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Yezosaurus

Say it: yeh-ZOH-sore-us

Name means: “Yezo lizard”1

Ate: MeatTyrannosaursLate Cretaceous

Yezosaurus was a meat-eating dinosaur that lived in what is now Japan. It was a type of tyrannosaur, so it was a relative of the famous T. rex!4

Lived

86 to 72 million years ago4

Late Cretaceous

Fossils found in

Japan (Hokkaido)2

Food

Meat4

When did it live?

Triassic

Jurassic

Cretaceous

252 million years ago20114566, the asteroid

cool stuff

Fun facts

Yezosaurus was first thought to be a dinosaur, but later scientists realized it was actually a mosasaur, a type of marine reptile.1

The name Yezosaurus comes from Yezo, the name of a group of rocks in Japan where the fossil was found.1

The fossil of Yezosaurus was discovered in a floating concretion, a hard lump of rock, on a riverbank in Hokkaido, Japan, in 1976.1

Yezosaurus was originally called a tyrannosaur, but it is now considered a species of Taniwhasaurus, a mosasaur.1

The Japanese government declared the Yezosaurus fossil a national treasure in 1976, even before it was officially named.1

AI-made picture of Yezosaurus — An AI-made picture of how Yezosaurus 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 Yezosaurus

?Was Yezosaurus a dinosaur?

No, Yezosaurus was originally thought to be a dinosaur, but scientists now know it was actually a mosasaur, a type of extinct marine lizard.1 4

?How big was Yezosaurus?

Yezosaurus was a medium sized mosasaur. The related Taniwhasaurus reached about 6.7 meters (22 feet) long, and Yezosaurus was probably a similar size.3

?Where was Yezosaurus found?

The only Yezosaurus fossil was found in a floating concretion on a riverbank in Hokkaido, Japan, in 1976.1 4

?When did Yezosaurus live?

Yezosaurus lived during the Late Cretaceous period, about 85 to 72 million years ago.4

?Could Yezosaurus swim?

Yes, Yezosaurus was a marine reptile that swam using its powerful tail and paddle-like limbs, just like other mosasaurs.3

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Myth buster

Myth: Yezosaurus was a dinosaur.

Truth: Yezosaurus was actually a mosasaur, a marine reptile, not a dinosaur.1

For dino experts

Scientific name: Yezosaurus
Named by: Muramoto and Obata 19774
Group: Tyrannosaurs
Family / clade: Tyrannosauridae4
Classification: Theropoda > Tyrannosauroidea > Tyrannosauridae4
Age of the rocks: 86 to 72 million years (Santonian / Campanian)4
Rock formations: Kashima4
Countries: Japan4
Fossil records: 1 in the Paleobiology Database4
Discovery: Yezosaurus was named by Kikuwo Muramoto and Ikuwo Obata in 1977, based on a partial skull found in Hokkaido, Japan.4 1
Still debated: Scientists are still debating whether Yezosaurus mikasaensis is a distinct species or just an indeterminate species of Taniwhasaurus.1

Where the facts come from

Taniwhasaurus (en.wikipedia.org)
PBDB Taxon (paleobiodb.org)
Taniwhasaurus (Wikipedia) (Wikipedia)
Yezosaurus in The Paleobiology Database (CC BY 4.0): age, places, rock formations, classification.

Every fact on this page has a number that points to its source. If we got something wrong, sorry, we are dino fans, not a science journal. Tell us at [email protected] and we will fix it.

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