My next step was to hit the Internet. Caterpillars are very interesting. You can quickly find lots of photos of butterflies and moths, but this stage in their development seems to be harder to document.
Finally, this morning I had luck on the Internet. I found out that this is a Pandora Sphinx Moth. As a caterpillar, it might have been green in it's earlier stages and had an antenna before I found it too. Very cool!
A helpful site in my identifying this guy was by Bill Oehlke. Thanks Bill! This mystery is solved.