Spinosaurus

Spinosaurus is a genus of large spinosaurid theropod dinosaurs that lived in what now is North Africa during the Cenomanian stage of the Late Cretaceous period, about 100 to 94 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 type species S. aegyptiacus is mainly known from Egypt and Morocco. Although a potential second species, S. maroccanus, has been recovered from Morocco, this dubious species is likely a junior synonym of S. aegyptiacus. Other possible junior synonyms include Sigilmassasaurus from the Kem Kem beds in Morocco and Oxalaia from the Alcântara Formation in Brazil, though other researchers propose both genera to be distinct taxa.
Spinosaurus is among the largest known terrestrial carnivores; other large carnivores comparable to Spinosaurus include theropods such as Tyrannosaurus, Giganotosaurus and the coexistent Carcharodontosaurus. The most recent study suggests that S. aegyptiacus could have 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 few to no Glossary of [dinosaur anatomy#serrations|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, 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. The hip bones of Spinosaurus were reduced, and the legs were very short in proportion to the body allegedly. 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, aquatic prey and small to medium terrestrial prey as well. Evidence suggests that it was semiaquatic; how capable it was of swimming has been strongly contested. Spinosauruss leg bones had osteosclerosis, allowing for better buoyancy control. 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

Initial finds

The first discovery of Spinosaurus may have been in October 1898, when French geologist Fernand Foureau unearthed two unusual teeth in Cenomanian-aged sediments of the Djoua Escarpment in what is now southern Algeria, then French Algeria. Foreau found the specimens while on the Foureau-Lamy Expedition of 1898-1900, which traveled across the Sahara from Algeria to Lake Chad. In 1905, French geologist Emile Haug described the fossils unearthed while on the expedition, including the two teeth which he assigned to the fish Saurocephalus. However, in 1915 German paleontologist and describer of Spinosaurus Ernst Stromer reassigned the teeth to Spinosaurus. Later studies have agreed with this assessment, however the teeth themselves has since been lost.
The first confidently referable remains of Spinosaurus were discovered in the autumn of 1912 by Austro-Hungarian paleontologist Richard Markgraf, a fossil collector who was financed by Stromer and the Bavarian [Academy of Sciences and Humanities|Bavarian Academy of Sciences], in deposits of the Bahariya Formation in the Bahariya Oasis of western Egypt. The sediments of the Bahariya Formation come from the Cenomanian stage of the Late Cretaceous period, one of many Cretaceous-aged formations of North Africa. In 1915, Stromer described these remains as belonging to a new genus and species of dinosaur, Spinosaurus aegyptiacus. The generic name Spinosaurus comes from the Latin spina, meaning "spine", and the Greek sauros, meaning "lizard", and thus "spine lizard". The specific name aegyptiacus derives from Egypt, where the fossils were unearthed. Spinosaurus aegyptiacus type specimen consists of elements of the mandible, a maxilla fragment, cervical, caudal, and dorsal vertebrae, including much of the, ribs, teeth, and some gastralia. On the basis of photographs of the mandible and 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 specimen was a chimera, composed of vertebrae and neural spines from a carcharodontosaurid similar to Acrocanthosaurus and a mandible from Baryonyx or Suchomimus, an analysis that was rejected in at least one subsequent paper.
In April of 1914, another expedition to the Bahariya Oasis by Markgraf unearthed an incomplete skeleton of a spinosaurid. This skeleton was poorly preserved and, as a result of illegal unpacking and insufficient repacking by Anglo-Egyptians during World War I, was greatly damaged. After much deliberation due to the war and poor Anglo-German relations, the skeleton arrived in Germany in 1922 where it was described by Stromer in 1934. Stromer assigned the skeleton to Spinosaurus, but considered it different enough from S. aegyptiacus that it would belong to its own Spinosaurus species, "Spinosaurus B". In 1996, a study by American paleontologist Paul Sereno and colleagues assigned cervical vertebrae referred to "Spinosaurus B" and the spinosaurid Sigilmassasaurus to the carcharodontosaurid Carcharodontosaurus. This was based on the erroneous belief that a cervical vertebra found nearby a skull of Carcharodontosaurus belonged to the same individual. Sereno and colleagues also reasoned that stout cervicals like those of Sigilmassasaurus would be needed to carry the skulls of carcharodontosaurids, however later analyses have proven that "Spinosaurus B" and Sigilmassasaurus are not synonyms or contain fossils from Carcharodontosaurus. Some studies have continued to refer "Spinosaurus B" to Sigilmassasaurus, although this is still debated.
In 1936, Stromer worked with Dr. Erhardt to create a skeletal reconstruction of Spinosaurus based on fossils of the holotype, "Spinosaurus B", and related taxa. Stromer, although hesistant due to the lack of known remains, and Erhardt worked meticulously with the little material they had and produced a restoration that filled in missing elements of Spinosaurus skeleton with the tyrannosaurid theropods Tyrannosaurus and Gorgosaurus.' Unfortunately, during the night of 24/25 April 1944, the building of the Paläontologisches Museum München of the Bavarian Academy of Sciences was severely damaged during the British Bombing of Munich during World War II. Here, fossils of Spinosaurus, including the holotype, were on display. Due to personal and political tensions between Stromer and the museum's curator, who was a fervent Nazi, the fossils were not rehoused and were subsequently destroyed as a result of the bombing. Stromer's finds, including Spinosaurus, received little academic or public attention. In 1995, Stromer's son donated Stromer's archives to the Paläontologische Staatssammlung München, leading to a 2006 study by American researcher Joshua Smith and colleagues of the photographs, two of which were of Spinosaurus'' holotype.

Resurgent interest

Additional fossils of Spinosaurus were recovered at the Kem Kem Beds in the Tafilalt Oasis region of Morocco, near the site of the ancient city of Sijilmassa. In 1996, Canadian paleontologist Dale Russell described these fossils, consisting of three cervical vertebrae, two mandible fragments, and the neural spine of a dorsal vertebra, as belonging to a new species of Spinosaurus, S. maroccanus. The specific name, maroccanus, derives from royaume du Maroc, where the fossils were unearthed. The site where S. maroccanus fossils were found is made up of 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. Of these fossils, a cervical vertebra, was selected as the holotype of S. maroccanus. S. maroccanus was differentiated from S. aegyptiacus based on the length of its neck vertebrae. Specifically, Russell claimed that the ratio of the length of the centrum to the height of the posterior 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 or as a junior synonym of S. aegyptiacus or Sigilmassasaurus brevicollis. Some studies have referred the holotype and other referred specimens of S. maroccanus as S. cf. aegyptiacus. The specimens previously ascribed as paratypes of S. maroccanus are reidentified as indeterminate spinosaurid specimens that are currently not identifiable at the generic level.
No more spinosaurid material would be described from Africa until the latter half of the 20th century, with Spinosaurus remaining an enigmatic and mysterious theropod. However, in 1986 the discovery of Baryonyx, a baryonychine spinosaurid from the Cretaceous of England, led to Spinosaurus and Baryonyx being recognized as relatives by American paleontologist Gregory S. Paul. Later studies have since grouped Baryonyx and Spinosaurus in Spinosauridae, which has grown to encompass several genera from the Cretaceous. Beginning in the 1980s, Spinosaurus material began being described from sites in Algeria, Morocco, and Tunisia, although these fossils were often isolated and fragmentary. In 1986, a paper referred several teeth found Cretaceous deposits in Tunisia to Spinosaurus, being the first evidence of the taxon's existence in the country. In 1989, French paleontologist Eric Buffetaut assigned two jaw fragments and a tooth that had been unearthed in a deposit of the Kem Kem Beds in Taouz, Morocco to Spinosaurus sp., expanding the known distribution of the genus to Morocco. In the 1990s, a wealth of spinosaurid remains were described from South America, Asia, Africa, and Europe, strengthening the understanding of Spinosaurus and Spinosauridae. However, much of the anatomy of Spinosaurus still remained obscure and many studies proposed that fossils previously assigned to the genus or Sigilmassasaurus were actually from iguanodont ornithischians, megaraptorans, carcharodontosaurids, or other forms of theropod.

Neotype

In 2008, a Moroccan fossil collector based in Erfoud presented a few fragmentary dinosaur fossils to Italian paleontologist Nizar Ibrahim, who suspected they may belong to Spinosaurus. The next year, several other fossils, constituting a partial skeleton, were acquired by the Museo di Storia Naturale di Milano from an Italian fossil dealer who had purchased them from the same dealer as Ibrahim. Later, Ibrahim visited the MSNM and was presented the material by Italian paleontologists Cristiano Dal Sasso and Simone Maganuco. Ibrahim recognized that the MSNM fossils and the ones he had seen in 2008 were from a similar sandstone matrix and that the neural spines of the MSNM fossils were similar to those depicted by Stromer in 1915, leading him to think that they may be from the same individual and from Spinosaurus. Collaboration between Ibrahim and several other paleontologists began, with the fossils from the MSNM getting sent to the University of Chicago for study and Ibrahim forming an international team of paleontologists to study the bones and visit the original site. In 2013, Ibrahim, Moroccan paleontologist Samir Zouhri, and British paleontologist David Martill ventured to Casablanca in search of the original fossil dealer, who they were able to track down. Subsequently, the dealer took them back to the site where he found all of the fossils. Over the course of several years, a skeleton consisting of skull fragments, some cervical, dorsal, and caudal vertebrae, neural spines, a complete sacrum, much of the hindlimbs, several pedal phalanges, and several dorsal ribs was unearthed. This skeleton comes from a locality of the Douria Formation of the Kem Kem Beds, making it from the Cenomanian stage of the mid-Cretaceous period, in Zrigat, Morocco. This skeleton was deposited at the Casablanca Museum under specimen number FSAC-KK-11888.
In 2014, Ibrahim and colleagues assigned the fossils to S. aegyptiacus, designated it the neotype, and stated that all North African Cenomanian spinosaurid material belongs to S. aegyptiacus. The description of these remains were met with intrigue, surprise, and controversy, as the authors claimed that Spinosaurus was a possibly quadrupedal, semiaquatic, short-limbed spinosaurid. 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. In 2015, British paleontologist Serjoscha Evers and colleagues rejected the neotype designation for FSAC-KK-11888 on the basis of the lack of association or locality information for FSAC-KK-11888, the geographical separation between the holotype and FSAC-KK-11888 localities, and anatomical differences between FSAC-KK-11888 and the holotype. Evers and colleagues argue for the validity of S. marrocanus and S. aegyptiacus, stating that FSAC-KK-11888 is likely from the former. Additionally, the geographical separation of FSAC-KK-11888 and the holotype as well as the detailed description of the holotype by Stromer are evidence that FSAC-KK-11888 does not meet the ICZN 's requirements for a neotype and that the creation of a neotype is unnecessary for S. aegyptiacus. Additionally, some paleontologists have suggested that the proportions of the dorsal vertebrae compared to the legs of FSAC-KK-11888 when compared to the proportions of "Spinosaurus B" illustrate that either the former is a composite /chimera between an individual known from dorsal vertebrae and an individual known from limb, pelvic, and tail material or that FSAC-KK-11888 is not from Spinosaurus. Between 2015 and 2019, several additional expeditions to the site unearthed additional fossils of FSAC-KK-11888 including many caudal vertebrae, composing about 80% of the tail, elements of the peses and hindlimbs, skull fragments, and more. Around 90% of this new material was found in late 2018 whereas some fragments, such as the skull fragments, were found in debris of previous expeditions. In 2020, Ibrahim and colleagues described the tail of FSAC-KK-11888, which they stated closely compares to the caudal vertebrae of the holotype and "Spinosaurus B". The material found on these expeditions perfectly matches elements of the FSAC-KK-11888, proving that they come from a single individual.

Specimens

''Spinosaurus aegyptiacus''

BSP 1912 VIII 19, described by Stromer in 1915 from the Bahariya Formation, is the holotype of S. aegyptiacus. This type specimen consisted of: 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; two cervical vertebrae; seven dorsal vertebrae; three ; one caudal vertebra; four thoracic ribs; and gastralia. Of the nine neural spines whose heights are given, the longest was in length. This specimen was part of the Paläontologisches Museum München collection, which was destroyed during World War II.
In 1934, Stromer described several specimens of Spinosaurus from the Bahariya Formation, one of which contained three cervical centra, two partial cervical neural arches, a dorsal neural spine, two dorsal ribs, and the distal part of a. Stromer stated that this specimen, IPHG 1912 VIII 22, "can almost all be referred to the B-form 'Spinosaurus B', but are more similar in the shape of the high proc. spin. to the type ." This specimen was destroyed along with the rest of Stromer's Spinosaurus material, only now being represented by a few illustrations.
Stromer assigned a collection of other fossils to S. aegyptiacus in his 1934 paper, including: a dorsal vertebra, a furcula fragment, and two teeth. These fossils were found at the same site as "Spinosaurus B" and did not survive the bombing of the Paläontologisches Museum München.
FSAC-KK-11888 is a subadult specimen referred to S. aegpticacus and is the proposed neotype of the species that was discovered in by a Moroccan collector and excavated by a series of expeditions between 2008 and 2019 in a layer of the Douria Formation, Kem Kem Beds in Zrigat, Morocco. As of 2025, specimen includes a partial,,,,, incomplete, fragments, additional skull fragments, teeth, the axis, the seventh cervical vertebra, a partial tenth cervical rib, an incomplete fourth dorsal neural spine, four partial dorsal vertebrae, an incomplete ninth dorsal neural spine, several partial dorsal ribs, gastralia, three sacral centra, elements of 30+ caudal vertebrae including 29 centra, 19 complete and incomplete, metacarpal II fragment, manual phalanx II-1, the proximal end phalanx II-2, manual ungual of digit III, pelves, femora, tibiae, fibulae, a nearly complete right pes, and elements of the left pes. Although suggested to be a chimera or composite, the material collected and described by Ibrahim and colleagues matches the material found in 2008 by the Moroccan collector.
From the Museo di Storia Naturale di Milano, Ibrahim and colleagues assigned a multitude of specimens that had been found in the Kem Kem Beds of Morocco to S. aegyptiacus, including a quadrate, two cervical vertebrae, three dorsal vertebrae, an ilium of a subadult, a distal caudal vertebra, a metacarpal III, the proximal portion of a manual phalanx, the distal end of a metatarsal, a pedal phalanx III-1, and two other pedal phalanges.
From the University of Chicago Paleontological Collection, Ibrahim and colleagues assigned an incomplete dentary of a subadult, a mid caudal vertebra, two distal caudal vertebrae, and a manual phalanx I-1 to S. aegyptiacus that were excavated from layers of the Kem Kem Beds in Morocco.
MHNM.KK374, MHNM.KK375, MHNM.KK377, MHNM.KK378 and MSNM V6896 are five isolated quadrates of different sizes that were collected by locals and acquired commercially in the Kem Kem region of southeastern Morocco, provided by Moroccan researcher François Escuillié, and are deposited in the collections of the Muséum d'Histoire Naturelle of Marrakesh. These five specimens were assigned to S. aegyptiacus by Portuguese paleontologist Christophe Hendrickx and colleagues, since these quadrates are more similar to the proposed neotype's quadrates than that of the other morphotype, which was assigned to Sigilmassasaurus brevicollis.
''Spinosaurus'' sp./''Spinosaurus'' cf. ''aegyptiacus''
Brazilian paleontologist Alexander Kellner and American paleontologist Bryn J. Mader described two unserrated spinosaurid teeth from Morocco that were "highly similar" to the teeth of the S. aegyptiacus holotype.
In 1989 and 1992, Buffetaut 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, a jaw fragment, and a tooth. These had been found in a Lower Cenomanian or Upper Albian deposit in southeastern Morocco in 1971.
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.
BM231 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.
In 2007, American paleontologist Steve Brusatte and colleagues tentatively referred several teeth from the Echkar Formation of Northern Niger to Spinosaurus.
In February 2008, Japanese paleontologist Hasegawa Yoshikazu purchased an isolated spinosaurid tooth at a fossil show in Tucson, Arizona which was later described by Yoshikazu and colleagues in a 2010 study on spinosaurid tooth sculpturing. They identified the tooth, which was originally labeled as Spinosaurus maroccanus, as Spinosaurus sp.
In 2018, Italian paleontologists Simone Maganuco and Dal Sasso described an isolated pedal ungual they assigned to cf. Spinosaurus aegyptiacus based on similarities to those of Moroccan Spinosaurus specimens. This pedal ungual had been legally acquired by the MSNM from fossil sellers who had found it in deposits of the Kem Kem Beds near Erfoud, Morocco. According to their study, this ungual belongs to a juvenile Spinosaurus which measured only long.
In 2019, British paleontologists Rebecca Lakin and Nicholas Longrich assigned an incomplete dorsal and nearly complete cervical vertebra to Spinosaurus cf. aegyptiacus on the basis of its proportions and differences with vertebrae typically referred to Sigilmassasaurus. These vertebrae are small, coming from juvenile individuals.
Nigerien ''Spinosaurus'' sp. nov.:
In 1998, French paleontologist Philippe Taquet and Russell described a rostrum, premaxilla fragment, a pair of cervical centra, and an isolated neural arch they assigned to S. maroccanus that had been found in the Albian-aged Gara Samani Formation near Tademaït, Algeria in the southern Sahara. They referred these fossils to S. maroccanus based on the proportions of the cervical centra, however they have since been reassigned to Spinosaurus sp, though Sereno and colleagues stated these fossils may belong to a new species of Spinosaurus.
In 2007, Brusatte and colleagues described a new species of Carcharodontosaurus, C. iguidensis, on the basis of an incomplete maxilla that had been found in layers of the Echkar Formation in Iguidi, Niger. In the same study, Brusatte and colleagues assigned a cervical centrum, a braincase, a collection of teeth, and a dentary to the species based on size and apparent similarities to bones in C. saharicus. However, a 2016 study by Italian paleontologists Alfio Alessandro Chiarenza and Andrea Cau stated that the cervical centrum belongs to Sigilmassasaurus instead while Sereno and colleagues reassigned it to Spinosaurus sp., stating it may also belong to a new species of Spinosaurus.
In 2019, an expedition to an outcrop of the Echkar Formation near Agadez, Niger unearthed a pair of maxillae associated with a partial right dentary and a tooth that Sereno and colleagues described as belonging to Spinosaurus, tentatively identifying it as the genus level but stating it may belong to a new species of Spinosaurus.
In 2024, a conference abstract at the Society of Vertebrate Paleontology 84th Annual Meeting by Sereno and colleagues announced the discovery of a new species of Spinosaurus from the Cenomanian-aged Farak Formation of central Niger. This abstract mentioned that this new species is known from several specimens, including skull material, some of which preserve a unique, scimitar-shaped skull crest.
''Sigilmassasaurus brevicollis/''"''Spinosaurus'' B"
CMN 41857, initially described by Russell as the holotype specimen of Sigilmassasaurus brevicollis, was collected by local collectors in an unknown locale, likely near Taouz, in layers of the Kem Kem Beds in Morocco and sold to the CMN by a Moroccan fossil dealer.
NMC 50791 is a mid-cervical vertebra, which was selected as the holotype of Spinosaurus maroccanus by Russell in 1996, that was unearthed from strata of the Kem Kem Beds of Morocco. Other specimens referred to S. maroccanus in the same paper were two other mid-cervical vertebrae, an anterior dentary fragment, a mid-dentary fragment, and an anterior dorsal neural arch. Russell stated that "only general locality information could be provided" for the specimen, and therefore it could be dated only "possibly" to the Albian.
In 1934, Stromer described BSP 1922 X45, a specimen from the Bahariya Formation that he tentatively considered to be from a distinct species of Spinosaurus, which he called "Spinosaurus B". This skeleton, consisting of two partial teeth, two dorsal centra, three dorsal vertebrae, two incomplete dorsal ribs, partial gastralia, two ilium fragments, the distal end of a femur, tibiae, three pedal phalanges, and a pedal ungual, was destroyed during World War II.
In 2018, British paleontologists Rebecca Lakin and Nicholas Longrich described an isolated cervical vertebra as belonging to a juvenile individual of Sigilmassasaurus brevicollis. This was done on the basis of its proportions, keel, and laminae anatomy, which are similar to that of S. brevicollis specimens. This vertebra was unearthed near Erfoud, Morocco in rocks of the Cenomanian-aged Ifezouane Formation of the Kem Kem Beds. This fossil comes from a small, immature individual, estimated at long.
From the Paläontologisches Museum München and the Natural History Museum of London, Evers and colleagues assigned two dorsal vertebrae, six cervical vertebrae, two cervical centra to Sigilmassasaurus brevicollis and tentatively assigned an anterior mid-dorsal vertebra, three anterior dorsal vertebrae, and a neural arch from a mid-cervical vertebra to the species as well. All of these vertebrae were found in the Ifezouane and/or Aoufous Formations of the Kem Kem Beds by private collectors in Morocco. Together, these specimens include much of the cervical column and some of the anterior dorsal column.
In 2012, American paleontologist Matthew Carrano and colleagues assigned an isolated mid-cervical vertebra, UCPC OT6, from the Kem Kem Beds of Morocco to Carcharodontosaurus saharicus. The next year, Canadian paleontologist Bradley McFeeters and colleagues reassigned the vertebra to Sigilmassasaurus brevicollis based on its anatomy and that the cervical vertebrae, an opinion echoed by Evers and colleagues.
SGM DIN-3-5 are three cervical vertebrae that had been found in 1995 by a University Chicago Expedition to deposits of the Kem Kem Beds in Errachidia, Morocco. Sereno and colleagues assigned SGM DIN-3 to C. saharicus in 1996 and Brusatte and Sereno assigned SGM DIN-4 and SGM DIN-5 to C. saharicus in 2007 based on the erroneous belief that they were associated with an incomplete skull that had been found by the crew. Later studies have argued that they belong to a spinosaurid, with McFeeters and colleagues and Evers and colleagues stating that they belong to Sigilmassasaurus brevicollis.
MHNM.KK376 is an isolated quadrate that was unearthed from the Kem Kem Beds of Morocco and later deposited at the Muséum d'Histoire Naturelle of Marrakech. It was described in 2016 by Hendrickx and colleagues as belonging to Sigilmassasaurus brevicollis based on the presence of two different morphotypes in the Kem Kem Beds, which, according to the study, is evidence of two, distinct spinosaurines in the Kem Kem Beds. However, a 2020 study on variation within Spinosaurus considers these differences in morphology to be indicative of variation in skull morphology within a single species, as is the case in the other theropod Allosaurus.
In 2024, Brazilian paleontologist Mauro Lacerda and colleagues assigned an isolated cervical vertebra that had been found in an unknown locality in the Kem Kem Beds of Morocco to Sigilmassasaurus brevicollis.
Validity

In 1996, Russell assigned "Spinosaurus B" to Sigilmassasaurus but considered it to be distinct at species level. A 1998 study assigned "Spinosaurus B" to the carcharodontosaurid Carcharodontosaurus saharicus; in 2005 and 2008 it was suggested that the presacral vertebrae assigned to Sigilmassasaurus and "Spinosaurus B" belonged to iguanodonts; a 2013 paper classified "Spinosaurus B" and Sigilmassasaurus as indeterminate members of Orionides, with the caudal vertebrae and some dorsal vertebrae being Dinosauria indet. and Tetanurae indet. respectively; and another 2013 study proposed that "Spinosaurus B" was a megaraptoran based on similarities in the pedal unguals to Australovenator.
Some scientists have considered the genus Sigilmassasaurus a junior synonym of Spinosaurus. In Ibrahim and colleagues, specimens of Sigilmassasaurus and "Spinosaurus B" were assigned to Spinosaurus aegyptiacus, FSAC-KK-11888 was the proposed neotype, and Spinosaurus maroccanus was considered as a nomen dubium following the conclusions of the other papers. A 2015 re-description of Sigilmassasaurus disputed these conclusions, and considered the genus valid, with inclusion of S. maroccanus as a synonym of Sigilmassasaurus instead. This conclusion was further supported in 2018 by Arden and colleagues, who consider Sigilmassasaurus to be a distinct genus, though a very close relative of Spinosaurus, the two unified in the tribe Spinosaurini which was coined in the study.
The 2020 study indicates synonymy between Spinosaurus and Sigilmassasaurus, and considered specimens previously referred to Sigilmassasaurus as those of Spinosaurus. For instance, the referral of an isolated quadrate to Sigilmassasaurus brevicollis, based on its difference from other specimens assigned to Spinosaurus aegyptiacus, was rejected by the 2020 study which noted that these differences in morphology are indicative of variation in skull morphology within a single species. Lakin and Longrich assigned a juvenile specimen FSAC-KK-18122 to Sigilmassasaurus brevicollis based on its identical proportions to BSPG 2011 I 115, which was assigned to the taxon in a 2015 study, and the presence of a median tubercle and median suture. However, this referral was also rejected in a 2020 study based on the fact that the median tubercle and median suture is present in BSPG 2011 I 115 but actually absent in FSAC-KK-18122, so the presence or absence of such feature should not be used to taxonomically separate isolated spinosaurid remains. Regardless of the synonymy of Sigilmassasaurus with Spinosaurus, some authors consider the possibility that there could be a second distinct spinosaurid in North Africa during the Cenomanian age based on quadrate, frontal, ilium, and other morphotypes. Additionally, in 2024, a complete posterior cervical vertebra was assigned to Sigilmassasaurus brevicollis.

''Oxalaia quilombiensis''

The holotype specimen of Oxalaia is a pair of fused premaxillae that had been found in 1999 on Cajual Island, Maranhão, in the Northeast Region of Brazil from the Cenomanian-aged Alcântara Formation. This specimen was described as belonging to a new genus and species of spinosaurid, Oxalaia quilombiensis, by Kellner and colleagues.
An isolated fragment of the left maxilla was unearthed from the same locale as the holotype and described along with it by Kellner and colleagues. It was assigned to Oxalaia based on its similarities to the maxillae of other spinosaurids like Spinosaurus.
Aside from the skull bones, numerous teeth and two distal caudal vertebrae have been unearthed in the Alcântara Formation. The latter were initially described in 2002 as belonging to Sigilmassasaurus, however later studies have declared them to be indeterminate spinosaurid vertebrae or from Oxalaia itself.
Validity

Since the National Museum of Brazil fire in 2018 engulfed the palace housing the museum, with specimens of Oxalaia possibly being destroyed, any classification should remain tentative. It was noted by paleontologist Rodrigo Vargas Pêgas in 2025 that the badly damaged remains of Oxalaia were recovered, and the publication for the recovered items is in preparation.
In a 2020 assessment of Kem Kem spinosaurine material written by British paleontologist Robert Smyth et al., it was suggested the Brazilian spinosaurine Oxalaia to be a potential junior synonym of Spinosaurus aegyptiacus. This was based on looking at the specimens assigned to Oxalaia, and the supposed autapomorphies of this taxon to be insignificant and fall within the hypodigm of Spinosaurus aegyptiacus. If supported by future studies, this would imply Spinosaurus aegyptiacus had a wider distribution and supports the faunal exchange between South America and Africa during this time.
However, subsequent studies have rejected the synonymy of Oxalaia with Spinosaurus aegyptiacus based on diagnostic features of the holotype and the referred specimen. In 2021, Lacerda, Grillo and Romano noted that the anteromedial processes of the holotype maxillae contact medially, a condition not observed in MSNM V4047 which has been referred to as a specimen of Spinosaurus, and thus adding a new possible diagnostic feature of Oxalaia. They also suggested that the premaxilla of Oxalaia is wider in the posterior portion than that of MSNM V4047, and that the lateral morphology of its rostrum was distinguished from other spinosaurines based on their morphometric analysis. In 2023, Spanish researcher Erik Isasmendi and colleagues considered Oxalaia as a valid taxon based on the examination of its referred maxilla which suggests that the position of its external naris would have been more anteriorly located, a condition similar to that of Irritator and baryonychines, differing from African spinosaurines including S. aegyptiacus.

Spinosaurinae indet:

In 1975, Moroccan fossil dealers unearthed a large, incomplete rostrum of a spinosaurid from a red sandstone deposit of the Kem Kem Beds near Taouz, Morocco. This rostrum was then sold to a private collection and remained in one until 2002, when it was acquired by the Museo di Storia Naturale di Milano. In 2005, Dal Sasso and colleagues described the rostrum as specimen of Spinosaurus cf. aegyptiacus on the basis of its similarities to a rostrum referred to S. marrocanus and its similarities in tooth count and alveolar anatomy to those of other Spinosaurine specimens. This specmenconsists of a snout long and an isolated fish vertebra, tentatively referred to Onchopristis, has been associated with the tooth alveolus of this specimen. Similarly, a dentary fragment of Spinosaurus aegyptiacus, MPDM 31, is associated with the rostral tooth of Onchopristis. 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.
In 1996, an expedition by the University of Chicago led by Sereno unearthed a pair of fused nasal bones, preserving a crest, from a deposit of the Kem Kem Beds in northern Morocco. This specimen was an unidentified bone fragment until 2002, when it was identified as spinosaurid and then described by Dal Sasso and colleagues in 2005. They assigned it to cf. Spinosaurus aegyptiacus due to a lack of overlap with other specimens of Spinosaurus. However, the nasal does have the level-plane figure observed in specimens of Spinosaurus like MSNM V4047, supporting its referral to the genus.
In 2002, Buffetaut and Tunisian paleontologist Mohamed Ouaja assigned a dentary fragment to Spinosaurus cf. aegyptiacus, the first non-dental specimen of Spinosaurus to be described from the country. Ouaja discovered the fossil in a deposit of the Chenini Sandstones, an Albian-aged site in Jebel Miteur near the city of Tataouine.
In 2015, Algerian researcher Madani Benyoucef and colleagues described several teeth they referred to Spinosaurus aegyptiacus that had been found in layers of the Cenomanian-aged "Grès rouges" Formation in western Algeria. These teeth were found at two sites, the Menaguir site and the Kénadsa site.
OPH2103 is a skull roof, made up of both frontals and parietals that was unearthed from the Kem Kem Beds of Errachidica Province, Morocco by a local collector, sold to the Ophis Museo Paleontologico e Centro Erpetologico in Teramo, and described by Cau and Paterna. This skull roof was recovered in Spinosaurinae and was grouped with "Bone Taxon A" from Arden and colleagues.
Lacerda and colleagues described several specimens they referred to as Spinosaurinae indet. that are in the possession of the Natural History Museum of London and were unearthed by Moroccan fossil collectors from layers of the Kem Kem Beds in the Tafilalt Region, Morocco. These specimens include a nearly complete rostrum containing both premaxillae, maxillae, and the anterior portion of the nasals that had first been described by British paleontologist Andrew Milner in 2003, a pair of premaxillae with a fragment of the maxilla attached, an isolated right premaxilla piece, a pair of nasals, a partial skull roof, a neural arch of a mid-dorsal, a neural spine of a mid-dorsal, two incomplete ilia, and a left femur. The former specimen bears several differences with the rostrum MSNM V4047 and was used as evidence that there are two spinosaurines in the Kem Kem Beds by Lakin and Longrich, however many of these differences, with the exception of tooth count, were a result of taphonomic distortion, poor preservation, or misinterpretation. Additionally, premaxillary tooth count has been demonstrated to be variable even within premaxillae of individual spinosaurids, indicating that it is simply a product individual variation. Lacerda and colleagues provisonally assigned these remains to Spinosaurinae indet. due to the lack of overlapp with the S. aegyptiacus holotype, the potential presence of Sigilmassasaurus as a distinct spinosaurid, and the lack of detailed study of the taxonomy of Spinosaurus.
In 2025, Cau and Paterna also described a pair of quadrates, a posterior cervical/anterior dorsal vertebra, two dorsal vertebral centra, a proximal caudal vertebra, a mid-caudal vertebra, a distal caudal vertebra, and a pedal phalanx. All of these remains were collected from layers of the Kem Kem Beds in Morocco. The pedal phalanx was noted to be extremely large, about 145% larger than the proposed neotype, a size comparable to that of the largest spinosaurine specimens like MSNMV4047.
Spinosauridae indet
In 2021, McFeeters described an isolated, unusual mid-cervical vertebra that had been found in the Kem Kem Beds of Morocco and purchased by the Royal Ontario Museum. This cervical vertebra was noted for being its own morphotype of spinosaurid cervical among those in the Kem Kem Beds, indicating that it may be its own taxon or an example of individual variation in Spinosaurus.
In 2018, Lakin and Longrich described a right premaxilla, right quadrate, incomplete mid-cervical vertebra, and anterior dorsal vertebra of juvenile Spinosaurus that had been found in the Kem Kem Beds of Morocco.
In 2019, Moroccan paleontologist Slimane Zitouni and colleagues described a fragmentary ilium that had been purchased from Moroccan fossil dealers and originally found in the Kem Kem Beds as belonging to an indeterminate abelisauroid. However, in 2020 Spanish paleontologist Elisabete Malafaia and colleagues suggested that the ilium comes from an indeterminate tetanuran whereas Smyth and colleagues stated it comes from Spinosaurus. Ibrahim and colleagues stated that it is a questionable ilium with unknown affinities, whereas Brazilian paleontologist André Luis de Souza-Júnior and colleagues followed Zitouni and colleagues' decision and identified it as Abelisauroidea indet. In 2025, a phylogenetic analysis and study by Thai paleontologist Adun Samathi found it to be from an indeterminate spinosaurine, possibly Spinosaurus itself, and that there are two morphotypes of spinosaurine ilia in the Kem Kem Beds based on several differences he observed between the neotype's ilium and MHNM KK04.
In 2001, fossils of cf. Spinosaurus were stated to be known from the Campanian-aged Mut Formation of southern Egypt. However, Spinosaurus is traditionally known purely from the Albian-Cenomanian ages of the Cretaceous.
Fossils from the Campanian Quseir Formation of western Egypt have been tentatively assigned to Spinosaurus and Carcharodontosaurus, but these specimens were never described in detail and thus classified as indeterminate.
In 2008, a thesis reported the discovery of dental and skeletal remains of dinosaurs, including Spinosaurus sp., from the Akhamil and/or Oued Ameregh localities at the southern margin of the Tihert Plateau in southern Algeria. The fossil fauna suggests that the strata of these localities comes from the Cenomanian.
In 2010, a conference abstract at the European Association of Vertebrate Paleontology 8th Annual Meeting described the discovery of a spinosaurid tooth "belonging to a spinosaurine close to Spinosaurus" from rocks of the Kiklah Formation, which dates to the Aptian-Albian, in Libya.
Material possibly belonging to Spinosaurus from the Turkana Grits of Kenya has been noted in 2004.
Description

Size

Since its discovery, Spinosaurus has been a contender for the largest theropod dinosaur. Both Friedrich von Huene in 1926 and Donald F. Glut in 1982 listed it as among the most massive theropods in their surveys, at in length and upwards of in weight. In 1988, Gregory S. Paul also listed it as the longest theropod at, but gave a lower mass estimate of.
In 2005, Dal Sasso and colleagues assumed that Spinosaurus and the related Suchomimus had the same body proportions in relation to their skull lengths, and thereby calculated that Spinosaurus was in length and in weight. The estimates were criticized because the skull length estimate was uncertain, and scaling Suchomimus, which was long and in mass, to the range of estimated lengths of Spinosaurus would produce an estimated body mass of.
François Therrien and Donald Henderson, in a 2007 paper using scaling based on skull length, challenged previous estimates of the size of Spinosaurus, finding the length too great and the weight too small. Based on estimated skull lengths of, their estimates include a body length of and a body mass of. The lower estimates for Spinosaurus would imply that the animal was shorter and lighter than Carcharodontosaurus and Giganotosaurus. The Therrien and Henderson study has been criticized for the choice of theropods used for comparison, and for the assumption that the Spinosaurus skull could be as little as in length.
In 2014, Ibrahim and his colleagues suggested that Spinosaurus aegyptiacus could reach over in length. In 2022, however, Paul Sereno and his colleagues suggested that Spinosaurus aegyptiacus reached a maximum body length of and a maximum body mass of by constructing a CT-based 3D skeletal model "with the axial column in neutral pose." They argued that the 2D graphical reconstruction of the aquatic hypothesis by Ibrahim and his colleagues in 2020 overestimated the presacral column length by 10%, ribcage depth by 25%, and forelimb length by 30% over dimensions based on CT-scanned fossils; these proportional overestimates shift the center of mass anteriorly when translated to a flesh model, and thus the estimate from Ibrahim and his colleagues cannot be considered a reliable body size estimate.

Skull

Its skull had a narrow snout filled with straight conical teeth that lacked serrations. There were six or seven teeth on each side of the very front of the upper jaw, in the premaxillae, and another twelve in both maxillae behind them. The second and third teeth on each side were noticeably larger than the rest of the teeth in the premaxilla, creating a space between them and the large teeth in the front of the maxilla; large teeth in the lower jaw faced this space. The very tip of the snout holding those few large front teeth was expanded, and a small crest was present in front of the eyes. Using the dimensions of three specimens known as MSNM V4047, UCPC-2, and BSP 1912 VIII 19, and assuming that the postorbital part of the skull of MSNM V4047 had a shape similar to the postorbital part of the skull of Irritator, Dal Sasso and colleagues estimated that the skull of Spinosaurus was long, but more recent estimates suggest a length of. The Dal Sasso and colleagues skull length estimate is questioned because skull shapes can vary across spinosaurid species and because MSNM V4047 may not belong to Spinosaurus itself, though recent studies have reconfirmed it as a specimen of Spinosaurus.

Postcranial skeleton

As a spinosaurid, Spinosaurus would have had a long, muscular neck, curved in a sigmoid, or S-shape. Its shoulders were prominent, and the forelimbs large and stocky, bearing three clawed digits on each hand. The first finger would have been the largest. Spinosaurus had long phalanges, and only somewhat recurved claws, suggesting that its hands were longer compared to those of other spinosaurids.
Very tall neural spines growing on the back vertebrae of Spinosaurus formed the basis of what is usually called the animal's "sail". The lengths of the neural spines reached over 10 times the diameters of the centra from which they extended. The neural spines were slightly longer front to back at the base than higher up, and were unlike the thin rods seen in the pelycosaur finbacks such as Edaphosaurus, Ianthasaurus and Dimetrodon, contrasting also with the thicker spines in the iguanodontian Ouranosaurus.
Spinosaurus sails were unusual, although other dinosaurs, namely Ouranosaurus, which lived a few million years earlier in the same general region as Spinosaurus, and the Early Cretaceous South American sauropod Amargasaurus, might have developed similar structural adaptations of their vertebrae. The sail may be an analog of the sail of the Permian synapsid Dimetrodon, which lived before the dinosaurs even appeared, produced by convergent evolution.
The structure may also have been more hump-like than sail-like, as noted by Stromer in 1915 and by Jack Bowman Bailey in 1997. In support of his "buffalo-back" hypothesis, Bailey argued that in Spinosaurus, Ouranosaurus, and other dinosaurs with long neural spines, the spines were relatively shorter and thicker than the spines of pelycosaurs ; instead, the dinosaurs' neural spines were similar to the neural spines of extinct hump-backed mammals such as Megacerops and Bison latifrons. In 2014, Ibrahim and colleagues instead posited that the spines were covered tightly by skin, similar to a crested chameleon, given their compactness, sharp edges, and likely poor blood flow.
Spinosaurus had a significantly smaller pelvis than that of other giant theropods, with the surface area of the ilium half that of most members of the clade. The hind limbs were short, at just over 25 percent of the total body length, with the tibia being longer than the femur. Unlike in other theropods, the hallux of Spinosaurus touched the ground, and the phalanges of the toe bones were unusually long and well-built. At their ends were shallow claws that had flat bottoms. This type of foot morphology is also seen in shorebirds, indicating that Spinosauruss feet evolved for walking across unstable substrate and that they may have been webbed.
From the caudal vertebrae of the tail projected significantly elongated, thin neural spines, akin to the condition observed in some other spinosaurids, though to a more extreme degree. Coupled with the also elongated chevron bones on the underside of the caudals, this resulted in a deep and narrow tail with a paddle or fin-like shape, comparable to the tails of newts and crocodilians.

Classification

Spinosaurus is the type genus of the family Spinosauridae, subfamily Spinosaurinae, and tribe Spinosaurini. Spinosaurinae includes Spinosaurus, Oxalaia and Sigilmassasaurus, Irritator, Angaturama and possibly Ichthyovenator, ''Siamosaurus, and Camarillasaurus. Spinosaurini is defined as a clade including all spinosaurids closer to Spinosaurus aegyptiacus than Irritator challengeri and Oxalaia quilombensis, which are distinguished from spinosaurins due to their less elongate premaxillae and premaxillae which are excluded from the external naris. Spinosauridae was a clade named by Stromer for just Spinosaurus. Stromer noted some similarities of Spinosaurus to other theropods known at the time like Dryptosaurus and Tyrannosaurus, however due to the unique and specialized nature of Spinosaurus teeth, vertebrae, and jaw he opted to put it in its own clade of theropods. Stromer proposed that Streptospondylus and Antrodemus were possible ancestors of Spinosaurus, but stated that the remains of Spinosaurus were too fragmentary to be sure. From the 1920s to 1980s, Spinosaurus was typically classified as the sole member of Spinosauridae, a megalosaurid, or a carnosaur. However, some studies by paleontologists like American researcher Alfred Romer included the high-spined theropods Acrocanthosaurus and Altispinax in Spinosauridae based on their tall neural spines. This has not been supported by later studies, which typically classify these taxa as members of Carcharodontosauridae or Allosauroidea instead of Spinosauridae.
In 1986, British paleontologists Alan Charig and Angela Milner described Baryonyx, which they considered distinct enough to be classified in its own family of theropod dinosaurs: Baryonychidae. However, in 1988 American paleontologist Gregory S. Paul argued that Baryonyx and Spinosaurus were related based on their notched snouts and stated they may be late-surviving dilophosaurids. In a 1989 paper, Buffetaut supported this conclusion, stating that they were both piscivorous, related theropods. Descriptions of Irritator, Cristatusaurus, and other spinosaurids led to the realization of a transcontinental clade of spinosaurids. As more spinosaurids were named, the interrelationships of Spinosauridae became better understood. In 1998, Sereno and colleagues described Suchomimus, a spinosaurid from the Cretaceous of Niger. In their description, Sereno and colleagues defined Spinosauroidea as a clade including spinosaurids and torvosaurids, however this clade is considered synonymous with Megalosauroidea, and Spinosauridae as a clade composed of spinosauroids closer related to Spinosaurus aegyptiacus than Torvosaurus tanneri. Additionally, Sereno and colleagues recognized the existence of two subfamilies within Spinosauridae: Baryonychinae, which included Suchomimus and Baryonyx, and Spinosaurinae, which included Spinosaurus and Irritator. In 2004, American researcher Thomas Holtz and colleagues defined Spinosaurinae as including all spinosaurids closer related to Spinosaurus aegyptiacus than Baryonyx walkeri. The spinosaurines share unserrated straight teeth that are widely spaced, as opposed to the baryonychines, which have serrated curved teeth that are numerous. Since the 1990s, spinosaurids have been recognized from the Cretaceous, and possibly Jurassic, of Africa, Asia, Europe, and South America.

Phylogeny

Spinosauridae has been the subject of many different phylogenetic analyses, with Spinosaurus commonly found in a clade with spinosaurids like Irritator and Oxalaia whereas Baryonychinae often includes Baryonyx and Suchomimus. However, research by Brazilian paleontologist Marcos Sales and colleagues indicate that the South American spinosaurids Angaturama, Irritator, and Oxalaia were intermediate between Baronychinae and Spinosaurinae based on their craniodental features and cladistic analysis. This indicates that Baryonychinae may in fact be non-monophyletic and that Spinosaurinae is reduced, including only Angaturama, Spinosaurus, and Oxalaia. Their cladogram can be seen below.
A phylogenetic analysis by Barker and colleagues separated specimens of Spinosaurus into their own OTUs, finding Sigilmassasaurus, several referred specimens of Spinosaurus, and the Spinosaurus holotype in a clade. Within this clade, Spinosaurus holotype and the proposed neotype as sister taxa. Their cladogram can be seen below:

Evolution

Spinosaurids appear to have been widespread from the Barremian to the Cenomanian stages of the Cretaceous period, about 130 to 95 million years ago. Possibly the earliest remains of spinosaurids are known from the Middle Jurassic of Niger and India, the latter of which otherwise has no remains of spinosaurids. They shared features such as long, narrow, crocodile-like skulls; sub-circular teeth, with fine to no serrations; the terminal rosette of the snout; and a secondary palate that made them more resistant to torsion. In contrast, the primitive and typical condition for theropods was a tall, narrow snout with blade-like teeth with serrated carinae. The skull adaptations of spinosaurids converged with those of crocodilians; early members of the latter group had skulls similar to typical theropods, later developing elongated snouts, conical teeth, and secondary palates. These adaptations may have been the result of a dietary change from terrestrial prey to fish. Unlike crocodiles, the post-cranial skeletons of baryonychine spinosaurids do not appear to have aquatic adaptations. Sereno and colleagues proposed in 1998 that the large thumb-claw and robust forelimbs of spinosaurids evolved in the Middle Jurassic, before the elongation of the skull and other adaptations related to fish-eating, since the former features are shared with their megalosaurid relatives. They also suggested that the spinosaurines and baryonychines diverged before the Barremian age of the Early Cretaceous.
Several theories have been proposed about the biogeography of the spinosaurids. Since Suchomimus was more closely related to Baryonyx than to Spinosaurus—although that genus also lived in Africa—the distribution of spinosaurids cannot be explained as vicariance resulting from continental rifting. Sereno and colleagues proposed that spinosaurids were initially distributed across the supercontinent Pangea, but split with the opening of the Tethys Sea. Spinosaurines would then have evolved in the south and baryonychines in the north, with Suchomimus the result of a single north-to-south dispersal event. Buffetaut and the Tunisian palaeontologist Mohamed Ouaja also suggested in 2002 that baryonychines could be the ancestors of spinosaurines, which appear to have replaced the former in Africa. Milner suggested in 2003 that spinosaurids originated in Laurasia during the Jurassic, and dispersed via the Iberian land bridge into Gondwana, where they radiated. In 2007, Buffetaut pointed out that palaeogeographical studies had demonstrated that Iberia was near northern Africa during the Early Cretaceous, which he found to confirm Milner's idea that the Iberian region was a stepping stone between Europe and Africa, which is supported by the presence of baryonychines in Iberia. The direction of the dispersal between Europe and Africa is still unknown, and subsequent discoveries of spinosaurid remains in Asia and possibly Australia indicate that it may have been complex.
In 2016, the Spanish palaeontologist Alejandro Serrano-Martínez and colleagues reported the oldest known spinosaurid fossil, a tooth from the Middle Jurassic of Niger, which they found to suggest that spinosaurids originated in Gondwana, since other known Jurassic spinosaurid teeth are also from Africa, but they found the subsequent dispersal routes unclear. Some later studies instead suggested this tooth belonged to a megalosaurid. Candeiro and colleagues suggested in 2017 that spinosaurids of northern Gondwana were replaced by other predators, such as abelisauroids, since no definite spinosaurid fossils are known from after the Cenomanian anywhere in the world. They attributed the disappearance of spinosaurids and other shifts in the fauna of Gondwana to changes in the environment, perhaps caused by transgressions in sea level. Malafaia and colleagues stated in 2020 that Baryonyx remains the oldest unquestionable spinosaurid, while acknowledging that older remains had also been tentatively assigned to the group. Barker and colleagues found support for a European origin for spinosaurids in 2021, with an expansion to Asia and Gondwana during the first half of the Early Cretaceous. In contrast to Sereno, these authors suggested there had been at least two dispersal events from Europe to Africa, leading to Suchomimus and the African part of Spinosaurinae.

Paleobiology

Function of neural spines

The function of the dinosaur's sail or hump is uncertain; scientists have proposed several hypotheses including heat regulation and display. In addition, such a prominent feature on its back could make it appear even larger than it was, intimidating other animals.
The structure may have been used for thermoregulation. If the structure contained abundant blood vessels, the animal could have used the sail's large surface area to absorb heat. This would imply that the animal was only partly warm-blooded at best and lived in climates where night-time temperatures were cool or low and the sky usually not cloudy. It is also possible that the structure was used to radiate excess heat from the body, rather than to collect it. Large animals, due to the relatively small ratio of surface area of their body compared to the overall volume, face far greater problems of dissipating excess heat at higher temperatures than gaining it at lower. Sails of large dinosaurs added considerably to the skin area of their bodies, with minimum increase of volume. Furthermore, if the sail was turned away from the sun, or positioned at a 90 degree angle towards a cooling wind, the animal would quite effectively cool itself in the warm climate of Cretaceous Africa. However, Bailey was of the opinion that a sail could have absorbed more heat than it radiated. Bailey proposed instead that Spinosaurus and other dinosaurs with long neural spines had fatty humps on their backs for energy storage, insulation, and shielding from heat.
Many elaborate body structures of modern-day animals serve to attract members of the opposite sex during mating. It is possible that the sail of Spinosaurus was used for courtship, in a way similar to a peacock's tail. Stromer speculated that the size of the neural spines may have differed between males and females.

Gimsa and colleagues suggest that the dorsal sail of Spinosaurus was analogous to the dorsal fins of sailfish and served a hydrodynamic purpose. Gimsa and others point out that more basal, long-legged spinosaurids had otherwise round or crescent-shaped dorsal sails, whereas in Spinosaurus, the dorsal neural spines formed a shape that was roughly rectangular, similar in shape to the dorsal fins of sailfish. They therefore argue that Spinosaurus used its dorsal neural sail in the same manner as sailfish, and that it also employed its long narrow tail to stun prey like a modern thresher shark. Sailfish employ their dorsal fins for herding schools of fish into a "bait ball" where they cooperate to trap the fish into a certain area where the sailfish can snatch the fish with their bills.
The sail could have possibly reduced yaw rotation by counteracting the lateral force in the direction opposite to the slash as suggested by Gimsa and colleagues.
Spinosaurus anatomy exhibits another feature that may have a modern analogy: its long tail resembled that of the thresher shark, employed to slap the water to herd and stun shoals of fish before devouring them.
The strategies that sailfish and thresher sharks employ against shoaling fish are more effective when the shoal is first concentrated into a 'bait ball'. Since this is difficult for individual predators to achieve, they cooperate in this effort. When herding a shoal of fish or squid, sailfish also raise their sails to make themselves appear larger. When they slash or wipe their bills through shoaling fish by turning their heads, their dorsal sail and fins are outstretched to stabilize their bodies hydrodynamically. Domenici and colleagues postulate that these fin extensions enhance the accuracy of tapping and slashing. The sail can reduce yaw rotation by counteracting the lateral force in the direction opposite to the slash. This means that prey is less likely to recognize the massive trunk as being part of an approaching predator.
Spinosaurus exhibited the anatomical features required to combine all three hunting strategies: a sail for herding prey more efficiently, as well as flexible tail and neck to slap the water for stunning, injuring or killing prey. The submerged dorsal sail would have provided a strong centreboard-like counterforce for powerful sidewards movements of the strong neck and long tail, as performed by sailfish or thresher sharks. While smaller dorsal sails or fins make the dorsal water volume better accessible for slashing, it can be speculated that their smaller stabilization effect makes lateral slashing less efficient. Forming a hydrodynamic fulcrum and hydrodynamically stabilizing the trunk along the dorsoventral axis, Spinosaurus' sail would also have compensated for the inertia of the lateral neck by tail movements and vice versa not only for predation but also for accelerated swimming. This behavior might also have been one reason for Spinosaurus' muscular chest and neck reported by Ibrahim and colleagues.

Diet and feeding

It is unclear whether Spinosaurus was primarily a terrestrial predator or a piscivore, as indicated by its elongated jaws, conical teeth and raised nostrils. The hypothesis of spinosaurs as specialized fish eaters has been suggested before by A. J. Charig and A. C. Milner for Baryonyx. They base this on the anatomical similarity with crocodilians and the presence of digestive acid-etched fish scales in the rib cage of the type specimen. Large fish are known from the faunas containing other spinosaurids, including the Mawsonia, in the mid-Cretaceous of northern Africa and Brazil. Direct evidence for spinosaur diet comes from related European and South American taxa. Baryonyx was found with fish scales and bones from juvenile Iguanodon in its stomach, while a tooth embedded in a South American pterosaur bone suggests that spinosaurs occasionally preyed on pterosaurs, but Spinosaurus was likely to have been a generalized and opportunistic predator, possibly a Cretaceous equivalent of large grizzly bears, being biased toward fishing, though it undoubtedly scavenged and took many kinds of small or medium-sized prey.
In 2009, Dal Sasso and colleagues. reported the results of X-ray computed tomography of the MSNM V4047 snout. As the foramina on the outside all communicated with a space on the inside of the snout, the authors speculated that Spinosaurus had pressure receptors inside the space that allowed it to hold its snout at the surface of the water to detect swimming prey species without seeing them. A 2013 study by Andrew R. Cuff and Emily J. Rayfield concluded that bio-mechanical data suggests that Spinosaurus was not an obligate piscivore and that its diet was more closely associated with each individual's size. The characteristic rostral morphology of Spinosaurus allowed its jaws to resist bending in the vertical direction, but its jaws were poorly adapted with respect to resisting lateral bending compared to other members of this group and modern alligators. This suggests that Spinosaurus preyed more regularly on fish than it did on land animals, although considered predators of the former too. In 2022, Sakamoto estimated that Spinosaurus had an anterior bite force of 4,829 newtons and a posterior bite force of 11,936 newtons. Based on this estimate, he asserted that the jaws of Spinosaurus are adapted for generating relatively faster shutting speeds with less muscle input force, indicating that the animal likely killed its prey with fast-snapping jaws rather than slow-crushing bites, a trait commonly observed in animals which have a semi-aquatic feeding habit.
A 2024 paper suggests that Spinosaurus and other spinosaurines in addition to fish also preyed upon small to medium-sized terrestrial vertebrates, and had relatively weak bite forces compared to those of other theropods.

Aquatic habits

A 2010 isotope analysis by Romain Amiot and colleagues found that oxygen isotope ratios of spinosaurid teeth, including teeth of Spinosaurus, indicate semiaquatic lifestyles. Isotope ratios from tooth enamel and from other parts of Spinosaurus and of other predators from the same area such as Carcharodontosaurus were compared with isotopic compositions from contemporaneous theropods, turtles, and crocodilians. The study found that Spinosaurus teeth from five of six sampled localities had oxygen isotope ratios closer to those of turtles and crocodilians when compared with other theropod teeth from the same localities. The authors postulated that Spinosaurus switched between terrestrial and aquatic habitats to compete for food with large crocodilians and other large theropods respectively. A 2018 study by Donald Henderson, however, refutes the claim that Spinosaurus was semiaquatic. By studying the buoyancy in lungs of crocodilians and comparing it to the lung placement in Spinosaurus, it was discovered that Spinosaurus could not sink or dive below the water surface. It was also capable of keeping its entire head above the water surface while floating, much like other non-aquatic theropods. Furthermore, the study found that Spinosaurus had to continually paddle its hind legs to prevent itself from tipping over onto its side, something that extant semiaquatic animals do not need to perform. Henderson therefore theorized that Spinosaurus probably did not hunt completely submerged in water as previously hypothesized, but instead would have spent much of its time on land or in shallow water.
Later studies of the tail vertebrae of Spinosaurus refute Henderson's proposal that Spinosaurus mainly inhabited areas of land near and in shallow water and was too buoyant to submerge. Studies of the tail, thanks to fossils recovered and analyzed by Ibrahim, Pierce, Lauder, and Sereno and colleagues in 2018 indicate that Spinosaurus had a keeled tail that was well adapted to propelling the animal through water. The elongated neural spines and chevrons, which run to the end of the tail on both dorsal and ventral sides, indicate that Spinosaurus was able to swim in a similar manner to modern crocodilians. Through experimentation by Lauder and Pierce, the tail of Spinosaurus was found to have eight times as much forward thrust as the tails of terrestrial theropods like Coelophysis and Allosaurus, as well as being twice as efficient at achieving forward thrust. The discovery indicates that Spinosaurus may have had a lifestyle comparable to modern alligators and crocodiles, remaining in water for long periods of time while hunting.
David Hone and Thomas Holtz published a paper in 2021 in which they argue that the anatomy of Spinosaurus is more consistent with a shoreline generalist lifestyle rather than an active aquatic pursuit predator as suggested by Ibrahim. They highlight the positioning of the nostrils and orbits as one reason why a crocodile-like lifestyle is unlikely: they are ventrally positioned in such a way that the whole head would have to be lifted inefficiently out of the water in order to breathe. Additionally, they argue that the general body shape of Spinosaurus is poorly adapted for this lifestyle, drawing on the amount of water drag and aquatic instability from the sail, as well as the rigid trunk and seemingly scarcely-muscled tail. Animals like crocodilians require a flexible body in order to move through the water and make sharp turns when chasing prey, and this is directly contradicted by Hone and Holtz's findings.
A 2022 study by Fabbri et al., made comparisons of Spinosaurus bone structure and compared it to that of Baryonyx and Suchomimus. The study revealed that Spinosaurus and Baryonyx had dense bones, which allowed them to dive and pursue prey underwater. Compared to these, Suchomimus had more hollow bones, suggesting it preferred to hunt in shallow water. These findings also suggest that various spinosaurid genera were more ecologically disparate than previously believed, as some were better suited to hunting in subaqueous environments than other, closely related genera.
In the same year, contradicting the study by Fabbri and colleagues, Sereno and his colleagues suggested that Spinosaurus was wholly bipedal on land and an unstable, slow moving surface swimmer in deep water. Their results, taken from reconstructing a CT model of the skeleton, and then adding internal air and muscles. Their results, coupled with fossils from Spinosaurus that showed it also lived further inland along rivers and lakes, suggest it was a semi-aquatic, ambush piscivore that preferred waterside environments both along the coasts and further inland along rivers and lakes. Simultaneously, they suggested that the large tail fin was probably utilized more for display than swimming, as tails in living animals have the same function when they possess comparably tall neural spines.
A 2024 paper by Myrhvold et al. also contends that Spinosaurus and Baryonyx were diving pursuit predators. Instead they also argue that Spinosaurus and Baryonyx hunted more like herons instead of diving after prey. Another paper in the same year analyzed the linear measurements of the skull of Spinosaurus, and concluded that the skull morphology and hunting method of Spinosaurus would likely be the most similar to those of wading birds like herons, though the authors noted that they are uncertain how beneficial the skull would have been for the diving pursuit predation method.

Locomotion and posture

Although traditionally depicted in the scientific community as a biped, Spinosaurus was occasionally depicted in the mid-20th century as an obligate quadruped akin to Dimetrodon. Starting in the mid-1970s, it was hypothesized Spinosaurus was at least an occasional quadruped, bolstered by the discovery of Baryonyx, a relative with robust arms. Because of the mass of the hypothesized fatty dorsal humps of Spinosaurus, Bailey was open to the possibility of a quadrupedal posture, leading to new restorations of it as such. Theropods, including spinosaurids, could not pronate their hands, but a resting position on the side of the hand was possible, as shown by fossil prints from an Early Jurassic theropod. The hypothesis that Spinosaurus had a typical quadrupedal gait since fell out of favor, however it was still believed that spinosaurids may have crouched in a quadrupedal posture, due to biological and physiological constraints.

The possibility of a quadrupedal Spinosaurus was revived by a 2014 paper by Ibrahim and colleagues that described new material of the animal. The paper found that the hind limbs of Spinosaurus were much shorter than previously believed, and that its center of mass was located in the midpoint of the torso region, as opposed to near the hip as in typical bipedal theropods. It was therefore proposed that Spinosaurus was poorly adapted for bipedal terrestrial locomotion, and must have been an obligate quadruped on land. The reconstruction used in the study was an extrapolation based on different sized individuals, scaled to what were assumed to be the correct proportions. Paleontologist John Hutchinson of the Royal Veterinary College of the University of London has expressed skepticism to the new reconstruction, and cautioned that using different specimens can result in inaccurate chimaeras. Scott Hartman also expressed criticism because he believed the legs and the pelvis were inaccurately scaled and didn't match the published lengths. However, Mark Witton expressed agreement with the proportions reported in the paper. In their 2015 re-description of Sigilmassasaurus, Evers and colleagues argued that Sigilmassasaurus was in fact a distinct genus from Spinosaurus, and therefore doubted whether the material assigned to Spinosaurus by Ibrahim et al. should be assigned to Spinosaurus or Sigilmassasaurus. In 2018, an analysis by Henderson found that Spinosaurus probably was competent at bipedal terrestrial locomotion; the center of mass was instead found to be close to the hips, allowing Spinosaurus to stand upright like other bipedal theropods.
A 2024 article co-authored by Sereno stated that the previous calculations by Sereno that were used to argue quadrupedality for Spinosaurus had erroneously shifted the center of mass in front of the hips. They instead suggested that the dinosaur fit the criteria of being a graviportal biped.

Ontogeny

An ungual phalanx measuring belonging to a very young juvenile cf. S. aegyptiacus indicates that the theropod developed its semiaquatic adaptations at a very young age or at birth and maintained them throughout its life. The specimen, found in 1999 and described by Simone Maganuco and Cristiano Dal Sasso and colleagues, is believed to have come from an animal measuring , making it the smallest specimen of Spinosaurus currently known.

Palaeopathology

A cf. Spinosaurus sp. tooth from the Ifezouane Formation displays enhanced lingual curvature to the tooth's crown, the development of three deep grooves extending from crown root junction in the direction of the crown's apex, an attenuated carina that does not extend apically nor to the base of the tooth, and a wear facet at the tip.

Paleoecology

The holotype specimen of Spinosaurus is known from the Bahariya Formation, one of many dinosaur-bearing Cretaceous-aged fossil formations in North Africa. However, fossils of Spinosaurus have been described from several sites including the Kem Kem Beds of Morocco, the Farak, and Echkar Formations of Niger, the Gara Samani Formation of Algeria, and the Chenini Sandstones. This would indicate that the distribution of Spinosaurus is similar to that of Bahariasaurus/Deltadromeus, a large theropod of unknown affinities, though Deltadromeus taxonomy and distribution too is debated. North Africa during this period bordered the Tethys Sea, which transformed the region into a mangrove-dominated coastal environment filled with vast tidal flats and waterways.
The composition of the dinosaur fauna of North Africa at this time is an anomaly, as there are fewer herbivorous dinosaur species relative to carnivorous dinosaur species than in most fossil sites. This abundance of theropods compared to that of non-theropods was dubbed "Stromer's Riddle", which despite suggestions that this is due to ecological, preservation, or other biases, is supported by the fossil record. This over prevalence of theropods indicates that there was niche partitioning between the different theropod clades, with spinosaurids consuming fish while other groups hunted herbivorous dinosaurs. Isotopic evidence supports this, which found greater quantities of sizable, terrestrial animals in the diets of carcharodontosaurids and ceratosaurs from both the Kem Kem Beds and Elrhaz Formation. North Africa was dominated by a triumvirate of Abelisauroidea, Spinosauridae, and Carcharodontosauridae during the mid-Cretaceous, with all of these groups present in the Kem Kem Beds, Echkar, Elrhaz, and Bahariya Formations. The abelisauroid affinities of Deltadromeus/Bahariasaurus suggest that they may be omnivorous or herbivorous. This would indicate niche partitioning in the large theropods in these localities, with Deltadromeus/''Bahariasaurus filling a niche typically filled by ornithischians, though no skull material is known from either.
File:Underwater Spinosaurus ecology.jpg|thumb|265x265px|Spinosaurus swimming underwater with an Onchopristis, a Ceratodus, two Bawitius, and a Mawsonia'' in the Bahariya Formation

Bahariya Formation

Fossils from the Bahariya Formation came from tidal flat deposits containing in the form of fossil leaves and root systems, a mangrove vegetation of seed ferns, Weichselia reticulata. This mangrove system bordered the Tethys Sea, which transformed the region into a mangrove-dominated coastal environment filled with vast tidal flats and waterways. Alongside the coeval theropods Tameryraptor and Bahariasaurus, Spinosaurus is one of several theropod dinosaurs known from the Bahariya Formation. Fossils of sauropods include those of the titanosaurs Paralititan and Aegyptosaurus, the former reaching great sizes. The faunal composition of both the Bahariya Formation and the Kem Kem Beds were thought to be similar in the past, but the describers of Tameryraptor suggested that such superficial comparisons require further examination. Contemporary abelisaurid dinosaurs from the Bahariya Formation were also terrestrial carnivores, preying on other terrestrial fauna. An isolated wing phalanx of a pterosaur, potentially Anhanguera, was unearthed from the Bahariya Formation. A diverse fauna of aquatic animals is known from the Bahariya Formation. Underwater life diversity exploded during this period in the mangroves of North Africa, with turtles represented by the pleurodian Apertotemporalis, large bony fish like Mawsonia and Paranogmius, sawskates Onchopristis and Schizorhiza, sharks like Squalicorax and Cretolamna, and a broad selection of invertebrates. Additionally, several crocodylomorphs like the stomatosuchid Stomatosuchus and the eunotosuchian Libycosuchus are known from the formation.

Kem Kem Beds

The Kem Kem Beds is composed of three geologic formations: the Gara Sbaa Formation, the Douria Formation, and the Izefouane Formation. Spinosaurus fossils are exclusively known from the latter two formations. Isotopes from Carcharodontosaurus and Spinosaurus fossils suggest that the Kem Kem Beds witnessed a temporary monsoon season rather than constant rainfall, similar to modern conditions present in sub-tropical and tropical environments in Southeast Asia and Sub-Saharan Africa. This river system was freshwater based on the presence of lungfishes and other typically freshwater vertebrates. This indicates that the Kem Kem Beds had a wide variety of features, including river channels, river banks, sandbars, and more. Fossils of giant fishes have been found in the Kem Kem Beds, including the sawskate Onchopristis, coelacanth Axelrodichthys, and bichir Bawitius. The Kem Kem Beds also preserves an abundance of crocodyliformes like the stomatosuchid Laganosuchus, the peirosaurid Hamadasuchus, and the pholidosaurid Elosuchus. This region also bore an abundance of pterosaurs like the toothed anhanguerids Siroccopteryx and Nicorhynchus and the edentulous azhdarchoids Alanqa and Leptostomia.
The Kem Kem Beds preserve many dinosaur fossils. Sauropod dinosaurs are known by the rebbachisaurid sauropod Rebbachisaurus, an indeterminate somphospondylian titanosauriform, and an indeterminate titanosaur, one comparable in size to the giant Paralititan. Ornithischian fossils are extremely rare, only being represented from an isolated thyreophoran tooth and footprints of an ornithopod, possibly similar to Iguanodon. As for theropods, many are known, including Spinosaurus, Sigilmassasaurus, if it is valid, and possibly another distinct spinosaurid taxon, one or two distinct indeterminate abelisaurids, the carcharodontosaurids Carcharodontosaurus and Sauroniops, and indeterminate noasaurids. However, many of these dinosaurs are known from isolated or incomplete remains, have complicated taxonomies, or are under study.

In popular culture

Spinosaurus appeared in the 2001 film Jurassic Park III, replacing Tyrannosaurus as the main antagonist. The film's consulting paleontologist John R. Horner was quoted as saying, "If we base the ferocious factor on the length of the animal, there was nothing that ever lived on this planet that could match this creature . Also my hypothesis is that T-rex was actually a scavenger rather than a killer. Spinosaurus was really the predatory animal." He has since retracted the statement about T. rex being a scavenger. In the film, Spinosaurus was portrayed as larger and more powerful than Tyrannosaurus: in a scene depicting a battle between the two resurrected predators, Spinosaurus emerges victorious by snapping the Tyrannosaurus neck. In the fourth film, Jurassic World, there is a nod to this fight where the T. rex smashes through the skeleton of a Spinosaurus in the climactic fight near the end of the film. The Spinosaurus would appear in many Jurassic Park games most notably Jurassic World Evolution, and its sequels. The same Spinosaurus from the third film returns in the fourth, and fifth season of Jurassic World Camp Cretaceous, this time battling two T. rex. Spinosaurus return in Jurassic World Rebirth in a more realistic depiction, and having a coexisting relationship with a Mosasaurus.
Spinosaurus has long been depicted in popular books about dinosaurs, although only recently has there been enough information about spinosaurids for an accurate depiction. After an influential 1955 skeletal reconstruction by Lapparent and Lavocat based on a 1936 diagram by Stromer, it has been treated as a generalized upright theropod, with a skull similar to that of other large theropods and a sail on its back, even having four-fingered hands.
In addition to films, action figures, video games, and books, Spinosaurus has been depicted on postage stamps from countries such as Angola, The Gambia, and Tanzania.