Dino card No. 1830 of 2,027

Trinacromerum

Say it: try-NAK-roh-MAIR-um

Name means: “three tipped femur”1

Ate: MeatPlesiosaursEarly Cretaceous to Late CretaceousNot technically a dinosaur

Trinacromerum was a fast-swimming marine reptile that lived in the Late Cretaceous seas. It used its long flippers like paddles to chase small fish. Even though it looked a bit like a dolphin, it was actually a plesiosaur, not a dinosaur.1 4

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

Lived

106 to 66 million years ago4

Early Cretaceous to Late Cretaceous

Fossils found in

Kansas, Texas, Utah, and Wyoming in the USA, and Manitoba and Saskatchewan in Canada4 1

Food

Meat1 4

Length

3 m1

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 Trinacromerum compared to YOU?

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

cool stuff

Fun facts

Trinacromerum's long flippers helped it swim very fast, and scientists think it moved like a 'four-flippered penguin'.1

Its name means 'three tipped femur', which refers to a bone in its hip that had three points.1

Trinacromerum had 46 vertebrae in its spine, including 20 in the neck, 3 in the chest, and 23 in the back.2

Fossils of Trinacromerum have been found in rocks that were once the bottom of a shallow sea that covered central North America.4

It lived from about 106 to 66 million years ago, during the Late Cretaceous period.4

Some scientists once thought Trinacromerum was the same as another plesiosaur called Dolichorhynchops, but now they are considered different.2

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

?How big was Trinacromerum?

About 3 meters (9.8 feet) long. That is roughly the length of a small car.1 3

?What did Trinacromerum eat?

It ate small fish. Its teeth were shaped for catching and holding slippery prey.1 3

?Could Trinacromerum swim fast?

Yes, its long flippers helped it swim very fast. Scientists compare its swimming style to a 'four-flippered penguin.'1 3

?Is Trinacromerum a dinosaur?

No, it is a plesiosaur, which is a marine reptile. It lived in the sea and was not a dinosaur.1 3

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Myth buster

Myth: Some people think Trinacromerum was a dinosaur because it lived in the sea and had flippers.

Truth: Trinacromerum was a plesiosaur, a marine reptile, not a dinosaur. Dinosaurs lived on land and had different body shapes.1

For dino experts

Scientific name: Trinacromerum
Named by: Cragin 18884
Group: Plesiosaurs
Family / clade: Polycotylidae4
Classification: Plesiosauria > Sauropterygia4
Age of the rocks: 106 to 66 million years (Albian / Maastrichtian)4
Rock formations: Carlile Shale, Greenhorn Limestone, Pierre Shale4
Countries: USA, Canada4
Fossil records: 18 in the Paleobiology Database4
Discovery: Trinacromerum was first named by Francis W. Cragin in 1888 from fossils found in Kansas, USA. Later, more fossils were found in Canada and other parts of the USA.1 4
Still debated: Scientists still debate whether some fossils belong to Trinacromerum or to its close relative Dolichorhynchops, because their skeletons are very similar.2

Where the facts come from

Trinacromerum (en.wikipedia.org)
PBDB Taxon (paleobiodb.org)
Trinacromerum — Triebold Paleontology, Inc. (trieboldpaleontology.com)
Trinacromerum 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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