Sigilmassasaurus - Disputed Validity

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).