Fossils discovered in Brisbane and thought to be 50m years old could shed light on a missing link in the evolution of animals since the death of the dinosaurs, according to scientists.

The fossils of ancient crocodiles, fish and plants were found in a layer of oil shale by workers on a $100m overpass project in the suburb of Geebung.

The workers’ drilling during excavation brought some of the fossils to the surface about a fortnight ago and more fossils have since been found in Queensland’s capital.

Queensland Museum Network’s CEO, Prof Suzanne Miller, said the find filled part of a gap in the scientific record of animal evolution since dinosaurs became extinct 66m years ago. "In the whole of northern Australia, this is absolutely unique," Miller said. "And depending on what we find, because we are just at the beginning of this project, this could be unique in the world."