noun
- extinct marine cephalopod mollusks with coiled shells that lived from the Devonian to Cretaceous periods
Usage: paleontology; geology
Examples
- Ammonoids are important index fossils for dating rock layers.
- The museum’s collection includes several well-preserved ammonoids from the Jurassic period.
- Scientists study ammonoids to understand ancient marine ecosystems.
- These ammonoids show intricate suture patterns on their shells.
- Ammonoids went extinct at the end of the Cretaceous period along with dinosaurs.
- The spiral shells of ammonoids are often found in limestone formations.