Sigilmassasaurus
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| Sigilmassasaurus Fossil range: Late Cretaceous |
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Sigilmassasaurus (see-jil-MAH-sah-SAWR-us; "Sijilmassa lizard") is a genus of tetanuran theropod dinosaur from the middle of the Cretaceous Period of northern Africa. Not much is known about this dinosaur, but it was almost definitely a bipedal carnivore like most other theropods.
Fossils of this dinosaur were found in the Tafilalt Oasis region of Morocco, near the site of the ancient city of Sijilmassa, for which it was named. Canadian paleontologist Dale Russell named Sigilmassasaurus in 1996, from the ancient city and the Greek word sauros ("lizard"). A single species was named, S. brevicollis, which is derived from the Latin brevis ("short") and collum ("neck"), because the neck vertebrae are very short from front to back. Russell also described another specimen as a possible second species of Sigilmassasaurus, although he chose not to name it due to its incomplete nature.
Sigilmassasaurus comes from sediments in southern Morocco, which are called by various names, including the Grés rouges infracénomaniens, Continental Red Beds, and lower Kem Kem Beds. These rocks date back to the Cenomanian, the earliest faunal stage within the Late Cretaceous Period, or about 100 to 94 million years ago (Sereno et al., 1996).
[edit] Disputed validity
The holotype, or original specimen, of S. brevicollis is a single neck vertebra, although Russell referred about fifteen other vertebra found in the same formation to the species. Other material was found in Egypt, and is known as "Spinosaurus B" (Stromer, 1934). Russell considered this Egyptian specimen to belong to Sigilmassasaurus or a closely related animal, and created the family Sigilmassasauridae for these animals (Russell, 1996). The neck vertebrae of these dinosaurs are wider from side to side than they are long from front to back. The exact position of Sigilmassasaurus within the theropod family tree is unknown, but it belongs somewhere inside the theropod subgroup known as Tetanurae.
Some scientists do not believe that Sigilmassasaurus is a valid genus. In 1996, Paul Sereno and colleagues described a Carcharodontosaurus skull (SGM-Din-1) from Morocco, as well as a neck vertebra (SGM-Din-3) which resembled that of "Spinosaurus B," which they therefore synonymized with Carcharodontosaurus (Sereno et al., 1996). A later study went further, calling Sigilmassasaurus itself a junior synonym of Carcharodontosaurus (Sereno et al., 1998).
More recently, however, it was revealed that SGM-Din-3, which was used to synonymize Carcharodontosaurus and "Spinosaurus B" was not actually associated with SGM-Din-1, the Carcharodontosaurus skull described in 1996, and shows clear differences with the holotype of Carcharodontosaurus. Other features of "Spinosaurus B" also clearly differ from Carcharodontosaurus, lending support to the notion that it (and therefore Sigilmassasaurus) is a separate taxon (Novas et al., 2005).
[edit] Paleobiology
Several large theropods (more than one tonne) are known from the Cenomanian of northern Africa, raising questions about how such animals would have coexisted. Species of Spinosaurus, the largest known theropod, has been found in both Morocco and Egypt, as has the huge Carcharodontosaurus. Two smaller theropods, Deltadromeus and Bahariasaurus, have also been found in Morocco and Egypt, respectively, and may be closely related or possibly the same genus. Sigilmassasaurus, from Morocco, and "Spinosaurus B", from Egypt, represent a fourth type of large predator. This situation resembles that in the Late Jurassic Morrison Formation of North America, which boasts up to five theropod genera over one tonne in weight, as well as several smaller genera (Henderson, 1998; Holtz et al., 2004). Differences in head shape and body size among the large North African theropods may have been enough to allow niche partitioning as seen among the many different predator species found today in the African savanna (Farlow & Pianka, 2002).
[edit] References
- Farlow, J.O. & Pianka, E.R. 2002. Body size overlap, habitat partitioning and living space requirements of terrestrial vertebrate predators: implications for the paleoecology of large theropod dinosaurs. Historical Biology 16(1): 21–40.
- Henderson, D.M. 1998. Skull and tooth morphology as indicators of niche partitioning in sympatric Morrison Formation theropods. Gaia 15: 219–226.
- Holtz, T.R., Molnar, R.E., & Currie, P.J. 2004. Basal Tetanurae. In: Weishampel, D.A., Dodson, P., & Osmolska, H. (Eds.). The Dinosauria (2nd Edition). Berkeley: University of California Press. Pp. 71-110.
- Novas, F.E., de Valais, S., Vickers-Rich, P., & Rich, T.H. 2005. A large Cretaceous theropod from Patagonia, Argentina, and the evolution of carcharodontosaurids. Naturwissenschaften 92: 226–230.
- Russell, D. A. 1996. Isolated dinosaur bones from the middle Cretaceous of the Tafilalt, Morocco. Bulletin du Muséum National d’Histoire Naturelle, Paris, Série 4 18: 349–402.
- Sereno, P.C., Dutheil, D.B., Iarochene, M., Larsson, H.C.E., Lyon, G.H., Magwene, P.M., Sidor, C.A., Varricchio, D.J., & Wilson, J.A. 1996. Predatory dinosaurs from the Sahara and Late Cretaceous faunal differentiation. Science 272: 986–991.
- Sereno, P.C., Beck, A.L., Dutheuil, D.B., Gado, B., Larsson, H.C., Lyon, G.H., Marcot, J.D., Rauhut, O.W.M., Sadleir, R.W., Sidor, C.A., Varricchio, D.J., Wilson, G.P., Wilson, J.A. 1998. A long-snouted predatory dinosaur from Africa and the evolution of spinosaurids. Science 282: 1298–1302.
- Stromer, E. 1934. Wirbeltierreste der Baharíje-Stufe (unterstes Cenoman). 13. Dinosauria. Abh. bayer. Akad. Wissensch., math-naturwiss. Abt. N.F. 22:1–79.
