Dinosaurs that roamed the land that is now Denali National Park and Preserve traveled in multigenerational herds, suggesting that older animals took care of their young in a way that might have been similar to how today's adult elephants mind their offspring, according to a new study published in the journal Geology.
The conclusion is based on thousands of fossilized hadrosaur tracks found over the past decade in the Cantwell formation, a fossil-rich geologic structure that bisects Denali. The tracks are different sizes, indicating four age groups -- very young animals, fast-growing juveniles, subadults and adults -- and that those duck-billed dinosaurs possessed a “social sophistication,” said the study’s lead author, Tony Fiorillo.
“It does imply that, at some level, there’s extended parental care,” said Fiorillo, curator of earth sciences at the Perot Museum of Nature and Science in Dallas and an expert on Alaska dinosaurs. Fiorillo is currently in Alaska to do follow-up field work in Denali, a site that has yielded many dinosaur discoveries.
The fossilized dinosaur tracks in Denali are the biggest such set found so far north, Fiorillo said. They are the first to show four different age groups of the same dinosaur species staying and traveling together, he said. The findings also support the growing consensus that polar dinosaurs, though they walked great distances to find the plants they needed to eat, did not migrate south to escape the dark and cold far-north winters. “They did not take a tropical vacation in winter,” he said.
The footprints left by the Cretaceous-era hadrosaurs were determined to have been made in summer because of the accompanying fossilized impressions of worms and insects.
About 70 million years ago, the area was an alluvial fan, with braided streams likely flowing into a finger of marine water that was gradually disappearing as the North American continent shifted. The climate was far warmer than it is now, but still not balmy. Mean winter temperatures are believed to have been 2 to 4 degrees Celsius (35.6 to 39.2 degrees Fahrenheit), and the area was farther to the north -- meaning winters were darker -- because the North American continent was in a different position then.
Today, the Cantwell formation is a belt of sandstone, shale and other rock, with much of it tilted sideways, exposing valuable fossils, the legacy of Cretaceous-era dinosaurs and other creatures. The corridor of the Denali Park Road, the gravel route used to bus visitors into the heart of one of the best-known U.S. national parks, roughly overlaps with and parallels part of the Cantwell formation.
“People taking the tour buses are going through some of the best dinosaur country of any national park unit,” Fiorillo said.
Though some of the discoveries have been in Denali’s backcountry and at relatively high altitudes, many of the fossilized footprints have been found within sight of the road and the tour-bus passengers traveling it. That has led to some interesting encounters between tourists, paleontologists and sometimes animals.
The first footprint, discovered in 2005, was only about 100 feet from the road, Fiorillo said. When he and his colleagues worked to excavate it, they found themselves at one point between a stopped busload of camera-clicking park visitors and a languid, photogenic wolf.
That initial footprint is now on display at the park’s Murie Science and Learning Center, and Fiorillo usually makes annual treks to talk to park visitors and staffers, many of whom are excited whenever the word “dinosaur” is mentioned.
The National Park Service, Fiorillo said, has been an enthusiastic and supportive partner in the research.
Perhaps park officials see some parallels between their work and the region’s ancient past, thanks to the discoveries of the hadrosaur tracks and the lessons learned from them.
“We had proven that Denali was a family destination for millions of years,” Fiorillo said.