Cretaceous sauropods from the sahara and the uneven rate of skeletal evolution among dinosaurs

Science

Volumn 286, Issue 5443, 1999, Pages 1342-1347

  Sereno, Paul C ^a   Beck, Allison L ^a   Dutheil, Didier B ^b   Larsson, Hans C E ^a   Lyon, Gabrielle H ^c   Moussa, Bourahima ^d   Sadleir, Rudyard W ^e   Sidor, Christian A ^a   Varricchio, David J ^f   Wilson, Gregory P ^g   Wilson, Jeffrey A ^h  

^a UNIVERSITY OF CHICAGO   (United States)

^b PSL RESEARCH UNIVERSITY   (France)

^c Project Exploration   (United States)

^d CNRS   (France)

^e UNIVERSITY OF ILLINOIS AT CHICAGO   (United States)

^f MONTANA STATE UNIVERSITY   (United States)

^g UNIVERSITY OF CALIFORNIA   (United States)

^h UNIVERSITY OF MICHIGAN   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

CRETACEOUS; DINOSAUR; EVOLUTION; MORPHOLOGY;

ARTICLE; EVOLUTION; FOSSIL; NONHUMAN; PRIORITY JOURNAL; REPTILE; SKELETON; SKULL;

NIGER;

EID: 0032725320     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.286.5443.1342     Document Type: Article

References (49)

1. P. C. Sereno, Annu. Rev. Earth Planet. Sci. 1997, 435 (1997).
2. L. Salgado and J. F. Bonaparte, Ameghiniana 28, 333 (1991); P. C. Sereno et al., Science 272, 986 (1996); R. A. Coria and L. Salgado, Nature 377, 224 (1995); J. Vertebr. Paleontol. 16, 445 (1996); S. L. Jain and S. Bandyopadhyay, J. Vertebr. Paleontol. 17, 114 (1997); S. D. Sampson et al., Science 280, 1048 (1998). See also (20).
3. L. Salgado and J. F. Bonaparte, Ameghiniana 28, 333 (1991); P. C. Sereno et al., Science 272, 986 (1996); R. A. Coria and L. Salgado, Nature 377, 224 (1995); J. Vertebr. Paleontol. 16, 445 (1996); S. L. Jain and S. Bandyopadhyay, J. Vertebr. Paleontol. 17, 114 (1997); S. D. Sampson et al., Science 280, 1048 (1998). See also (20).
4. L. Salgado and J. F. Bonaparte, Ameghiniana 28, 333 (1991); P. C. Sereno et al., Science 272, 986 (1996); R. A. Coria and L. Salgado, Nature 377, 224 (1995); J. Vertebr. Paleontol. 16, 445 (1996); S. L. Jain and S. Bandyopadhyay, J. Vertebr. Paleontol. 17, 114 (1997); S. D. Sampson et al., Science 280, 1048 (1998). See also (20).
5. L. Salgado and J. F. Bonaparte, Ameghiniana 28, 333 (1991); P. C. Sereno et al., Science 272, 986 (1996); R. A. Coria and L. Salgado, Nature 377, 224 (1995); J. Vertebr. Paleontol. 16, 445 (1996); S. L. Jain and S. Bandyopadhyay, J. Vertebr. Paleontol. 17, 114 (1997); S. D. Sampson et al., Science 280, 1048 (1998). See also (20).
6. L. Salgado and J. F. Bonaparte, Ameghiniana 28, 333 (1991); P. C. Sereno et al., Science 272, 986 (1996); R. A. Coria and L. Salgado, Nature 377, 224 (1995); J. Vertebr. Paleontol. 16, 445 (1996); S. L. Jain and S. Bandyopadhyay, J. Vertebr. Paleontol. 17, 114 (1997); S. D. Sampson et al., Science 280, 1048 (1998). See also (20).
7. L. Salgado and J. F. Bonaparte, Ameghiniana 28, 333 (1991); P. C. Sereno et al., Science 272, 986 (1996); R. A. Coria and L. Salgado, Nature 377, 224 (1995); J. Vertebr. Paleontol. 16, 445 (1996); S. L. Jain and S. Bandyopadhyay, J. Vertebr. Paleontol. 17, 114 (1997); S. D. Sampson et al., Science 280, 1048 (1998). See also (20).
8. P. C. Sereno, J. A. Wilson, H. C. E. Larsson, D. B. Dutheil, H.-D. Sues, Science 266, 267 (1994).
9. P. C. Sereno, Science 284, 2137 (1999).
10. Fragmentary sauropod remains from the Tiourarén Formation were initially described as a new species, Rebbachisaurus tamesnensis [A. F. de Lapparent, Mém. Soc. Géol. France 88A, 1 (1960)]. Type material, however, was not designated, and no diagnostic features were mentioned (3). Lapparent considered the Tiourarén sauropod to be a camarasaurid; elsewhere it has been referred to the Diplodocidae [J. S. McIntosh, in The Dinosauria (Univ. of California Press, Berkeley, CA, 1990), pp. 345-401]. Etymology: Jobar, Jobar (Tamacheck); ia, pertaining to (Greek); tiguidi, Tiguidi (Tamacheck); ensis, from (Latin). Named after the mythical creature "Jobar," to whom local Touregs had attributed the exposed bones, and after the Falaise de Tiguidi, a cliff near the base of which lie the horizons yielding all of its remains. Holotype: Partial articulated skeleton including the axis, forelimbs and hind limbs, pubes, and most of the tail, from the locality Tamérat, cataloged in the collections of the Musée National du Niger (MNN TIG3), Niamey, Republic of Niger. Referred material: Several partial skeletons and isolated bones from Fako, Tawachi, and other localities near the base of the Falaise de Tiguidi (Fig. 1A). Specimens include a partial skull and skeletons of adult individuals (MNN TIG4 and -5), a relatively complete subadult skeleton (MNN TIG6), and an isolated subadult braincase (MNN TIG7). Diagnosis: Eusauropod characterized by cervical prezygapophyses with an accessory anterior process (Fig. 3B, aapr), cervical neural arches with a deep fossa between centropostzygapophyseal and intrapostzygapophyseal laminae, dorsal prezygapophyses with a broad pendant flange, dorsal neural arches with fossa between the parapophyses and diapophyses (Fig. 3C), anterior caudal neural spines with a circular fossa at the base of the prespinal lamina, cervical ribs 3 to 6 with an accessory anterior process, U-shaped first chevron (Fig. 3C), and midcaudal chevrons with a rugose ridge across the distal end of blade (Fig. 3H, r).
11. Fragmentary sauropod remains from the Tiourarén Formation were initially described as a new species, Rebbachisaurus tamesnensis [A. F. de Lapparent, Mém. Soc. Géol. France 88A, 1 (1960)]. Type material, however, was not designated, and no diagnostic features were mentioned (3). Lapparent considered the Tiourarén sauropod to be a camarasaurid; elsewhere it has been referred to the Diplodocidae [J. S. McIntosh, in The Dinosauria (Univ. of California Press, Berkeley, CA, 1990), pp. 345-401]. Etymology: Jobar, Jobar (Tamacheck); ia, pertaining to (Greek); tiguidi, Tiguidi (Tamacheck); ensis, from (Latin). Named after the mythical creature "Jobar," to whom local Touregs had attributed the exposed bones, and after the Falaise de Tiguidi, a cliff near the base of which lie the horizons yielding all of its remains. Holotype: Partial articulated skeleton including the axis, forelimbs and hind limbs, pubes, and most of the tail, from the locality Tamérat, cataloged in the collections of the Musée National du Niger (MNN TIG3), Niamey, Republic of Niger. Referred material: Several partial skeletons and isolated bones from Fako, Tawachi, and other localities near the base of the Falaise de Tiguidi (Fig. 1A). Specimens include a partial skull and skeletons of adult individuals (MNN TIG4 and -5), a relatively complete subadult skeleton (MNN TIG6), and an isolated subadult braincase (MNN TIG7). Diagnosis: Eusauropod characterized by cervical prezygapophyses with an accessory anterior process (Fig. 3B, aapr), cervical neural arches with a deep fossa between centropostzygapophyseal and intrapostzygapophyseal laminae, dorsal prezygapophyses with a broad pendant flange, dorsal neural arches with fossa between the parapophyses and diapophyses (Fig. 3C), anterior caudal neural spines with a circular fossa at the base of the prespinal lamina, cervical ribs 3 to 6 with an accessory anterior process, U-shaped first chevron (Fig. 3C), and midcaudal chevrons with a rugose ridge across the distal end of blade (Fig. 3H, r).
12. R. T. J. Moody and P. J. C. Sutcliffe, Cretaceous. Res. 12, 137 (1991). Principal exposures of the Tiourarén Formation lie in an arc north of the Falaise de Tiguidi, which is formed by the resistant basal sandstone of the Tegama Group (Fig. 1, B and C). Nearly all fossils were found 20 to 30 m below the contact with the Tegama Group in sedimentary rocks consisting primarily of clay-rich overbank deposits with developed paleosols and rare fluvial channels. The Fako locality comprises two bone-bearing units. The lower one is a 50-cm-thick crevasse splay deposit that rapidly covered scavenged carcasses of Jobaria, including an adult individual with an estimated body length of 18 m (fig. 3A) resting on a subadult individual about 75% its size.
13. Despite relatively flat zygapophyseal articular surfaces, living long-necked herbivores (for example, Camelus domesticus, the dromedary camel) routinely engage in extreme neck postures. Sauropod necks, in general, may have been more flexible than inferred from computer modeling [K. A. Stevens and J. M. Parrish, Science 284, 798 (1999)].
14. O. C. Marsh, U.S. Geol. Surv. 16th Annu. Rep. 1894-1895, 133 (1896); B. J. Filla and P. D. Redman, Wyoming Geol. Assoc. Guideb. 1994, 159 (1994).
15. O. C. Marsh, U.S. Geol. Surv. 16th Annu. Rep. 1894-1895, 133 (1896); B. J. Filla and P. D. Redman, Wyoming Geol. Assoc. Guideb. 1994, 159 (1994).
16. J. A. Wilson and P. C. Sereno, J. Vertebr. Paleontol. 18, 1 (1998).
17. J. A. Wilson, thesis, University of Chicago (1999).
18. Originally described as a dicraeosaurid and allied with titanosaurs (14), the Gadoufaoua sauropod is better understood as a rebbachisaurid diplodocoid. Etymology: Niger, for the Republique du Niger; sauros, reptile (Greek); taqueti, after Philippe Taquet. Named after the country of origin and after French paleontologist Philippe Taquet, whose expeditions (1965-72) initiated large-scale paleontological exploration in Niger. Holotype: Partial articulated skeleton from the locality "niveau des Innocents" in the Gadoufaoua region (16°, 27′ latitude, 9°, 8′ longitude) that includes a partial skull (Fig. 2, C and D), neck, scapula, forelimbs, and hind limbs, cataloged in the collections of the Musée National du Niger (MNN GAD512), Niamey, Republic of Niger. Referred material: Several partial skeletons and isolated bones from other localities in Gadoufaoua (Fig. 2E). Diagnosis: Rebbachisaurid characterized by elongate frontal (much narrower than long) with a marked cerebral fossa on the frontal, transversely oriented upper and lower tooth rows, extension of the tooth rows lateral to the plane of the principal ramus of the lower jaw, tooth crowns with prominent medial and lateral marginal ridges, dorsal vertebrae with paired pneumatic spaces at the base of the neural spines, and a prominent rugosity on the medial aspect of the base of the scapular blade (Fig. 2E, ru).
19. The Tegama Group is composed of terrestrial rocks of mid to Late Cretaceous age that are divided into three formations [H. Faure, Mém. B.K.G.M. 47, 1 (1966); J. Greigert and R. Pougnet, Mém. B.R.G.M. 48, 1 (1967)] (Fig 1D). In the region called Gadoufaoua southeast of the Aír Mountains (Fig. 1A), the Tegama Group was divided into eight GAD levels ["GAD" is an abbreviation for Gadoufaoua; E. Molinas, Rapp. C.E.A. Marseille 1965, 1 (1965)]. GAD 5 corresponds with the upper part of the Elrhaz Formation and the lower part of the Echkar Formation, which yielded all of the sauropod remains described here from the Tegama Group.
20. The Tegama Group is composed of terrestrial rocks of mid to Late Cretaceous age that are divided into three formations [H. Faure, Mém. B.K.G.M. 47, 1 (1966); J. Greigert and R. Pougnet, Mém. B.R.G.M. 48, 1 (1967)] (Fig 1D). In the region called Gadoufaoua southeast of the Aír Mountains (Fig. 1A), the Tegama Group was divided into eight GAD levels ["GAD" is an abbreviation for Gadoufaoua; E. Molinas, Rapp. C.E.A. Marseille 1965, 1 (1965)]. GAD 5 corresponds with the upper part of the Elrhaz Formation and the lower part of the Echkar Formation, which yielded all of the sauropod remains described here from the Tegama Group.
21. The Tegama Group is composed of terrestrial rocks of mid to Late Cretaceous age that are divided into three formations [H. Faure, Mém. B.K.G.M. 47, 1 (1966); J. Greigert and R. Pougnet, Mém. B.R.G.M. 48, 1 (1967)] (Fig 1D). In the region called Gadoufaoua southeast of the Aír Mountains (Fig. 1A), the Tegama Group was divided into eight GAD levels ["GAD" is an abbreviation for Gadoufaoua; E. Molinas, Rapp. C.E.A. Marseille 1965, 1 (1965)]. GAD 5 corresponds with the upper part of the Elrhaz Formation and the lower part of the Echkar Formation, which yielded all of the sauropod remains described here from the Tegama Group.
22. Diagnostic titanosaur remains include a tall transversely narrow astragalus (10) and procoelous caudal vertebrae with spongy bone and a neural arch shifted to the anterior end of the centrum.
23. P. Taquet, Cah. Paléontol. 1976, 1 (1976).
24. _ and D. A. Russell, Ann. Paléontol. 85, 85 (1999).
25. P. C. Sereno et al., Science 282, 1298 (1998).
26. F. von Huene, An. Mus. La Plata Ser. 2 3, 1 (1929).
27. J. O. Calvo and L Salgado, Gaia 11, 13 (1995).
28. R. Lavocat, C. K. 19th Int. Geol. Congr. 3, 65 (1954).
29. L. L. Jacobs, D. A. Winkler, W. R. Downs, E. M. Gomani, Palaeontology 36, 523 (1993).
30. E. Stromer, Abh. Bayer. Akad. Wiss. Math. Naturwiss. Abt. 22, 1 (1934).
31. Age rank was established with the midpoint of the first stage (or longer temporal unit) in which the taxon has been recorded. Midpoint values were calculated from a recent time scale (33). Age rank was scaled from 0 to 1.
32. Clade rank (26) was established with recent phylogenetic analyses for Dinosauria (4, 9) with a few terminal taxa collapsed or omitted to achieve single most parsimonious, fully asymmetric cladograms. Clade rank was scaled from 0 to 1.
33. Only unambiguous character-state changes are plotted. If there was no missing ancestral lineage between two or more nodes on the tree (that is, 0 duration), synapomorphies were added to those associated with the next positive duration [method 2 of (28)].
34. The minimum duration for missing ancestral lineages ["ghost taxa"; M. A. Norell, Am. J. Sci. 293A, 407 (1993)] was calculated by subtracting the midpoints of the first occurrence dates at successive nodes.
35. J. A. Gauthier, A. J. Kluge, T. Rowe, Cladistics 4, 105 (1988); M. A. Norell and M. J. Novacek, Cladistics 8, 319 (1992).
36. J. A. Gauthier, A. J. Kluge, T. Rowe, Cladistics 4, 105 (1988); M. A. Norell and M. J. Novacek, Cladistics 8, 319 (1992).
37. A. B. Smith, B. Lafay, R. Christen, Philos. Trans. R. Soc. London Ser. B Biol. Sci. 338, 365 (1992).
38. C. A. Sidor and J. A. Hopson, Paleobiology 24, 254 (1998); P. J. Wagner and C. A. Sidor, Syst. Biol., in press.
39. C. A. Sidor and J. A. Hopson, Paleobiology 24, 254 (1998); P. J. Wagner and C. A. Sidor, Syst. Biol., in press.
40. The greatest missing lineages in higher level sauropod phylogeny occur at the base of sauropod phylogeny, but most of the terminal taxa (except Shunosaurus) still appear successively in time. Spearman rank correlation (corrected for ties) is positive (S = 0.603) and significant (P = 0.0035).
41. D. L. Fox, D. C. Fisher, L. R. Leighton, Science 284, 1816 (1999).
42. In higher level sauropod phylogeny, missing temporal lineages are shortest or nonexistent at the base of the neosauropod radiation, where a greater amount of skeletal change is known to have occurred. Within Sauropoda, skeletal change is not positively correlated with the duration of missing lineages or significant [Spearman rank correlation (corrected for ties) is negative (S = -1.00, P = 0.1573)].
43. An alternative data matrix for tetanuran theropods [T. R. Holtz Jr., J. Paleontol. 68, 1100 (1994)] was sampled with some terminal taxa collapsed or omitted to achieve a single most parsimonious cladogram. No iteration could produce a positive or significant correlation between the number of unambiguous synapomorphies and estimated elapsed time.
44. F. M. Gradstein et al., Soc. Econ. Paleontol. Mineral. Spec. Publ. 54, 95 (1995).
45. A. C. Smith, D. C. Smith, B. M. Funnell, Atlas of Mesozoic and Cenozoic Coastlines (Cambridge Univ. Press, Cambridge, 1994).
46. Y. Zhang, The Middle Jurassic Dinosaur Fauna from Dashanpu, Zigong, Sichuan (Sichuan Publishing House of Science Technology, Chengdu, China, 1988).
47. J. S. Mcintosh, C. A. Miles, K. C. Cloward, J. R. Parker, Bull. Gunma Mus. Nat. Hist. 1, 1 (1996).
48. C. W. Gilmore, Mem. Carnegie Mus. 10, 347 (1925).
49. Supported by the David and Lucile Packard Foundation, the National Geographic Society, the Pritzker Foundation, and the Women's Board of the University of Chicago. We thank C. Abraczinskas for drawing original specimens and executing the final drafts of all other figures; Q. Cao, D. Blackburn, J. Conrad, E. Dong, J. Komar, E. Love, C. Noto, and volunteer staff for fossil preparation and casting; and J. Conrad, J. Hopson, and F. Lando for reviewing an earlier draft of this report We acknowledge the assistance of I. Kouada and B. Gado of the Ministère de L'Enseignement Supérieur de la Recherche et de la Technologie and Institut de Recherches en Sciences Humaine, respectively (Niger). For permission to conduct field work, we are indebted to the Republique du Niger.