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Irritator, Early CretaceousRomualdo Formation, Brazil · named 1996
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Irritator

IH-rih-TAY-tor

"one who irritates"

Lived
120 to 113 million years ago, Early Cretaceous
Diet
Carnivore
Length
about 6.5 m (21 ft)
Group
Theropods, Spinosauridae
Found in
Brazil
Named by
Martill et al. 1996

Size comparison

To scale

Where its fossils were found

The evidence

Today

1 find

115 million years ago

Map: C. R. Scotese, PALEOMAP

Habitat

Coastal lagoons and nearby river channels in the Romualdo Formation of Brazil. Santanaraptor and Mirischia were among the small theropods of this region.

Field notes

About Irritator

What it was like

Irritator had a long, narrow, crocodile-like snout lined with straight, unserrated teeth built for gripping slippery prey. A low, bony crest ran along the top of its head, and it likely carried a sail of skin along its back like other spinosaurids. It grew to roughly 6.5 meters (21 feet) long, making it one of the smaller members of its family.

Its nostrils sat well back from the tip of the snout, an adaptation that may have let it breathe even with its jaws partly submerged. Paleontologists think Irritator hunted fish and other small prey near water, and one fossil shows it had eaten a pterosaur.

Its world

Irritator lived from about 120 to 113 million years ago, in the Early Cretaceous, in what is now Brazil. Its skull comes from the Romualdo Formation.

It shared its coastal habitat with smaller theropods such as Santanaraptor, Mirischia, and Aratasaurus, along with turtles, crocodile relatives, and many species of pterosaurs and fish.

How it was found

Martill and colleagues named Irritator in 1996, from a skull that had been damaged and reshaped before scientists could study it properly, which is how the genus got its name. Only one confirmed fossil find is known. Some paleontologists think the similar spinosaurid Angaturama, named from a snout tip found nearby, may be the same animal as Irritator, though this remains debated.

Field gallery

More views of Irritator

Scenes reconstructed from the available fossil evidence.

Irritator in its habitat, photo 1

1 of 7

Lived alongside

Found in the same rock formations

A rock formation can hold fossils laid down millions of years apart, so not every animal here met Irritator.

The evidence

The science behind Irritator

Which parts of the picture come from its own bones, and which come from its relatives.

From its own fossils

  • A nearly complete skull preserves long, narrow jaws with straight teeth lacking serrated cutting edges.
  • The nostrils sit well behind the snout tip, and a low crest runs along the top of the skull.
  • Scans of the skull show joints that may have let the lower jaws spread apart as the mouth opened.

Borrowed from relatives

  • The arms, legs and tail are restored from other spinosaurids, including Baryonyx and Suchomimus.
  • The enlarged first-finger claws follow its relatives; lips and mostly scaly skin are inferred from other theropods.

Still unknown

  • The proportions of its body, the height of its back and the shape of its tail.
  • Its color and the extent of any skin or feather covering.
  • Whether Angaturama represents the same animal.

Often drawn wrong

  • A tall horn on the head exaggerates the low crest preserved in its skull.
  • Its palms should face inward rather than flat toward the ground.

Discovery timeline

  1. 1996Named itMARTILL et al.
  2. 2002Full descriptionSues et al.
  3. 2017Family treeSales & Schultz
  4. 2020SkullSchade, Rauhut & Evers
  5. 2023How it fedSchade et al.

Key papers

The research behind what we know of Irritator

Close relatives

Other members of Spinosauridae

Sources: Wikidata