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Late Cretaceous Ammonite

Illustration of a coiled ammonite in life, swimming in the ocean
Ammonites were a diverse group of mollusk with distinct morphologies that varied among species.

Illustration by Lisa Marshall.

Marine Fossil
Scientific Name: Ammonoidea

Ammonites are an extinct group of mollusk related to living octopus and squid. Complete specimens are often difficult to find, but experts can sometimes identify species with just a small fragment. Ammonites have distinct morphology that varies across species. Paleontologists use physical features such as shape, coil, and ornamentation to identify ammonites and date the stratigraphic layers in which they are found. The remains of over 200 ammonite species have been found on multiple continents. Finding examples of the same species in multiple formations, even if they are miles apart, allows us to correlate those deposits and give them the same time stamp.

3D Late Cretaceous Ammonite—Ammonoidea
Chaco Culture National Historical Park, New Mexico

A 3D model. This model shows a rock slab with a coiled fossil shell exposed on the surface. The model can be rotated and tilted using a computer interface.

Ammonites are an extinct group of mollusk related to living octopus and squid . Complete specimens are often difficult to find, but experts can sometimes identify species with just a small fragment. Ammonites have distinct morphology that varies across species. Paleontologists use physical features such as shape, coil, and ornamentation to identify ammonites and date the stratigraphic layers in which they are found. The remains of over 200 ammonite species have been found on multiple continents. Finding examples of the same species in multiple formations, even if they are miles apart, allows us to correlate those deposits and give them the same time stamp.

To learn more, visit - https://www.nps.gov/articles/series.htm?id=7B32EA8A-A130-11C3-E755871E8385F30E

Footnotes linked to the model:

The many chambers, or camerae, within ammonite shells are separated by dividing walls called septa, which are visible here. These chambers may have provided structural support to the shell and helped control buoyancy.
After this ammonite died, its soft, squid-like body quickly degraded, but its hard shell remained. Water flowed through the exposed chambers, preserving their shape by filling them with minerals.

Footnotes

  1. The many chambers, or camerae, within ammonite shells are separated by dividing walls called septa, which are visible here. These chambers may have provided structural support to the shell and helped control buoyancy.

  2. After this ammonite died, its soft, squid-like body quickly degraded, but its hard shell remained. Water flowed through the exposed chambers, preserving their shape by filling them with minerals.

Last updated: April 30, 2021