Invertebrates are among the most diverse multicellular life forms on our planet, and the methods used to collect and study invertebrate fossils vary with the type of fossils in question. In this example, the Denver Museum of Nature and Science focuses on one type of fossil: 73 million-year-old giant ammonites from Kremmling, Colorado.
The ammonite site is about thirteen miles north of Kremmling, and is administered by the Bureau of Land Management (BLM). Although the site is open to scientists and the general public, vehicle access is restricted and the site has no visitors center. Therefore, visitors should contact the BLM office for directions, road conditions, and parking information at 970-724-3437. Please note that visitors are not permitted to collect fossils from the Kremmling site.
During the age of the last dinosaurs, the Western Interior of North America was covered by the Cretaceous Seaway, a shallow sea that advanced and retreated several times. Many species of ammonites lived in the Cretaceous Seaway, and their fossils can be found throughout western North America today.
Dr. Kirk Johnson is the DMNS curator of fossil plants and invertebrates. In August 1998, he was joined by research associate Dr. Emmett Evanoff and Alaskan artist Ray Troll (coauthor of Planet Ocean) to excavate ammonites from a site near Kremmling, Colorado. These fossils became the centerpiece of the Museum's Cruisin' the Fossil Freeway exhibition as well as the subject of an advanced invertebrate paleontology course in 1999.
As with vertebrates, prospecting for invertebrates starts with knowing where and how to look.
Fossil-bearing concretions are usually deposited in layers. These layers may erode out of the sediment, leaving clues for paleontologists as to where the fossil horizon is. If the land surface is flat, paleontologists can sometimes search for concretions by probing below the surface with a metal rod and listening for clinking sounds. Following the concretion layer in Kremmling has revealed a fossil horizon extending for several miles.