Irritator
Encyclopedia
Irritator is a genus
of spinosaurid
dinosaur
that lived in the early Cretaceous Period (Albian
stage), around 110 million years ago. Current estimations indicate a length of 8 meters (26 feet). It was found in Brazil
. Irritator was a theropod with an unusually shaped crest at the rear of its head, and probably ate fish
.
So far the only fossil that has been found was an 80 centimeter long fossil skull in the Romualdo Member, a layer member of the Brazilian Santana formation. This skull strongly resembles the skulls of Suchomimus
and Spinosaurus
. The genus is often regarded today as identical (synonymous) with Angaturama, which lived in the same time and the same place as Irritator.
The type species
is I. challengeri, which honors the character of Professor Challenger
in Arthur Conan Doyle
's The Lost World.
Irritator was first scientifically described in 1996 by paleontologists Martill, Cruikshank, Frey, Small and Clarke. Its only known fossil
, an 80 cm skull
discovered in eastern Brazil
, was badly obscured by plaster
which was added by the commercial fossil-collecting fossil-poachers who illegally sold it (the trade of fossils is prohibited by law in Brazil), in hopes of making the fossil look more complete and valuable. For example, "the posterior portion of the saggital [sic] crest... [was] fabricated by fossil dealers." The buyers were not aware of the modifications to the illegally collected specimen, and it required them a great deal of work to reconstruct the original features — hence the name.
It is probably synonymous with Angaturama limai, another spinosaurid from the same time and place, whose remains curiously seem to complete Irritators skull, meaning that they could belong to the same specimen.
in Brazil. The holotype is SMNS 58022, from the Stuttgart
State Museum of the Natural Sciences, and it consists of an incomplete skull, lacking the anterior (front) portion.
The skull was recovered nearly complete and is considered the most complete head find of a Spinosaurid. It is characterized particularly by its unusual length and curved lip region, which is strongly compressed laterally. The overall length of the complete head is estimated at approximately 84 centimeters. It possesses a clear Sagittal crest; such a comb is found also with some other dinosaurs. The teeth exhibit a single embedding of the strongly extended and straight teeth with conical tooth crowns, which indicates a continual tooth change, as new teeth were pushed up between the old ones. The teeth exhibit lengths from 6 to approximately 40 millimeters.
In the year 2004 parts of a spinal column were discovered in the Santana Formation. These have been assigned, due to their structure, to the Spinosauridae. With very high probability these fossils belong to Irritator, since this is the so far the only well-known Spinosaurid of the formation.
Angaturama limai, from the same time and place as Irritator challengeri, was described by A. Kellner and Diogenes A. Campos in February 1996 on the basis of a fossil from the Santana formation. It was named after Angaturama, a protective spirit in the aboriginal Tupi Indian culture of Brazil, and paleontologist Murilo R. de Lima, who informed Kellner of the specimen in 1991. Later research uncovered 60% of the complete skeleton, allowing a replica to be made and mounted for exhibit at the Federal University-owned Rio de Janeiro National Museum.Angaturama was diagnosed by the very strong lateral compression of the snout, and a thin sagittal crest (shape unknown) on top of the premaxillae. Fish may have formed a large part of its diet. However, a pterosaur
fossil was found with an Angaturama tooth embedded in it, pointing to possible predation.
Today many sources consider Angaturama a synonym of Irritator. Some scientists have even speculated that the two partial fossil skulls come from the same individual. Kellner and Campos (2000) as well as Machado and Kellner (2005) hold however the opinion that the fossils come from two different genera and that Angaturama had a clearly higher and laterally more flattened head than Irritator. If Angaturama and Irritator are actually regarded as a member of the same genus, Irritator challengeri would be the valid scientific name under the priority rules.
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. 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
.
and possibly Siamosaurus
, though this last genus is not well known from fossil material.
Irritator was originally described as a Maniraptora
n 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.
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 pterosaur
s 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 carnivore
s, 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 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 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.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of spinosaurid
Spinosauridae
Spinosauridae is a family of specialised theropod dinosaurs. Members of this family were large, bipedal predators with elongated, crocodile-like skulls, sporting conical teeth with no or only very tiny serrations. The front dentary teeth fanned out, giving the animal a characteristic look...
dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
that lived in the early Cretaceous Period (Albian
Albian
The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous epoch/series. Its approximate time range is 112.0 ± 1.0 Ma to 99.6 ± 0.9 Ma...
stage), around 110 million years ago. Current estimations indicate a length of 8 meters (26 feet). It was found in Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
. Irritator was a theropod with an unusually shaped crest at the rear of its head, and probably ate fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
.
So far the only fossil that has been found was an 80 centimeter long fossil skull in the Romualdo Member, a layer member of the Brazilian Santana formation. This skull strongly resembles the skulls of Suchomimus
Suchomimus
Suchomimus is a genus of large spinosaurid dinosaur with a crocodile-like mouth that lived sometime between 121-112 million years ago, during the late Aptian stage of the Cretaceous period in Africa.-Description:...
and Spinosaurus
Spinosaurus
Spinosaurus is a genus of theropod dinosaur which lived in what is now North Africa, from the lower Albian to lower Cenomanian stages of the Cretaceous period, about 112 to 97 million years ago. This genus was first known from Egyptian remains discovered in 1912 and described by German...
. The genus is often regarded today as identical (synonymous) with Angaturama, which lived in the same time and the same place as Irritator.
Etymology
Martill et al. (1996) wrote that the generic name Irritator came "from irritation, the feeling the authors felt (understated here) when discovering that the snout had been artificially elongated."The type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
is I. challengeri, which honors the character of Professor Challenger
Professor Challenger
George Edward Challenger, better known as Professor Challenger, is a fictional character in a series of science fiction stories by Sir Arthur Conan Doyle...
in Arthur Conan Doyle
Arthur Conan Doyle
Sir Arthur Ignatius Conan Doyle DL was a Scottish physician and writer, most noted for his stories about the detective Sherlock Holmes, generally considered a milestone in the field of crime fiction, and for the adventures of Professor Challenger...
's The Lost World.
Discovery
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
, an 80 cm skull
Skull
The skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...
discovered in eastern Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
, was badly obscured by plaster
Plaster
Plaster is a building material used for coating walls and ceilings. Plaster starts as a dry powder similar to mortar or cement and like those materials it is mixed with water to form a paste which liberates heat and then hardens. Unlike mortar and cement, plaster remains quite soft after setting,...
which was added by the commercial fossil-collecting fossil-poachers who illegally sold it (the trade of fossils is prohibited by law in Brazil), in hopes of making the fossil look more complete and valuable. For example, "the posterior portion of the saggital [sic] crest... [was] fabricated by fossil dealers." The buyers were not aware of the modifications to the illegally collected specimen, and it required them a great deal of work to reconstruct the original features — hence the name.
It is probably synonymous with Angaturama limai, another spinosaurid from the same time and place, whose remains curiously seem to complete Irritators skull, meaning that they could belong to the same specimen.
Material
Material of I. challengeri, not counting that of A. limai, hails from the Romualdo Member of the Santana FormationSantana Formation
The Santana Formation is a geologic Lagerstätte in northeastern Brazil's Araripe Basin where the states of Pernambuco, Piauí and Ceará come together. The geological formation, named after the village of Santana do Cariri, lies at the base of the Araripe Plateau...
in Brazil. The holotype is SMNS 58022, from the Stuttgart
Stuttgart
Stuttgart is the capital of the state of Baden-Württemberg in southern Germany. The sixth-largest city in Germany, Stuttgart has a population of 600,038 while the metropolitan area has a population of 5.3 million ....
State Museum of the Natural Sciences, and it consists of an incomplete skull, lacking the anterior (front) portion.
The skull was recovered nearly complete and is considered the most complete head find of a Spinosaurid. It is characterized particularly by its unusual length and curved lip region, which is strongly compressed laterally. The overall length of the complete head is estimated at approximately 84 centimeters. It possesses a clear Sagittal crest; such a comb is found also with some other dinosaurs. The teeth exhibit a single embedding of the strongly extended and straight teeth with conical tooth crowns, which indicates a continual tooth change, as new teeth were pushed up between the old ones. The teeth exhibit lengths from 6 to approximately 40 millimeters.
In the year 2004 parts of a spinal column were discovered in the Santana Formation. These have been assigned, due to their structure, to the Spinosauridae. With very high probability these fossils belong to Irritator, since this is the so far the only well-known Spinosaurid of the formation.
Angaturama limai, from the same time and place as Irritator challengeri, was described by A. Kellner and Diogenes A. Campos in February 1996 on the basis of a fossil from the Santana formation. It was named after Angaturama, a protective spirit in the aboriginal Tupi Indian culture of Brazil, and paleontologist Murilo R. de Lima, who informed Kellner of the specimen in 1991. Later research uncovered 60% of the complete skeleton, allowing a replica to be made and mounted for exhibit at the Federal University-owned Rio de Janeiro National Museum.Angaturama was diagnosed by the very strong lateral compression of the snout, and a thin sagittal crest (shape unknown) on top of the premaxillae. Fish may have formed a large part of its diet. However, a pterosaur
Pterosaur
Pterosaurs were flying reptiles of the clade or order Pterosauria. They existed from the late Triassic to the end of the Cretaceous Period . Pterosaurs are the earliest vertebrates known to have evolved powered flight...
fossil was found with an Angaturama tooth embedded in it, pointing to possible predation.
Today many sources consider Angaturama a synonym of Irritator. Some scientists have even speculated that the two partial fossil skulls come from the same individual. Kellner and Campos (2000) as well as Machado and Kellner (2005) hold however the opinion that the fossils come from two different genera and that Angaturama had a clearly higher and laterally more flattened head than Irritator. If Angaturama and Irritator are actually regarded as a member of the same genus, Irritator challengeri would be the valid scientific name under the priority rules.
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. 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
University of São Paulo
Universidade de São Paulo is a public university in the Brazilian state of São Paulo. It is the largest Brazilian university and one of the country's most prestigious...
.
Systematics
I. challengeri was a member of the Spinosauridae, more specifically the subfamily Spinosaurinae. It shares a close relationship with SpinosaurusSpinosaurus
Spinosaurus is a genus of theropod dinosaur which lived in what is now North Africa, from the lower Albian to lower Cenomanian stages of the Cretaceous period, about 112 to 97 million years ago. This genus was first known from Egyptian remains discovered in 1912 and described by German...
and possibly Siamosaurus
Siamosaurus
Siamosaurus is a genus of theropod dinosaur from Early Cretaceous Thailand. The size of the animal is unknown, but it may have reached a length of about 9.1 meters . The type species, Siamosaurus suteethorni, was formally described by Buffetaut and Ingavat in 1986...
, though this last genus is not well known from fossil material.
Irritator was originally described as a Maniraptora
Maniraptora
Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the dinosaurs that were more closely related to them than to Ornithomimus velox. It contains the major subgroups Avialae, Deinonychosauria, Oviraptorosauria and Therizinosauria. Ornitholestes and the Alvarezsauroidea...
n within the Tetanurae
Tetanurae
Tetanurae, or "stiff tails", is a clade that includes most theropod dinosaurs, as well as birds. Tetanurans first appear during the early or middle Jurassic Period.-Definition:...
. 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 ostracodOstracod
Ostracoda is a class of the Crustacea, sometimes known as the seed shrimp because of their appearance. Some 65,000 species have been identified, grouped into several orders....
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
Chapada do Araripe
The Chapada do Araripe, also known as the Serra do Araripe, is a chapada in northeastern Brazil. The chapada forms the boundary of Ceará and Pernambuco states, and forms the watershed between the Jaguaribe River of Ceará, which flows northward into the Atlantic, and the much larger basin of the...
, 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.
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
and South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
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
Santanachelys
Santanachelys gaffneyi is the earliest known sea turtle. It is the only species in the genus Santanachelys, which itself is a member of the extinct family Protostegidae. The species was first described from a 20-centimeter long fossil specimen unearthed in 1998 in Eastern Brazil...
, 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 pterosaur
Pterosaur
Pterosaurs were flying reptiles of the clade or order Pterosauria. They existed from the late Triassic to the end of the Cretaceous Period . Pterosaurs are the earliest vertebrates known to have evolved powered flight...
s 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 carnivore
Carnivore
A carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging...
s, which must tear or cut off the seized body parts. Particularly with Irritator and Suchomimus
Suchomimus
Suchomimus is a genus of large spinosaurid dinosaur with a crocodile-like mouth that lived sometime between 121-112 million years ago, during the late Aptian stage of the Cretaceous period in Africa.-Description:...
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
Baryonyx
Baryonyx is a genus of carnivorous saurischian dinosaur first discovered in clay pits just south of Dorking, England, and later reported from fossils found in northern Spain and Portugal. It is known to contain only one species, Baryonyx walkeri...
fossils from Portugal were originally described as Suchosaurus
Suchosaurus
Suchosaurus is as a spinosaurid theropod dinosaur from Cretaceous England, originally believed to be a genus of crocodile. The type material consists of teeth. Two species, S. cultridens and S. girardi have been named, though the S. girardi material was reclassified by Buffetaut as Baryonyx...
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
Iguanodon
Iguanodon is a genus of ornithopod dinosaur that lived roughly halfway between the first of the swift bipedal hypsilophodontids and the ornithopods' culmination in the duck-billed dinosaurs...
, a landliving herbivore, were found inside the fossil skeleton of one Baryonyx. Naish
Darren Naish
Darren Naish is a vertebrate palaeontologist and science writer. He obtained a geology degree at the University of Southampton and later studied vertebrate palaeontology under British palaeontologist David Martill at the University of Portsmouth, where he obtained both an M. Phil...
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.