Bactrosaurus

Among the earliest of all the hadrosaurs, or duck-billed dinosaurs--roaming the woodlands of Asia at least 10 million years before more famous descendants like Charonosaurus--Bactrosaurus is important because it had certain characteristics (such as a thick, squat body) more often seen in iguanodonts. (Paleontologists believe that hadrosaurs and iguanodonts, which are both technically classified as ornithopods, evolved from a common ancestor). Unlike most hadrosaurs, Bactrosaurus seems to have lacked a crest on its head, and it also had a row of short spines growing out of its vertebrae that formed a prominent, skin-covered ridge along this dinosaur's back.