When paleontologists discovered dinosaur tracks a decade ago in Denali National Park, the discovery was a breakthrough for knowledge about the prehistoric creatures that wandered the far north in the Cretaceous Period.

Now, for the first time, fossilized dinosaur bones have been discovered in the park — another breakthrough that better explains the ancient animal life of Interior Alaska.

Four fragments of bones were found in July during a survey of the park, a surprising turn because scientists had earlier believed Denali was a poor site for preservation of fossilized bones.

Paleontologists are excited about the discovery.

"The nice thing about bones is they help you actually tell what kind of a dinosaur you have living in a particular area," said Pat Druckenmiller, curator of earth sciences at the University of Alaska Museum of the North and the paleontologist leading the Denali project.

Tracks — the footprints left by dinosaurs in mud that later become rock — have been found in abundance in Denali since 2005. Tracks can give an idea of the type of dinosaur, but bones have much more specific information, Druckenmiller said. That is true even for the small specimens found this year, which were no more than 2 inches in length, he said.

Bones can reveal molecular structure and, if sliced open, can reveal growth rings, he said. That can give information about the physical characteristics of the long-ago animals, he said.

One of the bone fragments found this summer was an ossified tendon, Druckenmiller said. From that, the scientists were able to narrow down the discovery to being one of the duckbilled dinosaurs that were plentiful in Alaska of the Cretaceous geologic period, he said.

The project, funded by the National Park Service, is a joint effort of the museum and Denali National Park.

The discoverer of the first bone fragment was a museum research assistant working on the project, Heather MacFarlane. While walking with colleagues in a low valley area, MacFarlane picked up a "very unusual-looking, very interesting fragment" of what appeared to be rock, said Cassi Knight, a National Park Service paleontologist also working on the project. Knight and park intern Tyler Hunt immediately recognized it as bone, she said.

Just as modern bone is spongy and porous, so is fossilized bone, Knight said. "That texture gets preserved in fossils," she said. Even when the little holes are filled in with minerals, the porous structure is still apparent, she said.

Plant information also uncovered is particularly helpful in reconstructing the ancient climate, he said. "The great thing about these plant fossils is they are basically little paleo-thermometers," he said.

In the time of the animals that left behind the bone fragments, 70 million years ago, the area now known as Denali was a high-north forest with a climate much warmer than today.

"The temperature was more like Juneau, Alaska, or even a little warmer than that," Druckenmiller said.

The habitat was what is considered a polar forest, with a mixture of evergreens and deciduous trees, he said. There were mountains — a precursor to today's relatively young Alaska Range — but it is unclear how high they rose, he said. The sediments from those pre-Alaska Range mountains eventually washed over today's Denali National Park and the dinosaurs that died there, he said.

Recent discoveries of dinosaur tracks in Denali revealed a herd-type behavior among Cretaceous-era hadrosaurs, with generations traveling together in patterns somewhat similar to that of modern elephants.

But up to now, paleontologists were fairly pessimistic about the chances of finding actual bones in Denali, possibly because of the acidic nature of the sediments that enveloped the remains, Knight said. Decaying plant matter drives up acidity of sediments, and that acidity dissolves bones over time, she said.

The surveys in the park will continue for several more years, Knight and Druckenmiller said.