young hadrosaurs would have walked on only their two hind legs, while adults would have walked on all four. As the animal aged, the front limbs became more robust in order to take on weight, while the back legs became less robust as they transitioned to walking on all four legs. Furthermore, the animals’ front limbs were shorter than their back limbs. Daily activity patterns Comparisons between the scleral rings of several hadrosaur genera (Corythosaurus, Prosaurolophus, and Saurolophus) and modern birds and reptiles suggest that they may have been cathemeral, active throughout the day at short intervals. Pathology Spondyloarthropathy has been documented in the spine of a 78-million year old hadrosaurid. Other examples of pathologies in hadrosaurs include healed wounds from predators, such as those found in Edmontosaurus annectens, and tumors such as hemangiomas, desmoplastic fibroma, metastatic cancer, and osteoblastomas, found in genera such as Brachylophosaurus and Edmontosaurus. Osteochondrosis is also commonly found in hadrosaurs. References External links Timeline of hadrosaur research UCMP Tree of Life Trachodon "Mummified" Dinosaur Discovered In Montana, National Geographic 2002 Santonian first appearances Maastrichtian extinctions Taxa named by Edward Drinker Cope Fossil taxa described in 1869 Prehistoric dinosaur families