Sigilmassasaurus ( ; "Sijilmassa lizard") is a possibly dubious genus of spinosaurid dinosaur that lived approximately 100 to 94 million years ago during the Late Cretaceous Period in what is now northern Africa. Named in 1996 by Canadian paleontologist Dale Russell, it contains a single species, Sigilmassasaurus brevicollis. The identity of the genus has been debated by scientists, with some considering its fossils to represent material from the closely related species Spinosaurus aegyptiacus, while others have classified it as a separate taxon, forming the clade Spinosaurini with Spinosaurus as its sister taxon.
Sigilmassasaurus was a moderately-built, ground-dwelling, bipedal carnivore, like most other theropods. It may have had strong neck musculature as evidenced by the morphology of its vertebrae (backbones). Sigilmassasaurus may have had semiaquatic habits and a partially piscivorous diet. It coexisted with other large theropods in the Kem Kem Group.
History of research
Fossils of Sigilmassasaurus were recovered at the Kem Kem Formation 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. Sigilmassasaurus comes from red sandstone sediments in southern Morocco, which are known by various names, including the Grès rouges infracénomaniens, Continental Red Beds, and lower Kem Kem Beds. The rocks date back to the Cenomanian, the earliest stage of the Late Cretaceous Period, approximately 100 to 94 million years ago.
The holotype, or original specimen, of S. brevicollis, CMN 41857, is a single posterior neck vertebra, although Russell referred fifteen other vertebrae found in the same formation to the species. Other material had been found in Egypt, and was referred to by German paleontologist Ernst Stromer as "Spinosaurus B". Russell in 1996 considered the Egyptian specimen, IPHG 1922 X45, to belong to Sigilmassasaurus or a closely related animal, naming it as a Sigilmassasaurus sp. A second Sigilmassasaurus sp. was named by Russel based on specimen CMN 41629, an anterior dorsal vertebra. "Spinosaurus B" would be intermediate in build between this latter Sigilmassasaurus sp. and S. brevicollis. Russell created the family Sigilmassasauridae for these animals. The neck vertebrae of these dinosaurs are wider from side to side, about 50%, 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.
Specimen UFMA 1.10.240, a distal caudal vertebra which was discovered in the Alcantara Formation of Brazil was assigned to Sigilmassasaurus in 2002.
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.