Irritator

Source: Wikipedia, the free encyclopedia.
For other uses, see Irritation and wikt:irritate.

Irritator
Temporal range:
Ma
↓
Reconstructed skeleton at the National Museum of Nature and Science, Tokyo. The postcranium is based on remains that cannot be confidently attributed to the animal.
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Family: †Spinosauridae
Subfamily: †
Spinosaurinae
Genus: †Irritator
Martill et al., 1996
Type species
†Irritator challengeri
Martill et al., 1996
Synonyms
  • Angaturama limai?
    Kellner & Campos 1996

Irritator is a

paleontologists who found the skull had been heavily damaged and altered by the collectors. The species name is a 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

National Museum of Rio de Janeiro
in 2009.

Estimated at between 6 and 8 meters (20 and 26 ft) in length, Irritator weighed around 1 tonne (1.1 short tons), making it one of the smallest spinosaurids known. 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 challengeri's holotype remains the most completely preserved spinosaurid skull yet found. 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

crocodyliforms
, and a large number of pterosaur and fish species.

History of research

spinosaurine fossil specimens in the Araripe and São Luís-Grajaú Basins marked. From top to bottom: Oxalaia
, Irritator, and Angaturama

The holotype of Irritator was excavated from a chalk

theropod dinosaur.[2]

Historical reconstruction of the holotype skull by Martill and colleagues, 1996, above an outdated restoration based on said diagram
Outdated reconstruction of the holotype skull (top) based on the interpretations of Martill and colleagues in 1996.[1] Depictions (similar to the one at the bottom) based on this reconstruction were later featured in many dinosaur books and encyclopedias.[3][4][5][6]

The skull was flattened sideways somewhat and, as is common with fossils, was partly crushed. The right side was well preserved, while the left was extensively damaged during collection. Some of the skull's hindmost upper surface had eroded, and the lower jaw lacked its front end, both owing to breakage during fossilization. Parts of the specimen were also cracked due to being part of a septarian

Arthurdactylus conandoylei, after the novelist himself.[10]

When Martill and colleagues first described Irritator challengeri, the holotype was still extensively encased in

junior synonymy of Irritator with Spinosaurus. Sues and colleagues noted that more overlapping skull material was needed for further diagnosis.[7] As more of Spinosaurus's skull became known, later research maintained separation of the two taxa.[11][12][13]

Although the site of discovery is uncertain, the specimen most probably stems from the

ichthyodectid Cladocyclus, both found in the Romualdo Formation. Questioning of local fossil dealers hinted at a locality near the village of Buxexé close to Santana Do Cariri at the flank of the Chapada do Araripe, at a height of approximately 650 meters (2,130 ft). 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.[7] Irritator challengeri was the first dinosaur described from the Romualdo Formation, and its holotype specimen represents the most completely preserved spinosaurid skull known.[1][11]

Synonymy with Angaturama

paleontologist
Jaime A. Headden; the snout tip is from the Angaturama specimen.

Angaturama limai, another

Tupi Indian language of Brazil. The specific name honors the late Brazilian paleontologist Murilo R. de Lima, who informed Kellner of the specimen in 1991.[14]

Head silhouettes of Irritator and Angaturama with respective skull bones overlaid onto them, the Angaturama specimen is larger and overlaps with that of Irritator by one tooth
Holotypes of Irritator challengeri and Angaturama limai in place, showing the latter's larger skull size and overlapping third left 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.[15] 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).[16] Authors including Éric Buffetaut and Mohamed Ouaja in 2002,[17] Cristiano Dal Sasso and colleagues in 2005,[13] Tor G. Bertin in 2010,[18] Darren Naish in 2013,[19] and Madani Benyoucef and colleagues in 2015 supported this conclusion.[20] 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 Angaturama's premaxillae may correspond with that of Irritator's nasal bones.[7] Some objection has been raised to these assertions. 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.[2][21]

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

priority, since it was named almost a month earlier.[11] The paleontologist Marco Schade and colleagues could not confirm the overlap in tooth positions in 2023 due to interpreting them differently, and could not provide information to resolve the issue.[22]

Postcranial material and additional finds

National Museum of Rio de Janeiro

Besides the skull, the snout fragment, and some isolated teeth, the Romualdo Formation has also yielded

neural spines and the enlarged condition of the hand claw.[23][24][26] The skeleton was fully described in 2010 in an as-of-yet unpublished master's thesis by Machado.[27] An incomplete hind limb (MPSC R-2089) mentioned in 2013 might also pertain to the Spinosauridae.[28] In 2018, Tito Aureliano and his team described LPP-PV-0042, part of a left tibia from a particularly large individual.[23] As is common with fossils from the Araripe Basin, the majority of spinosaurid material from the Romualdo Formation was collected under uncontrolled circumstances for use in the illegal fossil trade. As such, many specimens are partly damaged and without precise geological field data.[8][23][29]

Some of the Romualdo Formation postcrania were used as the basis for the creation of a replica Angaturama skeleton, later mounted at the Federal University-owned Museu Nacional do Rio de Janeiro (

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. Oxalaia quilombensis is differentiated from Angaturama limai by its broader, more rounded snout and lack of a sagittal crest on the premaxillae.[32] In September 2018, a fire broke out at the palace housing the Museu Nacional, largely destroying the fossil collections and possibly the exhibited Angaturama skeleton and fossil elements.[33] The holotype of Oxalaia quilombensis, which was stored in the same building, may also have been destroyed.[34][needs update
]

Description

Silhouettes of two left-facing dinosaurs, a larger one in dark green and a smaller one in light green, compared with a blue human to their left
Estimated size of Irritator (light green) and Angaturama's (dark green) holotype specimens with a human

Even by maximal size estimates, Irritator was smaller than other known spinosaurids.

co-ossified (fused), indicating that the specimen belonged to a subadult.[7] The partial spinosaurine skeleton MN 4819-V represented a moderately sized individual, estimated by Machado at 5 to 6 meters (16 to 20 ft) in length.[27] Many elements from this specimen were incorporated into the skeletal mount in the National Museum of Rio de Janeiro, which had a length of 6 meters (20 ft) and a height of 2 meters (6.6 ft).[19][30] However, spinosaurids from the Romualdo Formation possibly attained greater sizes. Although LPP-PV-0042 is represented only by a tibia fragment, Aureliano and colleagues estimated its length at roughly 10 meters (33 ft). Bone histology indicates that this individual was a subadult, so the mature animal may have been larger.[23]

Anatomy of the Irritator challengeri holotype

Two photos of Irritator challengeri's holotype skull from the left and right sides
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

prefrontal bones were large and sturdy, while the thinner frontal bones, situated behind them, were smooth and concave on top; both of these bones formed the upper rim of the orbit.[7]

Life restoration
of Irritator

A thin

display function when the animal was alive.[39] The preserved part of Irritator's crest is deepest above the antorbital fenestra and lacks the vertical ridges seen in the crest of Spinosaurus.[13] 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.[7][40] 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 basipterygoid processes (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 surangular bone, which articulated with the shallower angular bone below it. The mandibular fenestra, a sideways-facing opening in the lower jaw, was oval and comparatively large. The dentary (tooth-bearing bone of the mandible) is unknown in Irritator, save for a possible remnant at the front of the surangular. Irritator challengeri's holotype is unique in that it is one of the few non-avian (or non-bird) dinosaur fossils found with a preserved stapes.[7]

Closeups of the Irritator challengeri holotype's upper jaw and teeth
Closeup of Irritator's upper jaw and dentition

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.

roots ran deep into the maxillae and converged close to the midline, nearly reaching the top of the skull.[1][7] Based on comparisons with Irritator's 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.[11] The hindmost tooth of the Irritator specimen's left maxilla was not yet fully erupted, and only the tip of it was visible.[7]

Anatomy of the Angaturama limai holotype

Photos of the Angaturama limai fossil snout from various angles
Holotype of Angaturama limai from various angles

The holotype of Angaturama limai consists only of the front part of the upper jaw, comprising the tips of the paired premaxillae and the frontmost ends of the maxillae. The specimen measures 19.2 cm (7.6 in) in height and 11 cm (4.3 in) in length, with the width of the palatal region being 4 to 5 mm (0.16 to 0.20 in). The suture between the maxilla and premaxilla was jagged at the front and straightened out towards the rear. The lower margin of the premaxillae was concave, with the concavity reaching its apex at the sixth premaxillary tooth. The front of the snout was expanded, forming the spoon-shaped terminal rosette characteristic of spinosaurids. This concave underside of the premaxillae would have complemented a convex and enlarged mandible tip.[14] The premaxillae connected with each other on the bottom to form Angaturama's secondary palate, which was also partially contributed to by two processes extending from the maxillae.[11] The snout was strongly compressed laterally, and the premaxillae gently tapered towards the top to form a tall sagittal crest 1 to 2 mm (0.039 to 0.079 in) in thickness. This crest was larger and extended farther forwards on the snout than in other known spinosaurids. The frontmost upper border of the premaxilla had a small bulge that overhung the base of the crest. This bulge was apparently damaged on its upper surface, indicating that the top of the crest may have extended even farther over and forwards from that point. The front of Angaturama's snout hence had a vertically straight or concave margin, atypical from the more smoothly sloping snouts of other spinosaurs.[11][14]

In the premaxilla, a broken-off tooth with partial tooth crown was recovered. The strongly extended and straight teeth with unserrated conical crowns, which measured 6 to 40 mm (0.24 to 1.57 in) in length, were singly embedded. This indicates continuous tooth replacement where new teeth were pushed up between the old ones. Judging by the alveoli (tooth sockets), the premaxilla had seven teeth altogether, the third tooth being the largest. The frontmost three teeth of the maxilla were also preserved. The premaxillary teeth increased in size from the first to third, shrank from the third to the sixth, and enlarged again from the sixth premaxillary to third maxillary positions. A 16 cm (6.3 in) diastema (gap in tooth row) was present between the last premaxillary and first maxillary tooth.[14]

Postcrania

Diagram showing fragmentary dinosaur hand and arm bones
Hand and arm bones of specimen MN 4819-V, the most complete spinosaurid hand known

Though no skeletal remains were discovered with the original Angaturama snout tip, one partial skeleton (MN 4819-V) from a different location may belong to the genus.

dorsal (back) and caudal (tail) vertebrae, five sacral (hip) vertebrae, a partial right tibia and fibula (shin and calf bones), most of the right femur (thigh bone), and part of an ulna (forearm bone).[23][25] It also has the most complete hand known from a spinosaurid, including metacarpals, phalanges, one carpals, and one claw.[41] Like in all spinosaurids, the claw of the first finger (the "thumb") was enlarged.[26]

The

pelvic bones are well preserved, with the right side better articulated than the left. The fused sacral vertebrae are still attached to the pelvis, which lacks the distal ends of both of its pubic bones and ischia (lower and rearmost hip bones).[25] The ilium (main hip bone) is 55.3 cm (21.8 in) long.[26] The preacetabular ala (front expansion) of the ilium was curved on the bottom and was somewhat shorter and deeper than the postacetabular ala (rear expansion). The preacetabular ala were somewhat enlarged at the front, in contrast to the more slender condition of the postacetabular ala. The brevis fossa (groove at the bottom of the postacetabular ala) was concave, as was the rear margin of the ischium. The pubis bore a relatively large and almost closed obturator notch, an indentation in the lower margin of the rear part of the bone that allowed for the passage of the obturator nerve. The upwards projecting neural spines of the sacrum were elongated, as is typical in spinosaurs.[25] In life, these would have been covered in skin, forming a "sail" down the animal's back.[21][39] MN 4819-V is distinguished from Suchomimus due to its longer and shallower ilium with a less curved upper margin,[2][25] and from Baryonyx by having a more developed obturator process, a blade-like structure on the bottom of the ischium.[25]

Classification

spinosaurids
(Irritator in purple, first from left) compared with a human

Martill and his team originally classified Irritator as a

sister taxon to the Megalosauridae.[39]

Diagram of four fossil skulls from different spinosaurids
Diagram illustrating skull elements from Irritator (bottom) and other spinosaurids, comparing the relative positions of the external nares, or bony nostrils, (labeled e.n.)

In 1998, Sereno and colleagues defined two subfamilies within the Spinosauridae based on craniodental (skull and tooth) characteristics. They were Spinosaurinae, where they placed Spinosaurus and Irritator; and Baryonychinae, to which they assigned Baryonyx, Suchomimus, and

paraphyletic (unnatural) group.[11]

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.[11] Although Angaturama limai's snout is generally narrower than in other spinosaurids, this might be due to damage sustained by the fossil; the holotype appears partly crushed and broken on its lower margin, with some of the preserved teeth having been sectioned off along their length. Therefore, Angaturama's only valid autapomorphy is its sagittal crest, which extends farther forwards on the rostrum and is more exaggerated than in other known spinosaurid skulls.[11][49]

Paleobiology

Diet and feeding

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

homogeneous pointed teeth,[39] an arrangement found particularly in animals like the Indian gharial—the most piscivorous extant crocodilian.[40][51] The long conical teeth, which in spinosaurines did not possess serrated edges, were suitable for grabbing and holding prey. They differed from teeth of other theropods, which seemed geared towards tearing or cutting off seized body parts.[39]

Closeup photo of the reconstructed head and neck bones in the Japan Irritator skeletal mount
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.[7][52] 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.[7] 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. 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.[53] 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.[11]

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.

crocodyliforms, juveniles of their own species, turtles, and small to medium-sized dinosaurs. This would have made spinosaurines apex predators within this particular ecosystem.[23]

Examinations and digital reconstructions of Irritator published in 2023 by Schade, Rauhut et al., suggests that the lower jaws of this spinosaurid could rotate and open laterally, with a gape similar to that of modern pelicans; this would have allowed the theropod to swallow very large prey items. It was also discovered to have a very weak but rapid bite as a result of this analysis. The study also reaffirms that Irritator likely possessed binocular vision and would have held its snout at an inclined orientation. Additionally, the examinations reaffirmed classification of spinosaurids as megalosauroids and that megalosauroids and allosauroidea were part of a monophyletic Carnosauria, with Monolophosaurus standing as a sister taxon to spinosauridae.[22]

Aquatic habits

Many spinosaurs likely had semiaquatic habits, as has been shown in studies using techniques like isotope analysis and bone histology. It has been found that they probably took advantage of aquatic prey and environments (usually marginal and coastal habitats[57]) to occupy a distinct ecological niche, therefore avoiding competition with more terrestrial theropods.[58][59] Spinosaurines appear to have been more adapted for such lifestyles than baryonychines.[23][60] A 2018 study by British paleontologist Thomas M. S. Arden and colleagues examined the morphology of spinosaurine skull bones for possible aquatic traits. 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.[61]

In 2018, Aureliano and colleagues conducted an analysis on the Romualdo Formation tibia fragment. CT scanning of the specimen in the

paleobiologist Donald Henderson argued that osteosclerosis would not have changed a theropod's buoyancy to a significant extent.[63]

Neuroanatomy and senses

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. In addition, the vestibular part of the endosseous labyrinth has a large anterior semicircular canal with a lateral oriented semicircular canal.[64]

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 1,950 Hz with a frequency band width of 3,196 Hz. However, they considered these ranges as rough estimates and established an overall frequency range of 350–3,550 Hz, making Irritator to be placed under bird hearing but above crocodiles.[64]

Paleoenvironment and paleobiogeography

Reconstruction of the head in front of a beach at dusk
Restoration of the head

Irritator and Angaturama are known from the

Cycadales and the extinct conifer Brachyphyllum were the most widespread plants.[68]

Artist's depiction of a coastline in the Romualdo Formation. In the foreground, Irritator approaches the water, surrounded by nearby patches of foliage. Above the coastline are two pterosaurs in flight, and in the distance at the far right, a small theropod dinosaur is being fended off by a pterosaur on all fours.
Restoration of Irritator walking down a coastline in the Romualdo Formation environment

This environment was dominated by pterosaurs, including:

niche partitioning, where different animals would have fed on prey of varied sizes and locations within the lagoon.[23]

Locations of spinosaurid fossil discoveries marked with white circles on a map of Earth during the Albian to Cenomanian of the Cretaceous Period
Generalized locations of spinosaurid fossil discoveries from the Albian-Cenomanian, 113 to 93.9 million years ago, marked on a map of that time span

Similarities between the fauna of the Romualdo and Crato Formations to that of Middle Cretaceous Africa suggest that the Araripe Basin was connected to the

Tethys Sea, though this link was likely sporadic, because the lack of marine invertebrates indicates the basin had a non-marine depositional setting.[79] Spinosaurids had already achieved a cosmopolitan distribution during the Early Cretaceous.[80] Sereno and colleagues in 1998 suggested that with the opening of the Tethys Sea, spinosaurines would have evolved in the south (Africa, in Gondwana) and baryonychines in the north (Europe, in Laurasia).[48] In following, Machado and Kellner theorized in 2005 that spinosaurines would have then spread to South America from Africa.[2] Sereno and colleagues postulated that divergent evolution between spinosaurines in South America and Africa likely occurred as a consequence of the Atlantic Ocean, whose opening gradually separated the continents and contributed to differences between taxa.[48] A similar scenario was suggested in 2014 by Brazilian paleontologist Manuel A. Medeiros and colleagues for the fauna of the Alcântara Formation, where Oxalaia has been found.[81] But the paleobiogeography of spinosaurids remains highly theoretical and uncertain, with discoveries in Asia and Australia indicating that it may have been complex.[82][83]

Taphonomy

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 disarticulated and displaced towards alternate regions of the head before burial.[7] 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.[42] 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).[23]

References

  1. ^
    S2CID 131339386
    .
  2. ^
    ISSN 0101-9759
    .
  3. OCLC 62384519
    .
  4. OCLC 227315325
    .
  5. OCLC 63835422
    .
  6. OCLC 428131451
    .
  7. ^
    S2CID 131050889
    .
  8. ^
    ISSN 0266-6979
    .
  9. PMID 24598620
    .
  10. S2CID 247538712
    .
  11. ^
    PMID 29107966
    .
  12. ^
    S2CID 85354215
    .
  13. ^
    S2CID 85702490
    .
  14. ^
    doi:10.1127/njgpa/199/1996/151
    .
  15. ^ Charig, A.J.; Milner, A.C. (1997). "Baryonyx walkeri, a fish-eating dinosaur from the Wealden of Surrey". Bulletin of the Natural History Museum of London. 53: 11–70. Archived from the original on November 17, 2015. Retrieved October 14, 2018.
  16. PMID 9812890
    .
  17. hdl:2042/216. Archived
    (PDF) from the original on January 22, 2015. Retrieved October 14, 2018.
  18. ^ Bertin, Tor (December 8, 2010). "A catalogue of material and review of the Spinosauridae". PalArch's Journal of Vertebrate Palaeontology. 7. Archived from the original on September 18, 2018. Retrieved September 13, 2018.
  19. ^ a b c d e f Naish, Darren (2013). "Brilliant Brazilian spinosaurids". Scientific American Blog Network. Archived from the original on October 1, 2018. Retrieved September 30, 2018.
  20. ISSN 0195-6671
    .
  21. ^
    PMID 11151018
    .
  22. ^
    S2CID 258649428
    .
  23. ^
    S2CID 134353898
    .
  24. ^ a b Bittencourt, Jonathas; Kellner, Alexander (January 1, 2004). "On a sequence of sacrocaudal theropod dinosaur vertebrae from the Lower Cretaceous Santana Formation, northeastern Brazil". Arq Mus Nac. 62: 309–320.
  25. ^ a b c d e f g Machado, E.B.; Kellner, A.W.A.; Campos, D.A. (2005). "Preliminary information on a dinosaur (Theropoda, Spinosauridae) pelvis from the Cretaceous Santana Formation (Romualdo Member) Brazil". Congresso Latino-Americano de Paleontologia de Vertebrados. 2 (Boletim de resumos): 161–162.
  26. ^ a b c Kellner, A.W.A. (2001). "New information on the theropod dinosaurs from the Santana Formation (Aptian-Albian), Araripe Basin, Northeastern Brazil". Journal of Vertebrate Paleontology. 21 (supplement to 3): 67A.
  27. ^ a b Sales, Marcos (2017). Contribuições à paleontologia de Terópodes não-avianos do Mesocretáceo do Nordeste do Brasil (PhD thesis) (in Portuguese). Vol. 1. Universidade Federal do Rio Grande do Sul. p. 54. Archived from the original on October 1, 2018. Retrieved September 30, 2018.
  28. ^ Sayão, Juliana; Saraiva, Antonio; Silva, Helder; Kellner, Alexander (2011). "A new theropod dinosaur from the Romualdo Lagerstatte (Aptian-Albian), Araripe Basin, Brazil". Journal of Vertebrate Paleontology. 31: supplement 2: 187.
  29. PMID 24598620
    .
  30. ^ a b c d e O Estado de S. Paulo (in Portuguese), 2009-05-14, available at [1] Archived January 14, 2010, at the Wayback Machine; O Globo, 2009-05-15, abridgement available at [2] Archived May 20, 2009, at the Wayback Machine; University's announcement at Moutinho, Sofia (November 5, 2009). "Inaugura dia 14 a exposição Dinossauros no Sertão". Archived from the original on July 6, 2011. Retrieved January 13, 2010.
  31. ^ Naish, Darren. "In Rio for the 2013 International Symposium on Pterosaurs". Scientific American Blog Network. Archived from the original on October 7, 2018. Retrieved October 7, 2018.
  32. PMID 21437377. Archived
    (PDF) from the original on August 18, 2017. Retrieved September 15, 2018.
  33. ^ Belam, Martin (September 3, 2018). "Brazil's national museum: what could be lost in the fire?". The Guardian. Archived from the original on September 4, 2018. Retrieved October 15, 2018.
  34. ^ Lopes, Reinaldo José (September 2018). "Entenda a importância do acervo do Museu Nacional, destruído pelas chamas no RJ". Folha de S.Paulo (in Brazilian Portuguese). Archived from the original on September 3, 2018. Retrieved September 3, 2018.
  35. ^ Paul, G.S. (2010). The Princeton Field Guide to Dinosaurs. Princeton University Press. p. 87.
  36. ^ Holtz, Thomas R. Jr. (2011). "Winter 2010 Appendix" (PDF). Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages.
  37. ^ Holtz, T.R. Jr. (2014). "Supplementary Information to Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages". University of Maryland. Archived from the original on November 2, 2014. Retrieved September 5, 2014.
  38. ISBN 978-1-84696-988-1
    .
  39. ^
    S2CID 90952478
    .
  40. ^
    S2CID 85854809
    .
  41. ^ Machado, E.B.; Kellner, A.W.A. (2008). "An overview of the Spinosauridae (Dinosauria, Theropoda) with comments on the Brazilian material". Journal of Vertebrate Paleontology. 28(3): 109A.
  42. ^
    S2CID 18592288
    .
  43. S2CID 2986017
    .
  44. PMID 28463233
    .
  45. ^ Kellner, A.W.A. (1996). "Remarks on Brazilian dinosaurs". Memoirs of the Queensland Museum. 39 (3): 611–626. Archived from the original on October 24, 2018. Retrieved October 24, 2018.
  46. ISBN 978-0-901702-79-1
    .
  47. ^ Holtz, Thomas; Molnar, Ralph E.; Currie, Philip (June 12, 2004). "Basal Tetanurae". The Dinosauria: Second Edition. University of California Press. pp. 71–110. Retrieved September 25, 2018.
  48. ^
    PMID 9812890
    .
  49. S2CID 85354215
    .
  50. S2CID 22646156
    .
  51. ^
    PMID 23724135
    .
  52. S2CID 85854809
    .
  53. PMID 26500829
    .
  54. ^ Milner, Andrew; Kirkland, James (2007). "The case for fishing dinosaurs at the St. George Dinosaur Discovery Site at Johnson Farm". Utah Geological Survey Notes. 39 (3): 1–3.
  55. S2CID 90573936. Archived
    from the original on October 24, 2018. Retrieved October 24, 2018.
  56. S2CID 4398855
    .
  57. PMID 26829315
    .
  58. doi:10.1130/G30402.1
    .
  59. PMID 29643213
    .
  60. ^
    S2CID 34421257
    .
  61. S2CID 134735938. Archived
    from the original on October 23, 2018. Retrieved October 22, 2018.
  62. ^ Witmer, L.M. 1995.The Extant Phylogenetic Bracket and the Importance of Reconstructing Soft Tissues in Fossils. in Thomason, J.J. (ed). Functional Morphology in Vertebrate Paleontology. New York. Cambridge University Press. pp. 19–33.
  63. PMID 30128195
    .
  64. ^
    PMID 32518236
    .
  65. S2CID 45430990
    .
  66. S2CID 90477315
    .
  67. ISSN 0031-0182
    .
  68. ^
    doi:10.1139/cjes-37-6-891. Archived
    from the original on September 5, 2018. Retrieved September 4, 2018.
  69. ^ Barrett, Paul; Butler, Richard; Edwards, Nicholas; Milner, Andrew R. (December 31, 2008). "Pterosaur distribution in time and space: An atlas". Zitteliana Reihe B: Abhandlungen der Bayerischen Staatssammlung für Paläontologie und Geologie. 28: 61–107. Archived from the original on September 5, 2018. Retrieved September 4, 2018.
  70. S2CID 30685981
    .
  71. doi:10.1016/j.cretres.2010.12.008
    .
  72. ISSN 0195-6671
    .
  73. S2CID 129166567
    .
  74. ISSN 2385-4499. Archived
    from the original on September 20, 2018. Retrieved September 29, 2018.
  75. S2CID 59449305
    .
  76. S2CID 85790134. Archived
    from the original on October 1, 2018. Retrieved September 29, 2018.
  77. S2CID 45417065
    .
  78. ISSN 0031-0182
    .
  79. ^ a b Brito, Paulo; Yabumoto, Yoshitaka (2011). "An updated review of the fish faunas from the Crato and Santana formations in Brazil, a close relationship to the Tethys fauna". Bulletin of Kitakyushu Museum of Natural History and Human History, Ser. A. 9. Archived from the original on September 25, 2018. Retrieved September 6, 2018.
  80. ISSN 0567-7920
    .
  81. ISSN 0895-9811
    .
  82. S2CID 2647367
    .
  83. doi:10.11646/zootaxa.2827.1.3
    .

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