Kremmling Ammonites Site

Ancient sea
On top of a mountain

Exploring the fossil site with the highest concentration of fossils and ammonites in particular in the world.

“Ocean on Top of a Mountain”

Kremmling Cretaceous Ammonite Locality in Colorado is called an “ocean on top of a mountain”. Around 72.5 MA in the Cretaceous period this place was a Western Interior Seaway.

This area was assigned a status of ACEC, Area of Critical Enviromental Concern, i.e. The Bureau of Land Management preserved this site for professional research and public enjoyment, fossil collection is prohibited. Location and directions are available on Bureau of Land Management website

Ammonites brooding site

The possible explanation of the diversity of invertebrates and abundancy of ammonites on this site could be that this area served as a brooding site, and many ammonites swam to that part of the sea to lay eggs.

Placenticeras meeki was a late Cretaceous ammonite that lived in Western Interior Seaway in the modern-day United States and Canada and could reach up to 1 meter in length.

I took this photo of P. meeki at In Stone Fossils gallery in Kemmerer, Wyoming


Some formations like Bearpaw formation in Canada produced Placenticeras with much better preservation of a shell and many specimens are found covered by ammolite. 

This fossilized ammonite shell gemstone is composed mainly of aragonite and may include calcite, pyrite, silica.

P. meeki, P. intercalare, and Baculites compressus 

Ammolite or “ammonite shell” is a very rare and iridescent material and it’s found only on P. meeki, P. intercalare, and Baculites compressus species. 

Bird Baths

This also known as a birds bath site. Sexual dimorphism could explain the size variations of ammonites’ shells of the same species.

A Macroconch, a female form of an ammonite, is much larger than microconch, a male form.

On the photo above you could see a female on top of a concretion and half of a male form at the bottom. In some species, a macroconch could be up to 4 times larger than the microconch. 

When it rains the female ammonites impressions are filled with water, and birds are used those fossils to bath.

The most abundant fossils on the site are Inoceramus, Scaphitids, and Baculites.

Inoceramus, big corrugated clams, that could reach up to 3 meters in length.

Scaphitids, small coiled ammonites, was widespread during the late Cretaceous period. Few specimens were found from Cenozoic era deposits, Paleocene sites, Danian stage, about 61.6 million years old.

Scaphites have a coiled shell that straightened when an ammonite grew, and then coiled again when an animal matured. Scaphites had ribs and tubercles (bumps), it provided an ammonite good friction and helped it to swim.

Baculites are the heteromorph ammonites with a straight shell. Few concretions on the site preserved both straight pointy-shelled baculites along with coiled ammonites.

Every concretion on the site has signs of oysters and burrowing animals, i.e. watch for shell material, lines or mold of a burrow.

Serpulids are tube-building arnelid worms. These animals are easily recognized by their dwelling tubes, which are compomised of calcium carbonate and typically secured to a hard substrate. Georgieva et. al., 2019. Serpulids formed vast reefs by using the tubes of conspecific as settlement substrate. 

Educational eight-part video series created by Ken Schauer for the BLM’s Kremmling Cretaceous Ammonite Locality are available in the Video Slider. The series is available through Youtube and not downloaded to this website. Credit: Ken Schauer.