Dino card No. 1857 of 2,027

Umoonasaurus

Say it: oo-MOO-nah-SORE-us

Name means: “lizard of the Coober Pedy area, named after the local Antakirinja word 'Umoona'”1

Ate: MeatPlesiosaursEarly CretaceousNot technically a dinosaur

Umoonasaurus was a small, crested marine reptile that swam in cold seas near Antarctica about 115 million years ago. It had three bony crests on its head, like a tiny underwater dinosaur, but it was actually a plesiosaur, not a dinosaur. Its fossils are famous because they are preserved in beautiful blue opal.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

121 to 100 million years ago5

Early Cretaceous

Fossils found in

South Australia, in opal mines near Coober Pedy, Andamooka, and other areas1

Food

Meat5 1

Length

2.5 m1 2

adult length estimate

When did it live?

Triassic

Jurassic

Cretaceous

252 million years ago20114566, the asteroid

How big was it?

How long was it?

as long as 2.5 dogs nose to tailas long as 14 bananas end to end

How big was Umoonasaurus compared to YOU?

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cool stuff

Fun facts

Umoonasaurus is known from several partial skeletons, and one of them is the most complete opalized vertebrate fossil ever found.1

It had three thin, blade-like crests on its skull: one along the top of its snout and a pair above its eyes. These crests may have been used for display, like a peacock's tail.1

Umoonasaurus lived in a cold, high-latitude inland sea near the South Pole, where water temperatures were near freezing.1 2

It was a small plesiosaur, only about 2.5 metres (8 feet) long as an adult. A juvenile specimen was less than 1 metre long.1

Umoonasaurus is the most primitive and also the last surviving member of its group, the rhomaleosaurids. It lived about 115 million years ago.1 2

Its tail ended in a 'pygostyle-like' structure made of fused vertebrae, similar to the tail tip of some modern birds.1

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

?What did Umoonasaurus eat?

Umoonasaurus ate small fish. Preserved gut contents show it ate small teleost fish.1

?Why did Umoonasaurus have crests?

Scientists think the three crests on its skull were used for display, like a peacock's tail, to help recognise each other or attract mates. They were too fragile for fighting.1

?Was Umoonasaurus a dinosaur?

No, Umoonasaurus was a plesiosaur, a type of marine reptile with four flippers. It was not a dinosaur.3 4 1

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For dino experts

Scientific name: Umoonasaurus
Named by: Kear et al. 20065
Group: Plesiosaurs
Family / clade: Leptocleididae5
Classification: Plesiosauria > Sauropterygia5
Age of the rocks: 121 to 100 million years (Aptian / Albian)5
Rock formations: Bulldog Shale5
Countries: Australia5
Fossil records: 4 in the Paleobiology Database5
Discovery: Umoonasaurus was named in 2006 by Benjamin Kear and colleagues. The holotype skeleton, nicknamed 'Eric', was bought by public donations and is preserved in opal from the Zorba Extension Opal Field near Coober Pedy, Australia.1
Still debated: Scientists are not sure what the three crests on its head were used for. They were too fragile for fighting, so they might have been for display or recognizing other Umoonasaurus.1

Where the facts come from

An archaic crested plesiosaur in opal from the Lower Cretaceous high-latitude deposits of Australia (pmc.ncbi.nlm.nih.gov)
An archaic crested plesiosaur in opal from the Lower Cretaceous high-latitude deposits of Australia (royalsocietypublishing.org)
Umoonasaurus (en.wikipedia.org)
Umoonasaurus demoscyllus - The Australian Museum (australian.museum)
Umoonasaurus 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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