Spinosaurus

''Spinosaurus'' (; ) is a genus of spinosaurid dinosaur that lived in what now is North Africa during the Cenomanian to upper Turonian stages of the Late Cretaceous period, about 99 to 93.5 million years ago. The genus was known first from Egyptian remains discovered in 1912 and described by German palaeontologist Ernst Stromer in 1915. The original remains were destroyed in World War II, but additional material came to light in the early 21st century. It is unclear whether one or two species are represented in the fossils reported in the scientific literature. The best known species is ''S. aegyptiacus'' from Egypt, although a potential second species, ''S. maroccanus'', has been recovered from Morocco. The contemporary spinosaurid genus '' Sigilmassasaurus'' has also been synonymized by some authors with ''S. aegyptiacus'', though other researchers propose it to be a distinct taxon. Another possible junior synonym is '' Oxalaia'' from the Alcântara Formation in Brazil.

''Spinosaurus'' is the longest known terrestrial carnivore; other large carnivores comparable to ''Spinosaurus'' include theropods such as ''Tyrannosaurus'', ''Giganotosaurus'' and '' Carcharodontosaurus''. The most recent study suggests that previous body size estimates are overestimated, and that ''S. aegyptiacus'' reached in length and in body mass. The skull of ''Spinosaurus'' was long, low, and narrow, similar to that of a modern crocodilian, and bore straight conical teeth with no serrations. It would have had large, robust forelimbs bearing three-fingered hands, with an enlarged claw on the first digit. The distinctive neural spines of ''Spinosaurus'', which were long extensions of the vertebrae (or backbones), grew to at least long and were likely to have had skin connecting them, forming a sail-like structure, although some authors have suggested that the spines were covered in fat and formed a hump.Molina-Pérez & Larramendi 2016. ''Récords y curiosidades de los dinosaurios Terópodos y otros dinosauromorfos'', Larousse. Barcelona, Spain p. 259 The hip bones of ''Spinosaurus'' were reduced, and the legs were very short in proportion to the body. Its long and narrow tail was deepened by tall, thin neural spines and elongated chevrons, forming a flexible fin or paddle-like structure.

''Spinosaurus'' is known to have eaten fish, and most scientists believe that it hunted both terrestrial and aquatic prey. Evidence suggests that it was highly semiaquatic, and lived both on land and in water much like modern crocodilians do. ''Spinosaurus'''s leg bones had osteosclerosis (high bone density), allowing for better buoyancy control, and the paddle-like tail was likely used for underwater propulsion. Multiple functions have been put forward for the dorsal sail, including thermoregulation and display; either to intimidate rivals or attract mates. It lived in a humid environment of tidal flats and mangrove forests alongside many other dinosaurs, as well as fish, crocodylomorphs, lizards, turtles, pterosaurs, and plesiosaurs.

Discovery and naming

Naming of species

Two species of ''Spinosaurus'' have been named: ''Spinosaurus aegyptiacus'' (meaning "Egyptian spine lizard") and the disputed ''Spinosaurus maroccanus'' (meaning "Moroccan spine lizard"). The first described remains of ''Spinosaurus'' were found and described in the early 20th century. In 1912, Richard Markgraf discovered a partial skeleton of a giant theropod dinosaur in the Bahariya Formation of western Egypt. In 1915, German paleontologist Ernst Stromer published an article assigning the specimen to a new genus and species, ''Spinosaurus aegyptiacus''.

Fragmentary additional remains from Bahariya, including vertebrae and hindlimb bones, were designated by Stromer as "''Spinosaurus B''" in 1934. Stromer considered them different enough to belong to another species, and this has been borne out. With the advantage of more expeditions and material, it appears that they pertain either to '' Carcharodontosaurus'' or to '' Sigilmassasaurus''.

''S. maroccanus'' was originally described by Dale Russell in 1996 as a new species based on the length of its neck vertebrae. Specifically, Russell claimed that the ratio of the length of the centrum (body of vertebra) to the height of the posterior articular facet was 1.1 in ''S. aegyptiacus'' and 1.5 in ''S. maroccanus''. Later authors have been split on this topic. Some authors note that the length of the vertebrae can vary from individual to individual, that the holotype specimen was destroyed and thus cannot be compared directly with the ''S. maroccanus'' specimen, and that it is unknown which cervical vertebrae the ''S. maroccanus'' specimens represent. Therefore, though some have retained the species as valid without much comment, most researchers regard ''S. maroccanus'' as a ''nomen dubium'' (dubious name) or as a junior synonym of ''S. aegyptiacus''.

Specimens

Six main partial specimens of ''Spinosaurus'' have been described. BSP 1912 VIII 19, described by Stromer in 1915 from the Bahariya Formation, was the holotype. The material consisted of the following items, most of which were incomplete: right and left dentaries and splenials from the lower jaw measuring long; a straight piece of the left maxilla that was described but not drawn; 20 teeth; 2 cervical vertebrae; 7 dorsal (trunk) vertebrae; 3 sacral vertebrae; 1 caudal vertebra; 4 thoracic ribs; and gastralia. Of the nine neural spines whose heights are given, the longest ("i," associated with a dorsal vertebra) was in length. Stromer claimed that the specimen was from the early Cenomanian, about 97 million years ago.

It was destroyed in World War II, specifically "during the night of 24/25 April 1944 in a British bombing raid of Munich" that severely damaged the building housing the Paläontologisches Museum München (Bavarian State Collection of Paleontology). However, detailed drawings and descriptions of the specimen remain. Stromer's son donated Stromer's archives to the Paläontologische Staatssammlung München in 1995, and Smith and colleagues analysed two photographs of the ''Spinosaurus'' holotype specimen BSP 1912 VIII 19 discovered in the archives in 2000. On the basis of a photograph of the lower jaw and a photograph of the entire specimen as mounted, Smith concluded that Stromer's original 1915 drawings were slightly inaccurate. In 2003, Oliver Rauhut suggested that Stromer's ''Spinosaurus'' holotype was a chimera, composed of vertebrae and neural spines from a carcharodontosaurid similar to '' Acrocanthosaurus'' and a dentary from '' Baryonyx'' or ''Suchomimus''. The analysis was rejected in at least one subsequent paper.

NMC 50791, held by the Canadian Museum of Nature, is a mid-cervical vertebra which is long from the Kem Kem Beds of Morocco. It is the holotype of ''Spinosaurus maroccanus,'' as described by Russell in 1996. Other specimens referred to ''S. maroccanus'' in the same paper were two other mid-cervical vertebrae (NMC 41768 and NMC 50790), an anterior dentary fragment (NMC 50832), a mid-dentary fragment (NMC 50833), and an anterior dorsal neural arch (NMC 50813). Russell stated that "only general locality information could be provided" for the specimen, and therefore it could be dated only "possibly" to the Albian.

MNHN SAM 124, housed at the Muséum National d'Histoire Naturelle, is a snout (consisting of partial premaxillae, partial maxillae, vomers, and a dentary fragment). Described by Taquet and Russell in 1998, the specimen is in width; no length was stated. The specimen was located in Algeria, and "is of Albian age." Taquet and Russell believed that the specimen, along with a premaxilla fragment (SAM 125), two cervical vertebrae (SAM 126–127), and a dorsal neural arch (SAM 128), belonged to ''S. maroccanus''.

BM231 (in the collection of the Office National des Mines, Tunis) was described by Buffetaut and Ouaja in 2002. It consists of a partial anterior dentary in length from an early Albian stratum of the Chenini Formation of Tunisia. The dentary fragment, which included four alveoli and two partial teeth, was "extremely similar" to existing material of ''S. aegyptiacus''.

UCPC-2 in the University of Chicago Paleontological Collection consists mainly of two narrow connected nasals with a fluted (ridged) crest from the region between the eyes. The specimen, which is long, was located in an early Cenomanian part of the Moroccan Kem Kem Beds in 1996 and described in the scientific literature in 2005 by Cristiano Dal Sasso of the Civic Natural History Museum in Milan and colleagues.

MSNM V4047 (in the Museo di Storia Naturale di Milano), described by Dal Sasso and colleagues in 2005, consists of a snout (premaxillae, partial maxillae, and partial nasals) long from the Kem Kem Beds. Like UCPC-2, it is thought to have come from the early Cenomanian. Arden and colleagues in 2018 tentatively assigned this specimen to ''Sigilmassasaurus brevicollis'' given its size. However, this assignment was later rejected by other researchers who considered the uniqueness of this specimen to be based on misinterpretations and poor preservation of another specimen, NHMUK R16665, another snout stored that is stored in the Natural History Museum, London.

FSAC-KK 11888 is a partial subadult skeleton recovered from the Kem Kem beds of North Africa. Described by Ibrahim and colleagues (2014) and designated as the neotype specimen (although Evers and colleagues 2015 reject the neotype designation for FSAC-KK-11888). It includes cervical vertebrae, dorsal vertebrae, neural spines, a complete sacrum, femora, tibiae, pedal phalanges, caudal vertebra, several dorsal ribs, and fragments of the skull.Supplementary Information
/ref> The body proportions of the specimen have been debated, as the hind limbs are disproportionately shorter in the specimen than in previous reconstructions. However, it has been demonstrated by multiple paleontologists that the specimen is not a chimera, and is indeed a specimen of ''Spinosaurus'' that suggests that the animal had much smaller hind limbs than previously thought.

Other known specimens consist mainly of very fragmentary remains and scattered teeth. These include:

*A 1986 paper described prismatic structures in tooth enamel from two ''Spinosaurus'' teeth from Tunisia.
* Buffetaut (1989, 1992) referred three specimens from the Institut und Museum für Geologie und Paläontologie of the University of Göttingen in Germany to ''Spinosaurus'': a right maxilla fragment IMGP 969-1, a jaw fragment IMGP 969-2, and a tooth IMGP 969-3. These had been found in a Lower Cenomanian or Upper Albian deposit in southeastern Morocco in 1971.
*Kellner and Mader (1997) described two unserrated spinosaurid teeth from Morocco (LINHM 001 and 002) that were "highly similar" to the teeth of the ''S. aegyptiacus'' holotype.
*Teeth from the Chenini Formation in Tunisia which are "narrow, somewhat rounded in cross-section, and lack the anterior and posterior serrated edges characteristic of theropods and basal archosaurs" were assigned to ''Spinosaurus'' in 2000.
*Teeth from the Echkar Formation of Niger

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