Sigilmassasaurus (/siːdʒɪlˌmɑːsəˈsɔːrəs/ see-jil-MAH-sə-SOR-əs; "Sijilmassa lizard") is a controversial and 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.

Canadian paleontologist Dale Russell named Sigilmassasaurus in 1996, from the ancient city and the Greek word sauros ("lizard").

The rocks date back to the Cenomanian, the earliest stage of the Late Cretaceous Period, approximately 100 to 94 million years ago.

[5] However, the 2022 study noted that these specimens are indeterminate spinosaurids, most likely belonging to Oxalaia considering the geographical and geological context.

[6] The 2016 study assigned an isolated quadrate (specimen MHNM.KK376) to Sigilmassasaurus brevicollis due to its difference from other specimens assigned to Spinosaurus aegyptiacus,[7] 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.

[4] 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 putative characters supporting Sigilmassasaurus's distinction as a valid genus were discussed and found to be invalid.

[8] A 2021 study conducted by Bradley McFeeters of Carleton University shed further light for the controversial existence of a second spinosaurid within northern Africa.

Furthermore, the vertebra displays two characters that are previously unknown in spinosaurid mid-cervicals from the Kem Kem Group: a rounded tuberosity present on the hypapophysis (a projection from the bottom of the vertebra) that is not continuous with a ventral keel, and a moderately developed, dorsally oriented epipophysis (a bump located on the postzygapophysis) that does not overhang the postzygapophysis posteriorly.

This revelation leads to the diagnostic value of positionally variable cervical vertebral characters in spinosaurid systematics is discussed.

These were suggested by Evers and colleagues as being possible evidence for substantial neck musculature, since the attachment sites of muscles and ligaments are often indicated by scarring on the bone surface.

The neck muscles inferred from Sigilmassasaurus in particular would have enabled it to rapidly snatch fish out of the water, as indicated by the use of similarly placed musculature in modern birds and crocodilians.

[4] This has also been proposed for the related genus Irritator, on account of the prominent sagittal crest running towards the back of its head.