Arctic Dinosaur Tracks Behind the 2021 National Fossil Day Logo

The 2021 National Fossil Day logo shows an Arctic dinosaur. It is the first official artwork in the series to feature a dinosaur, and it draws on thousands of Late Cretaceous footprints preserved in Denali National Park and Preserve in central Alaska. The National Park Service (NPS) explains what the tracks show.

The 2021 National Fossil Day logo. Image from the NPS page.

The scene on the logo

The logo shows an Alaskan tyrannosaur walking through a mudflat under a northern polar night sky and meeting a trackway left by a hadrosaur, a duck-billed dinosaur. An ancient boreal forest outlines the distant Cretaceous landscape. The Late Cretaceous, 100 to 66 million years ago, ended the Mesozoic Era at the height of dinosaur diversity. A massive extinction at its close claimed all non-avian dinosaurs, pterosaurs, large marine reptiles, several groups of early birds, a few families of fish and several groups of mollusks such as ammonites. It also began the Cenozoic Era and the great diversification of mammals.

Denali National Park and Preserve covers over six million acres of taiga, tundra, glaciers and mountains in Alaska's interior, and preserves North America's tallest peak, Denali, at 6,190 m (20,310 ft). It became a national park on February 26, 1917, named Mount McKinley National Park for President William McKinley, and was expanded and renamed in 1980.

What trace fossils are

Trace fossils, or ichnofossils, record the activity and behavior of past life: footprints, burrows, nests and scat. They differ from body fossils such as wood, bones and shells. They are an important source of information on ancient environments, on where ancient life lived and how it changed, and on soft-bodied animals that rarely become body fossils. National parks hold trace fossils spanning more than a billion years:

Dinosaurs in the Arctic

At Denali, the Cantwell Formation consists of sedimentary rocks interpreted as braided and sandy stream channels, floodplain and lake deposits, and trace fossils are common in it. First discovered in 2005, thousands of tracks of dinosaurs and other organisms have been identified. Small invertebrates left traces too, including nematodes, oligochaetes, bivalves, crayfish, beetles and fly larvae, which show a rich variety of invertebrates in the Cretaceous North American Arctic. Fish and pterosaurs also left traces. The pterosaur hand prints are the first fossil evidence of that group of flying reptiles in Alaska and this far north in the Cretaceous.

Image from the NPS page.

Plant-eaters are the most common. The most frequent tracks belong to hadrosaurs of different ages, and at one site thousands of tracks record a herd of mixed ages. Body fossils from similarly aged rocks in the Prince Creek Formation of northern Alaska suggest a hadrosaur similar to Edmontosaurus, which is also found in Montana, Wyoming, the Dakotas and western Canada. Horned ceratopsian dinosaurs also left tracks, and possible tracks of armored ankylosaurs have been reported.

Image from the NPS page.

Theropods, a group of mostly predatory two-legged dinosaurs, left a variety of tracks, and bird tracks lie alongside them in several types. Most theropod and bird tracks are three-toed with narrow claws, but a series of two-toed tracks is attributed to "raptorial" dinosaurs such as dromaeosaurs (the Velociraptor group) or troodontids, and an odd four-toed type to a therizinosaur or an oviraptorosaur. Either would be the first evidence of that group in Alaska and its northernmost occurrence. Large three-toed prints point to a type of tyrannosaur.

The Arctic tyrannosaur

A relatively small tyrannosaur lived in the Late Cretaceous Alaskan Arctic. It was named Nanuqsaurus hoglundi, "Hoglund's polar bear lizard," from the Iñupiaq word for polar bear, Nanuq, and in honor of the philanthropist Forrest Hoglund. A close cousin of Tyrannosaurus rex, it was half its size, estimated at 16 to 20 feet in length, and is known from a partial skull from the Prince Creek Formation on BLM-administered land on the North Slope. The largest theropod tracks at Denali are attributed to a tyrannosaur: one footprint measures half a meter and represents the largest carnivore known to have lived in Alaska.

The logo's tyrannosaur is based on the Nanuqsaurus body fossils and is feathered, based on complete earlier tyrannosaur fossils from the Early Cretaceous of China, Yutyrannus and Dilong, whose fine-grained sediments preserved impressions of filamentous feathers. The NPS says it is hypothesized that Nanuqsaurus also had feathers to help regulate its body temperature in the cooler climate of the Late Cretaceous Arctic.

Sources

• National Park Service, "Fossils of the 2021 National Fossil Day Artwork" (https://www.nps.gov/articles/000/fossils-of-the-2021-national-fossil-day-artwork.htm); rewritten in hubnx's own words. The page's mural by a named artist, a visitor-center photograph and a coloring-book illustration are left out.