Scientists are contesting a discovery of prehistoric proteins found in the fossils of dinosaur bones, saying the collagen is from laboratory contamination from an ostrich rather than a T. rex — crushing hopes of bringing dinosaurs back to life and creating a real-life Jurassic Park. University of Manchester

If you’re waiting for scientists to create a real-life Jurassic Park, don’t hold your breath. Researchers say some crucial organic material other scientists found was really just from laboratory contamination, not dinosaurs themselves.

The organic material in question involved proteins linked to a Tyrannosaurus rex that lived 68 million years ago in Montana. They were collagen, the most abundant type of protein and a fibrous one that our bones and tissues use on a structural level to stay strong yet elastic. Scientists who found the proteins 10 years ago suggested they had survived with the dinosaur leg bone fossil, giving people hope that when technology became advanced enough, it would be possible to recreate a living dinosaur using actual genetic and organic material. They also later repeated their results with a duck-billed dinosaur.

Read: What Do We Really Know About Dinosaur Sex?

But the University of Manchester reports a group of paleontologists dug into the matter and said the proteins were not really from the dinos at all — rather they came from other animals previously in the lab.

The group analyzed collagen from ostrich bone samples, which they chose because ostriches were one of the animals known to have been studied in the previous laboratory. The university said those samples strongly matched the proteins that allegedly were connected to the T. rex and the duck-billed dinosaur, suggesting the collagen came from laboratory contamination rather than the prehistoric creatures.

“We soon realized that our results were pulling the rug from beneath the paradigm that collagen might survive the ravages of deep time,” Manchester paleontologist Mike Buckley said.

In reality, apart from the contested dinosaur samples, no collagen older than 3.5 million years has been discovered.

“It seems we were trying to reproduce something that was beyond the current detection limits of our science,” co-author Phil Manning said in the Manchester statement.

This isn’t the first re-examination of dinosaur information, not even recently. One controversial paper has suggested dinosaurs emerged in the Northern Hemisphere, contrary to the popular belief it happened in the Southern Hemisphere. There is more to the assertion than just a geographical change — if true, that differing history would cause scientists to redraw the dinosaur family tree and what we know about how the creatures evolved, shaking up the world of paleontology.

Read: Thousands of Dino Tracks Are Set in Stone At This Beach

Also earlier this year, one paleontologist challenged the field’s labeling of dinosaurs as male or female based on their bone shape alone, saying that we don’t know enough about the extinct animals’ sexual dimorphism — the differences between the sexes — or lack thereof to make such conclusions. He called on his colleagues to instead rely on evidence like eggs found in a dinosaur fossil, which would indicate a female.

“I’m not saying that dinosaurs were not dimorphic, but I am saying that there’s no existing fossil evidence to suggest that they were,” Jordan Mallon said in a statement from the Canadian Museum of Nature. “The jury is still out.”

The Manchester researchers who concluded that those collagen proteins were from modern ostriches rather than ancient dinosaurs called on other scientists to use more “robust authentication criteria” when searching for biological clues in fossils.

Although Jurassic Park may never happen, for those who dream of one day bringing the extinct woolly mammoth back to life, there is still hope: They were living as recently as several thousand years ago, well within the 3.5-million-year timeframe collagen has been known to survive.