Irritator

Skelettrekostruktion of Irritator challengeri

• Santana Formation, Brazil

Irritator is a genus theropod dinosaur with only one described species ( type species ). Irritator is counted among the Spinosauriden, a group bipeder dinosaur with strongly elongated snout and straight teeth. Probably up to eight meters long animal lived approximately 113-100 million years ago ( Albian ) in the lower Cretaceous period in what is now South America.

From this dinosaur so far was only about 80 centimeters long fossil skull in the Romualdo Member, a layer member of the Brazilian Santana Formation, found. Since this is very similar to the skulls of Suchomimus and Spinosaurus, it is believed that he, like them, prolonged spinous processes had on the vertebrae.

This type is now generally considered to be identical ( synonymous ) with Angaturama limai who has lived at the same time and same place and is known of which only the front part of a skull.

• 7.1 Documents cited and footnotes
• 7.2 Literature

Fossil Description

History and features of the fossil - Irritator

Irritator was described in 1996 by paleontologists Martill, Cruickshank, Frey, Small and Clarke for the first time scientifically. This description is based on the discovery of a skull of the holotype, from the Santana Formation in eastern Brazil in the southern part of the state of Ceará in the Araripe Basin. He was in the Romualdo layer member is assigned to the Lower Cretaceous.

The Fund had made private collectors. They had tried the fossil skull complete with a plaster -like modeling clay, making the reconstruction by the taxidermy was very expensive. About a CAT scan could also be found that the skull was artificially extended by parts of the upper jaw were mounted on the intermediate jaw ( premaxilla ). Today, the fossil is preserved in the collection of the State Museum of Natural History in Stuttgart under the catalog number SMNS 58022.

The skull is nearly complete and is considered the most complete skull of a Fund Spinosauriden. It is characterized mainly by its unusually long and curved snout, which is laterally strongly compressed. The total length of the whole skull is estimated to be about 84 centimeters. He has a distinct sagittal crest, which runs from the forehead over the nasals to the premaxilla and thus draws on the entire skull; such a crest is indeed to be found in some other dinosaurs, but for the theropods he is seldom found. The nostrils are pushed back almost to the eyes and by the fusion of the premaxilla to a secondary mouth roof, the choana, the inner nostril shifted back towards the throat.

The teeth have a unique embedding of highly elongated and straight teeth with conical crowns, indicating a mesolingualen change of teeth to be pushed in the new teeth between the currently used teeth; This is believed due to the close relationship topical for Spinosaurus. The teeth have lengths of 6 to about 40 millimeters. The upper of the two temporal window ( Supra pace Ralf ester) of the skull is almost completely reduced, and also other features of the skull anatomy suggest that a clear demarcation of Irritator from other known genera to. A number of features such as the small number of maxillary teeth and the shape of shares Irritator with Spinosaurus. Many other features can be adopted for higher-level taxa, but not hedged due to the frequent lack of skull.

In 2004, also in the Santana Formation parts of a spine consisting of three cross and six caudal vertebrae, found that can be assigned to Spinosauriden due to the structure of the vertebrae. With very high probability, these vortices are also among Irritator, since this is the only previously known Spinosauride the formation.

Angaturama limai Kellner & Campos, 1996

Angaturama limai from the same period as Irritator challengeri was first also described by Alexander WA Kellner and Diogenes A. Campos on the basis of a fossil from the Santana Formation in February 1996 and is now mostly viewed as a synonym of Irritator. Some scientists even believe that it is part of the skull of the same individual acts in the two fossils .. Kellner and Campos (2000) and Machado and Kellner ( 2005), however, argue that there are two different ways and that Angaturama a significantly higher and more laterally flattened skull had as Irritator.

The fossil consists of only the front part of the skull, which is characterized in that it is very narrow and carries a premaxillary sagittal crest. In the premaxilla a broken tooth with a partially preserved tooth crown was obtained, which corresponds to a Irritator; total bore the premaxilla 7 teeth, as is apparent from the tooth sockets, where the third tooth was the greatest. The fossil described is now kept under the number USP GP/2T-5 at the Universidade de São Paulo. It has been described as the first known remains of a dinosaur skull from Brazil, the description of Irritator challengeri was, however, at a time when the was of Angaturama still in the tray Review and thus presented is actually the first dinosaur description from the Santana Formation there. In the event that Angaturama and Irritator really be considered as belonging to the same species, Irritator challengeri would thus be the valid scientific name (priority rule).

Fund locality and paleoecology

The exact location of the Irritator - fossil is unknown because the skull was only happened on fossil dealers and collectors of science. The mass of rock, which included the skull, the matrix could be assigned to a rock of the Romualdo Member of the Santana Formation because of lithologic characteristics; This classification was confirmed by micro- fossils of ostracods of the genus Pattersoncypris and fish scales that could be assigned to the Ichthyodectiden Cladocylus. A survey of local fossil dealers by the describer resulted in a locality near the village Buxexé near Santana do Cariri on the flank of the Chapada do Araripe at an altitude of about 650 m above sea level. Since there rock from the Romualdo Member is actually open, this location is considered to be very likely for the fossil.

The Romualdo Member of the Santana Formation is commonly associated due to the fish fauna of the Albian and thus the final section of the Lower Cretaceous, whereas the frequently used for biostratigraphy ostracods ( Ostracoda ) suggest a classification in the Aptian. The layers have according to an age of about 110 million years and come from a time when the continents of Africa and South America were still connected to each other in the northern part of Brazil.

The horizon of the Santana Formation, in which both fossils were found, there was a very high probability by sedimentation in a shallow lake, which was filled with fresh or brackish water. Regarding the salinity convey the fossil record so far made ​​an ambivalent picture, thus saith the presence of some freshwater fish for a salt-free or low-salt water but also forms were found, which are considered typically marine. The insects found are rather an indication of freshwater, the discovery of the adapted to salt water turtle Santanachelys gaffneyi turn suggests salt water. Therefore, the greatest recognition is the theory that it was a brackish lagoon, which was consistent with the sea in conjunction. The climate was tropical and warm to the current climate in Brazil have largely complied with.

Way of life

Irritator challengeri like the pterosaur found in large numbers in the Santana Formation probably fed on fish, which he was hunting in the former lake situated there. Irritator it was probably like today's crocodiles, a food generalist who ate next to the fish and all other animals he could catch. Through a fossilized cervical spine of a pterosaur with a fact stuck tooth Irritator is assigned, is considered certain that pterosaurs were part of his food spectrum. Whether he captured them as an active hunter or as scavengers eating dead animals is not known.

On a diet based mainly on fishing, suggests that prolonged in all Spinosauriden and very narrow snout with relatively uniform sharp teeth. It is a convergence of many other groups of animals that have adapted through evolution to fish as food. Thus one finds this design, especially in crocodiles ( very strong about the Ganges and the Sunda Gavial ), but also in whales, and many extinct marine reptiles such as ichthyosaurs, mosasaurs and the some plesiosaurs.

The elongated conical teeth that do not have sawn edges, are particularly suited to grab and hold the total prey and thus differ from the teeth of carnivores who must tear down or cut parts of the prey after the grab. Far to the rear shifted nostrils and the mouth secondary roof facilitate breathing even if the majority of the snout is underwater or a prey animal holds. In particular, the sagittal crest of Irritator is also an indication of a strong neck muscles that is necessary to pull the muzzle against the water resistance through the water and withdraw the head quickly. Sue et al. However, in 2002 point out that there is no reason to assume that the Spinosauridae have completely dedicated to fishing. They emphasize rather that this skull morphology generalist diet that fixes mainly on small prey, while including fishing advocates, and lead to this is that in the skeleton of also the Spinosauriden associated Baryonyx parts of a young Iguanodon, ie a terrestrial herbivore, were found. Naish et al. 2004, such acceptance for Irritator and represent that in the coastal area he hunted both aquatic and terrestrial prey than a generalist and also probably additionally sought carrion.

Especially with Irritator and in Suchomimus mainly a convergence to the crocodiles is discussed regularly at the Suchomimus ( = " crocodile mimic " ) is even eponymous. Individual fossils of Spinosauriden were even held in the past mistaken for crocodile fossils and described, such as Baryonyx fossils from Portugal, which were originally described as Suchosaurus and recognized as Baryonyx until 2007. With the exception of the skull, but there is no convergence with crocodiles in the Body of the known Spinosauriden, so that a general adaptation to an aquatic lifestyle is excluded.

System

Irritator challengeri was filed by his Erstbeschreibern 1996 in the Maniraptora within the Tetanurae. Here it should be a separate family Irritatoridae within the Bullatosauria. Angaturama, however, was filed in the Spinosauridae as a new genus and in the same year ranked waiter also Irritator in this family .. This classification took Sue et al. 2002 for the now recognized as synonyms fossils, so it is also regarded as generally accepted today.

Paul Sereno et al. 1998 was presented with the first description of Suchomimus tenerensis a phylogenetic tree of Spinosauridae, which divided them into the two subfamilies Spinosaurinae and Baryonychinae and defined Irritator as sister species of the genus Spinosaurus. Was confirmed this representation of dal Sasso et al., 2006. Accordingly form Suchomimus and Baryonyx, whose only representative Baronyx walkeri was described in 1986 from England, along the Baryonychinae while Irritator and Spinosaurus were compared as Spinosaurinae this. Sasso et al. add the Baryonychinae also the Cristatusaurus lapparenti described in 1998 added, the. in the original representation of Sereno et al was not yet described. As the sister group of the entire Spinosauridae the Torvosauridae with the genera Torvosaurus and Eustreptospondylus be named, but which are today slammed the Megalosauridae.

Spinosaurus

Irritator

Baryonyx

Suchomimus

This family tree is justified primarily by features of the skull morphology, as this part of the skeleton in most species is at least partly available. The Spinosauroidea be due primarily to the formation of strong forelimbs with a sickle-shaped claw thumb.

The carried out as specializing in fishing extension of the snout by a parallel extension of both the maxilla as well as the premaxilla, the specific configuration of the nasal cavity and the formation of a secondary mouth roof are very weighty independent features ( apomorphies ) that will underpin the monophyly of Spinosauridae. Here also characteristics are given as the shifted far to the rear nostrils and the conical teeth, a small postnasales cranial window and the specific configuration of the skull, which is compared with other theropods relatively short, but deeply formed. In Spinosaurinae there was a reduction in the number of premaxillary and maxillary teeth with a concomitant increase in the tooth gaps as well as an almost straight configuration of the teeth, which is present in both Irritator and in Spinosaurus. Spinosaurus is over Irritator mainly caused by the strong increase of the spinous processes of the spine and the spinal sailing formed thereby - as this is have looked at Irritator however, not known.

Reconstruction

Although of Irritator even after joining the two known fossils only a skull is present, a relatively realistic reconstruction of the entire animal is possible. The paleontologists benefit in this case largely on the species, which are classified into the closer relationship of Irritator and of which very complete skeletons exist or have existed ( the Munich preserved skeleton of Spinosaurus was destroyed in the Second World War). About a feature comparison many features in Irritator can as plesiomorphies, ie already in the common ancestral species existing features are provided - including especially the attitude and design of the limbs and the general physique and posture.

For example, since all fossil theropods were bipedal and country living, and this is also true for all other types Spinosauroidea, one can assume these features also for the Irritator - it is extremely unlikely that Irritator apomorphic this very central features has trained in highly modified form. Accordingly, you can almost all the features that the closely related species Baryonyx, Spinosaurus and Suchomimus have in common existent presuppose a very high probability than Irritator - this is a basic reconstruction possible. Not possible, however, for example, the secure adoption of a back sail that is only proven for Spinosaurus; however, since even Suchomimus had greatly prolonged spinous processes, this feature is at least accept for Irritator also.

Naming

Martill et al. described in their article published in 1996, both the genus and the first and only known species within the genus. The naming of the genus Irritator was established by the authors with the irritation that they felt when they saw the artificial prolongation of the snout of the fossil. The name derives from the nature of the fictional Professor Challenger was in Sir Arthur Conan Doyle's novel " The Lost World " ( "The Lost World"), which Irritator as second nature next to the pterosaurs Arthurdactylus conandoylei, which was also found in the Santana Formation, in its wording on Conan Doyle points.

Angaturama was chosen by Kellner and Campos for the designation of the fossil described by them, because the word in the language of the Tupi stands for " noble ". The epithet limai is a tribute to the work of the Brazilian paleontologist Murilo Rodolfo de Lima, who found the fossil, and has passed the Erstbeschreibern.

Documents

Cited documents and footnotes

The information in this article originate for the most part the limits given in literature sources, in addition, the following publications are cited: