Weaksid, you can create '2D' images from .tif format files and import them into Bryce (.tif format will save any transparencies, so fi you cut out lion and etc. and want the background to be transparent then that will work). As far as creating animals in Bryce...I don't think it's possible...unless it's a blob creature. Whatever you do...don't use dolphins or Jafo will have your head!
Here's an example of a 3D pic in a Bryce Scene http://www.lightningvolt.com/brycescenes.htm Scroll to the bottom of the page where it says Winter Wolf. You can download that whole scene and examine it to help you grasp the concept. As you can see...you can still achieve reflections and lighting FX even with a 2D imported picture.
Here are a few other Misc. links: http://www.rocketfin.com/fxlinks.html
http://www.cadtutor.net/dd/bryce/ktf/ktf.html
http://lonewolf.tierranet.com/tutor3.html
Also, don't forget to do a "google" search for Bryce tutorials because there are plenty out there...
Well, that's all she wrote! I don't us Bryce much at all any longer so that's all the help I can give ya. Have fun!