Dino card No. 0072 of 2,027

Alexeyisaurus

Say it: al-ek-SAY-ih-SORE-us

Name means: “Alexey's lizard”1

Ate: MeatPlesiosaursLate TriassicNot technically a dinosaur

Alexeyisaurus was a long-necked marine reptile that swam in the oceans during the Late Triassic, about 210 million years ago. It was not a dinosaur, but a plesiosaur, a type of sea creature with a small head and four flippers. It lived near what is now Franz Josef Land in Russia.1 2

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

Lived

227 to 211 million years ago5

Late Triassic

Fossils found in

Wilczek Land, Franz Josef Land, Russia1

Food

Meat2

Length

7 m2

estimated

When did it live?

Triassic

Jurassic

Cretaceous

252 million years ago20114566, the asteroid

How big was it?

How long was it?

as long as 7 dogs nose to tailas long as 39 bananas end to end

How big was Alexeyisaurus compared to YOU?

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cool stuff

Fun facts

Alexeyisaurus is one of the earliest known plesiosaurs, living during the Late Triassic period.3

Its body was about 7 meters (23 feet) long, which is as long as a small bus.2

The humerus (upper arm bone) was straight and very long, with flat ends that suggest the head of the bone was not fully hardened.2

Its femur (thigh bone) was slightly curved and had wider ends than the humerus, giving it a different shape.2

The vertebrae (back bones) were strictly amphicoelous, meaning they were hollow on both ends like a dumbbell.2

Scientists first thought Alexeyisaurus was an elasmosaur, but later studies say the skeleton is too poorly preserved to be sure.1

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

?Was Alexeyisaurus a dinosaur?

No, it was not a dinosaur. It was a plesiosaur, a type of long-necked marine reptile that lived in the ocean.4 1

?How big was Alexeyisaurus?

It was about 7 meters (23 feet) long, which is as long as a small bus.4

?When did Alexeyisaurus live?

It lived during the Late Triassic period, about 210 million years ago.4 1

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For dino experts

Scientific name: Alexeyisaurus
Named by: Sennikov and Arkhangelsky 20105
Group: Plesiosaurs
Family / clade: Elasmosauridae5
Classification: Plesiosauria > Elasmosauridae > Sauropterygia5
Age of the rocks: 227 to 211 million years (Norian)5
Rock formations: Wilczek5
Countries: Russia5
Fossil records: 1 in the Paleobiology Database5
Discovery: Alexeyisaurus was named by Russian paleontologists A. G. Sennikov and M. S. Arkhangelsky in 2010, based on an incomplete skeleton found on Wilczek Land in the Arctic.1 2
Still debated: Scientists are not sure if Alexeyisaurus was really an elasmosaurid plesiosaur, because the only skeleton found is incomplete and poorly preserved.1

Where the facts come from

Alexeyisaurus (en.wikipedia.org)
PBDB Taxon (paleobiodb.org)
On a typical Jurassic sauropterygian from the Upper Triassic of Wilczek Land (Franz Josef Land, Arctic Russia) (exa.ai)
Alexeyisaurus – Plesiosaur Directory (plesiosauria.com)
Alexeyisaurus 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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