What are these?

[Eastonian]

I was at Partridge Point in Alpena, Michigan, and picked these up on the shore.  Each is about two inches in diameter, and vary in length from four to 12 inches. There are no markings on the top, but some have hash on the bottom. Help!

 

 

[ynot]

Welcome to TFF!

These look like burrow casts.

[Kane]

I agree with @ynot. Neat find. 

[Eastonian]

I  contacted a paleontology professor at Michigan State University. After looking at the photo, she said they looked like gutter casts, made by infillings of small channels carved out by currents. 

[Rockwood]

Here are a couple examples that may help to visualize the suggestion.

[Eastonian]

I'm new to the whole fossil thing, but is an example of mold and cast?

[Rockwood]

2 hours ago, Eastonian said:

I  contacted a paleontology professor at Michigan State University. After looking at the photo, she said they looked like gutter casts, made by infillings of small channels carved out by currents. 

 

25 minutes ago, Eastonian said:

I'm new to the whole fossil thing, but is an example of mold and cast?

In this context the larger example can be thought of as representing a mold. The suggestion (as I see it) is that the pieces you have were cast in similar troughs.

The smaller example hints at what the process might look like. 

The secret is that nature provides a layer that acts like a seam between the features. It's what makes them visible now. Often that seam is a mineral like mica which is plate shaped and settles from slower moving water.