Definition

1. Noun:
   • An extinct marine mollusk with a coiled, chambered shell: An ammonite is a fossil of an extinct cephalopod that lived in the seas from the Devonian to the Cretaceous periods. Its shell is typically coiled and divided into chambers.
   • The fossil shell of such a mollusk: The term also refers specifically to the coiled, often ribbed, chambered shell that is commonly found as a fossil.

Usage Examples

• Noun:
  • The museum's collection includes a beautifully preserved ammonite from the Jurassic period.
  • Ammonites are important index fossils for dating rock layers.

Advanced Usage

• In Paleontology: The term is used to describe any member of the extinct subclass Ammonoidea. Their complex suture patterns (the lines where chamber walls meet the outer shell) are key to their classification.
  • The ammonite's suture pattern indicates it belongs to the genus Parkinsonia.

Variants and Related Words

• Ammonitic (adj): Relating to or resembling an ammonite.
  • The rock showed ammonitic structures.
• Ammonitiferous (adj): Containing or yielding ammonite fossils.
  • The ammonitiferous shale is rich in fossils.

Synonyms

• Fossil cephalopod: A more general descriptive term.
• Nautiloid fossil (Note: This is a related but distinct group; nautiloids have simpler suture patterns and are not extinct).

Related Phrases

• Ammonite suture: Refers to the complex, frilly pattern where the internal chamber walls (septa) join the outer shell.
  • The intricate ammonite suture is a marvel of natural geometry.

Noun

1. one of the coiled chambered fossil shells of extinct mollusks