Sigilmassasaurus ( see-jil-MAH-sə-SOR-əs; "Sijilmassa lizard") is a controversial 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. Two distal caudal vertebra (specimens UFMA 1.10.229 and UFMA 1.10.240) discovered in the Alcantara Formation of Brazil were assigned to Sigilmassasaurus in 2002. However, the 2022 study noted that these specimens are indeterminate spinosaurids, most likely belonging to Oxalaia considering the geographical and geological context. The 2016 study assigned an isolated quadrate (specimen MHNM.KK376) to Sigilmassasaurus brevicollis due to its difference from other specimens assigned to Spinosaurus aegyptiacus, though this was rejected by the 2020 study which noted that these differences in morphology are indicative of variation in skull morphology within a single species. The 2019 study assigned a juvenile specimen FSAC-KK-18122 to Sigilmassasaurus brevicollis based on its identical proportion to BSPG 2011 I 115 which was assigned to the taxon in a 2015 study, but this referral was rejected in a 2020 study based on the fact that the median tubercle and median suture is present in BSPG 2011 I 115 but absent in FSAC-KK-18122, so the presence or absence of such feature should not be used to taxonomically separate isolated spinosaurid remains. In 2024, a complete posterior cervical vertebra (specimen NHMUK PV R 38358) was assigned to Sigilmassasaurus brevicollis.
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