National Park Service. Illustration courtesy of Voltaire Paes Neto.

Artwork depicting the Coconino Desert environment and two primitive tetrapods, based on analysis of fossil footprints from Grand Canyon National Park.

An international team is studying 280-million-year-old fossil footprints recently found on a large sandstone boulder in Grand Canyon National Park.

The research appears in the journal Paläontologische Zeitschrift.

Before the age of dinosaurs dawned, Northern Arizona was a desert of dunes and blowing sand.

Today, evidence of that desert survives in a 1,000-foot layer of Coconino sandstone.

Of its animal occupants, nothing remains but fossil footprints, found in places like Seligman, Flagstaff and the Grand Canyon area.

Scientists have interpreted the newly found trackways as belonging to a group of four-footed animals called diadectomorphs.

The fossil tracks mark the first evidence of the large reptilelike amphibians living in a desert environment and could help scientists understand how animals first became fully land-dwelling.