| Sigilmassasaurus | |
|---|---|
 | |
| Middle neckvertebra, specimen CMN 50791 (the holotype ofSpinosaurus maroccanus)[1] | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Family: | †Spinosauridae |
| Tribe: | †Spinosaurini |
| Genus: | †Sigilmassasaurus Russell 1996 |
| Species: | †S. brevicollis |
| Binomial name | |
| †Sigilmassasaurus brevicollis Russell 1996 | |
| Synonyms | |
| |
Sigilmassasaurus (/siːdʒɪlˌmɑːsəˈsɔːrəs/see-jil-MAH-sə-SOR-əs; "Sijilmassa lizard") is a controversialgenus ofspinosauriddinosaur that lived approximately 100 to 94million years ago during theLate CretaceousPeriod in what is now northern Africa. Named in1996 by CanadianpaleontologistDale Russell, it contains a singlespecies,Sigilmassasaurus brevicollis. The identity of the genus has been debated by scientists, with some considering its fossils to represent material from the closely related speciesSpinosaurus aegyptiacus, while others have classified it as a separate taxon, forming the cladeSpinosaurini withSpinosaurus as itssister taxon.
Sigilmassasaurus was a moderately-built, ground-dwelling,bipedalcarnivore, like most othertheropods. It may have had strong neck musculature as evidenced by themorphology of itsvertebrae (backbones).Sigilmassasaurus may have hadsemiaquatic habits and a partiallypiscivorous diet. It coexisted with other large theropods in theKem Kem Group.
Fossils ofSigilmassasaurus were recovered at theKem Kem Formation in theTafilaltOasis region ofMorocco, near the site of the ancient city ofSijilmassa, for which it was named. CanadianpaleontologistDale Russell namedSigilmassasaurus in 1996, from the ancient city and theGreek wordsauros ("lizard"). A singlespecies was named,S. brevicollis, which is derived from theLatinbrevis ("short") andcollum ("neck"), because the neckvertebrae are very short from front to back.[1]Sigilmassasaurus comes from red sandstone sediments in southern Morocco, which are known by various names, including theGrès rouges infracénomaniens, Continental Red Beds, and lowerKem Kem Beds. The rocks date back to theCenomanian, the earlieststage of theLate Cretaceous Period, approximately 100 to 94 million years ago.[2]
Theholotype, or original specimen, ofS. brevicollis, CMN 41857, is a single posteriorneck vertebra, although Russell referred fifteen other vertebrae found in the same formation to the species. Other material had been found inEgypt, and was referred to by German paleontologistErnst Stromer as "Spinosaurus B".[3] Russell in1996 considered the Egyptian specimen, IPHG 1922 X45, to belong toSigilmassasaurus or a closely related animal, naming it as aSigilmassasaurus sp. A secondSigilmassasaurussp. was named by Russel based on specimen CMN 41629, an anterior dorsal vertebra. "Spinosaurus B" would be intermediate in build between this latterSigilmassasaurus sp. andS. brevicollis. Russell created thefamilySigilmassasauridae for these animals.[1] 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 ofSigilmassasaurus within the theropod family tree is unknown, but it belongs somewhere inside the theropod subgroup known asTetanurae and most likely was a member of the familySpinosauridae.[4]
Two distal caudal vertebra (specimens UFMA 1.10.229 and UFMA 1.10.240) discovered in theAlcantara Formation ofBrazil were assigned toSigilmassasaurus in 2002.[5] However, the 2022 study noted that these specimens are indeterminate spinosaurids, most likely belonging toOxalaia considering the geographical and geological context.[6] The 2016 study assigned an isolated quadrate (specimen MHNM.KK376) toSigilmassasaurus brevicollis due to its difference from other specimens assigned toSpinosaurus 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.[8] The 2019 study assigned a juvenile specimen FSAC-KK-18122 toSigilmassasaurus brevicollis based on its identical proportion to BSPG 2011 I 115 which was assigned to the taxon in a 2015 study,[9][4] 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.[8] In 2024, a complete posterior cervical vertebra (specimen NHMUK PV R 38358) was assigned toSigilmassasaurus brevicollis.[10]
The validity ofSigilmassaurus, however, did not go unchallenged shortly after it was named. In 1996,Paul Sereno and colleagues described aCarcharodontosaurus skull (SGM-Din-1) from Morocco, as well as a neck vertebra (SGM-Din-3) which resembled that of "Spinosaurus B," which they thereforesynonymized withCarcharodontosaurus.[11] A 1998 study went further, callingSigilmassasaurus itself ajunior synonym ofCarcharodontosaurus.[12]
In 2005, however, Argentine paleontologistFernando Novas and colleagues found that SGM-Din-3, which was used to synonymizeCarcharodontosaurus and "Spinosaurus B", was not actually associated with SGM-Din-1, theCarcharodontosaurus skull described in 1996, and shows clear differences with theholotype ofCarcharodontosaurus. Other features of "Spinosaurus B" also differed fromCarcharodontosaurus, lending support to the notion that it (and thereforeSigilmassasaurus) is a separate taxon. The same study claimed that the tail vertebrae by Russell assigned to the species were in fact those ofiguanodonts.[13] A study in 2013 by Bradley McFeeters and colleagues consideredSigilmassasaurus as valid and an indeterminate member of the Tetanurae.[14]
In 2014, German-Moroccan paleontologistNizar Ibrahim and colleagues referred the specimens ofSigilmassasaurus toSpinosaurus aegyptiacus, together with "Spinosaurus B" and created aneotype forS. aegyptiacus.Spinosaurus maroccanus was considered anomen dubium following the conclusions of previous papers.[15][16][17] In a 2015 re-description ofSigilmassasaurus by Serjoscha Evers and his team, it was considered a valid genus within the Spinosauridae. The authors also proposedSpinosaurus maroccanus as a junior synonym ofSigilmassasaurus, and rejected the proposal of aSpinosaurus aegyptiacus neotype.[4]
A study by British paleontologist Thomas Arden and colleagues in 2018 concluded thatSigilmassasaurus was a valid genus and formed atribe withSpinosaurus termed Spinosaurini. The largest specimen ofSpinosaurus cf.aegyptiacus, MSNM V4047, was tentatively assigned toSigilmassasaurus brevicollis. On the basis of vertebrae, the researchers suggested thatSigilmassasaurus may have grown larger thanSpinosaurus. Although in the absence of associated material, it is difficult to be certain what material belongs to which genus. Below is acladogram based on the analysis by Arden and colleagues:[18]
| Spinosauridae |
| |||||||||||||||||||||||||||||||||||||||||||||
A 2020 study by British paleontologist Symth and colleagues suggested thatSigilmassasaurus is synonymous withSpinosaurus and the Brazilian spinosaurine genusOxalaia, with both genera falling into theSpinosaurushypodigm. The putative characters supportingSigilmassasaurus's distinction as a valid genus were discussed and found to be invalid. If supported by future research, bothSigilmassasaurus andOxalaia would be rendered junior synonyms ofSpinosaurus and expand its range, which would further support the theory of faunal interchanges between Africa and South America during the Cretaceous.[8]
A 2021 study conducted by Bradley McFeeters ofCarleton University shed further light for the controversial existence of a second spinosaurid within northern Africa. The study concluded that, although limited, the new data could lend support to the controversial hypothesis that two spinosaurid taxa are represented in the Kem Kem Group. The study focused on an unusual mid-cervical vertebra belonging to a large spinosaurid from the Cenomanian Kem Kem Group of Morocco. It was compared to the characteristic morphology of each reconstructed cervical position inSpinosaurus aegyptiacus, based on a recent composite reconstruction that incorporates most previously referred material from this unit. Rather than conforming to any of the previously identified cervical positions in its morphology, the specimen displays a unique combination of mid-cervical characters, with the relatively compact centrum suggesting a position as C4, and the form of the neural arch laminae suggesting a position as C5 or C6. 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. However, according to the authors, the vertebrae could also show that there was more variation in the neck ofSpinosaurus and the authors cautioned that more material is necessary to draw a conclusion.[20]
On the bottoms of its cervical vertebrae,Sigilmassasaurus bore a series of highly rugged bony structures. 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 fromSigilmassasaurus 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 andcrocodilians.[4] This has also been proposed for the related genusIrritator, on account of the prominentsagittal crest running towards the back of its head.[21] However, Evers and colleagues noted that a more thoroughbiomechanical analysis is required for confirmation of this condition inSigilmassasaurus.[4]
Several large theropods (more than onetonne) are known from the Cenomanian ofnorthern Africa, raising questions about how such animals would have coexisted. Species ofSpinosaurus, the longest known theropod, have been found in both Morocco and Egypt, as has the hugeCarcharodontosaurus. Two other theropods,Deltadromeus andBahariasaurus, have also been found in Morocco and Egypt, respectively, and may be closely related or possibly the same genus.Sigilmassasaurus, from Morocco, and "Spinosaurus B", from Egypt, represent a fourth type of largepredator. This situation resembles that in the LateJurassicMorrison Formation ofNorth America, which boasts up to five theropod genera over one tonne in weight, as well as several smaller genera.[22][23] Differences in head shape and body size among the large North African theropods may have been enough to allowniche partitioning as seen among the many different predator species found today in theAfricansavanna.[24]
This article incorporates text available under theCC BY 4.0 license.
.jpg)
.jpg)
.png)
.jpg)
