The Field Museum has a very nice Silurian marine diorama, which includes crinoids, cephalopods, corals, trilobites, and more from the Silurian period. It’s meant to represent what the Chicago area looked like during the Silurian Period. Much of the insight comes from the the fossils found in Thornton Quarry.

There is a little secret with the exhibit. One of the museum’s staff hid a tiny cow in it. The cow represents Mrs. O’Leary’s famous cow, who was supposed to have started the great Great Chicago Fire, which happened from October 8th–10th, 1871.

Here’s a photo as a clue of where to look in the diorama.

So, next time you go to the Field Museum, have a look for the cow!