Is it still my work?

Ozzie asked me to post my side of the collaboration we did at the beginning of the year. It's an Abnepos (avatar) of Arista, the forest goddess.
So, I have a question. I've been working on these animal character templates for a roleplaying book that's going to come out in March 2008. We're wrapping up the last of the work. The guy I'm working for has tweaked my work, and actually made improvements on the characters. Mostly fine detail; I'm not a detail person. He's also added texture and refined the fur. There is a notable difference between my pieces and his tweaks on them, and his do look better.
So can I post these improved pieces in my portfolio? As my own work or with a disclaimer like "collaboration with so and so" at the bottom? Cause on the one hand, I think his improvements make the pieces nicer to look at, but on the other, I'm afraid my "style" won't count for diddly if people see it was a collaboration piece.
So, I guess I really don't know what to do, but I didn't want to ignorantly wonder into the world of plagiarism without meaning to.
More posts, I say!

Webcomic

Hey guys,
I teamed up with a writer in my area on a webcomic that's currently on his site. His name is Chris Wichtendahl and he writes a lot of sci-fi, fantasy and comic short stories. In looking for a writer to collaborate with, I figured the local comic shop would be a good place to find someone and it just so happened Chris was good friends with the owner. This is the first of a few collaborations in the works, including my Halloween story which he's already brought a bunch of cool ideas to the table for. This story was scripted and lettered by Chris, and I did the pencils and inks. Check it out and enjoy.
http://www.hemispherestudios.com/webcomic.html
PS Laura, you should post the colored Arista you did--it was really well done. :)