Irritator (‬In reference to the‭ ‘‬irritation‭’ ‬of the palaeontologists‭ ‬-‭ ‬refer to text for details‭)‬

Short Info

Irritator (‬In reference to the‭ '‬irritation‭' ‬of the palaeontologists‭ ‬-‭ ‬refer to text for details‭)‬

Phonetic : Ih-re-tay-tor.

Named By : D.‭ ‬M.‭ ‬Martill,‭ ‬A.‭ ‬R.‭ ‬I.‭ ‬Cruikshank,‭ ‬E.‭ ‬Frey,‭ ‬P.‭ ‬G.‭ ‬Small‭ & ‬M.‭ ‬Clarke‭ ‬-‭ ‬1996

Diet : Carnivore

Size : Estimated 6 – 8 meters long

Type of Dinosaur : Large Theropod

Type Species : I.‭ ‬challengeri‭ (‬type‭)

Found in : Brazil‭ ‬-‭ ‬probably the Santana Formation

When it Lived : Early Cretaceous, 112-99 million years ago

Irritator was a spinosaurid dinosaur genus that lived in Brazil during the Albian stage, which occurred around 110 million years ago. The Romualdo Formation in the Araripe Basin contains a complete skull. Fossil dealers had illegally purchased this skull from the State Museum of Natural History Stuttgart. The specimen was made the holotype for the Irritator challengeri in 1996. The word “irritation” is the genus name. It refers to the emotions of paleontologists who discovered that the skull had been severely damaged and altered by collectors. The species name is an homage to Professor Challenger, Arthur Conan Doyle’s fictional character.

Irritator challengeri mount 01Kabacchi, CC BY 2.0, via Wikimedia Commons

Some paleontologists consider Angaturama limai, which is known from a snout point that was later described in 1996, to be a junior synonym for Irritator. Both animals are from the Araripe Basin’s same stratigraphic units. It was previously believed that Irritator’s skull parts and Angaturama’s were the same part of the same specimen. This has now been ruled out, but more overlapping fossil material is required to confirm that they are one and the same animal. Another spinosaurid skeletal material from the Romualdo Formation could have been belonging to Irritator, or Angaturama. This allowed for the creation of a replica skeleton and mounting it at the National Museum of Rio de Janeiro for 2009.

Irritator was between 6 and 8 meters (20 ft and 26 ft in length), and weighed approximately 1 tonne (1.1 short tonnes). This made it one of the smallest known spinosaurids. The slender, long nose was lined with straight, unserrated conical teeth. A thin sagittal crown ran lengthwise up the top of the head, where powerful neck muscles were likely to be anchored. The nostrils were located far back from the tip if the snout. A rigid secondary palate covering the roof of the mouth would have helped strengthen the jaw during feeding. The holotype of Irritator challengeri, a subadult spinosaurid, is the best preserved. The Angaturama snout tip was rosette-like and had long teeth. It also has a tall crest. It may have had larger first-finger claws than other spinosaurids and a sail running down the back.

Initial mistake was made for Irritator as a pterosaur and then later as a maniraptoran dinosaur. The animal was later identified as a spinosaurid dinosaur theropod in 1996. This classification was confirmed by the thorough preparation of the holotype skull. Both Angaturama and Irritator are members of the Spinosaurinae family. It has been suggested that Irritator may have had a generalist diet, similar to today’s crocodilians. He might have mainly eaten fish and small prey animals. There is fossil evidence that an individual ate a petrosaur either by hunting it or by scavenging it. Semi-aquatic habits may have been the norm for Irritator, who lived in a tropical environment with dry areas around a lagoon. It lived alongside turtles, crocodyliforms and many other carnivorous species, including a number of pterosaur- and fish species.

A chalk concretion was excavated by fossil-poachers. It contained the rear of a large skull and lower jaws. The location is near Santana do Cariri, northeastern Brazil. The fossil was illegally sold by dealers. Fossil trading in Brazil has been banned since 1942. Rupert Wild, State Museum of Natural History Stuttgart (Germany) purchased it. It was initially thought to be the skull a huge basal pterosaur or flying reptile. The Chapada do Araripe area is well-known for its abundance of pterosaur fossils and the German museum frequently bought them. It was a rare and important discovery, so experts in pterosaurs from both Germany and Britain were invited to examine the specimen. The paper that described it as a Pterosaur was already submitted for publication. However, the peer reviewers discredited this idea and suggested that the fossil belonged a theropod dinosaur.

The skull was slightly slanted sideways and was partially crushed, as is typical with fossils. While the right side of the skull was preserved well, the left was badly damaged during collection. The skull’s hindmost surface was eroded and the lower jaw had lost its front end due to fossilization. Due to its septarian concretion, parts of the specimen also had cracks. The tip of the upper jaw was also missing. It was not evident that the fossil had been eroded. Some bones show signs of corrosion, which indicates that acid preparation was attempted. The skull’s middle was fractured vertically. This had been covered with car body filler. To make it more valuable and complete, fossil traders had covered the skull with plaster. This is a common practice in the Chapada do Araripe for fish fossils. The modifications made to the illegally obtained specimen were not known to the buyers until it was sent to universities in Britain for CT scan imaging. The scan revealed that the collectors had attempted to reconstruct the skull using parts of the maxilla (main lower jaw bone) grafted onto the front of rostrum (snout). The skull, designated SMNS 58022, became the holotype specimen for the new genus Iritator challengeri in February 1996 when it was scientifically first described by paleontologists David M. Martill and Arthur R.I. Cruickshank and Eberhard Frey. Martill and his colleagues wrote in this paper that the generic name Iritator was derived from irritation. This is the feeling that Martill and his team felt when they discovered that the snout had artificially been elongated. The type species, Irritator challengeri was named after Professor Challenger who is a character in Arthur Conan Doyle’s novels, particularly The Lost World. Frey and Martill had already named a new species of pterosaur from the Crato Formation Arthurdactylus Conandoylei two years prior to the novelist.

Martill and his colleagues first described Irritator problemri in 2002. The holotype was heavily encased within a calcareous rock matrix. American paleontologist Hans-Dieter Sues supervised Diane M. Scott, University of Toronto at Mississauga, who took on the task of removing all skull bones from the rock. This allowed for a detailed redescription of the specimen in 2002. Scott, Frey, Martill, Martill, and Scott published the fully prepared specimen. This inspection negated many of Martill’s original observations which were based upon misinterpretations and damage to the skull. The total length of the skull was estimated to be 24 cm (9.4 inches) shorter than originally thought. The original thought that the prominent head crest was a bone fragment with a definite attachment proved wrong. Sues and her colleagues considered the African genus Spinosaurus the closest taxon to Irritator. They shared many dental features including straight conical tooth crowns, thin teeth enamel, no serrations and well-defined edges. The authors were able to identify a junior synonym of Iritator with Spinosaurus because little was known about Spinosaurus’s skull. Sues and her colleagues pointed out that there was more skull material that overlapped to confirm the diagnosis. Later research confirmed that Spinosaurus’ skull was more complete than previously thought.

The exact location of the discovery is unknown, but it is most likely that the specimen came from the Romualdo Formation (previously called the Romualdo Member in the Santana Formation). Microfossils from the ostracod Pattersoncypris and fish scales taken from Cladocyclus (both found in the Romualdo Formation) confirmed this assignment. Local fossil dealers suggested a location near Santana Do Cariri, on the flank of Chapada do Araripe at a height approximately 650m (2,130ft). This area can be considered the likely site of discovery because the Romualdo Formation is exposed there. The matrix that surrounds the holotype is the same color as the rocks. The Romualdo Formation was home to the first known dinosaur, Irritator challengeri. Its holotype specimen is the best preserved spinosaurid skull.

Source: Wikipedia