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Science & Nature • Paleontology

Plesiosaurus

Plesiosaurus is an extinct genus of marine reptile from the Early Jurassic, known for its long neck, small head, broad body, and four flippers.

By Ethan Anderson| Reviewed by Olivia Bennett, Standards & Fact-Checking Lead| Updated July 27, 2026|2 min read| Fact-checked

Plesiosaurus is an extinct genus of marine reptile from the Early Jurassic, known for its long neck, small head, broad body, and four flippers. It is one of the best-known plesiosaurs and is not a dinosaur. Fossils were first discovered in England in the early 19th century, and the genus was named in 1824.

Description

Plesiosaurus was a marine reptile with a long neck and small head, adapted for swimming with four flippers. Sources describe it as a predator that fed on marine animals such as fish and other small sea life.

Discovery and naming

The first fossil discovery is credited to Mary Anning in 1823 in western Europe, and the genus was named the following year by William Conybeare. The name refers to its lizard-like appearance while indicating it is not a true lizard.

Classification

Plesiosaurus belongs to the broader group Plesiosauria, a lineage of marine reptiles distinct from dinosaurs. It is one of the classic genera used to describe plesiosaurs in popular and scientific writing.

Paleoecology

Plesiosaurus lived in shallow marine settings and is known from Early Jurassic deposits in Europe. Its fossils help researchers understand the diversity of marine reptiles during the Jurassic seas.

Key facts

  • Plesiosaurus was an extinct marine reptile, not a dinosaur.
  • It lived during the Early to Middle Jurassic in marine environments.
  • Its body plan included a long neck, small head, compact trunk, and four flippers.
  • The name Plesiosaurus means 'almost lizard.'
  • It was first discovered by Mary Anning in 1823 and named by William Conybeare in 1824.
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Canadian context

Plesiosaurus is relevant to Canadian readers through paleontology education and museum collections, because plesiosaurs are part of the broader marine reptile record commonly discussed in Earth history and evolution exhibits.

Frequently asked questions

Was Plesiosaurus a dinosaur?
No. Plesiosaurus was a marine reptile in the plesiosaur lineage, not a dinosaur.
When did Plesiosaurus live?
It lived during the Early to Middle Jurassic, about 135 to 120 million years ago.
Who discovered Plesiosaurus fossils?
Mary Anning discovered the first fossil in 1823.
Who named Plesiosaurus?
William Conybeare named it in 1824.
What did Plesiosaurus eat?
It was a predator that likely ate fish and other small marine animals.
What does the name Plesiosaurus mean?
It means 'almost lizard.'

References

  1. Encyclopaedia Britannica — https://www.britannica.com/animal/plesiosaur
    Supports: General plesiosaur context, marine reptile classification, and broad time range for plesiosaurs.
  2. New Dinosaurs — https://newdinosaurs.com/plesiosaurus/
    Supports: Plesiosaurus-specific dates, discovery by Mary Anning, and naming by William Conybeare.
  3. EBSCO Research Starters — https://www.ebsco.com/research-starters/zoology/plesiosaurus
    Supports: Plesiosaurus as an Early Jurassic marine reptile, size, anatomy, and habitat.
  4. Britannica Kids — https://kids.britannica.com/kids/article/plesiosaur/390390
    Supports: General plesiosaur body plan, marine habitat, feeding, and distinction between long-necked and short-necked forms.