the first Hadrosaurus appeared about 75-65 million years ago, and Terra Nova takes place about 85 million years ago which means that this species could be the earliest form of Hadrosaurus which could explain why it looks different or that it's not part of the Hadrosaurus but instead part of the Iguanodontidae as they lived around 161.2 million to 99.6 million years ago and this could be an unknown species that could have survived to the time of Terra Nova like the Brachiosaur. However, a third possible species group could be the Elasmaria as they lived around 140–66 million years ago, and some even grew to 20 feet (6 meters) long, making it the more likely species and could have filled the role of the Hadrosaurus.
Ecological speculations: if the hadrosaur was put into the series, it would most likely fill the role of typical Hadrosaurus species and would fill the small-mid size possible herd living herbivore unlike the Brachiosaur, which fills the giant tree foliage group living herbivore and may be the main prey to Carnotaurus, Allosaur and may be even the Acceraptor and Empirosaur.