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Thalassomedon

Say it: thal-ASS-oh-MEE-don

Name means: “sea lord”1

Ate: MeatPlesiosaursLate CretaceousNot technically a dinosaur

Thalassomedon was a huge marine reptile that swam in the seas of North America about 95 million years ago. It had an extremely long neck, over half its body length, and used its sharp teeth to catch fish and other prey.1

Fun fact: this sea reptile swam while dinosaurs walked on land. Everyone calls them dinos, but they were a different branch of reptiles.

Lived

100 to 94 million years ago3

Late Cretaceous

Fossils found in

Colorado and Montana, USA3 1

Food

Meat3 1

Length

10.86 to 11.95 m1

Weight

4.4 tonnes to 6.8 tonnes1

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 5 cars

as long as 2.5 cars parked in a rowas long as 66 bananas end to endabout as heavy as an elephantas heavy as 1400 watermelons

How big was Thalassomedon compared to YOU?

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cool stuff

Fun facts

Thalassomedon's neck had 62 vertebrae and was about 5.9 metres (19 feet) long, more than half of its total body length.1

Its flippers were about 1.5 to 2 metres (4.9 to 6.6 feet) long, helping it steer through the water.1

Stones have been found in the stomach area of Thalassomedon, which scientists think may have helped grind food or acted as ballast for diving.1

Its skull was only 47 centimetres (19 inches) long, but its teeth were 5 centimetres (2 inches) long.1

Thalassomedon lived during the Cenomanian stage of the Late Cretaceous, about 95 million years ago.1

Its closest relative is Elasmosaurus, another long-necked plesiosaur.1

Six specimens of Thalassomedon are on display in museums across the United States.1

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

?How big was Thalassomedon?

Thalassomedon was about 10.86 to 11.95 metres (35.6 to 39.2 feet) long and weighed around 4.4 to 6.8 metric tons (4.9 to 7.5 short tons).1

?Was Thalassomedon a dinosaur?

No, Thalassomedon was a plesiosaur, which is a type of marine reptile that lived in the oceans, not a dinosaur.2

?What did Thalassomedon eat?

Thalassomedon used its sharp teeth to catch fish and other prey.1

?How long was Thalassomedon's neck?

Its neck was about 5.9 metres (19 feet) long and made up of 62 vertebrae, which is more than half of its total body length.1

?When did Thalassomedon live?

Thalassomedon lived about 95 million years ago during the Cenomanian stage of the Late Cretaceous.1

?Where was Thalassomedon found?

Fossils of Thalassomedon have been found in North America, specifically in the United States.1

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For dino experts

Scientific name: Thalassomedon
Named by: Welles 19433
Group: Plesiosaurs
Family / clade: Elasmosauridae3
Classification: Plesiosauria > Elasmosauridae > Sauropterygia3
Age of the rocks: 100 to 94 million years (Cenomanian)3
Rock formations: Graneros Shale, Belle Fourche3
Countries: USA3
Fossil records: 2 in the Paleobiology Database3
Discovery: Thalassomedon was named by S. P. Welles in 1943, based on fossils found in Colorado and Montana, USA.3 1
Still debated: Scientists are not sure whether the stones found in its stomach were used for grinding food or for ballast to help it dive.1

Where the facts come from

Thalassomedon (en.wikipedia.org)
Thalassomedon (simple.wikipedia.org)
Thalassomedon 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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