Insect Plant Fish or ...?

[MightyPretzel]

Greetings, everyone. I spent the other day on the east side of Ventura County breaking open sedimentary rocks. I'm not experienced enough with that sort of material to positively ID it but I think it was siltstone. There was a leaf and something else on both sides of one of the rocks. I've been having a hard time figuring out what the "something else" is.  It measures about 35 by 14 millimeters.

 

I took a few pictures of both sides under different lighting conditions to help bring out some of the finer details. It comes from the Modelo Formation (Miocene). Thanks ahead of time for any help in figuring out what it is. Here are pictures of the first side:

 

Some pictures of the second side:

 

 

[MightyPretzel]

Just following up to see if anyone had any thoughts on what this might be. Guesses are welcome too

[Rockwood]

Shrimp like arthropod.

Looks to be to large for a copepod, but something like it.