Seeing an animal walk on all four legs may not even strike you as strange, but it wasn’t always this way for the creatures of the Earth. There must have been an evolutionary transition between the fossils that used various types of locomotion and the ones that walked upright on their appendages.

According to a report from the Huffington Post, paleontologists working in the Sahara Desert have discovered the fossils of a “pre-reptile” that lived nearly 260 million years ago. Bunostegos akokanensis, the knob-faced vegetarian, was likely one of the first species to walk upright on all fours.

The skull of Bunostegos akokanensis was discovered in the north of Niger in 2003, but a recent study reveals that scientists believe the species was the first to walk with its body raised off the ground. It likely lived on the supercontinent known as Pangaea.

According to Morgan turner, a PhD student at Brown University, the anatomy of Bunostegos is unlike any other prehistoric mammal or dinosaur researchers have ever seen. Its posture offers clues into the evolutionary history of locomotion, as creatures began to walk increasingly upright over time.

Researchers examined the elbow, shoulder, and forelimb bones humerus and ulna in the beast. They also found that the hip joint and rear limbs were much closer to those found in animals that walk upright.

Its elbow had a limited range of motion, another feature more commonly seen in animals that don’t rely on their front legs to walk. The animal, which was roughly the size of a cow, likely walked long distances across the Sahara in search of food.