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20.12.2015 16:40 - Encyclopedia Largest prehistoric animals Vol.1 Vertebrates part3 Dinosaurs ch.1 Theropods - Spinosaurus, Largest terrestrial predator or a piscivore
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Spinosauridae
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1. Suchomimus 2. Cristatusaurus 3. Oxalaia 4. Baryonyx 5. Spinosaurus
Spinosauridae is a specialized group of theropod dinosaurs characterised by a long, narrow skull, robust forelimbs with a hooked thumb claw, and tall neural spines forming a dorsal sail. The ecology of these unusual dinosaurs has been debated since the original discovery of Spinosaurus aegyptiacus in 1912. Morphological similarities to crocodilians, including tooth shape and an elongated rostrum, indicate a piscivorous diet, and in the giant Spinosaurus, a long body and short limbs suggest semi-aquatic habits.
Spinosauridae is divided into two subfamilies: Spinosaurinae, which contains the genera Icthyovenator, Irritator, Oxalaia, Sigilmassasaurus and Spinosaurus, is marked by unserrated, straight teeth, and external nares which are further back on the skull than in Baryonychinae.And Baryonychinae, which contains the genera Baryonyx and Suchomimus,is marked by serrated, slightly curved teeth, smaller size, and more teeth in the lower jaw behind the terminal rosette than in spinosaurines.Others, such as Siamosaurus, may belong to either Baryonychinae or Spinosaurinae, but are too incompletely known to be assigned with confidence.Siamosaurus was classified as a spinosaurine in 2018, but the results are provisional and not entirely conclusive.
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Among the more unusual of the theropod dinosaurs, spinosaurids were lightly built predators with elongated vertebral spines and crocodile-like jaws with specialized teeth. Fish probably formed most of their diet. Two main groups exist: the baryonychids, who are most famous for their elongated, many-toothed skulls and large hand claws; and the spinosaurids, which had more cranial ornamentation and generally a larger sail (reminiscent of Dimetrodon). Spinosaurids, like Baryonyx tenerensis (also known as Suchomimus), have very short and stocky arms, thumb claws which are dramatically larger than the other unguals, unguals with greater angles of curvature, a tapering shaft, and more oval slender cross-section (like that of a carnosaur or Torvosaurus claw). Spinosaurid teeth are much more oval in cross-section than in typical theropods. There are a number of crocodilian like features in the skulls of spinosaurids: including the elongate snout, conical teeth, secondary palate (so it could breath through it"s nostrils, even while the mouth is closed, a mamamlian feature not shared by most reptiles), and more. These features have been associated with the adoption of a piscivorous diet in crocodylomorph evolution. As with modern crocodiles, spinosaurs were not obliged to only eat fish. They could eat land animals as well. Remnants of Iguanodon bones as well as Lepidotes fish scales are found among the fossil stomach contents of Baryonyx walkeri. The paleoenvironments from which known spinosaurids come all support diverse communities of fish, some of which were very large. There is currently no evidence that these were seasonal communities, and would seem likely to be permanent residents. Thus, we have very large packages of fish meat not otherwise easily exploitable by theropods, although they would have been in competition with contemporary giant crocodiles. The relationship of the spinosaurids is not completely clear, although the most likely option is that the spinosaurs are cousins to the megalosaurids.
imageGreg Paul in his Predatory Dinosaurs of the World however suggests that they might actually be late surviving (and giant) coelophysoids (podokesaurs). An interesting piece of evidence here is the presence of a "subnarial gap" or kink in the jaw, under the nostrils, that is found only in the Podokesauridae (Coelophysoidea) and Spinosauridae. There is no evidence of a " subnarial gap " in any other theropods groups outside of those two. It is however a feature that is common in archosaurs in general. Eoraptor apparently has a subnarial gap, but Herrerasaurus does not. There are differing views over whether either is a true theropod. However in an scientific paper Paul Sereno et al. affirm Megalosaur (Torvosaur) relationships. There may be only a superficial resemblence between spinosaurids and coelophysids in respects to the premaxillary/maxillary portion of the skull in profile. In addition, the anatomical arrangement in coelophysoids differs from the condition in spinosaurids (although the latter could be derived from the former). But now that the postcranial anatomy of spinosaurids are a lot better known than back in the mid-1980s, it seems that there is not much in the rest of the skeleton to link spinosaurids and coelophysoids. Some restorations of spinosaurians made recently show them as quadrupedal, a mistake based on early descriptions of the arms of Baryonyx walkeri



Spinosaurus

The largest theropod as well as the largest terrestrial predator yet known is Spinosaurus aegyptiacus, with the largest specimen known estimated at 16–18 metres (52–59 ft) in length and around 7–20.9 metric tons (8–23 short tons) in weight.
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Spinosaurus (meaning "spine lizard") is a genus of theropoddinosaur that lived in what now is North Africa, during the lower Albian to lower Cenomanianstages of the Cretaceousperiod, about 112 to 97 million years ago. This genus was known first from Egyptian remains discovered in 1912 and described by Germanpaleontologist Ernst Stromer in 1915. The original remains were destroyed in World War II, but additional material has come to light in recent years. It is unclear whether one or two species are represented in the fossils reported in the scientific literature. The best known species is S. aegyptiacus from Egypt, although a potential second species, S. maroccanus, has been recovered from Morocco.

Spinosaurus was among the largest of all known carnivorous dinosaurs, possibly larger than Tyrannosaurus and Giganotosaurus.
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Estimates published in 2005, 2007, and 2008 suggested that it was between 12.6–18 metres (41–59 ft) in length and 7 to 20.9 tonnes (7.7 to 23.0 short tons) in weight.New estimates published in 2014 and based on more complete specimens, supported the earlier research, finding that Spinosaurus could reach lengths greater than 15 m (49 ft). The skull of Spinosaurus was long and narrow, similar to that of a modern crocodilian. Spinosaurus is known to have eaten fish, and most scientists believe that it hunted both terrestrial and aquatic prey; evidence suggests that it lived both on land and in water as a modern crocodilian does. The distinctive spines of Spinosaurus, which were long extensions of the vertebrae, grew to at least 1.65 meters (5.4 ft) 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. Multiple functions have been put forward for this structure, including thermoregulation and display.

Since its discovery, Spinosaurus has been a contender for the longest and 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 15 meters (49 ft) in length and upwards of 6 t (5.9 long tons; 6.6 short tons) in weight. In 1988, Gregory Paul also listed it as the longest theropod at 15 meters (49 ft), but gave a lower mass estimate of 4 tonnes (3.9 long tons; 4.4 short tons).
Dal Sasso et al. (2005) assumed that Spinosaurus and Suchomimus had the same body proportions in relation to their skull lengths, and thereby calculated that Spinosaurus was 16 to 18 meters (52 to 59 ft) in length and 7 to 9 tonnes (6.9 to 8.9 long tons; 7.7 to 9.9 short tons) in weight.The Dal Sasso et al. estimates were criticized because the skull length estimate was uncertain, and (assuming that body mass increases as the cube of body length) scaling Suchomimus which was 11 meters (36 ft) long and 3.8 tonnes (4.2 short tons) in mass to the range of estimated lengths of Spinosaurus would produce an estimated body mass of 11.7 to 16.7 tonnes (12.9 to 18.4 short tons).
Franзois 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 1.5 to 1.75 meters (4.9 to 5.7 ft), their estimates include a body length of 12.6 to 14.3 meters (41 to 47 ft) and a body mass of 12 to 20.9 tonnes (11.8 to 20.6 long tons; 13.2 to 23.0 short tons). 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 (e.g., most of the theropods used to set the initial equations were tyrannosaurids and carnosaurs, which have a different build than spinosaurids), and for the assumption that the Spinosaurus skull could be as little as 1.5 meters (4.9 ft) in length. Improvement of the precision of size estimates for Spinosaurus requires the discovery of more complete remains as available for some other dinosaurs,especially the limb bones of Spinosaurus which are "hitherto unknown".

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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 vertebral bodies 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 Edaphosaurus and Dimetrodon, contrasting also with the thicker spines in the iguanodontian Ouranosaurus.
Spinosaurus sails were unusual, although other dinosaurs, namely the ornithopod Ouranosaurus, which lived a few million years earlier in the same general region as Spinosaurus, and the South American sauropod Amargasaurus, might have developed similar structural adaptations of their vertebrae. The sail may be an analog of the sail of the Permiansynapsid 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 ("one might rather think of the existence of a large hump of fat [German: Fettbuckel], to which the [neural spines] gave internal support") 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 (which were known to have sails); instead, the dinosaurs" neural spines were similar to the neural spines of extinct hump-backed mammals such as Megacerops and Bison latifrons.
The 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 anterior maxilla; large teeth in the lower jaw faced this space. The very tip of the snout holding those few large anterior 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 et al. (2005) estimated that the skull of Spinosaurus was 1.75 meters (5.7 ft) long.The Dal Sasso et al. skull length estimate was questioned because skull shapes can vary across spinosaurid species.

A newly made study performed by scientists Andrew R. Cuff and Emily Rayfield showed that Spinosaurids like Spinosaurus had relatively poor resistance in their skulls for torsion compared to other members of this group (Baryonyx) and modern alligators, thus showing Spinosaurus preyed more regularly on fish than it did on land animals, although considered predators of the former too.
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Spinosaurus gives its name to the Spinosauridae family of dinosaurs, which includes two subfamilies: Baryonychinae and Spinosaurinae. The Baryonychinae include Baryonyx from southern England and Suchomimus from Niger in central Africa. The Spinosaurinae include Spinosaurus, Irritator from Brazil, and Angaturama (which is probably synonymous with Irritator) from Brazil.The Spinosaurinae share unserrated straight teeth that are widely spaced (e.g., 12 on one side of the maxilla), as opposed to the Baryonychinae which have serrated curved teeth that are numerous (e.g., 30 on one side of the maxilla).
Two species of Spinosaurus have been named: Spinosaurus aegyptiacus (meaning "Egyptian spine lizard") and Spinosaurus maroccanus (meaning "Moroccan spine lizard").
The first described remains of Spinosaurus were found and described in the early 20th century. In 1912, Richard Markgraf discovered a partial skeleton of a dinosaur in the Bahariya Formation of western Egypt. In 1915, German paleontologist Ernst Stromer published an article assigning the specimen to a new genus and species Spinosaurus aegyptiacus.
Fragmentary additional remains from Bahariya, including vertebrae and hindlimb bones, were designated by Stromer as "Spinosaurus B" in 1934. Stromer considered them different enough to belong to another species, and this has been borne out. With the advantage of more expeditions and material, it appears that they pertain either to Carcharodontosaurus or to Sigilmassasaurus.
S. maroccanus was originally described by Dale Russell in 1996 as a new species based on the length of its neck vertebrae. Specifically, Russell claimed that the ratio of the length of the centrum (body of vertebra) to the height of the posterior articular facet was 1.1 in S. aegyptiacus and 1.5 in S. maroccanus.Later authors have been split on this topic. Some authors note that the length of the vertebrae can vary from individual to individual, that the holotype specimen was destroyed and thus cannot be compared directly with the S. maroccanus specimen, and that it is unknown which cervical vertebrae the S. maroccanus specimens represent. Therefore, though some have retained the species as valid without much comment, most researchers regard S. maroccanus as a nomen dubium or as a junior synonym of S. aegyptiacus.

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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 nighttime 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 (Haldane"s principle), 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 (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.
Elaborate body structures of many modern-day animals usually serve to attract members of the opposite sex during mating. It is quite possible that the sails or humps of these dinosaurs were used for courtship, in a way similar to a peacock"s tail. Stromer speculated that males and females may have differed in the size of the neural spine.
Finally, it is quite possible that the sail or hump combined these functions, acting normally as a heat regulator, becoming a courting aid during the mating season, being used to cool itself and, on occasions, turning into an intimidating device when an animal was feeling threatened.

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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.A study by Cuff and Rayfield (2013) 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, however its jaws were poorly adapted with respect to resisting lateral bending.
In 2009, Dal Sasso et al. 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.
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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.
Although traditionally depicted as a biped, it has been suggested since the mid-1970s that Spinosaurus was at least an occasional quadruped.This has been bolstered by the discovery of Baryonyx, a relative with robust arms. Because of the mass of the hypothesized fatty dorsal humps of Spinosaurus, Bailey (1997) was open to the possibility of a quadrupedal posture, leading to new restorations of it as such. The hypothesis that Spinosaurus had a typical quadrupedal gait has fallen out of favor, though spinosaurids may have crouched in a quadrupedal posture.
Theropods, including spinosaurids, could not pronate their hands (rotate the forearm so the palm faced the ground),but a resting position on the side of the hand was possible, as shown by fossil prints from an Early Jurassic theropod.A 2014 paper describing new material of Spinosaurus, proposed that its legs were too short for it to move effectively on land. The reconstruction used in the study was an extrapolation based on different sized individuals, scaled to what was assumed to be the correct proportions. Palaeontologist John Hutchinson of the Royal Veterinary College of the University of London has expressed scepticism to the new reconstruction, and cautioned that using different specimens can result in inaccurate chimaeras.
The environment inhabited by Spinosaurus is only partially understood, and covers a great deal of what is now northern Africa. The region of Africa Spinosaurus is preserved in dates from 112 to 97 million years ago.A 1996 study concluded from Moroccan fossils that Spinosaurus, Carcharodontosaurus, and Deltadromeus "ranged across north Africa during the late Cretaceous (Cenomanian)."Those Spinosaurus that lived in the Bahariya Formation of what is now Egypt may have contended with shoreline conditions on tidal flats and channels, living in mangrove forests alongside similarly large dinosaurian predators Bahariasaurus and Carcharodontosaurus, the titanosaur sauropods Paralititan and Aegyptosaurus, crocodylomorphs, bony and cartilaginous fish, turtles, lizards, and plesiosaurs.In the dry season it might have resorted to preying on pterosaurs.This situation resembles that in the Late Jurassic Morrison Formation of North America, which boasts up to five theropod genera over one tonne in weight, as well as several smaller genera (Henderson, 1998; Holtz et al., 2004). Differences in head shape and body size among the large North African theropods may have been enough to allow niche partitioning as seen among the many different predator species found today in the African savanna (Farlow & Pianka, 2002)

Oxalaia
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Although only currently known from partial snout remains, it is still enough material to declare Oxalaia a spinosaurid due to the unique nature of the snout. Spinosaurid teeth were also known from the fossil site before the current material was discovered, and may have belonged to Oxalaia in life. With its total length estimated between twelve and fourteen metres, Oxalaia was smaller than Spinosaurus, yet larger than Baryonx and probably also Suchomimus. Also if the larger estimate of fourteen metres ever proves correct then Oxalaia may have been the one of the longest South American theropod dinosaurs, being just a bit bigger than the lowest estimate of Giganotosaurus.
The species name O. quilombensis is in reference to the quilombo settlements on Cajual Island that were originally built by escaped slaves. Along with Irritator, the discovery of Oxalaia is further proof that Africa and South America were once joined during the Mesozoic, something that allowed the spinosaurids to spread over the two continents.

Based on skeletal material from related spinosaurids, the skull of Oxalaia would have been an estimated 1.35 m (4 ft 5 in) long;this is smaller than Spinosaurus"s skull, which was approximated at 1.75 m (5 ft 9 in) long by Italian palaeontologist Cristiano Dal Sasso and colleagues in 2005.Kellner and his team compared the Dal Sasso specimen (MSNM V4047) to Oxalaia"s original snout in 2011; from this they estimated Oxalaia at 12 to 14 metres (39 to 46 ft) in length and 7 to 9 tonnes (7.7 to 10 short tons) in weight, making it the largest known theropod from Brazil,the second largest being Pycnonemosaurus, which was estimated at 8.9 m (29 ft) by one study.
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The Late Cretaceous deposits of the Alcвntara Formation have been interpreted as a humid habitat of tropical forests dominated by conifers, ferns, and horsetails. These forests were surrounded by an arid-to-semi-arid landscape that was probably subjected to brief periods of heavy rainfall followed by lengthy dry periods.A great abundance and variety of animal taxa, such as dinosaurs, pterosaurs, snakes, molluscs, crocodilians, notosuchids, and fish have been discovered in the formation. Aquatic taxa known from the deposits include the large coelacanth Mawsonia gigas; the ray Myliobatis; two sclerorhynchid sawfishes; as well as several bony fish, ray-finned fish, and lungfish species.Dinosaur fossil remains suggest the presence of diplodocoids, basal titanosaurs, the giant theropod Carcharodontosaurus, a noasaurid closely related to Masiakasaurus, and a possible velociraptorine dromaeosaurid. Also, characteristic teeth and a single vertebral centrum were referred to Spinosaurus sp.
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Most of the flora and fauna discovered in the Alcвntara Formation was also present in North Africa in the Kem Kem Beds of Morocco during the Cenomanian; with a few exceptions including Oxalaia quilombensis, Atlanticopristis equatorialis, Equinoxiodus alcantariensis, and Coringasuchus anisodontis. According to Medeiros and colleagues, the Laje do Coringa assemblage may also be linked to the contemporaneous Bahariya Formation in Egypt, which holds a distinct combination of key taxa constituting Spinosaurus aegyptiacus, Carcharodontosaurus saharicus, and Onchopristis numidus. This extreme similarity between the Cretaceous biota of Brazil with that of Africa is a result of their connection as parts of the supercontinent Gondwana (which comprised most landmasses of the modern southern hemisphere). This connection was broken by rifting and sea-floor spreading 130–110 million years ago. Afterwards, the transoceanic assemblages would have continued to evolve separately, contributing to small differences between taxa.Machado stated that Cajual Island was still attached to the African continent during the Cenomanian.Similarly, Medeiros and colleagues noted that the presence of an island chain or other lasting land connection during that time could explain the faunal similarities.

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