User blog comment:Jamintheinfinite/Subnautica Creature Evolution/@comment-35546951-20181012164522/@comment-28450065-20181012194112

uhh sudden release of some carbon dioxide gas due to the whole thing being a giant volcano which killed the creatures and also happened to coincide with a fault forming in the seabed, causing the bodies to sink down into the Earth over time before being uncovered later.