Irritator challengeri

Irritator challengeri was a long-snouted spinosaurid from the Early Cretaceous Romualdo Formation of northeastern Brazil. Its single known specimen, SMNS 58022, preserves most of a skull and lower jaws, making it uniquely informative even though the front of the snout and the entire postcranial skeleton are absent. Modern CT scans exposed a nearly complete palate, braincase, replacement teeth and jaw joints hidden within the limestone. The resulting reconstruction suggests an inclined snout, a relatively weak but rapid bite and lower jaws able to spread slightly sideways as the mouth opened. These features fit a predator that could seize fish and other small vertebrates without showing that it ate fish exclusively.

Its fossils occur between approximately 113 and 110 million years ago. Values shown here are approximate and reflect the current curated seed dataset.

The skull was long, low and narrow, with the nostrils set back from the missing snout tip. Conical teeth lacked the broad blade-like form of many large theropods and were replaced continuously inside the jaws. A small crest ran along the skull roof. CT reconstruction showed a robust palate, a near-complete braincase and a distinctive retroarticular process behind each jaw joint. The lower jaws could rotate outward during opening, enlarging the throat entrance, while the jaw muscles favoured speed over an exceptionally powerful bite. The familiar sail, limbs and tail in life reconstructions are inferred from related spinosaurids because no bones behind the skull are known.

• Most complete spinosaurid skull currently known
• Long, narrow jaws with conical, continuously replaced teeth
• Nostrils positioned well behind the inferred tip of the snout
• Nearly complete bony palate and braincase revealed by CT scanning
• Lower jaw rami capable of spreading and rotating during mouth opening
• Jaw mechanics favouring a relatively quick rather than extremely forceful bite
• Small midline crest along the skull roof

The exact collection date and collector are not documented. The limestone nodule came from near Buxexé, close to Santana do Cariri in Ceará, and passed through the commercial fossil trade before the State Museum of Natural History Stuttgart bought it from a German dealer in 1991. Preparators discovered that missing parts of the snout had been extended with plaster and pieces of unrelated material. David Martill, Arthur Cruickshank, Eberhard Frey, Philip Small and Mark Clarke named Irritator challengeri in 1996. In April 2026, Brazil and Germany announced an agreement to return SMNS 58022 to Brazil, with the Plácido Cidade Nuvens Museum named as its intended repository; the transfer and public-display status still require confirmation.

Naming authors: David M. Martill, Arthur R. I. Cruickshank, Eberhard Frey and 2 coauthors.

Irritator lived around the Araripe Basin's coastal lagoons, rivers and wetlands during the late Aptian. The Romualdo Formation preserves fish, turtles, crocodile relatives and pterosaurs alongside terrestrial animals transported into the basin. Abundant aquatic prey and the animal's long, sensitive-looking jaws support frequent feeding near water, but the skull does not prove a wholly aquatic lifestyle. The map marker represents the broad Buxexé and Santana do Cariri fossil region rather than the lost collection point.

Conical teeth, a narrow snout and neuroanatomical comparisons support catching fish, while the spreading lower jaws may have helped accommodate slippery or bulky prey. Like other spinosaurs, Irritator could also have taken small terrestrial vertebrates and carrion. No limb bones, trackways, stomach contents or group assemblage are known, so swimming style, hunting posture, sociality and nesting behaviour remain unknown.

• Its skull was artificially lengthened before scientists acquired it, inspiring the genus name Irritator.
• CT scans revealed the palate, braincase and replacement teeth without cutting open the fossil.
• The species name honours Professor Challenger from The Lost World.
• Irritator and Angaturama come from the same formation, but they are not demonstrably parts of one individual.
• Brazil and Germany announced an agreement in 2026 to return the holotype to Ceará.

A research repository is not necessarily a public exhibit. Loan and display status can change, so check with the institution before visiting.

1. 01
   A reappraisal of the cranial and mandibular osteology of the spinosaurid Irritator challengeri (Dinosauria: Theropoda)

   Marco Schade, Oliver W. M. Rauhut, Christian Foth and 2 coauthors · Palaeontologia Electronica 26(2):a17 · 2023

   Open source
2. 02
   Neuroanatomy of the spinosaurid Irritator challengeri (Dinosauria: Theropoda) indicates potential adaptations for piscivory

   Marco Schade, Oliver W. M. Rauhut, Serjoscha W. Evers · Scientific Reports 10, 9259 · 2020

   Open source
3. 03
   Irritator dinosaur directory entry

   Natural History Museum, London

   Open source
4. 04
   Governo do Ceará integra articulação internacional para repatriação do fóssil Irritator challengeri ao Brasil

   Government of the State of Ceará · 2026

   Open source