Horton Hatches the Egg

Note: Please, do not add "Disney took over Blue Sky Studios", because this was before that happened!

A film adaptation of the book of the same name by Dr. Seuss and a follow up to the film Dr. Seuss' Horton Hears a Who! was reported to be in production but nothing came of it.

Plot
Horton has to look after an egg belonging to a bird named Mazy while she's away.

Why It Was Cancelled

 * 1) It was presumably cancelled when Dr. Seuss' widow Audrey Geisel moved the film rights of Dr. Seuss' other story projects to Universal and Illumination either in 2008 or 2009.

Result

 * There haven't been any updates about the film for quite some time.
 * The Lorax was released in 2012 by Illumination Entertainment.