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. However, Bailey (1997) 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. 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 (2015). 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 (
Baryonyx) 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 Onchopristis 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 (found in Morocco and Tunisia) 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. 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 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 disputes 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, Because of the mass of the hypothesized fatty dorsal humps of
Spinosaurus, Bailey (1997) was open to the possibility of a quadrupedal posture, 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. Scott Hartman also expressed criticism because he believed the legs and the pelvis were inaccurately scaled (27% too short) 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. (2014) should be assigned to
Spinosaurus or
Sigilmassasaurus.
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, discovered in 1999 and described by Simone Maganuco and Cristiano Dal Sasso in 2018, is believed to have come from an animal measuring (assuming it resembled a smaller version of the adult), 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 ==