Illustration of ammonite
am·mo·nite
ˈa-mə-ˌnīt 
: any of a subclass (Ammonoidea) of extinct cephalopods especially abundant in the Mesozoic age that had flat spiral shells with the interior divided by septa into chambers
Am·mon·ite
ˈa-mə-ˌnīt
: a member of a Semitic people who in Old Testament times lived east of the Jordan between the Jabbok and the Arnon
Ammonite
adjective
Examples of ammonite in a Sentence
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Chantel Tattoli, New York Times, 20 May 2025
This colorful and iridescent ammonite is the only material classified as both a fossil and a gemstone.
—Laura Baisas, Popular Science, 16 Apr. 2025
The site's paleontological importance is underscored by the presence of fossils found in the sedimentary layers, including ammonites, marine reptiles and microorganisms, all of which provide critical insight into life before and after the extinction event.
—Jonathan Granoff, Newsweek, 29 Jan. 2025
Most commonly seen in marine fossils, such as ammonites or trilobites, pyritization can produce highly detailed, metallic-looking fossils that are both scientifically valuable and visually striking.
—Nina Turner, Newsweek, 29 Oct. 2024
See All Example Sentences for ammonite
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Noun
The swirly shell that held the voice of the Little Mermaid in Disney’s 2023 live-action adaptation looked like the ancient marine mollusk called an ammonite.
—Chantel Tattoli, New York Times, 20 May 2025
This colorful and iridescent ammonite is the only material classified as both a fossil and a gemstone.
—Laura Baisas, Popular Science, 16 Apr. 2025
The site's paleontological importance is underscored by the presence of fossils found in the sedimentary layers, including ammonites, marine reptiles and microorganisms, all of which provide critical insight into life before and after the extinction event.
—Jonathan Granoff, Newsweek, 29 Jan. 2025
Most commonly seen in marine fossils, such as ammonites or trilobites, pyritization can produce highly detailed, metallic-looking fossils that are both scientifically valuable and visually striking.
—Nina Turner, Newsweek, 29 Oct. 2024
See All Example Sentences for ammonite
Cite this Entry
“Ammonite.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/ammonite. Accessed 14 Jul. 2025.
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ammonite
noun
am·mo·nite
ˈam-ə-ˌnīt
: any of numerous flat spiral fossil shells of mollusks related to the nautilus that are especially abundant in the Mesozoic era of geological history
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