Antarcticoolithus is an oogenus of large fossil eggs from the Maastrichtian part of the Lopez de Bertodano Formation of Seymour Island, Antarctica.

[1] The fossil egg, the first found in Antarctica, was discovered in 2011 by a Chilean team of researchers.

[2] The fossil egg is visibly collapsed and folded and is characterized by a thin eggshell with a layered structure that lacks a prismatic layer and distinct pores.

The identity of the animal that laid the egg is unknown, but these preserved morphologies are consistent with the skeletal remains of mosasaurs found nearby.

Phylogenetic analysis suggests that the egg belonged to an individual that was at least 7 metres (23 ft) long, hypothesized to be a giant marine reptile.