'Enseignement Supérieur de la Recherche et de la Technologie (Niger). For permission to conduct fieldwork, we are indebted to the Republic of Niger.