Tracks for carnivorous non-avian dinosaurs were also found at the site, what is now the Hasandong Formation of South Gyeongsang Province, South Korea. The dinosaurs were, Lee said, "probably too big to worry about catching tiny lizards."
Nevertheless, being a small animal surrounded by much larger species — many of which were meat-loving — must have been a challenging existence. The pterosaur Pteraichnus koreanensis, which could have preyed upon the prehistoric iguana-like lizard, was a small and agile predator with sharp teeth and large eyes.
The pterosaurs "could have attacked prey from the air, like some birds do," Lee said.
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The lizard, with its longer muscular hind limbs and shorter forelimbs, somewhat resembles a miniature Tyrannosaurus rex. But Lee said that there is no close common ancestor shared between lizards and dinosaurs. Any resemblance is therefore due to independent evolution.
Non-avian theropod dinosaurs like T. rex had fully erect legs, while lizards maintained a sprawled posture when they ran. Carnivorous dinosaurs exhibited obligate bipedality, meaning that their evolution restricted them to two-footed navigation. The ancient lizard's bipedality was more passive, such that it could likely switch from being four-legged to two-legged, depending on its needs.
The early iguana-like lizard probably evolved this unique way of moving so that it could move as fast as possible away from predators. The genetic structure of lizard ancestors did not allow them to evolve four more evenly-sized muscular limbs, as with many mammals that can run fast. Running on two-limbs could also have allowed the lizard to hold its head upward, keeping a closer eye on tall or aerial predators like pterosaurs.