Oh, those fabulous Midwestern tropical seas!
For those of you not in the know, the middle of the United States spent a lot of deep time underwater as various inland seas rose and drained over millions of years. Today, you can see the result in a tendency toward decidedly marine fossils throughout the region. Kansas is full of great, little rice grain fusulinids and hunks of chambered, tubular shell broken off the bodies of long-dead baculites. I went through a phase as a kid where I was all huffy about the dearth of fossilized charismatic megafauna in my backyard, but I pretty quickly got over it, soothed by how easy it was to find the small stuff.
Case in point, these lovely shots of fossilized corals, taken by paleo-blogger David Orr at Indiana's Falls of the Ohio state park, where it's just a short walk through a shallow patch of river to reach an outcropping of exposed 380 million-year-old limestone.
The picture above is a horn coral, but Orr took a lot more shots of several different kinds of coral—some of which are even home to living animals today. You can check out some more photos and his descriptions at the Love in the Time of Chasmosaurs site.