Between 140 and 100 years ago inland seas flooded outback Queensland. This occurred due to global changes in sea level during this . The marine flooding of the continent left behind a rich fossil record which is preserved in the rocks of outback Queensland. These fossils tell the story of life in the shallow seas and include a diverse assemblage of fossil animals from shellfish to giant marine reptiles.
Swimming reptiles are well-known from the rocks of the Cretaceous inland seas. These include plesiosaurs, ichthyosaurs, and turtles. These animals are not and each have very different ancestries. They are a diverse group of marine reptiles of which Queensland has one of the richest fossil records worldwide.
Fossils of animals without backbones (invertebrates) are common in rocks formed in the inland seas from the Cretaceous Period of Queensland. These fossils include ammonites and a wide variety of molluscs, crustaceans, echinoderms (urchins and ). The different assemblages of fossils in each rock unit provide evidence of the changing environment during the Cretaceous Period.