Snake evolution has intrigued scientists for years because they knew that these complex vertebrates once had limbs and adapted over time to live without them in dramatic fashion.

But a limited fossil record didn't reflect how that transition happened since snakes first appeared during the upper Middle Jurassic Period between 163 to 174 million years ago.

Over the years, theories have suggested that these limbs were merely a transient phase before snakes quickly adapted to their current limbless form.

But newly discovered and well-preserved fossils of snakes, particularly snake skulls, suggest they had back legs for an extended period, according to a new study published Wednesday in the journal Science Advances, CNN reports.

Najash rionegrina was a type of early snake with hindlimbs. Researchers uncovered eight skulls, including one that was almost perfectly intact, as well as other fossils in the La Buitrera Palaeontological Area of northern Patagonia in Argentina.

Najash possessed primitive features more similar to lizards, such as a cheekbone arch, as well as more snakelike features including the lack of a bony arch connecting from the skull to the cheekbone. It also possessed something intermediate between snakes and lizard, like part of a jaw joint.