Santa Barbara Museum of Natural History

I found an egg that is about five inches around and looks very old. I would like to send you a picture of it so you can give me your thoughts.

Thank you.

Dave, Camarillo, CA - June 23, 2019

Curator Response

Thanks for sending in this interesting specimen, Dave! This is a tricky one to identify from a photo, but what follows is the collective wisdom of our geologists and paleontologists on staff:

This looks like a sandstone concretion with tafoni. The coarse, grainy texture suggests that it is sandstone (a sedimentary rock made of sand-sized fragments). The shape looks like a concretion: a rounded lump of rock that accumulated around a nucleus of something different from the rest of the “host rock” where it formed. “Tafoni” sounds like a delicious Italian dessert, but refers to the lacelike texture of holes on the surface of this specimen. Tafoni are caused by things like abrasion (for example, by wind, water, or particles of dust in wind and sediment in water), chemical forces like lichens breaking down the surface of the rock, and salt weathering (when salt crystals grow inside small openings in a rock’s surface, breaking apart the surrounding rock).

It doesn’t look like a fossil, but sometimes concretions have fossils inside. You could try carefully breaking this one open to see if there is a visible nucleus. Concretions are often mistaken for fossil eggs. Because eggs—even giant dinosaur eggs—are fragile, it’s quite rare to find fossils of intact eggs. Usually paleontologists find partial specimens of fossilized broken eggshells (sometimes accompanied by embryo parts).

Stay curious!

—Nature Education Manager Sabina Thomas, Ph.D., paleobiologist Teen Programs Manager Jenna Rolle, M.S., and Dibblee Collection Manager of Earth Science Jonathan Hoffman, Ph.D.