What does ichthyosaur mean?
An ichthyosaur was an extinct marine reptile that resembled a fish in body shape but was anatomically distinct from actual fish. These animals first appeared during the Triassic Period, flourished throughout the Jurassic Period, and disappeared before the end of the Cretaceous. They had long, streamlined bodies, dorsal and tail fins, and four paddle-like limbs, with especially large eyes in some species. Like whales and dolphins, ichthyosaurs breathed air and had to surface regularly, although they reproduced without returning to land. Fossils preserved in sedimentary rock have revealed their anatomy, diet, and behavior, including evidence of viviparity in some species. The name combines Greek roots meaning “fish” and “lizard,” an early description that captured their superficial resemblance even though modern classification places them firmly among the reptiles. Ichthyosaurs are especially important in the history of paleontology because their fossils helped scientists recognize that the prehistoric seas contained diverse vertebrate life long before the origin of whales.
nounAn ichthyosaur is an extinct, fish-shaped marine reptile that lived from the Early Triassic to the early Late Cretaceous. Ichthyosaurs had streamlined bodies, paddle-like limbs, large eyes, and generally breathed air.
- Any member of the extinct group of fish-shaped marine reptiles collectively known as ichthyosaurs.
"The museum displayed the fossilized skull of an ichthyosaur discovered in a coastal cliff."
"Fossilized ichthyosaur remains have been found in the cliffs of the Jurassic Coast."
"The documentary explained how ichthyosaurs used their paddle-shaped limbs to steer through the ocean."
The standard plural adds “-s” to the singular noun.
"The cliffs preserve the remains of several ichthyosaurs from the Jurassic Period."
Despite its name and fish-shaped body, an ichthyosaur was a reptile—and it breathed air at the surface.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does ichthyosaur come from?
The word was formed in the early 19th century from the Greek ikhthys, meaning “fish,” and sauros, meaning “lizard.” It was an early scientific coinage intended to describe the fish-like appearance of these extinct marine reptiles. Their classification was debated historically, but they are now understood as reptiles rather than fish, and the word's “fish-lizard” elements are best treated as a description of their outward form rather than a precise statement of their ancestry.
Related word forms
How ichthyosaur is actually used
The term is used in both scientific and general contexts. In paleontology, it refers to members of the broader ichthyosaur lineage, while “ichthyosaurian” is sometimes used more broadly for related marine reptiles.