Dinosaurs ruled the earth for at least 165 million years. During this period they evolved into a whole menagerie of wonderful and fantastical forms, and are survived today by the birds that flit from branch to branch in your garden. But when they first emerged from the evolutionary tree is a murkier story. It now seems that they may have evolved up to 20 million years earlier than thought.

The results come from a study published in Biology Letters, in which researchers from the Natural History Museum, London, have created the most detailed dinosaur tree ever formed. Using two separate methods, they created a massive phylogenetic tree that includes close to 1,000 different species of dinosaurs, enabling them to trace the animals right back to their roots.

Both methods came up with strikingly similar results, indicating the validity of the outcome. They both showed that while the oldest dinosaur fossil to have ever been dated, known as Nyasasaurus, is thought to be 240 million years old, the data from the trees suggest that dinosaurs may have evolved at least 10 million years earlier, and potentially up to 20 million years earlier.

This is possibly not too surprising. The dating of such ancient fossils comes with some leeway, as well as considering just how patchy the fossil record from this long ago for dinosaurs is. For example, while Nyasasurus is the best contender for the oldest dinosaur discovered so far, there is a full 12-million-year gap before the next one pops up. What is interesting, however, is how researchers are able to use phylogenetics to help fill in these blanks, and predict where there are fossils to be found that could potentially predate the known one.

It also means that if the dates are to be believed, the direct early ancestors to dinosaurs may already have been around before the dramatic Permian extinction event that occurred 252 million years ago, and so were one of the few lineages that managed to survive. Also known as the Great Dying, it is thought that up to a staggering 95 percent of all species alive at the time bit the dust, in what was the largest mass extinction event that has ever occurred.

Not only that, but the data also shows that the branch that includes all known birds may have split off between 108 and 69 million years ago, meaning that they may have already been flying, or at the very least gliding, around before the asteroid that killed off all their other relatives hit.