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uring the jurassic, sauropod dinosaurs rose to predominance among vertebrate herbivores, in terms of both species diversity and biomass (e.g., Romer 1966; McIntosh 1990). Their perceived decline on northern landmasses during the Cretaceous has been linked to the evolution of tooth batteries in ornithischian herbivores (e.g., Lull and Wright 1942; Ostrom 1961; Bakker 1978; Lucas and Hunt 1989). On southern landmasses, in contrast, sauropod diversity increased during the Cretaceous (Weishampel 1990; Hunt et al. 1994), and a newly discovered southern sauropod, the rebbachisaurid Nigersaurus taqueti, is now known to have evolved a complex tooth battery (Sereno et al. 1999). Rebbachisaurids are a poorly known sauropod clade, reported thus far only from Cretaceous rocks in South America (Calvo and Salgado 1995; Bonaparte 1996; Apestiguía et al. 2001; Lamanna et al. 2001), Africa (Lavocat 1954; Taquet 1976; Sereno et al. 1999), and Europe (Dalla Vecchia 1998; Pereda-Suberbiola et al. 2003). Many of these are fragmentary finds, leaving much of the skeletal anatomy of this group in question, especially the skull. In this chapter, we describe the tooth-bearing bones and dental battery of Nigersaurus taqueti and provide an initial cranial reconstruction. We outline the feeding specializations common to diplodocoids and how these were modified within rebbachisaurids. Institutional Abbreviation: MNN, Musée National du Niger, Niamey. SYSTEMATIC PALEONTOLOGY SAUROPODA MARSH 1878 EUSAUROPODA UPCHURCH 1995 NEOSAUROPODA BONAPARTE 1986 DIPLODOCOIDEA MARSH 1884 REBBACHISAURIDAE BONAPARTE 1997 NIGERSAURUS SERENO ET AL. 1999 TYPE SPECIES: Nigersaurus taqueti Sereno et al. 1999. AGE: Early Cretaceous (Aptian–Albian). DISCUSSION: Nigersaurus taqueti is the most common sauropod and one of the most common species recovered in the rich vertebrate fauna described from Gadoufaoua, Niger Republic 157 five Structure and Evolution of a Sauropod Tooth Battery Paul C. Sereno and Jeffrey A. Wilson D (Taquet 1976; Sereno et al. 1998, 1999, 2001, 2003; Larsson and Gado 2000). Nevertheless, because the skull and skeleton are delicately constructed and highly pneumatic, there are no complete skulls and only a few partially articulated skeletons. Nigersaurus taqueti was named and identified as a rebbachisaurid by Sereno et al. (1999). An earlier report from the same beds of a dicraeosaurid allied with titanosaurs (Taquet 1976:53) very likely pertains to the same species. NIGERSAURUS TAQUETI SERENO ET AL.1999 (FIGS. 5.1, 5.3–5.8) HOLOTYPE: MNN GDF512, partial disarticulated skull and partially articulated neck preserved in close association on 1 m2 of sandstone outcrop. Sereno et al. (1999:1346) also list a “scapula, forelimbs, and hind limbs” as part of the holotype. These and other bones, which we regard as referable to this species, were found at some distance from the skull and neck and cannot be reliably associated with the holotypic specimen. The partial skeleton described by Taquet (1976) also was discovered in the vicinity of the holotype and may pertain to the same species. LOCALITY AND HORIZON: Gadoufaoua (16° 27´N, 9°8´´E), eastern edge of the Ténéré Desert, Niger Republic; Elrhaz Formation. REFERRED MATERIAL: MNN GDF513, worn crown. Additional skeletal and dental material is described elsewhere. REVISED DIAGNOSIS: Rebbachisaurid sauropod characterized by five accessory fenestrae in the jugal, surangular, and angular; tooth number increased to 20 and to 34 in the maxilla and dentary, respectively; tooth replacement increased to as many as 10–12 in a single column ; premaxilla and dentary lacking alveolar septa; maxilla with oval (vertically elongated) replacement foramina; extension of the dentary tooth row lateral to the sagittal plane of the 158 S T R U C T U R E A N D E V O L U T I O N O F A S A U R O P O D T O O T H B AT T E R Y FIGURE 5.1. Preliminary reconstruction of the skull of Nigersaurus taqueti based on MNN GDF512. (A) Skull in left lateral view. (B) Left lower jaw in dorsal view with tooth batteries removed. 1–5, accessory cranial fenestrae; a, angular; altr, alveolar trough; antfe, antorbital fenestra; ar, articular, br, buccal ridge; cp, coronoid process; d, dentary; d1–d34, replacement foramina for dentary tooth positions 1–34; emf, external mandibular fenestra; en, external naris; f, frontal, fo, foramen; j, jugal; ltf, laterotemporal fenestra; m, maxilla; mc, Meckel’s canal; nf, narial fossa; pm, premaxilla; po, postorbital; popr, paraoccipital process; ps, parasphenoid; q, quadrate; qfo, quadrate fossa; qj, quadratojugal; sa, surangular; saf, surangular foramen, so, supraoccipital; sq, squamosal; sym, symphyseal surface; vc, vascular canal. [3.142.200.226] Project MUSE...

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