FAQS: Earth Sciences Unit

I found a round and smooth fossil - is it a dinosaur egg?

Probably not. It is most likely an egg-shaped concretion. So what’s a concretion? A concretion is is a sedimentary structure that often forms in the rocks of Saskatchewan. Concretions develop over a long period of time, as minerals are deposited around a “nucleus,” an object like a piece of shell or bone fragment. Eventually layers upon layers of mineral deposits build up, forming a round, smooth ball of rock. When split open these layers are visible, and they might look like the “yolk” of an egg to the untrained eye.

Round ironstone concretions

Split-open ironstone concretion showing layers

Fossil collectors often break open concretions to look for preserved animal or plant specimens that might have acted as the nucleus for the formation. Concretions are usually harder than the sediment surrounding them, and therefore erode more slowly. That’s why they are often left exposed on the surface after the surrounding sediments have long since disappeared. This is a common phenomenon in our Cretaceous-aged Bearpaw Formation, sediments that were formed approximately 70 million years in areas where a great inland sea covered most of Saskatchewan.

For further information contact the Curator of Earth Sciences

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