View source for Irritator

{{Short description|Spinosaurid theropod dinosaur genus from the Early Cretaceous Period}}
{{Other uses|Irritation|wikt:irritate}}
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{{Italic title}}
{{Use mdy dates|date=March 2025}}
{{Automatic taxobox
| name = ''Irritator''
| image = Irritator_challengeri_mount_01.jpg
| image_caption = Reconstructed skeleton at the [[National Museum of Nature and Science]], [[Tokyo]]. The {{Dinogloss|postcranium}} is based on remains that cannot be confidently attributed to the animal.
| fossil_range = [[Albian]]<br/>~{{fossilrange|113|110}}
| taxon = Irritator
| authority = Martill ''et al.'', [[1996 in paleontology|1996]]
| type_species = {{extinct}}'''''Irritator challengeri''''' 
| type_species_authority = Martill ''et al.'', 1996
| synonyms =
* '''''Angaturama limai'''''?<br/>{{small|[[Alexander Kellner|Kellner]] & Campos 1996}}
}}

'''''Irritator''''' is a [[genus]] of [[Spinosauridae|spinosaurid]] [[dinosaur]] that lived in what is now [[Brazil]] during the [[Albian]] [[Geological stage|stage]] of the [[Early Cretaceous]] [[Geological period|Period]], about 113 to 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 sold it to the [[State Museum of Natural History Stuttgart]]. In [[1996 in paleontology|1996]], the specimen became the [[holotype]] of the [[type species]] '''''Irritator challengeri'''''. 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 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  a few weeks later also in 1996—as a potential [[junior synonym]] of ''Irritator''. Both animals hail from the same [[stratigraphic unit]]s of the Araripe Basin. It was also previously proposed that ''Irritator'' and ''Angaturama''{{'}}s 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 {{convert|6|and|8|m|sp=us}} in length, ''Irritator'' weighed around {{convert|1|t|ST}}, 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 (design)|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 [[Neural spine sail|sail]] running down its back.

''Irritator'' had been mistaken initially for a [[pterosaur]], and later a [[maniraptora]]n dinosaur. In 1996, the animal was identified as a spinosaurid [[Theropoda|theropod]]. 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 [[crocodilia]]ns—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. ''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.

==History of research==
[[File:Spinosaur_Taxonomy_Map.png|thumb|left|upright=1.3|alt=Map of the Northeast Region of Brazil, with the marked fossil discovery sites of ''Oxalaia'', ''Irritator'', and ''Angaturama''|Map showing the [[Northeast Region, Brazil|Northeast Region]] of [[Brazil]], with the discovery sites of three [[spinosaurine]] fossil specimens in the [[Araripe Basin|Araripe]] and São Luís-Grajaú Basins marked. From top to bottom: ''[[Oxalaia]]'', ''Irritator'', and ''Angaturama'']]

The holotype of ''Irritator'' was excavated from 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 fossil traffickers and taken to the State Museum of Natural History in Stuttgart, [[Germany]]. At the time it was assumed to be the skull of a giant [[Basal (phylogenetics)|basal]] [[pterosaur]], or flying reptile, since the [[Chapada do Araripe]] region is famous for its copious pterosaur finds, and the German museum often bought such pieces. As it promised to be a unique discovery of singular importance, German and British pterosaur experts were contacted to study the exemplar. A paper describing it as a pterosaur had already been submitted for publication when the authors, German [[paleontologist]] Eberhard Frey and British paleontologist David Martill, were disabused of this notion by the [[peer review]]ers, who suggested the fossil belonged to a [[theropod]] dinosaur.<ref name="Machado2005"/>

[[File:Historical_Irritator_by_PaleoGeek.png|thumb|upright|alt=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 in paleontology|1996]].<ref name="Martill96">{{Cite journal |last1=Martill |first1=D.M. |last2=Cruickshank |first2=A.R.I. |last3=Frey |first3=E. |last4=Small |first4=P.G. |last5=Clarke |first5=M. |year=1996 |title=A new crested maniraptoran dinosaur from the Santana Formation (Lower Cretaceous) of Brazil |url=http://doc.rero.ch/record/14940/files/PAL_E2087.pdf |journal=[[Journal of the Geological Society]] |volume=153 |issue=1 |pages=5–8 |bibcode=1996JGSoc.153....5M |doi=10.1144/gsjgs.153.1.0005 |s2cid=131339386}}</ref> Depictions (similar to the one at the bottom) based on this reconstruction were later featured in many dinosaur books and encyclopedias.<ref>{{Cite book|title=The Usborne Internet-linked World atlas of dinosaurs|last1=Susanna|first1=Davidson|date=2005|publisher=[[Scholastic Corporation|Scholastic Inc.]]|last2=Turnbull|first2=Stephanie|last3=Firth|first3=Rachel|others=Slane, Andrea (designer); Rey, Luis V. (illustrator); Naish, Darren (consultant); Martill, David M. (consultant)|isbn=978-0-439-81840-7|oclc=62384519|page=51|url=https://archive.org/details/usborneinternetl00susa/page/51/mode/1up}}</ref><ref>{{Cite book|title=Encyclopedia of dinosaurs|last1=Malam|first1=John|date=2007|publisher=[[Parragon Publishing]]|last2=Parker|first2=Steve|isbn=978-1-4054-9923-1|oclc=227315325|page=53|url=https://archive.org/details/encyclopediaofdi0000mala/page/53/mode/1up}}</ref><ref>{{Cite book|title=Scholastic dinosaurs A to Z: the ultimate dinosaur encyclopedia|first=Don|last=Lessem|date=2004|publisher=[[Scholastic Corporation|Scholastic]]|others=Sovak, Jan (illustrator)|isbn=978-0-439-67866-7|oclc=63835422|pages=103–104|url=https://archive.org/details/oceanof-pdf.com-scholastic-dinosaurs-a-z-don-lessem/page/n103/mode/2up}}</ref><ref name="Dixon2009">{{Cite book|title=The ultimate guide to dinosaurs|first=Dougal|last=Dixon|date=2009|publisher=Ticktock|isbn=978-1-84696-988-1|edition=North American|oclc=428131451|url=https://archive.org/details/ultimateguidetod0000dixo/page/16/mode/2up|pages=16–17}}</ref>]]

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 [[concretion]]. The tip of the upper jaw was also missing. Since there were no signs of erosion, it had most probably broken off during or after the fossil's collection. Evident corrosion on certain bones indicates acid preparation had been attempted. A vertical fracture was present across the middle of the skull, which had apparently been sealed with car body filler.<ref name=":5">{{Cite journal|last1=Sues|first1=H.D.|last2=Frey|first2=E.|last3=Martill|first3=D.M.|last4=Scott|first4=D.M.|year=2002|title=''Irritator challengeri'', a spinosaurid (Dinosauria: Theropoda) from the Lower Cretaceous of Brazil|journal=[[Journal of Vertebrate Paleontology]]|volume=22|issue=3|pages=535–547|doi=10.1671/0272-4634(2002)022[0535:ICASDT]2.0.CO;2|s2cid=131050889 }}</ref> In hopes of making it look more complete and valuable, the fossil traders had severely obscured the skull beneath plaster;<ref name="Martill96"/> a widespread practice among local collectors in the Chapada do Araripe, especially on fish fossils.<ref name=":20">{{Cite journal|last=Martill|first=David|date=1994|title=Fake fossils from Brazil|journal=Geology Today|language=en|volume=10|issue=3|pages=111–115|doi=10.1111/j.1365-2451.1994.tb00882.x|bibcode=1994GeolT..10..111M |issn=0266-6979}}</ref> The buyers were unaware of the modifications to the specimen<ref name=":21">{{Cite journal |last=Gibney |first=Elizabeth |date=March 4, 2014 |title=Brazil clamps down on illegal fossil trade |journal=[[Nature (journal)|Nature]] |language=en |volume=507 |issue=7490 |page=20 |bibcode=2014Natur.507...20G |doi=10.1038/507020a |issn=0028-0836 |pmid=24598620 |doi-access=free}}</ref> until it was sent to universities in the United Kingdom for [[CT scan]] imaging. This revealed the collectors had tried to reconstruct the skull by grafting parts of the [[maxilla]] (main upper jaw bone) onto the front of the [[Rostrum (anatomy)|rostrum]] (snout).<ref name="Martill96"/> The skull (designated SMNS 58022) became the [[holotype]] specimen of the new [[genus]] and [[species]] ''Irritator challengeri'' in February [[1996 in paleontology|1996]], when it was first scientifically described by [[paleontologists]] David M. Martill, Arthur R.I. Cruickshank, Eberhard Frey, Philip G. Small and Maria Clarke. In this paper, Martill and his team wrote that the [[Genus|generic name]] ''Irritator'' came "from irritation, the feeling the authors felt (understated here) when discovering that the snout had been artificially elongated."<ref name="Martill96"/> The [[type species]], ''Irritator challengeri,'' was named after [[Professor Challenger]], a character in [[Arthur Conan Doyle]]'s novels, specifically ''[[The Lost World (Doyle novel)|The Lost World]]''.<ref name=Martill96/> Two years earlier, Frey and Martill had named a new pterosaur species from the [[Crato Formation]] ''[[Arthurdactylus conandoylei]]'', after the novelist himself.<ref>{{Cite journal|last1=Frey|first1=E.|last2=Martill|first2=D.M.|date=1994|title=A new Pterosaur from the Crato Formation (Lower Cretaceous, Aptian) of Brazil|journal=Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen|volume=194|issue=2–3|pages=379–412|doi=10.1127/njgpa/194/1994/379|bibcode=1994NJGPA.194..379F |s2cid=247538712}}</ref>

When Martill and colleagues first described ''Irritator challengeri'', the holotype was still extensively encased in [[calcareous]] rock [[Matrix (geology)|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 {{cvt|24|cm}} shorter than previously proposed. 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  and possibly South American<ref>{{Cite journal |last1=Smyth |first1=Robert S.H. |last2=Ibrahim |first2=Nizar |last3=Martill |first3=David M. |date=2020 |title=Sigilmassasaurus is Spinosaurus: A reappraisal of African spinosaurines |url=https://linkinghub.elsevier.com/retrieve/pii/S0195667120302068 |journal=Cretaceous Research |language=en |volume=114 |article-number=104520 |doi=10.1016/j.cretres.2020.104520|bibcode=2020CrRes.11404520S |url-access=subscription }}</ref> genus ''[[Spinosaurus]]'' as the most similar [[taxon]] to ''Irritator'', because they shared many dental features, including mostly straight conical [[tooth crown]]s, thin [[Tooth enamel|enamel]], well-defined edges with no {{Dinogloss|serrations}}, and lengthwise fluting. Since little was known of ''Spinosaurus''{{'}}s 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.<ref name=":5"/> As more of ''Spinosaurus''{{'}}s skull became known, later research maintained separation of the two taxa.<ref name=":6"/><ref name=":10">{{Cite journal|last1=Carrano|first1=Matthew T.|last2=Benson|first2=Roger B.J.|last3=Sampson|first3=Scott D.|s2cid=85354215|date=May 17, 2012|title=The phylogeny of Tetanurae (Dinosauria: Theropoda)|journal=[[Journal of Systematic Palaeontology]]|language=en|volume=10|issue=2|pages=211–300|doi=10.1080/14772019.2011.630927|bibcode=2012JSPal..10..211C|issn=1477-2019|url=https://www.researchgate.net/publication/230808558}}</ref><ref name=":9">{{Cite journal|last1=Dal Sasso|first1=Cristiano|last2=Maganuco|first2=Simone|last3=Buffetaut|first3=Eric|last4=Mendez|first4=Marco A.|date=December 30, 2005|title=New information on the skull of the enigmatic theropod Spinosaurus, with remarks on its size and affinities|journal=Journal of Vertebrate Paleontology|language=en|volume=25|issue=4|pages=888–896|doi=10.1671/0272-4634(2005)025[0888:niotso]2.0.co;2|s2cid=85702490 |issn=0272-4634}}</ref>

Although the site of discovery is uncertain, the specimen most probably stems from the [[Romualdo Formation]] (previously designated the Romualdo Member of the then [[Santana Formation]]).<ref name="Martill96"/> This assignment was confirmed by [[microfossils]] of the [[ostracod]] ''Pattersoncypris'', and fish scales from the [[Ichthyodectidae|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 {{convert|650|m|sp=us}}. 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.<ref name=":5"/> ''Irritator challengeri'' was the first dinosaur described from the Romualdo Formation, and its holotype specimen represents the most completely preserved spinosaurid skull known.<ref name="Martill96"/><ref name=":6"/>

===Synonymy with ''Angaturama''===
[[File:Irritator skull.png|thumb|left|upright|alt=Skull bones from Irritator and Angaturama plotted onto a silhouette of the head, by paleontologist Jaime A. Headden|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 Kellner|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 (geology)|nodule]] using a technique originally developed for pterosaur fossils. The generic name Angaturama means "noble" in the aboriginal [[Tupi Indian]] language of Brazil. The [[Specific name (zoology)|specific name]] honors the late Brazilian paleontologist Murilo R. de Lima, who informed Kellner of the specimen in 1991.<ref name="angaturama1996">{{cite journal|last1=Kellner|first1=A.W.A.|last2=Campos|first2=D.A. |year=1996|title= First Early Cretaceous theropod dinosaur from Brazil with comments on Spinosauridae|journal= Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen|volume=199|issue=2|pages=151–166|doi=10.1127/njgpa/199/1996/151 |bibcode=1996NJGPA.199..151K }}</ref>

[[File:Irritator_and_Angaturama_skulls.png|thumb|alt=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 [[Glossary of dentistry#Maxillary|maxillary]] tooth, as proposed by Sales and Schultz in 2017]]

In 1997, British paleontologists [[Alan J. Charig]] and [[Angela Milner|Angela C. Milner]] considered ''Angaturama'' a likely junior synonym of ''Irritator'', noting that both genera had retracted nostrils, long jaws, and characteristic spinosaurid dentition.<ref name="charigmilner1997">{{Cite journal|last1=Charig|first1=A.J.|last2=Milner|first2=A.C.|year=1997|title=''Baryonyx walkeri'', a fish-eating dinosaur from the Wealden of Surrey|url=http://biostor.org/reference/110558|journal=Bulletin of the Natural History Museum of London|volume=53|issue=1|pages=11–70|access-date=October 14, 2018|archive-url=https://web.archive.org/web/20151117032024/http://biostor.org/reference/110558|archive-date=November 17, 2015|url-status=live}}</ref> [[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).<ref name="serenoetal98"/> Authors including [[Éric Buffetaut]] and Mohamed Ouaja in 2002,<ref name="BufOua02">{{cite journal|last1=Buffetaut|first1=E.|last2=Ouaja|first2=M.|year=2002|title=A new specimen of ''Spinosaurus'' (Dinosauria, Theropoda) from the Lower Cretaceous of Tunisia, with remarks on the evolutionary history of the Spinosauridae|url=http://documents.irevues.inist.fr/bitstream/handle/2042/216/04.pdf|journal=[[Bulletin de la Société Géologique de France]]|language=en|volume=173|issue=5|pages=415–421|doi=10.2113/173.5.415|access-date=October 14, 2018|archive-url=https://web.archive.org/web/20150122004016/http://documents.irevues.inist.fr/bitstream/handle/2042/216/04.pdf|archive-date=January 22, 2015|url-status=live|hdl=2042/216|hdl-access=free}}</ref> [[Cristiano Dal Sasso]] and colleagues in 2005,<ref name=":9"/> Tor G. Bertin in 2010,<ref>{{Cite journal|last=Bertin|first=Tor|date=December 8, 2010|title=A catalogue of material and review of the Spinosauridae|url=https://www.researchgate.net/publication/235679976|journal=PalArch's Journal of Vertebrate Palaeontology|volume=7|access-date=September 13, 2018|archive-url=https://web.archive.org/web/20180918054304/https://www.researchgate.net/publication/235679976|archive-date=September 18, 2018|url-status=live}}</ref> [[Darren Naish]] in 2013,<ref name=":14"/> and Madani Benyoucef and colleagues in 2015 supported this conclusion.<ref>{{Cite journal|date=July 1, 2015|title=Overabundance of piscivorous dinosaurs (Theropoda: Spinosauridae) in the mid-Cretaceous of North Africa: The Algerian dilemma|journal=[[Cretaceous Research]]|language=en|volume=55|pages=44–55|doi=10.1016/j.cretres.2015.02.002|issn=0195-6671|last1=Benyoucef|first1=Madani|last2=Läng|first2=Emilie|last3=Cavin|first3=Lionel|last4=Mebarki|first4=Kaddour|last5=Adaci|first5=Mohammed|last6=Bensalah|first6=Mustapha|bibcode=2015CrRes..55...44B }}</ref> 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.<ref name=":5"/> 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''.<ref name="Machado2005">{{cite journal|last1=Machado|first1=E.B.|last2=Kellner|first2=A.W.A.|title=Notas Sobre Spinosauridae (Theropoda, Dinosauria)|journal=Anuário do Instituto de Geociências|volume=28|issue=1|date=2005|pages=158–173|doi=10.11137/2005_1_158-173|issn=0101-9759|language=pt|doi-access=free}}</ref><ref name=":19">{{Cite journal | last1 = Kellner | first1 = A.W.A. | last2 = Campos | first2 = D.A. | title = Brief review of dinosaur studies and perspectives in Brazil | journal = Anais da Academia Brasileira de Ciências | volume = 72 | year = 2000 | doi = 10.1590/S0001-37652000000400005 | pmid = 11151018 | issue = 4 | pages = 509–538 | doi-access = free }}</ref>

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. If ''Angaturama'' and ''Irritator'' are regarded as a member of the same genus, the latter would be the valid scientific name under rules of [[Principle of Priority|priority]], since it was named almost a month earlier.<ref name=":6"/> In 2023, German paleontologist Marco Schade and colleagues could not confirm the overlap in tooth positions due to interpreting them differently, and could not provide information to resolve the issue.<ref name="Osteology">{{cite journal |last1=Schade |first1=Marco |last2=Rauhut |first2=Oliver |last3=Foth |first3=Christian |last4=Moleman |first4=Olof |last5=Evers |first5=Serjoscha |title=A reappraisal of the cranial and mandibular osteology of the spinosaurid ''Irritator challengeri'' (Dinosauria: Theropoda) |journal=Palaeontologia Electronica |volume=26 |issue=2 |at=a17 |date=2023 |doi=10.26879/1242|s2cid=258649428 |doi-access=free }}</ref>

=== Postcranial material and additional finds ===
[[File:Spinosaurid_pelvis_specimen_MN_4819-V.jpg|thumb|left|upright|alt=Pelvis and sacral vertebrae from spinosaurine specimen MN 4819-V, on display at the National Museum of Rio de Janeiro|Spinosaurine [[pelvis]] and [[sacral vertebrae]] (specimen MN 4819-V), [[National Museum (Rio de Janeiro)|National Museum of Rio de Janeiro]]]]

Besides the skull, the snout fragment, and some isolated teeth, the Romualdo Formation has also yielded {{Dinogloss|postcranial}} remains that may belong to spinosaurids, many of which are hitherto undescribed, and all of them pertaining to the [[Spinosaurinae]] [[subfamily]].<ref name=":42">{{Cite journal|last1=Aureliano|first1=Tito|last2=Ghilardi|first2=Aline M.|last3=Buck|first3=Pedro V.|last4=Fabbri|first4=Matteo|last5=Samathi|first5=Adun|last6=Delcourt|first6=Rafael|last7=Fernandes|first7=Marcelo A.|last8=Sander|first8=Martin|date=May 3, 2018|title=Semi-aquatic adaptations in a spinosaur from the Lower Cretaceous of Brazil|url=http://osf.io/mjt95/|journal=Cretaceous Research|volume=90|pages=283–295|doi=10.1016/j.cretres.2018.04.024|bibcode=2018CrRes..90..283A |s2cid=134353898|issn=0195-6671}}</ref> 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.<ref name=":7">{{Cite journal|last1=Bittencourt|first1=Jonathas|last2=Kellner|first2=Alexander|date=January 1, 2004|title=On a sequence of sacrocaudal theropod dinosaur vertebrae from the Lower Cretaceous Santana Formation, northeastern Brazil|url=https://www.researchgate.net/publication/284508151|journal=Arquivos do Museu Nacional|volume=62|issue=3|pages=309–320}}</ref> In 2007, Machado and Kellner tentatively referred a rib fragment (MN 7021-V) to the Spinosauridae.<ref name=":42"/> However, the most complete spinosaur specimen retrieved from the Romualdo Formation is MN 4819-V, a partial skeleton lacking the skull.<ref name=":16"/> First reported in 1991, the specimen was referred by Kellner to the Spinosauridae in 2001 because of its tall [[Sacrum|sacral]] [[neural spines]] and the enlarged condition of the hand [[ungual|claw]].<ref name=":42"/><ref name=":7"/><ref name=":17">{{Cite journal|last=Kellner|first=A.W.A.|date=2001|title=New information on the theropod dinosaurs from the Santana Formation (Aptian-Albian), Araripe Basin, Northeastern Brazil|journal=Journal of Vertebrate Paleontology|volume=21|issue=suppl. to 3|page=67A|doi=10.1080/02724634.2001.10010852}}</ref> The skeleton was fully described in 2010 in an as-of-yet unpublished master's thesis by Machado.<ref name=":18"/> An incomplete hind limb (MPSC R-2089) mentioned in 2011 might also pertain to the Spinosauridae.<ref>{{Cite journal|last1=Sayão|first1=Juliana|last2=Saraiva|first2=Antonio|last3=Silva|first3=Helder|last4=Kellner|first4=Alexander|date=2011|title=A new theropod dinosaur from the Romualdo Lagerstatte (Aptian-Albian), Araripe Basin, Brazil|journal=Journal of Vertebrate Paleontology|volume=31|issue=suppl. to 2|page=187|doi=10.1080/02724634.2011.10635174}}</ref> In [[2018 in paleontology|2018]], [[Tito Aureliano]] and his team described LPP-PV-0042, part of a left tibia from a particularly large individual.<ref name=":42"/> 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.<ref name=":20"/><ref name=":42"/><ref name=":21"/>

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 ([[National Museum (Rio de Janeiro)|National Museum of Rio de Janeiro]]).<ref name=":1a">{{Cite news|language=pt|last=Cimieri|first=Fabiana|title=UFRJ expõe maior réplica de dinossauro carnívoro no País|url=http://www.estadao.com.br/noticias/vidae,ufrj-expoe-maior-replica-de-dinossauro-carnivoro-no-pais,370960,0.htm|work=[[O Estado de S. Paulo]]|date=May 14, 2009|archive-url=https://web.archive.org/web/20100114151410/http://www.estadao.com.br/noticias/vidae,ufrj-expoe-maior-replica-de-dinossauro-carnivoro-no-pais,370960,0.htm|archive-date=January 14, 2010}}</ref><ref name=":1b">{{Cite news|language=pt|last=Fonseca|first=Pedro|title=Museu monta réplica de dinossauro carnívoro de 6 metros no Rio|url=http://oglobo.globo.com/ciencia/mat/2009/05/14/museu-monta-replica-de-dinossauro-carnivoro-de-6-metros-no-rio-755870546.asp|work=[[O Globo]]|date=May 14, 2009|archive-url=https://web.archive.org/web/20090520011931/http://oglobo.globo.com/ciencia/mat/2009/05/14/museu-monta-replica-de-dinossauro-carnivoro-de-6-metros-no-rio-755870546.asp|archive-date=May 20, 2009}}</ref><ref name=":1c">{{Cite news|language=pt|title=Inaugura dia 14 a exposição Dinossauros no Sertão|url=https://ufrj.br/detalha_noticia.php?codnoticia=7486|work=[[Universidade Federal do Rio de Janeiro]]|date=May 11, 2009|archive-url=https://web.archive.org/web/20110706162356/http://www.ufrj.br/detalha_noticia.php?codnoticia=7486|archive-date=July 6, 2011}}</ref> The skeleton depicted the animal carrying an [[anhanguerid]] pterosaur in its jaws.<ref name=":14"/> It was the centerpiece of the ''Dinossauros no [[Sertão]]'' (Dinosaurs of Sertão) exhibit, which opened to the public in March 2009, becoming the first large carnivorous Brazilian dinosaur to be put on display.<ref name=":1a"/><ref name=":1b"/> Some of the original postcranial elements (including the fossil pelvis and sacral vertebrae) were presented alongside the mount.<ref name=":14"/><ref>{{Cite news|url=https://blogs.scientificamerican.com/tetrapod-zoology/rio-2013-international-symposium-on-pterosaurs/|title=In Rio for the 2013 International Symposium on Pterosaurs|last=Naish|first=Darren|author-link=Darren Naish|work=Scientific American Blog Network|access-date=October 7, 2018|language=en|archive-url=https://web.archive.org/web/20181007111425/https://blogs.scientificamerican.com/tetrapod-zoology/rio-2013-international-symposium-on-pterosaurs/|archive-date=October 7, 2018|url-status=live}}</ref> In press releases of the exhibit's opening, Kellner informally implied MN 4819-V as belonging to ''Angaturama''.<ref name=":1a"/><ref name=":1b"/> This is also reflected in the specimen's inclusion in the skeletal mount.<ref name=":14"/> 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''. ''Oxalaia quilombensis'' is differentiated from ''Angaturama limai'' by its broader, more rounded snout and lack of a sagittal crest on the premaxillae.<ref name="DescOxalaia">{{cite journal|last1=Kellner|first1=Alexander W.A.|last2=Azevedo|first2=Sergio A.K.|last3=Machado|first3=Elaine B.|last4=Carvalho|first4=Luciana B.|last5=Henriques|first5=Deise D.R.|year=2011|title=A new dinosaur (Theropoda, Spinosauridae) from the Cretaceous (Cenomanian) Alcântara Formation, Cajual Island, Brazil|url=http://www.scielo.br/pdf/aabc/v83n1/v83n1a06.pdf|journal=Anais da Academia Brasileira de Ciências|volume=83|issue=1|pages=99–108|doi=10.1590/S0001-37652011000100006|pmid=21437377|issn=0001-3765|access-date=September 15, 2018|archive-url=https://web.archive.org/web/20170818144524/http://www.scielo.br/pdf/aabc/v83n1/v83n1a06.pdf|archive-date=August 18, 2017|url-status=live|doi-access=free}}</ref> In September 2018, [[National Museum of Brazil#2018 fire|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.<ref>{{Cite news|url=https://www.theguardian.com/world/2018/sep/03/brazils-national-museum-what-could-be-lost-in-the-fire|title=Brazil's national museum: what could be lost in the fire?|last=Belam|first=Martin|date=September 3, 2018|newspaper=[[The Guardian]]|access-date=October 15, 2018|language=en|archive-url=https://web.archive.org/web/20180904011254/https://www.theguardian.com/world/2018/sep/03/brazils-national-museum-what-could-be-lost-in-the-fire|archive-date=September 4, 2018|url-status=live}}</ref> The holotype of ''Oxalaia quilombensis'', which was stored in the same building, was thought to have been destroyed.<ref>{{Cite news|url=https://www1.folha.uol.com.br/cotidiano/2018/09/entenda-a-importancia-do-acervo-do-museu-nacional-destruido-pelas-chamas-no-rj.shtml|title=Entenda a importância do acervo do Museu Nacional, destruído pelas chamas no RJ|last=Lopes|first=Reinaldo José|date=September 2018|work=Folha de S.Paulo|access-date=September 3, 2018|language=pt-BR|archive-url=https://web.archive.org/web/20180903160604/https://www1.folha.uol.com.br/cotidiano/2018/09/entenda-a-importancia-do-acervo-do-museu-nacional-destruido-pelas-chamas-no-rj.shtml|archive-date=September 3, 2018|url-status=live}}</ref> Luckily, the ''Oxalaia'' holotype, while heavily damaged, was recovered.<ref>{{cite tweet|last=Pêgas|first=R.V.|user=pegasaurus_42|date=February 9, 2025|title=It was destroyed (recovered but barely recognizable). A publication that will show the recovered items is almost finished and should be published soon!|number=1888728415253192884}}</ref>

==Description==
[[File:Irritator_Scale.svg|thumb|left|alt=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. [[Gregory S. Paul]] calculated its length at {{convert|7.5|m|sp=us}} and weight at {{convert|1|t|ST}}.<ref>{{cite book|last=Paul|first=G.S.|date= 2010|title=The Princeton Field Guide to Dinosaurs|url=https://archive.org/details/princetonfieldgu0000paul|url-access=registration|publisher= [[Princeton University Press]]|page= [https://archive.org/details/princetonfieldgu0000paul/page/87 87]}}</ref> [[Thomas R. Holtz Jr.]] published a higher estimate of {{convert|8|m|ft|sp=us}}, with a weight between {{Convert|0.9 to 3.6|t|ST|abbr=}}.<ref name="Holtz2012">{{cite book|last=Holtz|first=Thomas R. Jr. |date=2012|title=Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages|chapter-url=http://www.geol.umd.edu/~tholtz/dinoappendix/HoltzappendixWinter2010.pdf|chapter= Winter 2010 Appendix}}</ref><ref name="holtzsuplementary">{{cite web|url=http://www.geol.umd.edu/~tholtz/dinoappendix/appendix.html|title=Supplementary Information to ''Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages''|last=Holtz|first=T.R. Jr.|year=2014|publisher=University of Maryland|access-date=September 5, 2014|archive-url=https://web.archive.org/web/20141102224548/http://www.geol.umd.edu/~tholtz/dinoappendix/appendix.html|archive-date=November 2, 2014|url-status=live}}</ref> Estimates by [[Dougal Dixon]] were lower at {{convert|6|m|sp=us}} long and {{convert|2|m|ft|sp=us}} high.<ref name="Dixon2009"/> When scaled by Aureliano and colleagues, the reconstructions from the study by Sales and Schultz provided a length of {{convert|6.5|m|sp=us}} for the ''Irritator challengeri'' holotype, and {{convert|8.3|m|sp=us}} for the ''Angaturama limai'' holotype.<ref name=":42"/> Some of the skull bones of the former holotype had not yet fully [[co-ossified]] (fused), indicating that the specimen belonged to a subadult.<ref name=":5"/> The partial spinosaurine skeleton MN 4819-V represented a moderately sized individual, estimated by Machado at {{Convert|5 to 6|m|sp=us}} in length.<ref name=":18">{{Cite thesis|last=Sales|first=Marcos A.F.|date=2017|title=Contribuições à paleontologia de Terópodes não-avianos do Mesocretáceo do Nordeste do Brasil|type=PhD thesis|url=https://www.lume.ufrgs.br/handle/10183/181014|language=pt|publisher=Universidade Federal do Rio Grande do Sul|volume=1|page=54|access-date=September 30, 2018|archive-url=https://web.archive.org/web/20181001035816/https://www.lume.ufrgs.br/handle/10183/181014|archive-date=October 1, 2018|url-status=live}}</ref> Many elements from this specimen were incorporated into the skeletal mount in the National Museum of Rio de Janeiro, which had a length of {{Convert|6|m|sp=us}} and a height of {{convert|2|m|ft|sp=us}}.<ref name=":14">{{Cite news|url=https://blogs.scientificamerican.com/tetrapod-zoology/brilliant-brazilian-spinosaurids/|title=Brilliant Brazilian spinosaurids|last=Naish|first=Darren|date=June 2, 2013|work=Scientific American Blog Network|access-date=September 30, 2018|language=en|archive-url=https://web.archive.org/web/20181001031023/https://blogs.scientificamerican.com/tetrapod-zoology/brilliant-brazilian-spinosaurids/|archive-date=October 1, 2018|url-status=live}}</ref><ref name=":1a"/><ref name=":1b"/><ref name=":1c"/> 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 {{Convert|10|m|sp=us}}. Bone [[histology]] indicates that this individual was a subadult, so the mature animal may have been larger.<ref name=":42"/>

===Anatomy of the ''Irritator challengeri'' holotype===
[[File:Holotype of Irritator challengeri.PNG|thumb|upright|alt=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 [[mandible]]. The preserved skull is {{cvt|16.5|cm}} tall and {{cvt|10|cm}} wide, its full length has been estimated at {{cvt|60|cm}}, based on comparisons with ''Baryonyx''. ''Irritator''{{'}}s skull was long, narrow, and somewhat triangular in cross section. The {{Dinogloss|braincase}} was inclined backwards, and deeper than it was long. Extending from it was an elongate and low snout, with both sides relatively flat and slightly angled towards the skull midline.<ref name=":5"/> Only the rear ends of the paired {{Dinogloss|premaxillae}} (frontmost snout bones) remain intact, forming the front upper and lower borders of the {{Dinogloss|external nares}} (bony nostrils). As in all spinosaurids, the {{Dinogloss|maxillae}} (main upper jaw bones) extended below and past the nostrils in a long, low branch that formed the lower border of this opening, consequently separating the premaxillae and {{Dinogloss|nasal}} bones in that location. ''Irritator''{{'}}s [[maxillary sinus]]es (located in the body of the maxillae) bore a large oval opening, as in ''[[Allosaurus]]''. The nostril openings were oval and, as in all spinosaurids, positioned farther back on the skull than in typical theropods. ''Irritator''{{'}}s nostrils were both proportionately and absolutely smaller than in ''[[Suchomimus]]'' and ''Baryonyx'', but larger than those of ''Spinosaurus''.<ref name=":5"/><ref name=":6">{{Cite journal|last1=Sales|first1=Marcos A.F.|last2=Schultz|first2=Cesar L.|date=November 6, 2017|title=Spinosaur taxonomy and evolution of craniodental features: Evidence from Brazil|journal=PLOS ONE|language=en|volume=12|issue=11|article-number=e0187070|doi=10.1371/journal.pone.0187070|pmid=29107966|pmc=5673194|issn=1932-6203|bibcode=2017PLoSO..1287070S|doi-access=free}}</ref> The opening behind the [[Orbit (anatomy)|orbit]] (eye socket), the [[lateral temporal fenestra]], was very large, while the [[antorbital fenestra]], in front of the eyes, was long and elliptical. The orbit itself was deep and wider at the top (where the eyeball was placed) than the bottom. The {{Dinogloss|lacrimal}} bone separated the orbit from the antorbital fenestra, forming the upper and lower rear margins of the latter with two [[Process (anatomy)|processes]] that enclosed a 40-degree angle; similar to ''Baryonyx'', where it enclosed 35 degrees. Unlike in ''Baryonyx'', ''Irritator''{{'}}s lacrimal did not form a bony horn core. The [[prefrontal bones]] were large and sturdy, while the thinner {{Dinogloss|frontal}} bones, situated behind them, were smooth and concave on top; both of these bones formed the upper rim of the orbit.<ref name=":5"/>

[[File:Irritator_challengeri_by_PaleoGeek.png|left|thumb|alt=Artist's life reconstruction|[[Life restoration]] of ''Irritator'']]

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.<ref name=":5"/> Although the complete shape and height of this structure is unknown in ''Irritator'', these head crests were commonplace in spinosaurids, having possibly served a [[Sexual display|display]] function when the animal was alive.<ref name=":4">{{Cite journal|last1=Hone|first1=David William Elliott|last2=Holtz|first2=Thomas Richard|date=2017|title=A Century of Spinosaurs – A Review and Revision of the Spinosauridae with Comments on Their Ecology|journal=Acta Geologica Sinica - English Edition|language=en|volume=91|issue=3|pages=1120–1132|doi=10.1111/1755-6724.13328|bibcode=2017AcGlS..91.1120H |s2cid=90952478|issn=1000-9515|url=https://www.researchgate.net/publication/232687782}}</ref> The preserved part of ''Irritator''{{'}}s crest is deepest above the antorbital fenestra and lacks the vertical ridges seen in the crest of ''Spinosaurus''.<ref name=":9"/> Like others in its [[Family (biology)|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 [[crocodilia]]ns, but absent in most theropod dinosaurs.<ref name=":5"/><ref name=":12">{{Cite journal|last1=Rayfield|first1=Emily J.|last2=Milner|first2=Angela C.|last3=Xuan|first3=Viet Bui|last4=Young|first4=Philippe G.|date=December 12, 2007|title=Functional morphology of spinosaur 'crocodile-mimic' dinosaurs|journal=Journal of Vertebrate Paleontology|language=en-US|volume=27|issue=4|pages=892–901|doi=10.1671/0272-4634(2007)27[892:fmoscd]2.0.co;2|s2cid=85854809 |issn=0272-4634}}</ref> 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 {{Dinogloss|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 {{Dinogloss|surangular}} bone, which {{Dinogloss|articulated}} with the shallower {{Dinogloss|angular}} bone below it. The {{Dinogloss|mandibular fenestra}}, a sideways-facing opening in the lower jaw, was oval and comparatively large. The {{Dinogloss|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 dinosaur fossils found with a preserved [[stapes]].<ref name=":5"/>

[[File:Holotype of Irritator challengeri teeth.png|thumb|alt=Closeups of the Irritator challengeri holotype's upper jaw and teeth|Closeup of ''Irritator''{{'}}s upper jaw and {{Dinogloss|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.<ref name=":5"/><ref name=":6"/> Both sides of ''Irritator''{{'}}s teeth were fluted, as in ''Spinosaurus'', whereas ''Baryonyx'' exhibited them only on the [[Glossary of dentistry#Lingual|lingual]] (inward facing) side of its teeth. ''Irritator''{{'}}s teeth were circular in cross section, as opposed to the laterally flattened condition of most theropod teeth. The enamel (first layer of the teeth) was thin, with a finely wrinkled texture also observed in ''Baryonyx.'' Both of ''Irritator''{{'}}s maxillae preserve nine teeth, although the left maxilla's tooth crowns are more intact, and there are traces of a tenth tooth in the rock matrix. The teeth were deeply inserted into the jaw and widely spaced towards the front of the maxilla. The first and second preserved maxillary teeth were the largest, at {{cvt|32|mm}} and {{cvt|40|mm}} in crown length.<ref name=":5"/> The seven remaining teeth became progressively smaller towards the rear, one of the last ones measuring {{cvt|6|mm}} in estimated crown length. CT scans performed on the specimen revealed [[replacement teeth]] on both sides of the upper jaw. Their [[Tooth root|roots]] ran deep into the maxillae and converged close to the midline, nearly reaching the top of the skull.<ref name="Martill96"/><ref name=":5"/> 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 [[Museo Civico di Storia Naturale di Milano|MSNM]] V4047, an upper jaw fossil referred to ''Spinosaurus''.<ref name=":6"/> The hindmost tooth of the ''Irritator'' specimen's left maxilla was not yet fully erupted, and only the tip of it was visible.<ref name=":5"/>

===Anatomy of the ''Angaturama limai'' holotype===
[[File:Holotype of Angaturama limai.PNG|thumb|left|alt=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 {{cvt|19.2|cm}} in height and {{cvt|11|cm}} in length, with the width of the palatal region being {{cvt|4 to 5|mm}}. The [[Suture (anatomy)|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 (design)|rosette]] characteristic of spinosaurids. This concave underside of the premaxillae would have complemented a convex and enlarged mandible tip.<ref name="angaturama1996"/> 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.<ref name=":6"/> The snout was strongly compressed laterally, and the premaxillae gently tapered towards the top to form a tall sagittal crest {{cvt|1 to 2|mm}} 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.<ref name=":6"/><ref name="angaturama1996"/>

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 {{cvt|6 to 40|mm}} in length, were singly embedded. This indicates continuous tooth replacement where new teeth were pushed up between the old ones. Judging by the {{Dinogloss|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 {{cvt|16|cm}} [[diastema]] (gap in tooth row) was present between the last premaxillary and first maxillary tooth.<ref name="angaturama1996"/>

===Postcrania===
[[File:MN 4819-V manus skeletal by PaleoGeek.png|thumb|upright=0.73|alt=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.<ref name=":14"/><ref name=":1a"/><ref name=":1b"/><ref name=":1c"/> But since there is no overlapping material between the two specimens, direct comparisons cannot be made.<ref name=":16">{{Cite journal|last1=Machado|first1=E.B.|last2=Kellner|first2=A.W.A.|last3=Campos|first3=D.A.|date=2005|title=Preliminary information on a dinosaur (Theropoda, Spinosauridae) pelvis from the Cretaceous Santana Formation (Romualdo Member) Brazil|journal=Congresso Latino-Americano de Paleontologia de Vertebrados|volume=2 (Boletim de resumos)|pages=161–162}}</ref> MN 4819-V comprises a largely intact [[pelvis]], some [[Dorsal vertebra|dorsal]] (back) and {{Dinogloss|caudals|caudal}} (tail) [[vertebra]]e, five {{Dinogloss|sacral vertebrae|sacral}} (hip) vertebrae, a partial right {{Dinogloss|tibia}} and {{Dinogloss|fibula}} (shin and calf bones), most of the right {{Dinogloss|femur}} (thigh bone), and part of an {{Dinogloss|ulna}} (forearm bone).<ref name=":42"/><ref name=":16"/> It also has the most complete [[Manus (anatomy)|hand]] known from a spinosaurid, including {{Dinogloss|metacarpals}}, {{Dinogloss|phalanges}}, one {{Dinogloss|carpals}}, and one {{Dinogloss|ungual|claw}}.<ref>{{Cite journal|last1=Machado|first1=E.B.|last2=Kellner|first2=A.W.A.|date=2008|title=An overview of the Spinosauridae (Dinosauria, Theropoda) with comments on the Brazilian material|journal=Journal of Vertebrate Paleontology|volume=28|issue=suppl. to 3|page=109A|doi=10.1080/02724634.2008.10010459}}</ref> Like in all spinosaurids, the claw of the first finger (the "thumb") was enlarged.<ref name=":17"/>

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 {{Dinogloss|pubes|pubic bones}} and {{Dinogloss|ischia}} (lower and rearmost hip bones).<ref name=":16"/> The {{Dinogloss|ilium}} (main hip bone) is {{cvt|55.3|cm}} long.<ref name=":17"/> The {{Dinogloss|preacetabular process|preacetabular ala}} (front expansion) of the ilium was curved on the bottom and was somewhat shorter and deeper than the {{Dinogloss|postacetabular process|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 {{Dinogloss|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 {{Dinogloss|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.<ref name=":16"/> In life, these would have been covered in skin, forming a "[[Neural spine sail|sail]]" down the animal's back.<ref name=":19"/><ref name=":4"/> MN 4819-V is distinguished from ''Suchomimus'' due to its longer and shallower ilium with a less curved upper margin,<ref name="Machado2005"/><ref name=":16"/> and from ''Baryonyx'' by having a more developed {{Dinogloss|obturator process}}, a blade-like structure on the bottom of the ischium.<ref name=":16"/>

==Classification==
[[File:Spinosauridae_Size_Diagram_by_PaleoGeek_-_Version_2.svg|thumb|left|upright=1.3|alt=Scale diagram; Irritator was much bigger than a human, but small compared to other spinosaurids|Size of various [[spinosaurid]]s (''Irritator'' in purple, first from left) compared with a human]]

Martill and his team originally classified ''Irritator'' as a [[maniraptora]]n dinosaur in the [[clade]] [[Bullatosauria]] (a group no longer considered [[monophyletic]]<ref name=":13"/>), as a close relative to the feathered [[ornithomimosaurs]] and [[troodontids]].<ref>{{cite journal|last1=Lee|first1=Yuong-Nam|last2=Barsbold|first2=Rinchen|last3=Currie|first3=Philip J.|last4=Kobayashi|first4=Yoshitsugu|last5=Lee|first5=Hang-Jae|last6=Godefroit|first6=Pascal|last7=Escuillié|first7=François|last8=Chinzorig|first8=Tsogtbaatar|s2cid=2986017|year=2014|title=Resolving the long-standing enigmas of a giant ornithomimosaur Deinocheirus mirificus|journal=Nature|volume=515|issue=7526|pages=257–260|doi=10.1038/nature13874|pmid=25337880|bibcode=2014Natur.515..257L}}</ref><ref>{{cite journal|last1=Xu|first1=X.|last2=Currie|first2=P.|last3=Pittman|first3=M.|last4=Xing|first4=L.|last5=Meng|first5=Q.|last6=Lü|first6=J.|last7=Hu|first7=D.|last8=Yu|first8=C.|date=2017|title=Mosaic evolution in an asymmetrically feathered troodontid dinosaur with transitional features|journal=Nature Communications|volume=8|article-number=14972|bibcode=2017NatCo...814972X|doi=10.1038/ncomms14972|pmc=5418581|pmid=28463233}}</ref> Given that its dental [[Morphology (biology)|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 ''Irritator''{{'}}s 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 ''Irritator''{{'}}s upper jaw, and that other non-avian dinosaurs like ''[[Compsognathus]]'' and ''[[Ornitholestes]]'' also bore no serrations on some or all of their teeth.<ref name="Martill96"/> Some of these claims were questioned in 1996 by Kellner who found that ''Irritator''{{'}}s skull lacked the one [[autapomorphy]] (distinguishing feature) diagnosed in maniraptorans at the time, which was having its {{Dinogloss|jugal}} (cheek) bone forming part of the antorbital fenestra. He also pointed out that since ''Irritator challengeri''{{'}}s holotype lacked the tip of its snout, it would not be possible to know if ''Spinosaurus''{{'}}s dentary could complement it or not. Based on comparisons with ''Spinosaurus'', Kellner resolved ''Irritator'' as a spinosaurid and synonymized Irritatoridae with that family.<ref>{{Cite journal|last=Kellner|first=A.W.A.|date=1996|title=Remarks on Brazilian dinosaurs|url=https://www.biodiversitylibrary.org/item/123909#page/123/mode/1up|journal=Memoirs of the Queensland Museum|volume=39|issue=3|pages=611–626|access-date=October 24, 2018|archive-url=https://web.archive.org/web/20181024113154/https://www.biodiversitylibrary.org/item/123909#page/123/mode/1up|archive-date=October 24, 2018|url-status=live}}</ref> ''Irritator'' was then assigned to the [[Baryonychidae]] along with ''Angaturama'', ''Baryonyx'', ''Suchomimus,'' and ''Spinosaurus'' by Oliver W.M. Rauhut in 2003.<ref name=":3">{{Cite book|title=The interrelationships and evolution of basal theropod dinosaurs|last1=Rauhut|first1=Oliver W.M.|publisher=The Palaeontological Association|series=Special Papers in Palaeontology|year=2003|isbn=978-0-901702-79-1|volume=69|pages=35–36|url=https://www.researchgate.net/publication/235907153}}</ref> Holtz and colleagues in 2004 considered the Baryonychidae synonymous with Spinosauridae, and moved these genera to the latter family.<ref>{{cite book|last1=Holtz|first1=Thomas|last2=Molnar|first2=Ralph E.|last3=Currie|first3=Philip J.|chapter=Basal Tetanurae|year=2004|title=The Dinosauria|pages=71–110|edition=2|publisher=[[University of California Press]]|location=Berkeley, California|isbn=0-520-24209-2}}</ref> Most later revisions have upheld these classifications. As spinosaurids, ''Irritator'' and ''Angaturama'' are placed within the [[Superfamily (biology)|superfamily]] [[Megalosauroidea]], with Spinosauridae being a possible [[sister taxon]] to the [[Megalosauridae]].<ref name="bensonetal2009">{{cite journal |last1=Benson |first1=R. B. J. |last2=Carrano |first2=M. T. |last3=Brusatte |first3=S. L. |title=A new clade of archaic large-bodied predatory dinosaurs (Theropoda: Allosauroidea) that survived to the latest Mesozoic |journal=Naturwissenschaften |volume=97 |pages=71–78 |year=2009 |doi=10.1007/s00114-009-0614-x |pmid=19826771 |issue=1 |bibcode=2010NW.....97...71B|s2cid=22646156 |url=https://www.researchgate.net/publication/272152523}}</ref><ref name=":10"/><ref name=":4"/>

[[File:Spinosaurid cranial remains diagram.png|thumb|upright=1.3|alt=Diagram of four fossil skulls from different spinosaurids|Diagram illustrating skull elements from ''Irritator'' (bottom) and other spinosaurids, comparing the relative positions of the {{Dinogloss|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 ''[[Cristatusaurus]]''. Spinosaurines were distinguished by their unserrated, straighter, and more widely spaced teeth, as well as smaller first teeth of the premaxilla.''<ref name="serenoetal98">{{cite journal|last1=Sereno|first1=P.C.|last2=Beck|first2=A.L.|last3=Dutheuil|first3=D.B.|last4=Gado|first4=B.|last5=Larsson|first5=H.C.|last6=Lyon|first6=G.H.|last7=Marcot|first7=J.D.|last8=Rauhut|first8=O.W.M.|last9=Sadleir|first9=R.W.|year=1998|title=A long-snouted predatory dinosaur from Africa and the evolution of spinosaurids|journal=Science|volume=282|issue=5392|pages=1298–1302|bibcode=1998Sci...282.1298S|doi=10.1126/science.282.5392.1298|pmid=9812890|last10=Sidor|first10=C.A.|last11=Varricchio|first11=D.J.|last12=Wilson|first12=G.P.|last13=Wilson|first13=J.|doi-access=free}}</ref>'' In 2005, Dal Sasso and colleagues assumed ''Irritator''{{'}}s nostrils as being located above the middle of the maxillary tooth row; more posteriorly than in baryonychines, but less so than in ''Spinosaurus''.<ref name=":9"/> Sales and Schultz in 2017 found that ''Irritator''{{'}}s 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. 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.<ref name=":6"/>

''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.<ref name=":6"/> 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.<ref name=":6"/><ref name=":10"/>

{{col-begin|width=65%}}
{{col-break}}

'''Topology A:''' Benson and colleagues (2009)<ref name="bensonetal2009"/>
{{clade| style=font-size:90%; line-height:90%;
      |label1=[[Megalosauroidea]]
      |1={{clade
         |label1=[[Spinosauridae]]
         |1={{clade
            |1={{clade
               |1=''[[Baryonyx]]'' [[File:Baryonyx walkeri restoration.jpg|80px]]
               |2=''[[Suchomimus]]'' <div style="{{MirrorH}}">[[File:Suchomimus_tenerensis_by_PaleoGeek.png|80px]]</div> }}
            |2={{clade
               |1='''''Irritator''''' [[File:Irritator Life Reconstruction.jpg|80px]]
               |2=''[[Spinosaurus]]'' <div style="{{MirrorH}}">[[File:Spinosaurus_aegyptiacus_by_PaleoGeek.png|80px]]</div> }} }}
         |2=[[Megalosauridae]] [[File:Torvosaurus tanneri Reconstruction (Flipped).png|80px]]
        }} }}
{{col-break}}

'''Topology B:''' Sales and Schultz (2017)<ref name=":6"/>
{{clade| style=font-size:85%; line-height:85%
|label1=[[Spinosauridae]]
|1={{clade
 |1=''[[Baryonyx]] ''[[File:Baryonyx walkeri restoration.jpg|80px]]
 |2=''[[Cristatusaurus]]'' <div style="{{MirrorH}}">[[File:Cristatusaurus_lapparenti_by_PaleoGeek.png|80px]]</div>
 |3=''[[Suchomimus]]'' <div style="{{MirrorH}}">[[File:Suchomimus_tenerensis_by_PaleoGeek.png|80px]]</div>
 |4={{clade
  |1=''Irritator'' [[File:Irritator Life Reconstruction.jpg|80px]]
  |2={{clade
   |1=''[[Oxalaia]]'' <div style="{{MirrorH}}">[[File:Oxalaia_quilombensis_by_PaleoGeek.png|80px]]</div>
   |2=''[[Spinosaurus]]'' <div style="{{MirrorH}}">[[File:Spinosaurus_aegyptiacus_by_PaleoGeek.png|80px]]</div>
}} }} }} }}
{{col-end}}

==Paleobiology==

===Diet and feeding===
[[File:Gavialis_gangeticus,_ZOO_Praha_045_(Flipped_and_Cropped).jpg|thumb|left|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.<ref name="Martill96"/> Although much of the holotype's morphology turned out to be greatly different than they thought, later studies supported these observations.<ref name=":6"/><ref name=":4"/> Spinosaurids had very narrow and elongated jaws with relatively [[homogeneous]] pointed teeth,<ref name=":4"/> an arrangement found particularly in animals like the Indian [[gharial]]—the most piscivorous extant crocodilian.<ref name=":12"/><ref name=":15"/> 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.<ref name=":4"/>

[[File:Irritator challengeri mount 02.jpg|thumb|upright|alt=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 (mechanics)|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.<ref name=":5"/><ref name=":12"/> 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.<ref name=":5"/> 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.<ref>{{Cite journal|last1=Evers|first1=Serjoscha W.|last2=Rauhut|first2=Oliver W.M.|last3=Milner|first3=Angela C.|last4=McFeeters|first4=Bradley|last5=Allain|first5=Ronan|date=2015|title=A reappraisal of the morphology and systematic position of the theropod dinosaur ''Sigilmassasaurus'' from the 'middle' Cretaceous of Morocco|journal=[[PeerJ]]|language=en|volume=3|article-number=e1323|doi=10.7717/peerj.1323|issn=2167-8359|pmc=4614847|pmid=26500829 |doi-access=free }}</ref> 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 [[mechanoreceptor]]s on the tip of its snout, like those used by crocodilians to sense prey moving in the water.<ref name=":6"/>

[[File:20130825_Brazil_Rio_de_Janeiro_0144.jpg|thumb|left|alt=Reconstructed skeleton holding a pterosaur in its jaws against a painted backdrop|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.<ref name="milner2007">{{Cite journal|last1=Milner|first1=Andrew|last2=Kirkland|first2=James|date=2007|title=The case for fishing dinosaurs at the St. George Dinosaur Discovery Site at Johnson Farm|url=https://www.researchgate.net/publication/285906225|journal=Utah Geological Survey Notes|volume=39|issue=3|pages=1–3}}</ref> Although to a lesser degree than most known spinosaurs, this feature was also present in the ''Angaturama limai'' holotype.<ref name=":6"/> In 2002, Sues and colleagues pointed out, however, that there would be no reason to assume that the Spinosauridae specialized completely in fishing. They stressed rather that this head morphology indicates a [[generalistic feeding]], particularly on small prey animals. In fact, portions of a young ''[[Iguanodon]]'', a terrestrial herbivore, were found inside the fossil skeleton of one ''Baryonyx''.<ref name=":5"/> 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]].<ref name=":13">{{Cite journal|last1=Naish|first1=D.|last2=Martill|first2=D.M.|last3=Frey|first3=E.|s2cid=18592288|year=2004|title=Ecology, Systematics and Biogeographical Relationships of Dinosaurs, Including a New Theropod, from the Santana Formation (?Albian, Early Cretaceous) of Brazil|journal=[[Historical Biology]]|volume=16|issue=2–4|pages=57–70|citeseerx=10.1.1.394.9219|doi=10.1080/08912960410001674200|bibcode=2004HBio...16...57N|url=https://www.researchgate.net/publication/40663003}}</ref> A tooth belonging to ''Irritator'' was discovered still inserted into the fossil neck vertebral column of an anhanguerid pterosaur, likely with a wingspan of {{cvt|3.3|m}}. This indicates that ''Irritator'' ate pterosaurs as well, although it is not known if it actively hunted these animals or simply scavenged the remains.<ref name=":15">{{Cite journal|last1=Cuff|first1=Andrew R.|last2=Rayfield|first2=Emily J.|date=May 28, 2013|title=Feeding Mechanics in Spinosaurid Theropods and Extant Crocodilians|journal=[[PLoS ONE]]|language=en|volume=8|issue=5|article-number=e65295|doi=10.1371/journal.pone.0065295|issn=1932-6203|pmc=3665537|pmid=23724135|bibcode=2013PLoSO...865295C|doi-access=free}}</ref><ref>{{cite book |last=Witton|first=Mark P. |title=New Perspectives on Pterosaur Palaeobiology|year=2018|volume=455|pages=7–23|editor-last1=Hone|editor-first1=David W.E.|editor-last2=Witton|editor-first2=Mark P.|editor-last3=Martill|editor-first3=David M.|series=Special Publications|chapter=Pterosaurs in Mesozoic food webs: a review of fossil evidence |publisher=[[Geological Society]]|location=London|doi=10.1144/SP455.3|issn=0305-8719|bibcode=2018GSLSP.455....7W|s2cid=90573936|isbn=978-1-786-20336-6|doi-access=free}}</ref><ref name="pterosaurvert">{{cite journal|last1=Buffetaut|first1=E.|last2=Martill|first2=D.|last3=Escuillié|first3=F.|s2cid=4398855|date=2004|title=Pterosaurs as part of a spinosaur diet|journal=Nature|volume=430|issue=6995|page=33|bibcode=2004Natur.429...33B|doi=10.1038/430033a|pmid=15229562|url=https://www.researchgate.net/publication/8478211}}</ref> In 2018, Aureliano and colleagues presented a possible scenario for the [[food web]] of the Romualdo Formation. The researchers proposed that spinosaurines from the formation may have also preyed on terrestrial and aquatic [[crocodyliforms]], juveniles of their own species, turtles, and small to medium-sized dinosaurs. This would have made spinosaurines [[apex predator]]s within this particular ecosystem.<ref name=":42"/>

Examinations and digital reconstructions of ''Irritator'' published in 2023 by Schade ''et al.'', suggests that the lower jaws of this spinosaurid could rotate and open laterally, with a gape similar to that of modern [[pelican]]s; 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.<ref name="Osteology" />

===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<ref>{{Cite journal|last1=Sales|first1=Marcos A.F.|last2=Lacerda|first2=Marcel B.|last3=Horn|first3=Bruno L.D.|last4=de Oliveira|first4=Isabel A.P.|last5=Schultz|first5=Cesar L.|date=February 1, 2016|title=The 'χ' of the Matter: Testing the Relationship between Paleoenvironments and Three Theropod Clades|journal=PLOS ONE|language=en|volume=11|issue=2|article-number=e0147031|doi=10.1371/journal.pone.0147031|issn=1932-6203|pmc=4734717|pmid=26829315|bibcode=2016PLoSO..1147031S|doi-access=free}}</ref>) to occupy a distinct [[ecological niche]], therefore avoiding [[Competition (biology)|competition]] with more terrestrial theropods.<ref name="RMetal10">{{cite journal|last1=Amiot|first1=R.|last2=Buffetaut|first2=E.|last3=Lécuyer|first3=C.|last4=Wang|first4=X.|last5=Boudad|first5=L.|last6=Ding |first6=Z.|last7=Fourel|first7=F.|last8=Hutt|first8=S.|last9=Martineau|first9=F.|year=2010|title=Oxygen isotope evidence for semi-aquatic habits among spinosaurid theropods|journal=[[Geology (journal)|Geology]]|volume=38|issue=2|pages=139–142|bibcode=2010Geo....38..139A|doi=10.1130/G30402.1|last10=Medeiros|first10=A. |last11=Mo|first11=J.|last12=Simon|first12=L.|last13=Suteethorn|first13=V.|last14=Sweetman|first14=S.|last15=Tong|first15=H. |last16=Zhang|first16=F.|last17=Zhou|first17=Z.}}</ref><ref>{{Cite journal|last1=Hassler|first1=A.|last2=Martin|first2=J.E.|last3=Amiot|first3=R.|last4=Tacail|first4=T.|last5=Godet|first5=F. Arnaud|last6=Allain|first6=R.|last7=Balter|first7=V.|date=April 11, 2018|title=Calcium isotopes offer clues on resource partitioning among Cretaceous predatory dinosaurs|journal=[[Proceedings of the Royal Society|Proc. R. Soc. B]]|language=en|volume=285|issue=1876|article-number=20180197|doi=10.1098/rspb.2018.0197|issn=0962-8452|pmc=5904318|pmid=29643213}}</ref> Spinosaurines appear to have been more adapted for such lifestyles than baryonychines.<ref name=":42"/><ref name="Spinosaurus 2014"/> 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.<ref>{{Cite journal|last1=Arden|first1=Thomas M.S.|last2=Klein|first2=Catherine|last3=Zouhri|first3=Samir|last4=Longrich|first4=Nicholas R.|date=2018|title=Aquatic adaptation in the skull of carnivorous dinosaurs (Theropoda: Spinosauridae) and the evolution of aquatic habits in spinosaurus|url=https://www.researchgate.net/publication/326507888|journal=Cretaceous Research|volume=93|pages=275–284|doi=10.1016/j.cretres.2018.06.013|s2cid=134735938|access-date=October 22, 2018|archive-url=https://web.archive.org/web/20181023120104/https://www.researchgate.net/publication/326507888|archive-date=October 23, 2018|url-status=live}}</ref>

In 2018, Aureliano and colleagues conducted an analysis on the Romualdo Formation tibia fragment. CT scanning of the specimen in the [[Federal University of São Carlos|University of São Carlos]] revealed the presence of [[osteosclerosis]] (high bone density).<ref name=":42"/> This condition had previously only been observed in ''Spinosaurus aegyptiacus,'' as a possible way of facilitating submersion in water by making its bones heavier.<ref name="Spinosaurus 2014">{{Cite journal|last1=Ibrahim|first1=N.|last2=Sereno|first2=P.C.|last3=Dal Sasso|first3=C.|last4=Maganuco|first4=S.|last5=Fabbri|first5=M.|last6=Martill|first6=D.M.|last7=Zouhri|first7=S.|last8=Myhrvold|first8=N.|last9=Iurino|first9=D.A.|s2cid=34421257|year=2014|title=Semiaquatic adaptations in a giant predatory dinosaur|url=https://researchportal.port.ac.uk/portal/en/publications/semiaquatic-adaptations-in-a-giant-predatory-dinosaur(8f11a1ce-3265-4b3b-8c81-6f576856a87f).html|journal=Science|volume=345|issue=6204|pages=1613–1616|doi=10.1126/science.1258750|pmid=25213375|bibcode=2014Sci...345.1613I|doi-access=free}}</ref> The presence of this condition on the Brazilian leg fragment showed that compact bones had already evolved in spinosaurines at least 10 million years before the appearance of ''Spinosaurus'' in Morocco. According to [[phylogenetic bracketing]]—a method used to infer unknown traits in organisms by comparison with their relatives<ref name="witmer1995">{{Citation|last1=Witmer|first1=Lawrence M.|year=1995|chapter=The Extant Phylogenetic Bracket and the Importance of Reconstructing Soft Tissues in Fossils|title=Functional morphology in vertebrate paleontology|editor-last=Thomason|editor-first=Jeff|location=Cambridge|publisher=[[Cambridge University Press]]|isbn=978-0-521-44095-0|pages=19–33|chapter-url=https://people.ohio.edu/witmerl/Downloads/1995_Witmer_Extant_Phylogenetic_Bracket.pdf|archive-url=https://web.archive.org/web/20180724100725/https://people.ohio.edu/witmerl/Downloads/1995_Witmer_Extant_Phylogenetic_Bracket.pdf|archive-date=July 24, 2018}}</ref>—osteosclerosis therefore might have been the norm in the Spinosaurinae.<ref name=":42"/> The significance of these traits was questioned in a later 2018 publication, where Canadian [[paleobiologist]] Donald Henderson argued that osteosclerosis would not have changed a theropod's buoyancy to a significant extent.<ref>{{Cite journal|last=Henderson|first=Donald M.|date=August 16, 2018|title=A buoyancy, balance and stability challenge to the hypothesis of a semi-aquatic ''Spinosaurus'' Stromer, 1915 (Dinosauria: Theropoda)|journal=PeerJ|language=en|volume=6|article-number=e5409|doi=10.7717/peerj.5409|pmid=30128195|pmc=6098948|issn=2167-8359|doi-access=free}}</ref>

===Neuroanatomy and senses===
[[File:Irritator challengeri skull neuroanatomy 1.png|thumb|[[CT scan]] of the holotype showing [[endocast]] and [[endosseous labyrinth]]]]
In 2020, 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 (cerebellar)|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 reflex|vestibulo-ocular (VOR)]] and [[Righting reflex#Pathways|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.<ref name=Schade2020>{{cite journal|last1=Schade|first1=M.|last2=Rauhut|first2=O. W. M.|last3=Evers|first3=S. W.|date=2020|title=Neuroanatomy of the spinosaurid ''Irritator challengeri'' (Dinosauria: Theropoda) indicates potential adaptations for piscivory|journal=Scientific Reports|volume=10|number=9259|pages=1613–1616|doi=10.1038/s41598-020-66261-w|doi-access=free|pmc=7283278|pmid=32518236|bibcode=2020NatSR..10.9259S}}</ref>

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&nbsp;Hz with a frequency band width of 3,196&nbsp;Hz. However, they considered these ranges as rough estimates and established an overall frequency range of 350–3,550&nbsp;Hz, making ''Irritator'' to be placed under bird hearing but above crocodiles.<ref name=Schade2020/>

==Paleoenvironment and paleobiogeography==
[[File:Irritator at sunset by PaleoGeek.png|alt=Reconstruction of the head in front of a beach at dusk|thumb|Restoration of the head]]

''Irritator'' and ''Angaturama'' are known from the [[Romualdo Formation]], whose rocks are dated to the [[Albian]] [[Stage (stratigraphy)|stage]] of the [[Early Cretaceous]] [[Geological period|Period]], about 110 million years ago.<ref name=":42"/> During this time, the Southern [[Atlantic Ocean]] was opening, forming the series of circum-Atlantic [[Structural basin|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 [[Stratigraphic unit|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 [[shale]]s, and overlies the Crato Formation. It is well known for preserving fossils three-dimensionally in limestone concretions, including many pterosaur fossils. In addition to muscle fibres of pterosaurs and dinosaurs, fish, preserving gills, digestive tracts, and hearts, have been found there.<ref name="kellner&campos2002">{{cite journal|last1=Kellner|first1=A.W.A.|last2=Campos|first2=D.A.|s2cid=45430990|date=2002|title=The function of the cranial crest and jaws of a unique pterosaur from the early Cretaceous of Brazil|journal=Science|volume=297|issue=5580|pages=389–392|doi=10.1126/science.1073186|pmid=12130783|bibcode=2002Sci...297..389K|url=http://doc.rero.ch/record/14841/files/PAL_E1978.pdf }}</ref><ref name=":02">{{cite journal|last1=Pêgas|first1=R.V.|last2=Costa|first2=F.R.|last3=Kellner|first3=A.W.A.|s2cid=90477315|date=2018|title=New Information on the osteology and a taxonomic revision of the genus ''Thalassodromeus'' (Pterodactyloidea, Tapejaridae, Thalassodrominae)|journal=Journal of Vertebrate Paleontology|volume=38|issue=2|article-number=e1443273|doi=10.1080/02724634.2018.1443273|bibcode=2018JVPal..38E3273P }}</ref> The formation is interpreted as a coastal [[lagoon]] with irregular freshwater influence that contended with cycles of [[Marine transgression|transgressing]] and [[regressing sea levels]].<ref name=":42"/> The climate of the formation was tropical and largely corresponded to today's Brazilian climate.<ref name=":2"/> 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.<ref name=":11"/>

[[File:Romualdo_Formation_environment.png|thumb|left|alt=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: [[Anhanguera (pterosaur)|''Anhanguera'']], ''[[Araripedactylus]]'', ''[[Araripesaurus]]'', ''[[Brasileodactylus]]'', ''[[Cearadactylus]]'', ''[[Coloborhynchus]]'', ''[[Santanadactylus]]'', [[Tapejara (pterosaur)|''Tapejara'']], ''[[Thalassodromeus]]'', ''[[Tupuxuara]]'',<ref name=":0">{{Cite journal|last1=Barrett|first1=Paul|last2=Butler|first2=Richard|last3=Edwards|first3=Nicholas|last4=Milner|first4=Andrew R.|date=December 31, 2008|title=Pterosaur distribution in time and space: An atlas|url=https://www.researchgate.net/publication/279559638|journal=Zitteliana Reihe B: Abhandlungen der Bayerischen Staatssammlung für Paläontologie und Geologie|volume=28|pages=61–107|access-date=September 4, 2018|archive-url=https://web.archive.org/web/20180905141052/https://www.researchgate.net/publication/279559638|archive-date=September 5, 2018|url-status=live}}</ref> ''[[Barbosania]]'', ''[[Maaradactylus]]'',<ref>{{Cite journal|first1=Renan A.M.|last1= Bantim|first2=Antônio A.F.|last2= Saraiva|first3=Gustavo R.|last3= Oliveira|first4=Juliana M.|last4= Sayão|s2cid= 30685981|year=2014|title=A new toothed pterosaur (Pterodactyloidea: Anhangueridae) from the Early Cretaceous Romualdo Formation, NE Brazil|journal=[[Zootaxa]]|volume=3869|issue=3|pages=201–223|doi=10.11646/zootaxa.3869.3.1|pmid=25283914}}</ref> ''[[Tropeognathus]]'', and ''[[Unwindia]].<ref name="MartillUnwindia2">{{Cite journal|first=David M.|last= Martill|year=2011|title=A new pterodactyloid pterosaur from the Santana Formation (Cretaceous) of Brazil|journal=Cretaceous Research|volume=32|issue=2|pages=236–243|doi=10.1016/j.cretres.2010.12.008|bibcode= 2011CrRes..32..236M}}</ref>'' The known dinosaur fauna besides ''Irritator'' was represented by other theropods like the [[tyrannosauroid]] ''[[Santanaraptor]],'' the [[compsognathid]] ''[[Mirischia]],''<ref name=":11">{{Cite journal|last1=Martill|first1=David|last2=Frey|first2=Eberhard|last3=Sues|first3=Hans-Dieter|last4=Cruickshank|first4=Arthur R.I.|date=February 9, 2011|title=Skeletal remains of a small theropod dinosaur with associated soft structures from the Lower Cretaceous Santana Formation of NE Brazil|journal=[[Canadian Journal of Earth Sciences]]|volume=37|issue=6|pages=891–900|doi=10.1139/cjes-37-6-891|bibcode=2000CaJES..37..891M|s2cid=128675089}}</ref> an indeterminate [[Unenlagiinae|unenlagiine]] [[Dromaeosauridae|dromaeosaurid]],<ref>{{Cite journal|date=October 1, 2012|title=First evidence of an unenlagiid (Dinosauria, Theropoda, Maniraptora) from the Bauru Group, Brazil|journal=Cretaceous Research|language=en|volume=37|pages=223–226|doi=10.1016/j.cretres.2012.04.001|issn=0195-6671|last1=Candeiro|first1=Carlos Roberto A.|last2=Cau|first2=Andrea|last3=Fanti|first3=Federico|last4=Nava|first4=Willian R.|last5=Novas|first5=Fernando E.|bibcode=2012CrRes..37..223C |hdl=11336/17153 |hdl-access=free}}</ref> and a [[megaraptora]]n.<ref name=":42"/> The crocodyliforms ''[[Araripesuchus]]'' and ''[[Caririsuchus]]'',<ref>{{cite journal|last1=Figueiredo|first1=R.G.|last2=Kellner|first2=A.W.A.|s2cid=129166567|date=2009|title=A new crocodylomorph specimen from the Araripe Basin (Crato Member, Santana Formation), northeastern Brazil|journal=[[Paläontologische Zeitschrift]]|volume=83|issue=2|pages=323–331|doi=10.1007/s12542-009-0016-6|bibcode=2009PalZ...83..323F }}</ref> as well as the turtles ''Brasilemys'',<ref>{{cite journal|last1=de Lapparent de Broin|first1=F.|date=2000|title=The oldest pre-Podocnemidid turtle (Chelonii, Pleurodira), from the early Cretaceous, Ceará state, Brasil, and its environment|url=https://www.raco.cat/index.php/TreballsMGB/article/view/72439|journal=Treballs del Museu de Geologia de Barcelona|volume=9|pages=43–95|issn=2385-4499|access-date=September 29, 2018|archive-url=https://web.archive.org/web/20180920234541/https://www.raco.cat/index.php/TreballsMGB/article/view/72439|archive-date=September 20, 2018|url-status=live}}</ref> ''[[Cearachelys]],''<ref name="Gaffneyetal2001">{{cite journal|last1=Gaffney|first1=Eugene S.|author-link=Eugene S. Gaffney|first2=Diogenes |last2=de Almeida Campos|first3=Ren |last3=Hirayama|date=February 27, 2001|title=''Cearachelys'', a New Side-necked Turtle (Pelomedusoides: Bothremydidae) from the Early Cretaceous of Brazil|journal=[[American Museum Novitates]]|issue=3319|pages=1–20|doi=10.1206/0003-0082(2001)319<0001:CANSNT>2.0.CO;2|hdl=2246/2936|s2cid=59449305 |url=https://www.biodiversitylibrary.org/bibliography/178807|hdl-access=free}}</ref> ''[[Araripemys]]'', ''Euraxemys'',<ref>{{Cite journal|last1=Gaffney|first1=Eugene S.|author-link=Eugene S. Gaffney|last2=Tong|first2=Haiyan|last3=Meylan|first3=Peter A.|date=September 2, 2009|title=Evolution of the side-necked turtles: The families Bothremydidae, Euraxemydidae, and Araripemydidae|url=https://www.researchgate.net/publication/232682129|journal=[[Bulletin of the American Museum of Natural History]]|volume=300|pages=1–698|doi=10.1206/0003-0090(2006)300[1:EOTSTT]2.0.CO;2|hdl=2246/5824|s2cid=85790134 |access-date=September 29, 2018|archive-url=https://web.archive.org/web/20181001031126/https://www.researchgate.net/publication/232682129|archive-date=October 1, 2018|url-status=live}}</ref> and ''[[Santanachelys]]'', are known from the deposits.<ref>{{Cite journal|last=Hirayama|first=Ren|s2cid=45417065|date=1998|title=Oldest known sea turtle|journal=Nature|language=En|volume=392|issue=6677|pages=705–708|doi=10.1038/33669|issn=0028-0836|bibcode=1998Natur.392..705H}}</ref> There were also [[clam shrimp]]s, [[sea urchin]]s, ostracods, and [[Mollusca|molluscs]].<ref name=":2">{{Cite journal|last1=Mabesoone|first1=J.M. |last2=Tinoco|first2=I.M. |date=October 1, 1973|title=Palaeoecology of the Aptian Santana Formation (Northeastern Brazil)|journal=Palaeogeography, Palaeoclimatology, Palaeoecology|language=en|volume=14|issue=2|pages=97–118|doi=10.1016/0031-0182(73)90006-0|issn=0031-0182|bibcode=1973PPP....14...97M }}</ref> Various well-preserved fish fossils record the presence of: [[Hybodontidae|hybodont sharks]], [[guitarfish]], [[gar]]s, [[Amiidae|amiids]], ophiopsids, oshuniids, [[pycnodontids]], [[aspidorhynchids]], [[cladocyclids]], [[bonefishes]], [[Chanidae|chanids]], [[Mawsoniidae|mawsoniids]] and some uncertain forms.<ref name=":8">{{Cite journal|last1=Brito|first1=Paulo|last2=Yabumoto|first2=Yoshitaka|date=2011|title=An updated review of the fish faunas from the Crato and Santana formations in Brazil, a close relationship to the Tethys fauna|url=https://www.researchgate.net/publication/256422842|journal=Bulletin of Kitakyushu Museum of Natural History and Human History, Ser. A|volume=9|access-date=September 6, 2018|archive-url=https://web.archive.org/web/20180925025517/https://www.researchgate.net/publication/256422842|archive-date=September 25, 2018|url-status=live}}</ref> According to Naish and colleagues, the lack of herbivorous dinosaurs could mean that the local vegetation was scant and thus incapable of sustaining a large population of them. The abundant carnivorous theropods would have then likely turned to the lush aquatic life as a primary food source. They also hypothesized that following storm events, pterosaur and fish carcasses might have washed up on the shoreline, providing theropods with plenty of carrion.<ref name=":11"/> Multiple piscivorous animals were present in the formation, which might in theory have led to high competition. Aureliano and colleagues stated there must have, therefore, been some degree of [[Niche differentiation|niche partitioning]], where different animals would have fed on prey of varied sizes and locations within the lagoon.<ref name=":42"/>

[[File:Spinosaurid fossils palaeogeographic map.png|thumb|upright=1.3|alt=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.<ref name=":8"/> Spinosaurids had already achieved a [[cosmopolitan distribution]] during the Early Cretaceous.<ref>{{Cite journal|last1=Serrano-Martínez|first1=Alejandro|last2=Vidal|first2=Daniel|last3=Sciscio|first3=Lara|last4=Ortega|first4=Francisco|last5=Knoll|first5=Fabien|date=2015|title=Isolated theropod teeth from the Middle Jurassic of Niger and the early dental evolution of Spinosauridae|journal=Acta Palaeontologica Polonica|language=en|doi=10.4202/app.00101.2014|issn=0567-7920|doi-access=free|hdl=10261/152148|hdl-access=free}}</ref> 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]]).<ref name="serenoetal98"/> In following, Machado and Kellner theorized in 2005 that spinosaurines would have then spread to South America from Africa.<ref name="Machado2005"/> 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.<ref name="serenoetal98"/> 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.<ref name="medeiros2014">{{Cite journal|last1=Medeiros|first1=Manuel Alfredo|last2=Lindoso|first2=Rafael Matos|last3=Mendes|first3=Ighor Dienes|last4=Carvalho|first4=Ismar de Souza|date=August 2014|title=The Cretaceous (Cenomanian) continental record of the Laje do Coringa flagstone (Alcântara Formation), northeastern South America|journal=Journal of South American Earth Sciences|language=en|volume=53|pages=50–58|doi=10.1016/j.jsames.2014.04.002|issn=0895-9811|bibcode=2014JSAES..53...50M}}</ref> But the [[Biogeography#Paleobiogeography|paleobiogeography]] of spinosaurids remains highly theoretical and uncertain, with discoveries in Asia and Australia indicating that it may have been complex.<ref>{{Cite journal|last1=Allain|first1=Ronan|last2=Xaisanavong|first2=Tiengkham|last3=Richir|first3=Philippe|last4=Khentavong|first4=Bounsou|s2cid=2647367|date=April 18, 2012|title=The first definitive Asian spinosaurid (Dinosauria: Theropoda) from the early cretaceous of Laos|journal=Naturwissenschaften|language=en|volume=99|issue=5|pages=369–377|doi=10.1007/s00114-012-0911-7|pmid=22528021|issn=0028-1042|bibcode=2012NW.....99..369A}}</ref><ref>{{Cite journal|last1=Mateus|first1=Octávio|last2=Araujo|first2=Ricardo|last3=Natario|first3=Carlos|last4=Castanhinha|first4=Rui|date=April 21, 2011|title=A new specimen of the theropod dinosaur ''Baryonyx'' from the early Cretaceous of Portugal and taxonomic validity of Suchosaurus|url=https://www.researchgate.net/publication/285762094|journal=Zootaxa|volume=2827|pages=54–68|doi=10.11646/zootaxa.2827.1.3|s2cid=30193912}}</ref>

=== 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 process of the mandible|coronoid]], and right angular bones from the lower jaw, were lost. Other bones, mostly from the skull rear, had become {{Dinogloss|disarticulated}} and displaced towards alternate regions of the head before burial.<ref name=":5"/> 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.<ref name=":13"/> 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 [[allochthon]]ously (other than at their present position).<ref name=":42"/>

== Controversy ==
Following the publication of the reappraisal study in May 2023, the fact that the Brazilian holotype specimen was kept in a German collection attracted criticism. The authors had included an "Ethics Statement" which acknowledged recent debates surrounding the ethical and legal concerns regarding research on Brazilian fossils.<ref>{{Cite journal |last1=Cisneros |first1=Juan Carlos |last2=Raja |first2=Nussaïbah B. |last3=Ghilardi |first3=Aline M. |last4=Dunne |first4=Emma M. |last5=Pinheiro |first5=Felipe L. |last6=Regalado Fernández |first6=Omar Rafael |last7=Sales |first7=Marcos A. F. |last8=Rodríguez-de la Rosa |first8=Rubén A. |last9=Miranda-Martínez |first9=Adriana Y. |last10=González-Mora |first10=Sergio |last11=Bantim |first11=Renan A. M. |last12=de Lima |first12=Flaviana J. |last13=Pardo |first13=Jason D. |date=March 2, 2022 |title=Digging deeper into colonial palaeontological practices in modern day Mexico and Brazil |journal=Royal Society Open Science |language=en |volume=9 |issue=3 |at=210898 |doi=10.1098/rsos.210898 |issn=2054-5703 |pmc=8889171 |pmid=35291323 |bibcode=2022RSOS....910898C |doi-access=free}}</ref><ref>{{Cite journal |last1=Cisneros |first1=Juan C. |last2=Ghilardi |first2=Aline M. |last3=Raja |first3=Nussaïbah B. |last4=Stewens |first4=Paul P. |date=November 15, 2021 |title=The moral and legal imperative to return illegally exported fossils|journal=[[Nature Ecology & Evolution]]|language=en|volume=6|issue=1|pages=2–3|doi=10.1038/s41559-021-01588-9|issn=2397-334X|pmid=34782766|s2cid=244131555}}</ref> According to the authors, however, the fossils had been exported from Brazil before legislation requiring permits for the export of specimens entered into force. Accordingly, they claimed the holotype specimen to be the property of the German [[States of Germany|Bundesland]] of Baden-Württemberg, with a clarification of its legal status lying neither within the authors' power nor within that of the local curator.<ref name="Osteology"/>

Brazilian paleontologists disputed this claim and called for the return of the fossil to Brazil.<ref>{{Cite web |last=Araújo Júnior |first=Hermínio Ismael |date=June 19, 2023 |title=Open letter of the Brazilian Society of Paleontology (SPB) on the repatriation of Brazilian fossil holotypes |url=https://sbpbrasil.org/repatriacao-dos-holotipos-fosseis-brasileiros/ |access-date=March 14, 2025 |website=Sociedade Brasileira de Paleontologia |language=pt-BR}}</ref> They also formulated this demand in an open letter to Petra Olschowksi, State Minister of Science and Art of Baden-Württemberg; two authors of the criticised study were among the signatories.<ref>{{Cite web |last=Seta |first=Isabel |date=July 28, 2023 |title=Cientistas publicam carta pressionando Alemanha a devolver ''Irritator'', fóssil de dinossauro contrabandeado do Brasil |url=https://g1.globo.com/ciencia/noticia/2023/07/28/cientistas-publicam-carta-pressionando-alemanha-a-devolver-irritator-fossil-de-dinossauro-contrabandeado-do-brasil.ghtml |access-date=March 14, 2025 |website=G1 |language=pt-br}}</ref> A legal analysis of the potential restitution of the holotype specimen of ''Irritator challengeri'' in the ''International Journal of Cultural Property'' concludes that the Brazilian state is the legal owner of the fossil and that the State Museum of Natural History most likely did not acquire good title to it in good faith. A civil action of restitution under Article 985 of the [[German Civil Code]] is, however, precluded due to a statute of limitations of 30 years.<ref>{{Cite journal |last=Stewens |first=Paul Philipp|date=March 20, 2024|title=''Ubirajara'' and ''Irritator'' Belong to Brazil: Achieving Fossil Returns Under German Private Law |journal=International Journal of Cultural Property |language=en |volume=30 |issue=3 |pages= 298–318|doi=10.1017/S0940739124000031|issn=0940-7391|s2cid=268584406|doi-access=free }}</ref>

== References ==
{{Reflist}}

== External links ==
{{Commons category}}
{{Wikispecies}}

* [https://web.archive.org/web/20131219195023/http://archosaur.us/theropoddatabase/Megalosauroidea.htm#Irritatorchallengeri ''Irritator'' at The Theropod Database]
* [http://www.paleophilatelie.eu/description/stamps/brazil_1995.html ''Angaturama'' on a postage stamp]

{{Theropoda|T.}}
{{Portal bar|Dinosaurs|Brazil}}
{{Taxonbar|from=Q131211}}

[[Category:Spinosauridae]]
[[Category:Dinosaur genera]]
[[Category:Albian dinosaurs]]
[[Category:Romualdo Formation]]
[[Category:Fossil taxa described in 1996]]
[[Category:Dinosaurs of Brazil]]