A newly described crocodile relative from the Late Triassic period began life walking on four legs before adopting a bipedal stance in adulthood, scientists say. The poodle-sized Sonselasuchus cedrus, unearthed in Arizona, reveals unusual growth patterns in ancient reptiles. Researchers detailed the findings in a study published this year.
Fossils of Sonselasuchus cedrus, a shuvosaurid reptile, show it likely had proportional forelimbs and hindlimbs as a juvenile, with hindlimbs growing longer and more robust over time. Lead author Elliott Armour Smith, a University of Washington graduate student, said the team analyzed limb proportions to determine this shift. 'Essentially, we think these creatures started out their lives on four legs… they then started walking on two legs as they grew up,' Armour Smith explained. 'This is particularly peculiar.'