Dino card No. 0021 of 2,027

Acrotholus

Say it: AK-roh-THOH-lus

Name means: “highest dome”1

Ate: PlantsDome-headsLate Cretaceous

Acrotholus was a small, plant-eating dinosaur with a thick, bony dome on its head. It lived about 84 million years ago in what is now Canada. This dome might have been used for head-butting contests between rivals!1 2

Lived

86 to 84 million years ago4

Late Cretaceous

Fossils found in

Fossils were found in the Milk River Formation in southern Alberta, Canada, near Writing-On-Stone Provincial Park.2 1

Food

Plants4 1

Length

1.8288 m3

approximately six feet

Weight

40 kg3 1 2

When did it live?

Triassic

Jurassic

Cretaceous

252 million years ago20114566, the asteroid

How big was it?

How long was it?

How heavy was it?

as heavy as 10 house cats

as long as 4 house cats nose to tailas long as 10 bananas end to endas heavy as 8 watermelons

How big was Acrotholus compared to YOU?

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cool stuff

Fun facts

Acrotholus is the oldest known pachycephalosaur from North America, and possibly the world.2

Its dome was very thick, up to 55 millimetres (about 2 inches) above the brain, which is almost half the total length of the dome.2

The dome was fully developed even though Acrotholus lived earlier than other pachycephalosaurs, showing that this feature evolved earlier than scientists thought.2

The name Acrotholus means 'highest dome' in Greek, referring to its thick skull roof.1

The species name audeti honors Roy Audet, a rancher who allowed scientists to dig on his land where the first skull was found.1 2

Acrotholus had a smooth dome without the bumps or grooves seen in some other pachycephalosaurs, which suggests the known fossils are from adults.2

AI-made picture of Acrotholus — An AI-made picture of how Acrotholus might have looked, made by a computer from what scientists know. It is a guess: the real animal may have looked different, and nobody knows its true colours.

you asked

Most asked questions about Acrotholus

?How big was Acrotholus?

Acrotholus was a small dinosaur, weighing 40 kg (88 lb) or less. Its skull dome was about 55 mm (2.2 in) thick.1 2

?What did Acrotholus eat?

Acrotholus was a plant-eating dinosaur, like other pachycephalosaurs.1

?Why did Acrotholus have a dome on its head?

The dome was probably used for head-butting contests between rivals, though scientists debate exactly how they used it.1

?When did Acrotholus live?

Acrotholus lived about 84 to 83.5 million years ago, during the Late Cretaceous period.1

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Myth buster

Myth: Some people think Acrotholus used its dome to butt heads like bighorn sheep.

Truth: Scientists are not sure. The dome might have been for display or for fighting, but there is no direct evidence of head-butting in Acrotholus.1

For dino experts

Scientific name: Acrotholus
Named by: Evans et al. 20134
Group: Dome-heads
Family / clade: Pachycephalosauridae4
Classification: Ornithischia > Pachycephalosauria4
Age of the rocks: 86 to 84 million years (Santonian)4
Rock formations: Milk River4
Countries: Canada4
Fossil records: 1 in the Paleobiology Database4
Discovery: The first fossil, a nearly complete skull dome, was found on Roy Audet's ranch in Alberta, Canada, and was named by David Evans and colleagues in 2013.1 2
Still debated: Scientists still debate whether the dome was used for fighting between males or for showing off to mates, since no complete skeleton has been found.1

Where the facts come from

Acrotholus (en.wikipedia.org)
The oldest North American pachycephalosaurid and the hidden diversity of small-bodied ornithischian dinosaurs | Nature Communications (nature.com)
Study of new 'bone-head' hints at higher diversity of small dinosaurs | EurekAlert! (eurekalert.org)
Acrotholus in The Paleobiology Database (CC BY 4.0): age, places, rock formations, classification.

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