Researchers have found fossil evidence that suggests bidpedalism in lizards is not a new trait. In fact, it has been around for 110 million years. Many modern lizard species — including Mexico’s Jesus lizard, the spiny-tailed iguana, and the bearded dragon — have the unique ability to instantly switch from four legs to two. As they run, they pop up and leave their front limbs dangling in the air.
To figure out just how that ability developed, a group of researchers from Seoul National University analyzed a group of ancient fossils uncovered in Korea. This showed that some lizards were already moving around on two legs back when dinosaurs still ruled the earth.
Paleontologists uncovered 29 0.8-inch-long tracks in a mudstone slab while fossil hunting back in 2004. Though they first dismissed the prints, later study revealed their importance.
The remains are the oldest lizard tracks ever found. They were created by an iguana ancestor that measured roughly 6.8 cm long, and show that ancient reptiles could move around on two legs. That is because there more hind foot prints than front foot tracks in the slab, consistent with a two-legged running gait.
This study sheds light on when lizards developed the ability to run on two legs, which gives new insight into their evolution and shows how they may have changed over time.