Medioolithus is an oogenus of fossil egg laid by a paleognath.

[1] Medioolithus is known several eggshell fragments, and one complete, spherical egg.

M. geiseltalensis is very similar to modern ratite eggs, for example those of ostriches, rheas, and cassowaries.

At 9 cm (3.5 in) in diameter, however, it is smaller than the eggs of any of these birds, being more similar in size to the egg of a kiwi.

[1]