Animation doesn’t have to always be accomplished by rigging mesh characters. Animation can also be created realistically in-world by using animated gifs. Fred Beckhusen’s Outworldz website has a tool called G2SLA.
With this tool it converts an animated .gif [lossless format for image files that supports both animated and static images.]
to an image that is then uploaded inworld. By placing this image in a prim with the Gif script, the prim then becomes the animated Gif. When converting your gif to image make sure your output is set to transparent [.png format] or you will have a white background.
I used this method to create animated fish for our virtual ocean. You can obtain free gif fish from animatedimages.org Download the gif and save to a folder on your hard drive.
With your G2SLA tool downloaded and opened on your computer, you would simply load the gif, and choose your options, then choose output. The file saves to the folder where you have the G2SLA application saved.