Ammonite cephalopod — Placenticeras meeki

Geologic period: Late Cretaceous — Campanian

Age: Late Cretaceous, Campanian.

Feeding: Marine feeding ecology is inferred from ammonite anatomy and comparison with cephalopods; the soft feeding apparatus is not preserved in this shell.

Locomotion: Marine swimming using buoyancy control and jet propulsion is reconstructed from cephalopod biology and shell form.

Body plan: Planispirally coiled chambered shell surrounding a soft-bodied cephalopod.

Evidence: Shell shape, chambers and sutures are direct evidence. Soft-body reconstruction remains inferential.

Why it matters: Ammonites were abundant and diverse marine animals and are extremely useful for understanding and correlating Cretaceous marine rock layers.

Plain Language Identity: A coiled ammonite cephalopod from Late Cretaceous seas.

What You Are Looking At: A fossil chambered shell belonging to Placenticeras meeki.

Ecosystem: Late Cretaceous Western Interior Seaway.

Formation: Pierre Shale for documented Smithsonian material.

Find Location: South Dakota, United States for documented Smithsonian material.

Preservation: Mineralized or mold-preserved shell fossil.

Open Questions: Do not reconstruct exact soft-tissue color or behavior as direct evidence.

Source Urls: https://naturalhistory.si.edu/visit/virtual-tour/current-exhibits/deep-time-virtual-tour-fossil-list; https://nmaahc.si.edu/object/nmnhpaleobiology_3188007

Enrichment Method: SAGE curated research pass; title + scientific name + source scene matched; comparative chronology retained; evidence separated from inference

Scientific name: Placenticeras meeki

Evidence / representation: comparative_taxon_visual

comparative_taxon_visual

Cretaceous Worlds: Dinosaurs at Their Most Diverse.

Media license: CC0

http://creativecommons.org/publicdomain/zero/1.0/deed.en