click to enlarge...
The Cretaceous fossil vertebrates of Denali National Park and Preserve. Over the course of several field seasons we now recognize Denali National Park as having one of the most important fossil records in the world for understanding an ancient high-latitude continental ecosystem. Artwork by Karen Carr.
The Arctic World of Dinosaurs
Beringia in the Cretaceous
Article by Anthony R. Fiorillo (Curator of Earth Sciences, Perot Museum of Nature and Science, Dallas, Texas).
Alaskan National Park Service units contain some of the most exciting and informative fossil-bearing rocks anywhere in North America and the fossil resources on these public lands make Alaska the best place in the world to study an ancient high-latitude terrestrial ecosystem. That these park units fall within the region known as Beringia, the hypothesized land bridge connection between Asia and North America makes paleontological investigation in this region even more intriguing.
Beringia is important for many reasons foremost being that it is the gateway by which faunas, floras and cultures have communicated between these two continents. Erik Hultén, the Swedish botanist, originally conceived of Beringia as an ice-free refugium for some northern terrestrial plants during times when glaciers were at their maximum extent. Since the mid-twentieth century, biogeographers and paleontologists have studied Beringia over increasing spans of geological time. Understanding this gateway is the means by which one can understand the biology of two major landmasses. By linking similar aged Cretaceous rock units in National Park Service lands with the fossil resources found on other federally-administered public lands, we are learning a great deal about the this remarkable ecosystem as an entity in deep geologic time.
click to enlarge...
The first dinosaur remains in any national park unit in Alaska were footprints found in Aniakchak National Monument. This hadrosaur track is one of those footprints.
Late Cretaceous rocks of Aniakchak National Monument, Denali National Park and Preserve, Wrangell-St. Elias National Park and Preserve, Yukon-Charley Rivers National Preserve, as well as the North Slope of Alaska have produced a wealth of new fossil information, most notably a rich and growing record of dinosaurs. By studying not only these fossil animals, but the soils on which the walked and the plants that grew on the landscape we are learning not only about ancient biodiversity but patterns of faunal adaptation and ecology.
For example, we now have dinosaurs unique to the ancient polar world such the pygmy tyrannosaur Nanuqsaurus hoglundi and the horned dinosaur Pachyrhinosaurus perotorum, the former showing how reduced body size may have been an adaptation for survival in the ancient north. A reduction in body size reduced the metabolic needs of the animal as it lived in an environment where food availability was highly seasonal. In contrast, but also as an adaptation to the changes in light throughout the year, the relatively small and abundant predatory arctic dinosaur Troodon seems to have had an adaptative advantage with its big eyes which allowed it to access more food and grow larger than its more southerly versions found in places like southern Alberta, Montana, and Texas.
click to enlarge...
View north and down the Colville River in northern Alaska. The bluffs are of the Cretaceous Prince Creek Formation, the source of unique polar dinosaurs.
In addition to these dinosaurs, Denali National Park has provided us further insight into biodiversity with the remarkable record of fossil bird tracks, including two types of birds not previously found anywhere in the world. The dinosaur tracks of Denali preserve evidence of large herds of duck-billed dinosaurs, herds that included individuals ranging in age from very young to full-grown.
Detailed sedimentological work, combined with the detailed work in these fossil vertebrates is showing that rather than these animals having been spread evenly across the Cretaceous landscape, there were habitat preferences. Some dinosaurs such as the duck-billed dinosaur Edmontosaurus may have preferred habitat closer to ancient shorelines while Pachyrhinosaurus perotorum may have preferred more upland habitat. Similarly, fighter jet-sized pterosaurs seem to have preferred more open landscape while the smaller pterosaurs preferred a landscape with denser vegetative cover.
While the fossil record in Alaska is growing, it is also showing us how much more we still need to understand. Given that much of the key geology defining the antiquity of Beringia, as well as this ancient terrestrial arctic ecosystem, falls within federally managed public lands boundaries, these lands are ideal outdoor paleontological laboratories, laboratories where we can learn about ourselves through a well preserved rich and complex geologic past.
2014 Mesozoic Ecosystem Partner feature articles:
| January: Fossils of the 2014 National Fossil Day Artwork
| February: Petrified Forest National Park
| March: Garden Park Paleontology Society
| April: Big Bend National Park
| May: Fossil Cycad National Monument
| June: Alaskan National Parks
| July: Dinosaur State Park
| August: Bureau of Land Management, Hell Creek fossils