what, if any, animation files can be added to iBooks Author books?

Start here in the Help files. This should address your questions.

http://help.apple.com/ibooksauthor/mac/1.0/#bls321de519

- Fabe

2D animations might be best suited as a dashcode/interactive widget...

See iBA Help. If you need instruction in dashcode see: Dashcode

You are welcome. Good luck on your project. - Fabe

You'll be fine ~ have fun.😉

My books will include 2D animations, and I need to see what files they need to be to be included (imbedded?) in the iBook.

Since you seem to be asking about standalone media files to be embedded directly in iBA "Media" widgets, my advice would be to keep it simple. Audio only files containing AAC stereo in the 128 Kbps @ 44.1 KHz to 160 Kbps @ 48.0 KHz range audio in an M4A container would be a good choice combining reasonable fidelity in a moderate file size. This same audio can also be embedded as a "Podcast" M4A file which will automatically use the image as your default "Poster Frame" for the "Media" widget. As for videos, use an M4V file format containing an H.264 video track with AAC audio as previously described. While many video options are available, you may wish to stick with something like a L3.0/3.1 Main Profile in the 1.0 to 2.5 Kbps range since they are both easy to make and play on almost all mobile devices. Do not include extraneous track data in most cases. For instance, while the iPad can accept/AirPlay a secondary DD5.1 AC3 audio track, the iBA app seems to be programmed to prevent import of such content.

If I have a simple animation, no audio, (at this point) I will import it into first widgets, then move it from there to the file (book) to be uploaded to iTunes, correct?

Am sure K T or Fabe can better confirm this as everything I make/do is for my own personal use. But if you asking if you embed the H.264 video only data in an M4V wrapper directly into the iBA project to be included in the submission file rather than submitting it separately, then I assume the answer is yes.

what file is your little dog ?

It is an animated GIF file. GIF files are not directly import supported by the iBA app but can be included in things like an iFramed or URL resourced HTML widget. (Or you could simply create an HTML 5 animation widget.)