How big was Irritator challengeri?

Irritator challengeri was about 6–8 m long. It stood about 1.8–2.4 m tall at the hips. It weighed about 1 t. (Wikipedia: Irritator 2026; Paul 2016)

When did Irritator challengeri live?

Irritator challengeri lived during the Early Cretaceous, about 119.6–113.2 million years ago. (Paleobiology Database: Irritator challengeri … 2026; Schade et al. 2023)

Where have Irritator challengeri fossils been found?

Fossils of Irritator challengeri have been found in Romualdo Formation (Ceará) and Brazil. (Martill et al. 1996; Sues et al. 2002)

What did Irritator challengeri eat?

Irritator challengeri was a piscivore or carnivore. (Martill et al. 1996; Sues et al. 2002)

Who named Irritator challengeri, and when?

Irritator challengeri was described by David M. Martill et al. in 1996. (Martill et al. 1996; Schade et al. 2023)

Life restoration of the Brazilian spinosaurid Irritator challengeri, with a human for scale.Sauroarchive, CC BY 4.0, via Wikimedia CommonsCC BY 4.0Source

Irritator challengeri

Pronounced IR-ih-tay-tor chal-en-JER-eye

Tetanurae · Spinosauridae

A spinosaurid from the Early Cretaceous of north-east Brazil, known from the most complete spinosaurid skull ever found. Its long, narrow snout and conical teeth suited catching fish and other small prey on a tropical coastal lagoon.

Bipedal
Crested
Possibly semiaquatic

Compare

Period: Cretaceous· Aptian
Diet: Piscivore
Length: 6–8 m
Mass: 1,000 kg
Location: Ceará, Brazil, South America

Quick answers

How big was Irritator challengeri?: Irritator challengeri was about 6–8 m long. It stood about 1.8–2.4 m tall at the hips. It weighed about 1 t. (Wikipedia: Irritator 2026; Paul 2016)
When did Irritator challengeri live?: Irritator challengeri lived during the Early Cretaceous, about 119.6–113.2 million years ago. (Paleobiology Database: Irritator challengeri … 2026; Schade et al. 2023)
Where have Irritator challengeri fossils been found?: Fossils of Irritator challengeri have been found in Romualdo Formation (Ceará) and Brazil. (Martill et al. 1996; Sues et al. 2002)
What did Irritator challengeri eat?: Irritator challengeri was a piscivore or carnivore. (Martill et al. 1996; Sues et al. 2002)
Who named Irritator challengeri, and when?: Irritator challengeri was described by David M. Martill et al. in 1996. (Martill et al. 1996; Schade et al. 2023)

On this page

IR-ih-tay-tor chal-en-JER-eye

Period: Cretaceous119.6–113.2 Ma
Diet: Piscivore
Length: 6–8 m
Mass: 1 t
Location: Brazil, South America
Classification: Tetanurae · Spinosauridae
Described: 1996, David M. Martill et al.

Overview

Irritator challengeri lived in the Araripe Basin of north-east Brazil in the late Aptian, a little over 113 million years ago. Its skull came out of a limestone concretion near Santana do Cariri, Ceará, and was sold by fossil dealers to the State Museum of Natural History in Stuttgart, Germany.

Dealers had built up the snout with plaster to make it look longer, which "irritated" the researchers who had to remove it; the species name honours Professor Challenger of Arthur Conan Doyle's "The Lost World". Martill and colleagues (1996) first thought it was a maniraptoran, and Sues and colleagues (2002) showed it was a spinosaurid.

CT scans by Schade and colleagues (2023) revealed almost the whole palate and braincase. The skull had binocular vision in front of the snout and a relatively weak but fast bite, and the lower jaws spread sideways when opening, like those of pelicans. It probably snapped up fish and small vertebrates, and a spinosaurid tooth has even been found in a pterosaur neck bone from the same rocks.

Name meaning

From "irritation", for the frustration caused by the dealers' alterations to the skull; challengeri after Professor Challenger in Conan Doyle's "The Lost World" (Martill et al. 1996).

Biology & evidence

What scientists think about how this animal lived, and how strong the evidence for each idea is.

Feeding

Irritator ate pterosaurs as well as fish.
Evidence level: Hypothesis
A spinosaurid tooth stuck in a pterosaur bone shows that some spinosaurid of the formation fed on one, by hunting or scavenging; it is not certain the tooth belonged to Irritator.
Evidence for / against · 1
Evidence for
- Trace fossil · Spinosaurid tooth in a pterosaur vertebra (Romualdo Formation)
  A spinosaurid tooth embedded in a pterosaur neck vertebra from the same formation.
Irritator had a relatively weak but fast bite suited to snapping small prey.
Evidence level: Moderate evidence
Jaw mechanics and the inner ear suggest quick snaps at fish and small vertebrates rather than a crushing bite.
Evidence for / against · 2
Evidence for
- Specimen · CT reconstruction of the Irritator skull
  Medical and micro-CT reconstructions of SMNS 58022 reveal the palate and braincase, binocular vision in front of the snout, a weak but fast bite and lower jaws that spread sideways when opening.
  Specimen: SMNS 58022
- Comparative anatomy · Irritator braincase endocast
  A digital endocast and inner ear indicating fast, well-controlled downward head movements and a snout held angled about 45 degrees down.
  Specimen: SMNS 58022

Other

The Irritator holotype is the most complete spinosaurid skull known.
Evidence level: Direct evidence
Only the tip of the snout and the front of the lower jaws are missing, while other spinosaurids are known mostly from snouts and isolated bones.
Evidence for / against · 1
Evidence for
- Specimen · CT reconstruction of the Irritator skull
  Medical and micro-CT reconstructions of SMNS 58022 reveal the palate and braincase, binocular vision in front of the snout, a weak but fast bite and lower jaws that spread sideways when opening.
  Specimen: SMNS 58022

Size

Length: 6–8 m
Height: 2 mpublished range 1.8–2.4 m
Mass: 1,000 kg

Irritator challengeri was about 8 m (26.2 ft) long, roughly 4.4 times the height of a 1.8 m adult human.

Timeline

Lived from about 119.6 to 113.2 million years ago (Ma), within the Mesozoic era (252–66 Ma).

Periods: Aptian (121.4–113 Ma), Early Cretaceous (145–100.5 Ma)

Late Aptian (Schade et al. 2023, after Arai & Assine 2020); PBDB gives the same bin, 119.57-113.2 Ma. Older works, and Wikipedia, date the Romualdo Formation to the Albian.

Location

Formations

Romualdo Formation · Ceará

Places

Map data: Natural Earth (public domain). Modern positions, not where the continents were then.

Near Buxexé, Santana do Cariri, Ceará · Romualdo Formation · Ceará · position approximate

These are the places where fossils have been found, not the full area where the animal lived.

Ecosystem

Restoration of the Romualdo Formation environment with Irritator challengeri in the foreground, Mirischia and Thalassodromeus in the background and pterosaurs overhead.Composition and effects by PaleoGeekSquared Background by ItaiguaraLima Irritator and flying pterosaurs by Андрей Белов Thalassodromeus by PWNZ3R Dragon Mirischia by Ademar Pereira do Nascimento, CC BY 3.0, via Wikimedia CommonsCC BY 3.0Source

Lived in: Romualdo (Araripe Basin)

119.57–113.2 million years ago · marine margin, lake

A tropical coastal lagoon with irregular freshwater influence and marine incursions, surrounded by arid to semi-arid land; famous for fish, pterosaurs and soft tissues preserved in limestone concretions.

Classification

cladeDinosauria
cladeSaurischia
cladeTheropoda
cladeTetanurae
superfamilyMegalosauroidea
familySpinosauridae
subfamilySpinosaurinae
genusIrritator
speciesIrritator challengeri

Taxonomic status: Valid

Fossil record

Holotype skull of Irritator challengeri, SMNS 58022, in left and right lateral view (Sales & Schultz 2017).Marcos A. F. Sales, Cesar L. Schultz, CC BY 2.5, via Wikimedia Commons, Staatliches Museum für Naturkunde StuttgartCC BY 2.5Source

Specimens
Catalog number	Status	Institution	Found
SMNS 58022	Holotype	Staatliches Museum für Naturkunde Stuttgart (SMNS)	—

What has been found

Holotype: SMNS 58022

Preserved
Partial
Reconstructed
Unknown / not recorded

Region by region (table)

Skeleton regions of Holotype: SMNS 58022
Region	State
Skull	Partial · Missing most of the premaxillae and the front of the maxillae.
Mandible	Partial · Missing the front ends.
Teeth	Partial
Cervical vertebrae	Unknown / not recorded
Dorsal vertebrae	Unknown / not recorded
Sacrum	Unknown / not recorded
Caudal vertebrae	Unknown / not recorded
Ribs	Unknown / not recorded
Gastralia	Unknown / not recorded
Scapula / shoulder girdle	Unknown / not recorded
Humerus	Unknown / not recorded
Forearm (radius / ulna)	Unknown / not recorded
Hand (manus)	Unknown / not recorded
Pelvis	Unknown / not recorded
Femur	Unknown / not recorded
Tibia / fibula	Unknown / not recorded
Foot (pes)	Unknown / not recorded

Skull reconstructions of Irritator challengeri (SMNS 58022) and Angaturama limai (USP GP/2T-5).Marcos A. F. Sales, Cesar L. Schultz, CC BY 4.0, via Wikimedia CommonsCC BY 4.0Source

Gallery

Historical reconstruction: the Irritator head as originally interpreted by Martill et al. (1996), with a head crest now known to be based on a misidentified bone fragment.PaleoGeekSquared, CC BY-SA 4.0, via Wikimedia Commons (unmodified except resizing)CC BY-SA 4.0

All specimens

Discovery

Year described: 1996
Described by: David M. Martill et al.
Type specimen: SMNS 58022

Discovery timeline

1996 · Formally described
Martill and colleagues name Irritator
Named as a crested maniraptoran, the first dinosaur named from the formation.
People: David M. Martill
2002 · Revision
Irritator redescribed as a spinosaurid
After further preparation, Sues and colleagues confirm it is a spinosaurid.
People: Hans-Dieter Sues, David M. Martill
2023 · Major study
CT reappraisal of the Irritator skull
Schade and colleagues reconstruct the whole skull digitally.
People: Marco Schade

Sources

(2026). Paleobiology Database: Irritator challengeri occurrence and type collection 28052. The Paleobiology Database (paleobiodb.org), data service 1.2, accessed 2026-09-23. https://paleobiodb.org/data1.2/colls/list.json?coll_id=28052&show=paleoloc,strat,loc,ref,geo&pgm=gplates&vocab=pbdb (opens in a new tab)
(2026). Wikipedia: Irritator. Wikipedia (English), accessed 2026-09-24. https://en.wikipedia.org/wiki/Irritator (opens in a new tab)
Martill, D. M., Cruickshank, A. R. I., Frey, E., Small, P. G. & Clarke, M. (1996). A new crested maniraptoran dinosaur from the Santana Formation (Lower Cretaceous) of Brazil. Journal of the Geological Society 153: 5-8. doi:10.1144/gsjgs.153.1.0005 (opens in a new tab)
Paul, G. S. (2016). The Princeton Field Guide to Dinosaurs (2nd edition). Princeton University Press.
Schade, M., Rauhut, O. W. M. & Evers, S. W. (2020). Neuroanatomy of the spinosaurid Irritator challengeri (Dinosauria: Theropoda) indicates potential adaptations for piscivory. Scientific Reports 10: 9259. doi:10.1038/s41598-020-66261-w (opens in a new tab)
Schade, M., Rauhut, O. W. M., Foth, C., Moleman, O. & Evers, S. W. (2023). A reappraisal of the cranial and mandibular osteology of the spinosaurid Irritator challengeri (Dinosauria: Theropoda). Palaeontologia Electronica 26(2): a17. doi:10.26879/1242 (opens in a new tab)
Sues, H.-D., Frey, E., Martill, D. M. & Scott, D. M. (2002). Irritator challengeri, a spinosaurid (Dinosauria: Theropoda) from the Lower Cretaceous of Brazil. Journal of Vertebrate Paleontology 22: 535-547. doi:10.1671/0272-4634(2002)022[0535:ICASDT]2.0.CO;2 (opens in a new tab)

Irritator challengeri

Quick answers