The One, the Only, Tully Monster!

This one's just for fun:

The slender, pencil-like fish are Garden Eels (Gorgasia preclara and Heteroconger hassi). But what the heck is that thing in the middle?

That, my friends, is the Illinois State Monster -- (Tullimonstrum gregarium)! Well, okay, it's properly the Illinois State Fossil, since it's only known from the Pennsylvanian Era's Mazon Creek formation in Illinois. Obviously, this is a reconstruction, with a little photoshop work thrown in. Here's the original:

Tully Monster (Tullimonstrum gregarium), Kenosha Public Museum,
 Kenosha Co., WI  3/1/2014

The two slabs of rocks on the wall to the left are the actual fossils, in this case at the Kenosha Public Museum in Kenosha, WI. (The type specimen is at the Field Museum in Chicago, but as the name gregarium suggests, these are fairly common fossils where they're found.)

This fossil is an example of what's often called problematica. In other words, the question "What the heck is it?" hasn't been answered to anyone's real satisfaction yet. Given that it's 300 million years old, it's probably not surprising that we don't see anything quite like it on Earth today, but we can't even place it as an ancestral anything, and we can't find anything that it's likely descended from.

On the other hand, like so many other creatures, both extant and extinct, it's entirely soft-bodied, and presumably any relatives were as well. Since soft-bodied fossils are very rare and limited to a small fraction of fossil sites, it's probably not surprising that we can't figure it out yet.

Somehow, the idea that the state of Illinois chose a real mystery for it's state fossil makes me smile.