Irritator

*Irritator chalengeri*

***Irritator*** (meaning "Irritating") was a genus of spinosaurids, living during the early Cretaceous Brazil. It is estimated to be around 7.9 meters (26 feet) in length and around 1 metric ton. Like most spinosaurs, *Irritator* had a small back sail.
The main fossil piece is that of the skull, which bears a resemblance to that of *Suchomimus tenerensis* and *Spinosaurus aegyptiacus*. The genus presumably be a synonym to the genus ***Angaturama***. The only known species is ***Irritator challengeri***.

## Discovery

The first fossil, a skull, was found in the possession of fossil poachers, who had artificially added more teeth and plastered it to get a better price. The scientists who bought the fossil were unaware of this, and thus it took the poor paleontologists hours and hours to bring the skull to it's former glory, which is how the genus got its name. They also found the fossil had been artificially elongated, adding to the irritation.

The current fossil extraction point is not confirmed. After questioning the fossil dealers, they pointed to a village near Santana Do Cariri.
The skull is considered to be the most complete of any Spinosaur skull. The skull is approximately 83.8 centimeters (33 inches) in length. It possesses a Sagittal crest on its forehead. The teeth were most likely went through a continual tooth change, and were estimated to be up to 40 millimeters in length.

In 2004, parts of a spinal column were discovered in the Santana Formation, the same origin as the skull. They rose high to form a small sail, and because of this, were assigned to Irritator. Sail formations were also borrowed from the closely related Suchomimus which lived in Africa.

The fossil consists only of the front part of the head, which is characterized by the fact that it is very narrow and carries a premaxillary sagittal crest (although not seen much in popular media). In the premaxilla a broken-off tooth with partial tooth crown was recovered which corresponds to that of *Irritator*. Altogether the premaxilla had seven teeth; the third tooth was the largest. The fossil is kept today under the number USP GP/2T-5 in the University of São Paulo.

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, same-species juveniles, turtles, and small to medium-sized dinosaurs. This would have made the spinosaurines apex predators within their ecosystem.

## Santana Formation

The horizon of the Santana formation, in which both fossils were found, resulted with very high probability from sedimentation in a flat lake, which was filled with fresh or brackish water. The fossil finds made so far create an ambivalent picture. The fossil insects which have been recovered are an indication for fresh water; the find of the turtle *Santanachelys*, which was adapted to seawaters, indicate a saltwater environment. One theory is that the site was a brackish lagoon, which was connected to the sea. The climate was tropical and corresponded to today's climate in Brazil to a large extent.

*Irritator* probably nourished itself on fish, like the pterosaurs found in large number in the Santana formation. *Irritator* was probably, like today's crocodiles, a food generalist, eating all other animals that it could catch besides fish. A tooth belonging to *Irritator* still inserted into a fossil neck vertebral column of a pterosaur, indicates that *Irritator* ate pterosaurs as well, although it is not known if it actively hunted these animals, or simply scavenged the remains.

All Spinosaurids had very narrow jaws with relatively homogeneous pointed teeth. This arrangement is particularly found in crocodilian species. The long conical teeth, which do not possess serrated edges, are suitable particularly to grabbing and holding of prey. They differed from teeth of other theropods, which seemed geared towards tearing or cutting off seized body parts. Particularly with *Irritator* and *Suchomimus* tenerensis a convergence with crocodiles is regularly discussed in the literature. Individual fossils belonging to the Spinosauridae were regarded in the past as crocodile fossils. For example, *Baryonyx* fossils from Portugal were originally described as *Suchosaurus* and only in 2007 were they recognized as those of a spinosaurid.

The nostrils of *Irritator* were shifted far to the rear of the skull, and the secondary palate make respiration possible even if the majority of the jaw was under water or held prey. In particular, the sagittal crest of *Irritator* is an indication for a pronounced neck musculature, which would have been necessary in order to pull the jaw closed quickly against water resistance and withdraw the head fast. Sues *et al.* (2002) point out, however, that there would be no reason to assume that the Spinosauridae specialized completely in fishing. They stress 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*. Naish *et al.* (2004) support the theory that *Irritator* hunted both aquatic and terrestrial animals as a generalist within the coastal area and in addition probably also searched for carrion. One more thing for awhile the only part of skeleton that was found was a skull.

A tooth belonging to *Irritator* was discovered still inserted into the fossil neck vertebral column of an ornithocheirid pterosaur, likely with a wingspan of 3.3 m (11 ft). This indicates that *Irritator* ate pterosaurs as well, although it is not known if it actively hunted these animals or simply scavenged the remains. In 2018, Aureliano and colleagues presented a possible scenario for the food web of the Romualdo Formation. The researchers proposed that spinosaurines from the formation may have also preyed on terrestrial and aquatic crocodyliforms, same-species juveniles, turtles, and small to medium-sized dinosaurs. This would have made spinosaurines apex predators within their own ecosystem

## Systematics

A cladogram of the Spinosauridae showing the position of *Irritator*

*I. challengeri* was a member of the Spinosauridae, more specifically the subfamily Spinosaurinae. It shares a close relationship with *Spinosaurus* and possibly *Siamosaurus*, though this last genus is not well-known from fossil material.

*Irritator* was originally described as a Maniraptoran within the Tetanurae. It was assigned to the family Baryonychidae, along with *Angaturama*, *Baryonyx*, *Suchomimus*, and *Spinosaurus* by Oliver Rauhut in 2003. Holtz *et al.* (2004) considered the Baryonychidae synonymous with the family Spinosauridae, and placed these genera within that family. Most later revisions have upheld these classifications.

## Paleobiology

The exact discovery site of the *Irritator* fossil skull is unknown; the fossil was collected by illegal fossil dealers. The skull and the matrix have been assigned to a rock of the Romualdo Member of the Santana formation due to lithological characteristics; this classification was confirmed by microfossils of the ostracod *Pattersoncypris*. A questioning of the local fossil dealers resulted in the identification of the discovery site near the village of Buxexé close Santana Do Cariri at the flank of the Chapada do Araripe, at a height of approximately 650 meters. Since rock from the Romualdo Member is indeed exposed there, this discovery site is regarded as very probable for the fossil.

The Romualdo Member of the Santana formation is generally assigned to the Albian and thus the last section of the Early Cretaceous. The layers are aged to approximately 110 million years and to have come from a time in which the continents of Africa and South America were still connected with one another in the northern part of Brazil.

The horizon of the Santana formation, in which both fossils were found, resulted with very high probability from sedimentation in a flat lake, which was filled with fresh or brackish water. The fossil finds made so far create an ambivalent picture. The fossil insects which have been recovered are an indication for fresh water; the find of the turtle *Santanachelys*, which was adapted to seawaters, indicate a saltwater environment. One theory is that the site was a brackish lagoon, which was connected to the sea. The climate was tropical and corresponded to today's climate in Brazil to a large extent.

*Irritator* probably nourished itself on fish, like the pterosaurs found in large number in the Santana formation. *Irritator* was probably, like today's crocodiles, a food generalist, eating all other animals that it could catch besides fish. A tooth belonging to *Irritator* still inserted into a fossil neck vertebral column of a pterosaur, indicates that *Irritator* ate pterosaurs as well, although it is not known if it actively hunted these animals, or simply scavenged the remains.

All Spinosaurids had very narrow jaws with relatively homogeneous pointed teeth. This arrangement is particularly found in crocodiles such as the Sunda Gavial. The long conical teeth, which do not possess serrated edges, are suitable particularly to grabbing and holding of prey. They differ from teeth of carnivores, which must tear or cut off the seized body parts. Particularly with *Irritator* and *Suchomimus* a convergence with crocodiles is regularly discussed in the literature. Individual fossils belonging to the Spinosauridae were regarded in the past as crocodile fossils. For example, *Baryonyx* fossils from Portugal were originally described as *Suchosaurus* and only in 2007 were the recognized as those of a spinosaurid.

The nostrils of *Irritator* were shifted far to the rear of the skull, and the secondary palate make respiration possible even if the majority of the jaw was under water or held prey. In particular, the sagittal crest of *Irritator* is an indication for a pronounced neck musculature, which would have been necessary in order to pull the jaw closed quickly against water resistance and withdraw the head fast. Sues *et al.* (2002) point out, however, that there would be no reason to assume that the Spinosauridae specialized completely in fishing. They stress rather that this head morphology indicates a generalistic feeding, particularly on small prey animals. In fact, portions of a young *Iguanodon*, a landliving herbivore, were found inside the fossil skeleton of one *Baryonyx*. Naish *et al.* (2004) support the theory that *Irritator* hunted both aquatic and terrestrial animals as a generalist within the coastal area and in addition probably also searched for carrion.

## JPInstitute.com Description

Irritator was an early member of the spinosaur family, which included the JP3 villain Spinosaurus. It was a large meat-eater that had a small crest on its head. It received its unusual name because amateur fossil hunters modified the original fossil skull and didn't do a very good job. With all of the extra effort that was required to undo the damage, the professional scientists working on the project wanted to create a name befitting all of their hard work and the frustration that came with it.

Irritator is known from a mostly complete skull. It is important for two reasons: It was the first Early Cretaceous dinosaur found in Brazil, and it was the first South American maniraptorian found without bird-like features. The head crest is believed to have been a muscle attachment for neck muscles. Like its other family members, it is believed that Irritator hunted and ate fish regularly.

## Appearance in other media

### *Jurassic Park*

* *Irritator* can be created in *Jurassic World: The Game* as a rare carnivore. It has an error with its head. It has a form of horn or bump at the front of the snout when it should have a crest towards the back of its head.
* Irritator also appears in the mobile game, Jurassic World: Alive, as a rare piscivore, and has a Gen 2 clone which is a Common dinosaur.

## Links

https://web.archive.org/web/20031007001749fw\_/http://www.jpinstitute.com/dinopedia/dinocards/dc\_irrit.html

https://web.archive.org/web/20080415223210/http://kids.yahoo.com/dinosaurs/384--Irritator

## References

1. ↑ https://www.sciencedirect.com/science/article/pii/S0195667117305153?via%3Dihub
2. ↑ Mateus, O., Araujo, R., Natario, C., Castanhinha, R. 2011. A New Specimen of the Theropod Dinosaur *Baryonyx* from the Early Cretaceous of Portugal and Taxonomic Validity of *Suchosaurus*. Zootaxa 2827:54-68
3. ↑ Template:Cite journal
4. ↑ https://www.sciencedirect.com/science/article/pii/S0195667117305153?via%3Dihub