Dino card No. 1341 of 2,027

Pachycostasaurus

Say it: PAK-ee-ko-sta-SORE-us

Name means: “thick-ribbed lizard”1

Ate: MeatPlesiosaursMiddle JurassicNot technically a dinosaur

Pachycostasaurus was a pliosaur, a kind of short-necked plesiosaur that lived in the sea. It had very thick, heavy ribs that made its body barrel-shaped, like a fat sausage. This marine reptile was not a fast swimmer, but it used its heavy bones to stay stable underwater.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

165 to 162 million years ago2

Middle Jurassic

Fossils found in

Peterborough, England1 2

Food

Meat1

Length

3 m1

based on the only known specimen, which may not be fully grown

When did it live?

Triassic

Jurassic

Cretaceous

252 million years ago20114566, the asteroid

How big was it?

How long was it?

as long as 3 dogs nose to tailas long as 17 bananas end to end

How big was Pachycostasaurus compared to YOU?

Just maths in your browser. Nothing is saved or sent anywhere.

cool stuff

Fun facts

Pachycostasaurus had ribs and belly bones that were so thick they looked like sausages. This condition is called pachyostosis, and it also happens in modern dugongs and manatees.1

Its flippers were small compared to its body, and its neck was short. This made it a slow swimmer, unlike many other pliosaurs.1

The only known fossil of Pachycostasaurus was found by Alan Dawn, an amateur geologist and museum volunteer, in a quarry in Peterborough, England.1

Its head was about 20% of its total body length, which is typical for pliosaurs of its time.1

Pachycostasaurus lived about 165 to 161 million years ago, during the Middle Jurassic period.2

The bones of its backbone had a large canal for the spinal cord, and some parts were not fully hardened, suggesting the animal might not have been fully grown when it died.1

AI-made picture of Pachycostasaurus — An AI-made picture of how Pachycostasaurus 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.

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Myth buster

Myth: Pachycostasaurus was a fast, powerful predator like other pliosaurs.

Truth: Its heavy ribs, small flippers, and short neck show it was a slow swimmer that probably stayed near the seafloor, hunting soft prey.1

For dino experts

Scientific name: Pachycostasaurus
Named by: Cruickshank et al. 19962
Group: Plesiosaurs
Family / clade: Pliosauridae2
Classification: Plesiosauria > Pliosauridae > Sauropterygia2
Age of the rocks: 165 to 162 million years (Callovian)2
Rock formations: Oxford Clay2
Countries: United Kingdom2
Fossil records: 1 in the Paleobiology Database2
Discovery: The fossil was discovered by amateur geologist Alan Dawn in a quarry near Peterborough, England. Scientists Arthur Cruickshank, David Martill and Leslie Noè described and named it in 1996.1
Still debated: Scientists are not sure whether Pachycostasaurus lived in freshwater rivers and estuaries and was washed into the sea, or if it lived in the deep ocean and drifted to shallow waters.1

Where the facts come from

Pachycostasaurus (en.wikipedia.org)
Pachycostasaurus 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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