Hadrosaurs or duck-billed dinosaurs thrived in Alaska, footprints discovery in Denali National Park suggest

Duck-billed dinosaurs once walked the land we know as Alaska, new fossil evidence reveals.

Hadrosaurs were dinosaurs that possessed a bill, much like a modern duck. Researchers discovered fossilized tracks, left behind by hadrosaurs, in Denali National Park.

Paleontologists believe the animals lived in herds, containing parents and young, making the groups multi-generational. This is the largest track site known in regions of the far north.

"Preservation of the tracksite is exceptional: most tracks, regardless of size, contain skin impressions and they co-occur with well-preserved plant fossils and invertebrate trace fossils of terrestrial and aquatic insects," investigators wrote in an article announcing their findings.

Hadrosaurs were a family of dinosaurs which thrived in the upper Cretaceous Period, just prior to the extinction of most of the animals. They lived throughout North America, as well as Asia and Europe. The best-known member of the family is the parasaurolophus, marked by a distinctive horn on top of its head.

Some species of hadrosaur evolved skulls with flatted jaws, allowing them to easily tear their way through dense vegetation. The back of the mouth contained teeth for grinding the plants and leaves chewed off by the animal. They were the first dinosaur family to be recognized in North America.

Denali National Park is centered on a mountain of the same name, which is the highest peak in North America. The area stretches over more than six million square acres.

"Denali is one of the best dinosaur footprint localities in the world. What we found that last day was incredible - so many tracks, so big and well preserved... There were many invertebrate traces - imprints of bugs, worms, larvae and more - which were important because they showed an ecosystem existed during the warm parts [periods]," Anthony Fiorillo, curator of earth sciences at the Perot Museum of Nature and Science in Dallas, said.

The find shows hadrosaurs lived in the high-northern latitudes of Alaska, while global temperatures were, overall, higher than they are today. The wide range of other species of plant and animal found alongside the tracks suggests the region was once teeming with life.

The area is so rich with footprint fossils that Fiorillo and his team were unable to identify marks made by individuals. Instead, they counted all the prints, grouping them by size, ranging from five to 24 inches. They found more than 80 percent were made by full-grown adults, and 13 percent were created by young dinosaurs under one year old. The lack of evidence for adolescent members of the animals suggests they may have undergone a large growth spurt as they aged.

Discovery of the fossil footprints, and what the find could tell us about herd structure in polar dinosaurs was detailed [pdf] in the journal Geology

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