ich·thyo·saur
ˈik-thē-ə-ˌsȯr 
: any of an order (Ichthyosauria) of extinct marine reptiles of the Mesozoic specialized for aquatic life by a streamlined body with a long snout, limbs reduced to small fins for steering, and a large lunate caudal fin
Ich·thyo·sau·ria
: an order of Mesozoic marine reptiles most abundant in the Lias having an ichthyoid body, elongated snout, short neck, dorsal and caudal fins, limbs modified into paddles by the flattening of the bones, multiplication of the phalanges and addition of from one to four digits, eyes very large and protected by a ring of bony sclerotic plates, and numerous conical teeth set in grooves and adapted for catching fish
ichthyosauroid
adjective
-ˌrȯid
Examples of ichthyosaur in a Sentence
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Andrew Paul, Popular Science, 19 Feb. 2026
Jurassic-era ichthyosaurs are known for their long-snouts and their dolphin-like bodies, Massare said.
—Julia Jacobo, ABC News, 10 Oct. 2025
These giant ichthyosaurs had anatomy akin to the owls of today, Lindgren says in a statement.
—Sara Hashemi, Smithsonian Magazine, 21 July 2025
Whales and dolphins also descend from land-dwelling ancestors, but their transition happened over a comparatively short evolutionary timespan, especially when measured against the long reign of the ichthyosaurs.
—Discover Magazine, 13 May 2025
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Noun
This anatomy features a lower jaw with teeth that protrude out between the upper set—a trait previously only seen in flying pterosaurs, marine ichthyosaurs, and semiaquatic crocodilian predators.
—Andrew Paul, Popular Science, 19 Feb. 2026
Jurassic-era ichthyosaurs are known for their long-snouts and their dolphin-like bodies, Massare said.
—Julia Jacobo, ABC News, 10 Oct. 2025
These giant ichthyosaurs had anatomy akin to the owls of today, Lindgren says in a statement.
—Sara Hashemi, Smithsonian Magazine, 21 July 2025
Whales and dolphins also descend from land-dwelling ancestors, but their transition happened over a comparatively short evolutionary timespan, especially when measured against the long reign of the ichthyosaurs.
—Discover Magazine, 13 May 2025
See All Example Sentences for ichthyosaur
Cite this Entry
“Ichthyosaur.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/ichthyosaur. Accessed 19 Jun. 2026.
Copy CitationKids Definition
ichthyosaur
noun
ich·thyo·saur
ˈik-thē-ə-ˌsȯ(ə)r
: any of an order of extinct marine reptiles with a fish-shaped body and a long snout
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