He said ongoing excavations and analysis will enable his team to "paint a new picture of dinosaur evolution in the remote South Pacific."
William Hammer, a geology professor at Augustana College in Rock Island, Illinois, said the discovery was "good news because we don't have a lot of [fossil] dinosaurs from that part of the world."
Hammer, who has studied dinosaur fossils in Antarctica, says he isn't surprised that terrestrial dinosaurs lived on New Zealand, even though today's fossil record offers scant signs of their presence.
"It would be expected that they lived there, because we have them in Antarctica and Australia. Of course, New Zealand was closely connected to Australia and Antarctica in the past."
Most of the continents of the Southern Hemisphere once joined in a single supercontinent known as Gondwana.
New Zealand, which split off 80 million years ago, was among the last landmasses to separate from the supercontinent, shearing from Antarctica.
At the time present-day Chatham Island remained connected to the New Zealand mainland via a thin finger of low-lying land known as the Chatham Rise, which stretched for nearly 600 miles (1,000 kilometers).
Land-dwelling dinosaurs that lived on its tip inhabited a forested, mossy landscape of rolling hills and violent volcanoes.
Stilwell says these ancient animals lived in isolation for 10 to 15 million years until they went extinct along with the world's other dinos 65 million years ago.
"They were really on their own evolutionary path," he said.
Given this fact, the paleontologist hopes future digs will uncover new dino species previously unknown to science.
"I can't envisage that there would be that high a diversity of dinosaurs [that lived there]", Stilwell said. "But there could be. We just don't know yet."
Joan Wiffen, the amateur paleontologist who found the first land-dwelling dinosaur fossil in New Zealand in 1975, said via email that she is "delighted" with the new discovery.
The site of her findMangahouanga Stream on North Islandhas yielded isolated bones from a handful of ancient dinosaur and reptile species over the past 30 years, Wiffen said.
They include three species of meat-eating theropods; a pterosaur flying reptile; and three plant-eating dino species: an ankylosaurus, an ornithopod, and a titanosaurus.
Stilwell and his colleagues described their new fossil finds in the January 30 issue of the journal Palaeogeography, Palaeoclimatology, Palaeoecology.
Stilwell hints that an even bigger discovery from Chatham Island is currently under wraps.
"The story is just going to get better," he said.
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