Psittacosaurus’ abundance makes the job of studying its growth patterns a whole lot easier. After comparing the arm and leg bones of 16 specimens, Dr. Qi Zhao of the Beijing-based Institute for Vertebrate Paleontology found that hatchlings would’ve been consummate crawlers thanks to their relatively long arms and short, stubby legs. However, he also noted that between the ages of four and six, Psittacosaurus' hind limbs underwent a massive growth spurt, eventually dwarfing the forelimbs. Therefore, adults likely preferred upright, bipedal poses.