The source of a set of dinosaur footprints embossed on the roof of a cave near Mount Morgan, Australia has finally been identified. The explanation is not as wild as some previous theories, but the way it emerged shows how much chance can matter in science.

Dr Anthony Romilio of the University of Queensland explained to IFLScience that, sadly, dinosaurs did not dance on the ceilings of caves, bat-like. Instead, they frequently walked over soft clay sediments, leaving tracks. These depressions often filled with sand, and when both layers turned to stone under the pressure of still more material above, the sandstones were often harder than the mudstones.

Eventually, water erosion washed away the softer material to create caves, leaving the footprints sticking out of the rock above at many Queensland sites.

Although the ceiling prints created much confusion in the early 20th century, by the time those at Mount Morgan were discovered the formation process was well understood. More puzzling was the question of what sort of dinosaur made them. The prints here are in two sizes, and paleontologists initially attributed them to a theropod walking on all fours.

Theropods' arms weren't generally quite as puny compared to the rest of their bodies as those of the meme-inspiring T. rex, but their forelimbs were ill-suited to walking. If Mount Morgan did indeed show quadrupedal theropod movement it would be a very significant discovery indeed. "You don't assume T. rex used its arms to walk, and we didn’t expect one of its earlier predatory relatives of 200 million years ago did either,” Romilio said in a statement. 

For decades the question rested, and the site is now closed so those seeking an answer have been unable to find new evidence, until Romilio met dentist Dr Roslyn Dick.

Australian PhD scholarships are not very lucrative and Romilio told IFLScience: “I supplemented my income with a job at the market.” In between spruiking the price of cauliflowers and broccoli Romilio told the customers he got to know what he was studying. When Dick responded her father had discovered some dinosaurs Romilio was skeptical, but her revelation she was the daughter of Queensland fossil hunting legend Ross Staines left him speechless.

Staines took high-resolution photographs of the Mount Morgan caves, as well as detailed notes, all of which were now stored in a cupboard under Dick's sister's stairs.

Using techniques and knowledge unavailable to Staines, Romilio examined these records and revealed in a paper published in Historical Biology the prints were made by two bipedal dinosaurs of different sizes.

Romilio told IFLScience the larger dinosaur probably had legs a meter (3.3 feet) long, while the smaller one was about half as high. The larger prints were made first, but they could have been minutes or hours later. The two were probably different species, but Romilio can't rule out an adult and juvenile of the same species.

Given the prints' 200-million-year age, the more splayed print shape and shorter central toe mark the pair as herbivores, but Romilio couldn't provide more detail on their diet or lifestyle. The original theropod identification came about through confusion with subsequent dinosaur evolution, when two-legged herbivores developed thicker toes.