English: Prismatoolithus levis Zelenitsky & Hills, 1996 - fossil dinosaur eggs from the Cretaceous of Montana, USA. (MOR 299, Museum of the Rockies, Bozeman, Montana, USA)

Biogenic products are objects produced by ancient organisms. Many paleontologists refer to these as trace fossils, but they really aren't. Examples of fossil biogenic products include eggs, amber (fossilized tree sap), coprolites (fossilized feces), and spider silk. Eggs were originally small, living cells. But hard eggshells are mineralized - the material was never alive, and thus are biogenic products.

The most impressive fossil eggs are those of dinosaurs. Dinosaur nests having eggs in their original position are known from several localities. Sometimes, x-ray analysis or cat-scan analysis shows the presence of dinosaur embryos inside intact eggs. The embryos would be body fossils, but the surrounding eggshell material is a biogenic product.

Seen here is a dinosaur nest with the eggs arranged obliquely upright, radiating outward from the center of the nest. The host rock is siliciclastic mudstone.

The scientific name ("oospecies") for the eggs themselves is Prismatoolithus levis. They were produced by Troodon formosus, a theropod dinosaur.

Classification: Animalia, Chordata, Vertebrata, Reptilia, Dinosauria, Saurischia, Theropoda, Troodontidae

Stratigraphy: Two Medicine Formation, Upper Cretaceous

Locality: Egg Mountain, Willow Creek Anticline, Teton County, western Montana, USA