What is this marmot-like animal (Tigray, Ethiopia)?
This looks like some sort of ground squirrel. Especially in the second picture, the posture is  very characteristic of squirrels in general. The tail also looks very squirrel-like to my eyes. My best guess, without better pictures, is the Striped Ground Squirrel (Xerus erythropus). 

See the images at:
http://www.flickriver.com/photos/8834404@N02/2902284598/
http://www.flickriver.com/photos/kpzaremba/5094580855/