Scientists worked to solve the mystery behind 70 million year old animal mummies, and made some interesting discoveries. 

The findings will be presented on BBC's Horizon Program on May 11. In the program a team of researchers will be shown using the latest medical technology to determine the contents of a number of animal mummies from Egypt, the University of Manchester reported. The work shows many of these animal mummies are mysteriously empty.

"We always knew that not all animal mummies contained what we expected them to contain, but we found around a third don't contain any animal material at all - so no skeletal remains," said study leader Lidija Mcknight.

The scanned animal fossils included "wading birds, falcons, cats, shrews and a five-foot long Nile crocodile." In one unusual cases, a crocodile-shaped mummy was found to contain the bodies of eight baby crocodiles wrapped together meticulously. A cat-shaped mummy contained only a choice few pieces of cat bone.

The team looked at over 800 mummies, only a third of which contained complete animal remains, the BBC reported. Another third contained pieces of animal remains, such as the cat, and the final third contained only fillers like mud and egg shells.

"We think they were mummifying pieces of animals that were lying around, or materials associated with the animals during their lifetime - so nest material or eggshells," McKnight told the BBC.  "They were special because they had been in close proximity with the animals - even though they weren't the animals themselves.

The fake mummies may have been created due to high demand for mummified animals. Ancient Egyptians worshipped  many gods in animal forms, making mummified animals sacred religious gifts.

"You would go to a special site, buy an animal mummy," McKnight said. "You'd then give it to a priest, who would collect a group of animal mummies and bury them."