Other non- avian dinosaurs from the early Cretaceous Romualdo Formation include Irritator challengeri, Santanaraptor placidus, and Mirischia assymetrica.
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Nevertheless, Irritator also bore unserrated teeth, a trait associated with spinosaurines. Sales and Schultz thus noted that the Araripe Basin spinosaurids Irritator and Angaturama might represent intermediate forms between the earlier baryonychines and later spinosaurines, and that further research may eventually render the former a paraphyletic (unnatural) group. Irritator is further distinguished from Baryonyx, Suchomimus, and Cristatusaurus by having slightly over half as many teeth in the maxilla, and from Spinosaurus due to its comparatively larger and more forwardly positioned nostril openings, which, unlike in Spinosaurus, are also formed by the premaxilla. The narrow sagittal crest, which ends in a knob-like process above the frontals, is another autapomorphy separating Irritator from other spinosaurids.
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He also pointed out that since Irritator challengeris holotype lacked the tip of its snout, it would not be possible to know if Spinosauruss dentary could complement it or not. Based on comparisons with Spinosaurus, Kellner resolved Irritator as a spinosaurid and synonymized Irritatoridae with that family. Irritator was then assigned to the Baryonychidae along with Angaturama, Baryonyx, Suchomimus, and Spinosaurus by Oliver W.M. Rauhut in 2003. Thomas Holtz and colleagues in 2004 considered the Baryonychidae synonymous with Spinosauridae, and moved these genera to the latter family.
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Naish and colleagues in 2004 supported the theory that Irritator hunted both aquatic and terrestrial animals as a generalist within the coastal area and in addition probably searched for carrion. A tooth belonging to Irritator was discovered still inserted into the fossil neck vertebral column of an ornithocheirid pterosaur, likely with a wingspan of . This indicates that Irritator ate pterosaurs as well, although it is not known if it actively hunted these animals or simply scavenged the remains. In 2018, Aureliano and colleagues presented a possible scenario for the food web of the Romualdo Formation.
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It was also previously proposed that Irritator and Angaturamas skull parts belonged to the same specimen. Although this has been cast into doubt, more overlapping fossil material is needed to confirm whether they are the same animal or not. Other spinosaurid skeletal material, some of which could belong to Irritator or Angaturama, was retrieved from the Romualdo Formation, allowing for a replica skeleton to be made and mounted for display at the National Museum of Rio de Janeiro in 2009. Estimated at between in length, Irritator weighed around , making it one of the smallest spinosaurids known.
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Estimated size of Irritator (light green) and Angaturamas (dark green) holotype specimens with a human Even by maximal size estimates, Irritator was smaller than other known spinosaurids. Gregory S. Paul calculated its length at and weight at . Thomas R. Holtz Jr. published a higher estimate of , with a weight between . Estimates by Dougal Dixon were lower at long and high.
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Most later revisions have upheld these classifications. As spinosaurids, Irritator and Angaturama are placed within the superfamily Megalosauroidea, with Spinosauridae being a possible sister taxon to the Megalosauridae. Diagram illustrating skull elements from Irritator (bottom) and other spinosaurids, comparing the relative positions of the , or bony nostrils, (labeled e.n.) In 1998, Sereno and colleagues defined two subfamilies within the Spinosauridae based on craniodental (skull and tooth) characteristics.
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The holotype skull was thoroughly prepared before being redescribed in 2002, confirming this classification. Both Irritator and Angaturama belong to the Spinosaurinae subfamily. A generalist diet—like that of today's crocodilians—has been suggested; Irritator might have preyed mainly on fish and any other small prey animals it could catch. Fossil evidence is known of an individual that ate a pterosaur, either from hunting or scavenging it.
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The skull (designated SMNS 58022) became the holotype specimen of the new genus and species Irritator challengeri in February 1996, when it was first scientifically described by paleontologists David M. Martill, Arthur R.I. Cruickshank, Eberhard Frey, Philip G. Small and Malcolm Clarke. In this paper, Martill and his team wrote that the generic name Irritator came "from irritation, the feeling the authors felt (understated here) when discovering that the snout had been artificially elongated." The type species, Irritator challengeri, was named after Professor Challenger, a character in Arthur Conan Doyle's novels, specifically The Lost World. Two years earlier, Frey and Martill had named a new pterosaur species from the Crato Formation Arthurdactylus conandoylei, after the novelist himself.
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S. aegyptiacus head based on the 2005 reconstruction by Cristiano Dal Sasso Spinosaurus gives its name to the dinosaur family Spinosauridae, 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, Sigilmassasaurus, Oxalaia, Siamosaurus, Ichthyovenator, Irritator from Brazil, and Angaturama (which maybe be synonymous with Irritator) from Brazil. The Spinosaurinae share unserrated straight teeth that are widely spaced (e.g.
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Irritator is a genus of spinosaurid dinosaur that lived in what is now Brazil during the Albian stage of the Early Cretaceous Period, about 110 million years ago. It is known from a nearly complete skull found in the Romualdo Formation of the Araripe Basin. Fossil dealers had acquired this skull and illegally sold it to the State Museum of Natural History Stuttgart. In 1996, the specimen became the holotype of the type species Irritator challengeri.
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Discoveries in the 1990s shed more light on the relationships of Baryonyx and its relatives. In 1996, a snout from Morocco was referred to Spinosaurus, and Irritator and Angaturama from Brazil (the two are possible synonyms) were named. Cristatusaurus and Suchomimus were named based on fossils from Niger in 1998. In their description of Suchomimus, Sereno and colleagues placed it and Baryonyx in the new subfamily Baryonychinae within Spinosauridae; Spinosaurus and Irritator were placed in the subfamily Spinosaurinae.
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If Angaturama and Irritator are regarded as a member of the same genus, the latter would be the valid scientific name under rules of priority, since it was named almost a month earlier.
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Holotype skull of Irritator challengeri from left (top) and right side views The holotype skull of Irritator challengeri, although heavily damaged in certain places, is largely complete; missing only the tip of the snout and the front of the mandible. The preserved skull is tall and wide, its full length has been estimated at roughly , based on comparisons with Baryonyx. Irritators skull was long, narrow, and somewhat triangular in cross section. The was inclined backwards, and deeper than it was long.
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Irritator challengeris holotype is unique in that it is one of the few non-avian (or non-bird) dinosaur fossils found with a preserved stapes. Closeup of Irritators upper jaw and Irritator had straight or only faintly recurved conical teeth, bearing sharply defined but unserrated edges. Flutes (lengthwise ridges) were present on its tooth crowns, a common dental trait among spinosaurids. Both sides of Irritators teeth were fluted, as in Spinosaurus, whereas Baryonyx exhibited them only on the lingual (inward facing) side of its teeth.
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Kellner and Campos in 2000 and Brazilian paleontologist Elaine B. Machado and Kellner in 2005 expressed the opinion that the fossils come from two different genera, and that the holotype of Angaturama limai was clearly more laterally flattened than that of Irritator challengeri. A review of both fossils by the Brazilian paleontologists Marcos A. F. Sales and Cesar L. Schultz in 2017 noted that the specimens also differ in other aspects of their preservation: the Irritator specimen is brighter in color and is affected by a vertical crack, while the Angaturama specimen bears many cavities; the damage to the teeth of the Irritator challengeri holotype is also much less severe. Sales and Schultz also identified a possible point of overlap, the third left maxillary tooth, and observed that the skull of Angaturama could have been larger than that of Irritator based on the proportions of the closely related genus Baryonyx. They therefore concluded that the two specimens do not belong to the same individual, Sales and Schultz noted that synonymy at the genus level would need to be verified by more extensively overlapping remains.
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Also like its relatives, Irritator had two additional openings on the skull roof (called the postnasal fenestrae) as well as long and only partially diverging (bony extensions connecting the braincase with the palate). The back of the lower jaw was deep, its rear upper surface consisting mainly of the large bone, which with the shallower bone below it. The , a sideways-facing opening in the lower jaw, was oval and comparatively large. The (tooth-bearing bone of the mandible) is unknown in Irritator, save for a possible remnant at the front of the surangular.
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The regions surrounding the formation were arid to semi-arid, with most of the local flora being xerophytic (adapted to dry environments). Cycadales and the extinct conifer Brachyphyllum were the most widespread plants. Restoration of Irritator walking down a coastline in the Romualdo Formation environment This environment was dominated by pterosaurs, including: Anhanguera, Araripedactylus, Araripesaurus, Brasileodactylus, Cearadactylus, Coloborhynchus, Santanadactylus, Tapejara, Thalassodromeus, Tupuxuara, Barbosania, Maaradactylus, Tropeognathus, and Unwindia. The known dinosaur fauna besides Irritator was represented by other theropods like the tyrannosauroid Santanaraptor, the compsognathid Mirischia, an indeterminate unenlagiine dromaeosaurid, and a megaraptoran.
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Known skull elements of Irritator as interpreted by paleontologist Jaime A. Headden; the snout tip is from the Angaturama specimen. Angaturama limai, another spinosaurid from the same time and place as Irritator challengeri, was described by the Brazilian paleontologists Alexander W. A. Kellner and Diogenes de Almeida Campos in February 1996. Kept today under specimen number USP GP/2T-5 at the University of São Paulo, the holotype specimen consists of an isolated snout tip from the Romualdo Formation. It was extracted from a calcareous nodule using a technique originally developed for pterosaur fossils.
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Irritator may have had semiaquatic habits, and inhabited the tropical environment of a coastal lagoon surrounded by dry regions. It coexisted with other carnivorous theropods as well as turtles, crocodyliforms, and a large number of pterosaur and fish species.
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Although the complete shape and height of this structure is unknown in Irritator, these head crests were commonplace in spinosaurids, having possibly served a display function when the animal was alive. The preserved part of Irritators crest is deepest above the antorbital fenestra and lacks the vertical ridges seen in the crest of Spinosaurus. Like others in its family, Irritator possessed a long and bony structure on the roof of its mouth called a secondary palate, separating the oral from the nasal cavity. This is a feature observed in extant crocodilians, but absent in most theropod dinosaurs.
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What was originally thought to be a prominent head crest proved to be an unattached, indeterminate bone fragment. As in the previous study, Sues and colleagues regarded the African genus Spinosaurus as the most similar taxon to Irritator, because they shared many dental features, including mostly straight conical tooth crowns, thin enamel, well-defined edges with no , and lengthwise fluting. Since little was known of Spinosauruss skull at the time, these similarities were enough for the authors to suggest a possible junior synonymy of Irritator with Spinosaurus. Sues and colleagues noted that more overlapping skull material was needed for further diagnosis.
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Head of an Indian gharial, which has similarities to the head of Irritator In 1996, Martill and colleagues theorized that Irritator challengeri, with its elongated snout and unserrated conical teeth, likely had at least a partly piscivorous (fish-eating) diet. Although much of the holotype's morphology turned out to be greatly different than they thought, later studies supported these observations. Spinosaurids had very narrow and elongated jaws with relatively homogeneous pointed teeth, an arrangement found particularly in animals like the Indian gharial—the most piscivorous extant crocodilian. The long conical teeth, which in spinosaurines did not possess serrated edges, were suitable for grabbing and holding prey.
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The nostrils of Irritator were shifted far back from the snout tip; this, along with the secondary palate, which separated the animal's nasal passages from the inside of its mouth, made respiration possible even if most of the jaw was underwater or held prey. In particular, the sagittal crest of Irritator is an indication for pronounced neck musculature, which would have been necessary to close the jaws quickly against water resistance and withdraw the head rapidly. In 2015, German paleontologist Serjoscha W. Evers and colleagues found evidence for similar adaptations in the African spinosaur Sigilmassasaurus. The neck vertebrae of this genus have a heavily furrowed undersurface.
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They found that the frontal bones of Irritator, Spinosaurus, and Sigilmassasaurus were similar in being arched, concave on top, and narrowed at the front; features that would have resulted in the eyes being positioned further up on the head than in other theropods. In particular, the broad lower jaw and narrowed frontals of Irritator resulted in the orbits facing at a steep incline towards the midline of the skull, whereas most theropods had laterally facing orbits. These traits would have permitted the animal to see above the waterline when submerged. In 2018, Aureliano and colleagues conducted an analysis on the Romualdo Formation tibia fragment.
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However, authors like Sales and Schultz have questioned the monophyly of Baryonychinae (meaning it might be an unnatural group), stating that the South American spinosaurids Angaturama and Irritator represent intermediate forms between Baryonychinae and Spinosaurinae, based on their craniodental (skull and tooth) features. Their cladogram can be seen below.
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The generic name is in reference to Angaturama, a protective spirit in the aboriginal Tupi Indian culture of Brazil. The specific name honors the late Brazilian paleontologist Murilo R. de Lima, who informed Kellner of the specimen in 1991. maxillary tooth, as proposed by Sales and Schultz in 2017 In 1997, British paleontologists Alan J. Charig and Angela C. Milner considered Angaturama a likely junior synonym of Irritator, noting that both genera had retracted nostrils, long jaws, and characteristic spinosaurid dentition. Paul Sereno and colleagues in 1998 agreed with this possibility, and additionally observed that the holotype of Angaturama seems to complete that of Irritator (meaning that they could belong to the same specimen).
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Restoration of the head Irritator and Angaturama are known from the Romualdo Formation, whose rocks are dated to the Albian stage of the Early Cretaceous Period, about 110 million years ago. During this time, the Southern Atlantic Ocean was opening, forming the series of circum-Atlantic basins of southern Brazil and southwestern Africa, but the northeastern part of Brazil and West Africa were still connected. The Romualdo Formation is part of the Santana Group and, at the time Irritator was described, was thought to be a member of what was then considered the Santana Formation. The Romualdo Formation is a Lagerstätte (a sedimentary deposit that preserves fossils in excellent condition) consisting of limestone concretions embedded in shales, and overlies the Crato Formation.
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Based on comparisons with Irritators relatives, the maxillae were probably lined with a total of 11 teeth each, similar to the number of 12 teeth in MSNM V4047, an upper jaw fossil referred to Spinosaurus. The hindmost tooth of the Irritator specimen's left maxilla was not yet fully erupted, and only the tip of it was visible.
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BPA exhibits very low acute toxicity as indicated by its LD50 of 4 g/kg (mouse). In those mice, weight gain was reduced and exhibited estrogen-like properties. Reports indicate that it is a minor skin irritator as well, though less so than phenol. The FDA's National Center for Toxicology Research conducted its own research studies.
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In addition, the vestibular part of the endosseous labyrinth has a large anterior semicircular canal with a lateral oriented semicircular canal. Both floccular recesses and semicircular canal suggest that Irritator could coordinate fast head movements and had a downward inclined snout posture, enabling an unobstructed, stereoscopic forward vision, which is important for distance perception and therefore precise snatching movements of the snout. These inferences seem to be an agreement with a piscivore life-style. They also noted that the relatively well-developed cochlear duct may have enable an average hearing frequency of 1950 Hz with a frequency band width of 3196 Hz. However, they considered these ranges as rough estimates and established an overall frequency range of 350–3550 Hz, making Irritator to be placed under bird hearing but above crocodiles.
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Since the Romualdo Formation is indeed exposed there, and the matrix encasing the holotype has the same color and texture as those rocks, this locality can be regarded as the probable site of the discovery of the fossil. Irritator challengeri was the first dinosaur described from the Romualdo Formation, and its holotype specimen represents the most completely preserved spinosaurid skull known.
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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. Based on the size and positions of their nostrils, Marcos Sales and Cesar Schultz in 2017 suggested that Spinosaurus possessed a greater reliance on its sense of smell and had a more piscivorous lifestyle than Irritator and baryonychines. Reconstructed Irritator skeleton mounted as attacking an anhanguerid pterosaur, National Museum of Rio de Janeiro Direct fossil evidence shows that spinosaurids fed on fish as well as a variety of other small to medium-sized animals, including dinosaurs.
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CT scan of the holotype showing endocast and endosseous labyrinth In 2020, German paleontologist Marco Schade and colleagues analyzed the anatomy of the holotype skull braincase through CT scans, revealing numerous details about behavioral capabilities of Irritator. With the scans, they created a 3D model of the skull and braincase, discovering that Irritator had elongated olfactory tracts and a relatively large floccular recesses (area that pierces through the semicircular canals and connects the brain with the inner ear). The flocculus itself, is an important element in the coordination and control of head and ocular movements during gaze stabilization (visual ability during head movement), by being involved in the coordination of the vestibulo-ocular (VOR) and vestibulo- collic (VCR) reflexes. The flocculus appears to be enlarged in taxa that rely on quick movements of the head body.
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The Angaturama snout tip expanded to the sides in a rosette-like shape, bearing long teeth and an unusually tall crest. One possible skeleton indicates it, like other spinosaurids, had enlarged first-finger claws and a sail running down its back. Irritator had been mistaken initially for a pterosaur, and later a maniraptoran dinosaur. In 1996, the animal was identified as a spinosaurid theropod.
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Pterosaurs are known to have been eaten by theropods. In the 1 July 2004 edition of Nature, paleontologist Eric Buffetaut discusses an Early Cretaceous fossil of three cervical vertebrae of a pterosaur with the broken tooth of a spinosaur, most likely Irritator, embedded in it. The vertebrae are known not to have been eaten and exposed to digestion, as the joints are still articulated.
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Size of various spinosaurids (Irritator in purple, first from left) compared with a human Martill and his team originally classified Irritator as a maniraptoran dinosaur in the clade Bullatosauria (a group no longer considered monophyletic), as a close relative to the feathered ornithomimosaurs and troodontids. Given that its dental morphology, particularly long snout, and assumed fin-shaped crest were features unknown in "other" maniraptorans, the researchers erected the new family Irritatoridae within the clade. They recognized Irritators affinities with Spinosaurus, in that they both had similarly shaped and unserrated teeth, but noted that the latter's mandible would not conform with the front of Irritators upper jaw, and that other non-avian dinosaurs like Compsognathus and Ornitholestes also bore no serrations on some or all of their teeth. Some of these claims were questioned in 1996 by Kellner who found that Irritators skull lacked the one autapomorphy (distinguishing feature) diagnosed in maniraptorans at the time, which was having its (cheek) bone forming part of the antorbital fenestra.
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The taphonomy (changes between death and fossilization) of the Irritator challengeri holotype specimen has been discussed by some researchers. The skull was found lying on its side. Preceding fossilization, several bones from the back of the braincase, as well as the dentary, splenial, coronoid, and right angular bones from the lower jaw, were lost. Other bones, mostly from the skull rear, had become and displaced towards alternate regions of the head before burial.
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The genus name comes from the word "irritation", reflecting the feelings of paleontologists who found the skull had been heavily damaged and altered by the collectors. The species name is an homage to the fictional character Professor Challenger from Arthur Conan Doyle's novels. Some paleontologists regard Angaturama limai—known from a snout tip that was described later in 1996—as a potential junior synonym of Irritator. Both animals hail from the same stratigraphic units of the Araripe Basin.
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Its long, shallow and slender snout was lined with straight and unserrated conical teeth. Lengthwise atop the head ran a thin sagittal crest, to which powerful neck muscles were likely anchored. The nostrils were positioned far back from the tip of the snout, and a rigid secondary palate on the roof of the mouth would have strengthened the jaw when feeding. Belonging to a subadult, Irritator challengeris holotype remains the most completely preserved spinosaurid skull yet found.
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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 (2005) estimated that the skull of Spinosaurus was long, but more recent estimates suggest a length of .Molina-Pérez & Larramendi 2016. Récords y curiosidades de los dinosaurios Terópodos y otros dinosauromorfos, Larousse. Barcelona, Spain p.
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Map showing the Northeast Region of Brazil, with the discovery sites of three spinosaurine fossil specimens in the Araripe and São Luís-Grajaú Basins marked. From top to bottom: Oxalaia, Irritator, and Angaturama. Oxalaia stems from the Alcântara Formation, a succession of sedimentary rocks that is part of the Itapecuru Group of the São Luís-Grajaú Basin, in northeastern Brazil. These rocks have been dated by scientists to the Cenomanian stage of the Late Cretaceous period, 100.5 to 93.9 million years ago.
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Restoration of Spinosaurus swimming among contemporaneous aquatic animals A 2010 publication by Romain Amiot and colleagues found that oxygen isotope ratios of spinosaurid bones indicates semiaquatic lifestyles. Isotope ratios from teeth from Baryonyx, Irritator, Siamosaurus, and Spinosaurus 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, and Spinosaurus tended to have the least difference.
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In press releases of the exhibit's opening, Kellner informally implied MN 4819-V as belonging to Angaturama. This is also reflected in the specimen's inclusion in the skeletal mount. In 2011, a third Brazilian spinosaur, Oxalaia quilombensis, was named and described from the Alcântara Formation of the Itapecuru Group, part of the São Luís Basin. This larger species, known only from an isolated snout tip and upper jaw fragment, lived during the Cenomanian stage, around six to nine million years after Irritator and Angaturama.
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Some other creatures from the formation include the theropods Irritator, Mirischia and Santanaraptor, and the crocodylomorph Araripesuchus. The formation also includes several turtle remains, with some specimens referring to Santanachelys, Cearachelys and Araripemys. A few fish remains were also found within the Romualdo Formation, some of which were referred to Brannerion, Rhinobatos, Rhacolepis, Tharrhias and Tribodus. The Santana Group also consists of another Lagerstätte called the Crato Formation, which is not as diverse as the Romualdo Formation, but its fossil remains are still considered important.
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Baryonyx was found with scales of the prehistoric fish Scheenstia in its body cavity, and these were abraded, hypothetically by gastric juices. Bones of a young Iguanodon, also abraded, were found alongside this specimen. If these represent Baryonyx’s meal, the animal was, whether in this case a hunter, or a scavenger, an eater of more diverse fare than fish. Moreover, there is a documented example of a spinosaurid having eaten a pterosaur, as one Irritator tooth was found lodged within the fossil vertebrae of an ornithocheirid pterosaur found in the Romualdo Formation of Brazil.
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Northeast Region of Brazil, with the discovery sites of three spinosaurine fossil specimens in the Araripe and São Luís-Grajaú Basins marked. From top to bottom: Oxalaia, Irritator, and Angaturama. Commercial fossil-poachers excavated a chalk concretion containing the rear of a large skull with lower jaws near the town of Santana do Cariri in northeastern Brazil. This fossil was acquired by dealers who illegally sold it—fossil trade has been prohibited by law in Brazil since 1942—to Rupert Wild of the State Museum of Natural History Stuttgart, Germany.
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Authors including Éric Buffetaut and Mohamed Ouaja in 2002, Cristiano Dal Sasso and colleagues in 2005, Tor G. Bertin in 2010, Darren Naish in 2013, and Madani Benyoucef and colleagues in 2015 supported this conclusion. In their redescription of Irritator, Sues and colleagues pointed out that both holotypes are equally as narrow, and share transversely round teeth with defined yet unserrated edges. They also noted that a sagittal crest on Angaturamas premaxillae may correspond with that of Irritators nasal bones. Some objection has been raised to these assertions.
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Other pterosaurs from the Romualdo Formation include Anhanguera, Araripedactylus, Araripesaurus, Brasileodactylus, Cearadactylus, Coloborhynchus, Santanadactylus, Tapejara, Tupuxuara, Barbosania, Maaradactylus, Tropeognathus, and Unwindia. Thalassodromines are only known from this formation, and though well-preserved postcranial remains from there have been assigned to the group, they cannot be assigned to genus due to their lack of skulls. Dinosaur fauna includes theropods like Irritator, Santanaraptor, Mirischia, and an indeterminate unenlagiine dromaeosaur. The crocodyliforms Araripesuchus and Caririsuchus, as well as the turtles Brasilemys, Cearachelys, Araripemys, Euraxemys, and Santanachelys, are known from the deposits.
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Spinosaurines are characterized by straight, unserrated and more widely spaced teeth, and the small size of their first premaxillary teeth. Sereno and colleagues pointed out that the more retracted nostrils in Irritator and the tall sail of Spinosaurus could also be unique traits of spinosaurines, though material from other taxa is needed to know for sure. As with Suchomimus, the claw of Baryonyx had been the first discovered fossil of the animal. Sereno and colleagues in 1998 analyzed the distribution of forty-five traits to produce a cladogram that showed Suchomimus and Baryonyx to be distinct but closely related.
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Angaturama (a possible synonym of Irritator) had an unusually tall crest on its premaxillae that nearly overhung the tip of the snout with a small forward protrusion. Spinosaurid nostrils 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. Those of Baryonyx and Suchomimus were large and started between the first and fourth maxillary teeth, while Spinosaurus's nostrils were far smaller and more retracted. Irritator's nostrils were positioned similarly to those of Baryonyx and Suchomimus, and were between those of Spinosaurus and Suchomimus in size.
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When scaled by Aureliano and colleagues, the reconstructions from the study by Sales and Schultz provided a length of for the Irritator challengeri holotype, and for the Angaturama limai holotype. Some of the skull bones of the former holotype had not yet fully co-ossified (fused), indicating that the specimen belonged to a subadult. The partial spinosaurine skeleton MN 4819-V represented a moderately-sized individual, estimated by Machado at in length. Many elements from this specimen were incorporated into the skeletal mount in the National Museum of Rio de Janeiro, which had a length of and a height of .
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They differed from teeth of other theropods, which seemed geared towards tearing or cutting off seized body parts. Closeup of reconstructed skull and neck Irritator shared with crocodilians a stiff secondary palate and reduced antorbital fenestrae. In 2007, a finite-element analysis study by British paleontologist Emily J. Rayfield and colleagues found that these attributes, present in other spinosaurids as well, made the skull more resistant to torsion from prey item loads when feeding. The authors pointed out that in contrast, most theropods lacked secondary palates and had large antorbital fenestrae, exchanging strength for lighter skull builds.
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Comparison of a spinosaurid skull with that of Dubreuillosaurus and two extant pike conger eels 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.Sues, Hans-Dieter, Eberhard Frey, David M. Martill, and Diane M. Scott. 2002. “Irritator Challengeri, a Spinosaurid (Dinosauria: Theropoda) from the Lower Cretaceous of Brazil.” Journal of Vertebrate Paleontology 22 (3): 535–47. doi:10.1671/0272-4634(2002)022[0535:ICASDT]2.0.CO;2.
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Spinosaurine pelvis and sacral vertebrae (specimen MN 4819-V), National Museum of Rio de Janeiro Besides the skull, the snout fragment, and some isolated teeth, the Romualdo Formation has also yielded l remains that may belong to spinosaurids, many of which are hitherto undescribed, and all of them pertaining to the Spinosaurinae subfamily. In 2004, parts of a spinal column (MN 4743-V) were unearthed at the formation. Brazilian paleontologist Jonathas Bittencourt and Kellner assigned these, due to their structure, to the Spinosauridae. It is uncertain whether this specimen can be referred to Irritator or Angaturama, given that both are based only on skull material.
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They were Spinosaurinae, where they placed Spinosaurus and Irritator; and Baryonychinae, to which they assigned Baryonyx, Suchomimus, and Cristatusaurus. Spinosaurines were distinguished by their unserrated, straighter, and more widely spaced teeth, as well as smaller first teeth of the premaxilla. In 2005, Dal Sasso and colleagues assumed Irritators nostrils as being located above the middle of the maxillary tooth row; more posteriorly than in baryonychines, but less so than in Spinosaurus. Sales and Schultz in 2017 found that Irritators nostrils were in fact positioned closer to the front of the jaw, as in Baryonyx and Suchomimus; this more forward nostril placement was typically considered characteristic of baryonychines.
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When Martill and colleagues first described Irritator challengeri, the holotype was still extensively encased in calcareous rock matrix. Under the supervision of American paleontologist Hans-Dieter Sues, technician Diane M. Scott from the University of Toronto at Mississauga assumed the task of fully extracting the skull bones from the rock, allowing for a detailed redescription in 2002. Published by Sues, Frey, Martill, and Scott, this inspection of the now fully prepared specimen negated many of Martill and colleagues' original observations, which were based on misinterpretations of the damaged and largely concealed skull. The estimated length of the complete skull was shorter than previously proposed.
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Irritator mounted as attacking an anhanguerid, both from the Romualdo Formation, National Museum of Brazil Thalassodromeus is known from the Romualdo Formation, which dates to the Albian stage of the Early Cretaceous period (about 110 million years ago). The formation is part of the Santana Group and, at the time Thalassodromeus was described, was thought to be a member of what was then considered the Santana Formation. The Romualdo Formation is a Lagerstätte (a sedimentary deposit that preserves fossils in excellent condition) consisting of lagoonal limestone concretions embedded in shales, and overlies the Crato Formation. It is well known for preserving fossils three-dimensionally in calcareous concretions, including many pterosaur fossils.
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Likewise, the Khok Kruat skeleton shares mixed characteristics between Baryonyx and Spinosaurus, and its precise phylogenetic placement is uncertain pending a description of the material. The possibility that Baryonychinae is a paraphyletic (unnatural) grouping has been suggested by researchers such as Sales and Schultz, on the basis that genera such as Irritator and Angaturama (the two are possible synonyms) may represent intermediate forms between baryonychines and spinosaurines. As it is definitively known only from teeth, Siamosauruss exact position within the Spinosauridae is difficult to determine. In 2004, Brazilian palaeontologists Elaine Machado and Alexander Kellner suggested it as a possible spinosaurine, given its lack of dental serrations.
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Reconstructed skeleton of the related genus Spinosaurus, National Geographic Museum, Washington, D.C. On the bottoms of its cervical vertebrae, Sigilmassasaurus bore a series of highly rugged bony structures. These were suggested by Evers and colleagues as being possible evidence for substantial neck musculature, since the attachment sites of muscles and ligaments are often indicated by scarring on the bone surface. The neck muscles inferred from Sigilmassasaurus in particular would have enabled it to rapidly snatch fish out of the water, as indicated by the use of similarly- placed musculature in modern birds and crocodilians. This has also been proposed for the related genus Irritator, on account of the prominent sagittal crest running towards the back of its head.
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The bone separated the orbit from the antorbital fenestra, forming the upper and lower rear margins of the latter with two processes that enclosed a 40-degree angle; similar to Baryonyx, where it enclosed 35 degrees. Unlike in Baryonyx, Irritators lacrimal did not form a bony horn core. The prefrontal bones were large and sturdy, while the thinner bones, situated behind them, were smooth and concave on top; both of these bones formed the upper rim of the orbit. restoration combining specimens of Irritator and Angaturama A thin sagittal crest, constructed from the elongate nasal bones, extended along the skull midline before stopping just above the eye in a slightly flattened bulge.
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The holotype's smaller size, smoother surface, and lack of co-ossified (fused) sutures all indicate that it belongs to a juvenile individual; while MNHN GDF 365 probably represents an adult. The tip of Cristatusauruss premaxilla was short and expanded, while the rear end was narrowed near the suture with the maxilla; this rosette-like snout shape was characteristic of spinosaurids. The front of the upper jaw was concave on the bottom, shaped to interlock with what would have been the convex and also enlarged tip of the mandible's dentary bone. A thin sagittal crest ran lengthwise on top of the premaxillae, a condition present in Baryonyx and Suchomimus, and very prominent in Angaturama (a possible synonym of Irritator).
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The finding was a rare occurrence due to the erosive nature of the tides at the deposit, which are responsible for the fragmented state of most fossils in the bone bed; remains not found on site are often removed from the formation by wave action. Generally, the majority of fossil remains found at the Alcântara Formation consist of teeth and isolated skeletal elements, of which the Laje do Coringa site has yielded hundreds. Diagram illustrating known jaw material in place Oxalaia is one of three spinosaurid dinosaurs discovered in Brazil, the other two being Irritator and its possible synonym Angaturama, both of which were also initially known from partial skulls. They were discovered in the Romualdo Formation of the Santana Group, part of the Araripe Basin.
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Naish and colleagues in 2004 asserted that the Romualdo Formation dinosaur fauna is represented by animals that died near shorelines or rivers before being carried out to sea, where their floating remains were eventually fossilized. In 2018, Aureliano and colleagues argued against this scenario, stating that the Irritator challengeri holotype's mandible was preserved in articulation with the rest of the skull, whereas it would have likely detached had the carcass been floating at sea. They also noted that the corpse would have quickly sunk due to the osteosclerosis of the skeleton. The researchers, therefore, concluded that fossils from the Santana Group represent organisms that were buried in their natural habitat, instead of having been deposited allochthonously (other than at their present position).
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This is also evidenced by the discovery of Scheenstia fish scales in the stomach cavity of one Baryonyx skeleton and a Spinosaurus snout that was found with a vertebra from the sclerorynchid fish Onchopristis embedded in it. A more generalist diet has also been proposed for spinosaurs, based on fossils such as the bones of a juvenile iguanodontid that was also found in the same Baryonyx specimen, an "Irritator" tooth embedded in the vertebrae of a pterosaur, and tooth crowns from Siamosaurus that were found in association with sauropod dinosaur bones. It is thus likely that spinosaurids were also scavengers or hunters of larger prey. Though no limb bones are known from Ichthyovenator, all known spinosaurids had well-built arms with enlarged thumb claws, which they likely used to hunt and process prey.
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This is consistent with the attachment of powerful neck muscles for use in fishing or rapidly snatching small prey, a trait also observed in extant crocodilians and birds. Sales and Schultz in 2017 found that Irritator and baryonychines might have relied more on their sense of smell for hunting than Spinosaurus did, since they had larger, less retracted nostrils and more room in their skulls for the nasal cavity. Spinosaurus itself probably made heavier use of senses like vision or the mechanoreceptors on the tip of its snout, like those used by crocodilians to sense prey moving in the water. Skeleton mounted as attacking an anhanguerid pterosaur, National Museum of Rio de Janeiro Another trait spinosaurs shared with gharials was an enlarged snout tip that wielded a rosette-shaped array of interlocking teeth, adept for impaling and catching fish.
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Comparison between snout fossils of Suchomimus (A, B), Cristatusaurus (C, D), and Baryonyx (E) Spinosaurids were large bipedal carnivores with well-built forelimbs and elongated, crocodile-like skulls. The taxonomic and phylogenetic affinities of the group are subject to active research and debate, given that in comparison to other theropod groups, many of the family's taxa (including Cristatusaurus) are based on relatively poor fossil material. Traditionally the family has been divided into two subfamilies: Spinosaurinae, which includes genera like Irritator, Spinosaurus, and Oxalaia; and Baryonychinae, which includes Baryonyx and Suchomimus. Although the genus and species placement of Cristatusaurus lapparenti is disputed, its fossils certainly belong to a member of the baryonychinae, because of its more forwardly placed external nostrils; relatively larger first premaxillary teeth; and more closely spaced tooth sockets than in spinosaurines; as well as the presence of fine serrations, in contrast to spinosaurines lacking them entirely.
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Geological map of the Araripe Basin, with the extent of the Santana Group shown in dark blue Mounted skeleton of Irritator with a possible anhanguerid in its jaws Ornithocheiromorphs were present since the Early Cretaceous (Valanginian stage), and evolved throughout the rest of the period. Studies on the ornithocheirids Tropeognathus and Anhanguera, suggested that ornithocheiromorphs also expanded their distribution, while also evolving specialized features. The significant adaptions of the ornithocheiromorphs had also made them the top pterosaurs in almost every formation by the early Late Cretaceous, including the ones they were rare in, such as the Blesa Formation in Spain, where only Iberodactylus has been found.Borja Holgado, Rodrigo V. Pêgas, José Ignacio Canudo, Josep Fortuny, Taissa Rodrigues, Julio Company & Alexander W.A. Kellner, 2019, "On a new crested pterodactyloid from the Early Cretaceous of the Iberian Peninsula and the radiation of the clade Anhangueria", Scientific Reports 9: 4940.
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An Indian gharial, displaying the same interlocking rosette shape seen in spinosaurid snout tips As a spinosaur, Oxalaia would have had large, robust forelimbs; relatively short hindlimbs; elongated (upwards projections of the vertebrae) forming a ridge or on its back; and tall neural spines on its caudal vertebrae which—similar to the tails of modern crocodilians—may have aided in swimming. Spinosaurids likely spent most of their time near or in water and fed mostly on aquatic animals, avoiding direct competition with other large predators but being able to sustain themselves on terrestrial animals if necessary. Such behavior is observed in cases such as juvenile Iguanodontid bones found in the stomach cavity of a Baryonyx fossil and an Irritator tooth embedded in pterosaur remains. The conical, transversely oval-shaped teeth of Oxalaia and its nasal openings, that were retracted further back on the skull than in most theropods (likely to avoid water entering its nostrils while fishing) are characteristic of spinosaurids.
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Though prior spinosaurids had been named from the continent—including Siamosaurus from Thailand's Barremian Sao Khua Formation and "Sinopliosaurus" fusuiensis from China's Aptian Xinlong Formation—the authors noted that palaeontologists have debated the validity of these taxa because they are only confidently known from isolated teeth. Brazilian palaeontologists Marcos Sales and Caesar Schultz have suggested these teeth may eventually be attributed to spinosaurids similar to Ichthyovenator. In addition to tooth fossils, a spinosaurid skeleton that possibly belongs to Siamosaurus was excavated from the Thai Khok Kruat Formation in 2004 and was identified as a definite spinosaur in a 2008 conference abstract by Angela Milner and colleagues, eight years prior to Ichthyovenators description. Reconstructed skeleton of the spinosaurine Irritator, mounted at the National Museum of Nature and Science, Tokyo In 2012, Allain and colleagues assigned Ichthyovenator to the Spinosauridae; more precisely to the subfamily Baryonychinae in a basal position as the sister taxon of a clade formed by Baryonyx and Suchomimus.
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Likewise in 2010, British palaeontologist David Hone and colleagues placed Siamosaurus and "S." fusuiensis in the Spinosaurinae. British palaeontologist Thomas Arden and colleagues identified Siamosaurus as a basal (early diverging or "primitive") member of this subfamily in 2019; their cladogram can be seen below: Vertebra from specimen SM-KK14, which may belong to Siamosaurus Later in 2019, the Khok Kruat Formation teeth were also referred to the Spinosaurinae by Kamonrak and colleagues, on the basis that both the Khok Kruat and Siamosaurus morphotypes lack characteristics seen in baryonychines, such as long and slender roots, 0–10 flutes on each side, no well defined carinae, a sculptured surface of the crown base, and 45 degree orientation of the blood grooves. But they share with spinosaurines a sub-circular to oval cross section, fluted tooth crowns, well defined front and rear carinae, distinct striations on the crown, varying denticle size, and a wrinkled surface of the crown base. The authors also noted that unlike spinosaurines such as Irritator and Spinosaurus, Asian spinosaurines usually have more laterally compressed tooth crowns, and wrinkles across more of the enamel surface.
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