Spinosauridae (orspinosaurids) is a clade orfamily oftetanurantheropoddinosaurs comprising ten to seventeen knowngenera. Spinosauridfossils have been recovered worldwide, includingAfrica,Europe,South America andAsia. Their remains have generally been attributed to theEarly to earlyLate Cretaceous.
Spinosaurids were largebipedalcarnivores. Theircrocodilian-like skulls were long, low and narrow, bearing conical teeth with reduced or absentserrations. The tips of their upper andlower jaws fanned out into a spoon-shaped structure similar to arosette, behind which there was anotch in the upper jaw that the expanded tip of the lower jaw fit into. Thenostrils of spinosaurids were retracted to a position further back on the head than in most other theropods, and they had bony crests on their heads along the midline of their skulls. Their robust shoulders wielded stocky forelimbs, with three-fingered hands that bore an enlargedclaw on the firstdigit. In manyspecies, the upwards-projectingneural spines of thevertebrae (backbones) were significantly elongated and formed asail on the animal's back (hence the family's etymology), which supported either a layer of skin or a fatty hump.
The genusSpinosaurus, from which the family, one of itssubfamilies (Spinosaurinae) andtribes (Spinosaurini) borrow their names, is the longest known terrestrialpredator from the fossil record, with an estimated length of up to 14 meters (46 ft) and body mass of up to 7.4 metric tons (8.2 short tons) (similar to the weight of anAfrican elephant). The closely related genusSigilmassasaurus may have reached a similar or greater size, though itstaxonomy is disputed. Direct fossil evidence and anatomicaladaptations indicate that spinosaurids were at least partiallypiscivorous (fish-eating), with additional fossil finds indicating they also fed on other dinosaurs andpterosaurs. Theosteology of spinosaurid teeth and bones has suggested asemiaquatic lifestyle for some members of thisclade. This is further indicated by various anatomical adaptations, such as retracted eyes and nostrils; and the deepening of the tail in some taxa, which has been suggested to have aided in underwater propulsion akin to that of moderncrocodilians. Spinosaurs are proposed to be closely related to themegalosaurid theropods of the Jurassic. This is due to both groups sharing many features such an enlarged claw on their first manual ungual and an elongated skull.[7] However, some propose that this group (which is known as the Megalosauroidea) is paraphyletic and that spinosaurs represent either the most basaltetanurans[8] or as basalcarnosaurs which are less derived than the megalosaurids.[9] Some have proposed a combination of the two ideas with spinosaurs being in a monophyletic Megalosauroidea inside a more inclusive Carnosauria that is made up of both allosauroids and megalosauroids.[10]
The first spinosauridfossil, a single conical tooth, was discovered circa 1820 by BritishpaleontologistGideon Mantell in theWadhurst Clay Formation.[11] In1841, naturalistSir Richard Owen mistakenly assigned it to acrocodilian he namedSuchosaurus (meaning "crocodile lizard").[12][13] A second species,S. girardi, was later named in1897.[14] However, the spinosaurid nature ofSuchosaurus was not recognized until a 1998 redescription ofBaryonyx.[15]
The first fossils referred to a spinosaurid were discovered in 1912 at theBahariya Formation in Egypt. Consisting ofvertebrae, skull fragments, and teeth, these remains became theholotype specimen of the new genus and speciesSpinosaurus aegyptiacus in1915, when they were described by German paleontologistErnst Stromer. The dinosaur's name meant "Egyptian spine lizard", in reference to the unusually long neural spines not seen previously in any other theropod. In April 1944, the holotype ofS. aegyptiacus was destroyed during an allied bombing raid inWorld War II.[16][17] In 1934, Stromer referred a partial skeleton also from the Bahariya Formation to a new species ofSpinosaurus;[18] the specimen has since been alternatively assigned to another African spinosaurid,Sigilmassasaurus.[19]
In 1983, a relatively complete skeleton was excavated from the Smokejacks pit inSurrey,England. These remains were described by British paleontologistsAlan J. Charig andAngela C. Milner in1986 as the holotype of a new species,Baryonyx walkeri. After the discovery ofBaryonyx, many new genera have since been described, with the majority from very incomplete remains. However, other finds bear enough fossil material and distinct anatomical features to be assigned with confidence.Paul Sereno and colleagues describedSuchomimus in 1998, abaryonychine fromNiger, on the basis of a partial skeleton found in 1997. In 2004, partial jaw bones were recovered from theAlcântara Formation, these were referred to a new genus of spinosaurine namedOxalaia in2011 byAlexander Kellner.[17]
On 2021 a recent discovery inIsle of Wight an island off the south coast of England, remains of a spinosaurid which is said to be of a new species is found. As per the findings, it is about 10 meters in length and weighed several tons. The prehistoric bones of the spinosaurid were found in a geological layer of rock known as theVectis Formation in Compton Chine, it is the first identifiable theropod from the Vectis Formation. The study was led by Christopher Barker, a PhD doctoral student in vertebrate paleontology at theUniversity of Southampton.[20]
In February 2024, a new spinosaurid was announced with the name ofRiojavenatrix lacustris. Originally discovered inLa Rioja in 2005, it is the fifth spinosaurid species to be discovered in the Iberian Peninsula. It was found to have lived 120 million years ago and was around 7-8 metres long with a 1.5 metric ton body mass.[21]
Although reliable size and weight estimates for most known spinosaurids are hindered by the lack of good material, all known spinosaurids were large animals.[17] The smallestgenus known from good material isIrritator, which was between 6 and 8 meters (20 and 26 feet) long and around 1metric ton (1.1short tons; 0.98long tons) in weight.[22][23]Ichthyovenator,Baryonyx, andSuchomimus ranged from 7.5 to 11 m (25 to 36 ft) long, and weighed between 1 and 5.2 t (1.1 and 5.7 short tons; 0.98 and 5.12 long tons).[24][23][25]Oxalaia may have reached a length of between 12 and 14 m (39 and 46 ft) and a weight of 5 to 7 t (5.5 to 7.7 short tons; 4.9 to 6.9 long tons).[26] The largest known genus isSpinosaurus, which was capable of reaching lengths of 14 m (46 ft) and weighed around 7.4 t (8.2 short tons; 7.3 long tons), making it the longest knowntheropod dinosaur and terrestrialpredator.[27] The closely alliedSigilmassasaurus may have grown to a similar or greater length, though itstaxonomic relationship withSpinosaurus is uncertain.[28] This consistency in large body size among spinosaurids could have evolved as a byproduct of their preference forsemiaquatic lifestyles, as without the need to compete with other large theropod dinosaurs for food, they would have been able to grow to massive lengths.[29]
Spinosauridskulls—similar in many respects to those of crocodilians—were long, low and narrow.[17] As in other theropods, variousfenestrae (openings) in the skull aided in reducing its weight. In spinosaurs however, theantorbital fenestrae were greatly reduced, akin to those of crocodilians.[30] The tips of thepremaxillae (frontmost snout bones) were expanded in a spoon shape, forming what has been called a "terminalrosette" of enlarged teeth. Behind this expansion, the upper jaw had anotch bearing significantly smaller teeth, into which the also expanded tips of thedentaries (tooth bearing bones of the mandible) fit into, with a notch behind the expansion of the dentary.[17] Themaxillae (main upper jaw bones) were long and formed a low branch under the nostrils that connected to the rear of the premaxillae. The teeth at the frontmost part of the maxillae were small, becoming significantly larger soon after and then gradually decreasing in size towards the back of the jaw.[31] Analysis of the teeth of spinosaurids and their comparison to the teeth of tyrannosaurids suggest that the deep roots of spinosaurids helped to better anchor the teeth of these animals and distribute the stress against lateral forces generated during bites in predation and feeding scenarios.[32]
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Despite their highly modified skulls, analysis of the endocasts ofBaryonyx walkeri andCeratosuchops inferodios reveals spinosaurid brains shared a high degree of similarity with those of other non-maniraptoriform theropods.[33]
Lengthwise atop their skulls ran a thin and shallowsagittal crest that was usually tallest near or above the eyes, either becoming shorter or disappearing entirely towards the front of the head.[17][34][35]Spinosaurus's head crest was comb-shaped and bore distinct vertical grooves,[34] while those ofBaryonyx andSuchomimus looked like small triangular bumps.[36][6]Irritator's median crest stopped above and behind the eyes in a bulbous, flattened shape. However, given that no fully preserved skulls are known for the genus, the complete shape ofIrritator's crest is unknown.[31]Cristatusaurus andSuchomimus (a possiblesynonym of the former) both had narrow premaxillary crests.[37]Angaturama (a possible synonym ofIrritator) had an unusually tall crest on its premaxillae that nearly overhung the tip of the snout with a small forward protrusion.[35]
Spinosauridnostrils were set far back on the skull, at least behind the teeth of the premaxillae, instead of at the front of the snout as in most theropods.[17] Those ofBaryonyx andSuchomimus were large and started between the first and fourth maxillary teeth, whileSpinosaurus's nostrils were far smaller and more retracted.Irritator's nostrils were positioned similarly to those ofBaryonyx andSuchomimus, and were between those ofSpinosaurus andSuchomimus in size.[35] Spinosaurids had longsecondary palates, bony and rugose structures on the roof of their mouths that are also found in extant crocodilians, but not in most theropod dinosaurs.[30]Oxalaia had a particularly elaborate secondary palate, while most spinosaurs had smoother ones.[26] The teeth of spinosaurids were conical, with an oval to circular cross section and either absent or very fineserrations. Their teeth ranged from slightly recurved, such as those ofBaryonyx andSuchomimus, to straight, such as those ofSpinosaurus andSiamosaurus, and thecrown was often ornamented with longitudinal grooves or ridges.[35][38]
Thecoracoid bones of the shoulders in spinosaurids were robust and hook shaped.[6] The arms were relatively large and well-built; theradius (long bone of the forearm) was stout and usually only half as long as thehumerus (upper arm bone).Suchomimus is the only spinosaur known to have preserved afurcula (wishbone), which shows that spinosaurs had a V-shaped furcula.[39] Spinosaurid hands had three fingers, typical oftetanurans, and wielded an enlargedungual on the first finger (or "thumb"), which formed the bony core of akeratin claw. In genera likeBaryonyx andSuchomimus, thephalanges (finger bones) were of conventional length for large theropods, and bore hook-shaped, strongly curved hand claws.[17][24] Based on fragmentary material from the forelimbs ofSpinosaurus, it appears to have had longer, more gracile hands and straighter claws than other spinosaurids.[40]
The hindlimbs ofSuchomimus andBaryonyx were somewhat short and mostly conventional of othermegalosauroid theropods.[17][24]Ichthyovenator's hip region was reduced, having the shortestpubis (pubic bone) andischium (lower and rearmost hip bone) in proportion to theilium (main hip bone) of any other known theropod.[41]Spinosaurus had an even smallerpelvis and hindlimbs in proportion to its body size; its legs composed just over 25 percent of the total body length. Substantially complete spinosaurid foot remains are only known fromSpinosaurus. Unlike most theropods—which walk on three toes, with thehallux (first toe) being reduced and elevated off the ground—Spinosaurus walked on four functional toes, with an enlarged hallux that came in contact with the ground. The unguals of its feet, in contrast with the deeper, smaller and recurved unguals of other theropods, were shallow, long, large in relation to the foot, and had flat bottoms. Based on comparisons with those of modernshorebirds, it is theorized to be probable that theSpinosaurus's feet werewebbed.[40]
The upward-projectingneural spines of spinosauridvertebrae (backbones) were very tall, more so than in most theropods. In life, these spines would have been covered in skin or fat tissue and formed asail down the animal's back, a condition that has also been observed in somecarcharodontosaurid andornithopod dinosaurs.[17][42] Theeponymous neural spines ofSpinosaurus were extremely tall, measuring over 1 m (3 ft 3 in) in height on some of thedorsal (back) vertebrae.[43]Suchomimus had a lower, ridge-like sail across the majority of its back, hip, and tail region.[6]Baryonyx showed a reduced sail, with a few of the rearmost vertebral spines being somewhat elongated.[36]Ichthyovenator had asinusoidal (wave-like) sail that was separated in two over the hips, with the upper ends of some neural spines being broad and fan-shaped.[41] A neural spine from the holotype ofVallibonavenatrix shows a similarmorphology to those ofIchthyovenator, indicating the presence of a sail in this genus as well.[44] One partial skeleton possibly referable toAngaturama also had elongated neural spines on its hip region.[45][46] The presence of a sail in fragmentary taxa likeSigilmassasaurus is unknown.[19] In members of thesubfamily Spinosaurinae, likeIchthyovenator andSpinosaurus, the neural spines of thecaudal (tail) vertebrae were tall and reclined, accompanied by also elongatedchevrons—long, thin bones that form the underside of the tail. This was most pronounced inSpinosaurus, in which the spines and chevrons formed a large paddle-like structure, deepening the tail significantly along most of its length.[47][28]
The family Spinosauridae was named by Stromer in 1915 to include the singlegenusSpinosaurus. The clade was expanded as more close relatives ofSpinosaurus were uncovered. The firstcladistic definition of Spinosauridae was provided byPaul Sereno in 1998 (as "All spinosauroids closer toSpinosaurus than toTorvosaurus").[6]
Traditionally, Spinosauridae is divided into two subfamilies: Spinosaurinae, which contains the generaIcthyovenator,Irritator,Oxalaia,Sigilmassasaurus andSpinosaurus, is marked by unserrated, straight teeth, and external nares which are further back on the skull than in baryonychines,[6][48] and Baryonychinae, which contains the generaBaryonyx,Cristatusaurus,Suchosaurus,Suchomimus,Ceratosuchops, andRiparovenator,[49] which is marked by serrated, slightly curved teeth, smaller size, and more teeth in the lower jaw behind the terminal rosette than in spinosaurines.[6][48] Others, such asSiamosaurus, may belong to either Baryonychinae or Spinosaurinae, but are too incompletely known to be assigned with confidence.[49]Siamosaurus was classified as a spinosaurine in 2018, but the results are provisional and not entirely conclusive.[28]
The subfamily Spinosaurinae was named by Sereno in 1998, and defined byThomas Holtz and colleagues in 2004 as alltaxa closer toSpinosaurus aegyptiacus than toBaryonyx walkeri. The subfamily Baryonychinae was named by Charig & Milner in 1986. They erected both the subfamily and the family Baryonychidae for the newly discoveredBaryonyx, before it was referred to Spinosauridae. Their subfamily was defined by Holtz and colleagues in 2004, as the complementary clade of all taxa closer toBaryonyx walkeri than toSpinosaurus aegyptiacus. Examinations in 2017 by Marcos Sales and Cesar Schultz suggested that the South American spinosauridsAngaturama andIrritator may be intermediate between Baronychinae and Spinosaurinae based on their craniodental features and cladistic analysis. A study by Arden et al. 2018 named the tribe Spinosaurini to includeSpinosaurus andSigilmassasaurus. The results of the 2018 phylogenetic analysis by Arden and colleagues, which included many unnamed taxa, are displayed in thecladogram below:[28]
| Spinosauridae |
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In 2021, Barker et al. described two new spinosaurid species,Ceratosuchops inferodios andRiparovenator milnerae as part of a newly-proposed Ceratosuchopsini. In the paper, they performed a phylogenetic analysis focused on Spinosauridae. The results of their analysis appear below:[51]
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Spinosaurids appear to have been widespread from theBarremian to theCenomanianstages of theCretaceousperiod, about 130 to 95 million years ago. Possibly the earliest remains of spinosaurids are known from theMiddle Jurassic ofNiger and India, the latter of which otherwise has no remains of spinosaurids.[1][52] 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 (ziphodont) teeth with serrated carinae.[53] The skull adaptations of spinosauridsconverged with those ofcrocodilians; 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.[4][53] 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 theirmegalosaurid relatives. They also suggested that the spinosaurines and baryonychines diverged before the Barremian age of the Early Cretaceous.[54]
Several theories have been proposed about thebiogeography of the spinosaurids. SinceSuchomimus was more closely related toBaryonyx (from Europe) than toSpinosaurus—although that genus also lived in Africa—the distribution of spinosaurids cannot be explained asvicariance resulting fromcontinental rifting.[54] Sereno and colleagues[54] proposed that spinosaurids were initially distributed across thesupercontinentPangea, but split with the opening of theTethys Sea. Spinosaurines would then have evolved in the south (Africa and South America: inGondwana) and baryonychines in the north (Europe: inLaurasia), withSuchomimus the result of a single north-to-southdispersal event.[54] 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.[55] Milner suggested in 2003 that spinosaurids originated in Laurasia during the Jurassic, and dispersed via the Iberianland bridge into Gondwana, where theyradiated.[56] In 2007, Buffetaut pointed out thatpalaeogeographical 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 astepping 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,[57] and subsequent discoveries of spinosaurid remains in Asia and possibly Australia indicate that it may have been complex.[58]
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.[52] Some later studies instead suggested this tooth belonged to amegalosaurid.[59][60] Candeiro and colleagues suggested in 2017 that spinosaurids of northern Gondwana were replaced by other predators, such asabelisauroids, 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 bytransgressions in sea level.[61] Malafaia and colleagues stated in 2020 thatBaryonyx remains the oldest unquestionable spinosaurid, while acknowledging that older remains had also been tentatively assigned to the group.[62] 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 toSuchomimus and the African part of Spinosaurinae.[63]
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Spinosaurid teeth resemble those of crocodiles, which are used for piercing and holding prey. Therefore, teeth with small or no serrations, such as in spinosaurids, were not good for cutting or ripping into flesh but instead helped to ensure a strong grip on a struggling prey animal.[64] Spinosaurid jaws were likened by Romain Vullo and colleagues to those of thepike conger eel, in what they hypothesized wasconvergent evolution for aquatic feeding. Both kinds of animals have some teeth in the end of the upper and lower jaws that are larger than the others and an area of the upper jaw with smaller teeth, creating a gap into which the enlarged teeth of the lower jaw fit, with the full structure called a terminal rosette.[65]
In the past, spinosaurids have often been consideredpiscivores (fish-eaters) in the main, based on comparisons of their jaws with those of modern crocodilians.[48] In 2007, British paleontologist Emily J. Rayfield and colleagues conductedbiomechanical studies on the skull ofBaryonyx, which had a long, laterally compressed skull, comparing it togharial (long, narrow, tubular) andalligator (flat and wide) skulls. They found that the structure of baryonychine jaws converged on that of gharials, in that the two taxa showed similar response patterns to stress from simulated feeding loads, and did so with and without the presence of a (simulated) secondary palate. The gharial, exemplar of a long, narrow, and tubular snout, is a fish specialist. However, this snout anatomy does not preclude other options for the spinosaurids. The gharial is the most extreme example and a fish specialist;Australian freshwater crocodiles, which have similarly shaped skulls to gharials, also specialize more on fish than sympatric, broad snouted crocodiles and are opportunistic feeders which eat all manner of small aquatic prey, including insects andcrustaceans. Thus, spinosaurids' snouts correlate with piscivory; this is consistent with hypotheses of this diet for spinosaurids, in particular baryonychines, but it does not indicate that they were solely piscivorous.[30]
Further study by Andrew R. Cuff and Rayfield in 2013 on the skulls ofSpinosaurus andBaryonyx did not recover similarities in the skulls ofBaryonyx and the gharial that the previous study did.Baryonyx had, in models where the size difference of the skulls was corrected for, greater resistance to torsion and dorsoventral bending than bothSpinosaurus and the gharial, while both spinosaurids were inferior to the gharial, alligator, andslender-snouted crocodile in resisting torsion and medio-lateral bending. When the results from the modeling were not scaled according to size, then both spinosaurids performed better than all the crocodilians in resistance to bending and torsion, due to their larger size. Thus, Cuff and Rayfield suggested that the skulls were not efficiently built to deal well with relatively large, struggling prey, but that spinosaurids may overcome prey simply by their size advantage, and not skull build.[66] In 2002,Hans-Dieter Sues and colleagues studied the construction of the spinosaurid skull, and concluded that their mode of feeding was to use extremely quick, powerful strikes to seize small prey items using their jaws, whilst employing the powerful neck muscles in rapid up-and-down motion. Due to the narrow snout, vigorous side-to-side motion of the skull during prey capture is unlikely.[64] Based on the size and positions of their nostrils, Marcos Sales and Cesar Schultz in 2017 suggested thatSpinosaurus possessed a greater reliance on its sense of smell and had a more piscivorous lifestyle thanIrritator and baryonychines.[35]
Direct fossil evidence shows that spinosaurids fed on fish as well as a variety of other small to medium-sized animals, including dinosaurs.Baryonyx was found with scales of the prehistoric fishScheenstia in its body cavity, and these were abraded, hypothetically by gastric juices. Bones of a youngIguanodon, also abraded, were found alongside this specimen. If these representBaryonyx’s meal, the animal was, whether in this case a hunter, or a scavenger, an eater of more diverse fare than fish.[48][64][36] Moreover, there is a documented example of a spinosaurid having eaten apterosaur, as oneIrritator tooth was found lodged within the fossil vertebrae of anornithocheirid pterosaur found in theRomualdo Formation of Brazil. This may represent a predation or a scavenging event.[67][68] A fossil snout referred toSpinosaurus was discovered with a vertebra from thesclerorhynchidOnchopristis embedded in it.[34] In theSao Khua Formation of Thailand, isolated tooth crowns fromSiamosaurus have been found in association withsauropod remains, indicating possible predation or scavenging.[69] The Portuguese Iberospinus fossils were also found associated with isolated Iguanodon teeth, and those cases are listed; along with other such associations as support for opportunistic feeding behaviour in spinosaurids.[70]
A 2018 study by Auguste Hassler and colleagues ofcalcium isotopes in the teeth of North African theropods found that spinosaurids had a mixed diet of fish and herbivorous dinosaurs, whereas the other theropods examined (abelisaurids andcarcharodontosaurids) mainly fed on herbivorous dinosaurs. This might indicateecological partitioning between these theropods.[71] Later in 2018,Tito Aureliano and colleagues presented a possible scenario for thefood web of Brazilian Romualdo Formation. The researchers proposed that the diet of spinosaurines from this environment may have included—in addition to pterosaurs—terrestrial and aquaticcrocodyliforms, juveniles of their own species, turtles, and small to medium-sized dinosaurs. This would have made spinosaurinesapex predators within this particular ecosystem.[29]
A 2024 study by D'Amore et al., further vindicates the theory that spinosaurids were similar in niche to generalist or macro-generalist crocodilians. This study likewise suggests their jaws and teeth were well-suited to quick strikes and deep, puncturing bites, but not for slicing flesh or crushing bones. In particular, baryonychine spinosaurids probably did little oral processing of their prey when feeding, but by comparison, spinosaurines were found to be quite capable of processing the meat of relatively large vertebrate prey. None of these findings suggest any spinosaurids from either subfamily were restricted only to fish and small aquatic vertebrates.[72]
The use of the robust forelimbs and giant recurved claws of spinosaurs remains a debated topic. Charig and Milner speculated in 1986 thatBaryonyx may have crouched by the riverbank and used its claws togaff fish out of the water, similarly togrizzly bears.[73] In 1987, British biologist Andrew Kitchener argued that with both its crocodile-like snout and enlarged claws,Baryonyx seemed to have too many adaptations for piscivory when one would have been enough. Kitchener instead postulated thatBaryonyx more likely used its arms to scavenge the corpses of large dinosaurs, such asIguanodon, by breaking into the carcass with the large claws, and subsequently probing forviscera with its long snout.[74] In their 1997 article, Charig and Milner rejected this hypothesis, pointing out that in most cases, a carcass would have already been largely emptied out by its initial predators.[36] Later research has also ruled out this sort ofspecialized scavenging.[17]
In 1986, Charig and Milner suggested that the robust forelimbs and giant thumb claws would have beenBaryonyx's primary method of capturing, killing, and tearing apart large prey; whereas its long snout would have been used mostly for fishing.[36] A 2005 study by Canadian paleontologist the François Therrien and colleagues agreed that spinosaur forelimbs were probably used for hunting larger prey items, given that their snouts could not resist the bending stress.[75] In a 2017 review of the family, David Hone and Holtz considered possible functions in digging for water sources or hard to reach prey, as well as burrowing into soil to construct nests.[17]
Theropod heads are often decorated with some form of crest, horn, or rugose structure, which in life, would have been extended by keratin.[76] Though there has been little discussion on the head crests of spinosaurs, Hone and Holtz in 2017 considered that their most likely use was fordisplaying to potential mates or as a means of threatening rivals and other predators.[17] Such has been suggested for theropod cranial structures before, which may have been aided by unusual or bright coloration to provide further visual cues.[76]
Many theories have been proposed over the years for the use of spinosaurid dorsal sails, such asthermoregulation;[77] to aid in swimming;[78] to store energy or insulate the animal; or for display purposes, such as intimidating rivals and predators, or attracting mates.[79][80] Many elaborate body structures of modern-day animals serve to attract members of the opposite sex during mating. It is possible that the sail ofSpinosaurus was used for courtship, in a way similar to apeacock's tail. In 1915, Stromer speculated that the size of the neural spines may have differed between males and females.[80] In 2012, French paleontologist Ronan Allain and colleagues suggested considering the high diversity in neural spine elongation observed in theropod dinosaurs, as well ashistological research done on the sails ofsynapsids (stem mammals), the sinusoidal sail ofIchthyovenator was likely used for courtship display orrecognising members of its own species.[81] In a 2013 blog post,Darren Naish considered the latter function unlikely, favouring the hypothesis ofsexual selection forIchthyovenator's sail because it appears to have evolved on its own, without very close relatives. Naish also notes it is possible similar relatives have not yet been discovered.[82]
In 2015, the German biophysicist Jan Gimsa and colleagues suggested that this feature could also have aided aquatic movement by improving manoeuvrability when submerged, and acted as fulcrum for powerful movements of the neck and tail (similar to those ofsailfish orthresher sharks).[83][84]
Juvenile spinosaurid fossils are somewhat rare. However, an ungualphalanx measuring 21 mm (0.83 in) belonging to a very youngSpinosaurus indicates thatSpinosaurus, and probably by extent other spinosaurids, may have developed their semiaquatic adaptations at birth or at a very young age and maintained the adaptations throughout their lives. The specimen, found in 1999 and described by Simone Maganuco, Cristiano Dal Sasso and colleagues in 2018, is believed to have come from a very small juvenile measuring 1.78 m (5.8 ft), making said specimen the smallest known example of a spinosaurid currently described.[85][86]
A 2010 publication by Romain Amiot and colleagues found thatoxygen isotope ratios of spinosaurid bones indicates semiaquatic lifestyles. Isotope ratios from teeth fromBaryonyx,Irritator,Siamosaurus, andSpinosaurus were compared with isotopic compositions from contemporaneous theropods, turtles, and crocodilians. The study found that, among theropods, spinosaurid isotope ratios were closer to those of turtles and crocodilians.Siamosaurus specimens tended to have the largest difference from the ratios of other theropods, andSpinosaurus tended to have the least difference. The authors concluded that spinosaurids, like modern crocodilians and hippopotamuses, spent much of their daily lives in water. The authors also suggested that semiaquatic habits and piscivory in spinosaurids can explain how spinosaurids coexisted with other large theropods: by feeding on different prey items and living in different habitats, the different types of theropods would have been out of direct competition.[87]In 2018, an analysis was conducted on the partialtibia of an indeterminate spinosaurine from the earlyAlbian, the bone was from a sub-adult between 7 and 13 m (22 and 42 ft) in length still growing moderately fast before its death. This specimen (LPP-PV-0042) was found in theAraripe Basin of Brazil and taken to theUniversity of San Carlos for aCT Scan, where it revealedosteosclerosis (high bone density).[29] This condition had previously only been observed inSpinosaurus, as a possible way of controlling its buoyancy.[40] The presence of this condition on the leg fragment showed that semi-aquatic adaptations in spinosaurids were already present at least 10 million years beforeSpinosaurus aegyptiacus appeared. According to thephylogenetic bracketing method, this high bone density might have been present in all spinosaurines.[29] In 2020, a scientific paper by paleontologists published in the scientific journalCretaceous Research found taphonomic evidence in the Kem Kem group that would supportSpinosaurus being a semi-aquatic dinosaur.[88] However, research conducted in 2023 cited the immediate assumption of Spinosaurids being avid divers due to correlations in bone compactness as being subject to errors, such as flawed statistical methods and measurements, as well as sampling bias.[89] A study conducted in 2023 by Stephanie Baumgart also found similar results with the previous studies as; given amount of variation in specimens and in data collection techniques, they concluded that previous evidence isn’t strong enough to put Spinosaurus swimming and diving entirely submerged. Spinosaurus still more likely mostly hung out on shore, akin to wader lifestyle previously interfered.[90]
A 2018 study ofbuoyancy (through simulation with 3D models) by the Canadian palaeontologist Donald M. Henderson found that distantly related theropods floated as well as the tested spinosaurs, and instead supported they would have stayed by the shorelines or shallow water rather than being semi-aquatic.[91]
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Confirmed spinosaurids have been found on every continent except for North America, Australia and Antarctica, the first of which wasSpinosaurus aegyptiacus, discovered at theBahariya Formation in Egypt.[80] Baryonychines were common, such asBaryonyx, which lived during theBarremian of England and Spain.Baryonyx-like teeth are also found from the earlierHauterivian and laterAptian sediments of Spain, as well as theHauterivian of England.[17][58] Baryonychines were represented in Africa, withSuchomimustenerensis andCristatusaurus lapparenti as well asBaryonyx-like teeth from the Aptian ofNiger.[49][6][92] as well as in Europe, withSuchosaurus cultridens andS. girardi from the England.Baryonyx-like teeth are also reported from theAshdown Sands ofSussex, in England, and theBurgos Province, in Spain.[58] Other European spinosauridsCamarillasaurus cirugedae andIberospinus natarioi are known from theBarremian of Spain and Portugal, respectively.[93][94]
The earliest record of spinosaurines is from Europe, with the Barremian speciesVallibonavenatrix cani from Spain.[44] Spinosaurines are also present inAlbian sediments ofTunisia andAlgeria, and inCenomanian sediments of Egypt andMorocco. In Africa, baryonychines were common in the Aptian, and then replaced by spinosaurines in the Albian and Cenomanian.[49] such as in theKem Kem beds of Morocco, which housed an ecosystem containing many large coexisting predators.[37][87] A fragment of a spinosaurine lower jaw from theEarly Cretaceous was also reported fromTunisia, and referred toSpinosaurus.[49] Spinosaurinae's range also extended to South America, particularly Brazil, with the discoveries ofIrritator challengeri, Angaturama limai, andOxalaia quilombensis.[68][26] There was also a fossil tooth in Argentina which has been referred to the Spinosauridae by Leonardo Salgado and colleagues.[95] This referral is doubted by Gengo Tanaka et al., who offersHamadasuchus, a crocodilian, as the most likely animal of origin for these teeth.[96]
Partial skeletons and numerous fossil teeth indicate spinosaurids were widespread in Asia; three taxa—all spinosaurines—have been named:Siamosaurus suteethorni from Thailand,"Sinopliosaurus"fusuiensis from China, andIchthyovenator laosensis from Laos.[41][49][97] Spinosaurid teeth have been found inMalaysia; they were the first dinosaur remains discovered in the country.[98] Some intermediate specimens extend the known range of spinosaurids past the youngest dates of named taxa. A single theropod tooth attributed to Baryonychinae was found in the mid-SantonianMajiacun Formation ofHenan, China,[97] but this tooth lacked spinosaurid synapomorphies,[99][100] and it was reclassified as a sister taxon of a separate theropod familyAbelisauridae in 2023.[101] At la Cantalera-1, a site in the early BarremianBlesa Formation inTreul, Spain, two types of spinosaurid teeth were found, and they were assigned, tentatively, as indeterminate spinosaurine and baryonychine taxa.[102] An indeterminate spinosaurid was discovered in theEarly CretaceousEumeralla Formation, Australia.[103] It is known from a single 4 cm long partial cervical vertebra, designatedNMV P221081. It is missing most of the neural arch. The specimen is from a juvenile estimated to be about 2 to 3 meters long (6–9 ft). Out of all spinosaurids, it most closely resemblesBaryonyx.[50] In 2019, it was suggested that the vertebra instead belonged to amegaraptorid theropod, as opposed to a spinosaur.[104]
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