than they are long from front to back. Whether the neck as a whole was particularly short, is unknown: the holotype vertebra is a cervicodorsal, from the transition between the neck and the back, which would not be long anyway. The exact position of Sigilmassasaurus within the theropod family tree is unknown, but it belongs somewhere inside the theropod subgroup known as Tetanurae and most likely was a member of the family Spinosauridae. Disputed validity The validity of Sigilmassaurus, however, did not go unchallenged shortly after it was named. 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. A 1998 study went further, calling Sigilmassasaurus itself a junior synonym of Carcharodontosaurus. In 2005, however, Argentine paleontologist Fernando Novas and colleagues found 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 differed from Carcharodontosaurus, lending support to the notion that it (and therefore Sigilmassasaurus) is a separate taxon. The same study claimed that the tail vertebrae by Russell assigned to the species were in fact those of iguanodonts. A study in 2013 by Bradley McFeeters and colleagues considered Sigilmassasaurus as valid and an indeterminate member of the Tetanurae. In 2014, German-Moroccan paleontologist Nizar Ibrahim and colleagues referred the specimens of Sigilmassasaurus to Spinosaurus aegyptiacus, together with "Spinosaurus B" and created a neotype for S. aegyptiacus. Spinosaurus maroccanus was considered a nomen dubium following the conclusions of previous papers. In a 2015 re-description of Sigilmassasaurus by Serjoscha Evers and his team, it was considered a valid genus within the Spinosauridae. The authors also proposed Spinosaurus maroccanus as a junior synonym of Sigilmassasaurus, and rejected the proposal of a Spinosaurus aegyptiacus neotype. A study by British paleontologist Thomas Arden and colleagues in 2018 concluded that Sigilmassasaurus was a valid genus and formed a tribe with Spinosaurus termed Spinosaurini. The largest specimen of Spinosaurus cf. aegyptiacus, MSNM V4047, was tentatively assigned to S. brevicollis. On the basis of vertebrae, the researchers suggested that Sigilmassasaurus may have grown larger than Spinosaurus. Although in the absence of associated material, it is difficult to be certain what material belongs to which genus. Below is a